Flathead hard to start/running rough

bmwillia

bmwillia

Senior Member
I need some help. I have search the forum and found a few things but nothing exactly like I am experiencing. He is what I m dealing with.

I have a 35 flathead in my 33 5 window. I am still in the process of getting my car back on the road so keep in mind that this is not a road worthy car. I do not have all of the wiring installed just enough to run the motor.

I have had the engine running well in the past but the carb was leaking from the bowl so I sent it off to uncle Max to have it rebuilt.

Had the distributor and coil rebuilt by Skip a couple of years ago. very little running time on it.

Here is what I am dealing with now.

When the engine is cold, as in first start of the day, it will fire up ok. It takes a little longer than I would like but it will start. I have to almost full choke it to get it started and to keep it that way. If I give it a lot of fuel, it will backfire out of the carb. When it is running, it runs really rough almost like it is missing, but when I pull the plug wires there is a strong white spark jumping to the plug, but the engine does not run any rougher than when the wire is on the plug.

The warmer the engine gets, the weaker it gets. if I open the choke up it will die. Once it has ran and gets up to around 150 degrees, it is really hard to start. I have to wait about 10 to 15 minutes and even then it turns over forever before it will fire.

Also it seems as though gas is getting into the oil. The oil is now thin and smells like gas.

Any ideas would be appreciated.

Thanks,

Brad
 
It sounds like the fuel pump is busted. Have you tried putting the carb end of the fuel line in a jar and crank the engine over? You should see strong spurts of fuel from the pump.
 
If you've got thinning oil because gas is getting into the crankcase it is a result of your running with choke on pulling too much gas that's not combusting completely. Seems like as a result it's dumping a lot of un-burned fuel thru the engine into the crank case. Can't be sure but seems like your pumping plenty of fuel if so much is getting into the oil that it's thinning the crankcase oil. Really seems like a combustion issue as most of the gas is not being burned but just washing through the cylinders into the crankcase. It's very important not to run the engine again untill you get the thinned oil gas mixture out of your crank case as it will mess your cylinder walls up and is a potential explosive issue.
When it's running rough with choke on does the exhaust smell strong and is the engine pushing black smoke out of the tail pipe? If yes then the combustion isn't right. This could be from several problems. You say the spark is bright if that's the case then possibly your timing is out of wack and sparking way to soon or late? If your judgement on the spark is weaker than you think it could be you coil is bad causing a weaker spark as things heat up.
 
That is what I was thinking Anthony. I will check the pump, but I feel that it is good. It really seems like a combustion or timing issue as you say though. There is no black smoke out of the tail pipe but there is a strong exhaust smell and it also backfires. occasionally out of the carb, but most often out of the tail pipe.

Since the coil was rebuilt by Skip and has very little running time on it and the visual signs of the spark are good, I was leaning more toward timing but I have very little experience with engines. I know it is possible that the coil is the culprit.

I see fuel dumping through the carb. when I give it throttle so fuel is there.

Is there a good document on adjusting timing I could read?
 
With the stock distributor on a'35 flatty I'd get a hold of BUBBAS IGNITIONS, he's the distributor & timing Guru on the Barn. Send him a message if he doesn't see this post.
 
In my opinion Skip has the best equipment for testing and setting up the
old Ford distributors. A bad condenser will act like you describe, did skip
test yours? The hard start can also be a bad valve in the fuel pump allowing
the gas to drain back to the tank. It can take a while cranking to get fuel
back up to the carb. These engines can be flooded with to much choke.
A dirty ignition switch can also lower the voltage to the coil. G.M.
 
I don't think Skip tested my condenser. its been a few years though so I can't remember.

Is there a way I can test my condenser?
 
bmwillia said:
I don't think Skip tested my condenser. its been a few years though so I can't remember.

Is there a way I can test my condenser?
Click to expand...

Try searching "testing condensers" I posted the procedure on this
forum a number of times. You have to test them hot and cold. G.M.
 
Check the fuel pump first. Could be a bad power valve or massive vacuum leak.
Also, float sticking.
 
Last edited:
Thanks guys.

I did not get a chance to do much this weekend so I'll post updates later in the week on my findings.
 
Did a little troubleshooting this evening.

Pulled the fuel line going into the carb and found almost no fuel being pumped out.

I took the pump off and using my finger as the push rod, it pumps plenty of fuel.

What should the travel of the fuel push rod be? At its peak, it sits about 1" high, and drops about 3/8" at the bottom of the stroke. Is this normal?

Do I have a bad pump?
 
Brad,
Push rod stroke is .200. Crank the motor over until the push rod is all the
way up. Install the pump and stand and push down on the stand just enough to take
up the lost motion in the pump. With your 3rd hand you should be able to slid a 3/16
dia drill (.187) between the bottom face of the stand and it's mounting face on the
intake. If you can actuate the pump with a finger something is not happy. A good
pump requires you to hold it in one hand and actuate the arm with the other hand.. This action will leave a very nice 7/16" circle from the cup on your actuating hand.
Keep us posted.
Charlie ny
 
Changed the fuel pump out. Same symptoms persist.

Hard to start, stumbling when running. wants to die with open choke after a few minutes. can choke to make it keep running and add throttle but that produces an occasional backfire.

It ran fine before I had the card rebuilt. I had the carb rebuilt because it was leaking pretty bad around the bowl and from the three screws at the bottom of the bowl.
 
I just wanted to give an update.

I got it running good again.

I did some more troubleshooting this week and found very low voltage at the coil. I replaced the condenser because I had already ordered it and I also replaced the resistor. I still was not getting good voltage across the resistor so I bypassed it. Once I got 6 volts to the coil it fired right up and purred like a kitten.

Now I'll go back and figure out whats going on at the resistor.

Thanks to all for your help.
 
Now that your on the right trail I recall having a similar issue. I however have an electronic crab dist. Beings an external resistor was supplied ( I believe 4 V resistor) I wrongly assumed I should include in the power to ignition circuit. Forgetting or just not thinking about the fact that there was a resistor under the dash already in that circuit. The result was two resistors in line reducing the Voltage too much, it seemed to start OK but the engine ran rough above 1000 rpm and worse under load. Removed the external supplied resistor and went with the stock one under the dash and it all straitened out and runs great now.
 
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