Spitting at Carb

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Jun 19, 2003
First off, I must (once again) thank the board to all of its help over the last year. I must give some of the credit for the 8k that I put on my combat this season to your sound advice.

Anyways, one of the carburetors has taken to spitting gas all over the place at any rpm above idle. Like steady streams of gasoline dumping all over the cases. Let it drop down to idle, no spitting. I swapped the carb bowls, still spits. I checked the tickler to see if it could somehow work itself down and contact the float but it appears unlikely. All I can say is that it's a "didn't, but now it do" kind of thing.

Now, my "hints and tips for amal carburetter" pamphlet suggests that if "objectional spitting" occurs at the carb, either richen the mixture slightly (didn't work) or fit the throttle with a smaller cutaway.

What I would like to know is: (1) has anyone seen this before? It seems hokey to have different-sized cutaways. (2) is this a sign that I really should just have them rebuilt entirely, presuming that the next thing to go will be the body or the other carb? (current carbs are not sleeved) (3) if that's the case, should I just put a mikuni on instead?

Any help would be appreciated. I must say I'm tired of showing up to the bar smelling like a refinery.

Well, so much like a refinery, anyways. It is still a norton.


Answering your questions:

1) The only time I've seen this "gas dumping" is when there was a problem with the float height or float needle. The size of the throttle cutaway should not have anything to do with dumping raw gas on the ground.
2) Something needs adjusting rebuilidng to cure this problem. I would speculate that the problem is limited to the float, needle and or bowl. However, if you've already replaced these components, then I'm stumped. But, you should double check the float needle and make sure it has a Viton (rubber-like) tip and that it is in like new condition. Also, check the condition of your float seat.
3) Mikuni versus Amal is one of those long standing arguments; others are points versus Boyer and disc versus drum brakes. The carburetor decision is personal preference, and often a Mikuni emerges after seemingly unsolvable problems, like yours, with Amals.


I would tend to agree with Jason.

One problem a friend had was:

The round brass "pivot" bar/rod that slides through the float was "catching" the float & causing it to stay "down"
He told me he gave it a file & that fixed his problem.

Another one is when the float catches on a protruding bowl gasket.
But as Jason has stated, you seem to have looked at this area.
thanks, and clarification

thanks for your quick response. it's a strange problem, eh? i keep hoping it's one of those "duh" solutions but i'm running out of ideas. i'll go scrutinize the gaskets and brass pin.

i should have clarified that by swapping the carb bowls, i put the left on the right side and vice versa. the right side still leaks after the swap. i'm still quite new to this game and don't have any spares handy.

But, unless this one starts behaving again, i may have a spare amal carburetor lying around pretty soon. i spose i should be grateful that the carb gave out just as the rains started.

if anyone else is struck by some bit of insight, i'd love to hear it

'72 combat with ornery carburetor
Any chance it could be a split petrol line or bad ? The vibration could be opening the split - spilling petrol over the place.
so, after staring at the carb and scratching my head, i decided to clean out the carb AGAIN just to see if i had missed something the first time.

lo and behold: no spitting. and all it took was the application of more violence with the acupuncture needle and me making a joker out of myself on this message board.

sorry for the false alarm, folks.
so, it was only a little norton flu !
All's good if you sorted it for now.
Until next time.
My 73 850 with 932 Amals has had strange similar problem ever since I restored the bike. Today for example, after 10 miles it spits back thru the RH carb.
The plug/s colours are fine ~ new Iridium NGK, Boyer ignition and stainless steel inserts. :?:
I might add though that this spitting back is NOT constant and only occurs once or twice in say a 100 miles.. maybe twice in 10 or 50 miles with no pattern! :?:
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