Flathead V8 tuning

Dave Jones

Dave Jones

Junior Member
I am new to the old cars and need some help. I have a 41 sedan super deluxe that needs a bit tuning. it tends to pop and backfire a bit when getting into the throttle. Seems to be a lean condition. Has a little flutter also so I figure possible point or timing issues as well. It runs very smooth at idle. Just wondering if there are any publications that I could scan through to get my knowlege on?

I have been a mechanic most of my life and can usualy figure things out but the distributor caps and point set up look to be a little tricky. Looks as if there are two fuel mixture screws on the back of the carb. I saw a reference to a propane test to set up the fuel mixture which looked pretty interesting.

Any help or guidience y'all can offer will be greatly appreciated

Dave
 
Here's a start: http://www.vanpeltsales.com/FH_web/flathead_tuneup32-48_221-239.htm

Here's another great resource for all things flathead: http://www.btc-bci.com/~billben/flathead.htm

If you want a book to have and to hold this is a good one: http://macsautoparts.com/early-v8-f...d-mercury-vb222/camid/F30/cp/JS0R3CHL1071938/

VB222_pJPG.JPG
 
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The distributors aren't as bad as they look. They are serviced on the bench. The '41 distributor - if it's a '41 engine - should come off the block with 3 bolts arranged in a more or less triangular pattern. The distributors are cam driven and only go back in one way. Really hard to put one in wrong. The two screws on the carburetor may well be the idle mixture screws - one for each of the two carburetor barrels.

Lots of knowledgable people on here to help. A picture or two would help a lot. Good luck and keep us posted.
 
The first thing you should do is runa compression check to make sure the basic engine in in good working order. A bad valve can drive you nuts.
 
Ol' Ron said:
The first thing you should do is runa compression check to make sure the basic engine in in good working order. A bad valve can drive you nuts.
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o/Ron is right. It's suprising how so many people hate to take a comp teat. That'll do everything to an engine except take a comp test. And wonder why it still runs rough. Walt
 
Thanks for the input guys! I considered I may have a valve seating issue but I have not done a compression test as of yet. I put my had to the exhaust and did not feel any negative pressure. I have no idea what the range should be but I figure if it is nearly the same across the board I may be ok. As I said before it tends to be a bit fluttery as you accelerate. I did a choke test to see if it would improve, mid choke or less seemed to work best. I would say it drives best at lower rpms. So I figure if it is electirical it may be point gap is a bit close or timing is not advancing enough.( Again My first flat head so I may be way off base here.) I did put new plugs in it.

Another small issue is when I hook up the battery it makes a spark so I have a electrical drain to chase down. It will kill the batt over night.

I may be calling you Ken first of the week :)

Davy
 
My first suspicion if it idles fine and cruises fine but has problems on acceleration is the carburetor accelerator pump that's not giving the extra squirt when needed to accelerate. Might look down in the carburetor (with the engine off) and deflect the throttle and see if you can see any gas squirting.
 
A weak spark will also cause those symptoms. Check the plugs for correct color and not fouled. The Champion H10C pugs seem to fail with very little carbon deposits.
 
I checked the compression today an it was 60-70 across the board.That seems low to me. I saw one chart that said it should be 100. I did the vacuum test an it held pretty steady at 15 inches. I pulled the carb and checked the accelerator pump was stuck and the plunger rubber had popped off. So off to pick up a carb kit tomorrow. One distributor cap was a bit loose so I tightened it up and that improved it a bit.

Thanks for the help guys!

Davy
 
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