Engine running on choke only

[administrator]

Is the accelerator pump working?. You should be able to look down the primary choke and see it squirt fuel if activated by hand.

[Mike]

Still no joy

The carb is clean, I can blow through every jet and passage way with a WD40 spray can !!
The float height is spot on with plenty of petrol entering the carb.
Points, condenser, plugs, coil all replaced.
Even removed the exhaust cross-box and air filter just in case they were blocked.

STILLL engine starts and ticks over fine, as soon as any throttle or choke is applied the engine cuts out.
Let go of the throttle and it returns to a smooth quite tick over!!!!

[Mike]

Just placed a pair of spark testers in line and ran the engine.
At no time does the spark fail!!
The timing was set with a strobe light and it spot-on
So the problem must be carburettor or valve timing. As the engine runs fine on tick over I don't think the valve timing is out leaving the carburettor !

Any one got a good spare carburettor for sale??

[Geoff Ryall-Harvey]

Have had this before - nothing seems to get them to work right. Easiest to swap it out.

I may have a Solex - will have look tonight. I've got several SUs that would suit. Easy to make up an adapter....

[callum]

Out of interest, what size primary jet are you using? And are you sure that there's one in there?

What's the history of this carb? Has it suddenly stopped working, or is it new to that engine.

From what you've described, it's sounds mighty like an electrical problem - as most carb problems are...

You've talked about timing, but what ignition are you using? And is it auto advancing?

Rgrds
Callum

[Ken Hanna]

Mike,
it took a while for the penny to drop, but this seems to me to be one of those (very rare) cases where the linkage between the primary and secondary butterflies has seized up, so that they open simultaneously rather than sequentially.
The result is that the velocity of the air flow through the venturis is not high enough to create enough vacuum to draw fuel mixture out of the emulsion tubes, hence the engine stalls and will only run on the idle system or with the choke full on.

Easy enough to check; remove the intake hose (if there's one fitted) and look down into the carburettor mouth whilst opening the throttle.
The secondary butterfly should not start to open until the primary butterfly is about 2/3 open.

Maybe have a look and let us know what you find?
There's no point in giving instructions about how to cure an ailment until a possible diagnosis has been confirmed...

[Mike]

Well done Ken, looks like you'v nailed it!! That's why these forum are so important, if you can't fix it somebody else can !!!
Both butterflies do open together!!
Where do they tend to seize up and which butterfly should open first (big one or small one)?

[Mike]

Freed the butterfly linkage and I am pleased to say the engine now running and revving, again many thanks Ken
Now what's the best tips for tuning the carb

[Ken Hanna]

Mike,
the first step is to determine which version of the Solex 26/35 you've got.
It's most probably the later, 18-26 type as shown in the first link below, although it could also be the earlier 21-24, as in the second link.
Once you let me know which it is, as well as what type of exhaust system you've got, whether or not the pre-heat pipe has been removed and what type of air filter, I can let you know what settings I'd start with...

Freed the butterfly linkage and I am pleased to say the engine now running and revving, again many thanks Ken
Now what's the best tips for tuning the carb

18-26 carb. https://flic.kr/p/irT8zr

21-24 carb. https://flic.kr/p/irTZPc

[Mike]

Ken,
The car is running a 21-24 carb coupled to an original Lomax style air filter.
Exhaust is standard Lomax pipes into a standard cross-box silencer which feeds a Lomax side pipe/silencer.
All appears to be standard Lomax issue.