She bangs.. :(

[Lechy]

A couple of long shots. These bikes run off the battery, make sure you have good clean connections at the terminals especially both ends of the earthing cable. Make sure all cable connections in the ignition and firing circuits are clean and tight. Run the bike for a few minutes and check each exhaust header for temp, should all be hot, one cool one will narrow the problem down.
Check both sets of boots on the intake of the carbs for leaks or badly fitting. Pull the caps off the carbs and check the rubber diaphragms for cracks or tears.
Are you using the OEM air filter?

 

[dirtdigger]

I think you need to start checking the pulsor coils in the motor as they send the signal to the cdi boxes...if in fact you are sure that it is a spark problem and not a fuel problem.

 

[Mcgyver]

you allreadychecked to be sure of no air leaks to the carbs right?

 

[Lasper01]

Thanks again for all your posts!! We haven't had the time to work on the bike for some time now, but I will get back with updates a.s.a.p!!

We have checked for air leaks by spraying ether on the intake manifolds, but it didn't rev up..

Dirtdigger: We have measured the resistance of the pulsercoils. They showed 470 and 490 ohms, but the manuals saids they should be around 530 ohms (+/- 30 ohm) so could that be the problem?

All the exhaust headers are hot..

Its the stock airbox with stock airfilter..

To be continued...

 

[Andy]

Hey Lasper. Maybe some basics are in order. A compression check, maybe pull off a float bowl and have a look for varnish. This will give you a good indication of the condition of the carbs. See Stabler's and Pawl's carb cleaning threads they can get pretty bad. What does the air cleaner look like? Is there a mouse nest in there? Take out the spark plugs, hook them to the wires, ground against the motor and turn the engine over to check for spark. It should be bright and blue. While your're at it, set the plug gaps. Start eliminating possible problems. If the bike sat for more than a year, the carbs will need attention. Get them clean and back to spec. Make sure the fuel filter isn't plugged if there is one. Is there fresh fuel in the tank? Is the tank clean? Are you getting good flow through the petcock? I'm no expert, but you can correct a lot of problems just taking care of the basics. Once running don't forget the brakes and tires, both will need a look after a long time sitting. Most of all, don't forget to have fun working on it.

 

[Travis]

Huge long shot, but there was a guy chasing his tale trying to figure out spark issues on his XS650, and it turned out to be a bad plug. A brand new bad plug! Maybe something is amiss with the new parts? I would keep trying to figure out that spark issue. I know if I have a weak spark, it might be enough to fire the bike sometimes, but my timing light doesn't like it. Maybe you have a bad connection between the plug caps and the wires, or the coils and the wires. You have the ones that screw together right? Bad ground somewhere?

 

[750caferacer]

I am having what seems to be a similar problem with my 79 CB750. I'll let you know what I come up with.