'77 GS750 running on 1+2, not 3+4

[rightious]

im having a serious problem.

so i have a nice blue/white spark at all cylinders. 1+2 are running beautifully. 3+4, combustion is not happening. all the carbs are rebuilt and set to all the same specs. all carbs are definatly getting fuel.

any other information needed, let me know. any ideas i would really appriciate.

[BassCliff]

Hi,

Just a couple of questions, then we'll go from there...

Did you use aftermarket carb rebuild kits? Have you checked the valve clearances?


Thank you for your indulgence,

BassCliff

[rightious]

Hi,

Just a couple of questions, then we'll go from there...

Did you use aftermarket carb rebuild kits? Have you checked the valve clearances?


Thank you for your indulgence,

BassCliff

yes, they were aftermarket carb rebuilds. i have not checked the valve clearances.

[tkent02]

What did you do to clean the carburetors?

[rightious]

What did you do to clean the carburetors?

berrymens dip, rebuild kits.

[tkent02]

After dipping did you use carb cleaner to blow out all the tiny passages in each carb body until carb cleaner comes out the other end?

[rightious]

After dipping did you use carb cleaner to blow out all the tiny passages in each carb body until carb cleaner comes out the other end?

no, i rinsed it with water, shoulda used carb cleaner?

[Steve]

Yep, rinse with water, use spray cleaner to blast out the crud that was softened by the 'dip', then follow with compressed air.

Any particular reason you spent the money on the aftermarket carb kits? They usually run between $75-100 for the set of four, you get brass parts of questionable quality and you don't get nearly enough o-rings to do the job properly, so you have to spend even more money. A far better proposition is to clean the original brass pieces in the 'dip' with the carb bodies and put in a new set of o-rings from cycleorings.com. The carb o-rings are about $15, intake boot o-rings are another $5, new stainless bolts for the intake boots another $5 or so. So, ... for about $25 (the cost of ONE carb kit), you get enough to do ALL your carbs.

.

[tkent02]

no, i rinsed it with water, shoulda used carb cleaner?

My point is that no matter what you cleaned it with, if you spray carb cleaner spray into each passage and pay attention to where it comes out, you can ensure that all the passages are clear. Just make sure it comes out the same place on the other side of each carb, there are about five or so internal passages to clear on each carb.

The tiny holes in the choke pickup tube like to stay blocked, but you can easily see the spray come out each of the holes.

Same with the transition ports near the throttle slide.

One of these is likely your problem.

Wear safety goggles, the stuff WILL find it's way into an an eyeball otherwise.

[rightious]

Yep, rinse with water, use spray cleaner to blast out the crud that was softened by the 'dip', then follow with compressed air.

Any particular reason you spent the money on the aftermarket carb kits? They usually run between $75-100 for the set of four, you get brass parts of questionable quality and you don't get nearly enough o-rings to do the job properly, so you have to spend even more money. A far better proposition is to clean the original brass pieces in the 'dip' with the carb bodies and put in a new set of o-rings from cycleorings.com. The carb o-rings are about $15, intake boot o-rings are another $5, new stainless bolts for the intake boots another $5 or so. So, ... for about $25 (the cost of ONE carb kit), you get enough to do ALL your carbs.

.

well, i got them because i wasnt aware of any other options. hopefully they will do the trick. i did have all the o rings, so i dont think that will be a problem, but that is good to know for the future.
also, i agree with the 'dip'. that stuff sucks!

My point is that no matter what you cleaned it with, if you spray carb cleaner spray into each passage and pay attention to where it comes out, you can ensure that all the passages are clear. Just make sure it comes out the same place on the other side of each carb, there are about five or so internal passages to clear on each carb.

The tiny holes in the choke pickup tube like to stay blocked, but you can easily see the spray come out each of the holes.

Same with the transition ports near the throttle slide.

One of these is likely your problem.

Wear safety goggles, the stuff WILL find it's way into an an eyeball otherwise.

that makes sense, i do think i ran out after the first 2. i will give this a shot, thanks man....

also, reguarding the goggles, been there, and done that. wow does that suck

[rightious]

no dice

so i tried cleaning the carbs out with carb cleaner, didnt make a difference.

the cylinders 1 and 2 run fine, but 3 and 4 do not... however

when i put the r's up to about 3000, the cylinders 3 and 4 kick in, i am telling this by touching the pipes... they are cold untill the higher r's...


i am stumped, everyone i know is stumped, i really need your guys' help...

thanks

[rustybronco]

Have you synchronized (vacuum balanced) the carbs yet, or at least bench sync'd them?

does it idle on 3-4 after it gets warmed up? if not, it sounds like you still have plugged pilot circuits. (if you synch'd the carbs)

how are the carb boots? (I'm looking for vacuum leaks on 3&4)

did you clean the choke passage in the float bowls?

but first you need to check the valve clearances