Honda-SOHC

SOHC.co.uk Forums => CB750 => Topic started by: muttblbc on March 19, 2010, 09:56:46 PM

Title: help!
Post by: muttblbc on March 19, 2010, 09:56:46 PM

Im really starting to bang my head against the wall, I gotta 77f not running on 1&4 Ive been through the carbs, Compression is great, Ive got spark to all 4 and have swapped the coil with another known good one, timeing is on, points gap is correct, air fuel mixture screws are set to stock specs. electrical or carb? electrical or carb? Ilike to think I know these bikes inside and out but I cant figure this one out. anybody got any ideas?

Title: Re: help!
Post by: muttblbc on March 19, 2010, 09:57:24 PM

oh and the valves are set to spec too.

Title: Re: help!
Post by: Seamus on March 19, 2010, 10:01:49 PM

If its not running on 1 and 4, but OK on 2 and 3. I would suggest electrical as it would be a bit unusual for two carbs to fail at once. I would start at the plugs, points and condensors, then connections to coils, then coils, leads, etc.

Looks at first glance to be associated with one side of the ignition.

Good luck

Seamus

Title: Re: help!
Post by: Yoshi823 on March 20, 2010, 03:22:21 PM

Try swapping the condensers over.

If not this, swap the yellow & blue wires over that take the signal from the points to the coils.

There's not much else it could be as you've tried everything else.

Title: Re: help!
Post by: Spitfire on March 20, 2010, 03:54:51 PM

Sounds very much like electrical, points, coils, timing, condensers, wiring etc.

Cheers

Den

Title: Re: help!
Post by: steff750 on March 20, 2010, 10:42:38 PM

it could well be one of your coils has died (swop coils to check)or one of your set pionts are shorting on them cylinders(swap points feeds blue and yellow wires i think) check your points again that they are not shorting around the carbon washers that could be the problem or even swap condensors

Title: Re: help!
Post by: muttblbc on March 20, 2010, 11:42:09 PM

swapped the coil wires (blue yellow), wont start and back fires....

Title: Re: help!
Post by: Seamus on March 21, 2010, 12:32:57 AM

Take the plugs out, clean and dry them, then try to start it again. If the electrics are failing on 1 and 4, then those pots are probably flooded. Changing the points wires should get it to run on 1 and 4 if the points are the problem. If not, suspect the coils.

Title: Re: help!
Post by: muttblbc on March 21, 2010, 09:31:41 PM

swapped condensors, no change. checked for spark and its got a nice blue healthy one to all 4,  its funny its about 40 degrees out and the bike was dead cold but fired up at the first hit of the button, idles nice and smooth on only 2 cylinders. hit all 4 pipes with temp gun 1&4 are in the low 200s 2&3 400s pretty quick. pull the plug leads for 1&4 and theres no change in the idle. compression, spark, that only leaves fuel right? ??? >:(

Title: Re: help!
Post by: muttblbc on March 21, 2010, 11:42:12 PM

gotta be the carbs, pulled the vaccum screw sprayed some starter fluid over the port and the rpms spiked. gottem apart and back in the ultrasonic right now