QuestionQUESTION: Jo. My bj7 runs great around town but when the engine temp gets up to
190 the engine begins to cut out as I accelerate. Once up to speed it runs
fine. If you accelerate though it will cut out. Any idea what is the problem.
Thanks for your help.
ANSWER: I'm jealous--want to sell it? (I have a BT7, which regularly soaks me from leaks around the windshield if I get caught in the rain.) Some odds and ends thoughts...consider the most likely...
1) I'm assuming your carbs are *not* automatic choke, which I don't really understand anyway!
2) Check that your radiator is full, and that the overflow pipe to the reservoir is not cracked, i.e. the reservoir is working.
3) 190F sounds too high to me, even if you're in Arizona idling at the lights (you don't tell me how hot your neighborhood is). In a hot place I would change to a lower thermostat. The idling heat might also be doing bad things in your carbs, like vaporizing the fuel. Then when moving the airflow cools things down again. If you think this is possible, consider an electric fan to provide good air flow at low revs.
4) However, I really suspect it's nothing to do with the temp, but fuel starvation under acceleration. (Does this happen when the weather is colder as well?) That's a fuel supply problem: at low speed or idle, the float chambers fill up fine, but then you ask for more than they can provide. So (this won't take long)...
i) Disconnect at the front carb connection, put pipe in jam jar, turn on ignition and check that fuel pours out. If not, go back one: disconnect before the filter and repeat. If still only a dribble, you have a pump problem (probably dirt on the intake side from the tank).
ii) If all OK at the front carb connection, suspect the float chamber jet(s). For each carb, remove the top (taking care with the paper gasket) and dangle a can under the jet. Switch on ignition and dab the float valve up and down with your finger. With float hanging down, fuel must pour out; then must stop totally when up. That should cure a blockage. If still not enough flow, you'll need to remove the jet: quite simple, but get back to me on that if you like. While the lid is off, wrap an old piece of T-shirt or similar *lint-free* rag around a dowel or pencil and clean out the bottom of the float chamber. Then carefully reseat the gasket around the rim and reattach the top.
Good luck!
Jo
---------- FOLLOW-UP ----------
QUESTION: Jo Thanks - Let me add that the car runs generally at 160 and at that temp the car runs great. No problems at all. Once in traffic and the temp climbs up to 190 - which is as hot as it gets - it starts to miss during accelearation. If it cools down again while driving it runs great again. It feels like I am losing a carb when it occurs.
AnswerOK: I didn't know it was fine at lower temps. In which case my answer #3 (even though I have no experience myself of a hi-temp problem, except for my feet!). I think you have to get the temp down. High temps at the float chamber play havoc (and also increase the fire risk from vapor blowing out of the vent pipe). But first check that the heat shield is there. It's a large L-shaped sheet between the inlet manifold and the carbs, and it half-covers the exhaust manifold and headers.
So I'd recommend getting a Hayden electric fan, which will keep both coolant and under-hood temps down at low speed/idling, and save you some gas as well. Moss also sells a wrap for the exhaust headers: might help.
Hope it works!
Jo
