Engine not running smoth

L

lenandmy40

Junior Member
* Repair! I found the problem with the engine acting like it's missing. I was very surprised but am happy it's fixed. I had a cylinder that was 15 lbs. lower in compression. All were 70 to 75 except one that was 60. As I stated I just rebuilt this engine. Well I knew I had better pull the head and fix the problem. The intake valve wasn't totally seated. I re lapped it put it back together and holding my breath it doesn't miss any more. Apparently when I lapped the valves I didn't really check the seats to see that they were seated. This problem was masking the lean issue I had at mid load the engine keep jerking acting like it was out of fuel. I put in larger jets and that fixed the problem.I want to thank all who answered my post with Ideas to fix the problem
* Problem. Recently I rebuilt my stock Flathead for my 40. Since then it has a miss or a jerk if you call it. It idles smooth however when you are cruising about 50 mph it starts missing or jerking. If you speed up it gradually quits. Prior to rebuilding the engine I had no problem. I pulled the sleeves and bored it to 3 3/16 and put the low end Offenhauser heads on it. Put in 8ba 4 ring pistons and valves.
For carburation I have Holly 94 with a 48 jets (I'm at 6000 ft.) # 5 power valve. It also dose it with the stock 8 and with it plugged. I have taken out the valves in the fuel pump and running a electric fuel pump. I did replace the cam because I wanted the bolt on cam gear not the press on. I'm using a fiber bolt on.
The valves are adjusted to the middle Ext is .014 to 15--Intake .011 to 12
I'm baffled as to what is going on. Anyone have any ideas Regards Len
 
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#48's are mighty lean. I'm at 5300' +/- and was running the stock #51's in my 94. I ran it with an air/fuel meter connected up into the mountains and the altitude had very little effect on it. I would at least go to a #50.
 
It does sound like it is running lean. Keep driving steady at the speed where it is missing/jerking, and slowly pull the choke button out. If it improves, then that is the problem.
 
Hello B-O-B
I had a Holly 4 lb. pressure regulator on it with a 6 to 7 lb. 6 volt pump. I changed it to a 6 volt 3 to 4 lb. pump and took off the regulator. Does it with both pumps. The other set up is my spare. Thanks Len
 
Hello Ross F1 I changed the jets to 51 (because that's what I have for testing) today and took it for a test drive. It still has the same symptom. Len
 
Hello fordscript
Yes I have pulled out the choke on several occasions with no improvement. Thanks for the idea. Len
 
You might need to regulate the fuel pressure down to 2 psi. The needle valves may not be able to cope with 3-4 lbs.

I don't really know if it would effect you problem, but I had flooding with a stock pump, I had to fit a spring from a much older pump to lower the pressure. I also had to fit the old type needle valves, the modern ones wouldn't seal. I recently fitted an electric pump as a backup and had to fit a regulator to keep the pressure manageable.

Mart.
 
Hello Martin I'm taking the readings between my carb & pressure regulator. Also going by what is on the fuel pumps. I haven't had any fuel problems such as flooding. Len
 
Just to clarify, the regulator is up the front, close to the carbs?
And when you say "starts to miss at 50 and if you speed up it gradually quits" does the "miss" gradually quit, or the engine gradually quits?
If it's the engine that gradually quits, it sounds like you running out of gas.
I've seen before on a similar symptom engine. His problem was crap in the gas tank. Ruining along slow and idle was perfect. Start to build speed and it started missing, then gradually loose power. If he slowed down again it ran good. The crap in the tank would move and block the gas line when demand went up. When demand went down, it moved away.
Go through the gas lines make sure all is good and clean. They do get blocked up, or semi blocked up.
But don't rule out the ignition, been said many times. Most fuel problems are ignition, and most ignition problems are fuel.
Keep us posted,
Martin.
 
Scooder I have found nothing in the fuel even the filter is clean and the regulator was at the carb. I'm also running a 40 micro filter
 
I found the problem with the engine acting like it's missing. I was very surprised but am happy it's fixed. I had a cylinder that was 15 lbs. lower in compression. All were 70 to 75 except one that was 60. As I stated I just rebuilt this engine. Well I knew I had better pull the head and fix the problem. The intake valve wasn't totally seated. I re lapped it put it back together and holding my breath it doesn't miss any more. Apparently when I lapped the valves I didn't really check the seats to see that they were seated. I want to thank all who answered my post with Ideas to fix the problem.
 
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