ET: Engine (Twin) Uneven Running in Lower Gears

[nigsey]

I am not quite clear what type of Amals you got. The flanged type gets distorted easily from overtightening the flange nuts when some thick gasket is used there. So you should try to measure up the carb bore for oval shape. How to rectify this is next question.

Vic

Hi Vic, I have Amal 276 pre monoblock carbs.

 

[oexing]

So typically stub mounting, I think. Anyway, when you see the slide stuck at bottom there must be some step inside, from wear mostly. The slides are not very solid in o.d. dimension, so when someone did some bending on slides for having less wobble at half open to compensate a worn carb , that could have been too much for the slide to plunge down into the non-wear carb bottom . A reamer would restore a nice parallel bore but then the jet holder will be sloppy in there - not acceptable as well. A new body would be perfect but unavailable from Amal today, just complete carbs. Maybe you could remove any steps you feel in the body at bottom position of slide with a scraper and abrasive.

Vic

 

[nigsey]

So typically stub mounting, I think. Anyway, when you see the slide stuck at bottom there must be some step inside, from wear mostly. The slides are not very solid in o.d. dimension, so when someone did some bending on slides for having less wobble at half open to compensate a worn carb , that could have been too much for the slide to plunge down into the non-wear carb bottom . A reamer would restore a nice parallel bore but then the jet holder will be sloppy in there - not acceptable as well. A new body would be perfect but unavailable from Amal today, just complete carbs. Maybe you could remove any steps you feel in the body at bottom position of slide with a scraper and abrasive.

Vic

Thanks again for your time and advice including everyone else who kindly contributed to this thread, it’s much appreciated. I’ve been given a lot of advice so there’s a few things to look out for and to try out. Hopefully I’ll have some positive news to report in the coming days. Nigel

 

[greg brillus]

If the jet block was tapped out from the top, this can actually shift the top of the block to one side, this will cause the slide to hang up.........carefully straighten the same and all should be fine after that. Check the slide numbers....if its a 3 it will run too rich.........Float level is the next one.......Stand several feet behind or in front of the bike and check the bowl alignment verses the engine covers.......very often the bowl angle is too high or too low.......rotate the carby on its spiggot........easy fix.

 

[oexing]

That is another defect, but the actual question is about the slide not wanting to drop to bottom position. Less likely the root of hitting the jet block on top I guess ?

Vic

 

[nigsey]

That is another defect, but the actual question is about the slide not wanting to drop to bottom position. Less likely the root of hitting the jet block on top I guess ?

Vic

When I squeeze either side of the carb body the slide seems to run freely, which I guess is because it’s slightly elliptical, however this is is without jet block in at the moment. Once I’ve corrected the shape I’ll try it with the jet block.

 

[nigsey]

With your help gentlemen I’ve resolved my problem. I threaded fine wire through pilot jet holes, dropped both needles down a notch, reset the throttle stops and the pilot screws. I didn’t renew the needles or the needle jets and the bike is running really well now. I had a problem with a sticking slide which was due to the carb body becoming slightly elliptical, goodness knows why but it was, so I applied some pressure to either side of the body using a G clamp (not for the faint hearted) and it worked. I did a 80 mile test ride and it ran really well. Thanks again everyone for your help. Nigel