classic motorcycle forum

Motorcycle Discussions => British Bikes => Topic started by: bullrush on June 22, 2015, 06:31:45 PM

Title: Hot starting problem
Post by: bullrush on June 22, 2015, 06:31:45 PM: My 1957 Thunderbird starts great when cold but when the engine is hot it just does not want to know. I tried a plug change but no difference. There is a good spark and compression.
Title: Re: Hot starting problem
Post by: mini-me on June 22, 2015, 07:01:05 PM: check tappets, are they tight?

or condenser failing
Title: Re: Hot starting problem
Post by: mark2 on June 22, 2015, 07:50:18 PM: coil ?
Title: Re: Hot starting problem
Post by: JFerg on June 22, 2015, 11:28:09 PM: Magneto. An open circuit in the HT winding build a small track of carbon. This has a low resistance when cold, but a high resistance when hot. Great spark and easy starting when cold, but weak when hot.
Title: Re: Hot starting problem
Post by: R on June 23, 2015, 05:03:02 AM: Quote from: JFerg on June 22, 2015, 11:28:09 PM
Great spark and easy starting when cold, but weak when hot.

Exactly the same symptoms/behaviour from a failing condensor in the magneto also.

These neat little new fangled brightspark condensors that sit in the points housing (with original condensor disconnected) seem to be the answer to many an ailing magneto. Unless the wiring itself really is kaput, ot course, a much less common problem it seems though.

P.S. NOS condensors are to be avoided like the plague, they can degrade sitting on the shelf.
Title: Re: Hot starting problem
Post by: mini-me on June 23, 2015, 08:24:50 AM: 1957 6T should be coil ignition.
Title: Re: Hot starting problem
Post by: R on June 23, 2015, 09:21:56 AM: Duff coil or condensor then.

Covered all the possibilities now.
Hopefully....
Title: Re: Hot starting problem
Post by: mark2 on June 23, 2015, 06:26:53 PM: is the bike fitted with Amal or SU carb ? has it the insulation block fitted
Title: Re: Hot starting problem
Post by: R on June 25, 2015, 05:45:59 AM: Could even be limited fuel flow out of the fuel tap(s), or a blocked breather in the fuel tank cap.
Any pause, and a slightly limited fuel flow catches up ?
Title: Re: Hot starting problem
Post by: iansoady on June 25, 2015, 11:20:06 AM: Always worth fitting a new condensor / capacitor IMO as they're hard to test and very cheap.
Title: Re: Hot starting problem
Post by: 33d6 on June 27, 2015, 01:36:39 PM: You were right first time R, it's failing ignition. It's a no-brainer. Given it's a '57 T'bird the chances are very high at least parts of the ignition are still original and very tired. Not unless the owner can afford a professional restoration anyway.
Cheers,
Title: Re: Hot starting problem
Post by: mini-me on June 28, 2015, 09:05:25 AM: Do people just questions and bugger off? what was the result?
Title: Re: Hot starting problem
Post by: murdo on June 28, 2015, 10:47:31 PM: It appears so.
Title: Re: Hot starting problem
Post by: cardan on June 29, 2015, 03:38:05 AM: Stay calm - he's probably out in the shed studying the ignition on the Thunderbird. In a busy world it's sometimes hard to reply to every post.

Leon