Finally done with 2.0S rebuild, but won't rev past 4K!!

RetroSC · 07-16-2005, 02:21 PM

Had some carb teething problems just getting it to idle. That's pretty well sorted out and it revs and responds great up to 4.5K. After that it really just sputters, cough's, and just plain won't go anymore. I've only set the timing at idle, scared to check that at 6K right now.

It will rev up to 6K or so under no load, but it just doesn't sound strong once it get's past 4K, and seems reluctant to rev. I'm thinking maybe the distributor isn't advancing enough? Why would it advance fine up to 4K though??

Could it be my carb setup? I've got 40IDA's with 32MM venturies, tall booster aux venturies, 125 mains, 55 idles, and 180 air's and F3 emulsion's. I know 130 mains are correct for a 2.0s, would that really make much difference though? Could it be the tall aux venturies?

I've got pressure regulated at 3 PSI. Checked float levels while running, there're at the bottom line on the float level gauge. Can't imagine that would cause it to fall flat on it's face at 4K though.

Any troubleshooting tips would help now.. starting to get frustrated.

Anyway, here's some bonus pics of the finished motor and it's new home.

Early_S_Man · 07-16-2005, 02:35 PM

Sounds like inadequate fuel pump output to me ... do a flow test straight out of the fuel pump into a clear glass or plastic container. Anything less than 1000 ml in exactly one minute ... is not meeting factory specs.

You don't say what fuel pump you are using, but if output test is OK, then try bumping up the regulator pressure in 0.5 psi increments ... calibration may not be that accurate!

911pcars · 07-16-2005, 02:50 PM

My guess too. Fuel pump volume.

Got a close up shot of your FPR and distribution block we can see?

Sherwood

RetroSC · 07-16-2005, 02:54 PM

Hmmm. I'm pretty sure the pump is good, but of course I'd need to measure to verify. It's the old Bendix pump, original to the car I think. I emptied the tank of the car with it and it moved some serious fuel I thought. 8 gallons in about 15 or 20 minutes. The pressure holds steady too when running, and the float level's stay consistent, so I think if it's keeping the float bowls filled we should be fine fuelwise.

Also, last year when I drove it back from DC to Kansas, it would rev up fine.. ran like crap generally, but it did get into the powerband nicely.

As for fuel pressure, I started with 4 PSI and have regulated it down to 3 thinking maybe my floats were flooding. No difference though.

Guess I need to get off my butt and check the timing at high rpm's. Anybody have the advance curve for this distrubutor?

Also, I don't think there are any marks on this carnk pulley that indicate 30 degrees or whatever it's supposed to be at 6K.

RetroSC · 07-16-2005, 03:01 PM

Here's the regulator. I've actually got it around 2.5-3psi right now, but it still makes no difference. I've had it totally maxed out and the pump only runs around 4.5, still no difference.

911pcars · 07-16-2005, 03:12 PM

Question. If this is the original pump, why are you running a FPR? This pump should provide the needed pressure and volume as is.

Try bypassing the FPR and see how it runs.

In a not too unrelated example, I initially installed a cheapie Holly adjustable FPR on my rebuild with an aftermarket (AirTex) fuel pump (see below). It ran like crap like yours until I bypassed the regulator. Fixed the problem. The pump outputs 4psi w/o a regulator anyway. Your regulator looks like a better one, but still.....

Sherwood

Early_S_Man · 03:17 PM

Ditto on ditching that reg, and that filter looks too small to me! Missed that OEM Bendix pump in the pic ... it shouldn't need a regulator.

Here are some threads with early advance curves plotted:

Best ignition for a 2.7 on Aluminum case

68S Dizzy specs

RetroSC · 07-16-2005, 03:43 PM

Great info! I'll bypass it tomorrow and see how all goes.

The only reason I put one on was my float level's would slowly creep up unless the pressure is below 3psi. Now that's only with the key on and the engine off.

I'll update tomorrow!

911pcars · 07-16-2005, 04:15 PM

I hope the FPR is the culprit.

In regards to creeping fuel level, try installing Grose jets. If you haven't heard of them, they use a ball on ball type valve rather than the typical needle and seat. Supposedly, they provide more positive fuel shut off.

Sherwood

kenikh · 07-16-2005, 05:24 PM

Did I miss something? This could just as easily be electrical.

Fidalgo911S · 07-16-2005, 05:43 PM

I had the exact same thing happen to my '67 S when I first bought it. I would be able to rev just fine in the garage but once I got a load on it during acceleration, it would sputter and miss around 4500 rpm. The fuel pump worked fine, the electrical system was fine, but.....

I found the weights in the distributor were gummed up and weren't slinging around like they should. I disassembled the distributor, cleaned everything and reassembled. It ran great after that.

Grady Clay · 07-16-2005, 05:57 PM

Are the auxiliary venturi in the correct way around? If all six are
reversed, it has these symptoms. This image is from an early
Factory Workshop Manual. I’m pretty sure this is the incorrect
orientation of the auxiliary venturi (red arrow). The spring
(green arrow) goes away from the air correction jet.
"

"
© Dr. Ing. h.c. F. Porsche K.G.

Best,
Grady

Bobboloo · Bobboloo's Garage

That is a beautiful car!!!

RetroSC · 11:28 AM

I'm kind of thinking distributor too, but the fuel regulator has got me wondering now as well.

Grady, I'm sure the Aux venturies are in the correct orientation. The only thing I'm not sure about is how tall they are. The original one's are short like what's in your posted pic, but these are the "booster" or something and are about 3-4inches long, versus the normal 2". I had these laying around and also read something about them being used on motors with agressive cam's and it helping smooth out the idle. That was a long time ago though, so I'm still not sure if I know what I'm talking about.

Thanks Bobboloo, but it does look much better in pics than in person. Lots of bubbles, pitted chrome, etc.. Something you might find on Ebay!!

RetroSC · 07-17-2005, 12:22 PM

Allright, here's the results from today's testing. First, started with the fuel idea. Routed around the regulator and gauge setup, but not the filter (Warren, I purshased this filter from Pelican and it's 5/16 size just like all the other fittings so I think it's appropriate). Anyway, still no luck. I know I stated earlier that it would rev fine under no load, but that was not totally correct. Testing today proved that it indeed does not. I can get up to maybe 5K or so, but that's really it. Anything above 4.5K and it's all sputtering and missing. Kind of like a rev limitor... actually, just like a rev limitor come to think of it. Hmmmm! My rotor's a 7300rpm, do these ever malfunction? Maybe I'll mess with that a bit, I think I've got a 6500 one I'll put in there just to test.

Anyway, back to the other strange happenings. Checking the timing, I noticed I can't get it to idle at 5degrees. I have to keep it set at 10 or so and that seems to work great in the low revs. Revving it up though, I noticed it's around 40+ degrees at 4K. No pinging or detonation though. I did get it back to arond 7 or so at idle while tuning it on the fly, but if I shut it down and tried to restart it wouldn't even try to fire. Totally dead as I cranked it over! Move the distributor a bit and she fires right up, but again the timing is in the 10 degree range.

Am I looking at the crank pully right? I've got the mark's at Z1 which are clearly labeled. TDC right? Then I've got a set at what would correspond to 5, at exactly 5mm to the right of the Z1. Then two sets at what measure out to be 30 and 33mm from the Z1. I'm assuming those are 30 degrees. Like I said earlier, at 4K it's about 10 degrees past those!

So it appears the distributor is advancing properly, but why won't it run at 5 degrees? Could my cam timing be off and making everything else out of wack?

ErVikingo · 07-17-2005, 12:27 PM

I've had similar problems and all were traced back to low fuel pressure. I run PMO 46's at 3 lbs minimum; normally 3.5 to 4.

walt · walt's Garage

You have probably already checked but, did you verify your throttle linkage has full travel. Had the same issue after my rebuild.

RetroSC · 07-18-2005, 04:39 PM

Well, I think I may have sorted this out a bit. I had mentioned earlier that I couldn't keep it idling, or run at all for that matter, if the timing was set at 5 degrees. I had to keep it up around 12-15 at 1000 rpm's. Mentioned this to my Dad as one of the oddities of all this, and he said it sounds like a weak spark and to start looking into all the ignition components. The only thing I've changed since the rebuild was the coil. Well I switched it back to the old one and bingo. I got the timing set at 5 degrees and it rev's to the moon now.

Haven't tested it under load, so I'm not dancing a jig just yet... stay tuned!

Thanks for all the ideas,

Bill

DW SD · 07-18-2005, 04:56 PM

Bill,
Let us know how it runs.

Doug

john walker's workshop · 07-18-2005, 05:16 PM

be sure to check what grady posted. they go in either way. if one or a few are backward, you loose fuel delivery to that cylinder as the revs go up. they all run on the idle circuit up until about 2500, then the mains start kicking fuel in thru the venturis, as the idle circuit fades out.