[Double_Take]

I am trying to tune my 350 GM crate engine (not a zz4) with a 350 auto. I have been following the tuning proceedure outlined by lars, but have run into a few snags that dont make any sense for a properly functioning engine.

1) Set dwell. I have not done this due to my reluctance to buy the meter. Im going to buy one today but I want to know if my problem can be cured by a bad dwell setting.
2) Plug vacuum advance with golf tee, attach vacuum guage to manifold vacuum port. Pull dist rotor and cap. Place rubberband around centrifigal advance springs. Adjusted idle to around 600 rpm's, set timing to 10* as a good starting point for the rest of the proceedure.
3) Remove rubberband, recheck timing. My timing was advancing 3-4* from the previous spot and would float ~1-2* back and forth. Installed the stiffest springs I had. Timing is back at 10* and holding steady.
Then it got weird. I blipped the throttle to see if the engine would return to 10*, but it quickly came back to ~8*. Blipped again, timing was ~5, blipped again and again until the timing moved all the way to 6* retarted, but was still running at the same RPM's. At this point I shut it down, did some reading and was completely baffled.

The engine has 4500 miles on it, the distributor is a standard GM HEI. When I bought the car, the tranny would shift into 2nd right off of idle. As a result the previous tuner could (and probably did) change everything to get the car to run smoothly. My mixture screws are close enough to not be the problem. My first impression was the distributor is toast, possibly the gear. but with the rubber band in place, a little blip of the throttle will not result in a change in timing. Logic says it has to be something with the centrifigal advance, but I dont understand how this would retard the timing.

For referance, on the timing wheel I have a line at zero with a metal plate attached to the engine. CCW (as your looking at the car from the front) is labeled "before", CW is labeled "after". I had it set to 10* "before".

Thanks in advance.

 

[big2bird]

I am trying to tune my 350 GM crate engine (not a zz4) with a 350 auto. I have been following the tuning proceedure outlined by lars, but have run into a few snags that dont make any sense for a properly functioning engine.

1) Set dwell. I have not done this due to my reluctance to buy the meter. Im going to buy one today but I want to know if my problem can be cured by a bad dwell setting.
2) Plug vacuum advance with golf tee, attach vacuum guage to manifold vacuum port. Pull dist rotor and cap. Place rubberband around centrifigal advance springs. Adjusted idle to around 600 rpm's, set timing to 10* as a good starting point for the rest of the proceedure.
3) Remove rubberband, recheck timing. My timing was advancing 3-4* from the previous spot and would float ~1-2* back and forth. Installed the stiffest springs I had. Timing is back at 10* and holding steady.
Then it got weird. I blipped the throttle to see if the engine would return to 10*, but it quickly came back to ~8*. Blipped again, timing was ~5, blipped again and again until the timing moved all the way to 6* retarted, but was still running at the same RPM's. At this point I shut it down, did some reading and was completely baffled.

The engine has 4500 miles on it, the distributor is a standard GM HEI. When I bought the car, the tranny would shift into 2nd right off of idle. As a result the previous tuner could (and probably did) change everything to get the car to run smoothly. My mixture screws are close enough to not be the problem. My first impression was the distributor is toast, possibly the gear. but with the rubber band in place, a little blip of the throttle will not result in a change in timing. Logic says it has to be something with the centrifigal advance, but I dont understand how this would retard the timing.

For referance, on the timing wheel I have a line at zero with a metal plate attached to the engine. CCW (as your looking at the car from the front) is labeled "before", CW is labeled "after". I had it set to 10* "before".

Thanks in advance.

1) Dwell is adjustable on points only. HEI dwell is built in.
2) It sounds as if the "plastic buttons" are worn under the weights.
3) I would pull the dizzy, check the gear, check the "buttons" the weights slide on. You could also have slack in your timing chain.
4)Hopefull Lars will chime in.

 

[Double_Take]

When your talking about the buttons are you talking about the bushings the weights ride on? If so there are none, the weight is a slip on the post. Each weight has the #60 printed on it. I assume this is the weight. I have the gold springs from the mr gasket HEI 74-79 advance spring kit.

Does anyone else have an idea before I pull the distributor?

 

[Fred Mann]

I am trying to tune my 350 GM crate engine (not a zz4) with a 350 auto. I have been following the tuning proceedure outlined by lars, but have run into a few snags that dont make any sense for a properly functioning engine.

1) Set dwell. I have not done this due to my reluctance to buy the meter. Im going to buy one today but I want to know if my problem can be cured by a bad dwell setting.
2) Plug vacuum advance with golf tee, attach vacuum guage to manifold vacuum port. Pull dist rotor and cap. Place rubberband around centrifigal advance springs. Adjusted idle to around 600 rpm's, set timing to 10* as a good starting point for the rest of the proceedure.
3) Remove rubberband, recheck timing. My timing was advancing 3-4* from the previous spot and would float ~1-2* back and forth. Installed the stiffest springs I had. Timing is back at 10* and holding steady.
Then it got weird. I blipped the throttle to see if the engine would return to 10*, but it quickly came back to ~8*. Blipped again, timing was ~5, blipped again and again until the timing moved all the way to 6* retarted, but was still running at the same RPM's. At this point I shut it down, did some reading and was completely baffled.

The engine has 4500 miles on it, the distributor is a standard GM HEI. When I bought the car, the tranny would shift into 2nd right off of idle. As a result the previous tuner could (and probably did) change everything to get the car to run smoothly. My mixture screws are close enough to not be the problem. My first impression was the distributor is toast, possibly the gear. but with the rubber band in place, a little blip of the throttle will not result in a change in timing. Logic says it has to be something with the centrifigal advance, but I dont understand how this would retard the timing.

For referance, on the timing wheel I have a line at zero with a metal plate attached to the engine. CCW (as your looking at the car from the front) is labeled "before", CW is labeled "after". I had it set to 10* "before".

Thanks in advance.

A swing of 16 degrees in the timing (from 10 degrees advanced to 6 retarded) would change the idle speed, I would certainly think. Even if the mechanical advance is locked out, I would think the engine would slow down. Are the weights held firmly against the center cam or could they have been pulled up over it? Not sure the rotor would fit on if the weights were pulled together. Is the timing light an adjustable or fixed type? Could it be an indication problem and the timing isn't actually changing? Not being much help to you.

 

[redvetracr]

When your talking about the buttons are you talking about the bushings the weights ride on? If so there are none, the weight is a slip on the post. Each weight has the #60 printed on it. I assume this is the weight. I have the gold springs from the mr gasket HEI 74-79 advance spring kit.

Does anyone else have an idea before I pull the distributor?

I am not an HEI guy but if and when you pull the dist. check the lower bushing for side to side movement.....I see alot of loose ones in the earlier cast iron tach drive distributors....
...redvetracr