PDA

View Full Version : Amal tuning help....



choppermrns
07-02-2012, 9:44 PM
Hey gents,
I just finished my pre unit build, pics to come, but I'm having some issues getting the carb dialed. Bike won't idle consistently, and the plugs are black and sooty with black smoke out of the exhaust. Which indicates richness, yes? So I lowered the needle to its lowest setting, adjusted the air mix screw and got a better idle but it still stalls at lights or when I stop. I pulled and checked the main jet and saw it was a 320 jet, would a smaller main jet help at all at lower throttle settings? Or is it the pilot jet or something else?
Thanks!
And it's a monobloc 389 carb.

CRFyou
07-02-2012, 9:49 PM
try a 280 main.
3.5 slide
25 pilot
106 needle jet.


place the needle in the middle posish to start.

I'm assuming it's a 650, not 500 pre unit.

choppermrns
07-02-2012, 10:13 PM
Yup, it's a 650.
Where's a good place to buy jets?

CRFyou
07-02-2012, 10:21 PM
Call Tony at Classic Cycles in Orange, CA.

Torch
07-02-2012, 10:55 PM
On old Amals the main jet size was often increased to compensate for a worn out slide, a 320 main is not that big.
The biggest mistake people make when "Rebuilding" an Amal carb is they don't replace the needle and needle jet, that is the best improvement you can do on an old Amal.
And just to make sure of this..... you do know that the idle mixture gets richer when you screw the idle mixture adjuster screw in..... Right?

choppermrns
07-03-2012, 9:56 PM
Ok, here's where I'm at,
I spoke to tony on the phone this morning, I took the washer from under needle seat to lower the float bowl. I also put a smaller main jet, a 250, and placed the needle in the center notch. The motor still doesn't idle unless the air mix screw is way out and the slide stop is very high, with the slide about 1/4 inch open. Raw fuel also spits from the carb. I road the bike any way to see what it does at higher rpms. It's sluggish off idle, but when it comes up if runs nice. The right cylinder is still running intermittently, which I think is related.
Should I get a new slide and needle jet???
Tony, what would you charge to tune this up at your shop? I may just drop it off to you.

choppermrns
07-03-2012, 10:00 PM
The bike runs strong, at appears too, at mid to 3/4 throttle..

Arne
07-03-2012, 11:15 PM
Another possibility is that the slide is worn and there is play between the slide
and the carb body.

dazegoneby
07-04-2012, 6:40 AM
Agree with ^when trying to piece together some amals,, would get bike to run ok but didnt realize worn throttle bore/slide will give you fits .also check floats for fuel inside ,,if the old floats hold fuel ,," fun" on the road (will dump excessive fuel),,,glad i wasn,t running high pipes ,,woulda been flame on....

Torch
07-04-2012, 9:39 AM
Ok, here's where I'm at,
I spoke to tony on the phone this morning, I took the washer from under needle seat to lower the float bowl. I also put a smaller main jet, a 250, and placed the needle in the center notch. The motor still doesn't idle unless the air mix screw is way out and the slide stop is very high, with the slide about 1/4 inch open. Raw fuel also spits from the carb. I road the bike any way to see what it does at higher rpms. It's sluggish off idle, but when it comes up if runs nice. The right cylinder is still running intermittently, which I think is related.
Should I get a new slide and needle jet???
Tony, what would you charge to tune this up at your shop? I may just drop it off to you.

Bring it in and I'll look at it, we'll figure it out.