I just rebuilt the 302 in my carbureted 1985 F150.

I also have a new rebuilt starter (CarQuest), new starter cable, new Interstate battery, new battery cables, and Motorcraft starter relay. The engine runs GREAT, except the starter turns very slow when it is hot. It fires up fast when cold every time, so I guess that rules out the battery.

I'm wondering if my compression went up very much when I modified my engine to cause this condition?

Engine specs:
-302 Bored .060 over
-Thumper Performance ported and polished E7 heads
-Comp Cams 30-230-3 camshaft
-Performance Distributors Duraspark II distributor recurved to this engine combo, set at 12 degrees BTDC, 24 degrees at 3000 rpm
-Stock Duraspark II ignition (I thought this system is supposed to retard the timing at startup?)
-180 degree thermostat
-No headers yet, but that is the next thing

 

Take the wire off the coil and see if it cranks faster. If it does, I would turn the timing back a little bit and see if that fixes it.

 

Well, that is a pretty impressive list of stuff, I guess. But, two things come to mind. If the engine is hot then of course it has been running and well lubricated. Are you for sure your spark isn't sucking the life out of your battery, because there could be a regulator or alternator problem. When everything is 'cold', the bat has a chance to recharge. So vroom you go until you have sucked half the life out of it and then want to fire it up hot and the juice isn't there.
Or if you think you are now generating astromonical compression where the heads will blow off into the stratosphere (a easy compression check will tell the truth), you might want to look at a stronger starter and battery.
But I think your engine is sucking your battery dead, although I am also told I'm full of bullshiznet too.
Good Luck, Man
LNF

 

I would guess the starter is your problem. It's a common theme when they get hot!

 

Thanks for the tip, Franklin. I will try that on my day off tomorrow and see what happens. I drove my Jeep to work today until I can figure out this problem.

I contacted Performance Distributors, the company that I bought my custom-curved duraspark II distributor from, and they told me the timing should be set at 12 degrees, which is where it set right now.

Is there supposed to be a heat shield over the OEM starter? My rebuilt starter didn't come with one, and the one I took off didn't have one either.

I have been reading about these new "high torque" PMGR starters. Would this cure the problem?

 

The starter pulls more amps when hot, even new ones. What size is the battery, how many cranking amps, how many reserve amps? Also with a modified engine, it will take more amps and more torque to spin. The PMGR starters are just late model starters, but they are higher torque.

 

I never thought that a mildly modified engine like mine would require more amps and torque to spin.

The battery is an Interstate, 500 CCA, 90 minute reserve capacity.

 

Might wanna step up the battery to at least a 750 cca, with a higher reserve as well, I run a group 65 battery in mine, for the later fords and diesels. High performance and modified engines tend to run higher compression and thus take more to turn over, especially when hot. Having sold many different brands of batteries over the years, I would recommend ditching the interstate, they have always had the worst track record this side of the DieEasy from Sears, Honestly the best battery I have ever had/sold is the Duralast Gold from AZ. On average I get about 6-7 years out of one. The average for most batteries is 4-5 years. The group 65 in a gold, will have more than enough power for you. For the starter, since you are going to headers anyway, use one from a 92-96 5.0 truck and just add the solenoid wire from the output of your current solenoid to the new solenoid terminal on the starter. The starter part # should be a 3205 if they use the standard Lester numbers.

I also see you have put new cables on, where all does the ground connect to, with the external solenoid, you need a good ground to the frame/body as well as the motor. What size are the cables?

 

I used to have the common hot start problem on my carbed '86 351w with oem batteries and starters. Then I put in a Summit high torque starter, an Optima Red Top battery, and new 1ga cables. My truck has never started so fast, so reliably, and it sounds awesome when it turns over.

 

Mine was doing that for a little bit and I just had the timing up to high. Bumped it back down a little and was good to go.

 

I thought about the timing, but this distributor is custom curved for my engine combination and designed to run at 12 - 14 degrees BTDC. It is currently set at 12 degrees.

If I keep the timing where it is, will the "high torque" starter/battery change fix the hot start problem?

 

Yeah then I would look into a starter with a little more torque and see where that gets you. The battery I use in my truck has 900cca and I love it.

 

Another thing to consider is that you have a rebuild with tighter tolerances. I may be wrong but that may play a part. Also before I changed to a 1000cca Optima and high torque starter I tried a heat shield on the oem starter and routing the starter cable and ground cables as far away from heat sources as possible. I even wrapped the cables in heat insulation. This helped some but I was never happy with it. That's a low cost fix so it may be worth trying.