1976 GL1000 - Cylinder #3 runs cold when on choke

[BrittC]

I have a 76 GL1000 that I'm trying to finish up. It has only 7500 miles on the clock and sat for many years. This was a frame off restoration but I did not see a need to go into the engine, aside from valve lash adjustments and timing belts.

The carbs were restored by a Randakk approved carb rebuilder using Randakk's premium kit. The carbs also got new OEM float valves. They are extremely clean and were set up by someone with a ton of experience.

I've replaced just about every maintenance item on the bike that you can replace. Belts, hoses, cables, water pump, fuel pump, coils/wires/plugs, Dyna ignition, and on and on.

Cold compression is 147 to 151 psi on all four. The carbs are extremely clean. The linkages and butterflies are moving freely.

It's starting and running fine, however when on choke, the #3 intake tube cools off and sweats, and the #3 header stays cool compared to the others. A laser thermometer shows that the intake tube temp drops by 15 degrees shortly after starting it, which causes condensation to form. The header reads around 130 (or less) degrees as long as the choke is on. If I take it off choke, the header starts getting hot quickly and the intake tube warms up and dries off. All exhausts reach around 450 to 500 degrees F while idling off-choke.

Once warmed up and off choke, if I hold the throttle at 3500 RPM the #3 header stays hot. If I choke it so it's running at 3500 RPM, the header temp begins dropping quickly.

My theory is that it's getting excess fuel while on choke, causing the intake to cool as a rich fuel/air mix rushes through it. I've pulled the carbs twice since discovering this behavior and have removed and cleaned all jets and orifices with carb cleaner and compressed air. I didn't find any blockages and I can't find anything out of sorts.

The last time the carbs were out and everything was cleaned again, I let gravity fill the carb bowls with fuel with the CV slides removed. Then I used a huge syringe with rubber tubing to push fuel into the carbs. The new OEM float valves must be doing their job because no extra fuel came up through the jets, and I could not push more fuel in.


So, to recap my concern: Cylinder 3 intake and exhaust are cold while on choke. Off choke, #3 runs the same temperature as the others.


Any suggestions?

 

[bunsteve]

Welcome to the forum. I'm no expert, but if it's warmed enough to run well off choke, it should be off choke. The purpose of the choke is to enrich the mixture for cold starting. If you want it to run at 3500 rpm, you should use the throttle - they sell a "cruise control" that's really just a throttle lock. Ride safe.

 

[BrittC]

Welcome to the forum. I'm no expert, but if it's warmed enough to run well off choke, it should be off choke. The purpose of the choke is to enrich the mixture for cold starting. If you want it to run at 3500 rpm, you should use the throttle - they sell a "cruise control" that's really just a throttle lock. Ride safe.

I may not be as clear as I should have been. My comment about holding it at 3500 RPM was to emphasize that off choke it runs on all 4 cylinders. Applying the choke (no throttle), the RPM's raise to 3500 RPM and #3 cools down. So, it's not related to RPM, it's related to the choke being applied.

When warming up the cold engine on choke, the #3 cylinder is not firing. Its intake gets cold, and forms sweat. The header stays cool. The minute I take it off choke to ride it, the intake and exhaust both warm up. I don't use the choke as a cruise control. The engine runs great when warm and off choke.

Thanks for reading. I just want it to run as well as my 75 does but it's been a real struggle!

 

[bunsteve]

I haven't had to mess with mine at all, so I don't know if this makes any sense. Are the carbs all the same? What I'm getting at is, could you swap the position of two carbs and see if the problem follows the carb? I know there are all kinds of passageways in carbs, and some of them are extremely critical. I'm secretly hoping that by keeping mine clean and running it enough I'll never have to play with the carbs. Have you synced them?
Those are a couple of beautiful machines!

 

[BrittC]

I haven't had to mess with mine at all, so I don't know if this makes any sense. Are the carbs all the same? What I'm getting at is, could you swap the position of two carbs and see if the problem follows the carb? I know there are all kinds of passageways in carbs, and some of them are extremely critical. I'm secretly hoping that by keeping mine clean and running it enough I'll never have to play with the carbs. Have you synced them?
Those are a couple of beautiful machines!

I don't believe the carbs are interchangeable, but I do appreciate the suggestion. I've blasted every passage and orifice with carb cleaner and compressed air, and I believe they are 100% clear.

 

[Lowrider Bud]

I'm confused - you stated the when you are warming up the engine that # 3 is not firing. So, why are you missing with the carbs that were professionally rebuilt?

 

[Cobra 427 V8]

If it starts ok , use choke to warm it slightly , then ride it , no need to use choke again , maybe some fuel additive cleaner could help the carb passages that are hard to clean , like if you have the bowl off and puck out , it cuts a circuit in half , most of us have had the carbs in and out 3 times , sounds like you would be better of riding it (no choke) . Cheers .

 

[dan filipi]

Seems like problem could be with the choke system itself. Maybe the one carb is being choked more which would make it get more fuel which makes it run cooler?

 

[BrittC]

I'm confused - you stated the when you are warming up the engine that # 3 is not firing. So, why are you missing with the carbs that were professionally rebuilt?

They were professionally rebuilt and #3 is not firing on choke despite the rebuild. That's why I'm messing with them. Everything else is new, and since #3 doesn't fire while on choke, there's something going on with that carb.

 

[BrittC]

Seems like problem could be with the choke system itself. Maybe the one carb is being choked more which would make it get more fuel which makes it run cooler?

Seems like it to me as well. #3 is where the choke cable attaches, and when the carbs are out, the mechanism and linkages all appear to be moving freely and together. I'm stumped.

 

[Workinman]

For what it’s worth, I’ll toss in my 2 cents here. I recently restored a 77, and I too had a terrible time with the carbs. Even though the carbs were professionally rebuilt, by a person who is HIGHLY regarded by members of this forum, when firing up the bike, it ran pretty bad. I had to totally go through the carbs and make modifications that need to be made on a 77 to fatten them up. These modifications are on Randakks website, and I assumed that this carb guru would automatically do them, but no. Anyway, after redoing the carbs, doing these modifications, and syncing the carbs, it runs good. Moral of the story is… just because you had these carbs professionally rebuilt doesn’t necessarily mean they are correct.

My other story involves a different machine but is relatable here. Stick with me.

I purchased a 1980 Honda CB750F shortly after finishing my Wing, and this bike REALLY ran bad. I installed a new Dyna ignition, which helped, and rebuilt the carbs a couple or three times just like you have, with carb cleaner and compressed air. I had the bike running pretty darn good except for one small problem. After the bike warmed up good, maybe twenty or thirty minutes of riding, the idle was VERY slow to come down. It would hang there for 20-30 seconds and THEN fall gradually. Other than this, the bike ran flawlessly. I tried EVERYTHING! Pulled the carbs a couple/three more times, check all the hoses, checked the intakes for leaks, checked tha cable adjustments, NOTHING would fix this problem! And it was ANNOYING to ride this bike like this. Finally, I purchased an ultrasonic cleaner, which I had always deemed totally unnecessary in all the years I’ve worked on bikes. I had convince myself that SOMEWHERE inside this carbs was a passage clogged that was causing my problem. So I bought a BIG ultrasonic cleaner, some ultrasonic carb cleaner, and I pulled the carbs AGAIN. Pulling the carbs and reinstalling them on a CB750 DOHC is not a picnic! I tota cleaned the carbs again, same as before, except this time in the ultrasonic cleaner, and the problem Totally disappeared. The bike runs like a top now. Good as new. The moral of THIS story is although a different problem from what you’re having, the headache was very similar, and it was solved with an ultrasonic cleaner. After all these years of working on bikes and not believing in ultrasonic cleaners, at this point I won’t do a carb without one. It could very well cure your problem too.

I hope this helps.

 

[BrittC]

Thanks for sharing. I may look into purchasing one. There's a different Randakk approved rebuilder 2 hours from me and I may see if he's got one and wants to go through these again. I've removed and reinstalled the carbs 4 times now and am just about bored with it.

 

[kerryb]

The sweating is condensation from too much fuel, and not enough heat. You might want to check the air screw settings, but since it is during warm-up with choke I wouldn't get too excited about it. If it runs good off choke, that's pretty good. What does your carb rebuilder say about it. There must be some tuning required to match a set of carbs with an engine
I've set up 5 wings with their newly refurbished carbs, and when I get 45mpg without adversely affecting the plugs. I quit messing with it. As long as it starts right away on choke, I don't worry about a few stumbles during warmup.

 

[BrittC]

The sweating is condensation from too much fuel, and not enough heat. You might want to check the air screw settings, but since it is during warm-up with choke I wouldn't get too excited about it. If it runs good off choke, that's pretty good. What does your carb rebuilder say about it. There must be some tuning required to match a set of carbs with an engine
I've set up 5 wings with their newly refurbished carbs, and when I get 45mpg without adversely affecting the plugs. I quit messing with it. As long as it starts right away on choke, I don't worry about a few stumbles during warmup.

It starts and runs nicely but the sweaty intake tube bugs me because this was a frame off restoration with a lot of money invested, and I'd like it to come out perfect.

I've tried the screws in various positions with no change to the #3 cylinder behavior on choke. My carb rebuilder said if it starts and runs well, he would leave it alone. It still bugs me that it's not quite right.

 

[Workinman]

I would have to agree with that. If it runs good once warm I would count my blessings and move on. You do have two beautiful bikes there, so I’m not sure I would sweat a small choke issue.
And I know what you’re saying about being tired of messing with them. It took me quite awhile to get my carbs dialed in. There were a couple of times that I considered pushing it in the damn lake!

 

[BrittC]

Just spent the last 3 hours pulling the carbs again and swapping all of the internals between the #1 and #3 carbs. The behavior remains with #3. I was hoping it would move to carb #1, indicating something amiss with a float, jet, etc. I weighed the floats while they were out, and they're both 12 grams.


If it was nicer out, I'd have taken it for a ride to put my mind at ease.

(photo from the first ride after installing the freshly painted bodywork)

 

[Cobra 427 V8]

Just spent the last 3 hours pulling the carbs again and swapping all of the internals between the #1 and #3 carbs. The behavior remains with #3. I was hoping it would move to carb #1, indicating something amiss with a float, jet, etc. I weighed the floats while they were out, and they're both 12 grams.


If it was nicer out, I'd have taken it for a ride to put my mind at ease.

(photo from the first ride after installing the freshly painted bodywork)
View attachment 50024

I would imagine your intake rubbers are like plastic , mine were, I soaked mine in oil of wintergreen and isopropyl alcohol for 3-4 days , this helps soften and get a better seal (more vacuum) signal .

 

[BrittC]

I would imagine your intake rubbers are like plastic , mine were, I soaked mine in oil of wintergreen and isopropyl alcohol for 3-4 days , this helps soften and get a better seal (more vacuum) signal .

They are actually still pretty pliable. I like to warm them up on a radiator before installing them, and I'm able to get the clamps nice and tight. I believe that they are sealing well.

 

[85goldwing]

My two cents. Find someone with a ultrasonic machine, or buy one. They are relatively inexpensive. If you are only putting one carb in at a time, a small unit will do. If you buy one use deionized water for best results. Hope this helps

 

[BrittC]

Well, the carbs from my 75 just went into my 76 and the 76 starts and runs SO FREAKING GOOD. It revs better and idles better. It's crappy out so I won't ride it but at least I know it's definitely a carb issue with the 76.

I'm bringing the bike to a different Randakk approved carb guy and will let him have a go at it. I'm so tired of screwing with these carbs for months and I need my sanity back...