help determine mystery noise (long)

dfink · 05-30-2008, 05:38 PM

The car
1970 914-6
2.4 rods, crank and heads
2.2 "S" pistons
electromotive crank fire ignition 7200 limiter
Weber 40 IDF carbs
Unknown jets or venturies
European George Headers

The senario
I was out test the brakes we were having problems with the rears locking, I think that is solved now. Anyhow I was doing alot of run-up and slow downs trying to bed in the brake pads. I got to a spot where I could run it up a little higher around 70mph and then hit the clutch and then the brakes. It was little squirley but slowed pretty good. I didn't completely stop as this was on a highway.
As soon as I let off the brakes and blipped the throttle to go back in gear the noise began. I thought for sure I had broken something. It sounded like an exhaust leak, but here is the strange part. The engine revved like a motorcycle crazy fast throttle blips. I looked at the oil and had pressure. I pulled over to the side of the road expecting that the fan belt had broken and so wasn't pulling the fan. I found the fan belt just fine. I had never made it back into gear so my even worse thought was that I had somehow managed to mess up the clutch and the engine was just free wheeling. I started the car back up, still makeing the mystery noise and eased it into first. Everything worked just fine. I was able to drive back to the shop. I had locked the shop so I shut off the car parked in front of the door. Went in opened the door, went back out restarted the car and behold no more mystery noise. The revving of the engine had returned to normal and so far it has not done it again.
I hind site I think the noise was possible intake noise. I am not used to the intakes being 12 inches from the back of my head. But I can't figure out why it would make run like this for probably 15 minutes as I came back to town then just as suddenly stop as when it started. The car seriously sounded like an F1 engine. I thought of the carbs splashing over but that should have cleared or killed the engine. The only possible thing I can think of is the electromotive system was for some reason going nuts on the tiiming.
Any guesses........... Mostly looking for thing I can look for if it happens again.

R_Davis · 05-31-2008, 05:12 PM

Yo,

I had a weird noise yesterday after a 350 mile road trip. I got to my Mom's house and after the car sat overnight, I started it the next morning and it had a very noticeable whiny/geary/growling/ugly noise. At first I thought it was some bearing somewhere deep inside the engine or trans axle that had failed.

After listening to the engine through 'The Stethoscope" ( one end a piece of 1/2 rubber hose in one ear while sweeping the other end around the engine compartment) I heard the noise coming from the Distributor. I opened the cap (I use Pertronix) and dropped about 10 drops of oil into the center felt of the rotor button .... The Hole ... This is the second time I have had to do this. I think that that little detail is most easily overlooked and after spinning at God knows what speed for God knows how many Revs through the ages ... It Needs Oil as it is a mechanical part ...

This has worked for me ... May not for you, but a noise is a noise.

Best regards,

Rick

SGB · SGB's Garage

I was thinking distributor too. I assume that elecrtomotive unit has some kind of sensor in the diz? Sounds like the advance got hung up.

dfink · 06-15-2008, 04:55 PM

Electrotive unit is totally electronic. There is no distributor. There are three coils with a wasted spark on the exhaust stroke.

After thinking about it my best guess is that something got under an intake valve and held it open causing a loud intake noise. Turn off car and restart and no more noise. Maybe - maybe not....

Hasn't happened again yet.....

R_Davis · 06-15-2008, 05:12 PM

"Well; I said 'Great ... one less thing."' (Forrest Gump circa 1995)