´71 911T (w/ Zeniths) – right cylinder bank not firing!

[RetroGuy]

Dear guys!

As during my last drive with my 911T (back in November) the engine started to run rough (first only on and off) and has since - on all starting attempts - not returned to its usual sound I checked by pulling one ignition lead after the other and discovered that the whole right cylinder bank is not firing… The distributor and the ignition seem fine, the whole engine has in 2011, hence not even 2000 miles ago, been completely rebuilt by a reputable shop by the previous owner.

Even if only running on the left bank engine starts on first attempt and seems to idle quite stable at around 1.000 rpm (being normal for my engine when cold).

I therefore assume that the problem lies either with the right hand side carb or the fuel supply.

Would it therefore be sensible to check whether the right bank might work by (after first taking off the air filter housing) spraying a bit of starting fluid in the three trumpets of the right hand side carb, and do I further understand correctly that if the engine then runs (probably only briefly) there might be a problem with the fuel supply to the right hand side carb? If not, something might be wrong with the carb?

I have also been told that one could (engine not running, only ignition on) look inside the trumpets and pull the gas cable and one should see fuel being squirted in - nonsense or good advice?

Any precautions to be taken before attempting all of this? In any case a fire ext. will be kept handy.

Many thanks in advance!

Stefan

[edmayo]

Yes, with engine OFF, remove air cleaner, look down carb throats, and operate throttle linkage. If gas in carbs fuel will squirt from acellerator pumps.

[RetroGuy]

thanks for your Input!

I am now a bit further in my "diagnosis":

- I have good spark on all six spark plugs, in addition I put in new spark plugs on the right side cylinder bank (being the one which does not fire) - btw, the old spark plugs looked okay

- when I take off the air cleaner box and pull the accelerator I see fuel being squirted in

- when I start the engine and then pull the plugs of the left cylinder bank immediately afterwards they are wet

So, as ignition seems ok und fuel delivery probably too, what should be my next steps? check valve clearance and head studs, compression/leak-down-test?

many thanks!

Stefan



thanks!

[edmayo]

If I understand you right you say that fuel squirts from all six accelerator pumps, that when you short to ground the spark for the right side there is no ignition to the right spark plugs only, "the whole right cylinder bank is not firing" but you have "good spark on all six spark plugs" but yet the spark plugs "looked okay" but the left bank which is working has "wet spark plugs" and yet the engine ran fine until you drove it, then it suddenly "ran rough" So it sounds like you have fuel in both carburetors, the right bank is not working, but the spark plugs look good on that side, but the left bank which is working has "wet" spark plugs. Very confusing!!! With engine running use a infra red temp gun and aim at each exhaust port, temps should be in the 2-300 degree range, anything colder indicates cylinder not working right. I also think you need to check cam timing both sides in case you jumped a tooth in which case cylinders would not be making power even though as you've indicated they are all getting fuel and spark. Or you may have excessive float level on left side which is what wets the spark plugs, or the idle jets are all plugged at once on the right side,,,,,possible,,,,but unlikely.

[RetroGuy]

I am sorry, I meant that the plugs of the right side (non-firing) cylinder bank are wet! the right bank of cyl (4-5-6) definitely does not work, as it does not make any difference in engine sound whether I pull one or all ignition cables of cylinders 4-5-6...

car had Carrera chain tensioners installed when the engine was overhauled 2000 miles ago, so I hope not that it has jumped a tooth...

I will bring the car to specialist shop!

in any case, many thanks!

[Harvey Weidman]

Don't use starting fluid. I have seen rod bearings smashed on 911 engines using starting fluid.
Ed always has the best procedure for diagnosing.....
H