running on 2 cylinders

[84cb700scdlb]

I purchased an '86 engine for my '84 CB700SC and just finished installing. I also took the carbs apart which are off the '84 and cleaned them before putting them on. The bike fired right up and idled but is only running on #1 and #3 cylinders. #2 and #4 pipes stay cold. I changed plugs, switched them around cylinder to cylinder, checked pulse gen. coil. and wires according to the manual. I also swapped the wires around. If I pull the plugs from the non working cylinders and hold them to the frame they appear to be firing just as good as the other 2. I cannot seem to get #2 and #4 to work no matter what I try.I also checked and rechecked all of my connections. Could something in the carbs cause this or am i missing something?

[coffee_brake]

 I'm guessing carbs? Because one coil fires one and four, and the other coil fires 2 and 3.

What do the plugs look like on the non-running cylinders? You can clean them and put them back in, and DON'T rev the engine or touch the throttle but start the bike. Then when you look at them again, if they are wet then you are getting fuel to the cylinder. If they are dry then you know to go back to carbs.

You may also try swapping coils, just to be sure it's carbs.

It is often a problem after a carb clean, that the float bowl levels have been tweaked out of limits. It will be a bear to adjust them, be patient. But hopefully it's just some fuel feed issue.

[84cb700scdlb]

I took the carbs apart again and the slow jets on the two cylinders that weren't running had something plugging the through hole. I had already cleaned this once so they must have picked up some more trash. I replaced the fuel line this time also just to make sure, it runs good now, all 4 cylinders. Thanks for your help.

[coffee_brake]

You might save yourself some effort and grief on the roadside by installing a fuel filter. A funky old tank is only going to clog up the carbs over and over. A $2 fuel filter might prevent this.