dang Carb, bike idles, bogs down on accel

[Suzuki_guy]

i have searched the forms with lots of good tips, but i cant seem to get my 1980 gs750e to run right. its a stock bike with a 4-1 header
after the winter lay up, the bike would not run at all. I ordered a carb kit and cleaned the carbs. (they were really gummed up with old gas)
when i reassembled them, the bike would idle.
set the air initially at 1- 1/2. using the idle method, they are approx 2 1/2 now. Bike idles ok, begines to accel, but not above 2000rpm. Unless i pulled up the choke (en-richer), then the engine revs would climb to approx 4000rpm sputtering and puffing back thru the carbs.

i raised the float level from 24mm (from gasket) to 23, 22 and finally 21. Not much difference in performance.
I put the floats back to 22mm. raised the needle 1 notch (thick washer on top) this was the best improvement, i could coax the engine to rev to 4000rpm, but no much more.

i then raised the needle approx two notches by putting the c clip back to the middle position and putting the thick washer under the c clip. thin on top of the c clip.

bike ran worse, could barley coax it to 4000 rpm.

Checked the plugs, although i am not sure the bike ran lon enough to get a good reading, the centre is a bit brown/tan with blacker/sooter outside in the plug metal base.

One big caveat, all through the tests i was runnung the bike up and down the street without the air box on. i read this make a difference but is it that big that the bike will not accelerate only slowly and top out at 4000rpm? this bike just bogs and sputters. I am sure i have cleaned every nook and cranny.

I am getting totaly fustrated. Its such a nice bike, but it will not run.

Will listen to anybody, please help.

John

 

[semerm]

With pods and not the stock airbox, when I got my 81 850g it would only rev to 5000 rpm, back fired and bogged. It would only do 55mph, 60 with the wind to my back (really).
I'd put the airbox on correctly and your bike will probably have a different personality.
Now with the stock air box the bike at 65 acts like it will go over 100. RPM's = over 8000 easily.
The one probelm you may have if the header is not stock (I assume is is not), it may also effect your mixtures.

 

[earlfor]

It will not run without the airbox. To run without the airbox, you will have to rejet the carbs. Also, if you sucessfully rejet the carbs, you can expect aprox a 25% reduction in gas milage.

Earl

 

[KEITH KRAUSE]

Don't try to compensate by changing the jet needle settings or float levels to something other than factory settings.
It's true that your pipe may lean it out a bit, but the pipe isn't causing your problem. After you get it running right again, then you can focus on plug reads and decide if you need to make any main jet or jet needle changes.
Right now, after returning the floats and jet needles to factory spec's, you need to re-install the air box before anything else. Re-test how it revs, just on the centerstand is enough. Let us know the results. If it still has the problem, then we'll focus on a bench synch and then probable fuel starvation.

 

[Suzuki_guy]

OK OK OK, it seems I have learned allot about CV carbs this past week.
I followed the advice from the forum, and you folks were dead on.

I reset the carbs to stock settings. 22mm float height, and middle clip on the needles, thick washer on the top of the clip, jets etc.

Now, this is the important part, I re-installed the stock air box. Made sure the rubber semi velocity stacks were on correctly and went for a ride.

What a huge difference. Bike now revs to red line, no bogging down. I am sure I can tweak the carbs following getting them synced. But, as previously pointed out in the tips area of the forum. These carbs do not like turbulent airflow.

Thanks to the folks who replied. And thanks to those folks who share their successes/ lessons learned after they got their bike running well.

It sure helps us all out.

Cheers

John in Ottawa Ont.

 

[Rocketjock]

Wish I would have caught you earlier, John. I have exactly the same bike with a 4 into 1. The airbox is everything. Not to mention all rubbers, clamps and seals. If you got air leaks, you got problems.

 

[ghwrenchit]

These carbs do not like turbulent airflow.

Actually it's the lack of vacuum.... If you look at and measure the intake holes (2) in the stock airbox/filter housing, they don't even compare to the size of all four carb bores combined as the airbox is restricted by design. The throttle plates are governing the air going in for combustion, but if the slides won't raise due to low vacuum, there will be no fuel from the main jets pulled into the mix, causing the motor to starve. I'm currently working on a design that will place the restriction aspect in behind the filter, at the box manifold which attach's to the carbs. Vacuum gage readings are going well. With what I have in mind, you can use most any large single pod filter as a replacement, because the "restrictor" will be behind the filter instead of in front of it as is the stock setup.

ghwrenchit