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MG Midget and Sprite Technical - backfire thru carbs

I did a rebuild on my 71 mg midget 1275. I am so close to driving it but it seems I have one issue I cannot seem to resolve. I get backfire thru the carbs when I rev the engine (no real power either). I have tried to make sure the timing is correct and I have done lots of work on the carbs. I have had two sets of carbs on the car, friend had a old set.
Anyway I check the compression and all seems good. Could this be that the valves need better adjustment?
Could the carbs starving the eng of fuel cause this?

One other thing (kind of strange) I had the car up on jack stands and tuned it and when I put the second set of carbs on the car was running great. When I put it on the ground it started backfiring thru carbs?

I have been working on this restore for a long time and I am so close to driving the car I can hardly stand it!

Anyone thanks in advance for any ideas on this.

Ken Bargeron
Frustrated in Atlanta
Ken Bargeron

Have you got the plug leads on correctly, ie correct firing order?
Other than that you may have the timing wrong. I have known where a faulty coil tends to melt the foot off the points and very quickly (within a few minutes of running) reduces the gap on the points, effectively changing the timing and causing backfiring.
Bob (robert) Midget Turbo

Sounds like the mixture is too lean. Valve lash should also be checked as it not only affects how far the valve opens but also when it opens although usually it would have to be way off to cause the situation you described. Freewheeling on jackstands versus loaded is definitely affected by mixture.
Mike G

Spit-back through carbs normally due to timing being some way out... how did you set timing? and to what figure?

A
Anthony

OK GOT IT FIGURED OUT: Thanks for the inputs everyone. It was the timing. I have made so many DUMB mistakes on this restore.. I had the firing order backwards on the distributor cap!
I had it clockwise... it just sort of came to me this morning (like a light going off). I put the firing order in anti-clockwise order and it is running fine now. Still needs to be fine tuned.

Once I get this car on the road again (soon, very soon) I will post a picture to this tread.

Ken Bargeron
Not frustrated (for now)
Ken Bargeron

Glad you got it sorted, Ken!

Way back when I was in high school, we had a '71 Midget as a second car. One day we noticed it running really sick, and pulled the air filters for a look. Lo and behold, one of the filter elements was burned to a charred lump of rubber and paper scrap. Seems the engine had backfired through the carbs and torched the filter...

Take care,

-:G:-
Gryf Ketcherside

Exactly what I thought wish I had a £1 for everytime I have seen that done. :-)
Bob (robert) Midget Turbo

This thread was discussed between 08/06/2008 and 09/06/2008

MG Midget and Sprite Technical index

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