Board logo

Midget idle
Lightning - 23/1/13 at 07:28 PM

1275 midget on twin SU's I can't get the idle down far enoough. Both idle screws and linkage right down. Cleaned throttles to make sure they shut.

what else?


BTW idle approx 1300 sounds a bit fast too. Runs well bar that

cs3tcr - 23/1/13 at 07:39 PM

Check to see if the choke linkage/fast idle screw isnt holding the throttle open slightly. Also, are the throttle shafts or bushings worn at all?

vyperstrype - 23/1/13 at 07:51 PM

Check and make sure that it isn't drawing air in around the Carb area, and inlet manifold. also check carb diaphrams and Dashpot oil levels.

matt_gsxr - 23/1/13 at 07:57 PM

Relieved to see this isn't a Daily Mail style thread suggesting short people are lazy.

perksy - 23/1/13 at 08:06 PM

Air leak, Throttle cable 'snagging' ?
Double check linkage

Timing been checked ?

britishtrident - 23/1/13 at 08:13 PM

Assuming the car has twin SUs
First thing is to check the pistons in the carbs are sliding up and down freely and when coming to a stop with a distinct "click".
The next thing to do is synch the carbs.

The other thing to watch for is if the is idle speed is set too low on A & B series they tend to idle on only cylinders 1 & 4 --- all to do with the siamesed inlet ports.

The pre Metro 1275 A series engines are very prone to exhaust valve burning on the centre two cylinders so it is worth doing a compression test.

Lightning - 23/1/13 at 08:21 PM

Thanks for all your posts so far

Just had new exhaust valve seats/guides etc so now unleaded....ahhh timing ...now on unleaded.....could be....

choke linkage not stopping throttles from shutting, All new gaskets, cleaned pistons toped up dampers,

Lightning - 23/1/13 at 08:26 PM

oh also , no cable fitted yet so cant be that. There does seem to be a bit of play on the butterflys
BTW
really enjoying doing the midget, nice a simple And bbits really cheap!

rusty nuts - 23/1/13 at 08:35 PM

Check for air leaks especially carb spindles make sure the dip stick is sealing at the top as that will allow air into the crankcase as will a faulty oil filler cap, check the timing is correct and the auto advance is not partially siezed. try releasing the clamp on the throttle butterfly spindles between the carbs and running the engine.If that doesn't help strip the carbs and make sure that the throttle butterflies and centralised in the carb bodies, if they are not one side will jam and hold the throttle open. Finally balance the carbs and mixture

Lightning - 23/1/13 at 08:43 PM

I did centralise the butterfles as I had the same thing on the TVR throttle body and it jammed and wouldnt close properly.

I will check the rest. Timing could be wrong and possible air leak on spindles

whitestu - 23/1/13 at 09:25 PM

quote:

Relieved to see this isn't a Daily Mail style thread suggesting short people are lazy.


I was looking forward to it!

mark chandler - 23/1/13 at 10:35 PM

If its got the ghastly air bleed valves on the throttle plates remove and float solder over the holes to fill, these should not exist on a 1275cc engine but you never know how much is original.

Lightning - 23/1/13 at 10:58 PM

Thanks to all of you.

I've just come in from the garage took the carbs off again. Took off butterfly blades fully and I found a very very small burr on one . One very gentle sweep of a file removed it. Now the idle has dropped right down. If fact too low, so adjusted it up on the screws.

Job done , happy smile

Thanks again guys.