Advice on these plugs.

I switched out my worn out Amals for a single Mikuni 34. Plugs are NGK BP7ES. Starts on the first kick and idles nicely at 900 RPM. But the plugs after 20 miles on the highway and then a plug chop have a black dry soot on them. Almost to the point of where it looks like they would foul if they stayed in the engine much longer. I got the Mikuni from MAP. I’m not sure what the main jet is in there right now, but I’m thinking I need to lean the mixture out. Thoughts from the inmates? Thanks for any and all helpful suggestions!

750 or 850?

Kurt V said:

I switched out my worn out Amals for a single Mikuni 34. Plugs are NGK BP7ES. Starts on the first kick and idles nicely at 900 RPM. But the plugs after 20 miles on the highway and then a plug chop have a black dry soot on them. Almost to the point of where it looks like they would foul if they stayed in the engine much longer. I got the Mikuni from MAP. I’m not sure what the main jet is in there right now, but I’m thinking I need to lean the mixture out. Thoughts from the inmates? Thanks for any and all helpful suggestions!

Click to expand...

If you rode the 20 miles on full throttle, your problem might be main jets, but it is more likely to be needles and needle jets, or flooding.

Would be surprised a new Mikuni out of box pre jetted or not would be plug and play ... you will have to provide much more info for anyone to be able to offer even thoughts a on where your problem may be ... I have run a single VM for almost 20yrs , it was just a blank no jets, needle or slide , it did take a while to get it setup for proper performance , have not had to touch it since then , so patience is a virtue .... post up all info you are certain of and folks here should be able to get you close , then you will have to fine tune it ....

MPG?
Oil consumption?
Compression?
Drivability symptoms?
Notable rich smell?
Visible smoke?

Thanks for the input so far. I found a long article online on tuning that Mikuni. I’m going to follow the information I got on there and see if I can’t get it dialed in.

The Mikuni kits are always jetted rich for safety reasons. It will probably need leaning out, starting at the idle circuit first then working your way up, the main jet being the last to be changed.

I'd be happy to assist you, just call me at the shop, Rocky Point Cycle. Please have the numbers that are stamped on the:

Main jet, idle jet, needle, needle jet and the slide.

Piece of cake.

Best.