Double jet!

o0norton0o

o0norton0o

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So, a friend gave me some of his old parts after he did a big rebuild. His cam ate one of his followers which caused his engine melt down. He gave me his old amal 932's with look better than my 930's, but I am not changing mine out. Anyway, I decided to pull his carbs apart to see if he had new floats because I was going to maybe swap my floats for newer ones (not doing that either because his floats were as old as mine...) Here's what saw when I looked at his carbs.

20250123_120414.jpg


In this picture, I'm probing the pressed in idle jet with my homemade "#79 drill bit glued into a WD40 straw) and the jet is definitely there as the tool is blocked from going home all the way when I use the other end of the straw which is the next larger size bit which does not go in as deep...

Is there such a thing as using 2 pilot jets?? I always thought it was either one or the other... I know the bike ran ok. In 2018 I actually tuned these carbs for the owner to eliminate a stumble taking off from idle, so they worked ok like this. I just never heard of amal carbs having the screw in jet and the pressed in jet. I always thought the pressed in jet eliminated the screw in kind that earlier amals had.

What do you all think?? Could these carbs have come like that?

********* Also, the float needle seat holes on my 2 float bowls were different diameters, so one definitely could flow more fuel than the other, and now that I think of it, one tickler always overflowed fuel faster than the other. I changed the larger holed float bowl out for one that had the same side needle seat hole as my other bowl.... trying to make all things equal in both carbs hoping for a better sync and more steady idle. Are there 930 bowls that have a different sized float needle seat?? or could mine have been worn so much by the old metal float needles that it became larger???

It's like "Amal Mystery Day" around here today... 😏
 
Last edited:
o0norton0o said:
So, a friend gave me some of his old parts after he did a big rebuild. His cam ate one of his followers which caused his engine melt down. He gave me his old amal 932's with look better than my 930's, but I am not changing mine out. Anyway, I decided to pull his carbs apart to see if he had new floats because I was going to maybe swap my floats for newer ones (not doing that either because his floats were as old as mine...) Here's what saw when I looked at his carbs.

View attachment 118243

In this picture, I'm probing the pressed in idle jet with my homemade "#79 drill bit glued into a WD40 straw) and the jet is definitely there as the tool is blocked from going home all the way when I use the other end of the straw which is the next larger size bit which does not go in as deep...

Is there such a thing as using 2 pilot jets?? I always thought it was either one or the other... I know the bike ran ok. In 2018 I actually tuned these carbs for the owner to eliminate a stumble taking off from idle, so they worked ok like this. I just never heard of amal carbs having the screw in jet and the pressed in jet. I always thought the pressed in jet eliminated the screw in kind that earlier amals had.

What do you all think?? Could these carbs have come like that?

********* Also, the float needle seat holes on my 2 float bowls were different diameters, so one definitely could flow more fuel than the other, and now that I think of it, one tickler always overflowed fuel faster than the other. I changed the larger holed float bowl out for one that had the same side needle seat hole as my other bowl.... trying to make all things equal in both carbs hoping for a better sync and more steady idle. Are there 930 bowls that have a different sized float needle seat?? or could mine have been worn so much by the old metal float needles that it became larger???

It's like "Amal Mystery Day" around here today... 😏
Click to expand...
I don't know specifically about 930 float bowls having a different size needle seat
But they certainly vary in size
I accidentally fitted one with a very small seat to a 932 on my BSA b50 and it was causing a misfire at higher rpm that took me ages to discover
I'm guessing someone has fitted the extra idle jets somewhere along the line
 
It's either one or other, you are supposed to drill out the pilot bush well oversize if you add the pilot jet to the float chamber. You would normally do this if you wanted a 20 or 30 pilot jet instead of the 25 pilot bush. If you don't drill the pilot bush oversize then the pilot jet will not do much.
 
LAB, thanks for the link. I think I have a pair of both, the high flow, and the standard bowls in my parts bin. Do you think either pair of bowls would work, or am I in uncharted territory again??? The bike ran fine with a mismatched pair of bowls and I never new the difference. The only thing I would say is that one bleeder was slower than the other, which makes sense now when I think about why that would be.

Thanks in advance..
 
L.A.B. said:
All Commandos except for the 850 MK3 had the standard float bowls according to the parts books. If there's any benefit in the high flow bowls I really couldn't say but either should work it seems.
Click to expand...
What was different about the MK3 ones L.A.B? Were they the high flow ones?

IIRC the high flow ones were invented to reduce fuel starvation at sustained WOT where a big twin can suck the fuel out faster than it can be replenished, a situation unlikely to be encountered on a road bike (especially a vintage bike ridden by a vintage rider).
 
Maybe it was Amal's choice to standardise the high flow based on analysis of complaints resolved by the fitting of higher flow and with no downsides to fitting them when not needed. If that is correct then Meriden Triumph would have the same change in 75.
 
I'm pretty sure the only difference is the needle and seat set. These can be easily fitted to the earlier bowls. There is also an alcohol set which are larger than the .125" gasoline, but I don't think they have Viton tips
 
L.A.B. said:
But they didn't as they continue to list the standard /055 float bowls and that's what my 1978 T140 has which I believe to be the original carbs.
Click to expand...
Meriden probably wanted to inhibit their customers from riding at sustained WOT… especially during the warranty period!
 
Triton Thrasher said:
So, if want enough fuel flow to overtake buses
Click to expand...



When I bought my Mk3, it had a pair of generic 932/300 and /301 carbs on it, which are still there (with standard float bowls, flat-topped spray tubes, and standard 4-stroke needles). I've had no problems overtaking buses or anything else. I bought the high-flow float bowls some years ago, although I've never tried them.
 
L.A.B. said:
When I bought my Mk3, it had a pair of generic 932/300 and /301 carbs on it, which are still there (with standard float bowls, flat-topped spray tubes, and standard 4-stroke needles). I've had no problems overtaking buses or anything else. I bought the high-flow float bowls some years ago, although I've never tried them.
Click to expand...
I do not believe I am the only person who ever had trouble getting enough fuel through a Concentric float valve. I may be unlucky but I can’t be that unlucky!​
 

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