Engine running trouble with Chevy 350

Hello all. I am a new comer here in search for some assistance. I have a 67 Nova SS with a 355ci, fenderwell Hooker headers, Holley 650 double pumper, Edelbrock Performer intake, Fuelie 2.02 heads, TRW flat tops and a Vertex Magneto. The car is kept mostly in storage, sometimes for months at a time, and has seemed to develop a new problem. I noticed that the engine was running a little rough and figured that it was misfiring from a set of fouled plugs or something. So I changed the plugs, although they looked fine. Needless to say the problem still exists. I figured that maybe it might be the carb. The carb is old and beat and needs replacing regardless, but I haven't had the chance to do that yet. The more I drive it the more I think that maybe it's not the carb but the Vertex Magneto that’s causing the trouble. The car appears to be misfiring at all times and even produces some small backfiring with normal driving behavior. It's at its worst around 2500-3000 RPM where it shakes the car vigorously and almost seems to fall on its face. My tach is also going synchronously insane at this point. Once I am passed 3000 RPM it returns to its "normal" crappiness. After sitting for a day or so I'll take it out and it appears to run better and even seems to improve the more I drive it, but once it sits for a few hours after that, it REALLY runs like crap. Is it possible that something in the Magneto could be causing this or do you think that I have a completely different issue altogether? The car sat for year in a fairly damp warehouse before this problem began. Any thoughts would be appreciated. Thanks.

did you try a deferent dist like a hei? or is the carb a holley with a bad power valve and bad gas ?

Right, 1'st thing ! Is that tach wire in any way hooked up the magneto grounding post ? That has the black bakelite screw sticking out the side of the magneto. It is only to be used as a grounding wire. NO OTHER WRES MUST BE ATTACHED TO IT !!!! AS IT WILL BURN OUT THE MAGNETO.

Because what your describing is that the magneto is overheating and is beginning to break down. The grounding post wire should go through a toggle switch 10 amp in the wire and it should go straight to ground flicking the switch to close turns off your engine. For your speedo you need a seperate magnetic pickup, they are available from Magsaurus. You will probably need to get your mag checked out for damage.

Pat-
I have not tried another distributor yet. I dont have one to try at the moment. I'll see if I can get my hands on one. I want to be sure that the mag is the issue before I buy a new distributor or choose to have the mag repaired. What would you recommend for a replacement distributor?

As far as the gas goes, I filled up with a fresh tank of gas and still have the issue. The power valve could be shot at this point but these symptoms seem to be pointing towards someting else.

Southerner-
My kill switch is the only thing connected to grounding post on the mag.

If it's an older DP and the engine has backfired you can almost be sure that the power vavle is blown. www.summit.com sells an inexpensive kit to solve that problem.

So do you feel that the power valve is the issue or do you think that its more involved than that?

Did you check the wiring up to your mag, did it have 1 wire coming of that P post or several ?

i would look at putting in a no blow back check valve in the base plate like said . put a new power valve in it or two if it as one in the rear then you need two kits for this carb i would run the msd if you are looking for a new dist if you want to keep the mag any dist will work to see if it is the mag is going south make sure if it is a roller cam engine that any dist you use must have a bronze gear on it and if the power valve is bad it will empty the bowls of the carb to check this take out the sight plug and it will be empty

The only wire connected to the post on the mag is the kill switch.

The carb has clear fuel bowl sight plugs. I usually rock the front end to check the fuel level. I did this recently when I was adjusting the fuel mixture on the carb and there was definitley fuel in the bowl.

Any other ideas? Any idea what component inside the mag could be causing the issue. I know that an ignition module will start to break up at hot tempatures once they go bad, but I am not sure what to look for in the mag. Is this mag even worth fixing if it is indeed the problem? Will I get better performance from an MSD?

Thanks for your help thus far!

Okay, you have looked at the mag and verified that it has one wire coming off the p post. Next, now this may sound a bit weird, remove the grounding wire from the p post and wire a tempory wire and toggle switch onto the p post. and ground the wire downend from the p post to the body or engine. what you are doing is checking that there is no phantom wiring coming off that ground wire further up the loom. Try that and see what your results are. S

Yep mags are 100% reliable they last for years if treated right. They are a self contained generating plant that operate on AC voltatage. So those platinum points will probably outlast the life on the engine. Since the power is AC there is no metal to metal transfer on the points.They were first designed for airplanes when the engineers understood what would happen to the pilot if the old kettering ignition system should fail !!!!!

Wouldn't that be eliminated by removing the wire from the post altogether? At one point I did remove the wire from the post but I still had the issue. I just had to reconnect it when I was ready to kill the motor.

At this stage it is probably not the magneto then. Notice that I said at this stage. THe next thing to consider what type of rev counter you have is it electronic or manual, with a cable comong out the back and going down to a drive gear. If the rev counter is electronic or electric, where does it get it's signal sorce ? This will mean tracing it back through the wiring. So the easy way to do this is to:

1 check what kind of rev counter it is

2 If electronic see if the maneto has an electronic pickup mounted on the side of the magneto

3 If it does not have an electronic pickup then you will have to search through the wiring to see where the signal sorce is.

I am using a magneto signal converter. It has been hooked up this way from the day one. Here is a diagram showing exactly how I have it connected. https://www.autometer.com/download_instruction/753A.pdf

This issue is so strange. Now you got me thinking that its the carb again. I need to replace it anyway. I am thinking about installing the Edelbrock (Carter AFB type) carb, not too sure what size yet, maybe 750cfm. I might even get rid of the mag too. Maybe an HEI or MSD to replace it. I would eventually like to install the Edelbrock top end performance kit so I wanna make sure that I purchase the right carb as it is not included in the kit.

750 is too big unless you have the cam and heads to support it. Put a new power valve in the DP and a blow out protection kit along with it and it'll probably solve your problems or put a 750 Eddy on it and create more.

I'll see if I can't pick up some power valves tomorrow and 2 blowout kits. I work right next to a speed shop so I'll head over there tomorrow.

Thanks for the advice from everyone. I'll let you guys know how I make out.

Autolite 86's at .025 or so.

drop your plug gaps down to .020, see what that does.

I agree with NTFDAY time to look at the carb, while you have it apart pull the secondary bowl off and check to see if it has a powervalve in the metering block as wel.

drop your plug gaps down to .020, see what that does.

I agree with NTFDAY time to look at the carb, while you have it apart pull the secondary bowl off and check to see if it has a powervalve in the metering block as wel.

Stupid question: have you replaced the plug wires? Sometimes it's the little things... Foul wires cause your timing to go haywire no matter what dizzy you use, and sitting for a year doesn't make your wires better. Check them.
Any cracked vac hoses? These can also cause your engine to run like the Dutch National football team...
Second:
Take off the carb and clean it (dissassemble and soak it in carb cleaner). recheck whether it runs better or not. Alternatively borrow a similar carb off a running vehicle (from a friend or steal it from somebody you don't like :D )
If that doesn't help it's not the carb, so buy a crate of beer and visit your friend again. Borrow his dizzy (if it's a HEI or a good running points type thing).
Mostly there's no need to dish out a chunk of greenies until you've found the problem.
I mostly look for the problem with borrowed parts (of which I know they work well) first before I start dismantling things for fun when I don't even know they're the cause of the problem...
If the car was in a really damp environment it's just possible that you have rust inside your engine, which will give you crappy running any time. Small burrs on the cylinder walls from long use won't catch oil and thus rust if exposed to dampness for a long time. This would mean a complete teardown... But that I guess is the worst case scenario...
I would check carb and ignition with borrowed stuff and come back here if it's none of this.
If you're not into racing this vehicle, don't go bigger than 650 cfm with the carb, i would even go for a 600 and a good manifold.
Hope I could help,
Max

[QUOTE=southerner]drop your plug gaps down to .020, see what that does.

Why .020? I would think that the mag puts out a pretty healthy spark and I believe I'd increase the gap to at least .035.

Thanks for the reply. I appreciate all your advice. The rust in the engine is an interesting though that I was afraid to even think about.

So here is where things stand. The engine really started to misfire the other day. This engine used to have a problem fouling the #8 spark plug when it was in my old car. So I pulled the #8 spark plug last night and sure enough it was soaked with gas. I replaced that plug as well as #6, although #6 was fine. I need a special wrench for #4 and #2 so I wasn't able to check them. I am sure that the carb is the culprit. I am definitely going to buy a new carb and distributor. Not just because of this issue but because I know the carb is crap and I'm not really liking the mag anymore.

Can I get a low profile HEI that will fit in a 2nd generation Nova? I know that some people get lucky with a regular HEI, as far as firewall clearance goes, but it doesn't look like I will be able to. I really dont feel like spending alot of money on an MSD and ignition box.

Let me also ask you this, I plan on installing the Edlebrock Top End kit in the near future. I dont want to have to buy a carb twice. Will I be able to run the Edelbrock 750cfm carb on what I currently have now so that it will work with the top end kit when I decide to do that?

1969 Chevy 355 (4 bolt main w/steel crank)
Vertex Magneto distributor (internal coil)
Holley 650cfm DP carb
Edlelbrock Performer intake
Fuelie 2.02 cyl heads
Comp Cams 280H cam
TRW 10.1 flat top pistons
Hooker fenderwell headers
Aluminized 3" exhaust with H pipe
Flowmaster mufflers
Muncie M20 4 speed trans

Thanks again for all your help

IMHO opinion what you have is pretty good for the street except for two things. Pull the 650 DP and put a good rebuild kit in with power valve blow out protection and start with 66 jets in the primary and 76 jets in the secondary and also buy a primary shooter kit and the kit with different accelerator pump cams. Then buy a good book that explains how to tune a Holley. I'd scrap the Edelbrock performer (I believe Edelbrock manifolds are over rated) and buy an Offenhauser 360* square bore manifold. Square bore Holleys run better on a square bore manifold than they do on a spread bore manifold. If you are dead set on running aluminium heads that is fine, but iron heads like you have will work well on the street if they have hardened valve seats, a good three angle valve job, and springs to match the cam.

I agree. I never wanted that Performer manifold on there to begin with. It was the only manifold that would fit. I had my heads decked (I hope it was the heads and not the block) and after that it wouldn't accept even a brand new Edelbrock Performer RPM that I purchased. The bolt holes wouldn't line up. I can't remember why the heads/block were decked. Kinda strange that the performer even fits :confused: My intake ports may even be off some....that not good!!!

I dont think that I am going to rebuild the Holley. Its just not worth the effort to me. This particular carb is crap. I dont even think that the metering plates are the original :LOL: . I would just rather put a brand new carb on it. It doesn't have to be an Edelbrock but I heard some good things about them so I figured that I would go with it since I didn't have much luck with the Holley. Nothing against Holley at all. As a mtter of fact I might even consider getting a direct replacement for what I have now.

So you think that 650 is a good cfm even if I plan on changing the heads?

I will highly consider your advice. Thanks for all your help.

A few years ago I ran a pretty much stock 400sbc in a '62 pickup. It had an old Isky 30/30 solid lifter cam ( basically the same cam in a '64 375 hp Vette), Offy 360* hi rise manifold, 650 DP, and hedman headers hooked up to a 3 speed. It ran pretty good for the weight. Top end wasn't much, but it was killer stop light to stop light.

Do you want to sell that mag then ?

You can run smaller gaps with the magneto ignition because the AC voltage generates a hotter spark. So you can close up the gap and save your plug wires.

Quote:

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Originally Posted by DennyW

Not argueing with you, but I thought the purpose of a mag is the increased voltage to burn the fuel at the regular gap. Decreasing the gap gives you a fatter spark, but also is closes the ignition gap. My Judson puts out 70,000 volts, compared to a stock, or hi power coil of 40,000 volts. Never had a mis fire, even at 6200. And I'm still running dual points. :)

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sorry I just have to ask the question what type of ignition is a judson ?:confused:

HMMMMMMMMM interesring, so by looking at it , it repces the original coil and it goes to a normal distributor. looks fairly robust with that big heat sink to dissipate the heat.

I'll bet it is to all awnsers, ever been tickled by it ? 70 Kv that should put you into orbit quite nicely. So with it being transistor fired does it still use the old points as the trigger or is it electronically triggered as well, oh hang on you have had it since the 70's so it would still be points fired at the distributor. What is the voltage AC or DC because I am not sure if electronic circuits use either ac or dc voltages.

Exactly when did judson design this system ? I am just wondering at the possibilities that chrysler copied the idea of Judson. So TV's are dc then ! I'll take your word for it the only part of a TV I want to see is the frount. As I say to an often quoted phrase at work. You go HEAD AND DO YOUR WIRING, i'LL STICK TO MY DIESILS.

Sure looks pretty complicated in there, is there anything you cant do ?

:cool:
Yeah well I am more the mechanical bent, thats my baby, mainly like making things, so go pretty well with the welding and believe it or not carpentry as in house modifications or building. Pretty good at whacking up a bigger garage to.:rolleyes: :LOL: :LOL:

Another thing to think about: I know I'm always the one for worst case scenarios :LOL:
Are you sure the #8 plug is being fouled by gas? It might be that your heads have a crack. Then the plugs would foul very fast and they would smell of gas, because the cylinder won't fire with water in it, so you have unburnt gas and water on the plug. Looks really yucky and stinks to high heaven AND means you'll have to tear the engine down. To test this quickly take out #8 plug and spin the engine. Hold a piece of card near the plug hole and see if anything comes out. Water will most probably spatter out if there's any in your angine, gas won't spatter, because it's distributed finer. Even small amounts of water standing in on cylinder for only about a week will ruin any engine. I had that happen to me on a 3 year old rebuild I bought (not my rebuild:3dSMILE: )
Do a compression check! If your cylinders vary by more than a couple of points, then you'll have to at least pull the heads and give it new gaskets. Otherwise you'll seriously damage something.
Holleys are very good carbs, but not so easy to tune and deal with in general as for example Edelbrocks.
As I said earlier, first check everything and try to find the error BEFORE you spend any large money on parts you wouldn't have needed in the end...
As always, that's just my opinion...
Hope this helps,
Max

PS: Give us your compression results on all cylinders if your not sure if they're good or not. A compression test will give you a rubish reading in all sorts of cases: Rust anywhere on the cylinder wall, cracks anywhere, blown or weak head gaskets, valves not seating, rings worn... Almost all internal engine faults will show up on a comp test, the test will only be perfect if all internals are in perfect order.

I appreciate your thoughts MadMax. I don't belive that there is water in the engine. The oil would be "milkshake" like....yes? The fouling of #8 does not happen all the time. This is the first time that this occurred with the engine being in this car for over 3 years now.

I want to buy a new carb and distributor anyway, definitely carb first, so I am not too concerned about the $$$ although I appreciate the advice.

Thanks

It's never a bad thing to buy new things, I do that myself all the time :)
Just sometimes you don't have to go that way. Water in the engine won't neccesarily cause your oil to go milkshake. Not at once, only over a longer period. I only noticed after a thousand miles or so of using my "new" engine. And as I said, it's only a thought, and it's never a bad idea to do a comp test, just to be on the safe side. But of course it's your free choice :)
Best of luck,
Max