Hard to start, could it be vacuum leak?

[James West]

I have a fresh rebuild with less than 1500 miles on it. Very good rebuild job including balancing. My batteries spin the heck out of the engine too. After sitting for 24-36 hours or so, the carb seems to lose prime. This all started about the same time a windshield vacuum motor started leaking. I have tightened all of the fuel lines and what I could of the fuel pump from the outside with no results. Pull starting fires her right up after 20-30 feet. I do not suspect that the fuel diaphragm is bad since the oil smells, feels and tastes like there is no gas in it. The vacuum pressure feels strong as well. Could it be that the leaky vacuum motor in someway is causing the loss of prime since the vacuum pump runs off the fuel pump? I welcome all input.

[MSeriesRebuild]

I have a fresh rebuild with less than 1500 miles on it. Very good rebuild job including balancing. My batteries spin the heck out of the engine too. After sitting for 24-36 hours or so, the carb seems to lose prime. This all started about the same time a windshield vacuum motor started leaking. I have tightened all of the fuel lines and what I could of the fuel pump from the outside with no results. Pull starting fires her right up after 20-30 feet. I do not suspect that the fuel diaphragm is bad since the oil smells, feels and tastes like there is no gas in it. The vacuum pressure feels strong as well. Could it be that the leaky vacuum motor in someway is causing the loss of prime since the vacuum pump runs off the fuel pump? I welcome all input.

I doubt if it's vacuum related, but if you want to double check, unhook the vacuum tubing from the intake manifold and plug the hole with a 1/4" NPT plug. If that cures the issue, then you need to look more seriously for a leak source. My first initial thought would be that I would like more solid info on the details involved in performing the rebuild. Were you there to see what actually took place and how much attention was paid to detail of the various operations involved? Was ample time spent to do things the best they could be? Did all your accessory components get built and brought up to spec at the same time? If you don't have a definite positive answer to the above questions without reservation, I would perform a compression test to verify just how much quality workmanship actually went into this rebuild. If that turns up no proof in the pudding, then you can look at some accessory issues. There is a reason for this hard starting problem.

[cuz]

I find it odd that you say the battery spins her over just fine yet it won't start unless you tow or push it 20 feet. A 20 foot pull start would hardly turn it over as long or as fast as your starter. If she kicks off and runs well with a short pull like that I doubt you have anything wrong with the engine itself or the carb.

This type of problem usually happens on a civvy 12 volt electrical system where the start switch is wired through a resistor for ignition power. On those with the key in start there is a full 12 volts at the coil and with the key in run there is a lower voltage at the coil. Do you have a 12 volt conversion? If so you may have broken the full 12 wire or if you have a dual resistor the start side may be bad.

[M-Thrax]

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[James West]

Let me see if I can adress all of this with what everyone has said and what I need to add.

As for the rebuild, the engine was rebuilt by Robert Stroud in Kinston, NC and he has rebuilt several for me over the years including a previous 230 for another M37 I used to own. Robert is a darn good builder and I have 110% confidence in his work. The engine was reassembled following the machine work in a facility that resembles a lab as much as a machine shop, was fully tested and warranted.

As for the electrical, it is 24v and I have new wiring harness, new plug wires, electronic ignition from M-Series Rebuild and other new components. All plugs get plenty of fire on demand. The recent cold weather could being slowing the batteries down some but they still spin the snot out of her.

As for the fuel system, the carb was not rebuilt by me but by a neighbor of mine who has probably forgotten more about carbs than I will ever know. It has been performing well up until now for about 6 months.

Here is what I need to add. The fuel pump was purchased rebuilt at White Owl Parts In Kinston. I am sure the folks there know what they are doing too. It has been on the truck for about 6 months as well. Last night, I pumped the fuel lever a few times, hit the starter and she fired right off. That could mean a problem in the pump or leak in the system somewhere. I also forgot to add that when I tried to start her before, it would spin and almost seem to flood. Coming back later may or may not have been productive but pull starting always works. When it does fire off this way, she smells and smokes like a flood but not as bad as one that is truly wet on the inside. Starting back after a short while is not a problem. Six hours or more may be questionable. That is why I think that I am losing prime somewhere.

[Lifer]

Starts easy on a push or pull, but won't fire when spun by the starter, huh? Sounds like the starter is pulling too much current and not leaving enough for the spark. The colder temps could be a contributing factor, there.

[cuz]

Loosing prime equals a lean condition not rich/flooding. Vacuum leak equals lean condition and not rich/flooding. So you can rule out any suspected vacuum leak or fuel starvation. That comes right back to electrical. The rich/flooding/black smoke issues are probably the result of all the normal fuel during the start effort without a good strong blue spark while cranking with the starter. How did you determine that

All plugs get plenty of fire on demand.

? Can we assume it started and ran very well for the first 1500 miles? Have you already checked all the obvious things like all terminals and connections tight, points not loose and bouncing and coil resistance readings?

[James West]

All wires are tight from the distributer to the plugs. All plugs are tight, coil is in place. I don't have any way to check resistance at the coil but I did check to see if the plug wires would arc to the plugs and they do. I will do more tonight when I get home and report back.

[cuz]

I am referring to all starting and ignition wiring right back to the switch and the battery. That waterproof connector on the distributor from the switch can rot inside and create a short to ground that will reduce power to the coil while cranking with the starter. It is not uncommon for the wires inside the coil to get pinched from being mis-routed and create a short to ground again these shorts may be very intermittent or light contact and will only create a serious loss of power while cranking with the starter. You should have an inexpensive digital volt-ohmmeter in your tool box. They usually cost less the $20. Using the volt-ohmmeter you can check power at the coil with the cap removed and the switch on


This illustrates distributor inspection criteria. The illustrated distributor is a M38A1 4 cyl. but the coil and wiring is the same for the Dodge.


Same applies here.

You can remove the electrical connector at the side of the distributor and record voltage at the center pin with the master switch on. Then record the voltage while the starter is cranking. Now connnect that back to the distributor. Now read the voltage at the + terminal of the coil with the master switch on and then again with the starter cranking. If you don't get the same values within 0.10 volt something is wrong. The internal noise filter (capacitor) inside of that small square projection that the power in connector screws on to may have high internal resistance or be shorted. Remove it and retest with a jumper installed.

[MSeriesRebuild]

All wires are tight from the distributer to the plugs. All plugs are tight, coil is in place. I don't have any way to check resistance at the coil but I did check to see if the plug wires would arc to the plugs and they do. I will do more tonight when I get home and report back.

Any number of issues could be going on, as I suggested the process of elimination to rule out things down the line. Just eliminating any single issue in your mind without checking properly usually isn't a wise move. A compression test is easy and quick, I still suggest you do that just to be certain, 15 or so minutes ain't much time wasted and hopefully it would show a good result. Mind at ease on that subject then you would need to start checking accessory components. How old is the gas in your tank? This can create huge problems. I will be happy to verify that your distributor is up to par if you will send it to us since we sold you the electronic ignition, much of the info posted previously does not apply in your case since you have all electronic. It will be next day via UPS ground since you are in NC. Will turn right back around to you. It could certainly be an electrical issue, however to be honest, the likelyhood of some other issue or combination of issues being the cause is just as high. There is a high risk factor of any rebuilt fuel pump being bad, I have bought rebuilt pumps that were bad. After tear down I could find no reason for not pumping, the most likely cause, a pin hole in the housing somewhere. Most rebuilders glass bead blast the housings during a rebuild, a tiny hole would be next to impossible to detect, it happens. Shows up with no pumping at low RPM's lots of times. After the engine is running, it may pump good enough to sustain things even if not at full potential. I could talk all day about possibilities that could bring about the symptoms you have going on. Those of us trying to suggest helpful hints aren't there to actually see what is happening, any or all of us might suggest a different approach than has been mentioned here if we were. A simple down the line process of elimination in troubleshooting is the best course of action and may save you some $$$ and frustration also. I'll leave it with you here, don't know what else to say unless I had more solid info to run on.

[cuz]

Pointless ignition only replaces the contact points. Everything else in your distributor is the same as the illustrations with the wiring being the same for all the coil wiring.

All clears up and runs well after a pull start sure takes the fuel, vacuum and internal engine issues away from the equation.

Bad fuel makes starting tough with the starter or the pull rope and generally does not improve much after starting.

Fuel pump low output at low RPM's would more likely cause a no start on a 20 foot tow then with your wildly spinning starter cranking speed.

I'd start with the easy items that fit the symptoms first.

[Master Yota]

Just a thought off the top of my head, so bare with me:

Seems to flood out while cranking - but not during a rope tow

Engine cranking creates lots of vacume to activate the fuel pump - rope tow dosen't create as much vacume as engine is turning over slower, thus lessening the pump motion.

Truck starts under towing condition - engine probably under mild load, and can burn off excessive fuel quickly.

I'm going to suggest that your needle and seat assy. in the carb is stuck partially open, either from debris in the fuel line after the filter, or something else.
I had a similar problem with a flat head continental engine after we replaced the fuel pump with an electic pump. The pump generated enough pressure to push fuel right past the needle and seat during startup, quickly flooding out the engine. We installed a fuel pressure regulator and cleaned the carb again, and its ran like a champ ever since.

Good luck with your search for an answer - hope this helps...

[cuz]

Pull starting fires her right up after 20-30 feet

20 to 30 feet of tow start is only across two living rooms. Amounts to a few revolutions at most.

So, I would agree that starter cranking with a needle and seat stuck open overfilling the bowl could also be the problem. However if that were the case evry start then when running after the start the rich issue would not vanish. A quick disconnect and plug the fuel line from the pump to the carb and try a starter start again will determine if that is the culprit.

The electric fuel pump issue is an old problem and many folks learn that one the tough way and buy the regulator after the grief.

[Master Yota]

Pull starting fires her right up after 20-30 feet

20 to 30 feet of tow start is only across two living rooms. Amounts to a few revolutions at most.

So, I would agree that starter cranking with a needle and seat stuck open overfilling the bowl could also be the problem. However if that were the case evry start then when running after the start the rich issue would not vanish. A quick disconnect and plug the fuel line from the pump to the carb and try a starter start again will determine if that is the culprit.

The electric fuel pump issue is an old problem and many folks learn that one the tough way and buy the regulator after the grief.

I'll agree.

Perhaps the warm engine lights off faster than when its cold. The extra time when cold starting is enough to flood it out. Either way, I would check the carb over. Try rapping on it lightly with a small hammer or screw driver handle when its cold before starting. It might be enough to jar the needle loose. If it starts normally, then at least you've narrowed the culprit down to the carb...

[James West]

Wow, where do I start first? Lots of good input here from several angles and it all sounds good. Due to getting home late and other duties, some of the suggestions will have to wait. In the meantime, just for the heck of it, I pumped the fuel pump lever 5 gentle times prior to a cold start this evening. With no choke, no pedal pumping and regular throttle, the engine turned over less than two revelutions and cranked fine. To me this means that it must be a fuel issue. I once again checked all lines that I could reach, tightening as I went. The only one that seems even a little loose was the supply line into the carb. It could have worked loose and become the culprit. An overnight sit and a cold attempt in the morning will tell.