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Hanging Idle

  • Thread starter Thread starter stanger38
  • Start date Start date
S

stanger38

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This is my first post. I have a 1977 GS 750. I rebuilt the carbs and since then it is hard to start cold,and when it gets warm the idle hangs I have to turn the idle down to where the bike is almost stalling to get the idle to come back down some of the time. I started with the same jetting i used before the carb cleaning with 4 into 1 vance and hines pipes(pipes were installed pre carb cleaning) and the stock air box. I have tried the following:

cleaned, dipped, and replaced o rings in the carbs
vacuum synced carbs
adjusted valves
replaced points and condensers
lapped valves and replaced head gasket
replaced petcock
replaced manifold boot o rings
sprayed manifolds and carbs w/ card cleaner and starter fluid to check for leaks
added pods and rejetted carbs (right now running 122.5 mains and 22.5 pilots clip set @ 2nd from bottom slot).

Everything that I have tried has not made the idle stop hanging. Is it possible that the throttle shaft grommets are leaking or a problem with the enrichers? Does anyone have any Ideas?
 
Where are the pilot fuel and pilot air screws set?
 
i dont know if you are using stock pilot jets, but i rejetted mine I went up 1 size, and it starts real easy.
 
I changed the pilots. i've tried 15s, 17.5s, 22.5s, amd 25s. It seems to run the best on 22.5
 
Only thing I can think of is check your spark advance to make sure it's functional. The cam should spring back after you twist it by hand.

Only other thing is to double check your fuel screws to make sure they are pointy and that the sharp point isn't broken off inside one of the carb bodies. Also, double check your vacuum sync. Last resort is try opening the fuel screws a little more. A hanging idle usually means lean, so try dumping lots of fuel to see if the problem responds to that.

Good luck.
 
I pulled the advance weights and they are free and open and close easily. I tried to resynch no change and I am running 22.5 pilots which is way rich for this bike stock are 15's. I think I have an air leak somewhere but I can't find it
 
I tried putting the 17.5 jets in and it made the hanging problem worse. Does anyone have any suggestions? Any help would be appreciated
 
Based on your work so far, you seem to have eliminated everything but the intake boots
 
Did one of the intake boot orings possibly get pinched or damaged while installing the boots? Did the orings easily slip into the groove or need a bit of a stretch? If they needed stretched you have the wrong diameter orings. Stretching DECREASES the over all durometer and even though they are in and tight they still wont seal properly. Did you give each boot a squirt of starting fluid right where it meets the head while it was running...any changes? Is the airbox on and boots all the way onto the carbs and tight? Got washers on all the sync port bolts?
 
The air box is off I have pods on it. The o-rings fit correctly it put some grease in the groove to hold them in grove during the installation. I am not 100% positive about the washers on all the sync ports. I will double check.
 
I checked the sync ports they all had washers, I also put some thread sealant on the bolt before re-installing them. Idle still hangs. Does anyone else have any ideas of things i can check?
 
stanger38 said:
I tried putting the 17.5 jets in and it made the hanging problem worse. Does anyone have any suggestions? Any help would be appreciated
Click to expand...
You put in smaller jets and the problem got worse? That jives with what Nessism is saying, right? You made it run leaner by doing that.

You are running pods. They should be letting more air through than the stock airbox, which means even leaner.

What about your header? Nice and tight with no leaks? Are you getting any popping and crackling on deceleration?
 
BigD_83 said:
You put in smaller jets and the problem got worse? That jives with what Nessism is saying, right? You made it run leaner by doing that.

You are running pods. They should be letting more air through than the stock airbox, which means even leaner.

What about your header? Nice and tight with no leaks? Are you getting any popping and crackling on deceleration?
Click to expand...

He has gone up about 3 sizes on pilots. The stock pilot is 15 and he is running 22.5s.

One thing absent from your otherwise thorough list is the float levels. I have the same set-up and was getting similar idle problems until I changed the float levels. Of course, now I am wrestling with the reverse issue, namely fuel overflow issues.

See where your float levels are. The specs for 1977 are 26mm, but that might put you too lean. The 78-79 specs (which are for the same carbs IIRC) are 22mm - 25mm - depending on where you look for the spec. :mad: With all that extra air, you probably want to be on the higher end, which means lower measurements on the caliper. Unless the floats already measure at the low end of the specs (i.e., <23mm), try moving them down to 23mm or so. Then check the levels with a drain tool before putting the rack on the bike to make sure you won't flood the pods and (more importantly) the crankcase with excess fuel.

So far, I have my floats close to 23mm and the idle is much better with no hang, but one carb still gets too much fuel and spills from the overflow tube. So I need to work through that level and needle/seat to get it right. YMMV

Good luck.
 
Are you sure the stock pilots for those carbs are 15? Most were but the early bikes were well up in the 20s. I can't remember off the top of my head but the manual will tell what size is standard for your bike.
 
hampshirehog said:
Are you sure the stock pilots for those carbs are 15? Most were but the early bikes were well up in the 20s. I can't remember off the top of my head but the manual will tell what size is standard for your bike.
Click to expand...
I just checked here:

http://members.dslextreme.com/users/bikecliff/images/carbspec_float_height.html

Pilot jets may be 15 stock, but a couple of those numbers suggest 22.5 and 27.5, so the bike running better on the 22.5 with the stock airbox makes sense. If that is the case, you're likely going to have to upsize both pilots and main with your 4 into 1 and pods.
 
hampshirehog said:
Are you sure the stock pilots for those carbs are 15? Most were but the early bikes were well up in the 20s. I can't remember off the top of my head but the manual will tell what size is standard for your bike.
Click to expand...

Actually, you might be right. BassCliff's chart shows the early 750's with 22.5 and 27.5 pilot. Those also had larger stock mains (105s) and much leaner float height (26mm). My 1978 stock specs are 15 pilot, 100 main and float at 23mm +/- 1mm.

As I understand it, the physical properties of the VM26 carbs from 77-79 didn't change. Did Suzuki flip the specs after 1977, to enrich the float level but change to smaller jets?

Back to the OP, if you jetted the carbs in reference to the 1978-79 specs (or because a PO used those specs for jetting), but set the floats at 1977 specs, that could put you in the lean range.

Basically, I am projecting my lean idle float height situation onto you. :-) We could both be right though.
 
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