Running on one.

[Almar]

My 1980 Honda CB400 Superdream has developed a problem.

The right hand cylinder (looking forward over the bars) is not running properly.

In the workshop, on tickover, the cylinder doesn’t fire. Reving the engine sometimes brings it on-line then off again.

On the road with the revs below 3k it doesn’t fire but, once over 4k revs it fires up and continues to run until the revs are allowed to drop again.

There appears to be a reasonably good spark and fuel is reaching the carb itself. The left cylinder runs fine.

Has anyone had a similar experience and can offer advice?

All suggestions gratefully accepted.

 

[LongDistanceRider]

It's a wasted spark ignition, both plugs fire at the same time, so check the resistance of the right sparkplug cap. 5K ohms is spec. Also be sure you're using NGK D8EA plugs or the ND equivalent.
If that checks out good then you're likely looking at the idle/slow jet being plugged in the right carb.

This is assuming your compression is equal and good.

 

[J-T]

Try a NEW spark plug.

 

[Almar]

Thank you for the suggestions.

I will be away from home for two weeks but will order new plugs, caps and coils and fit on my return. When ignition system is renewed, if there is no improvement, will start on the carbs. Stripping and rebuilding them is beyond my expertise but I have been given a recommendation by members of my Classic Bike Club which I will use if necessary.

 

[Maraakate]

Be wary of aftermarket ignition coils for these bikes. Measure the primary (the two pin canon plug that goes to the CDI). They claim under 1.0ohm but I've seen them at 2.2ohm (an SOCH4 ignition coil) and a 5ohm. It will run OK briefly if outside 1.0ohm but then will overheat after a few minutes and refuse to idle. It will also goof up the pilot mixture.

Caps are getting hard to find. You're best bet is to go to David Silver Spare's and order them as they still have them in stock. They will also have the NGK D8EA plugs.

 

[Almar]

Be wary of aftermarket ignition coils for these bikes. Measure the primary (the two pin canon plug that goes to the CDI). They claim under 1.0ohm but I've seen them at 2.2ohm (an SOCH4 ignition coil) and a 5ohm. It will run OK briefly if outside 1.0ohm but then will overheat after a few minutes and refuse to idle. It will also goof up the pilot mixture.

Caps are getting hard to find. You're best bet is to go to David Silver Spare's and order them as they still have them in stock. They will also have the NGK D8EA plugs.

A belated thank you for the advice. (I have been away from home).

After much tinkering and help/advice from two very experienced motorcyclists, both good spanner merchants, I am now going to take the bike to a local “back street” motorcycle specialist who “knows about vintage bikes”.

If I get the solution I am looking for I will post the info for the possible benefit of other members.

 

[ancientdad]

I am now going to take the bike to a local “back street” motorcycle specialist who “knows about vintage bikes”.

If I get the solution I am looking for I will post the info for the possible benefit of other members.

I wish you good luck, only because we've seen so many horror stories from people who have taken their mechanical needs to vintage bike 'specialists' only to find they heavily inflated the description of their knowledge levels.

 

[Maraakate]

I wish you good luck, only because we've seen so many horror stories from people who have taken their mechanical needs to vintage bike 'specialists' only to find they heavily inflated the description of their knowledge levels.

This. Be careful who you pick. Ideally you'd like to know about others who have used this person and are satisfied with the work. A lot of places claim to know these bikes and they don't. Instead, they use vastly inferior aftermarket parts and carb rebuilding kits. They'll make excuses like "oh the heads all weep on these old bikes no matter what you do", "they're all tricky to get started first thing in the morning", etc. Keep in mind none of that is true. One of the reasons Honda became a big player is that their bikes were reliable.