I recently replaced the tired 390 in my '70 F100 with a 390 I built for my son's '55 F100 several years ago. It started and ran fine in the '55 with point-style distributor. When I did the swap, I used the durospark II ignition setup I had been using with the my 390.

The problem I have now is that the engine will start right away when it's cold, but once it's warmed up, it "kicks back" like there is too much advance in the distributor (electronic). It will sometimes go so far as to drag the battery down within seconds. I have two batteries in my truck, and can switch the starter from one to the other by the use of two start solenoids and a select switch. Both batteries are holding their charge (alternator OK). They are charged through a RV-style voltage splitter.

If I let the truck set for 20 minutes, it will start right up.

I had the later 'emissions' Durospark module (yellow connector) at first, but replaced it with the Durospark II (blue connector). No difference, except that I couldn't retard the timing at all with the 'yellow', no matter how far I twisted the distributor. I can retard the timing with the 'blue'.

There is no spring in the distributor for the vacuum advance to work against, so I run the advance with ported vacuum.

Any ideas?

OldFords

bad attitudes

 

Make sure you have the white wire going to the module hooked up. When the module receives voltage on the white wire during cranking, it will automatically retard the timing to make the engine turn over easier. After it starts, you release the key, and the 12v on the white wire will drop out, and the timing will revert to what you have it set at the distributor.

 

You nailed it , Dave.

When I converted to the Durospark, I installed the white wire from the module to the start solenoid, but somewhere along the way the push-on connector got pulled off (wonder what dummy did that; don't know his name, but his initials are OldFords).

It still kicks a little on occasion, but nowhere near like it was doing. I'm having a bit of a problem with my Holley 4160 leaking over into the manifold when I shut it off, and suspect that might be part of this problem, too.

Thanks
OldFords
bad attitudes

 

I am sorry but your reference to your Holley reminded me of an experience I had with a Holley once.It was letting gas leak passed,and my engine caught fire...even from the breather.Knowing I had a problem I towed it home and drained what seemed like a gallon of gas from the pan.Later in recounting my experience to a friend,without his knowing what carb I had and no hesitation I was told to take the Holley off and find a Carter for it.Now I can't claim alot of preference or knowlege in carbs,I just thought it was funny...maybe not all that funny,but it makes me smile...

 

All it takes is some dirt in the fuel, and any carb can leak fuel into the engine and or manifold. Also the fuel they use now is terrible. If you let the carb sit around for a month or two, the fuel turns into a gum that messes everything up. Last time I got a kit from advance auto(that's what it's called in my area, their website is partsamerica.com) they had the genuine Holley kits.

If your starter still struggles occasionally, it may be because the starter is too close to a header pipe, or I have had a small gasket leak that puffed exhaust down near the starter causing it to get too hot, and not want to crank the engine on a hot day.

If your starter seems ok, you might have to tweak the timing down just a hair. I know they run good sometimes with the timing advanced, but you may have just a little too much of a good thing.

 

I'm running stock exhaust manifolds which, in theory, should not cause a problem with starter overheating.

I retarded the timing from 8 degrees BTDC to six, and it's a lot better. Still struggles ever so often. I notice that now, with the timing at 6 it only kicks for one, maybe two, revolutions before it starts spinning as it sjould.

Also, interesting enough, I'm not experiencing the "percolation after engine shut-off" as often as I was.

I agree with you that today's gasoline leaves much to be desired; expecially with a carburetor. And you are right, a carb kit just doesn't last as long as they used to. Even if you have a daily driver (as I have), the carb gums up much quicker than I remember them doing, back in the stone ages ('50's).

OldFords
bad attitudes