Yesterday my 348 was being a bit troublesome, it stalled a fair few times when the revs got low. I put this down to the fuel level being low and maybe some dirt in the bottom of the tank.

So today I gave it some fresh fuel and I took the bike out for a ride. I thought I'd stretch it's legs. it seems underpowered and very smoky. After 10 minutes or so of riding, fairly fast, the bike was smoking way more than normal. I rode it staright back to the workshop and it didn't smell good. the exhaust was so hot it had meleted the rear mudguard and was even melting the transfers off the side of the fiberglass tank cover.

It was a warm day today but I really don't think that should cause the exhaust to get that hot.

Someone has suggested that I may need to decoke the exhaust, does this sound like it could be the cause of my problems?

Could a coked up exhaust cause the bike to be underpowered and the exhaust to overheat?

Any advice would be appreciated. Thanks.

If you have dirt in fuel or carb it could partially block jets causing bike to run weak / lean which would cause overheating.

Retarded ignition timing (worn points heel) will also cause overheating.

Smoke will just be old oil / carbon being evaporated out of exhaust due to extra heat

Thats a good point, this could account for the drop in power too if it's running too lean.

I think to be honest I will decoke the exhaust, as it's probably never been done.

I will also give the carb a clean.

Thanks for the reply.

With those symptoms, I'd check (and change) the left crankshaft seal. Forget the carb. Your crankshaft is being filled with the primary transimission oil ... and extra air that makes your carburetion too lean and generates tons of white smoke.

I am taking the casing off of that side this weekend, in order to fit a new clutch push pin, so I will take a look. Cheers

Don't take a look. Just change it.

I've been working on those engines for many years, and the symptoms are clear. It's a 2 pounds (and one hour) fix if you have the proper tools.

Agree leaking crank seal could give those symptoms but why do you suggest replacing only primary drive side seal (well lubricated) and not the ignition side seal which is only lubed by the 2T oil?

I nearly always find air ingress problems are caused by ignition side seal.

I had to check if my dad had any pullers in his workshop, he has a few, I understand I will be needing one for sure.

Seals are on order, should be a busy weekend.

Will it still be worth decoking the exhaust, I'm thinking thats lots of white smoke and oil is going to clog up the exhaust.

Agree leaking crank seal could give those symptoms but why do you suggest replacing only primary drive side seal (well lubricated) and not the ignition side seal which is only lubed by the 2T oil?

I nearly always find air ingress problems are caused by ignition side seal.

I agree, dadof2 but the first post was about a "smoky 348". I always change both seals when in doubt. It's worth the effort.