High idle speed after carb cleaning seems related to the petcock

[Json]

Hi there.

So I have an standard XS 1100 '80 that I bought recently and am going through piece by piece. I removed the carbs cleaned them up thoroughly and put on new carb intake manifolds. I did a bench tune and a sync with the carb synchronizer on the bike. All seemed to be tickety-boo until the bike warmed up on her first ride. The revs stay at around 2.000 rpm when standing idle for a good while before occasionally dropping to normal levels. Occasionally as in, once in a while after standing with a high idle they will drop to normal levels. Went back to the drawing board and have found that the problem comes from the hose attachment from the left petcock to the number 2 intake manifold. If i detach it from the petcock it idles fine. If I block the hose with my finger the problem arises.So this would indicate some sort of blockage in the petcock.The bike was idling fine before the carb service and I haven't touched the petcocks.

I guess my question is, how exactly do the petcocks on these things work, should I clean the petcocks even though they were functioning before or what am I not seeing here. Any experience here would be appreciated.

[DiverRay]

Petcocks are vacuum operated. The left petcock has a leak. I would buy a rebuild kit and go through both sides. Replace ALL vacuum and fuel lines if you have not done so, as well.

[Radioguylogs]

If you detach the vacuum hose from the petcock, it it supposed to stop the fuel flow in the petcock. Since, your engine is still running, there may be a problem in the petcock, but it is a separate problem from the issue you described.

Your symptoms are identical to an air vacuum leak.

Yet your test results are inconsistent, finding the problem goes away with the vacuum hose disconnected....and the problem recurs when the hose is plugged with your finger. Seems backward.

Note: Since you changed the rubber boots between the carbs and the intake manifold, they are suspect for air leaks. Butterfly shaft seals can be another culprit. Of course, that hose to the petcock my be related.

You can troubleshoot with starter spray, lighter fluid or unlit propane.

-Mike

[JeffH]

Hi there.

I removed the carbs cleaned them up thoroughly and put on new carb intake manifolds. I did a bench tune and a sync with the carb synchronizer on the bike. All seemed to be tickety-boo until the bike warmed up on her first ride. The revs stay at around 2.000 rpm when standing idle for a good while before occasionally dropping to normal levels. Occasionally as in, once in a while after standing with a high idle they will drop to normal levels. Went back to the drawing board and have found that the problem comes from the hose attachment from the left petcock to the number 2 intake manifold. If i detach it from the petcock it idles fine. If I block the hose with my finger the problem arises. So this would indicate some sort of blockage in the petcock. The bike was idling fine before the carb service and I haven't touched the petcocks.

I guess my question is, how exactly do the petcocks on these things work, should I clean the petcocks even though they were functioning before or what am I not seeing here. Any experience here would be appreciated.

Just some random thoughts based on the Info you provided so far

+1 on what Ray & Mike suggested.
Seems the two variables are #1 - the NEW CARB INTAKES #2 - Cleaning the carbs
You didn't mention float height you set but suspect that is not the issue or hung float the issue.

My first thought is where did you get the new Intake Manifolds. As I recall from other threads & posts some have had trouble with 'new' Intakes (poor quality control, poor fit etc.)
On Cold start you need full choke, half choke or no choke? So, Revs at 2,000 RPM and you can't adjust it lower?

Mike said, symptoms seem backwards from your conclusion. I agree. For example: if my bike is idling great and I remove say #1 or #4 Vacuum Cap to suck in air what happens? Starts running bad until I put the vacuum cap back on. So if your Petcock was leaking on the vacuum side then there would be no change whether the hose was On or Off since either way it was sucking air, connected or disconnected.

So your Vacuum Lines aren't cracked? #1 & #4 have new not leaking or cracked Vacuum caps? Advancer is working ok (not leaking) with Vac Line on that standpipe on #2 carb body?

Since you seem to think it is #2 then New Intake, Vac Advance, Condition of hoses all are suspect.
Hopefully some of the gurus can give you some other ideas on how to Troubleshoot & Remedy this 2,000 rpm idle issue and oddity with #2 vac hoses.

Keep us posted on what you find.

Jeff

[Bax]

This is what the seals usually look like after a few years.

[Bax]

K&L kit to repair has a flaw with the octy stem o ring being too small to seal against the valve seat. Replace this with a larger one, bit on is fuel compatible. The correct size is metric 2x4.5, I’ve used a 1/16 x 3/16 (2-008) and it worked for a few years, although it sits loose it did seal.

[bikerphil]

Just something else easy to check, make sure the clamp for the #3 carb boot is not interfering with the throttle linkage, it will if the clamp is put on with the screw on the top, it should be on the bottom away from the linkage.

[JeffH]

Hi there.

So I have an standard XS 1100 '80 that I bought recently
I guess my question is, how exactly do the petcocks on these things work, should I clean the petcocks even though they were functioning before or what am I not seeing here. Any experience here would be appreciated.

I don't think we answered your Question as to "How the Petcock works"

Referencing the K&L Kit that Bax posted for you and that plunger he is pointing to:


Basically how it works:
When that plunger with 'O' ring is engaged (static position with motor OFF) that plunger stops the flow of gas from the tank through the petcock to the fuel lines. But when you apply a vacuum to the vacuum port that vacuum on the opposite (back air side of the plunger) pulls out 1-2mm and allows the fuel to flow. Something like that ..................................
Really very simple. Both age and ethanol gas eat up the rubber parts as Bax showed you.

As Ray & Bax have said, if this is a new to you bike then I would buy the K&L kit and rebuild the Petcocks. Understand you have a "G" Standard.

As Mike & BikerPhil commented your immediate problem is not likely the petcocks but we certainly recommend rebuilding them. Likely something goofy with the new Intakes or the condition of the Vac Lines.


Keep us posted. Good Luck

Jeff

[bepenney]

I have a 79 xs1100sf. Oring in octopus is split. Looking for correct size.