Timing Help

JHEMSRIV

New Member
Hello, I recently installed a new D.U.I. distributor in my 71 Riviera. Its at about 12 degrees and runs smooth at idle. once I start to drive it it backfires and hesitates like crazy. I tried adjusting the Total timing but my Innova timing light kept going out, it would stay at 2500 rpm for 3 seconds then drop to 1200 rpm then 000 then back to 2500 for 3 seconds. I left it where it sounded smooth at 2500 rpm and drove it and same thing , no power, backfires through carb and pops out exhaust. Any suggestions?
 

LARRY70GS

Active Member
The hesitation and back firing sounds like something else to me. You need to take a vacuum reading to make sure you don't have a vacuum leak somewhere. If it is back firing out of the carburetor, that means it is lean.

Having said that, you do not need an RPM readout to set total timing. In fact, you are better off without one. Make sure your mechanical advance, and vacuum advance are working. First disconnect and plug the vacuum advance. Point the light at your balancer and rev the engine. If the mechanical advance is working, you should see the mark move up as the timing increases. Then hook the vacuum advance up to manifold vacuum. You should hear an increase in idle speed and see the mark move up.

If you want to set your total timing, use the dial back feature. First, disconnect and plug the vacuum advance again. Then set the timing light advance readout to the total you want to set, say 32*. Point the light at the timing tab. The mark should be somewhere below the tab. Slowly rev the engine. As you do, the mark should move up. When it reaches the 0 on the tab, you are at what you set the readout to. Now here is the most important part. You want to keep increasing the RPM to MAKE SURE, that all the mechanical timing is in, ie, the weights are FULLY EXTENDED. This doesn't magically happen at 2500 RPM, or any other RPM. It is a function of weight mass, and spring tension. The biggest mistake made is assuming that all the mechanical timing is in when it isn't. When the weights swing out to their limit, the timing mark will stop moving up no matter how much RPM you give it. If in the previous step, your mark moves ABOVE the 0 on the tab, you have MORE total timing than what you set your dial back readout to. In that case, you need to retard the distributor by turning it clock wise. Then check again. If you want 32* total, then set the readout to that. As you rev the engine, the mark should stop at the 0 and move no higher. If it moves higher, retard the distributor.

This is the main reason, I use the LIGHTEST springs I can find to set the total timing. Lots of springs don't allow full mechanical advance until 4000 RPM or higher. Guys set their total advance at 2500 RPM, and then wonder why the engine pings from too much timing. Use light springs, set the total to what you want, then put different springs to bring the total in where you want it. 2500-3000 is a good target.

Remember to reconnect the vacuum advance.

 

LARRY70GS

Active Member
Is this you?

 
I suppose you installed a new HEI plug harness on at the same time and the plug wires are all separted by the 1/2" rule to eliminate cross firing?
 
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