Question Regarding Engine Cutout on 69E/S
 

I have an issue with a new to me car that I need some opinions on. I have a 69E motor that has been rebuilt with S cams and crank, 2.2L P&C's, 67S heads, and Weber 40IDA carbs. When I got the car, it would cut out at about 6200 revs. I figured it was probably the wrong rev limiting rotor installed, so I ordered one from our host and was looking forward to it running up to 7300 on my next test drive. Well, I took it out and it still cuts out at about 6000 revs. :mad:

The motor is in great shape having been rebuilt not too long ago (2 years and 4k miles) by a reputable SoCal Porsche shop. No, it was not that one. :rolleyes: ;) Can anyone give me some ideas on what might be going on? Wrong jetting on the carbs? Dizzy points floating? Broken valve spring? Your ideas would be most helpful. Thanks. SmileWavy

Scott,

Be thankful it's not revving higher until you find out whether it's ignition or fuel. Either one is NOT good at that RPM level and load.

First, what distributor do you have? What does the curve look like?

As you can see, the Bosch "002" distributor has a curve that continues to advance after 6000 RPM. The curve is the last one posted in this thread. http://forums.pelicanparts.com/showthread.php?s=&threadid=316880&highlight=00+adv ance+curve

If you aren't getting enough advance, that could keep the engine from accelerating. The old distributors get rusty and the phenolic rubbing plate cracks. See this thread for everything I know about rebuilding old distributors. http://forums.pelicanparts.com/porsche-911-technical-forum/252299-before-there-bhkz-swb-engine-electrics.html

Second, how are your float levels and fuel pressure? The pressure is measured in the loop between the pump and the carbs, and the levels are measured with the special tool. If you were using an exhaust gas analyzer, you would see the mixture spike lean.

Thanks John. I am not sure exactly which distributor I have and will have to verify it when I am at the car next. What do I need to look for with respect to numbers or distinguishing marks? Also, I am not sure on the float levels - I will have to check. Ditto fuel pressure - I will check and document here.

Thanks for the links.

Do you have the stock ignition system? If you have an aftermarket set up maybe there is a rev limiter on it. I doubt the carbs would quit at a specific RPM. Maybe the coil craps out at a certain RPM. Check the point gap and condition also.

-Andy

Scott,

The distributor will have a number plate on the side if it's cast iron, or will have the number cast into the side if it's aluminum. A typical number is 0 231 159 007 with the 007 being the critical number.

Good luck and remember, it's easier than finding a bad plug on a radial engine!

The other fellas have you heading in the right direction for sure. Define "cutting off"... Does it sound like it's bouncing off 6200 rpm, doesn't go past 6200 or just dies at 6200? If it's bouncing, there's a rev limiter there..somewhere (even the dist rotor). Doesn't go past 6200 but runs; possibly timing off, cams out of sinc, valve spring or carb floats stuck? Just dies... you got me.

Were the carbs set up for your specific engine? If the engine seems to just run out of juice at 6k it may be too small venturies or jetting issues.

Regards,
Andrew M

All great points guys, thanks. The engine cuts out at about 6000 revs like it is rev limited. It does not just die. It acts as if it were electonically limited. Were the carbs set up for my engine? I have to assume so since they were installed for this application, but I could be wrong. Also, I do have the stock ignition system. I thought it might be the issues all of you mentioned, so I will start by the process of elimination.

First order of business - check dizzy P/N.
Second - check point gap and condition. It has been awhile, how do I do this?
Third - How do I check for the correct venturi size?
Fourth - How to check for correct jetting?
Fifth - Float settings
Last - Valve springs (hopefully not this)

Stay tuned and let me know if anyone has any other suggestions.

John, I don't know - I think replacing a plug on a radial is easier than this. But that could be just me.

If you're going to check your distributor, and replace points, maybe just as easy to set the engine at TDC #1, blow any dirt and grime away from what will become an open hole, and pull the distributor. Cover the hole. Cover the hole. Once on the bench, it's pretty easy to inspect, lube, and change points.

Before you pull the distributor. If you have an adjustable advance timing light, you could make some preliminary inspections of the current advance curve. Just another 2c.

Are you sure your tach is reading correctly. If you have had two different rev limiter buttons in there, each cutting at about 6k, maybe your tach is reading low. Get your hands on an inductive meter for a plug wire and compare the readings you get with that to what the tach is reading.

Brooke

Thanks Brooke. I thought about that too, but I am almost 100% certain that the tacho is correct. The car should come on the cam at about 5k revs to about 7300. It comes on the cam at 5000, but only lasts til about 6000. I think it may be something else, but I will take your advice and check for sure. Thanks again.