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Have spark, have compression, have gas, but no vroom on 3 and 4.

hje_326

CB750 Enthusiast
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Crawfordsville, IN
I'd like to thank you guys for all the help you have been giving me. But I'm still having trouble.

I've tried looking over the site for similar problems but haven't had any luck.
Coming out of the winter we cleaned the carbs out really well and put everything back together but starting it is quite a struggle. When I am able to get it to fire it's pushing out warm exhaust on 1 and 2 but only cold air out of 3 and 4. Pipes are hot on 1 and 2, cold 3 and 4.

I've switched my points and condensers to the PAMCO ignition system. It's been installed to the specs PAMCO gave and set to 1-4 like they recommended. By set to 1-4 I mean i aligned the notch at the starter motor in between the lines for 1-4 and had the hole in the ignition plate showing 1-4.

We first thought it was the coil or the inter-connecting wires but when I grounded the plugs to the frame they both sparked, so no apparent electrical problem. When we tested the compression the gauge read about 145-150 which Clymer said is good. Gas is in all the carbs so I don't think there is a problem with that either.

I'm currently at a loss and can't think of what else to check or what to do. Any help would be greatly appreciated.
 
If it was 1-4 or 2-3 that was cold I would suspect a weak coil but that's not the case. Are the plugs dry? Maybe 3 and 4 are running too rich to fire and the idle circuit needs some adjustment. Try switching the plugs (4 to 1 and 3 to 2) to see if the problem follows the plugs. If not, then try the plug wires (again 4 to 1 and 3 to 2). How about the valve clearances? If they are too tight maybe the gas mixture is just rushing through without being pre-heated through compression. You may have tried this stuff already, I'm just throwing out some suggestions.
 
I'll try moving the plugs and wires around but I'm not sure if that'll change anything. I'll also try adjusting the screws to make it thinner and see if that helps any. Could it be running too thin for it to start? When we put the carbs back together we set the idle screws at 3 1/2 turns from bottomed out, which is where they were before we tore them apart (but I'm not saying it's right).

Online I've seen people replace their stock Keihin carbs with the Keihin CR carbs. Is this worth the money? I'd like to know what I'd be getting into before I get ~$800 in.
 
3 1/2 turns seems like a lot. From what I have seen in the Clymers manual 1 1/2 to 1 3/4 seems to be the starting place.
 
Running with the choke would imply too lean. Maybe I have this backwards but I always thought that turning in the screw reduced the air flow through the circuit and thus pulled less gas into the carb. So In for Lean and Out for Rich. Can someone verify?
 
Had everything pulled apart today and we were running through all the options of what could be causing our fuel when we decided to take the brass jet assembly apart. I would expect there was almost 30 years of crud gumming it up. We'll get everything put back tomorrow and I'll let you know how it goes.
 
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