Poor running

[Thowdfella]

Volvo 122s 1966. Took it out yesterday and did about 25 miles running beautifully then lost its power and would not go when you accelerated.
Managed to get it home and suspected a fuel problem. Drained the tank and fuel looks OK - no water in it. Cleaned out fuel pump and filter and checked again. Still won't go BUT if I pull the choke out it's away and pulling fine. Is this telling me I have an air leak somewhere? Took the air filters off and both pistons are going up and down together when you blip the accelerator and when I lift them slightly that's fine as well. Ideas please?

[Ron Kwas]

Tf;

...not too much symptom description, but I can give some info and troubleshooting suggestions...Fresh fuel, and without water, is always good, but general performance loss is more a symptom of ignition problems...a small amount of water would cause specific dropouts as it is ingested (it doesn't ignite so good!)...a large amount of water causes complete engine stoppage... I'd check timing (with timing strobe) at idle and verify it is advancing as revs are raised (this is a Dynamic test of Centrifugal Advance)...timing should advance with revs, and return to starting point with good repeatability...if no timing light is available, statically check CA (See: http://www.sw-em.com/Volvo%20Ignitio...e_Spark_Timing )...if it seems OK, I'd static time Ignition while I was at it so I was certain of starting point of timing. Remember, Dist is a mechanical device which has a number of points, several critical, requiring lubrication.

Please post back with results, so we can help you narrow in on cause...

Good Hunting!

[Thowdfella]

The ignition was thoroughly checked and set up last week. Lasers on the plugs show all plugs are getting a spark OK.
An ignition fault wouldn't explain why the engine pulls fine when I pull the choke out.

[Derek UK]

Well, they do say that most carb faults are cured by sorting the ignition out. However, if you have been doing any "carb tuning" I'd consider reviewing what you've done. Recently, I wound up the jets a couple of flats. Seemed to run fine with a good tick over but I didn't road test it. The basic reason was that I thought my fuel consumption was a bit poor. Following day I went to a show, the SBKV. Straight away the car ran like cr*p, very jerky and lumpy but settled down a bit after it warmed up. Not too bad with a steady throttle but still unhappy. After rather more miles than I should, I was on the M25, I stopped and dropped the jets back down those 2 flats and all was right with the World.
Maybe by dropping your jets a couple of flats to richen things up will help. It is more or less the same as pulling the choke out a bit. Setting the choke cables along with the carb settings is a bit of an art so check those and reset by the book. The first fraction of the choke pull should just increase the revs a 100 or so before lowering the jets to richen things up.

[Ron Kwas]

Tf;

I should have reread your post a few more times...then I would have been less focused on the Ign and would have taken better note of the Choke comment...indeed, if "choking", really another term for enriching helps, I agree with Derek's advice about lowering Jets a couple of flats and road-testing...often this can make a noticeable improvement...but "...running beautifully then lost its power and would not go when you accelerated." does sound like something has changed, more than be corrected by a little Jet adjustment...

Cheers

[Thowdfella]

Thanks for your replies - it's never easy trying to help someone when the car isn't in front of you!. Anyway, an update. We noticed that there were bubbles in the plastic fuel filter and also quite a bit of sediment - even though I washed the filter last night so crap in the fuel tank. The fuel tank was refurbished two months ago but obviously it's still going rusty so dirt could well be the problem if it's getting past the fuel filter. If a car is running well for twenty five miles then suddenly stops doing so I don't think the jet adjustment is the problem - rather it's getting round the problem I think, so I think my next step is to remove the float chambers and check for dirt and also wash out the jets out as I now suspect there is dirt in them which is got over by pulling the choke out.
Unfortunately the car is going in for respraying the back end tomorrow so I hope it will get me there!

[Ron Kwas]

Tf;

If sediment is clogging filters, fuel delivery after a problemless period might well be an issue...check also Fuelbowl Sumps...if significant sediment is present, backflushing the Jets with carb cleaner is a good practice...

Good Hunting!

[Faust]

Just a thought: are you sure your coil is OK?

Classic symptom of a dodgy coil: perfect running when the engine is cold (ish) and then as the coil heats up it starts to break down.

As soon as it's cool again it'll run fine, and then when it gets too hot....

Ad infinitum.

Might be worth checking.

[Thowdfella]

Today I have taken the fuel bowls off the carbs and there was lots of sediment - like sand in the bottom. Don't know where this has come from as there is a line filter and I refurbished both carbs about two months ago.
Anyway, I cleaned them out and cleaned the jets with the help of my air compressor and the car is now running beautifully again. Thanks for all your suggestions, we got there in the end.

[Derek UK]

Rust can be fine enough to go right through the filters and that's what ends up in the float chambers and subsequently blocking the jet tubes. If you try to filter petrol that has come out of a rusty tank what comes through the filters will still come out like Newcastle Brown. I can show some pictures of this but I'll just say that it took less than a gallon for the filter to stop passing any petrol. Buy a bunch of filters and be prepared to change them as soon as they start to turn from yellow to brown. It should improve, but it might take quite a few before things settle down. Don't use washable filters for this, I don't think they filter anywhere near as good as the plastic ones.