'79 Raise Needle or Larger Primary Main

[FZBob]

Could anyone explain the interaction and overlap between needle position and primary main jet size? Do they completely overlap, or is the primary main circuit more influential at larger throttle openings/higher RPM? I am rebuilding my '79 carbs, and now is a good time to make any jetting changes. For the stock airbox, it appears that most people leave the primary main at 65, and raise the needle .020 or so. But I have seen a few posts where the primary main is increased to 72, and the needle is left alone. The needle change would be more convenient, as I can get at them without dropping the motor...

(I have jetted a lot of bikes in the past, but never one with the mysterious extra "primary main" circuit...)

Thanks, Bob

[daves79x]

For the stock airbox, no matter the exhaust, go up to a 68 on the primary main and don't shim the needles. Costs a bit for the jets, but you won't be changing them again. That will give you a faster warm-up and low-to-mid range smoothness.

Dave

[FZBob]

For the stock airbox, no matter the exhaust, go up to a 68 on the primary main and don't shim the needles. Costs a bit for the jets, but you won't be changing them again. That will give you a faster warm-up and low-to-mid range smoothness.

Dave

Dave, Thanks very much for the advice, it is most appreciated!

I now have the carbs completely apart, and am starting to clean everything. The Mike Nixon carb book is EXTREMELY helpful. I picked up a Harbor Freight Ultrasonic cleaner to clean jets and carb bodies, (but not float bowls - don't want to break the vent tubes). Also got the HF soda blaster (best $17 I ever spent) to clean the outsides and brackets. Removing the emulsion tubes under the primary mains was very scary. After a week of squirting with carb cleaner, it still took vise grips on my screwdriver (ground to a perfect fit) to twist them out.

I ordered the float bowl vent Tee's and linkage boots from Randakks, and have received their full rebuild kits

Will order the 68 primary mains shortly. Is Sirius Consolidated a good place to buy jets from or is there a better recommendation?

Also, can anyone recommend a place to order small miscellaneous carb parts? I need a couple of the aluminum washers that seal the float needle assembly to the carb body, and a few of the aluminum washers that seal the carb synch screws.

Thanks, Bob

[daves79x]

Go here for jets: http://pjmotorsports.com/ Don't worry about the washers on the sync screw plugs - they seal fine without them. I can send you all the float seat washers you want.

Dave

[FZBob]

Got the jets ordered. Will PM you on float seat washers.

Thanks, Bob

[preston]

You may want to check with Jack at Old School Carbs ( he's in San Jose also) or Mike Nixon ( somewhere in Ca.) for parts to rebuild your carbs.