Help, 911 running on three cyl's

kevin-ct · 10-07-2010, 11:02 AM

Hi, I’m new to this BBS.

I’m working on a 1971 911 with a 2.7L with Webers on it.

It looks like the left side of the engine is not firing, where the right side of the engine is working great.

What I have done so far is check compression on all cyl. Right side reads all 100psi
left side is (85, back cyl)110,(115 front cyl)

When I run the engine the exhaust temp on the right side reads 450 deg.
the left side runs at 150’s... I have check the spark plug & wires and swapped all spark plugs. I’m still getting the right side firing and not the left. I checked for spark and I’m getting the same spark on all cyl.

At this point I’m thinking checking the valve adjustments, fuel flow to the left carburetor.

Can it be the camshaft timing on the driver side that’s off?

Thanks,

Kevin

gshase · 10-07-2010, 11:14 AM

With dual webbers one side is not getting fuel. Check for filters,crimped line or anything that might starve only one side.

kevin-ct · 11:46 AM

yep, I just did that, didn't see anything wrong. I also spayed carb cleaner in the left side carb's when it was running with no change in RPM's

turborat · turborat's Garage

Problem could be the idle adjustment at the linkage. If you have the Webber Sync tool, check vacuum when running in all six trumpets and adjust for linear readings. I am surprised the engine will stay running on 3 cylinders, so the left side is probably getting a Little fuel and air.

Download the Webber manual if you don't already have it to save you a lot of grief. Unless the engine has had recent repair work etc, I assume your car has a carb problems of some sort.

kodioneill · kodioneill's Garage

Did you change anything in the ignition circuit ? May want to check Zundfolge.

kevin-ct · 10-07-2010, 02:38 PM

Quote:

Originally Posted by kodioneill

Did you change anything in the ignition circuit ? May want to check Zundfolge.

No, I didn't change anything in the ign system.

The customer stated the car runs poorly and back fires from the exhaust.

I did notice when checking for spark the spark would come every 3 sec (about) at idle, that seems very slow to me.

What is a Zundfolge? CDI?

Cheers,

kodioneill · kodioneill's Garage

Firing order

kevin-ct · 10-07-2010, 02:59 PM

Quote:

Originally Posted by kodioneill

Firing order

Nope, that was checked already.

2.70Racer · 10-07-2010, 03:53 PM

This seems like a classic issue of timing the left cam at TDC compression at the same time the right side is at compression.
Pull #1 and #4 sparkplugs. Rotate the engine clockwise until #4 cylinder is coming up on compression. Stop turning the engine before TDC. Check #1 cylinder. If it is also coming up on compression at the same time, you will have confirmed the left cam is off 360 crankshaft degrees, (180 camshaft degrees).

Rich Lambert · Rich Lambert's Garage

I had a similar problem when I first got my '66. Turned out the dowel pin on the right cam gear had sheared off. Take off one of the valve covers and see if the rockers move when the engine is turned over.

I hope this isn't what's going on with yours...or if it is, it's not a broken valve going through a piston like mine was (a gift from the PO).

kevin-ct · 10-07-2010, 04:35 PM

Doug, If the camshafts are out 180 deg, will the engine still run? Right now the engine runs well for 3.5 cyl..

Quote:

Originally Posted by 2.70Racer

This seems like a classic issue of timing the left cam at TDC compression at the same time the right side is at compression.
Pull #1 and #4 sparkplugs. Rotate the engine clockwise until #4 cylinder is coming up on compression. Stop turning the engine before TDC. Check #1 cylinder. If it is also coming up on compression at the same time, you will have confirmed the left cam is off 360 crankshaft degrees, (180 camshaft degrees).

john walker's workshop · 10-07-2010, 05:04 PM

Quote:

Originally Posted by kevin-ct

Doug, If the camshafts are out 180 deg, will the engine still run? Right now the engine runs well for 3.5 cyl..

reminds me of a wrecking yard engine where they wrote on it "runs good, dead hole".

kevin-ct · 10-08-2010, 01:21 PM

Is it possible that the engine can run with the left side camshaft out 180 deg?

Is there a quick way to tell if the camshaft is out of time?

Any help would be great, I'm loosing sleep over this car.

Thanks,

Kevin

john walker's workshop · 10-08-2010, 01:55 PM

i've seen them run on one bank after a chain broke on the other. pistons bent any valves that were in the way and the other side carried on. wouldn't hurt to check if the cams and rockers are moving on the dead side. pull an upper rocker cover off and watch as someone cranks the key or turn it over with a socket on the alternator pulley nut. at least get that out of the way.