911T revival- Webber problems?

[911TES]

Hi all:

I pretty far along in the revival of a '69 all-stock 911T that's been sitting for 25 years.
My current problem is that I can't seem to tune the Webbers. I've gotten to the point where it starts pretty easily, but won't idle or hold a given RPM without pumping the accelerator. It seems as if the engine is running off the accelerator pumps.

So far, I have:
1) Rebuilt carbs - pretty thoroughly and carefully, but I'm a bit suspect at this point...
2) Compression - all cylinders 145-155 psi. (done w/ engine cold).
3) Leak-down - all cylinders > 95% (done w/ engine cold).
4) Adjusted valves.
5) Set points and adjusted timing.
6) Verified fuel pump pressure at approximately 3.5 psi. I need to verify that I'm getting sufficient flow, but it seems ok. The see-thru filters show mostly gas, but a number of "air pockets". I haven't yet refurbished the fuel tank and am running the fuel thru three filters.

I've tried various initial settings, but they all seem second ordered effects. Generally, the more "out" the screws are the better. There has been a lot of excessive oil being burned - blue smoke in the exhaust, but seems to be diminishing a lot with running the engine.

Any ideas are greatly appreciated.

Thanks, Bill

[Steve@Rennsport]

Bill,

The very foundations for tuning and setting up carbs is clean fuel, proper fule pressure and perfect float levels.

Address those items before making ANY adjustments otherwise the whole exercise will be a waste of time.

[Rusty 356]

Bill, had a recent experience with my 69. Pulled the tank and had it cleaned and sealed. Car runs smooth with only the occasional pop when at idle. After setting for 25 years mine was full of sediment. Like Steve stated, carbs need clean fuel.
Good luck,

[911TES]

Steve, Rusty, thanks. Sometimes one needs to be told what they already know...

I did purge the tank and, I believe, am sufficiently filtering the fuel, but no sense in "building a house on a questionable foundation". I was hoping to combine the cosmetic and mechanical restoration on the fuel tank at a later stage.

Steve I did have a question of the float level:

I used the PMO sight glass and got all the floats to the point where the fuel level meniscus is between the two top lines. If I remember correctly, I had the "top" of the meniscus on the top line and the base of the meniscus on the lower line. I used the varying thickness of copper washers - sound right?

Thanks, Bill

[Steve@Rennsport]

Originally Posted by 911TES

I used the PMO sight glass and got all the floats to the point where the fuel level meniscus is between the two top lines. If I remember correctly, I had the "top" of the meniscus on the top line and the base of the meniscus on the lower line. I used the varying thickness of copper washers - sound right?

Thanks, Bill

Spot on, Bill,...

[911TES]

O.K., I've completely restored the fuel tank inside and out and replaced or cleaned all the lines to the carbs.




I believe I've done all the basics and am still having problems getting to the point where I can tune/balance the carbs:

Symptoms:

Engine will start, but won't idle.
Engine seems to mostly run off of the accelerator pumps. I.e., it will want to die unless I give it a few blips. Seems to accelerate reasonably. Will not hold RPM at higher throttle settings - will die unless I blip it. Some blue smoke is still present, but much reduced as are backfires.
After cleaning the Marelli distributor cap contacts there was noticable improvment and the engine now "almost" idles or "almost" hold RPM at higher throttle positions.

Things done:
1) Rebuilt carbs - pretty thoroughly and carefully, but I'm a bit suspect at this point...Floats are set accurately.
2) Compression - all cylinders 145-155 psi. (done w/ engine cold).
3) Leak-down - all cylinders > 95% (done w/ engine cold).
4) Adjusted valves.
5) New and adjusted points and dynamically adjusted timing. Advance seems to be working properly, but it does seem to advance more quickly vs. RPM than I'd guess, but I don't have it well quantified.
6) Verified fuel pump pressure at approximately 3.5 psi. I need to verify that I'm getting sufficient flow, but it seems ok. The see-thru filters show mostly gas, but a number of "air pockets".
7) Complete resoration of fuel tank and delivery.
8) Set all carb adjustments to commonly advised initial settings.

Not done:
1) Have not adjusted the accelerator pump volume, they seem to be doing their job fine. I will adjust soon.
2) Have not replaced spark plug wires.

Latest suspicion is based on a thread I saw commenting on the type of fuel pump that is installed: I believe this is a Beck Arnley which is designed to push the fuel.
I.e., is ok if located up front.

I assume the car ran ok with this set-up, but the PO did tell me where to put "the bag of ice" on hot days." Could this be part of my problem and would a Pierburg pump be part of the solution.

My plan at this point is new plug wires and possible replace the pump.

Thanks! Bill

[B D]

The fuel pump is not the issue if you have 3.5 psi, anyways it would still idle off the fuel in the bowls. You can always check it's flow by clicking it on a running it in to a gas can for a minute or two.

Have you checked the plugs, are some wet?

I bet it's an ignition spark issue. Check the plug wires for resistance, clean up grounds, and maybe figure out how to test the Mark Ten CDI.

[911TES]

Thanks BD.

I agree on the fuel pump - its job is to fill the bowls and I think that's o.k.

The plugs while not completely fouled are on the dark and damp side of normal.

The other clue is that when I cleaned-up the distributor cap it maybe the most significant improvement so far. I'll likely replace the wire and work all the grounding as you've suggested - also, research the Mark 10.

The car had been sitting for 25 years.

Thanks!

Bill

[Ericv]

Originally Posted by 911TES

Thanks BD.

I agree on the fuel pump - its job is to fill the bowls and I think that's o.k.

The plugs while not completely fouled are on the dark and damp side of normal.

The other clue is that when I cleaned-up the distributor cap it maybe the most significant improvement so far. I'll likely replace the wire and work all the grounding as you've suggested - also, research the Mark 10.

The car had been sitting for 25 years.

Thanks!

Bill

Do you have a dwell meter and did you check it? If it's not correct, you're timing won't be correct either. It sounds like an ignition issue as I have had similar problems. Once I went through and checked spark plug gap, plugs, wires, dwell, points, cap, and valves, there was a tone of improvement.

[911TES]

Ok, thanks!

Plan for this weekend is to:

1) Replace ignition wires with new Beru.
2) Clean all terminal connections including grounds.
3) Recheck and adjust gaps and dwell and timing. (I may have previously set to non-CDI recommendations)
4) Investigate and verify operation of the Delta Mark Ten unit. I have some specs on it, but need to familiarize myself more.
5) Check coil and condenser - again, probably need to familiarize myself more
6) Re-inspect Marelli rotor and cap - seem ok and they are the only ones I have - trying to avoid Bosch coversion.

Can anyone think of anything else?

Thanks, Bill

[rallye911]

Hi there,
Be very careful about checking the CDI unit. My 911T (on Webers) had very slight misfires and poor gas mileage after the PO and his mechanic changed all sorts of things in the carbs.

When you listened to the CDI unit (a Bosch original) you could hear the low hum from the inverter, so I guess everyone assumed it was fine. I changed it for a High-Energy Ignition unit built from a kit (total cost excluding a half-hour of my time $25), put new idle jets in and the problems went away. No more misfires and nearly double the gas mileage.

In the end it was an easy fix, but I and others before me spent a lot of time chasing phantoms before then.

Regards

Angus

[911 tweaks]

please share what the "high energy ignition" unit is that you used... the bosche cdi's have been for ever a mystery~unknown when trying to tune these enginse.
Thanks,
Bob

[rallye911]

Hi Bob,
I posted a reply to your query about 12 hours ago, and got a response that it had been referred to a moderator before posting Never had that happen before, and it seems that the reply has disappeared into the great moderator in-tray in never-neverland.

If it doesn't get through by tomorrow am UK time, I'll post again.

regards

Angus

[rallye911]

Replacement for the missing post:

The design of the high-energy ignition was published in an Australian electronics magazine - Silicon Chip. The magazine article is included in a compendium called "Silicon Chip's Electronic projects for Cars; Vol 2" which contains several interesting projects, including a key-pad programmable ignition timing module. I've got the kit for that as well, but haven't got around to building/trying it yet

The ignition is based on a purpose-designed Motorola IC, with a high-voltage switching transistor driving a high-energy coil - no CD involved. It will run .035" - .045" spark gaps and generates a good fat spark which CD will not do.

The kit was bought from a retail chain in Australia called Dick Smith Electronics while I was there on a business trip, but it is produced by a company called Jaycar Electronics (www.jaycar.com.au), and I believe they will ship worldwide.

Regards

Angus