Carb problems

[floatsmyboat]

I am having trouble with my 1979 Suzuki GS 750 carburators. I just cleaned them, set the fuel level to about 3MM below the gasket surface. I have syncronized them so they are all right together. They all read 8 inches. It idles great, but when I snap the throttle, it will stumble, and if I really open it the engine will stall. I noticed quite a bit of gasoline being blown backwards from the carbs. Is this normal. I have seen this with 2 cycle engines, but don't know if it is normal for a 4 cycle. I have also set the points and ignition timing. I did set the fuel level consideralby higher then the manual said. It said to set the float about 1 inch, and I set them about .675 or something like that, but what I was after was the fuel level in the bowl. It acts like a lean situation, so I raised the metering rods two notches. Could I actually be causing a flooding situation, or is it still to lean? Oh, I did a compression check, all were right around 135psi.

Any help will be greatly appreciated. I bought this bike 3 weeks ago and haven't had a chance to ride it yet.

Greg O.

[huh]

are you running the stock airbox??? stock jetting? i dont think those stock needles were adjustable. (i could be wrong on a 79) so they may be aftermarket needles. how many turns out do you have the air/fuel screws?

how does it run down the road? does it run better on the high end or low or just bad all over? or can you even ride it?

[9000white]

you need to set the float level to the factory specifications.if i understand your post you have increased the fuel level height in the bowl by 3/8 of an inch and raised the needles also.the only possible result of this is too much fuel.

[floatsmyboat]

I am using the factory air box. I don't know about the jetting as I just bought the bike 3 weeks ago. The needles are adjustable by moving the E clip. It was set 2n'd notch from the top, and I reset them two notches down from that, in effort to get a richer mix, thinking it is lean. I have not tried running the bike on the road, as I don't have it licensed yet, but it runs better in the low end. Idles perfect, and does well with mild acceleration. But hard acceleration, it just dies.

I tried running with the fuel turned off, and as the fuel in the bowls dropped, I kept snapping the trottle. Didn't seem to make a difference as the fuel levels dropped, eventually running out of fuel.

I set the pilots at 1 turn, then opened them another 1/2 turn. This seemed to make the bike run a little better.

I really don't think it is a mechanical problem with the bike, as it ran pretty good before I got into the carbs, except the throttle was sticking some, and leaking some. I checked the valve timing, and adjusted the points, and ignition timing.

Thanks for your replies.

Greg

[huh]

I am using the factory air box. I don't know about the jetting as I just bought the bike 3 weeks ago. The needles are adjustable by moving the E clip. It was set 2n'd notch from the top, and I reset them two notches down from that, in effort to get a richer mix, thinking it is lean. I have not tried running the bike on the road, as I don't have it licensed yet, but it runs better in the low end. Idles perfect, and does well with mild acceleration. But hard acceleration, it just dies.

I tried running with the fuel turned off, and as the fuel in the bowls dropped, I kept snapping the trottle. Didn't seem to make a difference as the fuel levels dropped, eventually running out of fuel.

I set the pilots at 1 turn, then opened them another 1/2 turn. This seemed to make the bike run a little better.

I really don't think it is a mechanical problem with the bike, as it ran pretty good before I got into the carbs, except the throttle was sticking some, and leaking some. I checked the valve timing, and adjusted the points, and ignition timing.

Thanks for your replies.

Greg

its hard to diagnose without being there how does using the choke affect it? also does it smoke any? black? and when?
do those carbs have a acelerator pump????? if you gently roll on the throttle how does it act. does it cut out only when you snap the throttle?
when you rasied the needles did it change anything? better,worse or the same. is it popping out the exhaust or intake track? what about the plugs,are they ghost white or black?


i would check for any intake leaks with some spray lube. (wd-40,brake,carb cleaner) spray all around the connection points, intake to head,carb, air box etc. to rule out any leaks.

you can also try to close of some of the air inlet with some duct tape. like the air filter or lid. if it gets better with it choked off, your to lean.. you can also shoot some carb cleaner into the airfilter while you open the throttle to inject some extra fuel to the mix at that point and see what happens. these tricks can give you an idea of were your at.

the main and pilot jets are they stock? should list them in the book.
also set the air/fuel screw to 2.5 turns out you may need to go to 3

having the fuel level set to high shouldnt really affect a snap of the throttle because your giving a big shot of air to the cylinders at that point. it would flood more at idle and overflow out of the carb. do those bowls have a long brass tube in the center? if so those are overflow tubes and if the level is to high it will leak out of the drain. but like i said before its better to be a little on the low side. when setting the floats. but by your fuel level you should be close.

will get you riding dont worry

[floatsmyboat]

The choke does not seem to make a difference. Does not smoke .

No acelerator pump. It does fine if I gently roll the throttle, but it stalls when I snap the throttle more than about 1/3 to 1/2.

Raising the needles did not seem to make much differance. Pops once in awhile through the carbs, but very seldom.

The plugs are black like they are running rich.

Greg

[huh]

The choke does not seem to make a difference. Does not smoke .

No acelerator pump. It does fine if I gently roll the throttle, but it stalls when I snap the throttle more than about 1/3 to 1/2.



Raising the needles did not seem to make much differance. Pops once in awhile through the carbs, but very seldom.

The plugs are black like they are running rich.

Greg

sounding like a vacum leak. did you check for that??? you said it was not running this way before you overhauled the carbs right? and you did'nt change anythig right? i know you did a carb sync and they were all = but carb syncing can be a little tricky so you may want to double check. otherwise its rich and you will have to get back into the carbs and double check everything. make sure a piece of dirt didnt find its way into a passage like in the pilot circuit. or a plug didnt fall out over the pilot jet.
then set that float lower. like i said better to be on the low side then high.
also make sure the jets are correct with the book. and the slides and needles are in good shape. no tears,holes or groves in the needles etc.

i know it sucks but it sounds like your gonna have to get back in them.
let us know

also what is your idle set at. make sure its 1300rpm idle when warm.
this can make a huge difference on a fast snap. (if its to low) you can turn the idle up as high as you can like 2000 rpm or more. then try a snap.

[floatsmyboat]

Thank You Huh, and 9000white!

With your help and persistance, I got it running, and it runs great and idles smooth. No hesitation, and lots of power. I checked for vaccum leaks and came up empty there. In the process I sprayed some carb cleaner into the carbs. I noticed I got no change from #3. So openened up the carbs, and found the pilot jet in #3 had dirt in it. Cleaned them all again and put them back on, and synced the carbs again. But still didn't respond to a snap. Well I had been using a lawn mower gas tank to run it on as the main tank was removed. So I decided to put the main tank on and see what happened when I ride it. Made all the difference. Must be the lawn mower tank just couldn't supply enough fuel. Ok at an idle, but can't supply enough fuel beyond that. I felt kind of dumb, but I guess we all have done stuff like that.

Just a note on some of these aftermarket manuals. I set the float level to their specs, and like you said Huh, the gas level was to low, and caused some hesitation, so after setting the float level back to about 2MM from the gasket surface, all hesitation went away. Point is, some of the manuals don't know what they are talking about.

Thanks again for your help.

Greg

[huh]

Thank You Huh, and 9000white!

With your help and persistance, I got it running, and it runs great and idles smooth. No hesitation, and lots of power. I checked for vaccum leaks and came up empty there. In the process I sprayed some carb cleaner into the carbs. I noticed I got no change from #3. So openened up the carbs, and found the pilot jet in #3 had dirt in it. Cleaned them all again and put them back on, and synced the carbs again. But still didn't respond to a snap. Well I had been using a lawn mower gas tank to run it on as the main tank was removed. So I decided to put the main tank on and see what happened when I ride it. Made all the difference. Must be the lawn mower tank just couldn't supply enough fuel. Ok at an idle, but can't supply enough fuel beyond that. I felt kind of dumb, but I guess we all have done stuff like that.

Just a note on some of these aftermarket manuals. I set the float level to their specs, and like you said Huh, the gas level was to low, and caused some hesitation, so after setting the float level back to about 2MM from the gasket surface, all hesitation went away. Point is, some of the manuals don't know what they are talking about.

Thanks again for your help.

Greg

awesome!! been there done that with the manual's. some manuals (factory) only list fuel level.
if unsure on the float level you can never go wrong with the 2mm fuel level setting!


ride hard and safe and dont let the fuel get too old. unless you want to clean those carbs again!

[Telesque]

Just a note on some of these aftermarket manuals. I set the float level to their specs, and like you said Huh, the gas level was to low, and caused some hesitation, so after setting the float level back to about 2MM from the gasket surface, all hesitation went away. Point is, some of the manuals don't know what they are talking about.

Where ever you keep your manuals you should keep two equally important things: A good highlighter, and a dark pen.

Highlight any useful/interesting info in your manual. It's your's, right? Who cares if it has a little color in it. It'll help you find that stuff again later.

Use the dark pen (markers bleed through) to make useful notes about things, especially the incorrect sort of things, so that you don't have to deal with it in a year or two or three when you're (possibly) going to be down this road again.