Solex problems

[philholzer]

Hi,
First post, but looking for some advice on my twin solex carbs. I bought a pair of second hand Solex 40 PII and have now rebuilt them several times! Spent a small fortune on replacement components, returning them back to factory spec. They have been apart so many times, I recon I could strip and re-assemble in less than 30 minutes.

There is little perceptible play in the in throttle shafts, a very small lip on the throats from the butterflies, but they appear to seal reasonably well. I have been through the entire ignition system and timing is all spot on. They've spent several hours in the ultrasonic cleaner. Last strip, I even removed the welch plugs to ensure all of the passages are clear.

The problem I am having is that I can not get the idle below 2500-3000 RPM. Normally this would be indicative of a vacuum leak. I have checked the flatness of the mounting flange, whilst not perfectly flat, they are not far off. During the last re-assembly I smeared a small amount of sealant on the gaskets to ensure there was no vacuum leak.

The only thing I haven't done yet is to set the float height, but I wanted the idle nearer 1000 RPM before doing this?

Any advice would be much appreciated. Not far off ditching them for a pair of brand new Webers!


Many thanks.


Phil

 

[john356]

Phil
Join the Porsche 356 Registry and post in the 356Talk forum, you will get the answer in 24 hours.
https://porsche356registry.org/
I only know Zenith carburators so sorry I cannot help.
Regards
John Hearn

 

[Nick_USA]

How have you been attempting to adjust the idle? Small or large screw and/or the throttle stop screw ?

Nick

 

[Robin]

My "Boys Book of the 356" has a section on the Solex 40.PII.4 carburettor which I found helpful when I owned a 356B S90 which had these Solex's as standard. Incidentally ou have not said whether your engine is standard or has been modified in some way ie, big bore, different camshaft etc.

If all the jets are as standard and the float height is correct, then some of the fast tickover may be due to the advance/retard weights in the distributor or their return springs. If your tickover is over 2500 RPM then these weights will be on full advance when you check the timing (best with a strobe light). Remove the distributor, (dont drop the washer at the bottom of the distributor shaft down the hole) check that the distributor advance weights are operating correctly and freely, you may need to replace the small springs to get the weights to return, they do become weakened with age and running at high revs.
(Weak springs show themselves as a slow return to normal tickover speed when you come to a stop, like stopping at traffic lights).
Replace the distributor, setting the timing as near to normal when at rest and start the engine to adjust the timing with the strobe light.
I hope this helps, Good luck.

 

[philholzer]

Thank you for the replies. Really appreciate the help.

I have the idle screw backed all the way out, so that is not affecting the idle speed.

Don't know the spec of the engine. I bought the 356 a couple of years ago in the US and it already had a 912 engine fitted. I will strip it down at some point, but just wanted to enjoy it for a bit, before I disappeared down that worm hole.

I hadn't thought about the advance. I had stripped the distributor down and the weights certainly seemed to move freely. Previously I was able to reduce the idle by pretty much winding the mixture screws all the way in. It ran very poorly, but I was able to see the ignition advancing when it revved. It a great suggestion and I will check again.

I haven't adjusted the float height yet, do you think this would impact on the idle by that much?

 

[Robin]

Regarding float height. I think there would have to be a large variation in float height to make a difference, either too high or too low, which would probably show up as poor running, but not a fast tickover like you have.
Just a thought, have you tried to run the engine with the throttle linkage disconnected from the carburettors ? What happens to the engine speed?
Are the linkages the correct length for the new carburettors? What happens when you slightly open one, then the other carburettor throttle lever with the levers disconnected, does the engine speed rise or fall?

 

[philholzer]

Hi Robin, I didn't think the float level would cause a high idle either. Yes, the throttle linkages are disconnected. That's when the idle speed is high.

The LH carb is drawing less air than the RH one. If I open the LH throttle the overall engine speed increases. Same when the RH is opened.

Going to have another look at the ignition advance hopefully tomorrow.

Thanks again for your help.

 

[chas3.2]

Hi
Are the inlet manifold gaskets ok take them off to have a look,

Do the butterflys snap shut in the carburettor venturi have the holding screws come lose on the spindle,

Regards
Charles.

 

[philholzer]

Hi Charles, apologies for the delayed response.

All the inlet gaskets are new. I even smeared a small amount of sealant before assembling. The butterflys snap shut ok, the venturing screws are all secure.

I messaged Dave Osborne for Carburettor Exchange in Leighton Buzzard. He thought it likely that the throttle bores were oval and allowing air to pass. It's the last thing left really, everything else is new. I don't see much light around the throttle. I asked a specialist near me, who thought it was ok and had seen much worse of Webber carbs that ran just fine, but the Solex's are a very different design I guess and perhaps more badly affected?

Many thanks


Phil