High idle speed

["Slack Alice" Simon]

Tried my engine for the first time after putting it together.

Apart from the usual burning paint/sealant smells, and a louder whirring noise than usual from the timing gears, it doesn't sound too bad.

It won't idle  - typically won't go below 1250 whatever I do.

Throttle stop and stop on choke lever adjusted to zero - I then took the linkage off and held the carb spindle closed with pliers.

Carb spindle one of my better ones.

Slow running adjustment appears to do almost nothing, maybe improves snap pick up a bit but doesn't affect the idle speed.

New carb to manifold gasket, new gasket plus goo between manifold and block, valves and guides are a motley collection but ok, I think.

Block and pistons pretty well worn, and not run together before, but on the road seems to pull ok.

2 bearing engine is standard apart from flattened cam followers.

What am I missing?

[Alan]

Have you had the carb to bits? Sounds like an airleak so is the butterfly valve centralised properly, is the wear in the spindle too much or have you not sealed the manifold as well as you think you have?

[David Stepney]

I had a similar problem with my RP saloon when I first had it. Apparently there are two versions of the 26V carburettor. If you get the wrong float chamber on, you get an impossibly fast tickover. There is a thread on this forum that I started on 10th April 2019, under the title 'Carburettor Problems'. Sorry I am too computer illiterate to post the link, but if you search for this, I am sure it will pop up, and it may assist.

["Slack Alice" Simon]

Sorted now, thank you.

I had forgotten that discussion about carb bowls.    Changed it, no difference.


Checked to see if this was the carb I used before - I built and fitted the engine at start of lockdown, so have forgotten lots of things.

No, it was a bitsa carb put together to see if it worked.


Took it off, and, as Alan suggested, the butterfly wasn't closing by just a whisker, even though it was going as far as it could when the lever operated.

Undid one screw holding the butterfly, much to my surprise, they almost never want to move.   Couldn't shift the other one, it will need drilling out.

Closed the butterfly, and the whisker of a gap went away - the thing had re-aligned itself.


Re-assembled, and now I have to adjust the idle up to stop it cutting out.

Result.  



As an experiment I had used a silicon gasket between carb and manifold.   Assembled, it was obviously sealing,   Dis-assembled, it was all puckered up where the petrol had got to it and was sort of cup shaped, not flat.   Bythe time I had made a paper gasket, put goo on it, and put everything back together, the silicon gasket had dried out and was nearly flat again.
Dunno what I have learned from that, but probably won't do it again.   They do seal luverly, though.