Jump to content

1926 citroen carb advice needed


Recommended Posts

Hi all, 

My dad's citroen has always blown fuel back out the carb. He's lived with it like this for 15 years and it's done it with 3 different carb assemblies. He's always been happy to ignore the dangers of fuel dripping everywhere but I'm determined to fix it. 

The car has recently felt down on power and was running rough so we had the magneto rebuilt,the spark looks strong but it's still not running right.

I gave him a hand setting the static timing this morning and then started looking into the fuel problem. 

PXL-20220205-094748690.jpg

 

PXL-20220205-100638552.jpg

 

 

Compression was fine last time he tested it and the oil is clean. 

To me, it looks like the exhaust is blowing back through the carb. Could a valve have packed it in? 

Or the timing just out enough for the mixture to be ignited before the inlet valves are closed? 

Any advice would be much appreciated! Cheers 

Link to post
Share on other sites

Could it be a non-closing inlet valve or valve timing slightly off (leaving the inlet valves open longer during compression stroke)?
The spitting back is more when cranking, looking at the videos.

I would first check compression ratio, and compare to a similar engine, if he knows one. That is a simple action.

Link to post
Share on other sites

Hi Eli,

I'm NO engine specialist at all, but this is what i know:

this is also the case on my Norton 16H and visible on the oil container vis-á-vis the carb,

because it runs with a simple funnel air filter and blows the petrol there, but less and it makes me no worry.

This is the case because the inlet valve starts ot open in the 4th stroke already before TDC while the piston still moves up

with expanding exhaust fumes - and pumps somee exhaust fumes (sadly) out of the inlet valve (beginning to open).

And the inlet is still not fully closed in the 1st stroke after BDC while the piston is alreday compressing.

This - and the overlap of the valve opening times is the case on every engine.

On my Norton it may be less because of a long "distance tube" from the carb to the valves,

while the carb on your B12 is direct in the cylinder head. I don't know.

Apart from this I would check the timing of the camshaft to the crankshaft.

And ask for example the "Citroen 10hp Club" https://www.citroen10hp.com/

Ciao, Marco

Link to post
Share on other sites

A leak down tester will be a good aid to verify if the inlet valve is leaking (with both closed).

It will not tell you if the timing is off.

Link to post
Share on other sites

Might be a sticking inlet valve that is slow to return. So compression reads OK, but when running mxiture flows back into manifold at s tart of compression

Link to post
Share on other sites

I had a similar problem on a 1916 Buick, it was caused by the cork floater not floating high enough to shut off the fuel valve causing overfilling of the bowl. In your solex carb the floater is brass, I would still check. It shuts off the fuel correctly and check the valve as well

cheers

Alan

Link to post
Share on other sites

Thanks everyone!

The carb in the photo is a spare I took apart for reference. I've never been too involved with the citroen until now so I'm just getting to grips with how it fits together now.

Marco, thanks for pointing out the Citroen 10HP club. The folks there have also suggested a faulty valve or timing out of whack.

I'm going to order a leak down tester as it seems a useful tool to have and we'll check everything we can before pulling the head off.

Cheers!

E

Link to post
Share on other sites

Hi Eli,

perhaps you know the diagramm, I know it from my "Book Of The Norton", this is a German animation of the same issue

You see on the 1st stroke (light green) the inlet valve is not 100% closed while the piston already moves up.

On a wrong timing the camshaft can be tristed earlier related to the crankshaft, or later.

Later the inlet valve is longer not fully closed while the piston already moves more up and is aready compressing (2nd stroke).

Ciao, Marco

Edited by Z320
Link to post
Share on other sites
  • 5 months later...

Hi all, apologies for not updating you after all the friendly advice 

In the end it took a lot of work to get the head off and I discovered that the valve timing was set up wrong. Dad had been driving for almost 2 decades with the inlet valve opening before the end of the exhaust stroke. 

She now starts on the button and even very easily with the starter handle and dad reached a gps certified top speed of 50mph but I don't think the engine enjoyed it... The spark plugs all unscrewed themselves! 

I learnt a lot getting his car back on the road and now desperately want a prewar car of my own. Maybe next year... 

Edited by EliTR6
Link to post
Share on other sites

Hi Eli,

I trust you are well. When will you be coming to the next London Group Club night!!!

Most car engines have the Inlet opening before the exhaust stroke is done  with as there are many degrees used with little piston travel.

But old cars are mysterious things.

Well done in sorting it out.

Roger

Link to post
Share on other sites

Hi Roger,

On this old girl, the inlet valve should start opening when the piston is 1mm past TDC according to the workshop manual

I left London in 2009 but we have a great monthly classic car meet here in Le Touquet is you can make it over!

Best,

E

 

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.