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No choke, no idle

  • Thread starter Thread starter Suzukizilla
  • Start date Start date
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Suzukizilla

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Replace the carb seal and will idle w/choke at about 2k (with airbox on). Try to ease off the choke after about 5 minutes and engine dies. Air & fule screws are 1 1/4 turns, main idle is 3 1/2 turns from bottom (thats where it was before I took it apart), didnt mess with sliders as they looked fine where they were at. With choke on 1&2 exhaust water evaporates instantly, 3&4 water disolves slowly. Plugs on 1&2 are balck/sooty and 3&4 are black/slightly wet. Tried to make minor adjustments but it only seems to make matters worse and I would assume you probably want to make fine adjustment with the choke off so I'm not sure where to start looking here. Why cant I shut the choke without killing the engine?
 
Sounds like you have very poor combustion on 3&4. This is not necessarily a carb problem or at least may not be totally a carb problem. Poor combustion could be ignition related but since it is on two cylinders that come off different coils, it seems like it may be related to compression. Have you checked compression on all cylinders? The number one reason for low compression on older bikes is lack of valve clearance. Check out the valve clearance article on my web site for details... the article is for a different make/model than you own but the theory is the same. As valve train wears, clearance decreases and valves can stay open just a tad ruining compression and thus yielding poor combustion.

If your plugs are black/wet, this indicates unburned gas. The normal culprits for "rich" plugs (black/fouled) are dirty air filter, incorrect adjustment of pilot circuit or floats set grossly high... In this case, I suspect none of these are affecting combustion but the problem lies elsewhere.

I suspect that due to the messy condition of the two plugs that appear to be firing consitently, you probably have weak spark across all four with some other issue such as lack of valve clearance making 3&4 worse. Take a look at the coil repowering article on my site and you might want to check voltage at your coils as described.
 
Try jumping your battery off a non running car. It could be a weak battery or bad grounds. Check all ignition related wire connections.
 
If carb related, I'm thinking they need a good cleaning. If the bike only runs with the choke on after 5 minutes, it's obviously depending on the choke circuit for fuel so the pilot circuit may be clogged.
Not sure if your intake is stock but try 1 turn out from LIGHTLY seated for the pilot fuel screws (underneath). If they were ever tightened too much, the sharp tips can break off inside the carb body and that could also explain your problem. You should see fuel shoot through the small hole into the carb throat if you remove these screws and shoot the holes. The screws tips should be sharp too.
The side air screws are to be set using the highest rpm method. If the bike runs poorly, initially set them at 1 3/4 turns out. Fine tune them when the bike is running decent. Synch the carbs when it runs better too.
Be sure the plugs are cleaned and are the correct NGK B8ES. Gap correctly. Clean/inspect all electrical connections.
I assume other basics are done already. Compression, clean filter, ignition timing, points(?) clean and dwell set, etc.
 
FYI this is a gs 750.
During the last week I dipped the carbs, hit it with carb cleaner and blew out all passages with high pressure then replaced the seals. I currently using the bat out of my car, the bike bat dropped dead about a week ago.

Tests I ran yesterday:
Compression: #1 130psi, #2 120psi, #3 120psi, #4 110psi
I think only the #3 went right up to 120 the other I had to 'bump' up to there pressures. By bump I mean hit the starter for 4 or 5 sec., stop then again for 4 or 5 sec and it would creep up. The pressure is really low (manual says it should be something like 130-170?).

Lifter check: Now the manual says to check with the lobes in the 12 o'clock position and in the 3&9 positions which were all in spek (between .05~.08mm) except for #4 intake is .010mm on 3&9 position but is .05@ 12 (?).

The compression has me really concerned though. How can an engine with 17k have such low pressure unless the valves are loaded with carbon and arent seating?

But I went and put the cover back on and plugs back in and it wont start at all now even with full choke. So I pulled the carbs back off and going to pull the bowls to recheck the idle circuts and floats. Btw this bike has already been switched to eletronic ign. and my main jet is 105.
 
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Put a cap full of oil in troubled cylinders and try another compression check. If the compression rises than it's rings, if not you may be right on the valves not seating.
 
Thanks Chef the oil worked. Have 150# from all cylinders now.

Pulled the carbs back apart reset the floats to 24mm like the instructons from Paul Musser (the manual says 24-28mm). I think they were set to 34mm from the looks of it. Rechecked all the little holes for clear passages and set the fuel pilot to 1 turn instead of 1 1/4. Will put the carbs back on tomorrow to see what I got.

Found a green and yellow wire (comming from a rubber gromit in the starter case) which I believe is to the oil pressure sensor. Its cut and taped. This doesnt effect the operation of anything does it? Maybe the sensor is bad and the light stays on or something and left it disconnected.

Also did the 750 come with an oil cooler? I have a hose that loops from the out to in (to the right of the starter) where I would assume is the oil sensor. Figure it had to go somewhere at one time, just not sure where.
 
34mm on the floats would be super lean if they can be adjusted at that setting. Don't forget to at least bench synch the carbs. I've made a detailed post how to if you don't know how. A search on synching VM carbs should find it.
 
KEITH KRAUSE said:
34mm on the floats would be super lean if they can be adjusted at that setting. Don't forget to at least bench synch the carbs. I've made a detailed post how to if you don't know how. A search on synching VM carbs should find it.
Click to expand...

Yep I'm surprised the needle even unseated to fill the bowl :-s . I totaly forgot about adjusting the floats when I put the carbs back together the first time:oops: .
The instruction from Mr. Musser want the slider adjusted all the way down which they are I cant even fit a wiretie under the opening. So I believe they are adjusted OK to get it running to do the fine tune. At least thats what I hope anyway [-o< . Lets see have my rabbits foot, four leaf clover, horse shoe, lucky penny and some curse words for backup....
Do they make a mental health guide for working on motorcycles?8-[
 
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