'83 GS750E stalls when throttle is opened

[JimW]

Hi folks! I'm a former member that hasn't been here for a long time.

I have an odd problem: my '83 GS750ED will start easily with choke but will stall the instant the throttle is opened, even a very small amount. It has fuel, and the carbs were professionally cleaned and synced 4-5 months ago. About 3 months ago, knowing I wasn't going to be riding for awhile, I added some Sta-bil to the fuel and rode it for about 5 miles to make sure the float bowls had the 'preserved' gas. Last week I put the battery back in and started it. It started, ran fine with good throttle response. But as it was idling I noticed fuel leaking, apparently coming out the bottom of the airbox. I drained the float bowls and checked the petcock. I had vacuum signal to the petcock and it flowed fuel in 'reserve' and 'on' positions (with vacuum) but not in 'prime'. No fuel was coming back through the vacuum line, and the petcock didn't leak without vacuum applied. I pulled the tank and removed the petcock; no signs of rust or debris on the screen or in the tank. I reinstalled the petcock, put the tank back on the bike and fired it up. No more fuel leak, but now it stalls as soon as the throttle is opened.

I replaced the petcock today. New unit, tested it and it works fine. The stalling problem persists. I replaced the fuel line, the vacuum hose, and checked the vent tube. Again, the bike starts immediately and will run as long as the choke is on. This seems like an extreme lean condition to me, but it doesn't make sense. Everything is stock, there are no false air leaks that I can find. I hope someone has run across this problem before and found a solution, 'cause I'm lost.

 

[Guest]

Sounds like the carbs need to come off and clean the pilot circuit's this is common for a bike that has sat for any time. Sta bil is not a guarantee that your carbs will stay good.

 

[JimW]

I got out the propane bottle today to check for vacuum leaks. I found a small bump in rpm around the manifold/boot to #4 cyl., but that was all. The boot didn't show any cracks and everything was tight. I sprayed some starting fluid into the air intake snorkel while working the throttle, and the throttle response was immediate. Unfortunately, so was the lack of response when I stopped spraying.

Getting into the carbs is an absolute last resort. I've rebuilt carbs before, but this bike is an absolute nightmare for access. Whoever designed the layout and especially that PoS airbox deserves some sort of eternal punishment (possibly having to work on the system he designed). I hate paying someone to work on my vehicles but I'll pay for carb work on this bike. I just want to be very sure that I've exhausted any other possibilities before I hand over the bike (and my money) to my local shop.

 

[cowboyup3371]

You keep delaying the inevitable you'll continue to have problems. It needs to be the first thing to do

 

[SVSooke]

Believe me Jim I know the pain of pulling 3 gen 750 carbs.One thing I've found is taking the clamps off both side of the boots really help.Not slide them up,right off.Bent up the boot clamps bad before I learned that.Bite the bullet and do it.

 

[JimW]

I talked to the tech that cleaned and synched the carbs awhile back and he suggested running some fuel system cleaner through it before I got crazy and pulled the carbs. I had a can of BG 44K in the cabinet and added a few ounces to a full tank of gas and let it idle for about 30 minutes with a big fan cooling the engine. Throttle response started to come back to the point where it was rideable (slowly and carefully) and has continued to improve. Now there's just a bit of sluggishness off idle under load, but it keeps getting better and I don't doubt that by the time I've burned through this tank of gas, I'll be a happy camper. Better living through chemistry, eh?

Anyways, thanks for the responses and recommendations. I guess I got lucky this time.

 

[koolaid_kid]

JimW, this is clear evidence that "professionally cleaned" does not mean they were rebuilt properly. This is how to do it correctly. If fuel system cleaner is clearing out the blocked passages, the rebuild procedure was not followed correctly.
Your tech probably took them apart, sprayed carb cleaner in them, and put them back together. Does not work with these Mikunis.

 

[JimW]

JimW, this is clear evidence that "professionally cleaned" does not mean they were rebuilt properly. This is how to do it correctly. If fuel system cleaner is clearing out the blocked passages, the rebuild procedure was not followed correctly.
Your tech probably took them apart, sprayed carb cleaner in them, and put them back together. Does not work with these Mikunis.

You may be right, although it ran much better after he was done. Could be the synch as much as the cleaning, though.

I followed your link regarding the pilot screw adjustment. I was definitely lean, and after resetting, the sluggishness off-idle is gone. Thanks for the help!

 

[koolaid_kid]

You are very welcome. Now get out and ride!