Need some help folks

Twobikesonewrist · October 27, 2019, 01:22:40 PM

I put up a few other posts. Having trouble with a recently purchased 89. I did the carbs and they have been completely gone through and everything set up properly. The first run it stalled once I did a few runs up and down the street. Petcock was on run. I switched back to prime and it ran fine. Good power and idle. When I switched back to run it idles for a few minutes then stumbled and stalled. back to prime and it ran good.

Someone on here suggested I check the vacuum line to make sure there were no leaks. It was fine. I pulled the petcock off the bike to open it up to see if anything was gummed up. It was clean, but the spring was missing behind the diaphragm. Someone had obviously been messing with it.

I bought a new K & L petcock and installed it today. Fires right up and ran fine on run for a few minutes (at idle) then it stumbled and stalled. I put it back to prime and she's good. Back to run and good for a few more minutes, then stumble. While stumbling, I switch to prime and it's good again.

Need some help here. I thought a new petcock would solve the problem. Hope I didn't waste the money. No vacuum leaks, new petcock, clamps.

I have seen a post showing how to modify the petcock by opening the holes in the restrictor plate on this website and on youtube. I hate to hack up a new part. Most of the posts I've seen refer to the carbs going lean at high speed. I'm having the problem at idle. Could there be too much vacuum?

Any help would be appreciated. I would like to hear any ideas you have. Last resort I would modify.

Pat108 · October 28, 2019, 04:38:34 AM

Was the bike sitting abandoned before you bought it? Maybe you have already cleaned the tank from old debris but sounds like the line is clogged, since you checked and changed the external parts maybe something is blocking the flow inside the tank? Have you tried inverting the lines prime to run and viceversa?

That's my two cents

Pat108 · October 28, 2019, 04:58:19 AM

Another way of knowing this is running it on the reserve selector, reserve and prime share the same line. Also maybe check the O-Rings on the vacuum line. I'm also new to gs world so I hope This works

Twobikesonewrist · October 28, 2019, 06:00:04 AM

I went through all of the lines, they are clean and the tank was completely cleaned. The carbs were cleaned and rebuilt using OEM parts. Runs very well on prime, so I'm ruling out a carb issue. When I pulled the tank "petcock" it was clean and the filter screen was in very good shape.

I thought the new fuel valve petcock would solve the problem. There is a new in-line fuel filter between the petcock and carb. Could that be limiting flow? Again it only happens on "run"

mr72 · October 28, 2019, 10:13:23 AM

You likely have a vacuum leak. This would give insufficient vacuum to the petcock to keep it open.

When you "did the carbs" if you didn't replace all of the o-rings then that's probably your problem.

Twobikesonewrist · October 28, 2019, 10:48:55 AM

Yes all O rings were replaced with OEM rings, and gaskets.

mr72 · October 28, 2019, 10:57:27 AM

including the intake boots o-rings?

You can use a vacuum gauge to ensure you have enough vac at the petcock.

Twobikesonewrist · October 28, 2019, 12:03:46 PM

I did not remove the intake boots. They look new, very pliable and no damage, but I did not check the o rings. How much vacuum should I have at the petcock? Should I connect the gage to the vac line coming off the backside of the petcock?

mr72 · October 28, 2019, 12:39:30 PM

the vacuum works the other way, the source of vacuum is the carb on one side. BTW one carb has that vac. port blocked off and the other does not (at least on mk1 carbs, dunno what year bike you have). I guess it's possible you connected the vacuum hose to the petcock from the wrong carb.

If the intake boot o-rings were not replaced then they probably need to be replaced. But they would have to be leaking a LOT to cause the petcock to not open.

IDK how much vacuum should be required to operate the petcock. Maybe the FSM would have it? Someone else here know? But if it operates on PRI and doesn't operate on ON, AND you are certain the petcock itself is not bad, then it is absolutely 100% a vacuum problem. Well, most likely

Bluesmudge · October 28, 2019, 12:51:08 PM

Did you try running on reserve yet?

Twobikesonewrist · October 28, 2019, 03:44:16 PM

I have not tried it on reserve yet. That's next.

To answer another response the bike is an 89 and only has the vacuum line coming from the left carb. It is in the correct position. I can borrow a vacuum gauge from a friend, but while I'm waiting, I had it running today and did the unscientific method of checking the boots by spraying some quick start on them, and around all of the connection points with no change in rpm.

Its not on the road right now so I can't really take it out to see what it's doing. I have a school behind my house so I ran it over there and it was fine on run, under load for a few minutes, then it started to stumble.

I really appreciate the responses.

I will try reserve next and see what happens. I will keep you posted. Thanks everyone.

herennow · October 28, 2019, 08:39:06 PM

I dont know the K&L petcock, dos it connect the same way as the original.

Note there is an error in the factory manual diagram showing the cable routings. This might or migh tnot affect you.

I like Shade tree diagnostic tools

When I overhauled my petcock I found it was easy to open just by sucking with my mouth

Get a long hose and connect it to the vacuum port on the petcock, open the two drain holes on the bottom of the carbs. Suck the tube and see if both carbs supply good fuel flow.

Whould be around 200 to 300 ml per minute per carb.

Obviosuly catch the fuel in a container and dont smoke while doing this, etc. etc.

This will confirm on which side of the hose the problem exists. Ive seen cases where the floa tneedle level is so low that the bike dies but this was always at higer RPMs.

Twobikesonewrist · October 29, 2019, 02:56:39 PM

OK Bluesmudge gets props for reserve! I got home today and put it on reserve and got it running for a few minutes no problems. Took my other bike out for a ride cause it was 70 in upstate NY today. Got home and took the gs out around the block a few times and no stumble, or stall. Since reserve operates off the vacuum, we can rule out a vacuum problem (there were no other indicators of a leak. That only leaves a clogged pickup in the tank, or a plugged fuel line.

I had the pickup out when I cleaned the tank. Can that be disassembled and cleaned?

News:

Need some help folks