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Exhaust Port Repairs, Plug Readings, and Smokey Starts

Keith gives advice on reading spark plugs, freeing a clutch and repairing exhaust ports.

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Ready to take your classic queries: Tech Editor Keith Fellenstein.

Exhaust port repairs

Q: Do you have any suggestions as to Norton Commando exhaust port repairs? Should I have the ports welded up and rethreaded or bored out and put in brass threaded inserts? Also, anyone you know have expertise in this area? Thank you for your help!
Mark Gwynn/Cleveland, Ohio

A: I’ve had great results from Jim Comstock, but he’s a busy man so you’ll have to be patient. His website nortonmachineshop.com is for information only. You’ll have to drop him an email at one of the addresses listed on that page.

Plug reading

Q: I was wondering if you have any experience with the Gunson Colortune. And I also have a related question about getting a plug reading at full throttle. Rather than running over 100mph, can a wide open plug reading be done in lower gear at or near the speed limit?
Ross Richards/via email

A: I’ve seen those visible spark plugs before, but don’t have any experience using them to tune a bike. They would be most useful I think, if the bike was on a dyno. I don’t know how you can read them in loaded conditions otherwise. As for plug reading in lower gears, full throttle under load at less than 100mph is perfectly valid for plug reading.

Smoky starts

Q: I have recently rebuilt a 1982 Triumph Bonneville 750. When I started and rode it, it blew lots of smoke. Is this normal? I have done around 80 kilometers on the bike but it is blowing too much smoke for my liking. Or am I being too picky?
Charlie Chodorowski/Pemberton, West Australia

A: Some smoke on a first restart wouldn’t be troubling, but continued smoking is. The first test would be compression, followed by a leak down test to see where the sealing issue is. Pressurizing each cylinder while at TDC on compression should give some clues. You’ll have to keep the engine from turning over, and then listen at the breather, intake and exhaust. If your rings aren’t sealing well, there should be some air noise at the breather. One possibility is piston rings installed upside down, another is rings that are sized incorrectly and not providing enough sealing against the cylinder walls.

Clutch issues

Q: Hi Keith, I have a 1973 Triumph Bonneville. I have had it for several years. I have done quite a bit of work on it in the past and need to sell it and get it out of my garage, however the clutch is jammed up, is there an easy fix for this?
Ian Rednall/via email

A: Those wet plate clutches always stick together if left unused for too long. You’ll need to start by unloading the clutch by pulling in the lever and tying it back with a zip tie. Leave it overnight and the next day kick the engine over with the ignition off until there is no resistance to the kick starter. At that point you can take the zip tie off and the clutch should behave itself, at least until it sits unused for a bit. I have that problem with my Triumph T100SC if it sits. For it I just pull the clutch in and kick start the bike. Sometimes the clutch frees up before the bike starts, but if the bike starts the engine pulses finish the job of freeing up the plates.

Reader feedback

A:I got some good suggestions to add to my method of fixing cracked overflow tubes in carburetors, and one of the easiest came from Lee M. Christof. He said go to a small engine repair shop and get Tygon tubing that just fits over the drain tube. Cut to fit and push on. Just make sure it doesn’t interfere with the float operation.

I can always count on subscribers to supply the knowledge I’m lacking. Regarding the Motorumi Formichino scooter question (from reader Joe Mensch) in the March/April issue, reader Paul has some information to share.

“I saw the reader question about a Motorumi Formichino scooter in the March/April 2021 issue. I’m pretty into vintage scooters, and there are not a lot of options for that scooter in the U.S. It is very rare, even in Europe. The first place I would send the reader would be Saint’s Cycle Works in Chattanooga, Tennessee. Joe Casola, the owner, is very into old scooters, and has a soft spot for the oddballs. He is an excellent machinist. If there is anyone in the U.S. that will take on engine work on a Formichino, it would be him. If Joe won’t do it, you can send the reader my email info. I do know a guy out here in San Francisco that has a large collection of Motorumi motorcycles. He may have a contact in Europe that can assist, if nobody in the U.S. is able to help.” — Paul

If Paul’s contact would be useful for anyone else out there, email editor Hall at lhall@motorcycleclassics.com and he’ll be happy to share it.


Send questions and feedback to keithsgarage@motorcycleclassics.com.

 

Updated on Jun 24, 2021  |  Originally Published on Jun 7, 2021

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