More carburettion questions. Inlet length.
Posted: Sun Dec 30, 2018 3:45 pm
So, having dumped my hopelessly worn Amal, I can now start my late model, classic engine, 350 bullet first kick again. I have been experimenting with a VM28 off a 500 bullet on it. Slow running is excellent but I think I'm going to have to experiment with a leaner needle jet/larger cutaway to get midrange to run right. But that's besides the point of todays question.
Due to cabin fever, I want to ride it tomorrow so I've put the original VM24 back on. It's set up to run pretty well on this (although I feel it's missing some top-end, hence fitting the larger amal in the first place and experimenting with the VM28, it's got a tuned head etc and a few other pokes).
When I got it, this bike had a PAV device which I blanked off and the carb was attached on the end of a veritable stack of spacers totalling one aluminium spacer plate (with the PAV nozzle in it), two plastic spacers, three paper gaskets and an o-ring. In other words, a huge number of oppertunities for an air leak. I also suspect this stack of slightly compressible plastic and card is in part responsible for warping of the carb manifold (now corrected).
I've just bolted the carb direct to the engine this time using the o-ring direct onto the head. Which is pretty much how the amal was attached. Seems to be working fine on a run around the block. However, here are a couple of questions:
Am I likely to run into heat transmission issues? Lookng at the parts book, earlier Indian bullets seemed to just attach the mikcarb direct to the head with a paper gasket. As time goes on, they seem to sprout increasingly more bits of plastic and metal between the carb and the engine? I also see the tunfoil heatproof spacers on our hosts website which makes me wonder if there is an issue here? (or is there just an issue in hot countries, I'm in Northern England).
I've used an o-ring rather than a paper gasket. Is this asking for trouble?
Just to confirm the overall effect of this change because I've removed a good 20+mm of spacers between the carb and the engine. A shorter inlet should move peak torque higher up the rev range yeah? So this should be good for road speeds but if I was to fancy offroading, fitting a spacer might be a plan so I get more torque at lower revs?
Due to cabin fever, I want to ride it tomorrow so I've put the original VM24 back on. It's set up to run pretty well on this (although I feel it's missing some top-end, hence fitting the larger amal in the first place and experimenting with the VM28, it's got a tuned head etc and a few other pokes).
When I got it, this bike had a PAV device which I blanked off and the carb was attached on the end of a veritable stack of spacers totalling one aluminium spacer plate (with the PAV nozzle in it), two plastic spacers, three paper gaskets and an o-ring. In other words, a huge number of oppertunities for an air leak. I also suspect this stack of slightly compressible plastic and card is in part responsible for warping of the carb manifold (now corrected).
I've just bolted the carb direct to the engine this time using the o-ring direct onto the head. Which is pretty much how the amal was attached. Seems to be working fine on a run around the block. However, here are a couple of questions:
Am I likely to run into heat transmission issues? Lookng at the parts book, earlier Indian bullets seemed to just attach the mikcarb direct to the head with a paper gasket. As time goes on, they seem to sprout increasingly more bits of plastic and metal between the carb and the engine? I also see the tunfoil heatproof spacers on our hosts website which makes me wonder if there is an issue here? (or is there just an issue in hot countries, I'm in Northern England).
I've used an o-ring rather than a paper gasket. Is this asking for trouble?
Just to confirm the overall effect of this change because I've removed a good 20+mm of spacers between the carb and the engine. A shorter inlet should move peak torque higher up the rev range yeah? So this should be good for road speeds but if I was to fancy offroading, fitting a spacer might be a plan so I get more torque at lower revs?