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Author Topic:   carb jetting
Dirt Roller

Total posts: 19
posted May 05, 2002 10:39 AM
377 cid 100 dome pistons @ .030 over with 64cc haeds and stock rods. Carb is a BG 750cfm on alcohol. We are unclear as to how you read the plugs so we have been going down on jet sizes one step at a time. Right now were at 130 primarys and 140 secondarys. Does this sound too rich yet. Every change we make seems to make the motor run better but then fouls the plugs after one weekend. Thanks for any help.


Dirt Freak

Total posts: 219
posted May 05, 2002 11:19 PM UIN: 40696038
what heat range plugs are you using?

Dirt Maniac

Total posts: 106
posted May 06, 2002 12:47 PM
I would think that it would be lean.

Wwe run 161's front and rear on a 355
and 173 on a 406.

Dirt Newbie

Total posts: 4
posted May 07, 2002 10:49 PM
Wow, that should be really lean. I have run as high as 185's and am now at 163. I don't think my jet board even goes that low. Be careful!!! watch you water temp as another tool in jetting. It is not a great way but just one more tool.

Dirt Full Roller

Total posts: 62
posted May 09, 2002 12:47 AM
Check to see if the power valve is leaking, had this problem with an out of the box BG. Maybe an increase in timing would help burn off excess fuel? Check the exhaust temps with a pyrometer to see if all of the fuel is being combusted. Now we run a Demon with 176 jets front and rear.

Dirt Roller

Total posts: 19
posted May 12, 2002 09:06 PM
I talked to Port City Racing where the carb was purchased and they said jet sizing would have to be on the low side for this carb because it actually flows 825 cfm. They say that is too much for our motor and that is why it seems too rich when we jet as others do. Does this sound right ??

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