Misfire on 1979 CB750 K

Posted by wernwilk on May 15, 2012; 12:47am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Misfire-on-1979-CB750-K-tp3987112.html

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.