I am not understanding what is going on with my timing so I’m reaching out to you gurus on this one. I had to replace my distributor as my original one keeps eating the pickup coils leaving me on the side of the road. I purchased a Procomp HEI from Amazon and it runs for more than 5 miles. Yay me. Ran ok, about as good as before but not great. Hard to start warm.

I drove about 700 miles on the interstate and noticed my coolant temp rose quickly over 2500 rpm (~80 mph 2.56 rear w/th400). Thinking it’s too advanced at that rpm and it’s hard to start when warm so let’s get some timing baselines.

So here’s what I got:
Idle at 550 rpm 8* initial 27* w/vac
1100 rpm 18* mechanical 35* w/vac
1500 rpm 23* mechanical 42* w/vac
2000 rpm 14* mechanical 23* w/vac (?????)
vacuum at idle: 18 in/hg, 21 solid up to 2000 rpm

1500 rpm is a very happy spot on the road for this cruiser. Even standing on the throttle the motor shifts under 2500 rpm until 3rd gear. I ran out of daylight and wife goodwill to document 2500-3000 rpm timing and stopped when I got my 2000 results. Stiffest springs I had in hand in the Procomp. Supposedly it has 22* mechanical and adjustable vacuum (but I can’t find that adjustment).

So what the heck could be going on with losing timing at 2000 rpm? What’s the correct order of a) timing b) idle mixture screw c) idle speed?

 

Your timing needs more advance, try 16/18 at idle without vacuum advance. Then limit your vacuum advance canister to 10.

 

Hmm, it shouldn't be hard to start with 8 degrees initial. With 22 mechanical, you want 14 to 16 at idle. Strange it starts losing vacuum advance at 2000 rpm, what port are you running it off? Was it running hot before?

 

I guess I’ll look into an aftermarket vacuum advance then. When I put the distributor in I looked for an adjustment but couldn’t find one. My concern with this distributor is it’s a “high performance” model and I’ve got a smog cruiser. It’s not a race car

 

There are adjustable vacuum canisters, and also adjustable stops for your existing vacuum canister.

I made this adjustable stop for my 24 degree vacuum advance canister.


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I run the vacuum from a manifold port on the carb. I used the same port for the vacuum readings — 21 in/Hg at 2000 rpm to verify. The car has never run alarm hot on me but the temps climb over 210 with a) AC on in traffic and/or b) over 75-80 mph. 180* thermostat. Slow cruise and no AC, the gauge never goes over the 1/4 tick mark. I’m probably over cautious of temp because of the Siamese cylinders.

I too am curious about WTH with timing loss at 2000 rpm. I will attempt to quadruple check it in daylight as 14* is readable with the eyeball. All measurements were from a dial-back light which has been accurate to date.

I’m trying to follow CSM procedures but my ignition system is so non-stock at this point and acting odd I’m not sure how to proceed.

 

​​​​​​​Thanks! It may have a similar mechanism, certainly not the Allen wrench in the vacuum port type.

 

The allen wrench in the port type is a rate adjustment not a limit. It has a spring behind the adjustment screw that you can adjust to compensate for variations of vacuum levels other than stock. The stop above or something like it is what you want.

If you have a dial back timing light set the light to whatever advance you want and then use the 0 on the timing tab to line up with the mark on the balancer.

 

Every adjustable vacuum advance I have seen is an Allen key type. It certainly does limit the amount of vacuum advance. It has to be the right size key and they can sometimes be tricky to engage. On a stock 403, you should be able to add much more than your current timing and not be a hard start. I ran close to 60 degrees part throttle with vacuum advance. I had hard starting with the tiny, wimpy 307 starter when warm, replaced a 307 motor. With a full size factory 403 or aftermarket mini starter, it should crank over fine.

 

Another thing you can try (w/o vacuum advance hooked up)is set your timing light up for 34-35 degrees and run the rpms up to a point where it isnt advancing anymore.
And set to your 0 on balancer.
Then go back to idle and check initial. That number you can use as a basis for other adv/retard adjustments.
Most all vacuum advances are stamped with the amout of advance (in dist degrees)they have built into them.
If you can make a stop great.
If not search for Lars Grimsrud? HEI papers.
He has compiled a list of factory vacuum advance canisters with specs. that you should be able to find one that fits the bill and can be usually picked up at any local parts store.

 

I’ll try adding advance and checking settings/drive feel again when the weather is nicer.

Does anyone have any idea why timing would DROP at part throttle 2k rpm? That’s what stumps me…

I really don’t trust that Chinesium distributor but attempts to fix the OEM has resulted in failure and side of the road distributor swaps.

 

If you get tired of the Chinese piece. Find an original HEI and use your OEM weights.
FYI, Have an extra HEI Olds distributor housing with the housing, shaft, and gear only. These have no electronics, no weights, and nothing more. It was an 30-1893 from A1-cardone before I stripped it for parts.
$50’plus the ship.
sigtauswt@yahoo.com
Central Tx.

 

Yeah, that timing drop is weird. I have also had two different HEI loose pickup coils and Dad the same. They were everywhere in the junkyards a few years back so I always had a spare. Try 16 degrees as base timing with the vacuum advance plugged. If it is hard starting or doing weird things, that reman distributor with your factory weights installed is a really good solution.

 

Hopefully during the holiday weekend I’ll have time to fiddle some more. I want to verify that 2k reading with a plain Jane light first to eliminate a failure of the other light. I was in a hurry so step 1 is to re-verify the findings I think.
The first time my factory unit ate a coil I fired the parts cannon at it so there’s plenty of spares to choose from. I kept every part of my old distributor including the GM branded ICM that came with the car. And as I found out then the answer is likely simple, if not convenient. I wonder if the OEM weights and vac can would transfer also…

 

I may take you up on that once I have time to look into it deeper. Thanks!

 

@oldcutlass @Fun71 @olds 307 and 403

Thank you all for your help. I added a vacuum stop plate to to limit vacuum to -9* then set timing to factory specs and all is well.

For my ‘77 403 setting timing to around 22* at 1100 rpm (vacuum disconnected) is a very solid baseline.

Hope this info helps someone in the future and again thanks to the people here who were all correct.

 

Was zero on the balancer confirmed to be #1 at exactly TDC?

Re: coil failure, is there full battery voltage to the distributor? Is the distributor well grounded?

Good luck!!!

 

What is your timing without vacuum advance hooked up at idle?

 

I want to say around 10. When I get an assistant I’d like to map it out again by 500’s for my own curiosity. That motor rarely goes over 2500 rpm so that seems a good spot to max assuming it’s happy.

The battery tested bad so I’m also curious if that had to with hard starts.

On a nice warm day with the A/C on the temp hung a needle past 210 at 75mph so looking better!

 

With an HEI 10* is not enough, you need to go to 16-18 at idle. You also need to limit your vacuum advance to 10*. Setting the timing at 1100 rpm, the distributor is already advancing.

 

The factory spec is 1100 rpm for many years Oldsmobile V8 with HEI. Factory is probably 20 at 1100 rpm. If it runs better, good stuff.