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78 GS750E Carb Questions.

  • Thread starter Thread starter Anonymous
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Anonymous

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I am bidding on some manuals on ebay, but until then I have a few questions.

I have read in a couple of places that there are some screws that a factory set and should not be removed. Can anyone shed some light on this?

I have purchased the o-ring kit and, but am considering a carb kit also. The bike has a 4 into 1 exhaust and I am not sure on the correct jetting. I don't plan to run anything other than it and the stock airfilter setup. Is there any recommendations for a starting point as far as jetting goes.

This is my first experience with rebuilding carbs. I have plenty of time to do it.

Thanks, Allen
 
First, download the PDF of the carburetor rebuild series from this site. This will be immensely helpful, even if your carbs are slightly different. If you have the older slide-style carbs, only the bits pertaining to the diaphragm will be different, and pretty easy to figure out. The manuals are nearly useless as far as the carbs are concerned.

Second, the forbidden screw is the idle mixture screw, and you definitely must remove it to clean the air passages and replace the teeny tiny itty bitty o-ring in there. The o-ring is probably bad by now, and it will be destroyed anyway by carb cleaner. Fie and a pox on the EPA!

If at all possible while rebuilding, clean and use the stock parts (the metal parts, not the o-rings and gaskets) instead of the low-quality junk in the rebuild kit. Sometimes it's unavoidable if there's severe wear or no way to get the stock parts clean. Pay close attention to the spring tension on the carb needles -- the aftermarket ones are commonly very weak, and will allow the gas level in the float bowls to be far too high. Ask me how I know this...

As far as jetting, I'll defer to others with more specific experience with a 750...
 
Thanks for the info. I am not afraid to take them apart just wondering the reasoning for not taking out the screw.
 
The reason it is stated not to remove them is because there is no standard "factory setting" on them. Each one is individually adjusted at the factory using an exhaust emissions analyizer. Be verrrrry careful when you turn them in to establish each ones setting. They have an extremely fine tip, and are very easily twisted off, plugging the oriface and even harder to extract. The actual term for these screws are pilot screws, and they control fuel flow into the idle circuit. The other "idle mixture" screw on the side of the carb controls air flow into the idle circuit (on the non-CV carb). Each screw is usually anywhere from 5/8 to 1 1/4 turns out from seated. Be cautious, it is fairly difficult to tell when the screw is actually seated.

Cheers
 
rickskeena covered the pilot screws pretty good. I'll just add, use a GOOD fitting tool on the pilot and side air screws because they can be tight and the heads strip easily.
I suggest replacing the o-rings in the rubber manifolds to avoid intake leaks. Apply a coat of hi-temp' bearing grease to help them last. Torque them to 6 ft/lb.
As for the jetting, if the air box is stock and still has its lid and the 4-1 pipe is a quality pipe, I would go up one full size (5) on the main jets. Leave the needles alone. You may want to turn the pilot screws out maybe an 1/8 to 1/4 turn too, but only if testing shows you need it.
A good vacuum tool synch is important too. It's an important part of jetting and needs to be done anyways. Then adjust your side air screws for the highest rpm's and re-set the idle to 1,100 rpm with the idle adjuster knob.
 
Good. I will be very careful when removing them then. The pipe on the bike appears to be a nice piece. I haven't found any brand name on it though.

Thanks for the tips.

Allen
 
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