Delmont 88 PA

One trick that might help, providing that the car will idle, is to disconnect and plug the vacuum line to the distributor, start the car and slowly turn the distributor back and forth until you reach the highest rpm or vacuum. If you don't have a tach or vacuum gauge you can usually ballpark this by ear. At this point you should be able to crack the throttle and not get a backfire through the carb. This should be done for testing only since chances are the car could be advanced to a point that it will ping when driven under load. Again, this is a good test to see if all other systems are operating correctly.

Properly time the car with a timing light prior to driving it. If you do this test and then check the timing it should be advanced too far. If you put a light on it and it doesn't read that it's way advanced your timing mark may be off. If it does read advanced then use your timing light and time it as oldscutlass mentioned above.

robgarner

Thanks guys. I read the posts since my last post and have been working on those things. So here's the latest. This morning i went to start the car trying to adjust the carb then distributor to get the best rpm and sweet spot. I had the car running longer than i ever have since it stopped, maybe 15 min. I said to myself what the hell I've been adjusting this distributor way advance let me put the light on it and by chance see what it says. The timing was 12* i was like what the hell! So i adjusted the distributor to have it dead on 8*. Now the difference is the car was warmed up. Would this have been the difference b/w my timing light reading 0* to it reading 12*? Just the car being warmed up?

Next i was adjusting the air/fuel mixture screws on my carb and trying to listen for a decrease in rpm's but nothing. Would getting a vacuum/boost gauge and adjusting for the highest vacuum value be better? The gauge is only $25 and to me would be worth it. OR is there another way to adjust it? Yes i have done the normal setting of secrewing them all the way down then backing them out 2 full turns like the rochester manual says.

Delmont 88 PA

Timing to highest vacuum was only to get you in the ballpark if you could not get it to run using the timing light. What you did actually set the timing correctly which is better.

If your car is warmed up your engine should be running at regular instead of fast idle. On fast idle you may have had some mechanical advance and if you set your timing then (as someone mentioned in an earlier post) it would not be advanced enough at regular idle speeds.

To set your carb make sure that the car is fully warmed up and idling at regular idle speed. Turn one screw in until the idle becomes rough and then back it out to its highest rpm. For economy you can usually turn it back it a quarter turn (leaner) if you like. If you turn your idle screws in all the way in and the idle doesn't change there is something wrong with your carburetor or the car is idling too fast and running in the transition from idle to main metering (getting some gas from the main metering circuit).

robgarner

Ok now i have the timing set and carb set i beleive, i drove the car around the block and it hesitates on takeoff and driving. I put a edelbrock 750 carb on the car to eliminate the carb issue and same thing. Do you think my timing should be 10* or 12* degrees? Any ideas?

Rickman48

Mentioned earlier - I time every car 'by ear'.
Advance until ping, retard 2 degrees, and lock the distributer.
As far as carb adjustment, I ALWAYS use a vacuum guage - highest reading while turning in.
Octane will make a difference in ping setting - use the same octane all the time, once set.

robgarner

Ok so this is what i have. I have a timing gun with the rpm setting. i set the timing to 1300rpm in park. hooked up vacuum guage and it measured 15. adjusted air/fuel mix screws to 2.5 out to give me 18 vac and 1500rpm. adjusted idle screw to get rpm back down to 1100rpm and vac measure 15 maybe 15.5. I still get hesitation when i hit the throttle. Should i be adjust the air/fuel mix screws when the car is in "drive"? where am i going wrong? i didnt used to have a hesitation. carb is new, plugs are new, timing is at 8*. what am i missing?

Rickman48

As said, MORE TIMING!

robgarner

what do you think i should set the initial timing to? i have it at 8* which is what is recommend for a stock 455.

robgarner

my timing tab goes 12 8 4 0 -4. I could go 10 or 12. 10 i guess would be the next best thing.

MDchanic

Okay, I think we need to stop and collect some basic information here, which we failed to do in the beginning.

You are working on an Oldsmobile of unknown year, body style, and drivetrain components with a 455 that you put into it (not its original engine), also of unknown year, compression ratio, heads, and cam, but "all original" except for the HEI distributor, a new timing chain, and possibly a new pair of head gaskets (I wasn't clear on that).
It ran fine until it quit suddenly on the highway and wouldn't restart.

So,

• What year, model, and body style are the car?
• What sort of transmission and rear end are installed?
• Are there any accessories, especially new or aftermarket ones?
• What year is the engine?
• What sort of car did it come out of?
• What is the letter on the heads?
• Did you have the heads off? IF so, were the pistons deep or shallow dish?
• If you had the heads off, what sort of head gaskets did you install?
• Why did you change to an HEI distributor (or replace the HEI distributor that was already there)?

As I said earlier:
If you have an HEI distributor in a motor that started out with a points distributor, you CANNOT time it to the original specification, because the HEI distributor has less mechanical advance than the points distributor did.

You HAVE to have it more advanced at idle than specified, or it will not run right.

Without knowing what year and model your engine is, we cannot know what speed you are supposed to set the idle at, but, as mentioned above, it wouldn't matter anyway after the change to HEI.

When you adjust the carburetor, FIRST, you adjust the timing, THEN you adjust the carb.
If you have not properly adjusted the timing yet, do not mess with the carb.
Once the timing is right, THEN you put the car in Drive, look at the specified idle for the car that that engine came out of (probably 550 RPM), adjust the idle speed screw so that you have 550 RPM, turn each idle mixture screw in and out SLOWLY, ¼ turn at a time, waiting a few seconds with each ¼ turn, until your idle and / or vacuum is at its highest, then you readjust the speed screw to 550 RPM, then you readjust the mixture screws, then you readjust the speed screw, and keep doing this until it's settled and happy.

That should take care of your off-idle bog.

- Eric

robgarner

MDchanic thanks for your enthusiasm. I apologize for not posting the info


What year, model, and body style are the car?
1971 Olds 98 with origial motor and transmission that has never been rebuilt. The only thing replace is the distributor with HEI and now it has a edelbrock 750.

What sort of transmission and rear end are installed?
Original 400 3 speed trans with shift kit. rebuilt about 2 years go. shifts great.

Are there any accessories, especially new or aftermarket ones?
hei distributor and edelbrock 750 is the only modified parts everything else original or replaced with original.

What year is the engine?
1971 olds 455 320hp i have all the paperwork with the car...bill of sale...owners manual..even options list with prices

What sort of car did it come out of?
original

What is the letter on the heads?
original

Did you have the heads off? IF so, were the pistons deep or shallow dish?
never took heads off

If you had the heads off, what sort of head gaskets did you install?

Why did you change to an HEI distributor (or replace the HEI distributor that was already there)? i changed from points to hei because it was easier.


You make sense when you say i can't set to original initial timing. How do i figure out what to set the initial timing to? from here i think i can figure out the rest. I was going off of the original degree initial timing of 8* and since i got that wrong it went all down hill from there. Do i just adjust the distributor until i feel its in a sweet spot? I understand you last point about adjusting the mixture screws and idle screws and i have that concept down. Now how do i figure out the initial timing? that seems to be my problem.

thanks for your reply as i know im close as heck to getting back on the road. I'll also try to figure out how to post pics of my beast that everyone has tried to help me fix.

robgarner

ok so the hei distributor came out of a 76 olds with a 455. could it be possible to find out the initial timing for the 76 and use that?

MDchanic

As I advised earlier, adjust the timing so that it maxes out at about 35° at about 3,500 RPM (vacuum disconnected). If it pings at this setting under full throttle on a hot day, then dial it back 2° at a time until it doesn't.

The idle timing will fall where it may, probably around 20° BTDC.
So long as the engine starts easily and doesn't buck against the starter while cranking, that idle timing is probably good enough at that setting (If it isn't, then you'll have to change weights and springs to change the mechanical advance curve).

That's it. Nothing fancy.

- Eric

MDchanic

Sure, you could look it up, but the specified timing in those years is way retarded, so you still wouldn't be ahead of the game.

Just set it to 35° at 3,500 RPM (vacuum disconnected).

- Eric

robgarner

Ok i'll set the initial to around 20 BTDC and go from there. i'll probably have to redrop the distributor we'll see. I'll have a response in about an hour. I gotta eat first. thanks again

MDchanic

Any time.

Unless the vacuum can hits something and prevents the distributor from turning where you want it, there should be no need to re-stab it.

- Eric

robgarner

exactly and thanks for saying that. sometimes its the little details that people take for granted that i could miss as this is my first time ever doing this but i'm feeling confident. I'm excited now. hopefully i can get up and running tonight.

robgarner

my other pics were too big. I'll have to adjust them but here is a quick one

MDchanic

8 mpg never rode so smooth .

- Eric

robgarner

heck yeah i tell ya. I spent around $200 driving from Chicago to philadelphia. It rides so smooth. i replaced damn near everything underneath with the exception of the sway bar bushings and it rides great. along with the interior which is 8/10. awesome. i'm going to try to set this timing. i'll let you know how it turns out in a few. BTW its my primary car now by choice. I love this thing.

robgarner

ok i set the timing gun to 21* and turned the distributor until it lined up with the 0* notch. I must say it runs sooth and i drove it around the block and still some hesitation but doesnt seem like as much as before. should i go higher than this for initial timing? should i at least adjust carb air/fuel mix screws to 1.5 out? yes i do have the advance disconnected from the distributor.

MDchanic

You're probably close. Since you've got a low compression motor, even if you're a bit too advanced, it probably won't ping.
Why not give it a rev and see where the timing settles at 3,500 RPM?
If it's around 34-36°, then you're good.
Have you tried starting it? You want to be sure it still starts.
Did you have the vacuum connected when you drove around the block?

If all the timing details are good, I would say, sure, set the idle properly, which will probably eliminate that transition hesitation.

- Eric

robgarner

i realized that i didnt have the vacuum connected when i drove around the block. i just have the hose off but not plugged. I'm going to plug it and rev it and see what happens at 20* 21*. then hook it back up and drive it and see what happens. I forgot about the vacuum advance hose.

robgarner

same thing. I set the timing to 20* solid and rpm to 1100 air/fuel mixture to 1.5 turns and still hesitates with vacuum hooked up. very puzzling. its like i could keep advancing it but not sure if i should. when i advanced it to 21 the rpm when up more and it went down when i went down to 20*. Seems like it would be more of a science to this.

MDchanic

There is no science.

It's all trial and error.

Wherever it runs better is the best place.

You want to set it for maximum mechanical advance at 3,500 RPM, to get the critical full-throttle end of things right, then make the idle whatever it has to be.

This is one of the reasons why, when people post asking about how to switch from points to HEI, I always counsel them to leave well enough alone - You lose your established landmarks, and have to figure out what works best from scratch.

You're headed in the right direction, keep going.

- Eric

robgarner

You're damn right about that. I haven't cranked it to 35000 rpm yet but will tomorrow. right now its set at 20* and 1100rpm. I'll keep with the trial and error tomorrow as i will have a second hand. thanks and tomorrow around 4est i'll reply.

Rickman48

Do you live near Chicago??

Please don't try to rev it to 35000 without a big pan under the motor and eye protection!!!

MDchanic

... And a fire extinguisher and a change of underwear.

robgarner

HA HA and yeah im orginally from chicago but now in PA. Do you think my spark plugs are making a difference? I went from a .060 gap to .035 gap?

MDchanic

0.035" was the original gap, and as such should work fine.

If you want to take advantage of the higher voltage of the HEI, you could go to 0.040" or 0.045".

There were some cars in the late '70s spec'd for 0.060", but the big gaps just didn't work out as well, and most people avoid them now.

- Eric

robgarner

Ok since 20* isn't working i was thinking of starting at 10* and moving up every 2* and see how it sounds. all the way up to 20*. The problem is that is sounds good and doesn't shake much but that's all at idle. should be also try going up to 3500rpm when i go every 2*? the highest rpm i've had it at is 2k but by accident and it was smoking up at storm at 8*.

MDchanic

I missed what's not working about 20°. It sounded to me like you were off to a good start.

Just set the timing light to 25°, then it should idle with the line at 5° ATDC, and as you rev it, it should climb from there to 10° BTDC (which will actually be 35°), and then hold around there. Set the distributor so that happens as you hit 3,500 RPM

- Eric

robgarner

Well i have it on 20* and it still hesitates with vacuum connected and air/fuel mix screws to 1.5 turns out at 1100 rpm.

My timing tab goes -4 0 4 8 12. right now at 0* with the balancer notch at 0* also the timing gun is on 20* and it still drivies with hesitation with the above setting.

It makes me think 20* isn't good either? or i have another problem.

As i rev the car the timing does advance but i havent reved it past 2k rpm. I'm going to try it now.

robgarner

Ok so I think I left out a critical aspect. When I measure the timing to set it the timing jumps all around. So I set my timing gun to 20* and align the notch on the balancer with the 0* mark. Well the timing jumps around from 0* to -4* to 0* to 6*. The distributor is tightened down all the way. I did that to eliminate that as a possibility. Any idea on what would cause this? It's been doing it this whole time I believe. I was originally using a timing gun without rpm and I don't remember it doing it when I set the timing to 8* but I'm going to adjust the timing back down and use that timing gun and see what happens but this could b the cause of my hesitation issue. Any ideas?

olds 307 and 403

You can go more turns out on your mixture screws. Adjust to your best idle. Make sure your vacuum advance is working properly. It could be ruptured or adding too much timing.

robgarner

Ok I'll got more turns out but the vacuum advance is working bc when I connect the line to it my timing increases

Delmont 88 PA

MDchanic, it's funny, and sometimes really appropriate, that you mentioned a change of underwear. When I started my 455 for the first time with open shorty headers I was 1/10th of a second away from needing a spare pair....

robgarner

ok. so this is what i just did. i set the intial to 20*and adjusted the air/fuel mix screws and it helped the timing from jumping around which decreased the hesitation. so im guessing its trial and error to set the timing at exactly 20* because when i adjust the air/fuel mix screws it effects the timing.

I set the timing and adjust the screws the timing moves a bit. its like i have to play with it to get them both steady. set the timing then adjust the screws to get a steady timing mark. then the timing is advanced so i move the distributor then the timing jumps around so i repeat the process. Sounds like trial and error but it seems like the hesitation improved some. Does this sound correct?

MDchanic

Alright, earlier you mentioned that you were trying to set this all at 1100 RPM.
Are you still doing that? If so, then stop, because that is NOT the way to do this.

The HEI distributor has something like 14° of mechanical advance built into it, which starts at zero, begins to advance somewhere around 800 RPM, and reaches a maximum of about 14° between 3,500 and 4,000 (depending on exact model).
If you are trying to adjust it at any speed above about 800 or 900 RPM, it is already into its advance curve, so slight increases in RPM will advance it slightly (thus increasing RPM more, etc.) and slight decreases will retard it slightly, and you can chase an exact adjustment forever.

You need to adjust your initial 20° or so of timing at a dead idle - about 550 to 650 RPM - so that it is set at the bottom of the curve, with another 14° of advance left to go, and not in the middle of the curve, with maybe only another 10° to go before it maxes out.

I already mentioned that the idle speed and mixture screws have to be adjusted in Drive at 550 RPM. The mixture screws are inoperative when the throttle plates are open any more than ____-hair, so if you have them open enough to get it to 1100, they are open too far, mixture adjustments are not doing anything, and a transition bog is a likely consequence.

And the timing does NOT have to be set precisely - Just set it to 34°-35° at 3,500 RPM.
It doesn't matter whether you start at 20° or 18° or 22°, it only matters that you end up at 35°.

Once you've done all that, let us know how it's working, and we can guide you further.

- Eric

robgarner

Ohhh I see! I wasn't doing it in drive. I was doing that in park. Thanks for the detailed explanation it was def needed. I will attempt this tomorrow night or Friday afternoon. I'm not sure if I can adjust the 20* at 500-600 idle rpm. Not sure if the engine will remain running at that low of an idle speed. But I will try. When I switch from park to drive my idle changes from 1100 to 750ish.

So in park adjust rpm to lowest setting to keep running then set initial 20*. Then put in drive at 500rpm and adjust mixture and idle screws. Then rev up to 3500-4000 and find total timing.

In park set the initial and in drive set the carb all at lowest rpm. When I go back to drive my idle rpm should b around 1100 then. Makes sense and I haven't been doing that at all.

Thanks either tomorrow night or Friday afternoon.