Classic cars forum & vehicle restoration.

[1935Hillman]

Wonder if anyone has any ideas about this small problem.
Last weekend I drove to my local show and by the time I got there (15mins) my '35 hillman was hard to keep running without applying some throttle at junctions etc. I notice today that when idling she is throwing a significant amount of black residue from the exhaust pipe and is pretty lumpy. Adjusting the mixture screw doesn't seem to help either down or up. Petrol flow seems good, petrol filter is clean, petrol is certainly getting into the carb (possibly too much) but cant get her running smoothly.
Please let me know what you think.
Carb is Stromberg downdraft type.
Thanks,
Tim Green

[Keith D]

Tim,

Sounds like she's running a bit rich.

Perhaps the choke is partially on. Check the cable is not sticking.

It could be a partially blocked air filter. Wash it out with petrol. (Assuming that it is an original wire type filter- don't wash a modern paper filter out in petrol!)

Check that the float in the carby is not leaking, causing the petrol to flood. These can be easily fixed by emptying the petrol out and then soldering the hole up.

It is possible that the car is running on three cylinders. This will cause very lumpy running at idle. Short out the plug leads one at a time with an INSULATED screwdriver and see if one doesn't slow the running. If so, then this plug is a passenger.

These are the things I would check out first.

Good luck- Keith

[1935Hillman]

Cheers Keith.
Thanks for those pointers. I am running short of time today but will spend the week exploring those possibilities and report back.
Regards,
Tim

[peter scott]

Hi Tim,

I'm sure Keith has hit the nail on the head with either the choke sticking on or the float level being wrong but just for clarification the mixture adjustment screw only applies to the mixture at tick-over. The choke and float level can give you over richness of much greater extent.

Peter
_________________
http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

[Churchill Johnson]

If you can't find the fault check the body of carb between the float bowl and the top this can distort use a small steel rule as a straight edge.

[Jim.Walker]

If the float is leaking you will hear petrol sloshing about inside. The trick is to remove the petrol AND locate the leak.
Submerge the float in hot water. That will expel the petrol and a string of petrol/air bubbles will locate the leak. Like a punctured inner tube. The leak can then be soldered up. Don't leave the float in the water once the petrol has gone or you may fill the float with water as it cools.
Check the float again in hot water to test the repair before re-fitting.
Needless to say, too much solder will upset the petrol level too.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

[1935Hillman]

Carb dismantled yesterday and nothing obviously untoward with float, needles, choke etc. Cleaned and reassembled, car started and ran on tickover for about ten minutes including a drive up the road and back but eventually stuttered and would not keep going without lots of throttle again.
Made very useful contact though, young engineer who lives just across a field from me and is working on vintage cars every day is coming over tomorrow to help me fault find. I am quite excited about it.
I will make a full report once we have something to say on the matter.

[Jim.Walker]

May be a little late now, but have you considered water in the fuel? it only takes one droplet to stop petrol flow through a jet and can be easily missed if un-looked for.
I had something similar with one of my motorbikes. Unable to get the last drops of water out of the tank I resorted to an additive (Wynes make one among others) which clears water by making it absorbable into the fuel.
It does work! I have had no re-occurence since I used it.
The actual effects of water depends on which jet is suffering. It is possible to tick over and nothing else or otherwise lose tickover - and so on.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

[MVPeters]

Has the car been used much recently?

I'm thinking of a blockage in the tank pickup or tank vent or cap. Obviously some fuel is getting through, but when you open the throttle wide at low revs the intermediate &/or main jets come into play. At low RPM the engine can't burn all the petrol, hence the black smoke.

I'd be tempted to drain & clean the tank as best you can Blow out the main fuel line from the clean filter backwards; refill the tank with fresh petrol, put your tools in the trunk & go for a nice long drive!
_________________
Mike - MVPeters at comcast.net
2002 MINI Cooper 'S'

[34HF90]

just read this and had a thought. Just to add more confusion.......

Although a bit unusual, I have seen this: excessive fuel pressure caused by the pump not idling. the high pressure forces the fuel past the needle seat and floods the carb.
If you can get a get a gauge on the line then it'll tell you (nothing exceeding about 2 psi).

As I say, I have seen this once before caused by the pushrod inside the pump gummed up and sticking in the diaphragm slot- caused buy lack of use I guess.

I'm wondering if the reason it appears after a while of running is that while the engine is cold, the rich mixture isn't noticed- it's only when it reaches running temperature that it's over-rich..

Maybe a long shot but worth a look if all else fails.....

[bob2]

This might be a stupid suggestion compared to all the others but I had something similar happen to me on a sidedraft stromberg.
The mixture setting screw at the bottom was far out, eventually I had to close it all and then open it up little by little until I got a good mixture and the car was literally transformed, beforehand it used to cut out and refuse to start and as you say needed lots of throttle to keep going, sometimes still cutting out.
I dismantled and cleaned the carb, got reconditioning kits, etc without ever thinking about that!!

[1935Hillman]

OK, update.
Pump removed and pushrod operating correctly when engine turned over.
Pump dismantled and rebuilt, working well with good suction etc.
This morning all reassembled and engine run at nice easy idle for half an hour while stationary, engine quite warm. Time for a drive. Very poor stuttery engine pick up and poor running at higher revs and yet again dies when throttle released back to idle, don't get as far as the end of the drive! VERY frustrating.
P.S. mixture screw wound right in during idle and still runs reasonably well, presumably this is not right. Stupid question?
Carburettor rebuild / replacement seems the only next option
I am in Newbury Berkshire so if anyone knows of a good vintage workshop mechanic near me I think it is time it went somewhere, I am reaching the limit of my abilities and frankly patience. Might need a fresh pair of eyes.

[MVPeters]

Since the idle mixture screw seems to make little difference, is there a vacuum leak somewhere?
_________________
Mike - MVPeters at comcast.net
2002 MINI Cooper 'S'

[Jim.Walker]

I have always maintained that "long range" diagnosis is very chancy.
The assumption here is that the problem MUST be fuel.
Is it worth checking the ignition carefully? i.e. Coil and condensor?
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

[1935Hillman]

How would the coil and or condenser affect the running as described and how would I check? I'm not sceptical, just ignorant.
Thanks