cold starting problem / engine "bounce"

[Blown4.6]

This has been going on for a long time. It just seems to have gotten worse and is now embarassing!

When the motor is cold, it is really hard to start. Usually, I have to pump the throttle like 6-8 times and then crank it. With a little throttle feathering, it will generally start. Lately, it's been a little tougher. It starts to catch but not quite. Eventually, I guess it becomes flooded. Last night, I was screwing with it and it backfired (exhaust) so freaking loud it scared the neighbors. I've got $40k in this damn thing and the neighbors prob. think it's some old junker that never starts.

Also, when I do get it lit, the engine "bounces" unless I floor it. Above 3000 rpm, it smooths out. Below 3000 it bounces. It's exactly like the ignition is being cut off and back on once per second. After I've let it run (above 3000 rpm) for say 10 seconds, it idles smooth as silk. ??????????????? I'm inclined now to think this has something to do with the ignition. A real idiot installed my pertronix distributor. Maybe it's there? Maybe the old ignition switch itself?? Ideas???

Here are some things that it's not:

1) fuel pressure (guage inside the car stays right at 7 psi
2) vacuum- 12 manifold at idle and 10 in gear (manifold). It does not really "bounce" with the engine (slightly but a result of not cause)
3) timing- I've played with every possible timing and vac advance setup. Once running, it's very smooth and very powerful.
4) Carb- doubt it....it's a new Speed Demon 650 and again, it runs perfectly once running and warm
5) Choke- don't think so....I've tried it with the choke operating (closed) and also set to simply stay open all the time....maybe, but I doubt it.
6) plugs- new



This is such a pain!!! I know if I take it to some mechanic, he's gonna charge me $500 and not fix a thing. I need to determine the issue. I'm really thinking it must be electrical (but why only when cold???)

 

[krash kendall]

Check the firing order first. If an idiot installed your distributor he may have crosswired it. Then timing and vacuum need looking at. You have to be methodic or you'll just get more frustrated.

 

[stangman16]

Check the firing order first. If an idiot installed your distributor he may have crosswired it. Then timing and vacuum need looking at. You have to be methodic or you'll just get more frustrated.

I'm kinda having the same issue w/my '66 302 - with electric ignition though.. I have to pump and pump about 5-10 times and/or feather the gas to get it to start. Some one told me to check the timing, well... now I've got to make sure the dampner I've got will work with the timing pointer, if it doesn't line up 0° at the pointer when the engine is at TDC, then that may be my problem. Have you checked yours? just trying to help... hope you get it fixed - I haven't had time to check the pointer/dampner on mine. good luck!

 

[mustangdave]

Check your float level before you start it: it could be that gas is leaking out of the bowl while sitting and you're trying to crank it while it is trying to refill. Just a guess but it is worth looking through the sight bowl to see. I have also heard alot of people complaining about Demons having small particles of metal in the passages from where they were machined and cleaned out thoroughly.

 

[Blown4.6]

You're right about Demons. The first one I had would flood all the time. I'm sure it was shavings in the float bowl. I didn't bother with it, bought a better one and tossed the first one in the trash.

Yea, I don't think it's timing. The "bounce" (on-off-on-off-on-off) thing happens at all different levels of initial timing. WIth manifold vacuum advance and with ported...and even with no advance. The hard starting could be a symptom of late spark; but, when I move it up more, it wants to ping under load.

The distributor is correct because it has tons of smooth power after I get it started and running.