Carb question: High RPM hesitation

[amad1972]

I just got this bike about 3 weeks ago. Here are the things I have done to it:
Adjusted valves
synced carbs
changed oil & filter
New air filter
New fuel filter

It now runs great, except for when I am running WOT, when it reaches about 9k rpm, it starts to hesitate, or bog, a little. It will rev on up to redline, but not as quickly as it should. Today, I took the carburetors off, took them apart, and gave them a good cleaning. All the jets and the needles came out and went in a carb cleaning chemical dip for about 30 or 40 minutes. I sprayed the carb bodies all out with spray carb cleaner. After getting the jets out of the dip, I ran wire through all the orifices to make sure they were clean and clear. After putting it all back together, it fired right up and ran great....except at higher RPM. Same issue. All vacuum lines are hooked up and seem snug. The seals around the carbs on the engine side and the airbox side seem good.

Is there something I'm missing? Can anyone tell me which jet specifically is the high RPM jet? Any other suggestions?

[j98sprint]

You didn't say anything about checking the float height. Very important to have the correct float height. Especially at WOT.

j98sprint

[Ninjinsky]

Originally Posted by j98sprint

You didn't say anything about checking the float height. Very important to have the correct float height. Especially at WOT.

j98sprint

I'm not entirely sure about that imperative. My experience is that if you run out of fuel an engine will stonk along nicely until the float bowl is as good as empty. Constant vaccuum and all that. The idle/ off idle circuit is the more critical on fuel level.

[Ninjinsky]

Originally Posted by amad1972

Is there something I'm missing? Can anyone tell me which jet specifically is the high RPM jet? Any other suggestions?

By WOT you are almost entirely on the main jet, the Idle circuit and Needle are out of it
http://www.thumperfaq.com/images/effects3.gif

[Hero Danny]

It's either 1 of 2 things. 1, you need to clean your carbs properly (you probably missed an area) or 2, you could have a vacuum leak.

[amad1972]

I completely cleaned my carbs again. REALLY well. All parts taken out. Jets soaked in Berryman's carb dip overnight. Rest of the carb bodies cleaned really well with carb cleaner. All jets open and clear. The diaphrams looked good with no tears in them. Put it all back together and it runs just the same. It starts "stuttering" at around 9k on up to about 13k. It still pulls, but not as hard and with some stuttering. At all other RPM ranges, it runs perfectly.
Not sure if I mentioned already, but I put new spark plugs in when I did the valves. It is completely rideable as it is, but I sure would like it to run as it is supposed to. I believe all the carb parts are stock.

One thing I did notice is this: On a diagram of carb parts, I saw a little cylindrical piece that goes into the bottom of the main jet. I did not see that on either of my main jets when I took them out. Am I missing a piece in each carb? Could that be the cause of my troubles?

[flitecontrol]

I always soak the carb bodies as well as the jets. There are passages in the body that can be obstructed too. 24-48 hours in Chem Dip usually gets all the crud loose. Only all-metal parts go in the Chem Dip.

[amad1972]

Originally Posted by flitecontrol

I always soak the carb bodies as well as the jets. There are passages in the body that can be obstructed too. 24-48 hours in Chem Dip usually gets all the crud loose. Only all-metal parts go in the Chem Dip.

I did soak the carb bodies in a solution of PineSol and water for 24 hours and then cleaned them well with spray carb cleaner. I saw this suggestion on a carb cleaning site. All orifices allowed a good stream of carb cleaner through.

[amad1972]

Here's another thought. If the main jet is the one working when at WOT, is the main jet working at WOT at lower RPM's? It runs great at WOT up until about 9k. Hmmmm.

[Ninjinsky]

Originally Posted by amad1972

One thing I did notice is this: On a diagram of carb parts, I saw a little cylindrical piece that goes into the bottom of the main jet. I did not see that on either of my main jets when I took them out. Am I missing a piece in each carb? Could that be the cause of my troubles?

Theres 3 bits
The main jet
The Needle jet holder
The Needle jet

The needle jet is a short cylindrical piece with a flange and it usually tends to stay in the carb body as a light press fit
Does the part you are thinking of look like this ?
http://www.grizzlycentral.com/forum/...o-img_4716.jpg

[amad1972]

Originally Posted by Ninjinsky

Theres 3 bits
The main jet
The Needle jet holder
The Needle jet

The needle jet is a short cylindrical piece with a flange and it usually tends to stay in the carb body as a light press fit
Does the part you are thinking of look like this ?
http://www.grizzlycentral.com/forum/...o-img_4716.jpg

Yes. That is the part I was thinking of. I did not see a part like that. Is it possible that it could have stayed in the carb body during both of my thorough cleanings?

[Ninjinsky]

Originally Posted by amad1972

Yes. That is the part I was thinking of. I did not see a part like that. Is it possible that it could have stayed in the carb body during both of my thorough cleanings?

Yes it would probably stay in place you would normally need to tap it out like this.
http://filipi.com/ngw/roady/carbover...2needlejet.jpg
(You don't need to remove it so don't bother to)
So you are okay

[amad1972]

Originally Posted by Ninjinsky

Yes it would probably stay in place you would normally need to tap it out like this.
http://filipi.com/ngw/roady/carbover...2needlejet.jpg
(You don't need to remove it so don't bother to)
So you are okay

Good, since I have all the parts there. Bad, because I still don't know the cause of my problem.

[jkv45]

Do you have an OEM air filter?

How old is the gas?

[amad1972]

Originally Posted by jkv45

Do you have an OEM air filter?

How old is the gas?

Gas is fresh. I have run two tanks through since I've owned it. One of the tanks had a can of Seafoam in it. I just now put a brand new OEM air filter in it. When I got it, there was no air filter, just the screen. No change from before or after filter.

[jkv45]

Check for a vacuum leak around the carb boots.

Are you still running the tank with Seafoam? A full can of Seafoam in a tank may be too much.

Are you running ethanol-free gas? What octane?

[amad1972]

Originally Posted by jkv45

Check for a vacuum leak around the carb boots.

Are you still running the tank with Seafoam? A full can of Seafoam in a tank may be too much.

Are you running ethanol-free gas? What octane?

I filled up another tank with no Seafoam. I am running 87 octane on this tank. The last tank, I ran 89. How would I check for vacuum leaks?

[Hero Danny]

I think it's a vacuum leak. Check all the lines, if you get a spray bottle full of water squirt it on the lines and search for bubbles. If you see some then it's leaking,

[jkv45]

Originally Posted by amad1972

I filled up another tank with no Seafoam. I am running 87 octane on this tank. The last tank, I ran 89. How would I check for vacuum leaks?

Easiest way is to use carb cleaner. With the engine warm and idling, spray it around where the intake boots seal. If there is a leak the RPMs will change when the carb cleaner is pulled into the intake track.

Make sure the boots are also attached properly at the back of the carb where they mount to the airbox. Check that there isn't anything near the intake snorkel that could be blocking intake air.

[amad1972]

Well, tonight I checked for any vacuum leaks using carb cleaner. I sprayed it around the airbox boots, the carb-to-engine boots, other vacuum hoses on the carburetor and nothing changed. I then took out the fuel filter just to see if it could be restrictive...no change. I rode with the gas cap open just in case it was the cap vent...no change. I checked in the airbox intake tubes for obstructions....nothing.

Could these symptoms be from faulty plug wires or faulty coils? The bike runs smooth as silk up to 9k rpm. Any other suggestions of what to try. I can get used coils/plug wires on eBay for about $25. Would that be worth a try?

[Ninjinsky]

Originally Posted by amad1972

Well, tonight I checked for any vacuum leaks using carb cleaner. I sprayed it around the airbox boots, the carb-to-engine boots, other vacuum hoses on the carburetor and nothing changed. I then took out the fuel filter just to see if it could be restrictive...no change. I rode with the gas cap open just in case it was the cap vent...no change. I checked in the airbox intake tubes for obstructions....nothing.

Could these symptoms be from faulty plug wires or faulty coils? The bike runs smooth as silk up to 9k rpm. Any other suggestions of what to try. I can get used coils/plug wires on eBay for about $25. Would that be worth a try?

One thing that might cause such a problem at those very high rpm is a weak or broken valve spring allowing valve bounce. I appreciate this is a hard thing to check especially the inner spring but if it is a high miler it is a "last resort" check if everything external has been double checked and is ok. (Obviously valve bounce won't show on a compression test)

[amad1972]

Originally Posted by Ninjinsky

One thing that might cause such a problem at those very high rpm is a weak or broken valve spring allowing valve bounce. I appreciate this is a hard thing to check especially the inner spring but if it is a high miler it is a "last resort" check if everything external has been double checked and is ok. (Obviously valve bounce won't show on a compression test)

Would valve springs be that worn with 16,000 miles?
I ordered two used coils and plug wires off eBay last night, so we will see if that might help, too.

[Ninjinsky]

Originally Posted by amad1972

Would valve springs be that worn with 16,000 miles?
I ordered two used coils and plug wires off eBay last night, so we will see if that might help, too.

16k should be fine
by 40-50k perhaps. I only mentioned it because it is a problem that manifests at high rpm but is fine in the slow and mid range

[jkv45]

What do the plugs look like? Are they correct?

[agentbad]

My moneys on a vacuum leak or maybe exhaust leak. Just out of curiosity what's the number stamped on your main jet? Have you tried using a little choke at WOT to see if it runs better or worse?

[amad1972]

Originally Posted by jkv45

What do the plugs look like? Are they correct?

Plugs are new and gapped correctly. The old plugs I took out looked good, too.

[amad1972]

Originally Posted by agentbad

My moneys on a vacuum leak or maybe exhaust leak. Just out of curiosity what's the number stamped on your main jet? Have you tried using a little choke at WOT to see if it runs better or worse?

I couldn't find a vacuum leak with the carb cleaner spray method. I have not tried a little bit of choke at WOT. I'll try that today on the way home from work. Thanks.

[alex.s]

Originally Posted by amad1972

Gas is fresh. I have run two tanks through since I've owned it. One of the tanks had a can of Seafoam in it. I just now put a brand new OEM air filter in it. When I got it, there was no air filter, just the screen. No change from before or after filter.

this is your biggest clue.

the PO set the main jet too big or the needle are too rich. once the needle gets close to all the way up it is letting in too much gas for the amount of air going in. before maybe it was better with no air filter because more air would go in to counteract the extra fuel up top.

probably more likely he had some aftermarket pipe on it and he just swapped back stock parts when he sold it without retuning.




or maybe your coils are going out.

[jkv45]

Originally Posted by amad1972

Plugs are new and gapped correctly. The old plugs I took out looked good, too.

Tan, not black and sooty?

As alex.s noted, if the PO had modded and changed things from stock, he may have done a quicko-fixo to make it run ok.

Selling it without an air filter is pretty sketchy.

[amad1972]

Originally Posted by jkv45

Tan, not black and sooty?

As alex.s noted, if the PO had modded and changed things from stock, he may have done a quicko-fixo to make it run ok.

Selling it without an air filter is pretty sketchy.

It ran poorly without the air filter, too. The bike doesn't look like it has been modded any. I bought it from a girl who had only had it for about 3 months. She was selling it to get a Harley, but said that she thought it needed the carbs cleaned, so she had noticed the running issue. She just didn't have the know-how to do it herself.

The plugs were nice and tan. Not black and sooty. Not burned looking, either.

[amad1972]

Originally Posted by amad1972

It ran poorly without the air filter, too. The bike doesn't look like it has been modded any. I bought it from a girl who had only had it for about 3 months. She was selling it to get a Harley, but said that she thought it needed the carbs cleaned, so she had noticed the running issue. She just didn't have the know-how to do it herself.

The plugs were nice and tan. Not black and sooty. Not burned looking, either.

When I say "ran poorly" I mean the stuttering at higher rpm. It is far from a poor running bike. Runs perfectly under 8k rpm and it is not un-rideable above 8k. It just stutters some.

[alex.s]

who knows what has been done to the bike. the problem you are describing sounds like it is running too rich toward the top of the vacuum band. so either you have washers on your needles when you shouldn't, or your main jet is too big, or maybe your needle jet orifice is worn into an egg shape and letting too much flow as the needle rises...

[amad1972]

Originally Posted by alex.s

who knows what has been done to the bike. the problem you are describing sounds like it is running too rich toward the top of the vacuum band. so either you have washers on your needles when you shouldn't, or your main jet is too big, or maybe your needle jet orifice is worn into an egg shape and letting too much flow as the needle rises...

I took the carbs out again tonight. I looked at the main jets and the number 18 is stamped on them. Would that be a 108? Should I take it back down to a 105 (stock size)? Also, the needles each have one washer on them. Is that what it is in stock form?

Also, do you know where the best place is to get the little metal washer and rubber washer that goes on the idle mixture screws? I seem to have lost those.

Thanks

[amad1972]

My wife looked at it and she thinks the stamp on it could say 1 B. What does this mean? Either 1 B or 18? Hmmm.

[flitecontrol]

Originally Posted by amad1972

Also, do you know where the best place is to get the little metal washer and rubber washer that goes on the idle mixture screws? I seem to have lost those.

Thanks

I've had good luck finding small metric washers at hobby stores. Many radio controlled toys use them. Many motorcycle shops and auto parts stores carry a selection of nitrile O-rings. Be sure what you buy is fuel resistant, because not all O-rings are.

[amad1972]

Yeeeee hawwwww!!! Problem fixed!

I took one of the main jets that I thought was stamped with an 18 to the dealer. He thought it could possibly be a 118 that wasn't stamped well, because there was a little mark in front of the 18 that could have been a 1. Anyway, They didn't have 105's in stock, so I got two 107.5 jets. I put those in, took out the washer on each needle, replaced the idle mixture screws and float needles (just because those things came in the kit) and took it for a ride. That sucker pulls hard all the way to redline now!

Thank you all for giving me suggestions.

[agentbad]