Misc: Carburettors Odd Amal 276 Carburettor Issues

[Whiteshadow15]

I have very little experience when it comes to carbs so forgive me.

Have a fresh rebuild that has had all sorts of issues, I sourced a stock set of carbs in very nice condition off of a running machine, sonic cleaned them and rebuilt.

Now, the bike has not been running great on the rear cylinder. I had spent tons of time trying to source the issue, checked compression, timing, spark, etc.

By random chance I swapped out the carbs and put the front carb on the rear just to rule out the carb itself. The weird part is that it runs perfectly in that situation. The suspect carb has no issues on the front and the front carb seems to solve the issue on the rear. I then looked over things and swapped back and once again the bike stumbles on the rear cylinder. Checking with a temp gun the rear cylinder is about 100 degree or more cooler, in the other setup the difference was minimal. All the slides are free as can be.

Is there something that I may be overlooking?

 

[oexing]

Have you swapped slides as well front to rear. Or just the carbs ?

Vic

 

[Whiteshadow15]

Just the carb bodies, They both slide freely in either body.

 

[greg brillus]

Sounds like it's either a float level issue and/or the pilot system could be blocked, perhaps the base gasket between the jet block and the base nut is home made and blocking off the pilot circuit. The base nut comes in about 4 different heights so this could be a big issue with the float level.

 

[greg brillus]

One other very common issue i missed just there.......Often the carb is not a good fit over the manifold stub, unless the pinch bolt is done up very tight........this will cause the carby to run very lean at idle and part throttle.........Sometimes you have to either replace the manifold with one that the stub is larger in diameter, or get some shim brass and cut a piece about 15 mm width and use this to shim the carb to the manifold.........Not ideal but it will work and prove the point..........This issue is common on these bikes, with either the 276 or 289 carby's.

 

[Whiteshadow15]

The floats themselves remained on the same side and just the bodies were swapped so I wouldnt think the float would be an issue.

I did remove everything and look for debris, everything was all clear. Is there any way to test the manifold fit? they appear very snug and tried spraying ether and didn't appear to make any difference.

 

[greg brillus]

It does seem strange that the carb with the issue runs fine on the front cylinder. Very difficult sorting tuning issues over the internet.

 

[Trickymicky]

If its had new valves and guides, could one be sticking in certain conditions ?

 

[Albervin]

Was it timed on No 1 cylinder? i.e. the rear cylinder????? Then we get to what is different between 1 and 2??

 

[timetraveller]

Note that WS wrote that it runs perfectly when the carbs are swapped over. It cannot be anything to do with timing or similar