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I wanted to get some opinions about the way the car is running to see if there are any tell tale signs that I may be missing. Sorry about the long rambling post and thanks to anyone who is able and willing to get through it.
First, work done since last fall that might impact this is new 2.5" dual exhaust, HEI upgrade from factory points with new 8MM wires, plugs gaped at 0.45 and intake manifold gasket.
Other things done earlier was a new rebuilt carb from Everyday Peformance including new carb to manifold gasket and carb torqued down properly and new vacuum lines everywhere and open ports capped trying to make sure there were no obvious vacuum leaks.
With the HEI upgrade the factory air cleaner doesn't fit so I now have one of those aftermarket 14" air cleaners with a breather on the passenger valve cover. Manifold port that the factory air cleaner connected to has been capped.
Vacuum now sits at about 17.2", which I thought was low but have recently found in a different post that this engine at factory specs could actually be more like 16"-17.5".
Two people that have taken a look prior to the new changes both covered the carb and noted how the RPM increased quite a bit and the engine smoothed out saying that it appears to be running lean caused by a vacuum leak. I did the propane test all over and didn't find anything, which lead to the thought that it might be internal at the intake manifold gasket.
I was really surprised at how well it started and ran first shot with the new distributor and all the other work. After doing my best with the timing and fuel mixture screws I have arrived at the 17.2" vacuum and it does run much better than before, including being able to cover the carb with next to no change which I think is good? But, it still seems to run rough. Last year it also didn't run well with the RPM set to 600ish in gear where now it does. It also was hard to keep running, where now it runs well on its own just rough, other than the same quirk where after sitting all night, I put the gas to the floor once, release and fire it up and it runs in high idle for about 5 seconds then stalls. One more shot of gas, turn the key and all is good like last year. I don't know if that points to anything or maybe I should just try two shots of gas first, start it and see what happens.
I also tried adjusting the timing based on vacuum rather than the timing light alone. While this helped get the vacuum up and run better, I was alarmed when I checked the timing light and saw that at 1100RPM with the distributor advance plugged it said I was at 36* - is it even possible to have that much base timing? I thought for sure the timing mark must have slipped, but after checking with a piston stop tool, it is maybe a degree or two out, certainly nothing that would cause the 36* number. I have heard that Olds engines in general like lots of base timing as well as total timing and that HEI doesn't offer much in the way of mechanical advance but I can't see it being a good thing for the base timing to be much more than maybe low 20's. I have also read posts of all of that being argued against so I don't know. The fuel mixture screws also seem to be a lot less turns out than where they had to be last year, so I think that must be a good thing too.
I am going to go take another shot at it tomorrow and see what I can do. I am also going to take a really good look at the brake booster. Everything appeared fine but being a large source of vacuum maybe there is a leak there somewhere.
You are on the right track with pumping the gas 2x before starting the engine. Also ensure that the choke is adjusted properly.
As for timing, the initial setting depends upon how much mechanical advance that particular distributor has. Remember that initial is just total - mechanical.
Ideally, you should set the total to 32-36 (or whatever gives the best performance for your engine) then just take note of where the initial ended up so you can easily verify / readjust later without going through setting the total at higher RPM.
Once you have the initial timing set, try connecting the vacuum advance to both ported and manifold vacuum to see which works better. On my engine, I found that connecting to manifold increased the vacuum and smoothed it out quite a bit - it went from a bouncy 15-ish to a steady 16+. This resulted in a smoother idle as well.
Thanks, I will give the manifold vacuum a try and see what happens. Also, what RPM do you check total timing at? I have read varying numbers but the highest seemed to be 3000RPM.
You note total timing at what ever rpm it actually stops advancing. Was this HEI bought and installed new by you and did you change the stop bushing or the springs.? If not you need to see whats installed and proceed from there. Initial timing of 36* is not good for your engine. On a side note, leave your vacuum advance disconnected until you get your timing correct and then set it up.
I took the cap and rotor off and there are silver springs in there. Based on online info, they appear to be the easiest or fastest advancing compared to the black and gold springs. There also looked to be heavy gauge silver springs that are the slowest, but these are for sure not those.
The instructions it comes with say that it adds 20 degrees of mechanical advance that will come in around 1800RPM and level off from there. So, base timing should be roughly 16 degrees to get 36 degrees total. If it is a little more like 38 or something is that acceptable or still too much?
So with the vacuum advance plugged, my plan is to reset base timing to 16 with the newly confirmed TDC mark, then rev it up to whenever it stops advancing as you mentioned above and see what number I get and at what RPM and adjust as required to get 36ish total. Once that is done, start looking into what kind of vacuum advance I am getting.
Is there a good vacuum advance number to aim for at the 800ish RPM in park? I read that some people add base, vacuum and mechanical to get total timing and the reasoning is situations like highway cruising at low RPM. Unless I misunderstand that doesn't make sense to me. Vacuum decreases as RPM goes up and mechanical kicks in right? So even cruising on a highway, the RPM might be low enough that vacuum advance is still contributing a lot, but mechanical would be very little, and if the throttle were to be increased vacuum would start to reduce as mechanical increases. I just can't think of a situation where vacuum and mechanical would both be near 100%...
Lets say you have all in at 2800rpm, mechanical. "Right" gearing, speed limit, running at 2900rpm at, for example, 70mph, with really low throttle opening and load-> also high vacuum.
Mechanical advance is a product of RPM, the higher the RPM the more it advances until it reaches the stops. Vacuum advance is related to load, the least load is idle and steady cruising. WOT throttle is the heaviest and drops vacuum to near or at 0 inches.
These are the instructions. There is also a picture of the distributor. I will start with firing it up and seeing where I am at as soon as I can get out there today. I was just surprised when the instructions noted 1800RPM but best to see what I am actually at first.
First note your initial timing at idle and what rpm. Then run the rpms up and note your mechanical timing and at what rpm it stops. 1800 is a bit soon for all your mechanical advance to to be coming in.
So with base timing backed down to 16*, and the fuel mixture and idle speeds set, it looks like total timing is about 36* at around 1800-2000 rpm. Other than coming in at a fairly low RPM I think I am happy with that.
But, when playing around with the vacuum advance, it would appear that the ported vacuum of the carb on the drivers side beside the fuel line is pulling 0 vacuum. I kept winding the canister screw on the distributor out a couple turns and then plugging it back into the carb, but there was no change in how it ran and the timing mark didn't move at all. I plugged it into the manifold and the timing mark moved a lot. I plugged the vacuum gauge into the carb port and it didn't register anything.
Should this port on the carb be pulling vacuum or has the distributor been incorrectly connected here at some point? If it should be pulling vacuum is that strictly a carb rebuild issue or is there another reason?
Last edited by 71OldsCut; May 23rd, 2019 at 06:26 PM.
Someone did not read the 2 links I provided above. Ported vacuum at idle is 0 of very close to it, but comes in once out of the idle circuit. Manifold vacuum has vacuum at all times. Manifold and ported are the same once out of the idle circuit.
So with base timing backed down to 16*, and the fuel mixture and idle speeds set, it looks like total timing is about 36* at around 1800-2000 rpm. Other than coming in at a fairly low idle I think I am happy with that.
You can mix springs to have the advance come a bit later. My distributor has one light and one medium spring. I found that using two light springs had some advance coming in at idle, so when I turned the AC on the RPM would drop, which caused the timing to decrease, which caused the RPM to drop - this caused a downward spiral until the engine bogged down and died. Swapping one light spring for a medium spring cured that issue.
You got me, lol. I was out working in the garage and figured I would dig into the reading material later.
But, I think other than having the timing come in earlier than I would like, I am happy with it now. It runs a steady 17.2" vacuum at idle with the 16* base timing, and covering the carb doesn't have any noticeable effect on the way the engine runs or the vacuum/rpm reading. I will see if I can find a set of springs for the HEI distributors. I have a set but it was for the points style I had before. Maybe I will try one light and one medium or just two mediums and check everything again. But the car doesn't get driven hard so I think it is all good for now.
I think all that is left is playing with the modulator on the transmission to see if I can get it to shift just a little sooner, and it looks like there may still be a very small leak on the pesky valve covers. Both minor issues.
Thanks to all for the help and knowledge. It is so nice to finally have all this work done. It runs good, sounds good, and has 3rd gear now. All that is left is the fun part of putting some miles on it and making sure no leaks develop or any other problems for that matter.... and a good wash/wax, lol.
May 22nd, 2019, 04:30 PM
