One cylinder not running

[Jeff K]

Guys, I am brand new to this site and this is my first thread. Thanks for letting me in.

My 74 CB 750 is not running on one cylinder. The second cylinder in from the right (as you sit on the bike) is not firing. I know because the other three pipes are hot as heck and that one is just warm. I can turn up the idle and let it idle at about 2500 and take the spark plug right off and no change in the idle. I hold the loose plug wire to the block and get all kinds of spark so I know it's getting spark to the new plugs. I also unscrew the brass plug on the bottom of that bowl and gas comes out so I know it's getting gas to the carb.

Any ideas on what I should do or does anyone know anyone close to me (West Michigan) that knows how to fix these things.

Thanks in advance,

Jeff

 

[dirtdigger]

idle jet is plugged. Its the small long jet in the float bowl. Or the idle mixture screw is turned in too far or the passage is plugged. I would bet its the jet.

 

[Jeff K]

Thanks Dirt. Normally I would agree with you on this one and I am going to dig into that carb today but I can feel the missing cylinder at speed also.

Thanks for helping.

Jeff

 

[dirtdigger]

So have you done a compression test then? You can still have carb issues. The idle jet still has some influence at a cruise rpm...it all depends on what speed, what rpm, nothing says the main jet is also not restricted.

 

[Jeff K]

I do have good compression. I am going to hoist it up and have a look at the carb again. I am going to clean the jets and anything else I see in there with carb cleaner. Can you suggest anything else to look at while I have the bowl and floats off? I am embarrassed to tell you that I left the gas in it the carbs for about 3 winters and there was a lot of "blue colored goo" in that particular carb when I cleaned it. I am almost certain I did not clean it enough so I am going to give it another go. I know enough to take the jets out and not to let the float needle drop into oblivion when I take the floats off. I don't want to take the carbs off. I have been through that before and frankly I'm not up to it.

Thanks again,

Jeff

 

[Jeff K]

Hey Dirt, I did indeed find that the idler jet was clogged. I cleaned it and it runs much better. Twice as good I would say. I still have a little "throaty" delay and lack of power so I am going to go through a compression test and then I am going to clean all the other carbs all over again. I will see if that helps.

Thanks again,

Jeff

 

[tommycarl]

It wouldn't hurt to run some Seafoam through one tank of gas. Might clean things up a bit. Maybe not as effective as a carb-off cleaning, but sure is easier and worth a try.

 

[K2750tracy]

It wouldn't hurt to run some Seafoam through one tank of gas. Might clean things up a bit. Maybe not as effective as a carb-off cleaning, but sure is easier and worth a try.

1+ on the seafoam

 

[Jeff K]

OK Seafoam it is. I will let you know how it works.

Thanks guys.

 

[Jeff K]

Seafoam was the answer. it worked great. Thanks everyone.

Jeff