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Old September 28th, 2017, 04:22 PM   #1
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Question Hanging idle and dies with throttle?

Welp now that I have spark, the bike will start, but when it does start it jumps up to 4000 or 5000 rpm and then dies when given throttle. If its idling below 5k and its revved it will die out at 5k.

CA emissions have been removed, and the valve cover, T on carbs and air box have all been capped off.

From what I can tell, it sounds like its running lean. Anyone have a differing opinion?

Pulled the carbs off and cleaned them and its still doing it. Anything I'm missing? or just keep pulling the carbs and cleaning them until I get it right?

Thanks
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Old September 28th, 2017, 04:46 PM   #2
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An air leak and/or dirty carb passages.
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Old September 28th, 2017, 05:44 PM   #3
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Quote:
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An air leak and/or dirty carb passages.
Dumb question, is there a better way to clean carb passages other than hosing them with carb cleaner and blowing them out with compressed air? I know theres other ways to clean jets, i.e. guitar strings or copper wire but ive never heard of another way to clean the passages in the carbs
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Old September 28th, 2017, 06:02 PM   #4
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I use copper wire on the passages too, with lacquer thinner to dissolve varnish. Sometimes I make little brushes out of stranded hookup wire to clean the passages, depending on their size. Some guys use ultrasonic cleaners.
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Old September 28th, 2017, 06:26 PM   #5
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some guys use sodablast in conjunction with ultrasonic

Hey gitter...make sure you've not capped off any carb vent hose(s) in your CA hose delete...they must be allowed to "breathe" from the upper (black) rail.
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Old September 29th, 2017, 06:21 AM   #6
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Vacuum leak somewhere, and blocked fuel circuits elsewhere.
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Old September 29th, 2017, 09:46 AM   #7
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do both slides operate smoothly and did you remove the a/f needles when you cleaned the carb?
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Old September 29th, 2017, 09:48 AM   #8
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Is choke ON or OFF when it's idling at 5000 RPMs?

For any engine to run at certain speed, enough air has to be entering engine to support that speed. Couple of areas that may introduce more air than necessary:

1. choke
2. idle-speed adjuster too tight and opening throttle too much
3. throttle-cable too tight and keeping throttle open
4. vacuum-leak in carb/boots or somewhere after throttle


As for dying when you open throttle, yeah, that sounds like fuel-flow circuits in carbs are clogged and not metering fuel to match extra air-flow.
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Old September 29th, 2017, 11:31 AM   #9
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Quote:
Originally Posted by bob706 View Post
do both slides operate smoothly and did you remove the a/f needles when you cleaned the carb?
Yes and Yes. That being said, the brass sleeve that the needle slips into, which way are those supposed to sit in the carb? or do they only go in one way? reason i ask is because they came out while i was cleaning the carbs and i put them back in, but not sure if they went in the right way.
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Old September 29th, 2017, 11:34 AM   #10
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Quote:
Originally Posted by JacRyann View Post
Is choke ON or OFF when it's idling at 5000 RPMs?

For any engine to run at certain speed, enough air has to be entering engine to support that speed. Couple of areas that may introduce more air than necessary:

1. choke
2. idle-speed adjuster too tight and opening throttle too much
3. throttle-cable too tight and keeping throttle open
4. vacuum-leak in carb/boots or somewhere after throttle


As for dying when you open throttle, yeah, that sounds like fuel-flow circuits in carbs are clogged and not metering fuel to match extra air-flow.
I'm debating ordering a k&n filter and tossing the airbox. Thats usually the route that ive gone on all the pre-gens ive had because the airbox is a pain.

That said, any suggestions on jet sizing and carb settings for pod filters and stock exhaust?
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Old September 29th, 2017, 11:48 AM   #11
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Quote:
Originally Posted by gitter View Post
Yes and Yes. That being said, the brass sleeve that the needle slips into, which way are those supposed to sit in the carb? or do they only go in one way? reason i ask is because they came out while i was cleaning the carbs and i put them back in, but not sure if they went in the right way.
brass sleeve fits both ways but only works one way
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Old September 29th, 2017, 11:50 AM   #12
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Quote:
Originally Posted by gitter View Post
I'm debating ordering a k&n filter and tossing the airbox. Thats usually the route that ive gone on all the pre-gens ive had because the airbox is a pain.

That said, any suggestions on jet sizing and carb settings for pod filters and stock exhaust?
108 Keihin Main Jets and a shim or 2 on the stock needles worked well with 87 octane ethanol-free in our 250 with pods and a (leaky) stock exhaust.
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Old September 29th, 2017, 11:53 AM   #13
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Quote:
Originally Posted by gitter View Post
Yes and Yes. That being said, the brass sleeve that the needle slips into, which way are those supposed to sit in the carb? or do they only go in one way? reason i ask is because they came out while i was cleaning the carbs and i put them back in, but not sure if they went in the right way.
Aim so that larger tapered opening faces outwards towards needle. Jet goes on the smaller inside end.
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Old September 29th, 2017, 12:34 PM   #14
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I have two sets of 108s laying around from other projects. The darker set on the right are factory pro the lighter set on the left are stock keihin jets. Do either of the center two look two chewed up to use? Does it matter which set i use?

do i need to change the pilot jets too?

where should the mixture screws be set?
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Old September 29th, 2017, 01:00 PM   #15
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As long as the orifices are not damaged and are clean, and they thread in and seal OK, they're fine.
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Old September 29th, 2017, 01:05 PM   #16
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just curious have you messed with the valves and timing?
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Old September 29th, 2017, 01:08 PM   #17
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Quote:
Originally Posted by gitter View Post
I have two sets of 108s laying around from other projects. The darker set on the right are factory pro the lighter set on the left are stock keihin jets. Do either of the center two look two chewed up to use? Does it matter which set i use?

do i need to change the pilot jets too?

where should the mixture screws be set?
Factory Pro uses Keihin jets, DynoJet does not - so both of your jets are the same.

I'd use the Keihin set.

Pilot Jets don't need to be changed.

Start at 2.5 turns out on the idle mixture screw, which should be close. Gas with ethanol will require richer jetting and overall carb settings than gas without.

Best way to fine tune the idle mixture, in my opinion, is to adjust them to get the highest idle speed, then go slightly richer (1/8 turn out or so) until you just begin to hear the RPMs drop.

Always make adjustments when the engine hot enough to be painful if you touch it while making the adjustments!
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Old September 29th, 2017, 01:16 PM   #18
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just curious have you messed with the valves and timing?
Nope. I can’t speak to what the previous owners may have done though
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Old September 29th, 2017, 04:33 PM   #19
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Dumb question, if the hose that runs from the bottom of the air box to the engine was disconnected, would that cause the bike to lean out?
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Old September 29th, 2017, 09:09 PM   #20
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I think you mean the breather hose, so no.
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Old September 30th, 2017, 04:55 PM   #21
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got the k&n pod filter and 108 mains in. It'll start but will only run with the petcock in the prime position. I'm assuming this means i have a vacuum issue some where in the carbs or the petcock needs to be rebuild / replaced. Thoughts? start with the carbs (for the 3rd time)? or petcock?

side note, im seeing lots of blue-ish smoke when it does start up.
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Old September 30th, 2017, 05:24 PM   #22
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Disconnect the petcock output line and hold a cup under it. Then suck on the vacuum line to the petcock and see if fuel flows. It doesn't take much suction to open it if it's working right.
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Old October 4th, 2017, 07:56 PM   #23
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Finally had time to test this. Attached a length of hose to each part of the petcock. Used a vac bleeder on the vacuume side, fuel flowed easily out of the output.

So I’m guessing I’m having vacuume issues in the carbs somewhere?
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Old October 4th, 2017, 09:01 PM   #24
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If your petcock is flowing well, I doubt if lack of vacuum is causing your problem. But an easy suck with your mouth on the petcock's vacuum fitting should start the flow. It doesn't take a bleeder to do it.
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Old October 4th, 2017, 11:18 PM   #25
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Tried both ways actually, and it worked fine. So at this point, pull carbs apart again? Is there anywhere specifically that I should be looking / cleaning?
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Old November 8th, 2017, 04:44 PM   #26
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If this is still an issue for you, here's a couple suggestions.

1. check your intake boots on both side of the carbs. Spray soapy water and see if it bubbles, that'll tell you if your boots are cracking, causing a vacuum leak. You can do this to all of your vacuum lines on the carburetor as well.

2. check your diaphragms, make sure they are in good condition and intact. There's an air cutoff diaphragm on the carb as well that gets dirty, take it out, clean the housing, make sure the diaphragm itself is intact and clean.

If it's still happening after all that, just rebuild the entire carburetor. Soak all metal parts is carb cleaner or fuel, replace all rubber gaskets and diaphragms, replace the float needle and mixture needle, get new jets if necessary, start fresh.

It could be something as simple too as the intake boots not being all the way on or the clamps not tightened enough.
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Old November 8th, 2017, 05:21 PM   #27
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If this is still an issue for you, here's a couple suggestions.

1. check your intake boots on both side of the carbs. Spray soapy water and see if it bubbles, that'll tell you if your boots are cracking, causing a vacuum leak.
How would a vacuum leak between the carb and head make the soapy water bubble?
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Old November 8th, 2017, 05:46 PM   #28
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If air is escaping it'll bubble. Same way you find air leaks on a tire. Another method to check vacuum leaks in that spot would be to spray starting fluid on the boot. If it increases in RPMs, there's a leak. If nothing happens it's fine.
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Old November 8th, 2017, 06:35 PM   #29
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That method will work, although something like WD40 will work too, but is less dangerous. The propane propellant does the job as well as starting fluid. The RPM may rise or drop when spraying, depending on the particular circumstances, so the thing to look for is a change in RPM.

Air won't be escaping if there's a vacuum leak, so the soap won't help find the leak.

Last futzed with by Triple Jim; November 8th, 2017 at 08:41 PM.
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Old November 8th, 2017, 11:37 PM   #30
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Yeah with leak air will always move from outside to inside. So no bubbles.
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Old November 9th, 2017, 08:32 AM   #31
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Yeah thats true, I usually use starter fluid and a cloth to keep it contained.
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