The V8 Owners Forum -

Hi, My late P6 3.5 with twin SUs which I have fitted in my stag runs great, but only when it's cold. As soon as the temperature gauge lifts off cold the misfiring and backfiring start. The exhaust pipes are pretty black and the engine's running too rich, but I don't quite know what to do first.

I'm assuming I'll have to check the carbs for wear first - there's some virtical play on the throttle spindles, should there be any at all? I'm guessing I need to serivce the carbs, get them balanced and check the timing, in that order. If the mis/back firing persists after that, should I then go through the electrics - I have already fitted lumenition. What do you think?

Russ

sounds like your running rich for some reason. Make sure the chokes are coming off properly. What do the plugs look like? If your running rich then the plugs could fowl which will lead to misfires and stuff. Check your float heights are correct and that they are sealing properly. Basically give your carbs a service but a few of the things above can be checked without taking things apart. When you say hot do you mean running temp? If its running temp then its possible something is failing due to heat like the ignition amp.

Hi, The plugs were black when I checked them (after grinding down my plug spanner so that I could get them out!). I'll service the carbs, get the service kits from Burlens and check the floats/choke as you suggest. The misfiring/backfiring starts long before the engine reaches running temperature, the gauge has hardly moved off cold before it starts. Does that pint to anything specific?

Hi,
Do your SUs have waxstat jets? If they've jammed they'll be richening the mixture at all temperatures, not just when the engine's cold. The best solution is to replace them with ordinary jets and fit a manual choke.

Hi, a manual choke is fitted now, but I don't know what jets are fitted, how do I tell if they're waxstat?

sounds rich then. Your sooted up plugs wont help but I think their a symptom other than a cause.