Thanks for your reply. You're correct in that each throat feeds a manifold runner that then splits into two.

The engine runs well on wide open throttle, the problem is at small openings. To accelerate to a decent speed where it will take full throttle, I have to quickly pump the throttle in and out. The problem is worse when cold.

I figured that by doing this I'm effectively running it with the acceleration pump. The tuner seemed to think that the flow through the carb at low engine speeds wasn't enough to let the carb add fuel to the mixture.

Could someone reccommend a good tuner in Brisbane?

Nathan

There's no way that carb is too big. Minis with 1275cc engines run 45dcoe webers with 38mm chokes (from memory) which is way more carb on a smaller engine, and one that has less potential flow-wise with the intake ports such as they are.

What exactly is the engine doing that they can't seem to fix?
Without knowing more, completely off the top of my head I'd suspect that they might be going wrong with regard to emulsion tube specification. This particular issue requires it's own set of solutions on minis. I bring them up because more often than not they use a single weber to feed the whole engine (1 and 2, and 3 and 4 each share an intake port - 2 total - so there's no advantage to twin webers. I bring this up because a single sidedraught like this on a 4 will likely (the ports are separate but the intake manifold runners will be shared just prior to splitting at the manifold/head area, so the carb requirements will likely be more like a mini a-series engine, than what you'd run with twin webers on a dedicated manifold.

there's also a chance (for the same reasons) that the sort of acc pump setup would have to be more like a mini engine setup than for twin webers on a 1.5. The latter would (for the same setting) dump twice as much fuel on throttle opening, so you might have to ramp up the output if running a single dellorto (and I don't know how much scope you'd have to do that) - this alone could (if not addressed) cause a sizeable flat spot when flooring the throttle.

I'd be lying if I said I knew off the top of my head what emulsion tubes to try, but there is a book by Des Hamill which isn't 100% perfect, it needs more detail, but they do at least from memory have a few pages devoted to good 'starting point' choke and emulsion tubes for carbs where each throat is shared by 2 cylinders. there is some info in David Vizards mini/a series books that might help, but the ones I have are on loan to a friend. I can maybe get them back this weekend if I see him, and can post anything relevant. If a post doesn't turn up by this time next week, pm me incase I forgot.

The vehicle is a Honda S800, hence the lack of space.

Seems like the camshaft and cylinder head is too big. Find a shop that specializes in racing engines... they can tune it. Don't expect a smooth idle, or smooth off-idle performance.

what car is it in? a 1200 would fit the other carby options easily

people run two side draught carbs (dellorto or weber) with 32mm or 34mm chokes on 1200cc a-series

the problem is the people tuning it..... 2 weeks!!!

Hi everyone, I'm in a bit of a bind and was hoping to get some opinions.

I've just had the car in for a tune. The shop had it for a couple of weeks but didn't have any success. Their opinion was that the carbi is too big.

Specs are A15, 1mm overbore, 9.5:1, 41mm and 34mm valves, 4-2-1 extractors, light flywheel, double valve springs, cam is 66-30 degrees exhaust and 33-68 degrees inlet. Carbi is a 40mm Dellorto side draught, with 34mm chokes on a custom manifold.

So is the carbi too big? What other options would you suggest? Problem is that there isn't enough under bonnet clearance for a downdraught, and not enough width for dual SU type carbis.

Thanks, Nathan