classic motorcycle forum

Motorcycle Discussions => British Bikes => Topic started by: dirtybootboy on October 10, 2008, 03:49:50 AM

Title: back firing
Post by: dirtybootboy on October 10, 2008, 03:49:50 AM

I'm getting a bad misfire/backfire all-of-a-sudden on my 1968 tr6c. There is also milky oil coming out of the crank case vent. I just bought the bike and don't really know much about it. Anyone out there have any suggestions?

Title: Re: back firing
Post by: TBS on October 10, 2008, 08:12:31 AM

Milky white oil from the crankcase vent pipe is emulsified oil and is common on a newly built engine, and will eventually go when everything is run in. Was it misfiring when you bought it and did you buy from a dealer?

Title: Re: back firing
Post by: Blue on October 10, 2008, 08:50:19 AM

If it has just been rebuilt, how many miles has it done?  If it's around the 500-mark, now is the time for a thorough once-over.  Change the oil, clean the filter (if it has one), check the head and barrel studs for tension, check the clutch and brake adjustments, check the carburettor (idle mix/cable/slide etc) and check the ignition and valve timing.

It sounds like and ignition problem, possibly too far advanced - is it still on the old system or has it been replaced with electronic ignition?
It could be carburettor, perhaps the main jet, but if it's been working fine until now I'd lean more towards ignition.

Title: Re: back firing
Post by: thunderbird on October 10, 2008, 09:52:02 AM

as has been said check the ignition system, also check the valve clearances you may have a valve not seating properly,the milky oil may be due to a little condensation if the bike had been standing for a while.

Title: Re: back firing
Post by: dirtybootboy on October 11, 2008, 01:57:20 AM

I don't really know how long its been since a rebuild. I bought the bike from a nice little Asian chick who brought it to a vintage British bike shop regularly. Also it has an electronic ignition update. I'm new to these bikes, but very mechanically inclined. How do you go about timing these things? I kind of figured the ignition was the problem.

Title: Re: back firing
Post by: 33d6 on October 11, 2008, 04:36:06 AM

If the exhaust pipe is slightly loose where it inserts into the head it can suck in air and cause very impressive backfiring especially on the over run when you have shut off the throttle and are slowing down.
It doesn't need to be really rattly loose for it to be a problem, just loose enough for the joint to be no longer airtight can cause the problem.
Cheers,

Title: Re: back firing
Post by: L.A.B. on October 11, 2008, 08:27:50 PM

Quote

Also it has an electronic ignition update. I'm new to these bikes, but very mechanically inclined. How do you go about timing these things?

But what is the actual make/type of electronic ignition, as there's more than one?

Title: Re: back firing
Post by: dirtybootboy on October 11, 2008, 08:35:29 PM

L.A.B-boyer bransden eletronics, mirco-mk111

Title: Re: back firing
Post by: L.A.B. on October 11, 2008, 09:06:06 PM

Quote

-boyer bransden eletronics, mirco-mk111

OK, here's the link to the Boyer Bransden instruction sheet (pdf) for the Micro-MkIII ignition:  

http://www.boyerbransden.com/pdf/KIT00052__BOX00023_.pdf

Title: Re: back firing
Post by: L.A.B. on October 11, 2008, 09:16:08 PM

And here's some useful diagnostic information for Boyer ignitions:
http://www.tioc.org/boyertest.htm