tuning and timing questions???

alright i think its about time to do this, and im hoping i can get the answers im looking for. 283 chevy, 262/468 lunati cam, hei distributer, holley 600 carb.. 700r4 trans, 4.10, 3800 lb. + truck. ever since i put on the holley carb, (nothin special. http://holley.com/0-80457S.asp ) i have always had hesitation issues romping on it from a start. even in park. i knew that was always a tuning issuses, but i just delt with it and got around it. finally tying the knots and fixing the little quirks in the truck i figured its time to tackle this.

after reading up on the problems i had, i found out i needed a bigger accelorator pump squirter * ordered * but not yet installed. and a timing light. So basically all i am wanting is just about ALL of the steps, precausions, and knowledge about timing as i can find out. i know the bare basics of timing. but everything is better than not enough information.

here is the light i bought. http://www.jegs.com/i/Equus/390/3568/10002/-1/962916|10711

if you have anymore questions about anything i will try to be quick to respond.

Go to Amazon - http://www.amazon.com/s/ref=nb_ss_b?...ey+Carburetors

Buy two of the manuals listed.

Holley Carburetors by Dave Emanuel - an SA book.

Holley Carburetor Handbook by Mike Urich.

They're on sale right now.

well to be completely honest, i dont need a book on the carburators, just the whole timing deal. if anyone has a link or a website that i could go to to read up on this that explains things sufficiently, then that would be great.!

There will be many opinions on how to set timing... Usually a good rule of thumb is 36* total mechanical timing all in around 2500 rpm. With an initial (idle) timing somewhere around 8-12-16*. This depends on many variables including static and dynamic CR of the motor, fuel octane, altitude, and on and on....

What kind of ignition system do you use? Vacuum advance? Timing should be set with vac advance disconnected and plugged...

I would start at 36* degrees total (without vac) drive it a bit including some wide open throttle then check the spark plugs. You can read the plugs to tell you whether you need more or less timing based on the heat line on the ground electrode of the plug... you want this line to be at or just past the bend in the electrode... adding more timing moves this line further from the tip...see this page for more tips on reading spark plugs (I'm sure there are more/better resources but this one is pretty good):
http://www.dragstuff.com/techarticle...ark-plugs.html

There are links to other related articles on that same page...

As for your off idle stumble that is usually accelerator pump shot too small or too late... usually bigger pump nozzles cure this problem... could also be an indication of vacuum leak or excessively lean mixture...

There will be other suggestions from more experienced folks here but I hope this helps in the meantime...

-Chris

Great link Chris, thank you. :toocool:

If you are looking for some excellent information on igintion timing, check out this link. It is one of my favorites of all time and very educational.

http://www.chevelles.com/forums/show...t=ignition+101

- Skids72 - yes it does have vacuum advance. and as far as a lean mixture? im not trying to say ur wrong, but a 600 cfm carb on a 283 shouldnt be lean AT ALL throughout any rpm should it?? if so i guess i could start looking into that problem some more. next week i will have installed that bigger accel. squirter. and i will let you know how that works. and i will definitely read up on those links which are much appreciated!! thank you!


65ny- also thank you for the link! i will also check it out!

any carb can be too lean on any motor if it's not jetted right... another thing the plugs can tell you is if you are too lean or too rich. Also if you have a vacuum leak you'll be too lean no matter how your carb is jetted...

Probably beside the point as your stumble is most likely the accelerator pump shot ... (also a matter of being too lean when the throttle cracks open)

-Chris

alright well i finally got back to my pickup to check things out, this is the info im reading up on and going off of.. so if theres anything you see different would you let me know? not tryin to stray from clubhotrod but this is about the best discription i could find for the problem.

http://forums.corvetteforum.com/show....php?t=1430339

ok base timing is at the "about appropriate" 12 degrees

the next step was to find my total timing and what not. at just above 2500 rpm, the mark wont go any closer to the pointer , and thats when its set at 36 degrees for a starting point. i had to back it down to about 29 degrees. thats when my marks lined up. i went to check to see if i could turn my distributer any further *counterclockwise* is advanced right? well either way, thats the way i needed to go to get my mark closer. but the distributer is maxed out. i guess what im wondering, is if i may have the distributer set down in there a tooth of of something? or if the 29 degrees total timing is going to be fine?

forgot, i do not have a vaccum canister. do i need one? when i checked the vaccum the other day, it wouldnt get above 11. ill recheck this once i get everything timed.

also, i just took it out for a test drive just to see if anything had changed and it ran perfect. (vaccum advance unhooked and pluged) but when i turned around to head back into town, i just tried to powerbrake it a little to see if that was fixed as well but it just poped and died.

any suggestions?

You need a vacuum advance distributor with vacuum source selected to manifold vacuum and not ported vacuum.
If not, your car will most likely overheat in low speed traffic and at idle.


I've had several people argue that they're doing fine using ported vacuum, but what most people don't realize is that GM developed the ported vacuum system so the engine would run hot at idle and low speeds thereby improving the nox and hydrocarbon factor.
Moh bettah for the smog situation in other words.

GM did have a thermostatic switch to swap over to manifold vacuum when the engine got hot enough and the theory was it would cool down.
True, it did, but sometimes the thermo switches let things get too hot and occasionally engines suffered heat damage.

And . . . some guys are bad about admitting things.
Friend of mine stuck a mechanical advance only distributor on the 327 engine in his roadster.

He claimed it didn't overheat in traffic, but later on I found that the reason he didn't want to go anywhere except Saturday night rod runs and car shows was that the engine overheated.

alright well which one is which.. for vaccum hookups on the carb that is? its a holley, with one on the front mixutre plate and one underneath the front fuel bowl. ?? and with my knowledge i can tell that it is a vaccum advance distributer. hei, little chrome vaccume jobby with a vaccum line hookup on it. ???

does anyone think i could be a tooth off on my distributer? at about 650 rpm idle, the vaccum reads aobut 9. i know its low, and i cant turn my distributer any more because the vacc. advance hits on the intake

I would say 29* is not enough timing and will cause you to run hot (and poorly, including hesitation off of idle). If you physically can't rotate the distributor to get where you need to be, you can rotate the position of the plug wires on the distributor cap to get in the range of where you need to be...

mark the position of the number 1 cap terminal on the intake manifold with a marker, then rotate the distributor (clockwise I presume) to line up the next terminal with your mark, now shift the connections of the plug wires so your number one wire goes to this new terminal and so forth... now you should still be at ~29* but will have room to advance your distributor further if you need to. Alternatively, you can pull out the distributor and try to get it on the next tooth...

Manifold (full) vacuum is on the port below the front fuel bowl and there should also be a larger one in the middle of the baseplate at the back. The one in the metering block is ported vacuum.

Have you checked for vacuum leaks? Do you know if your a/f mix is right? Are all your unused vacuum ports capped?

Also, do you know how your advance curve is? Do you advance more at higher rpm's or did you only check at 2500? You may need to change some springs in the distributor (I don't know the HEI's so I can't help here)

You haven't mentioned much about your motor... compression, cam specs (262/468? does this mean 262 duration .468 lift? 262 advertised or at .050"?), etc... for any kind of "hot" street or performance cam I think 650rpm is quite low for the idle speed. If it's more of a factory cam then 650rpm sounds in the ballpark.

Also, what is the stall of your torque converter? If you're having these hesitation problems in park, then this probably doesn't matter for now...

Hope some of this helps... please excuse the rambling :)

-Chris

dont worry about the rambling, im glad you were specific in ur descriptions! this kind of stuff helps, im just a young buck tryin to catch up to my problems.

alright engine, short block is a stock rebuild 283 with 4 valve relief flat tops. other than that for comp, i couldnt help you, *oops*

gm performance vortech iron heads, proform 1.5 self align rockers, 64cc. headers, performer rpm manifold

carb, holley 600 http://holley.com/0-80457S.asp
thats it if you want to know any more about the carb, i just installed a .35 squirter in it *as reccomended by holley and jegs guys*

newley installed cam is lunati voodoo, and yes, sorry advertesed duration is 262/268 and the lift is 468/489.

air to fuel mixture, havent messed with it that much, ive done the basic deal as in turn all the way in, * i didnt tighten them, just till i felt pressure then i stopped* then i turned each side a turn and a half out. all three vaccum ports are used, under the fuel bowl, for advance. one on the metering block used for trans. big one used on brake booster.

**(Also, do you know how your advance curve is? Do you advance more at higher rpm's or did you only check at 2500? You may need to change some springs in the distributor (I don't know the HEI's so I can't help here) )****

this is where i get lost, i read up on a little bit today for the total timing and went from there. i had the idle set all the way up to 3300ish rpm and the mark still didnt go up any further from 2400ish.

and vaccum leaks i havent checked for. i suppose it wouldnt hurt seeing how it is only pulling 11" if i would bring up my idle a little more would that also increase?

trans is a tci streetfighter 700r4 with a stock lockup type converter

umm, anything else you want to know, please pry!!! i want to know! but thank you skids for being so informative!!!

also, it is running alot better after messing around with it all day, but its still not where it should be.

Did you note Skids72 comment about setting the timing with the vacuum advance disconnected?

If you don't you'll end up with retarded timing.

With the cam you have and assuming the timing is retarded 11" vacuum is about right.

If . . . the engine is idling at 600 rpm or so and you increase rpm to about 1500 the vacuum gauge will indicate 17"-19" of vacuum.

I'm asuming your vacuum gauge is connected to full time manifold vacuum.
If it's connected to ported vacuum you'll get readings that are not correct.

Quote:

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Originally Posted by C9x

Did you note Skids72 comment about setting the timing with the vacuum advance disconnected?

If you don't you'll end up with retarded timing.

With the cam you have and assuming the timing is retarded 11" vacuum is about right.

If . . . the engine is idling at 600 rpm or so and you increase rpm to about 1500 the vacuum gauge will indicate 17"-19" of vacuum.

I'm asuming your vacuum gauge is connected to full time manifold vacuum.
If it's connected to ported vacuum you'll get readings that are not correct.

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yes, i did all timing with the advanced disconnected. and that is good to know that the 11" of vaccum is alright, less to worry about then.

well thank you all for your help, finally got the purple people eater running good!!

Quote:

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Originally Posted by tim_bo16

yes, i did all timing with the advanced disconnected. and that is good to know that the 11" of vaccum is alright, less to worry about then.

well thank you all for your help, finally got the purple people eater running good!!

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Keep in mind that if you don't pick up to 17"-19" vacuum at 1500-2000 rpm with no load on the engine things still aren't correct.
If it does, then everything is probably ok and you just need to pursue the timing the engine wants.

If you can't get the vacuum above 15"-16" you may have the cam a tooth off.

glad to hear you made some progress...

Is your hesitation problem better? another thing you could look at that could cause your hesitation would be vacuum secondaries opening too quickly... this can be adjusted by changing a spring I believe... I haven't actually worked on a vacuum secondary holley (I've always had double pumpers) but I understand that this can sometimes be a problem and is not hard to fix... hopefully others will have some details on this if you're still chasing this problem.

Cam sounds like a pretty good match to your combo...

Have you managed to get the timing advance up? I think you get a few more degrees up there you will be in good shape... Get to 36* and see how it goes... beyond that I think you could get some more power with a little more advance especially if you run premium but be careful and make sure you don't get any ping... then you went too far.

-Chris

C9X - alright well awsome, i will deffinetally check the vaccum at 1500-2000 rpm and check that, and if i cant get the vaccum should i try turning the cap as listed on the first page by skids?? but i was also thinking, if i would advance it more, the idle is going to raise up more as well wont it? im wondering this because i already have the curb idle screw almost all the way out as it is now.

and as for the hesitation problem... yes and no. it is a LOT more responsive and i can really feel the power curve but with that being a plus, it still cant turn the tires over on dry pavement. and trying to do so it still pops and farts. but like i said, on the plus side, i dont think ive ever seen my truck run as good as it does above the hesitation.

and as for the vaccum advance deal skids was talking about, that accually was my first thought just reading up on the manuals and holley troubleshooting crap. but after talking to holley tech, he said i would need the bigger .35 squirter instead of the .32. so after doing that, i believe that DID help a little bit, but i still have some messing around to do.

but all in all, i will keep you guys informed as soon as i mess with it a bit!

Don't go to the trouble of pulling the timing cover until you get the other stuff squared away.
Right, now, a cam off a tooth is a possibility, but do the easy stuff first.

If you're familiar with cams etc., you can check to see if it's installed properly by finding true top dead center and using a degree wheel and dial indicator.
A subject for another time, but in case every thing else checks out....

Like Skids said, make sure your accellerator pump adjustment is correct.

Looking from here, I don't think the carb is your problem.
More than likely a timing issue.

There's a lot of confusion about how vacuum advance works and where it comes in at.

The basics are, mechanical - or centrifugal as some call it - responds to engine rpm only.

Vacuum advance responds to load - or vacuum level which is lower when the engine is under load.

Ported vacuum operates similar to manifold vacuum, but ported is at zero at idle, 10" or so in the mid-range under light load and back to zero at full throttle.
Vacuum advance does not stack up the advance as rpm comes up whether selected to ported or vacuum unless the engine is running with no load and above the idle rpm.
It can help to think of a vacuum advance cannister as a vacuum retard device.

Double check the plug wire firing order.
An easy mistake to make and double checking is a good idea.

So if everything is correct, you nail the throttle, the vacuum advance drops out and you're running on mechanical advance only as the engine rpm comes up and you're 'all-in' at 2200-2800 rpm or wherever in the curve you set up the 'all-in' point.

Basically, you don't want a drag racing advance curve in a street driven car.

Looking from here, it looks very much like the distributor is a tooth off.
Get the engine up on TDC - Top Dead Center - on the firing cycle with both intake and exhaust valves closed.

Install the distributor so the engine will fire at that point.
Make sure you haven't set things up so distributor rotation is limited.

Disconnect and plug the vacuum advance line at the distributor so there's no vacuum leakage from the manifold.
A golf tee makes a great plug.

Start the engine, set the initial timing with a light and if everything is working right it should run ok.

Install the vacuum advance line and you should see or hear the engine rpm increase a couple hundred rpm at idle.

Don't sweat it if you run the engine up to 1500-2000 rpm with no load and see the advance as high as 45-50 degrees BTDC.
Doesn't hurt and in fact is what you want.
The extra timing advance is required to give the lean idle mixture time to burn.

Do you have a PCV setup on the engine?
If a PCV valve hangs up it can create a major hesitation coming off idle.

Just in case....http://i49.photobucket.com/albums/f2...ticles/PCV.gif

Good advice, C9x!

But I don't know where the cam timing/degreeing came from :confused: ... all I suggested above was juggling his plug wires around to give tim_bo16 more room to adjust the mechanical advance due to the interference he's having now with the vac can on the dist.

I agree you don't want to go messing around with cam timing at this point and probably want to focus on getting the ignition timing nailed down...

Thanks, C9x for helping out here. You have much more experience with this than I. BTW, tim_b016, I'm fairly new to this stuff too and a great deal of what I've learned the last few years came from the wise(guys :LOL: ) on this forum...

-Chris

alright, well i just checked it again, and yes, at the 650 -750 rpm, it does have about 11 inches of vaccum, with about 9-10 * of timing (vaccum advance unhooked) checking for the "all in" timing, it does quit moving about 2300 rpm, and there and anywhere past that, its about 23-24* timing.

the vaccum at 1500 - 2000 rpm is about 17-18" vaccum

so were you saying that if my "all in" timing comes in at the 2300 mark, then is that too soon?

and as far as the pcv valve, i believe i have that, just the biggest vaccum port hooked up to the brake booster. the lines are not kinked or squished either.. so would that be my next step is to move the distributer a tooth ?

2300rpm for all in timing should be fine... yes either pull the distributor and move it a tooth to give you more room to adjust (can be tricky to get the oil pump drive shaft properly aligned with the dist when you do this... you'll need a BIG flat screwdriver or an oil pump priming tool to get it aligned right)... or as I suggested before, shift the connections of your plug wires on the dist and realign to the new #1 terminal...

good luck,

-chris

Tim is correct that 2300 rpm all-in is workable.
Thing to look out for is ping at part throttle, it probably won't happen, but it can so be aware.


The 17"-18" of vacuum at 1500-2000 rpm shows that the cam is probably installed correctly.

Keep in mind that every 1000' of altitude vacuum levels at idle will drop 1".
Looks like you're probably at the 1000' altitude mark assuming your engine is in good shape.

well i kinda got ahead of myself in waiting for a reply from you guys on the distributer turn, so i just went ahead and did it. re-timed everything, 12" vac at idle, still the 18" at 1500-2000 rpm. base timing was about 12, and all in was right at 32*.

took it out on the highway, listened for ping and all that and it turned out good!! and yep, my low end is back and no hesitation!! friggin amazing. hah

but yeah i really wanna thank you 2 guys for all ur help and input. just hope i can keep learning more as my problems will ALWAYS keep coming. :)

one thing, what is ur guys' imput on av-gas.. i believe my source is 100 low lead but i'd have to check back on that. i know i would have to mess with the timing again but thats not too much of a hassle now. we got a cruise comin up tomorrow and i was just wantin something more to have fun with. ??

Unless you're running a fairly high static compression ratio, you won't gain anything by running high octane.

High octane is all about slowing down the burn rate which helps to prevent detonation.

If your engine will run on 87 octane - and it might, skip the high price stuff.


The 462" Buick engine in my 32 is 9.0/1 compression ratio and I run 87 octane in it year round with no probs.
Not even in the summer heat waves here in the Dez.
104 degrees F today.


There are a few things you can do if you have an overly high compression ratio and none of them require the crank & pistons to be removed.

alright well i know that its not all that high compression. but my guess is somewhere close to 9.5ish.. just judging by the 76cc heads that i used to have and with the 64's that i have on there now.

but yep i was just curious on what the 100 would do. but screw it. yeah i know that it has run off of 87 once before. oh well... begining to save up for a new small block build.. either 406, or 383. i got a 350 and a 400 crank that i gotta get checked out and a guy owes me a 400 so if i can find a 509 casting 400, then thats the way ill go. streetability i dont mind, just simply because if im gonna eat the gas, i wanna go fast. so im gonna try for 375ish-400ish wheel hp. any suggestions?

The Chevy guys need to come on board here, but what looks good is a 383 with under 10/1 CR, 600 CFM Holley vacuum secondary or similar in an Edelbrock.

Take a look at Edelbrocks cam/intake manifold combos.
Dyno proven to work well together.

Considering the price of gas today, you'll probably want to opt for a mild cam, somewhere around 265 degrees advertised duration.

Try to find someone who's running a similar combination and see what they think about it as well as anything they would have done differently.

Experience counts for a lot and simply parroting things they've read in a magazine . . . I don't have to explain that....

You guys are awsome...I did a search and found this thread.

After reading the entire thing i realized this is the place to get answers. I have a similar set up and problems with my bored 60 over 283. Edelbrock 600 electric choke out of the box. Edelbrocks 400 cam 214/214 @. 050 .442/.442 lift. Here is the kicker.....Summit roller tip alluminum rockers 1.6 ratio. I have no idea what this is doing to the valve train......DOES ANYBODY FEEL LIKE TAKING A STAB AT IT???

waste of money on the roller tip rockers. from what just happened to me, i just bought a set of stamped steel rockers for my 400+ hp small block build.

you should be fine with them tho, do you kick the $h!t outta it or not?

It has very little miles. Maybe 1500 or so...It screams!

I am trying to get my throttle response where it should be. I'm where you were. Can't wait to get it right. Great motor though I love the fact that it is so old.

Quote:

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Originally Posted by espo1980

You guys are awsome...I did a search and found this thread.

After reading the entire thing i realized this is the place to get answers. I have a similar set up and problems with my bored 60 over 283. Edelbrock 600 electric choke out of the box. Edelbrocks 400 cam 214/214 @. 050 .442/.442 lift. Here is the kicker.....Summit roller tip alluminum rockers 1.6 ratio. I have no idea what this is doing to the valve train......DOES ANYBODY FEEL LIKE TAKING A STAB AT IT???

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If the cam lift is 0.2946" at the lobe, then theoretical valve lift with 1.6 ratio rockers will be 0.471", bringing the valve heads closer to the piston crown during the overlap period. Depending on piston crown configuration, piston deck height, gasket thickness, whether or not the heads have been shaved and how far the valves are sunk on the seats, you may want to run through the operation of checking valve to piston clearance, either with the clay on the piston crown method or the light checking spring and dial indicator method.

As far as whether your valve train geometry is gonna work out or not, read this answer I posted for another board member.....

Sean, I think what Pat was sayin' is that the checker you're using might work differently rocker to rocker, as he has gotten different results using using it and prefers not to use it any longer. Apparently he uses the same method most of us use and that is to verify that the rocker tip travels through its arc making the shortest possible trip across the valve tip and the extremes to the intake side and the exhaust side are equal.

The rocker changes its effective ratio as it swings through its arc. The ideal setup would be: Starting off at zero lift with the rocker tip on the intake manifold side of the valve, then moving to the exhaust manifold side of the valve at mid-lift, then coming back to the intake side of the valve at full lift. On the return trip to zero lift, the roller would cross the center of the valve tip and go to the exhaust side of the motor at mid-lift, then back to the intake side of the motor with the valve back on its seat. In this way, the rocker would be at its longest effective length halfway through the lifting of the valve. Its effective length would be shorter at both zero and full lift.

Whether you're using an adjustable checking pushrod or a pushrod that you think might work correctly, de-grease the valve stem tip and color it with a black Sharpie pen. Then, install the pushrod and rocker arm while the lifter is on the base circle of the cam. With hydraulic lifters, jiggle the pushrod up and down while tightening the adjusting nut until all play is removed. Twisting the pushrod with your finger and thumb will not work. You'll be compressing the spring and not even know it. Jiggle the pushrod up and down to remove play. With all play removed, tighten down the rocker adjusting nut to your normal preload. Using a socket on the damper retainer bolt head at the front of the crankshaft and long bar for leverage, turn the motor over several times clockwise. Obviously this is more easily done if the spark plugs are out of the heads. Remove the rocker and check the mark left on the valve tip. The roller tip on the rocker should leave a shiny spot in the center of the valve tip where it wore away the ink you put on the valve tip. The width of the shiny area will tell you the intake side to exhaust side extremes of travel of the rocker tip across the valve tip. Measure this width with your dial caliper and record it in your toolbox notebook.

If the pushrod length is correct, this mark should be centered across the valve stem. If it's too high (closer to the intake manifold), try a slightly longer pushrod. If it's too low (closer to the exhaust manifold), try a slightly shorter pushrod. This method works well when using an adjustable checking pushrod.

Every time i take it out I blast it up to 7000rpm or so. So far so good with the new build up.

With so many variables in tuning a motor, I have not had it performing at 100% yet. Need to nail down timing, Initial timing, curve, vacuum, carb jeting, idle , and so on. I've been doing my homework though... and with this forum i think I'll get her tuned right for good.. Would like to here more about how your 283 runs. Power band details. How it Idles and sounds. Where the redline is and so on.....Those sort of things. I realy have nothing to compair to. They would help.

Once it tuned perfectly I want to introduce nos into the picture. HeHe

Techinspector,

I have been running this set up without it being tuned. It has worried me though the plugs look ok and for the most part it sounds great. I did not relize how different building a 283 compaired to a 350.

I did check the clearence when I put it together. The question I'm wondering about now is the cam set up and the 1.6 rockers to much for the little 283? Keeping in mind it is bored 60 over.

Must sleep tonight...be back tomorrow.....