Not running well, GS1100 with uncurable carb issues!

[ironsheik]

Hello all,
I'm trying to get my 83 gs1100ed back on the road after a bunch of upgrades and a Yoshi 4-1 exhaust. The valves are all in spec and the bike ran fine before the carbs were rebuilt and exhaust added. They've been dipped, all parts cleaned and new o-rings were installed. Floats are all at 22.4mm and the needle valves function well. I've also got all new rubber hoses on the intakes. The bike ran OK but quite lean when the carbs were stock and the Yoshi was installed. That's why I opted to clean and jet the carbs properly.

After rebuilding them and adding a DynoJet stage one kit I cannot get the bike to run well. It starts right up with choke, then takes a bit to warm up and run without choke. It then won't rev past 3k without dying on me. I can finess it past and then it continues revving. Off choke or on at this point the same thing happens. If I put my hands over the intake on the airbox it will rev fine. I must confess, I haven't played too much with the air screws in the front of the carbs which are now set about 2.5 turns out but I didn't think they would make this much of an impact.

So as of now, I can get it to run with stock needles and jets (112) but it's popping like crazy. When I then go up to 117.5 mains and the DynoJet needles set on the 3rd clip I get these symptoms. This is with a stock airbox and K&N filter and the lid on. Any advice is greatly appreciated. Thanks!

Josh

[Katarat]

Try the mixture screws out 2 turns. My 80 GS1100E has the stock airbox with a Vance & Hines pipe, 115 Mikuni {not Dynojet}jets, stock pilots and runs great. It has Dynojet needles in the center groove. Have you checked for fuel flow or tried the petcock in the prime position ? Im also at 3700 fft so your results may vary. Theres a whole lot of people on here a lot smarter then me that can help you too

[Big T]

Try some duct tape over 50% of your airbox inlet and see what happens

Sounds like a lean condition

You did sync the carbs?

[ironsheik]

I have not yet synced the carbs. It's been hard to get a steady idle and I didn't have a fan handy. I did a really good bench sync though. I didn't imagine a slightly off sync would cause this problem? I'm sure the duct tape would work since I already tried this with just my hand and it immediately runs better and revs.

I didn't mention that the pilots are stock too.

[Nessism]

DynoJet jet sizes are different than Mikuni jet sizes but I think you need something in the range of 120 main jets for that setup. Carb sync won't cause the problems you describe but you are silly to try to fine tune the bike without performing this critical step. Oh, and 2.5 open on the pilots is fine.

[OldVet66]

Each cylinder is going to be a little different, valve condition, compression, etc. The sync fine tunes each carb so the power from each cylinder is equal. It makes the motor smoother and eliminates a lot of vibration. It is not critical to getting the motor running and idling.

[ironsheik]

Understood. The reason I haven't done the sync is because I can't get a very smooth idle easily. I'm just looking for clues as to why it would be lean. Even without a proper sync the bike should rev with no issues.

And I've got 120s here but I started with 117.5s as per Chef's suggestion on an 1100 with stock airbox and 4-1. I don't think this would be the issue though. The mains wouldn't really affect revving below 4k, right?

[Suzuki mad]

Normally mains come on at about 4,000rpm.

[Katarat]

A 112 dynojet jet is equal to a 105 mikuni, so if your using DJ jets you would be way lean. Set the idle up to 1500 or so and do the synch there

[TheCafeKid]

A 112 dynojet jet is equal to a 105 mikuni, so if your using DJ jets you would be way lean. Set the idle up to 1500 or so and do the synch there

Which is too small...

Try the larger of the smaller jets in the stage one kit... Or the smaller of the larger jets in the stage 3. A yosh exhaust flows VERY VERY freely, even with an airbox and filter installed the stage one is still probably a hair lean.

I cant remember the sizes in the kit.. I seem to think they were 112, 114, 132 and 138 (all DJ sizes) Id try the 132 first... Are you using a stock air filter or a K&N in box? If K&N you definitely need the 132 IMO. Needle clip suggestions in the instructions are a little bit of BS shot in the dark as well. try (counting from the bottom clip slot) 2.5, 3 or 3.5 clips from the bottom. The needle will start to come on at around 2.5 to 3K as you roll on... Where you say you're breaking up is pretty much all needle, and it sounds like its lean...

Looked at the plugs?

[ironsheik]

Crazy, it was all needle! I moved them up one notch to 4th from the top and it's running beautifully. After reading and reading about possible culprits and other people's stories I can't believe that's all it was! It seems like everyone uses the 3rd clip from the top and issues arise in other places. It's a hair lean with the airbox lid off so I put that back on.

Now I'm trying to do a sync without the adjustment tool. What a pain in the A! I guess I should get one but adjusting carb #2 on these CVs seems impossible to get to easily since there is so much in the way. I'll try again tomorrow with more time and actually remove the throttle cable assembly for better access. If that doesn't help I'll order the Motion Pro tool. Also, with a 4-1 exhaust do I set all the carbs equally or do I still leave 2-3 down a bit from 1 and 4? Thanks for all the advice!

J

[TheCafeKid]

IIRC the reasoning behind the offset sync levels in the middle cylinders were due to the crossover pipes in the exhaust system. You don't have that anymore, and a yosh pipe has equal or close to equal length headers so sync them all the same.