So Ive got a 300 in my 78 truck. Stock carb, stock everything pretty much just been de-smogged. Theres literally 3 vacuum lines. (Advance, brake booster, and Vac gauge)

Before anyone says anything...YES my vacuum advance is working and is connected to the correct port for ported vacuum.

The problem Im having is when I adjust the timing to run the fastest at idle (havent looked with a light, probably should) I get great power, great mileage, and even cruise at 15" of vacuum easily at 60mph. However, when the motor is cold it kick backs on the starter and the starter ends up grinding. <- That just started this winter, been fine the past three winters. I have new flywheel, and starter. (also, Ive never experienced pinging with this setup, and I haul some heavy stuff sometimes so the motor DOES work)

When Its retarded enough to where I can breath on the key and it starts, its kinda boggy, and you can sense the slowness compared to when its stupidly advanced. When running like this, Its a huge challenge to maintain 15" of vacuum, 10" is more common. Also, MPGS SUCK. We're talking like 10-12mpg. Truck smells rich. No amount of tuning fixes it. (carb is fine, just rebuilt it a month ago)

No matter if the timing is way advanced, or retarded enough to start as easily as a tractor, it always pulls 20-21" of vacuum at idle.

The first solution I thought of, was put a washer under the hold down bolt on the distributor, so the distributor would be loose, but not come out. Then connect a manual choke cable to the distributor body. That way when you want to start, pull the cable, the distributor turns and retards the timing. Then after it idles for a second, push in the cable, setting the distributor back to being advanced like I, and the truck, like it.

BUT that idea is too kludged together and just a band aid to the actual problem.

So, maybe a larger vacuum advance canister? One with more pull?

 

Sounds to me like you've only got part of the engine timing adjusted.

The crank timing is only approx. 1/3rd of the total engine timing. Distributor mechanical weights/slot make up the second, and vacuum advance (for part throttle and cruise) makes up the third.

Generally want (have to) to back off on the crank timing for easy starts, maybe 12 - 14, and usually limit the amount of advance brought in by the distributor compared with stock OEM. The key is also bring what mechanical advance there is much earlier in terms of RPM, than is the case of a stock distributor.

It's not simply a matter of giving a big ole twist to the dizzy C/W. You will need a light and a tach and decipher the amount of mechanical advance at different RPMs and then make some spring and slot adjustments. That will keep the motor from falling on its face. The total amount of timing advance will be about the same, the difference will be when the advance comes in. Many V8 run best with 45 to 55 degrees BTDC at steady cruise, in a well built motor with good fuel.

 

step 1: replace your starter motor with a late model 4.9 gear reduction starter motor. they spin the engine way easier especially when hot.

step2: put a toggle switch in the ignition power supply wire. then, with that switch off, turn the key to get all the mechanical bits moving then flip on the ignition.

I use both these techniques on my race car's engines that have locked-in mag advance and 13:1 compression ratio.

 

Whoa whoa whoa whoa, there's mechanical weights in a late 70s early 80s I6 distributor? If so, that sounds like they're stuck. Ive got no problems taking the distributor apart, Itll just have to wait till I get home tomorrow.

Flyer, Ive been seeing your post on the HAMB and just wanna say, your intakes are awesome.

As far as the starter goes, I dont have a problem when its warm. 0 issues. Whether I just shut the truck off, or its an 80* day (we've had a few this winter) I dont have any problems.

I like the toggle switch idea. Im definitely gonna use that.

You got a thread on how you upped the compression in your 300? Id assume flat top pistons, but from what? Are they custom?

 

Dunno never looked inside one. Ford did have a vacuum advance only distributor in the 1950s. If I had to bet though, would say yes there are advance weights, springs (and slot) inside.

Old dizzys will provide erratic operation for sure. Even if the mechanical advance is working perfectly though, the advance curve is probably stock (terrible). Buy a new one and curve it to your liking. They are pretty cheap and provide a BIG bang for your buck. Distributor is the "brains" of your ignition.

 

Not ready to delve into adjusting my advance curve just yet.

Ill start reading up on all of that eventually.

 

Buy one. The .10c spring has a bit of a markup, you know the saying, but you'll be glad you did.

 

Thanks Jon.
I use custom forged pistons on my race cars - in the past I've used Ross, Venolia, and Diamond.

Depending on displacement and head cc they are either flat topped or domed. My current 13.4 engine os 'zero decked' and has flat tops using a crossflow head.

From a combustion efficiency standpoint the optimum piston shape is either flat or slightly concave. Domes are just a band aid to get you to the



desired compression ratio at the expense of mass flow and maybe even a little thermodynamic efficiency.