c2 surging

[Mark F.]

I need help. Just finished with a complete chasis restoration on an 67 L36. During its first test drive, I had after fire (popping) lilke no tomorrow. I went over the timng and the carb two or three hundred times already. I have it to were I can drive the car. But every once an a while I get a pop out of the exhaust (one side). The car seems to be surging. The plugs read good, there new ac delcos, (tan). Timing is set at 10* intial. It happens at about 40mph at approx 1500- 2000 rpm. very light throttle. Car idles perfectly 600rpms it will free rev with no problem.
I have removed the points previously and installed one of the electronic conversion kits years ago on it. Never touched it since then. I have added the coil capicitor (+ side) for the radio this time around. Could this be giving me the problem. The reason I ask that is based on what I have read. Capicitors did not come on TI cars. This is a points car, not a TI car. However, with the elctronic Igniton, I'm wondering if this is some how effecting my coil. Which in turn is effecting my secondary ignition.

What I Have: Same new holley carb used for two years
same distributor -untouched
same engine untouched during the process.

[Joe C.]

Re: c2 surging

I need help. Just finished with a complete chasis restoration on an 67 L36. During its first test drive, I had after fire (popping) lilke no tomorrow. I went over the timng and the carb two or three hundred times already. I have it to were I can drive the car. But every once an a while I get a pop out of the exhaust (one side). The car seems to be surging. The plugs read good, there new ac delcos, (tan). Timing is set at 10* intial. It happens at about 40mph at approx 1500- 2000 rpm. very light throttle. Car idles perfectly 600rpms it will free rev with no problem.
I have removed the points previously and installed one of the electronic conversion kits years ago on it. Never touched it since then. I have added the coil capicitor (+ side) for the radio this time around. Could this be giving me the problem. The reason I ask that is based on what I have read. Capicitors did not come on TI cars. This is a points car, not a TI car. However, with the elctronic Igniton, I'm wondering if this is some how effecting my coil. Which in turn is effecting my secondary ignition.

What I Have: Same new holley carb used for two years
same distributor -untouched
same engine untouched during the process.

Make sure that the MAIN air bleed on the offending side did not get any debris in it during the restoration. Blocked/restricted air bleeds will cause poor fuel emulsion and resulting rich condition leading to afterfire.

A less likely scenario would be an exhaust leak on the offending side.

Joe

[Mark F.]

Re: c2 surging

I don't have any obvious exhaust leak. Nothing really loud. Maybe a minor one at best. I went through the air bleeds. Actually , I took both bowls and metering blocks off. Blew out both with comressed air. Also blew out the air bleeds. Any way for sure to check the air bleeds?

[Joe C.]

Re: c2 surging

Submerge metering block in solvent or gasoline. Blow compressed air into bleed hole. Check for bubbles out of ports connecting to float bowl and booster nozzle.
If the carb was well covered or removed during restoration, then there's no need to knock yourself out checking any further.
Does the engine have K19, air injection reactor?

[Mark F.]

Re: c2 surging

NO A.I.R.
I did have the carb. covered, during the process. Not air tight but covered with rags/plastic.

[Joe C.]

Re: c2 surging

Mark,

I've been thinking about the noise suppression cap on the coil, and don't believe that to be a problem. Besides, I suspect that you've temporarily removed it but to no avail.

Technically, I don't think that you have a "transistorized" ignition. You probably have one of the "Hall effect" transducers, such as Pertronics, Breakerless SE, or similar. I have the coil capacitor still installed on an old, original 202 coil, with Breakerless SE, and I have NO ignition problems whatsoever, up to and beyond 7000 RPM.

I also assume that your air and fuel filters are not restricted, and that your fuel pump is supplying 5-6 psi pressure.

What has me baffled is that you seem to be reporting two conditions that result from opposing causes:
Afterfire, or popping out the exhaust is caused by unburned fuel igniting in the tailpipe, and is a result of rich mixture.
Surging, or a "flat spot" is generally caused by a lean mixture. It is possible that the throttle plates aren't adjusted properly, resulting in a lean transient in going from idle to off-idle and before the main venturi boosters begin to take over. Check the idle transfer slots on the primary side, and be sure that they are adjusted properly. If you don't know how to do this, get back and I'll advise, or check the archives.

Joe

[Duke W.]

Re: c2 surging

Mark,


Afterfire, or popping out the exhaust is caused by unburned fuel igniting in the tailpipe, and is a result of rich mixture.


Joe

No, if the mixture is beyond the lean ignition limit, the cylinder can misfire then the mixture ignites in the exhaust system causing the afterfire. Another common cause is a burned valve, but that's probably not the case here if it idles okay. A very overly rich mixture will usually ignite, but create black smoke.

I would suggest checking all electrical connectors and installing a set of points to see if the "electronic conversion unit" is the culprit. I've never understood why people install these things. One benefit of vintage cars is that they are SIMPLE - no black boxes to choke and puke.

Then check the float level.

Is the "new Holley" and exact OE replacement configured to GM specs? If no electrical fault it found, I would disassemble the carb and check jets, etc. to verify if it is calibrated correctly, and thoroughly "boil out" the carb. The problem could be in the off idle system, which has a lot of small passages and air bleeds. They could have deposit buildup. An improper float level that results in too low fuel level in the bowls can lean out the transistion from the off-idle to main system resulting in a lean mixture.

If it doesn't surge at freeway speed, the main jets probably not the problem.

Duke

[Randy R.]

Re: c2 surging

Have you checked the order of the spark plug wires?

[Joe C.]

Re: c2 surging

No, if the mixture is beyond the lean ignition limit, the cylinder can misfire then the mixture ignites in the exhaust system causing the afterfire. Another common cause is a burned valve, but that's probably not the case here if it idles okay. A very overly rich mixture will usually ignite, but create black smoke.

I would suggest checking all electrical connectors and installing a set of points to see if the "electronic conversion unit" is the culprit. I've never understood why people install these things. One benefit of vintage cars is that they are SIMPLE - no black boxes to choke and puke.

Then check the float level.

Is the "new Holley" and exact OE replacement configured to GM specs? If no electrical fault it found, I would disassemble the carb and check jets, etc. to verify if it is calibrated correctly, and thoroughly "boil out" the carb. The problem could be in the off idle system, which has a lot of small passages and air bleeds. They could have deposit buildup. An improper float level that results in too low fuel level in the bowls can lean out the transistion from the off-idle to main system resulting in a lean mixture.

If it doesn't surge at freeway speed, the main jets probably not the problem.

Duke

He didn't report a lean misfire, and a lean misfire will also mimic an overly rich condition by creating excess HC emissions (watery eyes and nasty fumes).

I don't see why the ignition system would be at fault if the problem presents at low engine speeds and loads. Normally an ignition fault would present under load, and get worse as the engine (and coil) heats up.

Good idea to check the floats. He reports having adjusted the carb numerous times, but did not specifically mention the floats.

Reports runs OK at cruise, so main jets should be OK. Problem presents during transition from off idle to main systems.

[Timothy B.]

Re: c2 surging

Mark,

If the ignition is one of those Petronics 3 units I can't offer any advice.

Start the car and let it warm good then turn the idle RPM set screw to increase RPM through the spot you report surging pop etc. If you have a transistion problem from idle to main metering circuit it may reveil itself.

If so, try to open the emulsion A/F screws another 1/4 turn to richen curb idle and this may be enough, keep both sides balanced approx the same. If this does not work then there could be internal vacuum leak in the carburetor. If the carburetor sat for a while without gasoline a gasket may be leaking. Nice Holley carburetors!! What # Holley is on the engine??

Don't rule out a bad spark plug or wire!!! Take them off one at a time if you can recreate that spot to see if you can isolate the cylinder. Also, check to be sure there are no egg shaped hoses causing vacuum leak like the one that plugs to the vacuum can etc.

[Mark F.]

Re: c2 surging

Guys thanks for all your advice. I have found the culprit. Car runs excellent now. The wire for the electronic pick up in the distributor was hitting the advance plate. As the advance plate would try to rotate the wire was bounding up the plate where it enters/exits the housing and goes around the vac. Rerouted the wire . BINGO! Car runs great. Carb flawless. Good night sleep.......priceless.

[Stuart F.]

Re: c2 surging

Had the same problem years ago with a Prestolite kit (Wards). The insulation on the wires to the sensor had become stiff and brittle after some time which restricted the movement of the plate. I had to replace them with Silicon jacketed wires to make it work right. Restriction of plate movement or plate tipping due to bushing wear can be a real hard thing to diagnose, and that can occur with points or electronic "Hall" effect pickups. I know because I have experienced both.

Stu fox

[Jack H.]

Re: c2 surging

There are several 'attraction' aspects to folks wanting electronic ignition. Here are three that I've encountered, Duke:

(1) Owner believes he's making a 'hot' car for bona fide competition use (drag strip or wheel to wheel) and thinks it needs the rev limiter feature some of the electronic ignition systems have built in to protect their investment in the classic engine from over-rev situations.

(2) Owner is simply used to today's electronic ignition systems and that's what he/she wants...

(3) Owner is a typical 'weekend warrior' putting very little annual mileage on the car. So, when he/she pulls it from storage for that occassional drive, the last thing they want to do is to 'squander' time tweaking the ignition to achieve peak performance.

[Timothy B.]

Re: c2 surging

I installed the breakerless SE ignition on my 67 and I love it. The car really does not run any better but to me the idle seems better without any skips.

Super easy to install and most importantly it's made to work with all stock componets..

[Joe C.]

Re: c2 surging

There are several 'attraction' aspects to folks wanting electronic ignition. Here are three that I've encountered, Duke:

(1) Owner believes he's making a 'hot' car for bona fide competition use (drag strip or wheel to wheel) and thinks it needs the rev limiter feature some of the electronic ignition systems have built in to protect their investment in the classic engine from over-rev situations.

(2) Owner is simply used to today's electronic ignition systems and that's what he/she wants...

(3) Owner is a typical 'weekend warrior' putting very little annual mileage on the car. So, when he/she pulls it from storage for that occassional drive, the last thing they want to do is to 'squander' time tweaking the ignition to achieve peak performance.

Hi Jack,

I agree fully with your third point, above, because with the Hall Effect system, the primary side of the ignition is always delivering peak performance. This amounts to no special, magic bullet, and adds no "horsepower" to a mechanical trigger (primary side) ignition system that happens to be in a top state of tune at the time of comparison. What it DOES do, by virtue of the above, is provide additional "margin" for deteriorated secondary ignition system components. It also eliminates the need for high spring tension points on SHP engines where points bounce can be a problem with standard tension points. The problem with higher spring tension points, is that the additional pressure causes faster wear on both the rubbing block, and to a lesser degree, the points cam. High tension points require more frequent adjustment/replacement than standard tension points. The Hall Effect triggers also feature "adaptive dwell", which keeps dwell angle constant, beyond 10,000 RPM, thereby maintaining constant secondary voltage of about 10KV. Conventional points (and you can explain it better than I can) cause voltage to drop off, and by the time 6-7000 RPM is reached, voltage is significantly less than (about) 10 KV. This is where the "margin" comes into play, so that even with a properly adjusted set of points, any deficiency in the secondary system will be the cause of misfire.

As far as your first point, above...............I can honestly say that I NO LONGER HAVE a built-in rev limiter because of the Breakerless SE. If I'm not careful (as I have found out on a couple occasions), I can easily over rev the engine well past 7500 RPM with no misfire.