Misfire

[yatesfox]

Evening All - looking for some help with misfiring problem. I have a '66 saloon which has run fine for the last 2 years during fine weather only in both summer and winter. I am non-techy but get some advice from older family members and can do a few bits and bobs under supervision.Anyway, this season it starts and idles fine while stood, will run ok for a mile or so but under load / accelerating then starts to misfire and dies. I have fitted a brand new SU fuel pump, coil, points, plugs, drained fuel tank and no debris to be found but still no joy. Having read the technical tips, I see that it could be a blocked vent in the fuel tank. I have got the sender unit out but cannot get to the fuel pick-up as the access hole is very small. Is it a case of a new tank? Any ideas?

[sgray]

you didn't mention the condenser.. did you change that too?

[mike.perry]

If the fuel tank vent is blocked, it usually vents through a small hole in the filler cap, it will clear itself for a while if you remove and replace the cap, and you should hear a hiss as the vacuum is released. You will travel further before the car stops if the tank is nearly empty than if it is full.

[bmcecosse]

Tech tips!! As mentioned above - it's likely to be the condenser, or perhaps faulty rotor arm/dizzy cap/spark plugs. Leave the tank alone!

[leyther8008]

Sometimes its the simple things, have you checked theres oil in the carburetta dashpot, can give symptoms like you describe as well. As your on choke for the first mile or so.

[dalebrignall]

are the connections to the coil nice and tight

[minor65]

I would recheck the points. My minor misfired under load 6 months after new points fitted. Try a small bit if sand paper between the points and reset them, doing this cured mine 4 years ago.
[frame][/frame]

[yatesfox]

Thanks for the advice. I have changed the condensor and also blown through the fuel line from pump to tank and is free and clear. Took it a run today and no better. I removed the fuel filler cap and it went much better even under heavy acceleration. I have since removed the fuel filler pipe and ensured the vent was clear. It was a little dirty but no major obstruction. I now intend to purchase a new locking filler cap as the current cap which came with car had no key anyway. Any other ideas?

[bmcecosse]

Is the engine in good condition, and are the valve gaps set correctly ? A compression test will tell all. And have the ignition timing and fuel/air mix been set up correctly?

[mike.perry]

If removing the filler cap cured the problem then the cap you are using has not got a breather or the breather is blocked. The standard Minor fuel cap has a small hole in the top. A replacement locking cap should also have some form of venting

[bmcecosse]

Aye - but a vacuum doesn't build up (or should that be 'down'?) in the tank immediately! It takes a while - so any immediate improvement from running with cap off is surely just psychological ! Unless of course - the vacuum had already built up - and was destroyed by removing the cap.

[yatesfox]

I should have the new petrol cap by the weekend (on mail order) and if that doesn't cure it, look like I will be asking the father-in-law for some help re-timing and checking through everything again. Hoping to be up and running for the National in late June. Don't fancy being towed by the AA back from Leeds! [frame][/frame]