Author Topic: Odd backfiring  (Read 778 times)

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Offline Patrick

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Odd backfiring
« on: December 20, 2007, 12:01:01 PM »
Except for the fact that it leaks oil like a West Texas cotton field, my K0 project is running pretty well. It starts very easily and idles well and it's quicker than grease through a puppy when you get above 5,000 rpm or so. I say "or so" because my stock tach bottoms out at 3,000 rpm when the bike is parked, and spends a lot of time showing me well above red line when the bike is running. I don't think it's working right.

Sometimes at hard acceleration, or sometimes even while cruising, the bike will backfire. It isn't consistent and when it happens ity only happens a few times before it stops. The bike doesn't stumble or anything when it does this. The performance doesn't seem noticeably affected, but it happens and it annoys me. Except it does sound kinda cool.

FWIW, the bike has an 810 overbore, which I believe to be 64mm pistons from a 350, and a hot cam of undetermined origin. The head is stock except for Ape valve springs. The coils are 3-ohm from a 198x V45 with new wires and caps. I haven't checked the compression, but the vapor than comes gushing from the breather tube when the bike is running tells me the engine is running at quite high compression.

What do I need to adjust to make this backfiring go away?

And I've read on the forum about will tapping the two and three intake valve access caps to reduce case pressure - will that slow the oil leak? I can't tell where the oil is coming from, but it seems to be more than what I've experienced from head and base gasket seeps and seems confined to the left side of the bike. That gaskets are all new and the head nuts are torqued to 20 pounds.

Thanks,

Patrick
 
1970 CB750 K0
1982 VF750S Sabre
1987 VT1100 Shadow
1979 Yamaha XS11
1969 Yamaha DT1B
etc.

Offline dusterdude

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Re: Odd backfiring
« Reply #1 on: December 20, 2007, 12:40:13 PM »
is it a backfire thru the pipes or a spit thru the carbs?
mark
1972 k1 750
1949 fl panhead
1 1/2 gl1100 goldwings
1998 cbr600 f3

Offline Patrick

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Re: Odd backfiring
« Reply #2 on: December 20, 2007, 01:15:42 PM »
Through the pipes.
1970 CB750 K0
1982 VF750S Sabre
1987 VT1100 Shadow
1979 Yamaha XS11
1969 Yamaha DT1B
etc.

Offline dusterdude

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Re: Odd backfiring
« Reply #3 on: December 20, 2007, 01:18:56 PM »
im no expert but i would say it is either a rich mixture or a timing issue.
mark
1972 k1 750
1949 fl panhead
1 1/2 gl1100 goldwings
1998 cbr600 f3