Weber Carbs and Pertronix ignition

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Dean, an accurate diagnose of the problem is almost impossible with just the information you've given. There are just too many possible causes.

But, if you're starting your sleuthing from scratch, most gurus would say check for reliable ignition across the full rev range first before monkeying with the carbs.

That said, hooking up a timing light is a good place to start. Besides checking your max advance (at about 3000 rpm), it will tell you (more importantly) how consistent  the spark is across the rev range from idle all the way up. Modern distributors from many makers may wear fancy labels, but are often based on inexpensive mechanicals of dubious origins and are famous for weak spots at certain speeds. Hook up the light, slowly  advance the revs, and check to see if the timing mark disappears somewhere along the way.

That said, electronic bits, like coils and electronic distributor modules are sensitive to heat, and moreso as they age. They'll be fine at startup, act up when hot, and then be fine again when cooled back down.

If you don't have a timing light, getting one is a good idea in general, as it's something you should be using often with an engine like this. You don't need anything fancy. An old-school $25 wonder will tell you pretty much everything you need to know.

Tell us a little more about the history of this problem. Has this engine configuration always run this way? If not, when did it change? How long have you had it and how much do you drive?

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Impossible to diagnose over the internet IMHO. Follow Mitch's advice above.

We had this same problem with Bruce Stumpp's car when tuning it. It had such low compression it simply needed MORE timing advance, about 5 degrees more. It was a 1776cc, basically a small increase over a stock 1588cc. Try that, and if it pings(very bad:detonation) back it off immediately.

95% of "carb problems" are ignition problems. Fact.

While I agree with all the comments up above, would it be possible to swap out your distributor for whatever was in there before?

At least you could eliminate or confirm a potential cause of the stutter.  If going to a different distributor/electronic module makes the stuttering go away, then you know where to look.  If, OTOH, nothing changes then you can begin looking at the carbs.

It seems counterintuitive, but Gordon is 100% right - sooner or later, everybody ends up with a set of ignition components which are "known good". You'd think you could just buy new parts and know that the new stuff is good - but you can't and you don't.

It might not be the stuff you want to run long term for one reason or another - but having a good spare set of everything is important.

Good luck. Forewarned is forearmed.

Guys, Thanks for the great input. I checked the distributor, since there is only one mark on the pulley at top dead center, it is hard to take a tape measure to get 5 BTC, I also check at 3,500 rpm's to get 30-35 degrees, unless someone can give me any other ideas, I am going to go back to the points, condenser and ignition coil and see if that works, remember, this only happens as the engine heats up.

Thanks again

@Dean

Forgetabout that 5º number.  That's only used when setting up a vacuum advance distributor at engine idle.  Your MagnaSpark is a Centrifugal advance distributor and must be set with the engine running at 3,000 rpm, giving maximum advance at 30º-32º at that engine speed.  So you bring it up to speed and then rotate the disti until you see it land on 30-32º.  That's how it works.

How to do that with your crankshaft pulley:

Line up your Top Dead Center scribe line on the crank pulley at the top (12 o'clock)

Then using a straightedge ruler, measure straight over to the right from the TDC line 1"-24/32"   Don't measure around the circumference, just go straight across.

Put a Sharpie mark on the pulley right there.  THAT is 30º advance.

If you want 32º advance, go to 1"-26/32"

Measure straight across.  DO NOT measure around the circumference (but don't worry - If you do, nothing is gonna blow up or anything).

Good luck.

I thought this was wasted on my Spyder where you couldn’t see it. Lol.

Until I had to set a new set of points.  I took the opportunity to mark TDC and BDC with a yellow paint pen, and 5° and 30° with an orange one on the edge where I could shine my timing light down from the top.

I used a punch on the edge of the pulley, 1 punch at 10, 2 at 20, etc.

Now there is a file mark at 35 and 37 on my Vee engine, so you can set it at 35,36,or 37 total advance depending on how it's running. Yes, we run that much timing at 7.3:1 compression.

Which is why I suggested adding more timing to Dean. I had set Bruce Stumpp's car at 30 degrees, and it wasn't enough. Being a low-compression 1776, it needed more and had an AWFUL hesitation between 1500 and 2500 rpm. Advanced the timing 5 degrees and it all went away.

@Dean as Gordon says, completely IGNORE the 5 degree mark. It means nothing on a centrifugal advance distributor. The only thing that matters is total advance and how the car runs. You want the most advance your engine will tolerate without pinging. That's where you get best performance.

I had a thought or two. Since Dean has a 356/912 engine, we all know his crank pulley is NOT a standard VW diameter. So following that, Gordon's distance per degree measurement may not be correct.

It's a simple formula to do this. Circumference = Diameter x pi(I use 3.141592654 yes, I rounded last digit up). Measure the diameter as accurately as possible, then multiply with pi. HINT: It's a lot easier to use a metric ruler if you want accurate results without doing decimal to fractional/inch conversions.

Take that answer and multiply by say 30 and 35 degrees. Measure accurately clockwise from zero(TDC) and make some marks. Set the timing, test drive, re-set, and you're DONE.

The cool thing is this will work for ANY pulley diameter.

Basic geometry used in everyday life. I use trigonometry too when I do an alignment. Math, one of the only things from school I still use today!

Somewhere in the dim recesses of my mind, I remember Glenn Ring saying that Porsche pushrod 4-cylinders like timing brought in more quickly than a T1.

There are adjustable distributors out there. You can adjust total timing and how quickly it comes in with a MagnaSpark and various others (MSD?). I don't know if it's possible to adjust the timing curve with this Pertronix, but I'd watch the spark curve all the way up before I made a blanket statement.

Given the legendary QC of Pertonix (/s), it's possible (likely?) that the curve of the Pertronix doesn't bring enough timing in fast enough. We keep telling @Dean that initial timing doesn't matter, that it's only the total timing - but the timing at idle and just off is where his issue is.

I've got no idea what his engine will tolerate for total timing, but in my experience, detonation happens under heavy load, between 2000 and 3000 RPM. It's possible that Danny is right and the engine would be perfectly happy with 35+* of total timing.

Ideally, I think he wants to see at least 20+* of timing at 2000 RPM. I'd watch there - set it at 20* at 2000 RPM, then check where total advance falls, and where idle advance is. If things are out of whack, I'd adjust the distributor curve to bring things back in line. I'd think 25* of total advance (pull) would be pretty close to ideal, with 5* at idle and 30* all in - but perhaps 20* of pull would be OK, with 10* at idle and 30* all in, or 30* of total advance (pull) with 5* at idle and 35* all in... as long as it's at about 20- 25* at 2000 RPM.

There's a bit more to it than just set and forget.

Stan, you are exactly right. When the timing comes in and by how much can make a HUGE difference in the mid-range.

I'm going to assume here but I think Dean took the points out AND did the Pertronix module, along with the coil. So I believe the distributor was NOT changed. And we don't know exactly what distributor is in there. I may be wrong but in the initial post it sounded like Webers were also added at the same time. Only Dean can clarify this. I will add that one should only make ONE major change at a time, makes troubleshooting later a crap-ton easier.

I don't believe Dean ever said he had a Magnaspark. He has a Pertronix module and Pertronix coil.

@DannyP posted:

I don't believe Dean ever said he had a Magnaspark. He has a Pertronix module and Pertronix coil.

I know he doesn't have a MagnaSpark (or MSD) - I was just pointing out that those distributors have adjustable curves. It was my understanding that his distributor was a Pertronix, not just a Bosch 009 or Bosch 009 copy with a Pertonix module - but I could be 100% wrong there as well.

This hobby would be so much better served with better distributors in universal use, as opposed to the terrible 009 copies out there by the thousands. 

It wasn't you, Stan.

I would like to know what he does have: full engine/carb specs and WHEN everything was installed and WHEN the problems started. Also which coil, wires, cap, etc....the WHOLE ignition system.

It could be as simple as Iridium plugs and their gap. I use REGULAR NGK as that is what the original builder recommended.

And then there is the thing with the Flamethrower coil low resistance which might possibly be overheating the points replacement module.

One of the Speeduino guys just came out with an ignition only version. It's pretty small(pack of cigarette size)and will directly drive smart coils. Get Mario's trigger wheel and sensor, a coil and BAMMMMMMM! With 4 individual coils, wasted spark COP. You could even do sequential with a cam position sensor.

I bet it could be done(I could do it for sure) for less than $150 total investment per car.

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Gentlemen, gentlemen, please!

It's too early on a Sunday morning for this squabbling.

First, Dean was pretty clear about what he did. He put in the "Pertronix  9847A ignition 2" and the "flame thrower 2" coil.

Which are these:

(I think he left out the '1' in the middle of what Pertronix calls its "91847A" module.)

So, he kept whatever dizzy was already installed and just swapped out the module for the points.

Second, he's pretty clear about the 'popping' problem being intermittent. It's only there when the engine is hot. So, if the advance curve isn't the best, it's not bad enough to cause popping when the engine is cold. And swapping just the module wouldn't have changed the shape of the advance curve.

What he has changed are the two ignition elements most likely to be affected by heat, though.

And he has in hand (as Gordon suggested)  the old parts to go back to.

So, I would suggest he go back, one part at a time, to see which part makes the popping go away.

And then, maybe tell us why he started swapping out ignition bits to begin with.

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If I set 30 degrees at 3000 rpm it seems like I could have greater advance at higher rpm.

@Michael McKelvey posted:

If I set 30 degrees at 3000 rpm it seems like I could have greater advance at higher rpm.

It would continue to advance if there weren't stops  to keep it from doing so.

Yeah, but why would it stop at 3000 rpm?

I think I set it at max. advance at whatever rpm.

I guess it is time to get out my timing light.

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Came across a thread on a P-Car forum where Glenn Ring described the mechanism in a Bosch distributor that limits advance.

Apparently, a steel pin moves, side-to-side, inside a hole drilled into another piece. That limits the total advance for that distributor. So, if that's 25 degrees of advance and you set idle advance to five degrees, max advance will be 30 degrees, period.

He says folks will often increase that range by either drilling out the hole a little larger or filing down the diameter of the pin.

The Magnaspark lets you change the maximum range of advance a lot easier with a series of different diameter collars (if memory serves), and you have the option of steepening the curve with different strength (supplied) springs.

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I have a Mallory distributor.  I don't recall where the stop is.  I have changed the springs.

It seems like the strength of the spring and any weights determine at what rpm max. advance occurs.

To reach the stop it seems like the distributor would have to be spinning fast enough to overcome the springs.  I don't understand how the springs happen to be overcome at 3000 rpm.  It seems like the springs might be strong enough that it would have to spin faster to reach the stop.

Do commonly used distributors just happen to have springs that allow the distributor to reach the stop at exactly 3000 rpm?

Michael, 3000 rpm is the number we use because MOST distributors are all-in by that rpm. Some require 3500 or 4000, which is why you check for max advance with a timing light. Then you'll know what rpm you need for YOU.

Mitch, I knew what parts Dean installed. I want to know the REST.

@DannyP, you seem to confirm what I thought.  You seem to say I can ignore the tach and just set it for max. advance.  I would just rotate the distributor until it hits max. advance and no more.

Kind of. Just make a note of what rpm your advance maxes out at. For future reference, if anything changes you'll have a way to check.

For reference, I went through over 40  10 x 10 ignition maps when I tweaked my Megajolt. It's a lot more complicated(read that time-consuming) than two or three advance springs LOL! Thankfully, it translated easily to the Speeduino, just made the map 16 x 16 instead. Easy peasy: Start with the highs and the lows and interpolate the rest using the Tunerstudio software.

@Stan Galat posted:

This hobby would be so much better served with better distributors in universal use, as opposed to the terrible 009 copies out there by the thousands.

Glen and Ed can both make perfectly good distributors. Problem is most eschew the cost. Ed turned my Brazilian 009 into a great distributor with a perfect factory curve while I waited for him to finish rebuilding an original German 009. IIRC, he told me he could modify just about anything but the most recent Chinese 009s.

He even set my points. Popped it in and it was perfect 5° at idle and 31° max advance.

BTW:

plus

= Period correct-looking Coil. That what I’ve got on my Spyder. The Flame Thrower label comes right off with a little bit of heat.

https://www.ebay.com/itm/16341...temis&media=COPY

Guys, thank again for all the great advise, what I diddn't mention was the distridutor I have, it's an Bosch 050. I will try advancing the dwell more, but being that this problem only happens when the engine is heating up, I don't mean overheating, I just mean it is no longer cold, when starting up ( good) and when I take the first 15 minute ride all is good, then it happens.

Thanks

5 bucks and a donut says it's the module.

I'm with @Stan Galat on the module..  and with @Gordon Nichols on swapping back in old parts to determine problem. 

Historical example:

I had a '81 Maxima.  ran fine until it got good and warmed up.  Then it would cut OFF every time it dropped to idle (so a lot with a 5spd and city traffic).   Took it to a specialist and all the way there it acted up.  He put an ignition light on it and we went for a drive.  It did not act up... until we pulled in the parking lot, it cut off.  He says "Ok, I got good news and bad news.  I know what it is. (that's the good) Its an ignition module and its expensive (that's the bad).  The ignition control module on that car is a 'electronics potted in a box' & mounted to the side of the distributor so it gets heat build up from the head.  (really smart)  --   so being me, after replacing the module (and $400 1989 dollars lighter) I stuck the module in the ol'box-o-spares bin that I keep for no reason other than "know what this does".  About 6months later my Parents '83 Maxima started not being able to rev past 3K rpm..  hmm this sounds ignition control related... where's that old  module... swap out, go for test drive, and motor zooms past 3k all the way to 6500 for gears 1 & 2,  then cuts off when it drops to idle at a stop sign before I could get home...  I tell my Step-dad "I got good news and bad news.. "

@Wrenn Smith

It could-a been worse.  Same thing failed on my Ford F250 Diesel, but that module is a $1,600 tid-bit.

Good to see I'm not the only hoarder or "old part swapper" on here!

@Gordon Nichols posted:

@Wrenn Smith

It could-a been worse.  Same thing failed on my Ford F250 Diesel, but that module is a $1,600 tid-bit.

Good to see I'm not the only hoarder or "old part swapper" on here!

Wait… the ignition module on your diesel died?!? That’s some weird diesel.

I though it was a cam position sensor, Gordon.

@Lane Anderson

That was on Chris’ F250 at Carlisle one year.  Much easier and less expensive fix.

@Stan Galat

Mine was an ECU Equivalent.

On the diesel it’s called a “FICM” for “Fuel Injection Computer Module”.

It does all of the engine management that a gas engine ECU does at 4X the cost.

It also sits right up on top of the engine where it becomes a big heat sink.  It’s one of the “top five” Ford diesel engine failures.

That 6.0 Powerstroke was not Ford’s highpoint.

Yeah, when it was running right, it was awesome, but the Ford 7.3, the Cummins and the Duramax were all so much better.

I used to think that the newer Ford 6.7 had improved on all of those five major faults, but recent info makes me question that.  A lot.

It should be no wonder that I sold it and bought a gas car that took 75% less $$$ to run it!

@Gordon Nichols posted:

Yeah, when it was running right, it was awesome, but the Ford 7.3, the Cummins and the Duramax were all so much better.

I used to think that the newer Ford 6.7 had improved on all of those five major faults, but recent info makes me question that.  A lot.

It should be no wonder that I sold it and bought a gas car that took 75% less $$$ to run it!

I had the 7.3. The day I bought it, a friend said, it'll be a love/hate relationship. I had no idea what he meant - everything was awesome! Then the warranty ran out and it needed $1500 worth of work every couple of months. Ditto the Mercedes diesel in my Sprinter.

Duramax or Cummins - all the way.