Solex DIDSA35 carburetor

[lotuseater]

Please don't answer - 'use it as a doorstop and fit a Weber!' I'm keen to get my Solex carb working. It's a UK version on non-crossflow Renault1470cc (non-emissions type). It's been cleaned, all jets are free (blown air through). Ignition set to 4 BTDC (static with test lamp). Runs OK (though bit fast) on choke - revs pick up well and will sit at higher rpm fine. As soon as release choke (engine fully warmed up), it's lumpy and though it will rev up, at a steady higher rpm, its not happy. Pulled each plug lead - and each one gives same result of almost killing it. Have tried to combat possibility of air leaks using a high temp silicon either side of manifold gasket and all the gaskets/ faces in the insulator blocks under the carb.
The manual for the federal spec version refers to screws which are factory set and mustn't be touched (but if they have been.....it describes a way of setting default)As far as I can see, there are no adjustments on this F35 DIDSA other than idle mixture and tick-over speed.  I checked the jet numbers against manual and the 2 compensator jets were the wrong way round (according to manual - which I'm finding has errors in it - ignition timing seems illogical). Have tried switching both jets, no change.
Any advice or direction to a more details tune up article for this carb appreciated. It may not be the greatest carb, but it must have worked at some point !

Thanks

Richard

[EuropaTC]

Hi Richard,

I wouldn't dream of telling you to fit Webers. Nope, not in a million years, far too complicated. Now Dellortos......   

Ok, I don't and have never had one of these so what follows is guesswork and a bump up the page in case someone who actually knows what they're doing will see it and chip in.  Firstly, is the manual you have from this page ?

http://lotus-europa.com/manuals/s2work/l/s2l.pdf

There's a trouble shooting section in there for slow running (p13) and if it's the same one you have, then I guess you've tried those things. 

From what you say it does infer a mixture problem so the first wild guess is - you've cleaned the carb, but have you flushed out the tank/lines/fuel pump or got a filter between the newly cleaned carb & the rest ?  Just thinking that your sparkly clean carb might have been blocked up with something drifting through as you first started up.

Second thought is the fuel - is it old stuff ? If it's been around a while then maybe it's lost some volatiles and needs a boost with some fresh petrol.

As an aside I find the Gunson's Colortune plugs really good in situations like this. Pop one in and just look at the colour of the spark, it soon tells you if your idle mixture is too rich or too weak. OK, maybe not so useful with non-adjustable units, but as a step in problem solving it might throw a pointer ?

Brian

[jbcollier]

Don't use silicone sealers where they will be exposed to fuel as it will cause the sealer to swell and fail.

4° seems insufficient to me, try advancing the timing somewhat.

What is the compression?

Have you adjusted the valves?

How many turns out is the idle mix screw?

[Murramor]

The solonoid controlled anti run-on jet was prone to blockages on my car.  Have you checked this?

[lotuseater]

Thanks for the replies - my 'car' was bought a few months ago as a pile of parts and I'm piecing it back together , bit by bit.

Current test setup has engine in chassis, fuel tank is a clean spare 1 gallon can, new fuel lines and new filter. Mechanical pump seems OK - at least, engine runs fine when choke is on and fuel is pushing through filter. new coil, new leads, new points. Compression is about 120psi (not sure what the this should be, but seems pretty good according to the 1950's data sheet on the gauge I'm using !)

Valve clearances have been set as manual.
I've just posted another question on ignition timing - manual says 4 degrees Static - which seem nice with the choke on. Lumpy when choke is off. Tried advancing the distributer, but no effect of the problem..

Using 95 RON? UK unleaded petrol - about to try Super Unleaded (98? RON) - not sure if it will make a noticeable difference but clutching at straws.

I used some high temp silicone gasket sealer as a means of eliminating possible air leaks in the problem solving route, not as a long term fix.

Have tried idle screw at various positions.

It is possible, when holding the carb up to the light, to see a very slight gap between the main choke tubes and the carb body - don't know if this is normal but they don't appear to be removable or able to adjust/tap them in any further. Should they be sealed with something ?
Carb has been cleaned via Ultra Sonic tank. I've since the last test, blown through all holes, and blown through the solenoid with it connected up to a battery (this didn't go in the ultra sonic tank ). Could this cleaning have removed some 'sealer' between choke tube and body ?

I will in the next couple of days be bolting it back onto the engine to see if any of the latest checks have made any difference.

Any comments or thoughts appreciated. Seems a shame to go Weber after all this effort !