Engine won't run help

[Jim deCordova]

Gentleman, I am hoping one of you might recognize these symptoms, and have a fix or, test to help me diagnose and fix the problem.
I recently installed a 3.0L engine in my 74 Carrera, during the installation we decided to add a little more pep. So we sent the stock cams to Web cams for a 964 spec regrind. The cams were installed and timed, and the rest of the engine assembled. I also sent the fuel distributor and WUR to Brian at M&K to be rebuilt as well.

So the engine is ready for ignition, here is what is happening. While cranking the motor, but before ignition I can see the pop off valve popping up and down slightly and I can hear a light puffing/popping sound coming from the exhaust. After several seconds the engine fires and runs for 5 to 10 seconds and then we hear a loud popping/banging sound coming from coming from the air mixture control unit then the motor dies. On the next attempts the same exact thing happens, but when my guy move the arm up and down on the arm under the air control unit it seems too allow the engine to run slightly longer and the popping/banging sound seems to dissipate slightly then the motor stops again.

We are currently pulling the air mixture unit off my 2.7L and swapping it onto the
3.0L in the off chance the 3.0L air mix unit may be bad. Before we pull the motor and recheck the cam timing I am hoping one of you might have some other ideas??????

Any ideas/thoughts will be appreciated.

Thanks
Jim

[kach22i]

Start with the simple stuff, are all the ignition wires going to the right spark plugs?

Is the ignition timing spot on, or did it get reversed 180 degrees?

There is one or two years where the firing order is different, 1983 perhaps?

Z1.....TDC...........good times.

Setting 911 Distributor
Static Timing
http://www.pelicanparts.com/techarticles/911_static_timing/911_static_timing.htm

[emac]

I say your timing.
Ernie 81 sc

[Bob Kontak]

Originally Posted by Jim deCordova

the engine fires and runs for 5 to 10 seconds and then we hear a loud popping/banging sound coming from coming from the air mixture control unit then the motor dies.

How does it run for those 5-10 seconds? Only time I had huge backfires from the intake was when I had a massive false air leak.

Regarding cam timing, I don't think you have to pull the motor to do this.

Is the engine popping when the pop off valve flutters when trying to start? This seems odd to me if it's not sputtering.

Are the cams on the correct side? No disrespect, I don't even know if you can do this. I do remember Bruce Anderson's book went over in detail on how to check if you have the correct cam on the correct side, so I suspect it may be do-able.

[Bob Kontak]

Originally Posted by kach22i

There is one or two years where the firing order is different, 1983 perhaps?

Pre 78 distributors ran one way (clockwise) and 78-on (SC's) ran the other. I think that is the date cutoff.

Pretty sure all 162435.

[ossiblue]

My question is, why would the pop off valve lid be moving up and down during engine rotation (without ignition hooked up)? I'm no expert on valve timing but it seems to me that if the pop off lid is lifting, then the intakes must not be fully closed during compression. I am really posing this because I don't know the answer but logic tells me the lid should not be moving off the seal at all during rotation of the engine w/o ignition. Since I've never observed the lid during slow rotation of the engine, I don't know if this is normal. Anyone?

[Bob Kontak]

Originally Posted by ossiblue

Since I've never observed the lid during slow rotation of the engine, I don't know if this is normal. Anyone?

Agree. I have the same /concern above but it is buried in post 4. This does not make logical sense for mechanical pressure to flap the valve if all is happy.

That is why I asked about the cams - left to right placement.

[pors1968]

Did web cam send you your cam.Doyou know number on the cam.Just to make sure you have right cam.

[Jim deCordova]

Thanks guy's. I may not have made my self clear. There is no back firing from the motor. There is a puffing/popping sound coming from the exhaust when cranking then a loud banging coming from the air mix unit 5 to 10 seconds after ignition. I tend to believe it is timing related as well. I will share some of your thoughts with my engine guy.

Thanks
Jim

[Bob Kontak]

Originally Posted by Jim deCordova

then a loud banging coming from the air mix unit 5 to 10 seconds after ignition.

So it's a mechanical sound?

[ant7]

check your cam timing...
A...

[kach22i]

Can you pull your plugs, take off the valve covers, take the distributor cap off, put it in neutral and turn the engine by hand via the pulley and see if the parts (valves) are all moving in proper synchronization?

I would not know what to look for myself without seeing a similar video in action.