Unsolvable stutter/hesitation under load while driving...

[Ljrig]

Hey guys, been a while since I have posted on here but I am always reading on here. Just turns out that this time I cant find the information I am looking for.

So... In my 1970 standard I have a 2027cc engine with a stroker crank, 1.25 rockers, cam, single Empi HPMX 44 carb, etc. So I recently had the engine out to replace the transmission with a late model tranny, while I had the engine out I added a full flow system using CB Performance's MAXI30 oil pump and cover, stainless lines and AN fittings, additional external oil cooler, oil temp/press. sensors and gauges, the works. Since doing this and putting the engine back in, somehow/someway the engine has developed a bad misfire and stutter while accelerating under load, and at random points while cruising just maintaining speed you can hear one or two of the cylinders missing here and there...

So far I have tried different plugs (making sure the proper gap was set), tried different plug wires, a different distributor and ignition puck (now have the Empi Accu-Fire in it), put a different coil in it (currently it has a pertronix flame thrower 3.0 ohm epoxy filled coil), I made sure the valves were all set and not tight (the gap is set at .008), I have made sure all the wiring is nice and neat and no wires are broken or anything, and most recently I put in an MSD Street-Fire ignition box in it in hopes of giving it more accurately controlled (and hotter) spark to get rid of the hesitation, but nothing has worked.

Also today I checked the plugs and they were slightly fouled, after I put the MSD box in I cleaned the plugs re-set the plug gap from .025 to .035 and the engine stutter SLIGHTLY improved (I think) but not by very much...

What else could i possibly do???

[VW_Jimbo]

Picture?
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[Ljrig]

What, just a picture of the engine bay? I don't have an updated pic of it with everything added, I will have to get a pic of it in the morning.

[VW_Jimbo]

[ashman40]

You seem to have described everything but the distributor. What make and model distributor are you running? How have you set the timing?

You mentioned cleaning the spark plugs. What method did you use? I have found the only good way to clean spark plugs is to use a dry media blast (pneumatic spark plug cleaner). If you used anything metal (eg. wire brush) to clean the fouling off the spark plug/insulator you may have opened a path for the spark to ground w/o jumping the electrode gap. Basically creating a misfire. If you cannot clean the plugs with dry media (glass bead) then just replace the plugs with new ones when they foul.

The MSD ignition is a CDI ignition system and produces very high voltage in the secondary circuit. This means the voltage passing thru the distributor and plug wires will be much higher than originally designed. The 3-ohm Pertronix coil is probably not the best coil for use with a CDI ignition. While it is not required, a coil with lower resistance will generate higher secondary current.
The MSD instructions call for non-solid core plug wires. Are you running spiral cored wires?
You should also run your engine in the dark and look for stray sparks at higher rpms. This would show where the sparks are jumping to ground. Spraying a mist of water from a bottle will also encourage the spark to jump to ground. There should be no where between the coil and the spark plug that a spark should “leak” out of the secondary circuit. Check the distributor cap/rotor looking for evidence of arcing to ground.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[frenchroast]

[Ljrig]

[vwoldbug]

Have you tried cleaning carb jets.

[Ljrig]

[ashman40]

Have you taken a look at the underside of your distributor cap? Does it look anything like this:

Ok, that’s an extreme example of arcing at the distributor cap. The lines are examples of arcing. Any lines would suggest sparks are jumping between posts and not flowing thru the normal path thru the plug wires.

As a secondary test to the in the dark test, take a length of grounded wire and pass the exposed end along the plug wires in the dark/shade. Keep the wire a few mm away from the spark plug wire. You could even create a loop that wraps around the plug wire and pass it over the entire length of each wire. The ground wire offers a ground path for sparks to jump to. Any cracks in the spark plug wire will allow the spark to “escape” and jump to the ground wire.


The last thing to check is fuel. How long ago since you replaced the fuel filter? More than 2yrs or can’t remember when you replaced it... time to install a new filter. Most fuel filters are metal canisters and not see-thru. They get changed after a set time to ensure a clean fuel delivery system.

Also confirm the carb accelerator pump is discharging immediately upon movement of the throttle arm. If there is any delay it appears as hesitation on acceleration. Just look down the carb opening while you quickly pull on the throttle arm. You should see a stream of fuel from the carb discharge nozzle.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[Starbucket]

Sounds like raw fuel getting to the plugs. Feel under the manifold under the carb (careful it should be real hot after running a few min.s) and if its ice cold, that's the problem (cold weather will bring on the symptoms).

[Ljrig]

[Starbucket]

After market exhaust manifolds do not feed hot air well because the spacing from exhaust ports to the heat riser doesn't draw the hot air through the heat riser pipes. Compare to a stock one and you will see. The answer is probably a stock muffler.

[MuzzcoVW]

Your describing almost exactly what my symptoms were on my '75. After much hair pulling it turned out to be a faulty capacitor! Brand new NON German bosch...and I had a second one fail . Both lasted about 200 miles. Now running an old used bosch made in Germany and no problems. I need to do some research on who makes a good one!

[anthax]

Ground strap between tranny and pan?
Your spark have nowhere to go if you don't have a good ground.

[ashman40]

[Ljrig]

[Ljrig]

[Ljrig]

Ashman, I appreciate the feedback. The magnetic disc for the Accu-Fire doesn't sit on the magnetic pickup as of now, the small ring was only there to give ADDITIONAL space between the disc and the pickup, I assume different distributors might need the spacer ring but mine does not seem to need it. The instructions that came with the module said, I think, around .010 was the correct spacing between the disc and the pickup.

I had the same problem you describe with the distributor cap "dancing" while the car was running! Until i removed the spacer ring of course. It's a wonder that doesn't do more damage or create worse running problems than it does when that happens... Seems now my only problem is getting the headers modified to get good airflow through the heat risers to keep my intake manifold hot and keep the fuel vaporized.

[ashman40]

That spacer ring that sits below the magnetic disc is there to maintain the air gap between the magnetic disc and the top of the electronic module for some distributor models. If you were running the spacer when not needed it means the magnets in the disc were being held further away from the pickup that senses them. I could see how this could cause a misfire especially at higher rpms as the pickup would have a harder time sensing the magnet passing by.

Also, based on your timing settings from earlier (12BTDC @idle) and your updating timing (5BTDC @idle and 30BTDC total)... it sounds like you were running 37BTDC total timing earlier? That is way too much total timing and will likely result in detonation when under load (acceleration) at higher rpms. This is further supported by you saying after you reduced the timing you can no longer hear the “knock sound”. It appears you were running too much timing advance. This is one of the problems with the OO9 distributors... inconsistent advance curves between makers. This is why their timing is set at total advance to make sure they don’t take you past 32BTDC where you risk detonation. Depending how long you were running with this ignition timing and how often you took the engine into detonation you could have physically damaged your engine.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}