1981 GS650E Choke/fuel Issue

[Bryan22]

We have a GS650E that we finally got the timing figured out on. We did not know about the 2 sets of timing marks and had it set 180 off.

But now even after going through the carbs as well we are still left with a problem the bike had when we got it. The engine will not run without the choke being on. Would a bad diaphram on the vaccuum side of the petcock cause this? Can we get some opinions on this?:?

[t3rmin]

You can check that easy enough by plugging the vacuum port (that goes to the petcock) on carb #2 and switching the petcock to prime. If the problem goes away, it was petcock/vacuum leak related.

Are you running with or without the filter/airbox?

Have you done any syncing of the carbs? This can make a bigger difference than you might think.

Are you getting spark on all cyls?

[t3rmin]

Also, make sure your intake boots and the o-rings that seal the boots to the head are intact. To check this, spray water or wd-40 or whatever liberally all over the rubbers with the motor running and see if the RPMs change. Also observe whether the rubbers are still supple and undamaged.

I was beating my head against the wall trying to get my 650 E running and one of the major things I had ignored were those intake o-rings. Makes all the difference in the world if they're leaking. They get old and turn into what feels like hard paper gasket material, but they should be rubbery and round (not flattened).

[Bryan22]

Yes, the airbox and filter are in place... everything is in place as it should be.

All 4 cyl are firing and on choke the engine run smoothly, so other issues cleared up when we tore the motor down and did some work. It is just that you push the choke off and she dies right down.

The carbs were all gone through and cleaned as the bike had been sitting for a few years initially before we tackled this. We tore it down a bit to put a gasket set into it. This choke problem has been the one persistant issue.

Pinch off the vac line and keep it on prime?

We have not done anything with the synching yet. Nothing on that end has been changed from when it did run well a few years ago.

Bryan

[Bryan22]

Yep, the rubbers are all in place and sealed well and everything is tight.

[t3rmin]

Pinch off the vac line and keep it on prime?

Yeah, if you want to see if there's a petcock-related vacuum leak, plug the vacuum tap on the #2 carb and put the petcock on prime. I'd use a rubber vacuum cap rather than pinching the hose, so you can be sure you've got it sealed.

One obvious question I've got to ask: have you adjusted the idle speed screw? The choke may be raising the idle to a sustainable speed, but when you take the choke off, it's just dropping down too low. Try turning the idle screw/knob (between #2 and #3 carbs in the back) in a bit and try it again.

[Bryan22]

We will try that.

The idle adj hasn't been toyed with at all.
The dying off when backing off the choke issue has been there since we got it running after it had been sitting for a few years. It would only run on choke. Even now after cleaning the carbs, etc it is still the persistant problem.

[t3rmin]

The idle adjuster is just a finger knob/screw thingy, so that's an easy one. That'd be the next thing I checked...

[Nessism]

No to belabor the point but did you pull off the carb boots that attach to the head and replace the large o-rings sandwiched in there?

[GS850_Coug]

No to belabor the point but did you pull off the carb boots that attach to the head and replace the large o-rings sandwiched in there?

This can never be stressed enough!!!

Having to run with the choke means running lean. Either you have an air leak, or you need to adjust fuel mixture (assuming all fuel screens are clean, fuel hose is proper inside diameter/not kinked, and floats are set properly). Keep in mind that the most common thing on these old bikes is deteriorated rubber parts/bad gas lines (rust in tank, plugged screens/carb ports, etc). Check the rubbers and orings for leaks with a mist of water while it is running. Adjust the idle up to where can run without choke (if possible), and it should rev up/smooth out when the mist is sprayed on the intake boots if there is a vacuum leak. If there is no effect, it is pretty safe to say you are short on fuel. Check the lines for kinks/proper size, filters clean, and floats set properly. If they are all good, you should be good to just adjust the fuel mixture to richen it up.

Good Luck!

[Nessism]

I'm not a fan of the spraying water test to look for leaks at the carb boot O-rings - it can give you a false sense of security and make you think all if fine when it isn't.

If the O-rings are old, replace them. Period. Takes some time but it's the ONLY to assure there are no leaks.

[t3rmin]

If the O-rings are old, replace them. Period. Takes some time but it's the ONLY to assure there are no leaks.

Agreed.

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