81 dohc coil/ignition upgrades

[brugmand]

Hi guys,

Running murray carbs, d8ea plugs, mk2 b6 coils, stock harness, resistorless caps, and delkevic exhaust

I found some ignition issues with my 81 cb750 and as a temporary fix I dropped in coils from a mk2 bandit 600 which I had lying around and bypassed the signal wire to coil 2.3.

The bike is now running on all 4 with strong spark but the spark is inconsistent, testing with a strobe light it will will spark consistency then won't trigger the strobe light for a second or 2 then fire back up again.

Could this be caused by the coils having the wrong ohm resistance ? I'll be replacing them anyway so if anyone has coil recommendations thay would be awesome!

Also the bike has very low power at low rpm, like it will stall under 3k or 4k very easily and breaks up around 7 or 8k

 

[animaljim]

Hi guys,

Running murray carbs, d8ea plugs, mk2 b6 coils, stock harness, resistorless caps, and delkevic exhaust

I found some ignition issues with my 81 cb750 and as a temporary fix I dropped in coils from a mk2 bandit 600 which I had lying around and bypassed the signal wire to coil 2.3.

The bike is now running on all 4 with strong spark but the spark is inconsistent, testing with a strobe light it will will spark consistency then won't trigger the strobe light for a second or 2 then fire back up again.

Could this be caused by the coils having the wrong ohm resistance ? I'll be replacing them anyway so if anyone has coil recommendations thay would be awesome!

Also the bike has very low power at low rpm, like it will stall under 3k or 4k very easily and breaks up around 7 or 8k

One thing I found with mine when it was doing something similar to that is the rubber plugs in the float bowl to block off the one Jet access were leaking so I put oring on it and it fixed it. Sucks that I took it to two different motorcycle mechanics and they couldn't find this but it worked out

 

[John9en]

One thing I found with mine when it was doing something similar to that is the rubber plugs in the float bowl to block off the one Jet access were leaking so I put oring on it and it fixed it. Sucks that I took it to two different motorcycle mechanics and they couldn't find this but it worked out

I got a some similar issue; Carburettors cleaned, leak stopped with new floats and needle valves 6 months ago. Now some carbs are leaking again.
I also have an unstable rewing between 2K and 3K, chasing up and DOWN, and when i ride in this range i look like a CLOWN. Rhyming with intent.
Suspecting bad ignition pickup coil. But in my carburettor parts box there is to rubber plugs, that i do not know where should be, i have done some carbs on different bikes.
To complicate futher, I have VB52 carburettors on my 1981 CB750C, should be VB 42 A or B or C.


The recistance in the pickup coil is too low on both pairs of wire, so I am guessing i have a multiple problem here.
Any thougts or tips on this?

I am not dyslectic, just Norwegian.

 

[brettp]

The rubber plugs go in a port on the carb, inside the bowl. Likely contributing to your issue. You need to fix that anyway, so just go ahead. Then test your bike again.