Mechanical Carb Tuning Question

[KrazyKarl02]

Ok so I just picked up a 1978 GS 1000. I got it running, but was not impressed, I cleaned the carbs up and it starts and runs well. My problem is it runs VERY rich particularly if I gas it at around 2000 to 3000 RPMS. I have tuned CV carbs, but never mechanical ones, what do I adjust?
My main question is there are two air mixture screws on each carb, I assume one is the idle air mixture adjustment (that would be found on a normal CV carb) The other is larger and on the side of the carb ( I think this is a mid range adjustment anybody know?? the repair manual tells me these are factory set and should not be adjusted, but I don't like answers like that!)
The bike has a 4 into 1 pipe and a UNI filter (they came with the bike) and I believe it has stock jets.

Suggestions are appreciated.

[Anonymous]

Double K,

The screw visible from above the bike is the idle mixture screw. This is an air bleed. If you turn it out, it leans the idle mixture.
The screw on the bottom of the carbs right before the in take port is the pilot screw. This adjusts the volume of fuel air mixture entering the engine to sustain an idle.

Notice in both those descriptions the word "idle". If your bike idles fine, don't worry about those two.

My guess is that when the 4 into 1 and the filter were added the bike was rejetted. This would involve a change in the main jets (originals are 95) and moving the needles. I think the needles might have been raised too far. Try lowering them one or two notches and see how they work.

I have the original service manual for this bike. If you would like I could scan and send the fuel section.

Steve

[Anonymous]

could you send me a copy of that scan?

[Anonymous]

I'm experiencing technical difficulties. My scanner is proving to be smarter than me.

The file will be about 24M. I'll send it when I can.

Steve

[Anonymous]

weird

I have the exact same bike with the same gear and some brilliant mechanic decided he'd better change the carbs back to factory specs, and it runs well but on the rich side, so let me know if you figure out the right setup

[robinjo]

Double K,


My guess is that when the 4 into 1 and the filter were added the bike was rejetted. This would involve a change in the main jets (originals are 95) and moving the needles. I think the needles might have been raised too far. Try lowering them one or two notches and see how they work.
Steve

Do you know if my 1000S with the 28mm carbs also has 95 main jets as standard? When I bought the bike it was running without a filter in the airbox and running 110 main jets, now that I have the engine apart to fix the leaky headgasket I bought a new filter (original Suzuki) and put in 96 mains as that was the closest I could find. Would that be correct for my carbs or do I need bigger ones? ( It has the stock 4-2 exhausts on it)

[Anonymous]

Robinjo,

Yes, your bikes original jets were 95's. This is assuming it's a '78 or '79 model.
The original carbs were Mikuni VM26SS. If you have 28 mm carbs, do a little happy dance because you are a very lucky. These carbs were produced for a very short period of time and will work with more modifcations than the 26's.

Steve

[robinjo]

Robinjo,

Yes, your bikes original jets were 95's. This is assuming it's a '78 or '79 model.
The original carbs were Mikuni VM26SS. If you have 28 mm carbs, do a little happy dance because you are a very lucky. These carbs were produced for a very short period of time and will work with more modifcations than the 26's.

Steve

*Doing a little happy dance* Thank you for the information, it is indeed a '79 model ''S''