Won't start when hot. What to do next?

I've searched the past posts and can't find anything although I know this comes up a lot. The car will start up cold and run great, but when I park somewhere and come back out 5 minutes later, it won't restart at all. It will maybe run on two cylinders for a couple seconds then die out, and will just crank but not turn over. If I let it sit for about 15 to 30 minutes, then it will start back up and run great all over again.

At first I thought that with all the heat I was building up pressure that my tiring and old fuel pump just couldn't overcome. I've had issues with it a little this year already. I had a new one here, so today I switched them out. This fuel pump is stronger, and I'm getting a better flow, so I thought maybe I had fixed it. I took it out on a test drive, got it nice and hot, and brought it home. Same thing happened. Here is what I've tried: took off the gas cap, and there wasn't any rush of air, so its not a venting problem there. Put rags around the floatbowls and poured water on them to cool them off but that didn't do it either.

I took out the plugs and they are all bone dry, indicating that it is fuel problem, and not ignition. If I disconnect the fuel line at the carbs, I can get fuel to pump out of it. I need to get the car back on the road without these issues. What can I try next?

Will it start if you jump start it in 2nd gear?

just trying to figure out if its fuel related or electrical..

James, My gut tells me it is something electrical. When the condition occurs have you check the spark at plugs to see if it is there and strong? It's almost like something is expanding during the heat up process and then making a partial contact during your warm up and run but then it shrinks during the cool cycle and the connection is remade.

I would try changing the condensor or coil one at a time, and check the connection of the hi tension lead from the disty to to the coil.

my guess is that you've got vapor lock ( air bubble in the fuel line ) happens when the engine is hot, and goes away when things cool down again.

I have this problem as well sometimes, and I'm thinking about insulating the manifold with special wrapping so the heat in the engine compartment will be less.

Others hopefully chime in as well, but that would be my first guess.

I'd throw my inductive timing light and digital meter in the trunk. Next time it happened I hook the timing light to #1 wire and see if I had spark. I'd would check the others as well. If you have spark then that narrows the field down a bunch. If no spark at the sparkplug wire, I'd look for spark on the wire from the coil to the dizzy. I'd also look for 12VDC at the coil. If all of these check out OK then you have a fuel problem. I have never seen a MGB with SUs properly installed vaporlock but I will not say it will not happen. Need to check if fuel is available to the carb when it will not run. Either pull a fuel line off and turn the key on to see if the pump is working or pull the tops off the bowls if you have HS4s.

I suspect the problem is electrical but sometimes you just cannot tell until you rule out everything else

Why is it that the fact that James is old enough to drive makes me feel really old? :D

I don't think it's ignition related. Normally with heat related ignition problems (such as a bad coil), the problem will show up while you're driving. If I'm reading you correctly, your cars is running perfectly until you shut it off, then simply won't restart. Sound more like a fuel/vapor lock type of issue to me.

But I'm probably wrong...:F

I'm pretty sure that it is fuel related too. Like I said, I pulled the plugs when it happened after I had cranked it multiple times and the plugs are dry. If they were wet, it would lead me to believe that I was getting fuel but it wasn't igniting. Also, combined with the fact that when I try to start it, it usually will start on two cylinders and run for a few seconds leads me to believe that I have spark, and it is using up the fuel in the system when that occurs.

Meanwhile, the new fuel pump is leaking, so I get to pull it out again, for the third time today, and try to seal the sucker up. If that happens, I will toss a new coil on there and see what happens, but I highly doubt that is the issue.

James,
In your last thread you mentioned you have a new fuel pump. I had a problem very similar to yours and like an idiot I had installed my new electronic SU fuel pump with the outlet marked top on the bottom. It is not an effective pump this way. My car would die on me and not restart for 10-15 minutes until everything had cooled off and the presumed vapor lock spontaneously resolved. Check to make sure you didn't do the same thing and report back.
Frank

Well now, that certainly would give new meaning to the words "this side up" :)
Seriously, I do suppose that installing the pump incorrectly would cause undue strain on the pump.

Okay, I'm back to this thread. The new fuel pump is in there and leak free, and is in the right way. I am getting fuel at the carbs. My floats are not stuck. I installed a new heat shield because mine was missing an asbestos pad. I put a new coil on. I have tuned the carbs somewhat since they went out of whack when I had them off. The car ran great. I took it on a test drive, came home, waited 5 minutes, and it started. Turned it off, waited another 5 minutes, it started again. Its fixed, I thought. NO.

Driving out to see the girlfriend tonight it died at the top of a hill intersection. Fantastic. I was able to coast most of the way home after it wouldn't start even after cooling down. The car started on the way home from popping the clutch and ran really roughly, then gradually got a little better. I am stumped, as is my dad. Tomorrow I am going to take the dizzy out, and put a new condensor, points, etc in it. The cap and wires were new 2,000 miles ago. I WILL drive the car to the show on Sunday. I NEED to fix it first though. Any other suggestions other than distributor crap?

tap the fuel pump to see if its pumping

The fuel pump is pumping. I am getting fuel to the carburetors. My floatbowls are full. I'm thinking it is the condensor. My points are kind of pitted, and the condensor might be overheating once the car is shut off and air is no longer circulating.

I fixed it this morning. Who can guess what it was?

How about a defective distributor cap?

Russ

Nope. It is the absolute last thing I would have checked or seen.

New condenser?

I would have thought that rich mixture was the culprit originally, but it also could be the carbon terminal between the rotor and coil wire. It could also have been a crappy rotor. It could also be one of the jets sticking.

It was the "ground wire?" between the two base plates. One end of it was nearly shredded and barely held onto the little tab. I raided a distributor with a lot of slop in it and put a better one in there and its been great. After that, I went through and did a complete tuneup and redid the timing on it. The car runs much better, but like always, has a good ways to go. The carbs could use some more fiddling. I'm still running rich.

Someone wiser than me once said "90% of all carb problems are electrical" Guess he was right?

Glad you got it fixed. Read the third and fifth posts in the thread!

pmittler Wrote:

James, I still could not beat you in an MG Trivia contest.

Cheers.

Its alright. You live in Canada already. The last thing you need to win is more Canadian Wine. :D

Same thing happened to me last year. Wouldn't have noticed it but I removed the distributor to replace the points since I tried everything else. Wish I'd spotted this earlier so as to have helped you out.