Triumphrat

williambonney

I have a 1964 Bonneville w/ twin amal monobloc 389's.
It's running so lean, it's overheating.
the engine is a recent rebuild, with big bore kit.
I can't get it to run rich enough, even though I have
changed the needle and main jets.
Any ideas?

TIA Paul

649cc

is your timing right?...auto advance working?...what do your plugs read colorwise?...are both sides the same?.....airleaks on carbs? float levels correct? oil system working properly?...was it all Ok before the work and what did you alter

GrandPaulZ

I hope you had the cylinders carefully re-bored to "sloppy" (relative to modern) tolerances.

Sounds like you are scuffing your pistons; they'll stick solid if you don't have enough clearance for expansion.

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649cc

a bigbore kit would surely come complete ready to assemble and not have been rebored

williambonney

All of your questions have been addressed except for the auto advance.
How do I tell if that is working?

I went up one more size in the main jets and it's running
pretty well now.


Thanks, Paul

quagmire

Take the auto advanced unit out and make sure the springs work easily. there are two weights that move out as the rpm's go up. The springs give some resistance at lower rpm's so the timing isn't advanced until about 3000 rpm's. (don't quote me on those rpm's)

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Hey, What's this oil on the floor?

666Bonneville

are you running straight pipes? the bike leans out with straight pipes.

you could get new slides; size 2 1/2 make the bike run richer

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649cc

strobed the timing on both cylinders...advancing OK...dont mess with the carbs before setting the timing properly

Mecchanica

The idle jet is replaceable, but if you can get highest idle by lightly bottoming the idle mixture screw and backing two revolutions out, plus or minus a revolution, then you are in the ballpark with the idle jet.
You should have a 106T needle jet stock, and you should be able to get a 107T if you order one. Er, two.
You want to make the bike overrich, and then tune back to ideal.
Are you running a new kit (Aerco) or have you redone an old Routt, Morgo, or Chantland kit?

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