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Old October 12th, 2020, 06:25 PM   #1
notunderweight
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Question Engine Bogs at High RPM

Hey all,
I just bought my first bike a few months ago, and have been learning to ride/wrench on it. It's a 2006 ninja EX250F.
About a week ago, I was out riding (like, an hour in) when the engine began to bog HARD above about half throttle. Like, unable to rev past it regardless of gear position. After checking the carb hoses and fuel levels, I went ahead and replaced the petcock vacuum line and fuel filter. It helped a little, but the bike still bogs above 5k.

THINGS I'VE DONE
- Changed petcock fuel and vacuum lines
- Cleaned air filter and checked airbox
- played with the idle screw (this helps the issue, but then I'm idling at 3k.... not ideal)

THINGS I HAVEN'T DONE
- Fixed it
- Changed any gaskets
- touched the carb other than the idle screw
- drained gas lines

THINGS I'VE NOTICED
- engine has more power when throttle is at 1/4 than 1/2
- exhaust smells a little different (i think?)
- adding choke helps
- no trouble starting, with or without choke
- I am at 5300 ft ASL
- head gasket looks a little iffy



Any ideas? What should my next step be? Should I just give up and find a good mechanic? Spray carb cleaner at it every time it acts up?
Thanks,
Jake
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Old October 13th, 2020, 08:04 AM   #2
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A few things it could be -

Plugged or restricted gas tank vent. Open the cap and see if air rushes in and it runs better for a while.

Plugged or restricted Main Jet. Carbs need to come off and be cleaned and adjusted.

Restricted fuel flow. Check the small filter inside the fuel line at the carb inlet. Check the inside of the tank for debris that would clog the petcock screens inside the tank.

Plugged or restricted intake. Extra dirty or broken-down filter element or blocked intake snorkel.
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Old October 13th, 2020, 08:10 AM   #3
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Ok, awesome. I've checked the air filter and intake path, and changed the fuel filter, so i guess my next step is to pull the carbs and check the jets?

I've never messed with a carburetor before - any tips or warnings?
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Old October 13th, 2020, 08:12 AM   #4
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also, here's some pictures of the bike. I'm aware they don't aid in diagnostics, I just love her!
IMG_2515.jpg
IMG_2218.jpg
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Old October 13th, 2020, 08:25 AM   #5
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Quote:
Originally Posted by notunderweight View Post
Ok, awesome. I've checked the air filter and intake path, and changed the fuel filter, so i guess my next step is to pull the carbs and check the jets?

I've never messed with a carburetor before - any tips or warnings?
Check all the other simple stuff before pulling the carbs.

Plenty of people rush into the carbs and end up having to redo them numerous times because they miss the details. To do it right takes more than a "sponge and a rusty spanner" (Smiths reference for you music fans...) or a can of carb cleaner and a screwdriver.

If it gets to that point, speak up and we'll direct you to more info - or ducatiman for a pro job. Local shops know nothing about what needs to be done to clean and rebuild carbs at this point - so don't go there.
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Old October 13th, 2020, 10:49 AM   #6
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Don't EVER let anyone under 60-yrs old touch your carbs!!!

They'll try to plug computer diagnostics into it and scratch their head with it doesn't spit out answer on what parts to replace.
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Old October 13th, 2020, 02:07 PM   #7
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just realized both drafts of my first post posted. that's rough...

Anyway - spent some more time on the bike today. Updates & Highlights:

- Pulled the fuel tank for the first time (!) to get a closer look at the carbs
- Redid fuel filter hoses because I didn't like how they turned out last time
- Took some pictures
- Checked the fuel vent line, it's clear and unclogged.

So, as of right now, the bike will run and drive, but just has NO power, especially past half throttle. maxed it out at like 25 in my uni parking lot :P. Engine bogs at 3/4k RPM and will rev, but just, SUPER slowly.

Here's some pictures:

IMG_2774.jpg
Carbs without the fuel tank [image is sideways]

IMG_2787.jpg
Residue at the bottom of my fuel tank; pretty sure it's ash from the wildfires

IMG_2789.jpg
Replaced fuel filter, complete w/ super long lines bc the Advance Auto Parts didn't have a 90 degree version

IMG_2790.jpg
Worrying(?) bit missing from a headgasket.



Anyway, so going down @jkv45's list:
- Pretty confident that fuel tank backpressure / clogged vent isn't the issue
- No idea if it's the carbs, leaving that as the last resort.
- Air filter and intake snorkel are clear. Replacing filter tomorrow just to be sure.

This leaves me with (at least to the best of my knowledge): a clogged petcock screen, or a plugged main jet in the carbs. How should I check the petcock screens? They seem pretty ... inaccessible
Thanks for the advice & motivation. I'll err on the side of doing my own work here, it won't kill me to learn some more about fuel systems.

P.S. That headgasket is sketching me out. Could this be lack of compression from a cylinder leak? Could I check by putting some gasket maker on the outside & seeing if that helps?
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Old October 14th, 2020, 06:35 AM   #8
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Originally Posted by notunderweight View Post
Attachment 47372
Replaced fuel filter, complete w/ super long lines bc the Advance Auto Parts didn't have a 90 degree version
Having a long fuel line with a low spot isn't a good idea - I'd change that. Because the carb inlet is so close to the petcock there really isn't much room for an aftermarket filter.

There should be a filter inside the fuel line at the carb inlet. This link has some info and photos of it - https://faq.ninja250.org/wiki/File:Fuel_Filter_12.JPG

If everything is clean, and the small oem filter is in place, you shouldn't need an additional aftermarket inline filter.
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Old October 14th, 2020, 07:13 AM   #9
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Quote:
Originally Posted by jkv45 View Post
Having a long fuel line with a low spot isn't a good idea - I'd change that. Because the carb inlet is so close to the petcock there really isn't much room for an aftermarket filter.

There should be a filter inside the fuel line at the carb inlet. This link has some info and photos of it - https://faq.ninja250.org/wiki/File:Fuel_Filter_12.JPG

If everything is clean, and the small oem filter is in place, you shouldn't need an additional aftermarket inline filter.

Just to clarify, there was a 90-degree filter already in place. The plastic was a little cracked so I wanted to replace it. Something like this:
s-l640.jpg
Was that added by the previous owner? I don't see an inline filter at the carbs.
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Old October 14th, 2020, 07:15 AM   #10
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Quote:
Originally Posted by notunderweight View Post
Was that added by the previous owner? I don't see an inline filter at the carbs.
Actually, it doesn't really matter. I grabbed the OEM one online, should be here in a few days.
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Old October 14th, 2020, 11:27 AM   #11
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Not to worry, this is just valve-cover gasket, it doesn't appear to be leaking. Headgasket is between head and cylinder-block.

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Old October 14th, 2020, 11:32 AM   #12
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Quote:
Originally Posted by notunderweight View Post
Actually, it doesn't really matter. I grabbed the OEM one online, should be here in a few days.
OEM filter that fits inside fuel-line going to carbs? Might be better to use inline external filter. It has more capacity and won't get clogged up as quickly. And it's visible so you can inspect it. That filter you have should work OK. Just cut hoses short with scissors, knife, teeth, so fuel doesn't have to flow back up to carb-inlet.


Last futzed with by DannoXYZ; October 23rd, 2020 at 06:38 PM.
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Old October 14th, 2020, 11:45 AM   #13
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Quote:
Originally Posted by DannoXYZ View Post
Not to worry, this is just valve-cover gasket, it doesn't appear to be leaking. Headgasket is between head and cylinder-block.
Ok, love that . Thanks for the clarification.

Quote:
Originally Posted by DannoXYZ View Post
OEM filter that fits inside fuel-line going to carbs? Might be better to use inline external filter. It has more capacity and won't get clogged up as quickly. And it's visible so you can inspect it. That filter you have should work OK. Just cut hoses short with scissors, knife, teeth, so fuel doesn't have to flow back up to carb-inlet.
I grabbed a right-angle clear Kawasaki filter. Not sure if it's a spec part for the original bike, but it matches the part on the bike when it was last working [going for a failure-analysis kinda approach]. Either way I'll definitely cut the hoses shorter later today. Probably won't use my teeth
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Old October 14th, 2020, 11:52 AM   #14
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You can use an aftermarket inline filter, but I'd use a shorter one like in Danno's photo. The factory filter at the inlet will plug easily if the system isn't clean.

If everything is clean and there's no debris in the system it doesn't matter, but Danno's would show you if you did.

You just don't want to create a low point in the system.
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Old October 14th, 2020, 12:01 PM   #15
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Quote:
Originally Posted by jkv45 View Post
You can use an aftermarket inline filter, but I'd use a shorter one like in Danno's photo. The factory filter at the inlet will plug easily if the system isn't clean.

If everything is clean and there's no debris in the system it doesn't matter, but Danno's would show you if you did.

You just don't want to create a low point in the system.
Makes sense. I'll replace it when the new one shows up, and just cut the lines shorter in the meantime.

Anything else I should replace/check/take photos of? Given that the running condition is the same with all fuel line/filter/vacuum hose combinations, I'd be surprised if it was a clog in that section..?
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Old October 14th, 2020, 12:17 PM   #16
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Not likely issue. Hydraulic pressure at carb-inlet should be sufficient regardless since it's below outlet of tank. However, in low-vacuum situations such as cold-starts, every little bit helps.

Having some measured numbers would help:

- vacuum at petcock-inlet when cranking
- petrol volume flowed from petcock in 10-seconds of cranking (aim fuel-hose into measuring cup)

There have been instances of leaking/crimped vacuum-hoses limiting vacuum to petcock, thus it doesn't open enough for full fuel-flow. Or petcock is clogged/damaged such that it doesn't flow sufficient fuel. Ultimate test is just to measure output-flow in 10-seconds and compare to spec in manual.

Then you can rule out completely: tank, tank-cap vent, petcock, vacuum-line, fuel-line, fuel-filter.

Also do compression test.
After that, carbs would need closer examination.
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Old October 14th, 2020, 04:17 PM   #17
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Do the exhaust pipes get equally warm upon starting?
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Old October 14th, 2020, 06:47 PM   #18
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Quote:
Originally Posted by DannoXYZ View Post
Having some measured numbers would help:

- vacuum at petcock-inlet when cranking
- petrol volume flowed from petcock in 10-seconds of cranking (aim fuel-hose into measuring cup)

There have been instances of leaking/crimped vacuum-hoses limiting vacuum to petcock, thus it doesn't open enough for full fuel-flow. Or petcock is clogged/damaged such that it doesn't flow sufficient fuel. Ultimate test is just to measure output-flow in 10-seconds and compare to spec in manual.
I'll run the fuel-flow test tomorrow morning, check the service manual, and report back. Vacuum pressure is trickier, as I don't own a gage or know where I could borrow one... Is that something I could rent from an auto part store, do you think?

Quote:
Originally Posted by Triple Jim View Post
Do the exhaust pipes get equally warm upon starting?
Interestingly, no! I'm not super familiar w/ the characteristics as I just got it a few months ago, but it definitely feels like the pipes are taking longer to warm up. Same temp each side, though.
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Old October 15th, 2020, 03:47 PM   #19
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Autozone has quite selection of loaners: https://www.autozone.com/tools-and-e...t/loan-a-tools

I haven't gone through all categories to see if they have vacuum-gauge. Simple enough to get one from Harbour Freight. Can also use it to bleed brakes!
https://www.harborfreight.com/brake-...kit-63391.html

Catch with testing petcock by manually applying vacuum with tongue, syringe or vacuum-pump is that may be higher-vacuum than is availble under normal operations. That's why you want to measure actual vacuum from carbs first. Then apply that same amount to petcock and see how much it flows.

I had case where bike runs for 1/2-lap (about 1-minute) and then it dies. Brought bike back, tested petcock and it flowed plenty. Went out again and it died exactly 1/2-lap. Brought it back, had empty float-bowls... wtf! Instead of testing petcock's flow, I looked at vacuum-hose in between and AHAH!!! It was little on long side and I had looped it over backbone of frame. Then when I lowered tank, it crushed loop and cut off vacuum! So, petcock and carbs may be perfectly fine!

If you're up to challenge of cleaning carbs, do search for "clean carbs ducatiman" to find many threads with photos and process to thoroughly restore carbs to factory-fresh clean condition. Note that unclogging jets is just first 5%, you'll also have to scrub and clear entire flow-path of petrol from tank to carb-venturi. Dried petrol tends to leave dark-brown varnish everywhere it flows. And modern carb cleaners don't work due to removal of chlorinated compounds. I've found 50/50 mixture of acetone and PEA-based fuel-system cleaners along with nylon brushes work much, much better. Also replace all rubber O-rings and seals.

You should at least make an attempt to learn. Many extremely skilled mechanics have had to remove carbs 4-5x for ever deeper cleaning before their bike ran like off showroom floor. In end, it may be simplest, fastest and cheapest to send carbs to ducatiman for full restoration.

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Old October 23rd, 2020, 12:56 PM   #20
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Hey all - just figured I'd post a brief update, it's been a while.
I've made some progress! Finding time to work on the bike with the wildfires and everything has been kinda tricky, but i made it out there yesterday and today. Some highlights:
I got the right diameter vacuum hose for the petcock, and that helped. I think the old hose was leaking or something; the last owner confirmed it's been an issue for him in the past. Anyway, that helped a lot (if not quite enough for me to be comfortable with it on public roads).
@.Danno, I tried to get a vacuum gage a couple times this week, but neither of the auto parts stores I frequent had them as loaners. I went ahead and just ordered one online, itll be here soon. In the meantime, I noticed that, while both are jerky and stuttery above like 6k, switching the petcock to reserve actually makes a difference in power. I think I'm gonna drain the tank and clean the petcock filter this weekend.

Here's a pic from Boulder this week - really spooky:
IMG_2977.jpg

Anyway, thanks for all your help so far! Couldn't have gotten this far without you.
blessings!
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Old October 23rd, 2020, 01:15 PM   #21
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You might just order a double gauge stack which will also allow you to synchronize your carbs - you need 2 gauges. BTW a leaking petcock hose will create mixture issues as well as it will essentially be leaning the mixture out. You can sometimes detect these leaks by spraying starter fluid into the area of a suspected leak. It will change the RPMs if there is a leak. Once all your leaks are fixed make sure you resynch the carbs and adjust the idle mixture screws
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Old October 23rd, 2020, 01:47 PM   #22
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Quote:
Originally Posted by notunderweight View Post
Hey all - just figured I'd post a brief update, it's been a while.
I've made some progress! Finding time to work on the bike with the wildfires and everything has been kinda tricky, but i made it out there yesterday and today. Some highlights:
I got the right diameter vacuum hose for the petcock, and that helped. I think the old hose was leaking or something; the last owner confirmed it's been an issue for him in the past. Anyway, that helped a lot (if not quite enough for me to be comfortable with it on public roads).
@.Danno, I tried to get a vacuum gage a couple times this week, but neither of the auto parts stores I frequent had them as loaners. I went ahead and just ordered one online, itll be here soon. In the meantime, I noticed that, while both are jerky and stuttery above like 6k, switching the petcock to reserve actually makes a difference in power. I think I'm gonna drain the tank and clean the petcock filter this weekend.
(SNIP)
That would suggest the petcock needs to be cleaned, rebuilt, or replaced.

The screens on the normal pickup inside the tank may be partially plugged if it runs differently on Reserve.
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Old October 24th, 2020, 02:46 PM   #23
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You might just order a double gauge stack which will also allow you to synchronize your carbs - you need 2 gauges. BTW a leaking petcock hose will create mixture issues as well as it will essentially be leaning the mixture out. You can sometimes detect these leaks by spraying starter fluid into the area of a suspected leak. It will change the RPMs if there is a leak. Once all your leaks are fixed make sure you resynch the carbs and adjust the idle mixture screws
Yeah, that's what I ended up doing. They should be here next week ish, and I'll try to get some hard fuel-flow numbers.

In less quantifiable news - swapping the fuel filter for a nicer right angle one helped even more. At this point, the bike will run nicely up till about 35mph and then just lose power. Wide open throttle is still weirdly jerky but works in 1st and 2nd. It's also taking forever to warm up: I was riding this morning around town and it took easily 20 minutes to warm up completely. Granted, it's cold today, but not THAT cold!
IMG_3020.jpg
i know the hose clamps are ugly... nicer ones are in the mail :/


Anyway, all of that is making me think jkv45 is right, and the bike is running lean from a fuel flow issue. My next step is gonna be to clean the petcock filter - just gotta get the solvents and stuff that the service manual recommends.
Will update when I do. It felt great to be back out again, even if just around town.
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Old October 25th, 2020, 01:31 PM   #24
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"I was out riding (like, an hour in) when the engine began to bog HARD above about half throttle." "engine has more power when throttle is at 1/4 than 1/2"

new to you '06....mileage? Sitting dormant a long time prior to your purchase?
Initially during your ride it was able to rev past the 1/2 throttle point without bog?
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Old October 25th, 2020, 01:51 PM   #25
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new to you '06....mileage? Sitting dormant a long time prior to your purchase?
Initially during your ride it was able to rev past the 1/2 throttle point without bog?
Yeah, so some background:
- 7.5k miles
- was the last owner's daily until he got a Ducati (lol)
- was running fine, I had been learning to ride on it since about September, and could make it to 90mph easy
- just kind of started bogging on my way home after a long ride - slightly at first, but noticeably. by the time I had it parked it was definitely down on power. Next time I tried to ride, it was slow to the point where I wasn't comfortable riding it outside of a parking lot... That's where I started asking around here for advice
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Old October 25th, 2020, 02:31 PM   #26
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You might have more than one issue here. Even if petcock has slow flow, from initial start, you should still have sufficient petrol-levels in float-bowls for at least a minute. So do this test:

- warm up bike for 5-minutes
- turn off, leaving petcock on, let sit for 5-minutes. This should re-fill bowls to proper float-level
- aim bike down empty road, start it up and immediately redline 1st & 2nd gear!

Does it run like bat-out-of-hell to redline? If so, problem may be petcock not flowing enough. However, if it still bogs in upper-RPMs, then it’s not petcock and carbs need complete disassembly and restoration.
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Old October 25th, 2020, 03:25 PM   #27
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Nasty, extreme example pics of "petclogs"

Flow areas within require aggressive tactics, vacuum diaphragm area demands care and some finesse.

And if its this bad, chances are the carbs are not far behind.

PS I routinely stock petcock rebuild kits and every carb consumable (salvage spare parts too)
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File Type: jpg petc2.jpg (65.7 KB, 5 views)
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Old October 25th, 2020, 04:44 PM   #28
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. It's also taking forever to warm up: I was riding this morning around town and it took easily 20 minutes to warm up completely. Granted, it's cold today, but not THAT cold!
What do you mean by saying “warm up completely”?

I rode mine for an hour and a half today in 6C weather (41F) and the gauge was always staying just 1/8 above the lowest mark. Even in 25C (76F) it stays 1/4 off the bottom. It only gets to 1/2 when I ride in traffic and never above that(the fan kicks in)
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Old October 25th, 2020, 05:37 PM   #29
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Originally Posted by ducatiman View Post
Nasty, extreme example pics of "petclogs"

Flow areas within require aggressive tactics, vacuum diaphragm area demands care and some finesse.

And if its this bad, chances are the carbs are not far behind.

PS I routinely stock petcock rebuild kits and every carb consumable (salvage spare parts too)
Sweet! I'll tear it down when the snow melts and post some pics, see what's going on. If it ends up being a rebuild, I'll shoot ya a PM


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What do you mean by saying “warm up completely”?
It was 35F out when I was riding, and it took like 15 minutes to really properly get out of the little 'cold zone' between the 2 initial temp bars. After about 30-45 it reached 1/3 temp - that's typically where I expect it to be outside of sitting out in traffic on a hot day. I gave it about 3 minutes to just warm up with half choke, too.
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Old October 25th, 2020, 05:58 PM   #30
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Yeah, cooling system design on these bikes are antiquated. Really need ThermoBob to update. Then it’ll warm up properly and actually stay at operating temps.
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Old October 25th, 2020, 07:14 PM   #31
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It was 35F out when I was riding, and it took like 15 minutes to really properly get out of the little 'cold zone' between the 2 initial temp bars. After about 30-45 it reached 1/3 temp - that's typically where I expect it to be outside of sitting out in traffic on a hot day. I gave it about 3 minutes to just warm up with half choke, too.
That does not sound wrong at 35F. It looks just like mine. If anything lean translated into hot, not cold
I find the block surface area on these 250c bikes is relatively pretty large to keep them cool when moving when the outside temp is below 60F
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Old October 25th, 2020, 08:02 PM   #32
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Quote:
Originally Posted by ducatiman View Post
Nasty, extreme example pics of "petclogs"

Flow areas within require aggressive tactics, vacuum diaphragm area demands care and some finesse.

And if its this bad, chances are the carbs are not far behind.
True, one or other may start acting up first, but other has had similar neglect.

EDIT: I fat-fingered your post and accident hit thumbs-down! Sorry!!!
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Old October 27th, 2020, 05:56 AM   #33
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EDIT: I fat-fingered your post and accident hit thumbs-down! Sorry!!!
I thought I remembered that there was a way you could then change it to a thumbs-up so I tried it on your post. Apparently you can't. I must have been thinking of a different board. (members can experiment on this post if desired.) I did go back and thumbs-up another post above to keep your score fair.
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Old October 28th, 2020, 09:34 AM   #34
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You might have more than one issue here. Even if petcock has slow flow, from initial start, you should still have sufficient petrol-levels in float-bowls for at least a minute. So do this test:

- warm up bike for 5-minutes
- turn off, leaving petcock on, let sit for 5-minutes. This should re-fill bowls to proper float-level
- aim bike down empty road, start it up and immediately redline 1st & 2nd gear!
They just plowed the road to my parking lot, so I figured I'd give this a shot! There was no noticeable difference in power after letting it sit. Engine still bogged at like 6k and past 3rd gear. Is there any way the leaking vacuum line could've messed up the carb tuning? is that a thing that happens?

Either way it was very fun. Silver linings..
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Old October 28th, 2020, 09:56 AM   #35
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Leaking vacuum line would just result in poor petcock performance. And yes, it would mess up carb-metering as well.

Hmm, ok, so most likely clogged carbs, with petcock not far behind. Best to do full restoration on both.
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Old October 28th, 2020, 10:21 AM   #36
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Like others suggested just do a proper carb cleanup or send it to a reputable rebuilder. Purchasing a bike from someone who let it sit for a while will guarantee the carbs will be messed up. You are just wasting your time trying to triage.
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Old October 29th, 2020, 06:15 PM   #37
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Leaking vacuum line would just result in poor petcock performance. And yes, it would mess up carb-metering as well.

Hmm, ok, so most likely clogged carbs, with petcock not far behind. Best to do full restoration on both.
Got the vacuum gages in today - connecting it to the carb vacuum line while cranking makes it spin around like crazy. If I had to guess, I'd say the midpoint of the fluctuations was about 400-500mmHg, but I can't see that being particularly useful. I drained the fuel tank too, and the fuel flow looked like plenty and plenty steady to my (admittedly untrained) eye,

I would like to do the petcock cleaning myself, just to learn some more about the bike and have fun learning to wrench, but I don't think I have the free time to go about learning to do a carb rebuild on my own. Do you guys have suggestions as to a rebuilder I could send it to?
As always, thank you for your time & patience
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Old October 29th, 2020, 06:18 PM   #38
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Like others suggested just do a proper carb cleanup or send it to a reputable rebuilder. Purchasing a bike from someone who let it sit for a while will guarantee the carbs will be messed up. You are just wasting your time trying to triage.
Yeah, I'll do that for sure. I'm just trying to confirm it's a carb issue before I mess with them - it threw me for a loop that the carbs would start being finicky after working consistently for a few months.
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Old October 29th, 2020, 06:46 PM   #39
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Do you guys have suggestions as to a rebuilder I could send it to?
Ducatiman here on the board is the guy. He does spectacular work, does it quickly, and at a fair price. See post #24 above.
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Old October 29th, 2020, 06:55 PM   #40
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Ducatiman here on the board is the guy. He does spectacular work, does it quickly, and at a fair price. See post #24 above.
Oh, awesome. Shot him a PM, thanks!
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