Amal Carb Issue

Just some info in case its useful to others.

Synchronised my 2 concentric carbs the other day and all was well for a while. Then started misfiring and actually ended up only firing on one pot! Obviously I had not done such a good job! So decided to do them again by following "Bushmans" method. Short story is that when I adjusted the cables so the slides appeared at the same time (from fully open), one cable adjuster was at max and the other on minimum! More importantly, when fully closed, one slide was about 1/4 inch from the bottom and the other was about an inch or so up from the bottom! Only conclusion, after a lot of fiddling, was maybe the cables were different lengths. I took the carbs apart to find them both identical cables (both look pretty new as well). However, I noticed that the slide return springs WERE very different lengths and strengths (therefore fully compressed they are different lengths as well)
Maybe one just wore out, I don't know. Anyway, 2 new springs on order and I hope this will bring both carb slides into line and solve my problem.

 

Thanks. 2 separate cables. Checked and oiled for smoothness.
Replaced both springs with new. But haven't actually got my head around why they made such a difference in slide action, height,lift etc. You could be right that one cable was caught up or squeezed too tight under the tank, but I've done my best to make sure they both move ok now. Haven't had the time to test out my "re-balanced" carbs yet.

For interest, the previous owner had drilled out the blank side of the air screw so the pilot jets can be cleaned easily Whilst still on the bike. Not sure I would be brave/skilled enough to do that myself (he was an engineer), but would recommend the adaptation.

 

Just as a matter of interest, as the T100 inlet manifolds have a balance pipe, has anyone bothered or has anyone tried to balance the idle using vacuum guages? Maybe a bit of overkill? Just interested if anyone uses guages on any classic twin (650/750 bonnies maybe?) with somewhere to attach the gauge pipes?

 

Good to know. Many thanks.

 

Logical thought I agree. However, the new springs are both the same length and syrength as the longer, stronger spring! Maybe whatever they are doing, they are doing it the same now!

 

Well. I wasn't going to bore people but seeing as you asked...

Balanced carbs. Initially ok then rough running then onto one pot only or just rough. Looked at carbs again, replaced the slide springs etc. No change! So checked the spark, all ok. Much head scratching and fruitless kicking over (!) I checked the sparks again and although ok when I pulled one plug cap off when running, I got a shock. Renewed both plug caps, same again. Seems like the plug was fine outside the engine but once under pressure it wasn't working! Replaced that plug with a spare and she runs consistently on 2 cylinders. Need to do some fine tuning again as I messed with the carbs so much but I'm hoping that she's OK now. Only had time for a run around the block so far so need a longer run to check properly. So hopefully she is or soon will be running correctly.