Runs great on Prime?

[tsassman]

'79 GS1000E that started having serious missing issues. Tried a number of things myself-didn't help. Sometimes it runs perfect and others it starts missing bad like it is running on 2 cylinders. I have had my electronic ignition checked, coils checked, new spark plug wires and plugs. What I found today is that when it starts missing and I moved the fuel valve to prime it quit missing. Can anyone give me things to check and or replace that would help me with this issue?

[Rein]

replace the petcock? If prime is working, but run isn't, then something is wrong with the petcock, and it's not giving enough fuel when running. But when you're on prime, and flow is not dependent on vacuum or the diaphragm, you're getting enough gas.

correct me if i'm wrong, shouldn't your petcock have only on and off? I thought 79's only had non vacuum petcocks?

[tkent02]

'79 is the last year for the good petcocks, but this one probably needs to be replaced. The other possibility is that the screen in the petcock is clogged with something. Take the tank off, stand it up on it's nose so you can remove the petcock without spilling any fuel, take it apart and have a look. It should be obvious what's wrong once you see the inside of it.

New ones are available from any place that sells Suzuki parts, or from Z1.

Edit, have the tank fairly empty, if it's too full fuel will come out the filler cap when you stand it up on it's nose.

[tsassman]

Thanks for the advice. Will take the petcock off first thing tomorrow evening and give an update on what I find.

Thanks Again
Tim

[goggleboy]

[wasn't sure whether to post a separate post or not, but I'm having similar issues]

I just put some fresh boots on my 78' gs750, but I'm still having fuel problems. It seems like I can't start it without the choke on no matter what. Then once I get it running, it runs okay but then starts to stumble after a few minutes of riding. At one point I shifted the petcock to prime while she was going and it seemed to catch up or something. Oh, and it won't idle by itself either ...sheesh. Could this be petcock related? or float height?
I have an "on", "reserve", and "prime" positions for my petcock by the way

[almarconi]

I just put some fresh boots on my 78' gs750, but I'm still having fuel problems. It seems like I can't start it without the choke on no matter what. Then once I get it running, it runs okay but then starts to stumble after a few minutes of riding. At one point I shifted the petcock to prime while she was going and it seemed to catch up or something. Oh, and it won't idle by itself either ...sheesh. Could this be petcock related? or float height?
I have an "on", "reserve", and "prime" positions for my petcock by the way

Could be many problems. When was the last time you adjusted the valves and cleaned your carbs? When you cleaned the carbs, did you set the float height and bench sync them? Have you vacuum synced them and check the fuel level in the bowls (service fuel level)? Are you running stock airbox and pipe or pods?

[koolaid_kid]

[wasn't sure whether to post a separate post or not, but I'm having similar issues]

I just put some fresh boots on my 78' gs750, but I'm still having fuel problems. It seems like I can't start it without the choke on no matter what. Then once I get it running, it runs okay but then starts to stumble after a few minutes of riding. At one point I shifted the petcock to prime while she was going and it seemed to catch up or something. Oh, and it won't idle by itself either ...sheesh. Could this be petcock related? or float height?
I have an "on", "reserve", and "prime" positions for my petcock by the way

For the best responses, I suggest starting your own thread. Your issue is more to do with jetting or intakes leaks.
Best of luck.

[Kerry]

'79 GS1000E that started having serious missing issues. Tried a number of things myself-didn't help. Sometimes it runs perfect and others it starts missing bad like it is running on 2 cylinders. I have had my electronic ignition checked, coils checked, new spark plug wires and plugs. What I found today is that when it starts missing and I moved the fuel valve to prime it quit missing. Can anyone give me things to check and or replace that would help me with this issue?

This is how I discovered my identical problems were a result of the petcock (after 2 "experts" told me it was fine!) Just replace the petcock - will give you another 30 yrs of service.

...and Basscliff will probably soon be along with a welcome chock-a-block full of wonderful information, including a list of common maintenance issues and detailed tutorials.

[tsassman]

I removed the petcock this evening and the screen was clean. I disassembled it and didn't see anything wrong with it there. It did give me a better understanding on how it works though. All thing o-rings and gaskets are good.

It looks like about the only thing that can go wrong internally is the vacuum diaphragm valve. It appears to function like it should. I pulled suction through the vacuum pipe and the diaphragm engaged. Don't know what else to check.

I called Z1 today and inquired about a new one. I will measure the bolt dimensions and probably order a new one. I'm not quite sure I like the appearance of their design. Are there any other manufacturers that make better looking ones that will function good also?

[tkent02]

Now test it, put it back on the bike, suck on the vacuum line, make sure fuel flows out as a steady stream. Make sure the vacuum doesn't leak down, and make sure no fuel gets into the vacuum line. If it tests good, there's no reason to replace, but you still need to find out why the engine was only running well on PRI.

[oldgrumpy]

had similar fuel problem....

hi guys i have a 1980 gs1000e,, i,ve had a similar problem or like our friend is talking about....make sure your carbys are clean... then pull the vac. line off and gently suck on it doing this on run if its only a little dribble ,, buy a new vacume petcock from suzuki or z1 i have found trying to rebuild them has given me dramas.. peace of mind .. and of course good quality fuel line the correct size cheap rubbish is dramas as well ,a new petcock isn,t that expensive for peace of mind and your bike will know you lov it ... regards david

[goggleboy]

Now test it, put it back on the bike, suck on the vacuum line, make sure fuel flows out as a steady stream. Make sure the vacuum doesn't leak down, and make sure no fuel gets into the vacuum line. If it tests good, there's no reason to replace, but you still need to find out why the engine was only running well on PRI.

could worn or notched float needles play a bad role? I'm having the exact same problem and my petcock seems fine.