Ignition Timing for Hot Starts, which is better?

Ron Earp

Ron Earp

Administrator
If we have a motor with a compression ratio of about 9:1 that runs rich at idle, which ignition timing would be better for hot starts (all other things being equal):

1. 34 degrees BTDC
2. 10 degrees BTDC
3. Doesn't make a damn bit of difference.
 
It will start easier at 10 deg. BTDC than at 34 deg. I assume there will be some sort of advance curve off idle, because it won't run worth a lick much past idle at 10 deg.
 
Our solution [Pinto guys] is to ttake the heavy springs out of the dist. and replace them with the lightest ones you can find...

Now the car starts & idles fine and as soon as it gets past 2000 rpms it goes right to 36 degrees advanced.
 
I've done different things now to investigate but the hot start isn't going away.

Locked timing at 34 BTDC - hot start is present. Standard dizzy at 10 degrees BTDC initial advancing to 34 degrees > 2800 RPM, hot start still present.

With either combination (including the old retarded timing setup) the car push starts VERY easily. All you need to do is have it going a a walking pace, second gear, and bang off she goes.

I have replaced the starter with a new one - no change.

It seems like if I could just spin it a tiny bit faster than what the starter is doing now it'd have no problem.

Ron
 
Dave--I like that Pinto advice (I do the same thing but I also have to weld-up the plate slot to prevent too much advance at high RPM).
 
Some people have to hit the starter before turning on the ign.

Could you be vapor locked?...(float bowl or line)

Or are you leaking fuel internally only when hot...(empty float & wet intake runner like when a evap/vent line is plugged)

I can't remember what carb set-up a 260Z has.
 
Ron, sounds like you have eliminated the ignition as the source of the problem. On the slow cranking thing, maybe the battery is getting hot and losing cranking umph. Living in Florida, I've seen such during the summer, even with good new battery. Maybe an insulation blanket wrapped around it. Have you tried one of the hi torque starters? I'm just throwing stuff out there. The other thing that occured to me, when I asked how to wire up the kill switch, you said run the positive cable to the switch then back to the starter. You said (I think) to use 2 gauge wire. That sounded thin to me, I understand thicker wire meant more weight, so I figured if it worked, should be thick enough. Maybe when hot is not enough. Could test theory by temporarily removing long cables to switch with short stock type cable.
 
Have you tried one of the hi torque starters? I'm just throwing stuff out there. The other thing that occured to me, when I asked how to wire up the kill switch, you said run the positive cable to the switch then back to the starter. You said (I think) to use 2 gauge wire. That sounded thin to me, I understand thicker wire meant more weight, so I figured if it worked, should be thick enough. Maybe when hot is not enough. Could test theory by temporarily removing long cables to switch with short stock type cable.
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The hi torque starter would be illegal, but it might work.

The wire I am using is huge, like 000, or almost 1/2". If I told you 2 gauge it is my fault, I meant 1/2". It was a bitch to get in the lugs and it is heavy, but there is no lack of current capacity nor resistance issue at fault here. Besides, I on'y have to use about 3 foot of the stuff so no big deal. The battery is fresh and fully charged in all of these "experiments".

My ignition is wired separately. The old push starter, get motor turning, then flick on ignition does not do the trick either.

I built a nice heat shield (illegal the way I made it turns out, will fix that) for the carbs too and they now remain relatively cool even after racing. I was concerned they were getting too hot and indeed they used to get hot but no longer.

We estimate we're cranking over around 125-200 RPM with the starter on the car now, a stock Z starter. But with our second gear push starts we're figuring we're getting around 450 RPM, or about twice as much turning. All I know is the pushing works. If I could get a starter that would turn about twice as fast I think it would do the trick.

I'm not the old 260Z with the issue I don't think. Seems I saw 260ZMike worried a bit about his on the grid too and needing a push.
 
The issue is that the float bowls are at the bottom of the carbs. Right above the header. Ceramic coat the header, wrap it, wrap it again, wrap it with aluminum. If your carbs are right, you will start. The time you saw me, I had a bent needle and it appears about 40-50 degrees of advance. It is a wonder it started at all, and no wonder it blew up.

I wish you the best, I changed so many things on mine that I don't know what to tell you to fix, I just know it can be done. Email me about the carbs.

Mike
 
I'll make a list of stuff and email you.

But I'm about 100% certain it isn't heat. Those things would never work when they were hot to the touch, and now it won't work when they are cool to the touch. I'm serious, it can run for 30 mins on track at practice and the heat shield is doing a good enough of a job that they carbs are just barely warm. They used to be so hot you couldn't touch them for more than a second or two.

Damn MSD failed on the thing though when I took it over to a shop to have some work done. Race cars, always something.

R
 
I'm kinda 'old school' when it comes to starting problems....

1st check spark
2nd check fuel
3rd mechanical

And I especially like reading plugs.

Heat screws with electronics & fuel.
Can you get a good signal on a timing light when hot?
What are your plugs telling you.

Of course you could LM-1 it but, I'm sure if you had one you would have used it by now.
You could remove the carb and 'hand carb' it w/ a squirt bottle to see if it tries to start.
(watch for back-fire :unsure: )
 
Ron, how is your car's spark when hot cranking with the starter? Some electronic ignitions are sensitive to voltage and hot wires have more resistance to electricity and could cause voltages to drop. Push starting doesn't draw the current from the starter.

Long shot, but maybe worth checking.

-Joe
 
Ron... I think Joe is on the right track. When we were push starting your car at VIR it just kicked over too easy. It was my opinion at the time that your starter was robbing the ignition of voltage. Have you tested the supply to the ignition with the starter engaged? Just another step in the process of elimination.
 
I'll check it out. I have looked at the spark when trying to find out why it wouldn't start and it was quite bright and fat. But, I've never checked the supply voltage. Plugs are typically a light tan color, not black or oily.

I don't suspect that is it, but I'll leave no stone unturned - you never know until you check it. I'll measure current draw and voltage and report back.

At VIR that was the first time I'd ever had the heat shield on the car and I was surprised that my problem didn't go away. But, remember my started died and we had to replace it Sunday morning. Could be that ailing starter couldn't turn it over fast enough to do the trick during hot starts. We'll have to re-check that situation now that a new one is on there.

R
 
Ron, if you have tested your spark when cranking under the hot no start conditions and verified a normal spark then I don't think the voltage is the problem.
 
Or...install a Mallory HiFire that an ignition timing "kick-back" that starts your engine at 10 degrees and then runs it at your designated setting.
 
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