White scout car stalls
 

Hi All, Please help! Here is what is happening:
I put a new coil , condenser, rotor, plugs, in the scout car, a full tune up. and it runs fine for about 15 minuets then sputters, backfired and stalls. I am going to pull the carb and see if I can spot a problem I pulled the coil wire and was getting good spark, so i am guessing it is a fuel/carb problem. After it cools down, about 20 minutes, She starts right up and is fine. It did wrap as best i could under and around the carb with heat shield. Any thoughts.??? Thanks, Again, Rob Cell 914 382 5929

Have you checked to see that the fuel tank breather is not blocked. I have come across a similar fault where the breather was a small hole in the filler cap which had been blocked with paint, after running for a while you get a vacuum in the tank and no fuel!

Ditto! Saw it with a motorcycle.

How old is your gas?
 

Hi Rob

First question with any engine not running correctly these days is how old is your fuel? When did you do your most test did it happen to be during the recent heat?

Recently did a three day convoy in that heat in the Northeast and we had a number of vehicles exhibiting similar problems in our case they would run down the road fine but if we got held up at a standstill for any length of time one or more would start running rough.

Two or three of the trucks this was probably actual vapor lock, or boiling of the ethanol which boils at something like 170F. One Jeep it probably was a coil that had become temperature sensitive.

I had problem with my 3ton CMP at one point after long hard runs pulling over to deal with somebody else problem my truck would start running rough. In that case I suspect the change was because I had switched over from one tank to the other. The second tank may have been 2-3 months old.

You said you "put a new coil , condenser, rotor, plugs" were the old parts known to be bad or was this just precautionary? Did you replace the points? If old coil, and condenser were OK, might try putting the old coil back and see if the problem goes away or remains. Unfortunately "new" doesn't necessarily mean good.

I concur on checking that the tank is venting, mud wasps like to plug the vents.

Please keep us posted on what you find, learning experience for us all.

Cheers Phil

Scout car, White stalls
 

Hi All, thanks for all the help. I have replaced the coils and condensers twice, new points and plugs, full tune up. I tried the vent cap, leaving it very loose. I do think it is a few problem. Using new fuel in the tank with an additive, seafome. I am using an electric fuel pump. In am thinking it is vapor locking.

Next up is to build a heat shield for the carb... Thanks, Rob

Scout car, White stalls
 

Here is what another Gent said... Applies to many vehicles:

Rob,
Next time you stallt-pull the high tension lead out of the distributor and hold it near a ground-a cylinder head bolt usually works well. Make sure all the paint and rust are cleaned off the bolt head. If there is no spark, the bolt may not be well grounded(rust on threads,etc.) so clean off something else and try the spark test again. Hold the lead about 1/16" away from the ground. An ignition in good shape can usually spark up to 1/4" gap.

Vapor lock occurs when gas in the fuel system(carb, fuel lines, and fuel pump) gets heat soaked-i.e. the engine is hot and gets shut off. There is no movement of fuel so it sits there cooking away. Eventually it gets so hot that it starts to boil and floods the engine. The problem is much worse these days because the gas has ethanol in it which has a much lower vapor pressure so it vaporizes at a lower temperature than gasoline. To clear a flooded engine, hold the gas pedal down at full throttle and crank the engine over. Eventually it will suck all the raw gas and gas vapor thru the engine and start. Don't pump the gas pedal because every time you pump the pedal the carb squirts a shot of gas into the engine.

It's been my experience that vapor lock rarely occurs when driving because the gas is cool going into the carb and passes right thru and thereby cools the carb. Air is also being blown by the carb and intake manifold by the fan and road wind which also keeps the intake system cool.

Usually it is an ignition problem. The condensor in the distributor can go bad gradually and it will short out when it gets hot. This keeps the ignition coil grounded so it can't produce a spark. The ignition coils can go bad also. There can be a break in the internal coil wiring but the wire ends are still touching, or the insulation between the coils can go bad. When the coil heats up, the wire expands and wire ends at the break quit touching or the insulation breaks down so the spark jumps from coil to coil with the end result of the coil not working. Let everything cool down and it starts to work again.

It might be easier to install new points, condensor, coil, and spark plug wires. Other than the coil, the other stuff is really cheap and it is basically just a tune-up which the truck probably needs anyway.
Hope this helps.
Dennis

condenser
 

Be cautious of using the new replacement recently manufactured condensers , even the supposedly good quality BOSCH brand ones don't last that long in service. As a general rule they should be around .025uF capacity. I sometimes see the old condenser testing sets at swap meets . The condenser is dealing with the primary low voltage circuit but from memory the primary voltage kick back can be as high as 300 Volts across the condensor, this is something to do with the collapsing field across the primary windings in the coil collapsing at a faster rate than when the field is growing . :teach:

Hi Mike, Could you recommend a brand? and where I can get one? Thanks, Rob

Rob, my suggestion would be to buy a Pertronix with one of their coils. No condenser in the system and pretty trouble free. You would also need to go away from the copper H.T. leads.
I agree with the lines of thought already presented.
Most likely a coil or condenser as running for 15 minutes it is not likely fuel (other than the blocked vent)
Do a careful job. Everything matters.

Hi Lynn, Thanks for your help. What has me confused is when it happens, I pull the coil wire from the distributor, and check the spark and it is good. So I am thinking it is the fuel vapor locking, but I really like your Pertronix recommendation. It can only help it run better. Thanks, Rob

Hi Rob, can you "jerry rig" a fuel supply that by passes direct to the carb and try that? (do it carefully to be safe) That should isolate the problem one way or the other.

Bypassing the fuel system may be a good idea. I had an M37 Dodge that acted similar to what you are describing. Turned out there was the body of a bug or fly in the fuel system that would get caught in a brass elbow fitting. When the engine would die, he would slip back a ways in the fuel line, only to eventually come back into the fitting on the next run.

Another option would be to crack the fuel line to the carb when it happens and see if there is fuel. Or, after it stalls, you can simply pour a little fuel into the carb and see if the truck runs on that. Some gasoline into a hand oiler will do the trick and limit the fire should things go awry.

The hidden shuttle valve Rob. :)

No-one has mentioned a fuel filter. I had a similar problem on a run a few years ago and ended up getting the scout car towed home at great expense only to find that it was a blocked fuel filter. Once the engine stopped the blocking sediment dropped down and after restarting and driving for a short while the sediment reblocked the filter once again. Now I carry a spare filter everwhere I go.

Scout car, White stalls
 

Thanks for all the help. I have a new filter... I will keep you guys posted! Rob

Can also be sediment or debris in the fuel tank, same sort of idea as the blocked fuel filter but sucking up some debris into the pick up pipe. Weird though it sounds I had this on a modern Land Rover where following some accident damage repair the body shop managed to drop a Scotchbright pad into the fuel tank resulting in exactly the symptoms you describe. I had forgotten all about it until this thread!

That is on my to do list. , auxiliary tank trick. Thanks, Rob

scout car stalls
 

Sorry for the delay. I just realized that I forgot to update what was wrong. The scout car was missing the Phenolic block that goes in between the Carb and the head. This was causing vapor luck. Thanks for all the help! Rob

Hello Rob, thanks for the update. I hope it didn't take you three years to solve this issue :)

Yes closing the loop on diagnostic stories will help
 

Hi Rob

Closing the loop at the end of one these diagnostic tales will help someone, first in the group of us who reads all the MLU replies. We sort little bits information like the missing insulation block under the carb away. Lots of other vehicles have the same design.

The other group that will be help is those who search the web for engines that stall.

Cheers Phil