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1600sp mid range stumble help

I'm running out of things to try to diagnose my mid-range stumble. The patient is my 1967 Beetle w/ 1600 Single Port motor.

The car starts and idles just fine. Parked and cold, I can rev the engine and if I rev it slowly up I have no problems. If I goose it, the engine cuts out entirely. On the road, it's very similar. If I just barely accelerate, I'm fine. If I put it to the floor, I'm fine. Anywhere in the middle and the engine sputters until I get off the gas, or all the way on it.

As the engine warms up it gradually reacts better and better to throttle action - it takes a good 15 minutes of driving for it to be "normal." Even after it warms up I'll get the same sputter from time to time, but it's plenty driveable at that point.

Here's what I've done:

1) Torqued the manifold bolts 2) Replaced plugs, wires, cap, rotor, condensor, points (009 Distro w/ square mounting hole, mechanical advance) 3) Rebuilt carb, Solex - float is new (and properly adjusted), accelerator pump diaphram is new, etc 4) Swapped in a known good Bosch Blue Coil 5) Swapped in a new fuel pump 6) New fuel filter 7) Spritzed appropriate bits with soapy water while running and didn't see any vacuum leaks

Here's what I can measure:

1) My points are at around 48 degrees. 2) My timing is about a thumb's width counter-clockwise of the TDC mark on the pulley (the only mark I have) but moving it around doesn't seem to have any effect on the stumble. 3) Compression is even. 4) My idle is set a bit high 5) My mixture is roughly right. Set both idle speed and mixture per Muir. 6) Valves are adjusted close to spec, if anything a bit loose.

It started this up a year or two ago, but I don't drive it much so have just been letting it sit and idle for 15 minutes before going anywhere .. but that's a pain in the neck.

Planning to drive it up to Toccoa for the Beetle Show this weekend, would love to have this fixed :-)

Any suggestions?

Thanks,

Cole

Reply to
JackR
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Check that the inlet manifold preheat tube is not blocked. When you start the engine, after a minute the right side tube must be too hot to touch. If not, the preheat tube is blocked and you need to remove the manifold to unblock it.

Bill, '67 bug.

Reply to
Bill Spiliotopoulos

Hmmmmmmm You've actually looked at the accel pump dischg stream??

If that's OK, smells like lack of manifold heat.

BTW, I don't think soapy water is too good a vac test; you won't see bubbles since the mix will be sucked *into* the leak.

Speedy Jim

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Reply to
Speedy Jim

Reply to
ilambert

Reply to
Speedy Jim

Got it! Finally :-)

Went over the car again last night - the manifold tube on the passenger side gets plenty hot, plenty quick. Re-checked the bolts, and it was tightly secured. Adjusted the idle down, reset the mixture and checked the timing - while I was dorking with the carb, noticed a small fuel leak from the accelerator pump. Took the carb off and tightened down the screws for it, put it back on and then gave it a close going over.

While the accelerator pump was pumping and I was getting some flow from the jet, after comparing it to a friend's '56 it seemed I wasn't getting a whole lot of gas moving through the jet. The screws were pretty tight for it initially as well, so figured it might be building enough pressure to squirt some past the gasket - anything that wouldn't go out the jet.

Took it out to Tim's VW in Austell today over lunch and explained what was going on. They took the carb apart and were able to flush some junk out of the channels inside the carb which had been partially blocking the accelerator jet. That fixed it.

Also, he showed me something I didn't realize about my car - while it's a '67 with a 1600 sp, I had a superbeetle pulley on it. I had been timing it to the notches on the block side, where I should've been timing it to the dimple on the outside of the pulley. Wasn't a huge difference as I had been largely ignoring the notch and was adjusting by ear and checking it with the light - but still good to know.

Two hours and $20 later, it's like a whole new car! :-) Incidentally, highly recommend Tim's VW in Austell. They do great work, they worked me right in and were incredibly cheap.

Thanks so much for all your help!

Cole

Reply to
JackR

Glad you sorted it out.

BTW, the "dimple" is TDC. I don't recall what distrib you had on there but that may not be the correct timing mark either.

Speedy Jim

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Reply to
Speedy Jim

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