LsxMatt

iTrader: (4)

I just finished rebuilding the 350 in my 86 sport coupe. Car was originally a 2.8 automatic. I used stock internals, and just replaced the bearings, freeze plugs, and pistons rings with a ball hone. Im using dart 64cc aluminum heads with 2.02 intake valves. Cam is a comp cams XR276HR, with comp 1.6 roller rockers. Intake is an edlebrock rpm air gap, with a holley 600 cfm carb. Using a t56 trans. base timing is set at 10 degress BTDC.

So i took the car out today, and it just doesnt seem to have the power it should. If i let go of the clutch, and floor it going around 10 mph, i cant get any wheel spin. It doesnt seem to want to pull until around 5,000 rpm.

I would think with this combo i should be around 300RWHP at least, and around the same torque, but it only feels around 200 RWHP/TQ. Any suggestions would be greatly appreciated. Also, occasionally on take off under load, i get a spit of fuel out the carb.

bwiencek

That's a lot of cam for a lower compression engine but you should still be able to pull pretty good before 5000 RPM.

I'd say you've got a tuning issue - check these things in the order listed (from easy to a little effort:
- check for vacuum leaks.
- check base and total timing as well as vacuum advance (a lazy curve and not enough timing will kill the torque)
- check jetting in the carb (Wideband O2 makes this easier)
- Check valve lash (too tight and you'll be hanging the valves open and bleeding off compression - try backing off the preload a bit and it should help torque by making the cam act a tiny bit smaller - use 1/8 to 1/4 turn past 0 lash and see if the torque picks up
- check cam timing - remember most 'performance cams' have advance already ground in so most should be installed per cam card 'straight up' or tweaked a bit to get a DCR # where you want it...

LsxMatt

iTrader: (4)

I had the timing marks line up perfect on install, and as far as i know it suppose to be installed straight up. Did a compression test and got 150psi on all cylinders. Seems low, but the rings havnt been seated yet so it should go up. Plugs were all black so its running rich. I did notice that the mixture dont seem to change the idle much when running. I can turn them almost all the way out and the rpm doesnt change.

bwiencek

150 PSI sounds fairly good on a lower compression engine (guessing in the low 9.x:1 range with stock dished pistons and 64cc heads.... What's your idle vacuum reading look like? Bouncy, steady but low, etc?

Rich and the plugs black along with no change with the idle mixture screws - sounds like it could either be a blown power valve (on a holley carb), a vacuum leak (vacuum hose or even the intake or carb base is likely) or if it's a q-jet you may have leaking core plugs...

Check for a vacuum leaks and post up what kind of carb it is.

LsxMatt

iTrader: (4)

Got the carb off craigslist, its a holley, not sure what model. Know is an older 600cfm model with electric choke. Has a fuel bowl in the front and rear, but only one fuel inlet on the front. Noticed when i opened the site screw for the rear bowl, fuel poured out. The front level was ok, just below the sight hole. Going to try to re adjust the valves and see what happens. Vacuum was around 12 psi at idle, but very bouncy.

bwiencek

12" of vacuum and bouncy - thow much 'swing' does the needle have - less than 1" or 3-4" - is it regular like every time a specific cylinder comes around or??? Whatever the case 12" sounds awful low for that combo... I'd say you've got a vacuum leak and possibly tight vlave lash (and/or leaky valve seats) as well as retarded engine timing at idle (what is the idle timing with vacuum unplugged and then with vacuum connected?)

List number for the carb is on the choke horn. A needle/seat that doesn't seal will cause the holley to dump fuel into the intake - which would cause your over-rich problem.... Since you've picked up an unknown carb I'd rebuild it. If not then at least pull off the bowls, clean out everything and inspect the needles for grooving around the seat area and floats for fuel saturation (sunk float) and then you'll just need to re-adjust the floats and assemble it with a new bowl gasket, transfer tube o-rings and bowl screw gaskets.

LsxMatt

iTrader: (4)

Needle moves less than an inch. Re adjusted the valves with only a 1/4 turn of pre load. Last time i did 1/2 turn. Also found out that number 7 exhaust rocker wasnt seated properly. I notciced the nut was sitting higher than the rest of the cylinders, and it turned out the nut wasnt sittin in the recessed area on the stud. Fixed that, but now i have no spark��.

I have 12 volts at the pink coil wire, but nothing coming off the main coil wire. Pretty sure the module in the dizzy crapped out. Swapped out a new coil but still no spark. Gonna warrenty the dizzy with summit, and see what happens.

Thanks for all the help so far. Wont be able to see if the rocker adjustment helped until i get the new distributer. Ill keep you guys updated, really want to drive this thing.

LsxMatt

iTrader: (4)

Also, timing at idle with no vacuum advanve connected jumps between 10 and 12 degress BTDC. With the advance connected its around 12-14 at idle BTDC.

LsxMatt

iTrader: (4)

Think i foun something very helpful out. Starting playing around with the engine tonight, and decide to make sure the aftermarket timing tab is lining up correcty with the aftermarket balancer. Well i pulled out the number one plug and started moving the piston to TDC while feeling for compression out the spark plug hole. Turns out, air stops coming out at 8 degrees BTDC, instead of on 0.

So, this means instead of my timing being at 10 degrees BTDC like the timing gun and tab read, it was really at 2 degrees BTDC.

FRMULA88

sounds like the distributor was not installed with #1 at TDC and timing was way off.
Now if you are sure #1 is at TDC, you can re-install the distributor with the rotor @ #1 spark plug post.
This will get you much closer, timing wise.
I doubt anything was wrong with the new distributor check your wiring to make sure you are getting power to coil..

If you cannot adjust the idle speed with the idle speed & idle mixture screws.. you have timing / jetting issues.

Get the timing right first.. then try to dial in the carb.. you may have to install smaller main jets to adjust to fuel curve, sounds like it is too rich.

with 12" of vacuum you should have a #6 power valve on the primary. But again if timing was screwed up this will throw off the vacuum reading.

Once you have the timing right.. you can play with the carb... install a vacuum gage on a full vacuum port of the carb and adjust the idle speed and mixture screws to get the highest vacuum reading at idle.

You can also do the same with timing... adjust timing until you have highest vacuum reading at idle.

bwiencek

Sounds like you need to get back to the basics - start with finding TDC and marking it on the aftermarket balancer/pointer... Get a piston stop and then rotate the engine by hand 'forward' and backwards and marking both spots where it stops - then split the difference and the center of those two is where true TDC is - once you have that then you can start adjusting from there.

I'd say you've still got a vacuum leak and that's causing some of what you're having - as well as the timing is low for idle with the vacuum connected - which if you've used a cheap chinese HEI style distributor the curve is usually set tight and the vacuum advance limited - the curve can be adjusted with the spring kit and the vacuum canister usually has a stop screw that can be adjusted with an allen wrench through the vacuum port.

Plus having an unknown carb with an unknown calibration isn't helping - you really should pull it, clean it, check the jets and float levels and get them to the 'stock' calibrations as a baseline to start to adjust. (google the list number of the carb or look it up on Holley's site and they'll have the 'stock' calibrations listed) I'm going to guess that the power valve is going to be a 6.5 and that should be 'ok' to start with *IF* it is working properly and not blown - if it's blown you may be dumping fuel all the time and running rich

Since you said that the rear bowl flowed fuel out - Did you adjust the rear float level and get it to be where it needed to be??

JaBoT

While doing that may give you an idea of where your are it's not very accurate. You should find tdc using a piston stop. I'm sure you can find how to do it somewhere on the net.

It doesn't matter how the distributor was installed. If the timing light says your at 10 degrees, they you're at 10 degrees (assuming the timing tab and balancer are correct). Technically you can install a distributor 180 out and just spin the housing 180 and its no longer out. If the timing is where it should be according to the light then the distributor install is not the problem. Now with that being said you should always refer to the engines service manual to see where the # plug wire terminal should go otherwise you're plug wires might not reach, the vacuum can might hit the manifold or firewall and if anyone ever works on the car the plug wires will be in the wrong place visually.

If the idle air screws aren't doing anything then either your carb needs to be rebuilt or the idle speed screw has been turned in so much that it is no longer using the idle circuit, which is pretty common.

Absolutely, You will never get the carb set up right if the timing isn't set up right.

This is a very big problem and it's caused by holley! (although they have changed some documentation to talk about this)
A power valve on a street car should be 2 - 3 inches lower than cruise vacuum. Not idle vacuum. The power valve has no bearing on idle whether its open or not.
Most street engines that have small to medium sized cams cruise over 12 inches of vacuum. Now since they don't make power valves bigger than 10.5, most street cars should just use a 10.5.


Do not adjust timing until you get the highest vacuum or best idle. You can very easily wind up with over 40 degrees total!

LsxMatt

iTrader: (4)

Well the engine runs much better with more timing. I have it at, what i believe to be, 12 degrees BTDC base timing. Anything more or less, and i lose power. Plenty of seat pinning power now, and no fuel spitting from the carb. Running 93 octane and I cannot hear any pinging. Going to order a new carb from summit next week as i do not like this one. I dont even think the secondaries are opening.

I also just ordered a piston stop which should be coming in tomorrow. Going to find TDC, and go from there. Once i get the new carb i can get everything fine tuned.

mmadden55

Just out of curiousity is there any chance you had set the timing with the EST wire connected?

JaBoT

Do yourself a favor and get an advance curve kit for the distributor. It will really wake up the bottom end.

There is no est wire. It has an aftermarket crab and a non computer controlled distributor.

rusty vango

got to love those "trouble free" holley carbs

LsxMatt

iTrader: (4)

Ok tried to find tdc with the piston stop. Installed the stop on number 1 conpression stroke, spun the engine clock wise until it stopped, marked the balancer. Then spun it counter clockwise until it stopped, marked the balancer again. Halfway between those two points is my original TDC mark on the balancer, the point where the car has no power. What would this mean?

bwiencek

That means that the balancer and timing pointer are correctly matched and installed and you've got a tuning problem or parts installation problem...

Until you get the idle mixture screws to be effective and the plugs to be burning clean you're not going to get too far...

LsxMatt

iTrader: (4)

ok thanks. Hopefully when i get the new carb i can sort this out. I went back out and tried out the mixture screws again. At idle i have around 12-13 inches of vaccum. The needle sort of flickers between the two, but the cam does have an agressive idle. If i turn the screws in far enough the engine starts to die. As i turn them out the highest i can get to is 13 on the vaccum gauge, then it doesnt rise anymore. I can however turn the screws all the way out, and the engine doest die either.

bwiencek

That's actually better - as long as when you're cutting off fuel via turning the mixture screws 'in' the engine wants to die - that's good - that means it's not pulling fuel from somewhere else. Your carb might be OK after all and it's just a matter of tuning...

Try following the directions on Holley's site for idle mixture adjustment:
http://forums.holley.com/entry.php?4...n-Holley-Carbs

Then - where is your vacuum advance canister plugged into (manifold vacuum or ported vacuum?) Also try using a tiny allen wrench (like 3/32 on most generic HEI distributors) to go into where the vacuum line connects and turn the stop screw counter-clockwise in the advance canister

JaBoT

Don't turn the screws all the way out, it is not supposed to kill the engine. It will just make it so rich no one will be able to stand near the car! Just set the screws for max vacuum. How much timing do you have at idle and is the vacuum can hooked up to manifold vacuum?
Also did you base set the idle screw by turning the carb upside down and making a square out of the transition slot?

Have someone hold the engine at 2500 rpm. Does the vacuum gauge still bounce or is it smooth?
Also what rpm is the idle set at?

manolis1969

Few things i want to note here that were said in this thread that are not correct..

1) going 1/2 turn on hydraulic lifters and then adjusting to 1/4 turn only affects the theoretical duration of the camshaft at IDLE..anything past that, the lifters pump up to zero lash..unless u adjusted past zero lash, only then u might hang a valve.
2) adjusting the carb idle mixture screws all the way out should not kill the engine..only all the way in should kill it.



Soo as a few guys above stated..if ur spitting fuel out the exhaust and the car felt better (also no pinging) after you adjusted the timing. And now that you found approx TDC with a piston stop and you resetted to the last timing u were and the issues appeared again...Leads me to believe its a timing issue .. check what was outlined above about ur inital timing..see if u connected it to the wrong vacuum port..and take it from there..

ALSO make sure you are doing ur timing correctly..and have someone else doublecheck ur work

FRMULA88

correct..

Double check your distributor, with the balancer & pointer at "0" the rotor should be at #1 spark plug post.

You also may want more initial timing at idle. 12 degrees seems a bit low

You should take timing readings and make timing adjustment with vacuum advance disconnected.

Plug the vacuum advance port. Check your base timing at idle again. then rev the car up to 2500-3000 to see what your total mechanical timing is, should be in neighborhood of 28-34 degrees for a SBC.

Since your cam is only producing 12-13" of vacuum at idle you may not have enough to even use the vacuum advance & this would also explain why your vacuum secondaries are not opening.

This is why most racers use mechanical secondaries and don't bother with vacuum advance.

None of this is an issue with EFI, but a carb with vacuum secondaries relies on vacuum, so does the vacuum advance & the power brakes.


Set total timing to 32 degrees and try a test drive without the vacuum advance.

FRMULA88

turning the idle mixture screws "in" on a Holley leans the idle mixture

the engine should die when you turn the idle screws all the way in

LsxMatt

iTrader: (4)

Numbers on the choke horn of the carb read 80457-3, followed by 1413. Im using ported vacuum off the front right side of the carb for vacuum advance. I didn't touch any idle screws under the carb. I also just realized that I can back out the base idle screw all the way, and the engine will not die. Turning clockwise does raise the idle, like it should.

bwiencek

Just an FYI - He's hinted at an aftermarket distributor - if it's the "house brand", MSD street fire, or one of the cheap ebay china HEI's I've found the timing curves so lazy they're still coming in at 4500 RPM... (or you can call it 'safe' - so don't assume - keep increasing the engine RPM's until you see the timing stop advancing and about 500 RPM increase with NO advance...

Also - the way the Vacuum secondary on the carbs works is a little off - it does require vacuum but it's not manifold vacuum - it's from load on the engine being high enough to create enough air velocity by the secondary vacuum port in the bore of the primaries - It's a little complicated to think of since most think the high manifold vacuum is required to open the secondaries - when in fact it's not related at all to manifold vacuum. (here's a holley reference - http://www.holley.com/data/TechServi...ech%20Info.pdf - it *should* have the info in there - I just searched their site and that was the first hit so don't shoot me if it doesn't)

Also - total *mechanical* timing plus vacuum advance will often be way over the 32-34* mentioned during light load/cruise/decelleration - once you flat foot it and manifold vacuum drops to nearly 0" there will be no more vacuum advance and it will be all centrifugal advance.

bwiencek

Ahh - the old single inlet, single metering block holley... (it's an 80457 the "-3" is a revision number)

Switch to the manifold vacuum port (it's the small one on the baseplate by the front of the carb)

Since you can back out the idle screw all the way you may be pulling air from somewhere it's not supposed to be coming in from (check vacuum lines, PCV, brake booster, etc.) Also there might be a tab on the throttle shaft linkaga or tiny set screw that holds the throttle plates slightly opened - make sure someone hasn't adjusted this to hold the plates open more than just enough to not get stuck in the bore when shut....

FRMULA88

So what screws are you screwing around with?!
use the right terminology would help:

On a 4150 style Holley you have the idle speed screw and the idle mixture screws.. the idle mixture screws are on the metering block(S)
the idle speed screw is on the throttle bracket, that's it.

if you have a choke, make sure the choke plate is fully open, after 5-10 minutes the electric choke will shut off and plate should be fully open.

Don't adjust the carb with the choke plate partially or fully closed, this will make the carb run richer and throw off the whole tuning process so make sure this is correct.

The choke should be connected to switched ignition source.

if you can back out the idle speed screw all the way and engine does not die then, you are into the transition circuit of the carb or the choke is mis-adjusted. this is another problem to check / correct.

At idle with the engine warm the choke plate should be open.. the throttle plates should also be more or less shut closed... sometimes guys adjust the throttle plates to improve idle (let more air in lean the idle mixture) however and most times they wind up opening the plates too much & exposing the transition circuit which just dumps more fuel ... making it even harder to adjust the idle speed and mixture..

best bet is return the carb "baseline" settings then try

FRMULA88

That is why I said most racers do not bother with vacuum advance, because at WOT, there is no vacuum.

which is why I also said total mechanical timing will be 28-34 degrees on a SBC because without a vacuum advance this is all the timing the engine will ever see.

Typically this is the sweet spot for peak HP / TQ. but that really depends on OP's combo of heads, cam, etc.

fast burning, small chamber heads need less timing. OP's combo may like 34-36 total timing.. he will have to find out what his engine likes


I am not concerned about part throttle fuel economy on a drag race car, which is why vacuum advance is not part of my timing equation because my cam has only 2" of vacuum at idle..

JaBoT

You have a vacuum leak somewhere or your carb is just jacked up. Probably a vacuum leak.
When you figure that out it should run a lot better. Also hook the vacuum advance can up to full manifold vacuum, not the ported one on the side. Then readjust the adle air screws.

FRMULA88

Just be sure when setting initial timing & total mechanical timing you want to make sure the vacuum advance is capped off (not connected)

At idle there is no need for vacuum advance, and you will never get the total mechanical timing correct if you have the vacuum advance connected.

A decent running SBC should like 28-36 degrees total mechanical timing that depends on your combo.. try 30 degrees and see what it likes. (this is safe starting point you will have to pull the plugs and read them)

However even with the vacuum advance you should still should not need more than 36 degrees total timing.

Vacuum advance is based on engine load (vacuum). Vacuum advance is used to add timing at low speed / low load (high vacuum) to improve fuel economy because the engine is not spinning fast enough for the total mechanical timing curve to come in.

A 3/4 throttle to WOT you are using only the mechanical advance, because there is insufficient vacuum for vacuum advance.

This is why Racers don't bother with vacuum advance since race engine camshafts do not create sufficient vacuum for the vacuum advance to work properly a low speed low load, and race engines don't operate in the is RPM range for vacuum advance to matter.


with a carb you have to compromise.

Do your homework on your cam shaft, see if 13" vacuum is enough to run vacuum advance.

FRMULA88

Now part of the problem you could be having is the mechanical advance curve on your dist. is "fighting with" the vacuum advance.

it may be that your total mechanical timing is "all in" by 3000 rpm, then your vacuum advance tries to add more timing and killing the part throttle performance.


Again you need to check initial and total mechanical timing with the vacuum advance disconnected and see what you have..

if you want run vacuum advance you may have to adjust the mechanical advance curve.

JaBoT

Read this article. It explains it way better than I ever can.

http://www.maliburacing.com/forum/vi...php?f=4&t=2484

FRMULA88

Thanks for the insight, but I don't use vacuum advance.

My cam only has 2" of vacuum at idle.

Initial timing is 19 degrees, idles @ 900-1000 RPM
timing is all in by 2500, 34 degrees total.

idle AFR is between high 13s & 14s, which is just fine for a carb.

WOT AFR in the mid 12s

and those are the 2 main things I care about.. A crisp idle so I can drive & stage the car and safe AFR @ WOT.

I am not trying to pass an emissions test or drive cross country.

JaBoT

Here is another great article explaining things

http://classicinlines.com/spark.asp

FRMULA88

I stopped reading after this sentence:

Although a drag race car may not realize much in the way of an advantage, none of it performance related, it’s about the only type of race car that falls into this category.

LOL

JaBoT

If your car has plates on it, it's not just a race car!

LsxMatt

iTrader: (4)

Just to check, i set number 1 at TDC today and pulled the distibuter cap. Rotor was off a tooth, pointing at 6 o clock. Pulled the distributer, got it pointing towards 5 o clock where it should be, Unfortunately that didn't fix my timing mark line up issue. I did notice that the number one plug was a nice tan color, so at least it not running ridiculously rich anymore. I would really like to figure out why i still cant get the marks to line up correctly.

LsxMatt

iTrader: (4)

Just to check, i set number 1 at TDC today and pulled the distibuter cap. Rotor was off a tooth, pointing at 6 o clock. Pulled the distributer, got it pointing towards 5 o clock where it should be, Unfortunately that didn't fix by timing mark line up issue. I did notice that the number one plug was a nice tan color, so at least it not running ridiculously rich anymore. I would really like to figure out why i still cant get the marks to line up correctly.

Also, i am setting the timing with the advance unplugged, and comp says my cam should have around 12 inches of vacuum at 800 rpm, which is what i have, so i dont think i have a vaccum leak.

JaBoT

a few days ago you wrote

This is TDC. It doesnt matter what tooth the distributor is on!! As long as tdc on the balancer is at 0 on the marker. What ever your timing light reads is the actual timing. It doesn't matter if the distributor is 5 teeth off. What the timing light reads is still the actual timing.

Today you wrote
What timing mark issue? If you used the piston stop like you said there should be no timing mark issue.
What marks aren't lining up?

LsxMatt

iTrader: (4)

The mark on the balancer lines up with the 0 on the pointer at TDC. However the engine will not run this way. I have to turn the distributer so far retarded, until the mark on the balancer is at 12 o clock, waaaay past the timing pointer. This is the only way the car makes any kind of real power. Im running an 8 inch balancer, and timing tab mounted to the right of thew timing cover.

LsxMatt

iTrader: (4)

Casting on the block is 14093638, Im pretty sure im using the correct balancer/ pointer combo.

JaBoT

There is something else wrong then. It's not the timing.
The balancer / marker need to match each other not the engine. And if they didn't then they wouldn't line up with the piston stop.
This may sound like a dumb question, but which plug wire are you hooking the light up to and also have you tried a different light?

LsxMatt

iTrader: (4)

Im going to try to make a video demonstrating the issue. Its driving me crazy

JaBoT

yea that would probably help a lot

LsxMatt

iTrader: (4)

Ok i made a video, im gonna upload it and post it in a bit.

LsxMatt

iTrader: (4)

Here is the link to the video. Currently being uploaded, should be live in a few minutes. http://www.youtube.com/watch?v=tjnhl...ature=youtu.be

LsxMatt

iTrader: (4)

Video was uploaded but is still processing.... In the meantime, i noticed if i turn the advance **** on the timing gun to 43 degrees, i can get the timing mark on the balancer lined up to 10 degrees BTDC on the pointer.

http://www.youtube.com/watch?v=tjnhl...ature=youtu.be

FRMULA88

make sure the timing light is connected to #1 spark plug.

if it is you and you need 43 degrees on the gun for base timing the dist was installed wrong, if your ballancer is fully degrees you could tell that right away by setting the dial on the light to zero..

get #1 back to TDC, loosen the dist and put it the right positon.. with the rotor at #1 spark plug terminal.

leave the dial on timing light at "0" and check your base timing again.. see what you have... then set the dial to that number...then you should see "0" line up on the balancer & timing tab. so you check mech. adv the same way. leave the dial at "0" reconf the total mech advance then set the dial to that number. you should see "0" line up again on the balancer... that is the best way I can explain this on the internet... if you are connected to #1 spark plug and you can't do this the dist and or cam are not at #1 TDC

who installed the camshaft? was it degreed correctly.

JaBoT

According to the light that's about 53 degrees at idle. I'm guessing that's not correct
When you set the timing to where it runs best (about 53) does it knock or ping when you go wot?
Have you tried another timing light?

Also where in ny are you located?