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MG MGB Technical - Do you readjust mixture with temp changes?

I took my MGB out today for a short drive because the temps finally reached into the mid 60's. Everything was going fine for a while but then after about 25 or so minutes, the engine just sputtered and died. I rolled over to the side and cranked and cranked and it would not start. I'd give it a bit of gas as I cranked and it was just politely backfire. I sat there for a minute or so, then gave it another try with the choke on fast idle and my foot lightly on the pedal and the car started reluctantly. Luckily I was only a quarter mile from home and I made it back.

I think that maybe the engine got flooded? My only explanation would be that because the air was warmer and thus less dense, the mixture wasn't correct. It had previously been adjusted for lower temps, like in the 40's or maybe 50's. Is this sound reasoning? Could it be something else? Thanks a lot for the advice.

Alex
AJ Hu

Oh, I forgot to mention that while the carbs were not precisely tuned, this has never happened to me before. Also, the temp gauge needle was reading slightly hotter than N.
Thanks

Alex
Alex

Alex: To answer your basic question: No. Thats what the choke is for. On HS series SU carbs the choke pulls the jets downward to enrichen the mixture. The basic "warm" engine mixture should not be adjusted. The function of the engine thermostat is to ensure that the correct engine temp is maintained in (almost) any weather.
What did the tach needle do when it died? An immediate and sudden return to zero usually means an ignition problem, while a more gradual drop as you coast to the side of the road, along with some bucking and literal sputtering, may indicate a fuel starvation problem. Perhaps from crud (like rust from a fuel tank over the winter) is blocking a filter screen in the fuel pump or elsewhere.
The temp gauge reading may indicate a hotter running engine due to lean mixture or simply an faulty gauge or voltage regulator.
What year is your B?
Andrew Blackley

The SU and Zenith are constant vacuum devices so are self compensating to a large degree for changes in air density and pressure.

Fixed jet Webers etc are so so accomodating.......
Chris Betson

Whoops - that should have been NOT so accomodating!!
Chris Betson

Do you have heat shields on the carbs? The gas may be boiling

rn
RN Lipow

I agree about the heat shields, the bowls may be vapor locking. The only time I ever had to adjust the HS carbs was in the mountains of New Mexico, needed to lean them out for the altitude.
Robert Dougherty

Hmmm...... your comments about the heat shield might be valid. The metal heat shield is there but I think some of the insulation padding is missing on one side. The thing is though, that I've run this car in much much hotter weather with the temp. needle basically all the way to the red without this kind of problem coming up. My car has a problem of overheating which will need to be addressed soon.

Andrews,
My B is a 1973 with HIF4 carbs. The car kind of sputtered and died (this was at a light) so I guess the ignition system was ok. Again, when I cranked it (for a few seconds) and gave it a little gas it would gently backfire when I stopped cranking. So, I thought that the engine was flooding. I'll try richer settings and I'll try leaner settings and see what happens.

Thanks everyone for the replies.

Alex
Alex

This thread was discussed between 09/04/2002 and 10/04/2002

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