Carb balancing

Eggsy · Aug 20, 2026

I just installed new Wassell carbs on my 1973 Norton commando 750. It runs very rough at low speeds. It accelerates well and cruising seems fine.

Torontonian · Aug 20, 2026

Eggsy said:
I just installed new Wassell carbs on my 1973 Norton commando 750. It runs very rough at low speeds. It accelerates well and cruising seems fine.

I run Wassell's . Pull the plugs and post images .
Chokes left on ?
750 or 850 ?

Eggsy · Aug 20, 2026

Tks
Left side a little darker but not too bad
750
No chokes

Tornado · Aug 20, 2026

New carbs can have machining swarf in the pilot drillings...got to go through them thoroughly. Confirm jets/needles are correct. Next confirm no air leaks at mounting flanges...carb to mani, mani to head. I use Locktite gasket maker compound btwn these flanges. Confirm the balance tube on the mani spigots is fully seats, not cracked/leaking. Go thorough the mechanical balancing procedure using chop sticks/drills etc to ensure both slides begin to move at precisely same moment as throttle rolled on. and confirm both reach maximum open position at same moment...adjust at carb top cable adjusters.

Eggsy · Aug 21, 2026

Tks.
I’ve done all that but it’s good to check again
Cheers

htown16 · Aug 21, 2026

What pilot jet are you using. Some Commando's seem to prefer the 17 others the 19. Check the fuel levels in the float bowls with a u-tube. Lot's posts on here on how to do that. Wassells likely use same fuel level, .21 below top of bowl as Amals. At least mine did.

Eggsy · Aug 22, 2026

htown16 said:
What pilot jet are you using. Some Commando's seem to prefer the 17 others the 19. Check the fuel levels in the float bowls with a u-tube. Lot's posts on here on how to do that. Wassells likely use same fuel level, .21 below top of bowl as Amals. At least mine did.

Thanks for the info. More stuff to check

Torontonian · Aug 25, 2026

Overtightening the float bowl screws can warp bowls tangs .

jontg428 · Aug 26, 2026

Did you order the correct jets and needles to go with them? Also as mentioned, check float levels first, then tune.

Triton Thrasher · Aug 26, 2026

How was it running before got new carburettors?

jseng1 · Aug 29, 2026

Have you considered another brand of carburetor that doesn't have so many problems?

Eggsy · Saturday at 8:39 AM

Triton Thrasher said:
How was it running before got new carburettors?

It was running good but I think the slides were stickin

Torontonian · Monday at 1:11 PM

Eggsy said:
It was running good but I think the slides were stickin

Stickin' slides are typically from overtightening the carb mount nuts . Warps the body . Torque values real important here , they are low . Nylocs .

Alan L · Monday at 3:23 PM

Hi, I don’t know if this is valid but I tried all sorts of self invented methods to balance the carbs on my T160. The usual method was to trap small drill bits beneath the slides and adjust the throttle rods so that all 3 drill bits move or ‘twitch’ together. I then tried shining a bright light through the carbs and adjusting to the just the tiniest sliver of light was visible beneath the slides. This seemed to allow incredibly fine adjustment, the tiniest fraction of a turn of the idle screw was very visible. Then I hit on the idea of attaching a vacuum cleaner to the manifold side and checking with a vacuum carb balancer. With the carbs on the bench this was the easiest and best way. I guess that unlike other methods it takes into account wear on the slide. Just my experience.

Tornado · Monday at 3:57 PM

Alan L said:
Hi, I don’t know if this is valid but I tried all sorts of self invented methods to balance the carbs on my T160. The usual method was to trap small drill bits beneath the slides and adjust the throttle rods so that all 3 drill bits move or ‘twitch’ together. I then tried shining a bright light through the carbs and adjusting to the just the tiniest sliver of light was visible beneath the slides. This seemed to allow incredibly fine adjustment, the tiniest fraction of a turn of the idle screw was very visible. Then I hit on the idea of attaching a vacuum cleaner to the manifold side and checking with a vacuum carb balancer. With the carbs on the bench this was the easiest and best way. I guess that unlike other methods it takes into account wear on the slide. Just my experience.

I just use a Morgan Carb Tune connected to the two manifold balancer pipe spigots and adjust cable ferrules accordingly.

ashman · Monday at 5:23 PM

I just use my fingers on the slides, you feel both slide moving and adjust till they start to lift together, I use my ears and eyes when tuning and hands at the end of the mufflers to feel the pressure from both exhaust pipes, been doing it this way for 50 years, but of course jetted right, timing, valves all have to be set right as well, but since installing the Joe Hunt magneto my Amals and JH work so well together and the last 15 years has ran the best it ever has with that big spark, my Norton start first kick every time and runs smooth down low and right through the rev line when I fully open the throttle, as it should, no special tools just a small screw driver, my eyes and ears as well my fingers is all I use for a sweet running Norton and idles perfect when stopped.
I think I might have a freak Norton and I am no tuning expert, I just know my own bike.

Ashley

Torontonian · Monday at 7:39 PM

Alan L said:
Hi, I don’t know if this is valid but I tried all sorts of self invented methods to balance the carbs on my T160. The usual method was to trap small drill bits beneath the slides and adjust the throttle rods so that all 3 drill bits move or ‘twitch’ together. I then tried shining a bright light through the carbs and adjusting to the just the tiniest sliver of light was visible beneath the slides. This seemed to allow incredibly fine adjustment, the tiniest fraction of a turn of the idle screw was very visible. Then I hit on the idea of attaching a vacuum cleaner to the manifold side and checking with a vacuum carb balancer. With the carbs on the bench this was the easiest and best way. I guess that unlike other methods it takes into account wear on the slide. Just my experience.

Cable adjustments and stretch ?

Fast Eddie · Monday at 11:56 PM

Torontonian said:
Cable adjustments and stretch ?

T160 has a gantry.

Grandad · 2026-09-08T02:04:44-0600

Years back for carb balancing on bikes and cars I used to use two lengths of garden hose, placing one in each carb entry and listening to the suction noise when opening the throttle. Worked very well for me.
When I had a BMW R90 my mate had one as well and I used to tune his carbs for him with garden hose, he never had issue and very much liked the way the bike ran after I'd done the work but one day he said what about using vac gauges ? He was set on getting a set as he thought they would be better and being peeved with this I said if the gauges would give a better tune I'd pay for them - never did need to make the payment.
Nowadays after years in noisy industry the old lug 'oles arn't so efficient so no longer use that method but it is an excellent method.
I dare say gauges make sense on four cylinders .. Lol !

Triton Thrasher · 2026-09-08T03:07:05-0600

Eggsy said:
It was running good but I think the slides were stickin

I have, at times, squeezed a Concentric body with big pliers to get the slide moving freely.

Carb balancing

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