Possible ignition problem

by WyldeBill66 Mon Oct 22, 2012 8:31 pm

On my 75 Chevelle with an 87 vintage crate 350, if I get on it kind of hard, it will act like it's losing spark. If I'm just cruising easy no problem. My wife said when it does that while she was following me, there is white "smoke" coming out of the exhaust. I'm thinking that is un-burnt fuel. If I get completely out of it, and then feather the throttle it runs fine again. It has the HEI ignition. Any suggestions on what this could be? I've only had the car about a month, so still learning about it's idiosyncracies. It revs fine in neutral without a load on it. It has an Edelbrock 650 carb and electric fuel pump with a regulator set to 4.5 pounds if that makes any difference.

Thank you in advance

Bill

by Dead Man Mon Oct 22, 2012 9:54 pm

in most cases white smoke is burnt coolant, not un burnt fuel, that should be brownish,

by WyldeBill66 Mon Oct 22, 2012 10:00 pm

If it was constantly, I'd agree with you, but this is only when it is acting up. It does not give out white smoke when it is running normally. I'm not 100% sure of the color of the smoke, because the description came from someone who knows nothing about vehicles. I do know it's not a head gasket or something as such. That is constant, not intermittent.
Thank you for your suggestion though.

by JB2wheeler Mon Oct 22, 2012 11:01 pm

Just a guess, but it sounds to me like a lean condition caused by your timing being off a little bit. Hows your timing chain doing? A rich condition will cause black smoke from exhaust. JB

by ant7377 Mon Oct 22, 2012 11:08 pm

Maybe the coil starting to go, sounds like it since you are seeing a problem with a load on it,check the wires going to the distributor,make sure they arent burned or crappy looking, coil is cheap too.

by WyldeBill66 Tue Oct 23, 2012 1:05 am

No black smoke, but I had thought about the coil. Weather a little crappy this week, but nicer this weekend and I'll go check it then. Hopefully it will be a simple fix and get her running strong. Thanks all.

Bill

by pila Tue Oct 23, 2012 3:55 am

White smoke usually means coolant or transmission oil. You might check the modulator on the transmission. Pulling the vacuum line off & checking for oil in the line & nipple on the modulator will eliminate that possibility if it's dry. Of course any bubbles visually coming up in the coolant, with the rad cap off should indicate if there's a problem there.. just some ideas....

by ant7377 Tue Oct 23, 2012 7:52 am

I had white/gray smoke once when the carb float stuck.Not that that is the problem here but it was unburned fuel coming out of the exhaust, which also could be a sign of a bad coil at high rpm not firing all cylinders. The modulator could certainly be the problem as well. Right side of tranny.

by davesr_7 Tue Oct 23, 2012 9:19 am

does this car have heior was it converted to hei? cat converter still on it and does it do it when weaqther has alot of humitiy in the air? what about plug wires when its cold and humid runs bad when it dries off it runs better spray some water on the wires and if it starts missing or running ruff go for them also check for vaccum leak

by WyldeBill66 Tue Oct 23, 2012 10:50 pm

It does have HEI as I wrote in my original post. No cat converter. Headers and flowmasters. I did find tonight after I got home that the vacuum line had come off of the PCV valve. I hope that was the issue. The first time it did this when I was driving it home from buying it. When I got home I found a big vacuum line just hanging off the side of the carb. I sure hope this is the problem. Although in looking at it tonight, I found a wire on the side of the distributor with duct tape on it. WTF???

I have to see what it going on there. Some of the stuff the guy did on this car is just Half-assed...

by ant7377 Wed Oct 24, 2012 7:53 am

A big vacuum leak like that would certainly make it do something like that. You really should just go through everything,you are porbably going to find more stuff. Make sure the carb bolts are snug too. Dont really crank on them but they shuld be snug,use carb cleaner while the car is running to check for vacuum leaks,the idle will go up slightly when you find something.

by pila Wed Oct 24, 2012 9:12 am

Vacuum leaks have helped sell a lot of un-needed parts. Best way is to replace all the vacuum hoses, and remove all the guess-work and future problems.
Using an un-lit propane torch along the manifold & carb gaskets works good too, and maybe less messy than gas, (dangerous), WD-40 etc.

by WyldeBill66 Mon Oct 29, 2012 8:19 pm

I just read another post that makes me ask another question. The car is running an electric fuel pump, and the second line which I believe is the vent line back to the tank is just plugged off since it isn't used now. Would that cause the tank to basically cause a vacuum and not let fuel out of the tank at higher RPM's?

by JB2wheeler Mon Oct 29, 2012 9:32 pm

Do you have a vented gas cap? JB

by WyldeBill66 Mon Oct 29, 2012 9:39 pm

I have the stock cap it looks like, but I haven't gone out and looked at it yet to see if it's vented.

by ant7377 Tue Oct 30, 2012 12:52 pm

Try running it without a cap ,see what happens.

by pila Tue Oct 30, 2012 9:44 pm

If you don't have the canister up front anymore, where the 1/4 inch vent line was originally hooked up, at least open the end of the vent line & plumb in a 1/4 inch fuel filter on the end of it. with a short section of hose. It will allow the tank to vent, & the filter will keep debris out of the line. Does your tank unit have the 5/16 inch return line ? Some do, and some don't...

by WyldeBill66 Tue Oct 30, 2012 11:27 pm

It ran better tonight, but I didn't get a chance to push it. I'll take it out this weekend and see what it does. The return line is plugged off, but I may get a fuel filter to go in it just to let it vent properly. What if I drilled a small hole in the stock cap to let it vent there?

by JB2wheeler Wed Oct 31, 2012 1:25 pm

WyldeBill66 wrote:It ran better tonight, but I didn't get a chance to push it. I'll take it out this weekend and see what it does. The return line is plugged off, but I may get a fuel filter to go in it just to let it vent properly. What if I drilled a small hole in the stock cap to let it vent there?

No, don't drill the cap. Just try what ant7377 said about trying it with the cap off and see what it does and that will tell you whither you have that issue or not. Then do the right solution once you find what the trouble is or is not. JB

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