Misfire on 1979 CB750 K

[wernwilk]

Hi, posting regarding a very low range misfire on my 1979 cb750K.

The bike has been standing and was a non-runner, i have done the following;
new battery
checked the valve clearances, all good.
then checked ignition timing with the strobe, all correct plus the advance works.
Next I synched up the carbs using the correct gauges, then tweaked the air/fuel screws by ear to get the optimum revs at idle.

sounds ok except there is a stumble as i give it some gas, its almost enough to stall the engine.

I have been through the carbs twice and blown all through and checked float heights as a matter of course.  The accelerator pump seems to be working at the mechanical end of things anyway and the diaphram is not split...any other way of testing these?

The bike was standing for a long time and did have some debris in the float bowls however as i said i cleaned the carbs thoroughly...twice!

I am running the bike on the bench using a remote resorvoir which rules out any tank or filter problems.

also, holding my hand over the exhausts there is slightly less gas out of 1 and 4 cylinders which made me think of a possible coil problem but it honestly feels more fuel to me....

any ideas people???

thanks.

[seestheday]

Did you test the accelerator pump by putting a little gas into the carbs while you had the bank off and giving the throttle a push?

Gas should shoot out of the little posts in each carb throat when you do this.  

Also, see what is said by Lucky and Tools in this thread regarding the accelerator pump: http://honda-cb750-s.456789.n3.nabble.com/DOHC-carb-cleaning-procedure-td867809.html

[wernwilk]

update.....stripped the ball valve in the accelerator pump base plate...all seems well now although there is a little pause from low down on the bench...i have not received my new air filter and i am hoping that with that in it will improve it as it seems a little lean at the moment.

thanks for the advice so far

[seestheday]

If it's running lean you could make it a little richer by turning out the air/fuel mix screws, but the air filter could also change that.  Those screws are really the last thing that you adjust.