Off topic - engine misfires under heavy load

[Rich Hanlon]

Hi folks,

Sorry to hijack the forum for a non-DMC query,

Just wondered if anyone had had this problem before (not on the Deorean this one, it's on the Maxi, 1748cc BL E-series). Basically it starts up and runs absolutely fine, drives 100% but after it's got thoroughly hot it'll misfire under heavy load - but backing off the gas will return everything to normal.

Have checked fuel system for air leaks, thought I'd found one, but no improvement. Next port of call is the coil and plugs I think.

Anyone else have any ideas?

Thanks team,

Rich

[NickT]

Does it use the good old Variable Venturi carb(s) like SU / Stromberg or is it a fixed jet carb like Weber/ Pierburg/ Solex ?

If it is a fixed jet carb let me know. I have a data book on them.

The misfire could also be pre-ignition where the ignition timing and/ or the timing curve is too far advanced for the current fuelling. On older distributors you could actually adjust the rate of advance using a knurled knob on the side.

Good luck.

NickT

[Rich Hanlon]

Hey Nick, thanks mate. It's an SU variable venturi job. Unfortunately too new for the knurled vernier adjuster on the distributor, but I've adjusted it by hand until it ~just~ doesn't 'pink'.

Never did anything more on it last night in the end, but will have a crack this evening. Will try swapping coil leads plugs etc for known good ones and go from there.

The consensus here in the office is that its electrical but still I'm not so sure...!

Rich

[NickT]

It might be worth removing the distributor and seeing if both advance weight springs are intact.

The miss-fire under load that you hear could be "pinking/ detonation".

I assume that you have filled the dashpots up with oil and the fuel mixture isn't weak.

Nick.

[Guinney1971]

I had a similar problem to this with my first Mini (1978/S Mini 998cc) and my Metro (1983/A 998cc).

Turned out to be the ignition coil both times.

Not saying it is in your case, and Nick could well be right about your carburettor, but its worth
looking at, as I stripped and rebuilt the carb on my Mini three times before tracing the fault
to the coil.

[Rich Hanlon]

Thanks both, will Look into this. Swap with Allegro bits for the time being and see how far that gets us!

[Rich Hanlon]

Problem solved - I think. Excess point gap had been compensated for by retarding the timimg far too much. That also helps explain some earlier symptoms I was having. Closing the gap back up and altering the timing seems to have made a lot of difference. First MOT in ten years coming up this Thursday!

[Guinney1971]

cool!!! glad you got it sorted mate, and good luck for the MOT

[Rich Hanlon]

Thanks! Will let you know the outcome. Just got a door to spray, handbrake to tighten and the brake servo to do up before Thurs. What could possibly go wrong? (famous last words!)

[Guinney1971]

lol - retrotastic dude!!! - you'll have to come round in it for a cuppa one weekend (as you missed out on the barby
2 weeks ago )

Good luck for the MOT

[Rich Hanlon]

Thanks very much - will do!

Yeah, sorry about that, DIY coming out of my ears. Just got some wiring to finish and a bathroom to fit, a new run of wardrobes and and three rooms to decorate and we'll be all back to normal! All in a day's work...

[Guinney1971]

Rich Hanlon Wrote:Thanks very much - will do!

Yeah, sorry about that, DIY coming out of my ears. Just got some wiring to finish and a bathroom to fit, a new run of wardrobes and and three rooms to decorate and we'll be all back to normal! All in a day's work...

Blimey, so at this rate we'll be seeing you in June 2010 then!! lol :lol: :lol: :lol:

Chill dude!! lol