1971 Supreme

Today I was going to install the Crane dist. kit onto the car. First I wanted to see what kind of performance tune the Proform HEI dist had. Disconnected the vacuum advance plugged port on the manifold where it was plugged into and tried to start the car. Real hard to start, just backfires up thru the carb, which I assume means its running lean? When i can manage to get it started, any movement of the throttle will stall the engine. But now if you plug the vacuum advance back it, starts right up and will idle around 900 or so. Pulled the dist cap to see if any wires from the module could possible be interfering with the weights, it all looks good. No binding when physically moving the rotor, everything works smoothly. Tried it again, same result, hard to start and pops back thru the carb. Plug the advance in and it starts easily and runs smoothly at 900 rpms? Checked the timing with the advance hooked up due to thats the only way it will run and it about 30* at 900 to 1000 rpms?? The engine is a performance built 403, everything is new on it. During the break in a few weeks back it went fine, but the vacuum advance was plugged in too. The distributer is for an olds engine. I havent checked total timing yet cause it wont run unless the vac adv is plugged in. The carb is a Holley 750 vac sec. The mixture screws are about 1.5 turns out from full in position. Im missing something here, but just cant figure it out?? Any ideas would be greatly appreciated.


Engine Specs

M&J 403
+.024 KB Pistons -.030 deck
Cometic Head gaskets .040
Ultradyne Cam 231/239 .517/541 LC 109
Cloyes Timing chain
#2 cylinder heads, street/strip port, 2.072/1.625 Milidon Valves 64cc ARP Main studs and straps ARP Head studs All Clevite Bearings Edelbrock Performer Intake
Full block machine, bake, blast, bore, hone, deck, line hone 330 Crank grind 10/10 full rotating assembly balanced

What I've added:
Flowcooler Water Pump
Robbie Mac Fuel Pump
Holley 750 Vac Sec. Carb
160* Thermostat
Hedman Ceramic Coated Headers
TH350 Trans
Hughes 2500 Stall Converter
3;23 Limited Slip Rearend


Thanks
Brian

oldcutlass

When you disconnect your advance, since it is hooked to manifold vacuum your idle speed at the carb needs to be increased. Then you can do what you want to figure out the settings.

1971 Supreme

ive tried that, Ive adjusted the idle speed up and tried make up for the lean condtion by adjusting the mixture screws. It runs really poor with it (vac sec) disconnected and any attempt move the throttle, it will spit back thru the carb and dies, I cant seem to get it to run long enough to be able make changes as the car is runing. When turn the idle up a little bit, any movement of throttle will usually result in a flame out of the carb.Funny thing is, if you plug the vac adv in, it will smooth out and the idle speed will increase over the 2000 rpm, then I have to readjust the mixture screws back to where they were before I ajusted them when trying to get it runnung with the vac adv disconnected. I have been chasing this all day, so Im sure Im missing something. Never seen one not wanting to run with the vac adv disconnected before???

78Delta

Your cam specs look good. What is static compression pressure? Or Compression ratio? What is your vac gage showing?

Plug the line going to the vac advance pot, loosen hold down bolt and manually advance your distributor. Your mechanical setting is retarded, which is why it is sparking on the intake stroke. I.E.: flame through Carb.

If you are running good compression 130psi or higher, you might not need vac advance at all. Vacuum advance was an add on by the automakers to increase compression pressure for stock engines running with lower compression ratios. Predominately Vacuum Advance purpose is only acceleration, it should be fairly benign at idle.

Try your setup with heavier weights and light springs to move the mechanical advance quicker. Also if this is HEI, check the two wires going to the pickup coil. This could be and intermittent issue with one of the wires. They are known for breaking and giving the symptoms you describe. The wire ends move with the plate, the back and forth action weakens them.

If your stock engine came from the factory with 8.5:1 compression and you are running 10:1 or more, etc... You can not use the factory tune up specs.

Use the Vac gage when you set the baseline mechanical timing and carburator idle adjustments. Make sure the butterflies are shut and throttle shaft is not drawing air. Adjust up and down watching the vac gage needle, the engine should not knock or ping under acceleration, and yet perform with crisp response.

1971 Supreme

Thank You 78 Delta. I messed around with it till I got it right last weekend, The Proform HEI dist that I have in it says it has a performance curve. I can see how that was possible since both springs were as stiff as the stock GM dist. springs were? I ended up using the Crane kit, one heavy spring and one light spring and it put me all in at about 34* right around 3100 rpm. Tried a couple different spring but it seem to like this one the best. Also my initial seemed a little high to me at 16*, but thats where it seems to run the best at. No ping or rattle as of yet. With that cam the best I can get it to idle at is between 850-900 in park, which puts me at 650 to 700 in gear. I may bump the curd idle up just a little bit, although it doent die in gear,,,,it sure sounds like it wants to. I just need to keep it idling under 800 in gear cause thats roughly when the advance starts to come in at and finishes up around 34 at 3100rpm.

Thanks for the help

Brian


The highest vacuum I can get on the gauge is right around 12" at idle dropping to between 9 & 10" in gear. I probably should change my power valve, cause if I remember right, the rebuild kit came with a #65. If you divide the total vacuum in gear by two, like I've read several times a 45 or even a 35 would maybe be what I need?

Intragration

16 degrees initial sounds good. It's higher than factory, but it's right about where it falls when you have the centrifugal advance set up correctly. At 34-35 degrees total, as long as you're not getting any detonation and you don't have any hot start problems, you're where you need to be. I used the two light Crane springs which seemed to give me a little more centrifugal advance, but I needed to keep my initial at 14 degrees to avoid hot start problems.

JOHNNYOLDS442

This seems simple to me the timing is alittle off .
Like it is too retarded but i guess thats what you guys figured out already.
It reminds me of my 70 455 does the same thing when i disconnect the advance it wants to stall!

78Delta

Brian;

It sounds like you are getting closer. Here is a good link to Kens Speed Shop, RE Holley Info: http://www.angelfire.com/fl4/pontiacdude428/HolleyInfo2.html

I wouldn’t tear apart the Carb until you rule out some other things first. Also a PV as low as 4.5 – 2.5 might really hurt your midrange and transition air fuel ratio when cruising and under light load.

You really need to drive the car with the vacuum gage attached. I used to do this temporarily by using a longer hose and camp it under the wiper blade just enough so I could read it for diagnostics. Of course the best is a dash or console mounted gage that connects to the manifold that is reading the actual average vacuum that is under the butterflies, and not a fitting stuck in one of the runners.

You need to see what the engine is doing at the various ranges; idle, light load, moderate load, heavy acceleration and wide open throttle (WOT). At WOT you should be about 1.25 to .75, without any popping, pinging, dead spots or other issues.

A value of 12 that drops to 9 isn’t correct, that is a 25 percent drop and it almost kills the engine. What is the needle doing at 12? Flicker lightly with the valve pulses, or wide fluctuation but keeping time with valves does it start low and then just continue lower until stall?

I would unhook and plug off all vacuum connections including the booster and pvc. Start the engine and read the gage, watch the needle.

Then take a clean rag or towel and choke off the Carburetor at the airhorn; does it abruptly die, slowly die, or speed up and die?

Next check for vacuum leaks, the starting fluid in a can works good, it just ether, wd40 also works, as does alcohol in a squirt bottle. Spray the intake manifold where it mates with the head first. Do both sides. Notice for change in vacuum reading and audible “flare” in engine speed. Then spray base of carburetor and notice for items as mentioned before. Double check any areas where it caused a change in reading or immediate increase in RPM. If intake manifold is leaking re-torque the intake manifold bolts in proper pattern and see if this fixed the problem. Do the same for the carb bolts, ensure the carb has a good gasket.

Recheck your work, re-evaluate for vacuum leaks using same technique after making any adjustments. Some flaring is normal, especially when near the throttle shafts of the primaries and secondary’s. If it is excessive, check for excessive play at the throttle body, it is a replaceable part through Holley and usually less money than buying a whole new carburetor.

Start plugging the vacuum controlled items back in one at a time and watch the needle of the Vac Gage. The most suspect items would be the valve in the brake booster and the regulator or hose connecting the transmission regulator to the manifold source. The next would be any vacuum motors to head lamps doors or etc…, or the dash motors on the heater and hot air distribution door controls under and behind the dash.

This will be a noticeable hiss. The hiss on this year GM car when switching from defrost, to vent, to heat is normal, but should stop within 2 – 3 seconds. This is also true for any door controls attached to the head lamp switch. If it is hissing constantly it is a vacuum leak that is harming runability of the engine.

Once vacuum leaks are ruled out and you still have the problem; the next is to rule out problems with mechanical timing. Pull #1 Spark plug at find the true Top Dead Center of the piston for #1 Cylinder. Mark where the tower is for the #1 Wire at the distributor and remove the cap. Does the rotor point to #1? If not re-orient the distributor so that the rotor is pointing to #1.
Restart the car, did this fix it? If it did it is most likely your distributor is one tooth off of where it should be. If you can adjust it on the car then you don’t need to Reset it , otherwise you will have to pull out the distributor and make sure the rotor is correctly pointing to the #1 wire tower in the cap, than make your final adjustment with the car running.

If none this effort fails to change anything, most likely your cam was degree’d incorrectly at install or the timing gear and timing chain was lined up with one tooth off. …Any more than this and unlikely it would run at all.

Once all this is verified, or corrected, turn out the idle mixture screws a quarter turn at a time with engine running and Vacuum gage hooked up. Watch the needle until it hits the highest setting and then starts back down on the gage. This is the correct idle mix.

You should now be in the ball park to final tune.

1971 Supreme

Thanks for the article 78Delta, its funny, cause a couple days ago I read that exact same article. You were correct about it having a vacuum leak. It was in the brand new brake booster. The only reason I replaced the original was it was rusted very badly and I had read some article that stock boosters required 18 to 20" to operate correctly. I really dont think that article was correct? All week I had been doing tests on the car checking for any vac leaks, everything seemed good. Just for the hell of it, I disconnected the booster from the main vac port on the back side of the carb and the vac gauge actually increased a little to about 12.5" and just a hair below thatin gear, at the most I would say it dropped a 1/2 " of vac on gauge. So I changed out the hose and the valve on the booster which didnt help at all, removed the new booster and put the old crusty stock one on, and I'll be damned,,,,,,the drop in vac is gone. Plus it feels like the old booster works fine under 18" of vac unlike the article I read somewhere about that. That new booster came as a package deal with a bunch of other brake components. So I called OPG and they are sending me out a replacement. I just sent the bad one back to them Thursday morning. Plus I decided to mount a vac gauge in the car. So the new 4 hole bezel and gauge came in the mail yesterday. Going to reposition my other gauges and installed the vac one with them this weekend. Thanks for all the info, I did all the tests you mentioned hear and even went down to the modulator on the trans for any leaks. I never would have suspected the booster due to it being new, but I have been burned by thinking like that many times before so you'd think by now I would have learned. Going to put the rest of my front end on too this up coming week so that when I test drive it down the road I can pay more attention to the what the car is doing rather than constantly scanning for police cars,,,,lol. I must have read your thought before you even wrote them down, honestly the past couple evenings I've been out back trying to figure out why it was dropping like that. Hopefully I get the new booster today and "fingers crossed",,,,,it works fine. My original one is just ate up with rust and although its working now,,,,,I dont think it will last for vey long,,,,,some spots are getting pretty thin.


Thanks again, I really appreciate the help.

Brian

Intragration

Glad to hear you pinpointed the problem.

One thing about the article, in case anyone else is reading this, the only way it's possible for the distributor to be "off a tooth" is if you're trying to turn it to get to your desired timing and you're hitting the firewall or the manifold. If you can turn it within a range and reach your desired initial timing and the number one terminal is generally pointing towards number one cylinder, it's not "off". It's not like a timing set, where if you're off a tooth it's wrong.

78Delta

Brian;

Very glad everything worked out.

Also; Intragration, you are also correct the distributor being "off a tooth" is a shop term, and it is usually because you can't get the adjustment you need with the current distributor install. You have to pull the distributor, and re-install moving the shaft a tooth rtd. or adv. to get the rotor to point where you want it.

Technically the distributor will turn all the way around and is fully adjustable in either rotation as long as it doesn't bump into something. Typically it is the firewall for rear mounted, or the water inlet or other brackets and pieces on the front mounted units.

EF