Recommissioning 911t

dpetteng · 08-15-2019, 06:45 AM

So, we are recomminsioning my 911t that I imported 4 years ago and has sat in a garage. My restorer has changed spark plugs, points, rotor, dizi cap, oil change, HT leads, fuel etc and the carbs were completely rebuilt by a reputable rebuilder.

So, the car just about starts, will idle but pops and backfires if you even tweak the throttle. Any ideas where to start looking?

Trackrash · Trackrash's Garage

When you look down into the carb and push the throttle do you see steady streams of gas shooting out of all the accelerator nozzles?

When you hold one of the spark plug wires pulled from a plug using another plug held to the motor is there a strong spark?

Have you put a timing light on the car and checked the timing when the motor is being cranked or idled?

Have you checked and set the float levels with the glass vile, assuming Webers?

Also pull out the idle jets and make sure they are clean and probably a good idea to check the gas flow and pressure at the carbs.

AND we don't know what year motor or make of carbs but eliminating the simple stuff is a good start.

dpetteng · 08-15-2019, 11:12 PM

So this is a 1970 911t 2.2. Thanks for the advice.

dpetteng · 08-16-2019, 02:05 AM

So, it seems we have a valve issue. Compression tests all pistons at around 150 except the middle head on the right coming in at 75...

So, I'm assuming stuck valve or valve seat damage. Anyone know any good places in the UK to rebuild heads and what price I should expect to pay? I am assuming the right thing to do is all 6 heads at once?

Dave

dpetteng · 08-16-2019, 04:11 AM

So, next question, what parts do I need for a top end rebuild and is it worth doing any engine work to improve performance while we are at it?

Trackrash · Trackrash's Garage

I would try to get it running first. After it is running it may be OK. Stuck valves can unstick themselves. Your motor should still run OK with one low cylinder.

You could do a leak down test to determine where the compression is going. My guess is there is carbon holding the exhaust valve open.

If you search around here there have been a number of discussions about upgrading 2,2 motors.

dpetteng · 08-18-2019, 05:47 AM

So we had it running, it idled well but as soon as you blipped the throttle is popped and backfired and it didn't seem to be fixing itself. The engine is now out of the car so will will see tomorrow what the head shows us. interestingly the clutch is completely knackered.

dpetteng · 08-18-2019, 10:36 AM

So, I am assuming head rebuilds. As I want to increase B&P's and cams in the future, would you recommend opening up ports now?