Rebuild 2.2 or replace with used engine?

[Hi_Fi_Guy]

1971 911 T with matching numbers engine suffered a fire in one of the Zenith carbs during the spring. It seems some molten metal and/or debris may have made it's way into the intakes and possibly two of the cylinders. The 911 has been at the shop for diagnosis and repair and they have managed to get the damage cleaned up and get the engine running again but leak down on 2 of the cylinders is 10% vs less than 5% on the rest. They also report lots of popping and spitting below 2000 RPM (it did not do that before). Advise the car is drivable as is for the short term but suggest I consider an engine rebuild along with replacement carbs in the near future. Well respected/trusted shop and mechanic I have no reason to doubt their diagnosis or advice.

So the question of the hour is this: If it were your money would your rebuild the 2.2 (stock or modified) and purchase replacement carbs? Or look for a good used motor of same or larger displacement for the same $$$?

My usage is pleasure driving, road trips, etc. No track days.

[Neil Harvey]

Not trying to find fault with your shop, but if they cleaned up the damage did they not check the leak down first and while in there, measure parts that are involved in sealing the engine.

The popping is probably the carbs not sync'ed properly and the 10% is not worth rebuilding yet if all other things are Ok. I cannot image the extra 5% is giving you any grief.

What you actually have is not 10% but only 5% as you should consider all the cylinders are producing torque. 5 have 5% loss and the other has an additional 5 more.

First ask where the leak is heard? Valves or breather or both. If valves, which I suspect if something went down there, try tapping in the adjuster while the leak down tester is connected. Often this can dislodge any trash the numbers go down.

[Hi_Fi_Guy]

Thanks for the feedback Neil. I am told the intake valves were cleaned up along with the rest of the intake and the valves where checked to ensure they were seating properly and not sticking.

As you say, once I have the car back I can be the judge of if the 10% is noticeable seat-of-the-pants or not.

As to the carbs I have never been 100% happy with this pair of Zeniths compared with other carbs on other air-cooled cars I have owned. After a full rebuild a few years ago, the carb fire this year, and the resulting expense, I am beginning to wonder if a replacement set of carbs may be the best investment/insurance I can add to this engine whether it gets a rebuild or not.

[Trackrash]

Dumb question, but did they have the air cleaner on when the carbs were popping and spitting? Zeniths, are very finicky, but run great on an otherwise stock 2,2. A 2.2 with stock Zeniths will not run well with the aircleaner removed.

Plugged idle jets or poor adjustments can lead to popping as well.

How loose are the throttle shafts? When were the needle and seats replaced? What kind of fuel filter are you running? Zeniths have been known to have the needle and seats stick causing fuel to spew. It might also be a good time to replace ALL the rubber fuel hoses on your car.

FWIW Webers will not gain you much on your stock motor, but will suck a lot more fuel.

IMO the 2,2 is one of the nicest running 911 motors, and they are a nice platform for many upgrades.

[Richey]

Trackrash is spot on . Zeniths can be tuned to run well . How much money will you spend on the used engine ? There will be surprises . Buy some used Zeniths if necessary and have them sorted .Good luck .

[Hi_Fi_Guy]

FYI the Zeniths were running very well before the fire without issue. Fuel pump and lines replaced 2 years ago when the carbs were rebuilt.

Shop guessed the fire was due to fuel percolation but could have been stuck float/needle as well.

[Mark Henry]

3.2 complete with FI swap would be nice. Likely you could buy one, do the top end and studs for the same or less than a full rebuild on the 2.2.
Wrap the 2.2 and store it if numbers matching.