Carb Questions

[chef1366]

Pulled the carbs off again and put in the 45 pilot jet and set the floats to 22mm. Set the air screw for highest idle per cylinder and sync. The bike runs the best ever. Pulls like a train in 5th gear from 3.5 rpm to red line. Still one problem. If I run 85+ for a mile or so and back off it wants to die. If I run 70 to 80 it is fine. Pulled the petcock off and there was a broken metal tab halfway over the air port that connects to the vaccum line. Cleaned it up and took the tab out and checked the valve and it appeared to operate properly. Still same problem. Is this a bad petcock symptom or could this be a result of using the slides with the drilled ports or maybe I need to set the floats richer?

[chef1366]

Pulled the carbs off again and put in the 45 pilot jet and set the floats to 22mm. Set the air screw for highest idle per cylinder and sync. The bike runs the best ever. Pulls like a train in 5th gear from 3.5 rpm to red line. Still one problem. If I run 85+ for a mile or so and back off it wants to die. If I run 70 to 80 it is fine. Pulled the petcock off and there was a broken metal tab halfway over the air port that connects to the vaccum line. Cleaned it up and took the tab out and checked the valve and it appeared to operate properly. Still same problem. Is this a bad petcock symptom or could this be a result of using the slides with the drilled ports or maybe I need to set the floats richer?

[KEITH KRAUSE]

If you have any doubt about the petcock flow, just be sure it's clean and run the bike on prime. This will eliminate any vacuum related issues. Fuel line should be 5/16" also. If the bike still has the 85+ problem, it's not because of the petcock. Also, be sure the two floatbowl vent lines are clear/not kinked. Be sure the gas cap vent is clear.
I don't know exactly what would cause a problem at 85 but not up to 80.
Mixture or a vacuum issue? Both? Drilling out the slides with stock intake will effect the vacuum. Throttle response will be negatively effected, but I don't know why a small difference in speed would create such a drastic problem. Float level will always change things, but if the floats are set within the factory range, they should be fine.
You mentioned the same problem about a week ago and you said the plugs looked lean when you pulled over. Marking the throttle would help as to which jetting circuit the bike was using at the time of the problem. If you were going a steady 85 in top gear, you would be solidly on the jet needle (about 1/3 throttle position). If so, and the plugs were lean at this position, then it's obvious you need to raise the jet needles a position and test again. Raise the needle by lowering the e-clip one position.
Incorrect mixtures can cause all kinds of performance issues. I don't know if the stalling problem will go away, but your lean plug reads tell you the mixture must be richened.

[chef1366]

The 1980 had the legendary petcock with no switch, only vaccum. Just bought a brand new one and am going to try pulling the vent lines in the morning.

[KEITH KRAUSE]

The 1980 had the legendary petcock with no switch, only vaccum. Just bought a brand new one and am going to try pulling the vent lines in the morning.

I'm familiar with that petcock. It has prime and on positions only, by turning with a slot screwdriver.
For some reason, the prime on this petcock needs the engine cranking to initiate fuel flow while on prime. Other vacuum petcocks don't require vacuum/cranking while on prime. But since you have a new one, the old one and possible problems don't matter.

[chef1366]

I have read your comments about a "vortex" that can occur in your vent line hoses. Will it do any harm at all just to remove them as long as I don't spray water directly into them? The symptoms of my woes also fits the description of the vortex symptom.

[KEITH KRAUSE]

I have read your comments about a "vortex" that can occur in your vent line hoses. Will it do any harm at all just to remove them as long as I don't spray water directly into them? The symptoms of my woes also fits the description of the vortex symptom.

It won't change a thing to remove the vent lines and leave the ports open, as long as you're careful with water.
With a stock intake, removing the lines shouldn't improve fuel flow/venting. Your model is made to run with the lines on. If removing them does help you, and they're the correct size and clear, I couldn't explain it.
Without reading back, I think you said the carbs are clean, but it doesn't take much to screw up the venting. I've seen a small piece of rubber break off from the tubing between carbs and PARTIALLY block the vent passage that would vent two carbs. This partial block drove the owner nuts for months, thinking it was a surging/lean jetting problem. Only because of experience did I try blowing evenly into both vent lines. I could tell a small difference in resistance at the partially blocked vent. Found the little rubber piece by blowing it out with almost 200 psi. Bike ran fine. Turns out he pushed the carbs together during a rebuild and broke off a bit of his 1/2 rubber vent coupling hose.
A wad of spider webs will do the same thing. Doesn't take much.

[chef1366]

The petcock was the issue with the highway speed meltdown. Now I'm back with the top end issue. Running great with good plug coloration from idle to 1/4 throttle, 1/4 to 3/4 but lean from 3/4 to full throttle. What higher jet would you start with, 120 or 122.5? Is the stock needle for this bike pointed or rounded at the end. The one I have is rounded and I've read that that could be an old dynojet needle. It does not have adjustable clips though. I tried the Factory brand needle but could not find a clip position that worked well. Believe it or not I tried all six( I did not have to remove the carbs to do this) If I increase the main jet size am I back to the drawing board on needle position and pilot jet size?

[KEITH KRAUSE]

To get good plug color/performance while on the jet needle, you must have shimmed the stock needles? The Factory jet needles may be the wrong ones for your carbs, so they didn't help. I don't know the tip shape of your stock needles.
If you have lean plug reads at 3/4 to open throttle, I'd go up a full size to 122.5 and test. I don't know HOW lean the plug reads are, but it sounds to me like one step (2.5) wouldn't be enough of a change.
Hopefully the larger main won't create any bogging while rolling on full throttle from 60 mph in top gear. Sometimes there's an overlap between the needle and main circuits that forces you to decide. I like to jet a little "backwards" of what some like to do. I insist on getting the jet needle right. Then I go with the main that gives me the best top speed WITHOUT creating any roll on bog. If a bog does occur, I'll sacrifice 2-3 mph top speed to eliminate roll on bog/hesitation. Responsive/steady passing power is too important. Some decide to go with the main that gives them the best top speed, and they downshift a couple gears during a roll on to "bypass" any bogging. A motor like yours shouldn't have to be downshifted like this to have good roll on power.

[chef1366]

I did not shim the needles just rebuilt the carbs with new o-rings, set the floats properly and got a new petcock. To shim the needles you would just add tiny washers to the underside of the top of the needle just above the spring? The ceramic is snow white on the plug during a full throttle chop. Can you remove the main jets without removing the carbs? Seems like you could.

[KEITH KRAUSE]

I did not shim the needles just rebuilt the carbs with new o-rings, set the floats properly and got a new petcock. To shim the needles you would just add tiny washers to the underside of the top of the needle just above the spring? The ceramic is snow white on the plug during a full throttle chop. Can you remove the main jets without removing the carbs? Seems like you could.

Yes, you can remove the mains by taking off the float bowls if you like.
As for your jet needles, you said yesterday the plug colors were good up to 3/4 throttle position. If the color is good at this position, the jet needles are set.
It sounds like there's some uncertainty if these needles are stock.
If your only mod's are that pipe and a K&N replacement filter then your bike SHOULD be running lean on the stock needle circuit, at least some. But if your 1/4 to 3/4 reads say the plugs are burning right, then leave it be. Maybe the needle jets have been changed by a PO or who knows?
Just to answer your shimming question, a jetting spacer used to raise jet needles, is placed directly under the jet needle e-clip. The e-clip attaches to the needle and there should be a thicker plastic spacer above the e-clip and a thinner plastic spacer below the clip. The two plastic spacers are always re-installed in same order regardless of jet needle type.
If a full throttle chop shows a snow white insulator, and you're SURE the float levels are set to factory recommendations and the carbs are operating correctly, I might try two full sizes up (10) on the mains at this point. It really is hard to guess. You just have to try and re-test. That's jetting. Two full sizes up from 117.5 (?) might be too rich, but snow white plugs generally suggest one full size up may not be enough.
Some shops will be cool and let you return/swap jets if you return them in new condition.

[jgordon]

I did not shim the needles just rebuilt the carbs with new o-rings, set the floats properly and got a new petcock. To shim the needles you would just add tiny washers to the underside of the top of the needle just above the spring? The ceramic is snow white on the plug during a full throttle chop. Can you remove the main jets without removing the carbs? Seems like you could.

It's a lot easier to get a DJ kit and install some pods. It makes it a lot easier to get them on and off. I live in Bakersfield too and it took me about 12 times on and off with the carbs to finally get them right and being the glutton for punishment that I am i just got through putting some 36 mm carbs off of a 1990 GSXR on and went through the same thing again. Sure runs a lot better than the stock 34's, anyway, the pods make it a lot easier to change things around in the carbs.

Jgordon

1983 GS1168 W/ 1150 head

[chef1366]

Is there a way to switch out diaphragms? I'm going to either get stock slides(not drilled) or switch the diaphragms if possible. I think Keith was right about throttle response being too quick with a stock air box. I'm also going to get .5 mm shims and raise the needle. I read that one shim is like 1/2 notch on an adjustable needle. Should I try one full notch at first(2 shims) or work my way up from from 1/2 notch(1 shim)?

[KEITH KRAUSE]

You're confusing me. You said the plugs were burning a good color at 1/4 to 3/4 throttle. If this is true, why would you want to adjust the jet needles?
You said the full throttle test was giving lean reads. Seems you only need to get the main jet right now.
A typical jetting spacer is approx' .023"
This would raise the jet needle about 1/2 a position.

[chef1366]

Sorry Keith, just getting anal with my bike. I just want perfect throttle response and probably won't get it with the drilled slides. It is very good and I should be happy with it . I'm ordering 122.5 jets from Dennis Kirk. I've ridden all over So Cal. Are there any scheduled GS get togethers in the area?