Firing. Suzuki Gs750 Answers Please. And New Problems,also.

Ok so shes not firing on cylinder 3 unless I remove the vacuum hose that comes off the tank (smaller one at the back) then it runs on 3 then 4 stops firing?
All ideas and solutions please.
I have a hose going into the opening on the right.hand side of carb 1 in a loop to rhs carb 3 .
The vacum hose goes from tank to rhs carb 2.

 

A = the hose from tank to carb 2
B= Main tank hose to rail
C= loop between 1 and 3
D= engine breather to airbox
E= clutch cable

 

So started again today.

Bike starts right up, running on three.

Third cylinder no show again. I fear my oil level is increasing which would suggest its getting fuel and its not igniting and getting past the rings. I have good compression, over 120 on all cylinders.

I have good spark.

So it must be mixture, (guess).

I have the carbs off again and have rebuild and cleaned again carb 3 and 4, ( 4 for reference and they both seem good.

These are my inlet rubbers they all seem different and although very similar have different numbers stamped by the Suzuki Made in Japan logo.



The one with the rubber o ring is from 4 and the other from 3.



26, 19, 24, 39, they look identical except two have o rings and two don't ,the offending cylinder had no o ring and some clear silicone around it.

No cuts or tears

How poorly does it need to fit to loose air and upset the mix enough to stop it firing?

My only other thought is the bottom adjustment screw on the bottom was further in than the others.

I cleaned and bench sync these carbs last week the all, have new Main and Primary jets, all other passage ways cleaned and the needle was raised 1 notch on all.

All input appreciated.

 

I piped them all up, vacuum, unused vacuums, and overflows ( on the bottom). Then tryed to run it.

 

Yeah I did bench set em,Keep the ideas coming please.

 

Is that something I could get done after its on the road?
I may have your problem where it will run on 4 when hot It would just be good to put it on the road square one everything working.

 

If I am getting a good spark does that mean I can look elswhere.?

 

I dont know about older bikes and I will be looking at that. The bike has only 23,000 miles.

 

Thanks Rocker I will.

 

Plugs leads and coils and ignition system are new so I may have made a boob, Its on the list.