DUI distributor help

[gt4660]

I am posting this in multiple forums.

I recently acquired a 79 CJ7 , AMC 258 i6 / 4.2l , T-150 , Dana 20 , 4 inch lift, 33's and 3.54 gears. Recent rebuild, under 3500 miles on engine. It has a DUI distributor and I wanted to check the timing. After reading as many forums as I could find I followed the following procedure:
disconnected the vacuum advance( which was not connected to manifold vacuum) plug the line and the port, set idle to 500, set timing to 12deg btdc, As suggested by DUI and various threads I read, reconnected the vacuum and set idle to 700. I checked timing again and it was way off the scale.

I have not found any information about this. I have checked forums, DUI's webpage and nothing. Do I run it like that?

It is holding good vacuum, about 20.5 at idle. I have tried tuning the carb using a vacuum gauge and it runs very good. I noticed a slight ping on a steep hill in townIt has a 30 mph speed limit and I was running in third. Using it as a test strip for any tweaking I do to see if it is going to ping. I ran it down the highway and accelerates great.

I am just looking for some info to confirm what I have down is right or stop me before I screw something up!

 

[hutchman]

Your procedure for setting the initial advance is correct. It should be set with the vacuum advance disconnected and plugged. The fact that the timing is advanced after the vacuum advance is hooked up indicates that you are getting some manifold vacuum at idle.....and there is nothing wrong with that.

Without knowing how much advance is in the distributor, it is hard to say what the initial setting should be. Total advance should be in the range of 32-34 degrees for your Jeep I believe, so if you have an initial setting of 12, then you would want no more than 11 in the distributor......11 in the distributor is equal to 22 at the crankshaft.

So here is what I would do. Your harmonic balancer is most likely marked in 2 degree increments up to 12 degrees or so. Assuming the marks stop at 12 degrees, measure that distance around the balancer. Measure from 12 degrees and equal amount around the balancer and make a mark......this should be about 24 degrees. Measure from you 24 degree mark another distance equal to the 12 degress and make another mark. This should be approximately 36 degrees.

Now start the motor and measure the total advance with the engine reved up to approximately 3600 rpm. You want the engine to be running fast enough that all of the advance is in and you can measure it with the timing light. This will not be exact as you timing marks are not exact, but it will give you an idea of where you are at. It you get a reading greater than 36, then you can take some of the initial out to reduce the total timing and not have damage to your engine from pinging and detonation.

My guess would be that 12 degrees initial is too much, but it does depend on what's in the distributor......

 

[BajaEdition]

first, welcome to the forum
second, Hutchmans advice is spot on, go do it
third, I see you have an 08 Rubicon, I feel sorry for you, I sold mine after having bent the rear axle twice, having to replace the swaybar disconnect because it is in the way of anything on trail, had to have the computer reflashed twice, and blowing the driveshafts on not to difficult trails. I mean it was a nice truck to drive down the street, but man it did not like crawlinf the rocks out here in SoCal.

 

[gt4660]

Your procedure for setting the initial advance is correct. It should be set with the vacuum advance disconnected and plugged. The fact that the timing is advanced after the vacuum advance is hooked up indicates that you are getting some manifold vacuum at idle.....and there is nothing wrong with that.

Without knowing how much advance is in the distributor, it is hard to say what the initial setting should be. Total advance should be in the range of 32-34 degrees for your Jeep I believe, so if you have an initial setting of 12, then you would want no more than 11 in the distributor......11 in the distributor is equal to 22 at the crankshaft.

So here is what I would do. Your harmonic balancer is most likely marked in 2 degree increments up to 12 degrees or so. Assuming the marks stop at 12 degrees, measure that distance around the balancer. Measure from 12 degrees and equal amount around the balancer and make a mark......this should be about 24 degrees. Measure from you 24 degree mark another distance equal to the 12 degress and make another mark. This should be approximately 36 degrees.

Now start the motor and measure the total advance with the engine reved up to approximately 3600 rpm. You want the engine to be running fast enough that all of the advance is in and you can measure it with the timing light. This will not be exact as you timing marks are not exact, but it will give you an idea of where you are at. It you get a reading greater than 36, then you can take some of the initial out to reduce the total timing and not have damage to your engine from pinging and detonation.

My guess would be that 12 degrees initial is too much, but it does depend on what's in the distributor......

12 degrees is what is recommended as a starting point( from the company website). I am unsure what this exact dizzy has for mechanical advance. I think 24 from reading the website. So that would make it 36 total.

 

[gt4660]

first, welcome to the forum
second, Hutchmans advice is spot on, go do it
third, I see you have an 08 Rubicon, I feel sorry for you, I sold mine after having bent the rear axle twice, having to replace the swaybar disconnect because it is in the way of anything on trail, had to have the computer reflashed twice, and blowing the driveshafts on not to difficult trails. I mean it was a nice truck to drive down the street, but man it did not like crawlinf the rocks out here in SoCal.

No issue with mine! But anything can happen.