My truck vs the cooler outside temps

[jdheff1982]

Originally Posted by rs72z

You need to get that problem fixed before you do anything else.

Well, that is the plan this morning. tranny vacuum will be easy.

[Redcap]

Originally Posted by jdheff1982

Seriously, you all need to back off on the size of carb I have. I'm not rich and can't go replacing things at will. I have to make do with what I have. When I bought this carb, I was looking at price and brand. I saw jegs had the 750 reman'd on sale for $200. That was cheaper than a reman 600 by 40 or 50 dollars.

The truck had a stripped down 600 performer on it to begin with. It ran like **** then too. After I installed the 750, I was able to start the motor w/o having to pump 15 times.

I think the progressive loss of driveability has something to do with an open vacuum line to the tranny and I need to spend more time adjusting the IMS. If I have to, I'll get the calibration kit and try to adjust that way.

BTW, the cam that is on the truck is the most agressive Comp Cams put out in the Big Muther Thumper line.

Are there not air restrictors made that would cut down on the over all air intake I could use during the winter?

Should have just fixed the 600cfm that was on there instead of buying another carb that is too big...you know, since you aren't rich and all.

[jdheff1982]

got the tranny line fixed. bought a vacuum gauge to dial the ons. best I can get is 8 to 9". I had to adjust the one way out before I reached max vacuum. so, the next thing to tackle is the dizzy.

can I adjust timing based on vacuum since the balancer is not reading right?

[INSIDIOUS '86]

Originally Posted by jdheff1982

If anyone cared to check out the truck specs at the link in my sig, they would find the heads have been port and polished with the valves enlarged. It also has a 2700 to 3000 RPM stall converter. Flat top pistons, Scat crank and rods, and full roller rockers. My brakes actually do work even w/o a vacuum canister.

I believe the progressive loss of low driveability is due to the blown tranny vacuum line and poorly adjusted IMS.

you still have hardly enough vacuum for idle circuits to work bigger valve and head work dont help vacuum, i have alot of the same stuff you do so trust me on the fact i know what does and dont work with these cams my brakes work to as well

with that tube melted the combination of low vacuum and a leak causes a real bad idle issue not to mention these cams perk up around 25-3thou rpm

[jdheff1982]

Originally Posted by INSIDIOUS '86

you still have hardly enough vacuum for idle circuits to work bigger valve and head work dont help vacuum, i have alot of the same stuff you do so trust me on the fact i know what does and dont work with these cams my brakes work to as well

with that tube melted the combination of low vacuum and a leak causes a real bad idle issue not to mention these cams perk up around 25-3thou rpm

The idle is holding better now that the vacuum is up. When I first checked, the vacuum was sitting around 5. I still get a slight hesitation going from 1500 to 2000 RPMS. Its not as bad as before, but still there.

The timing needs some help though (I think). The erradic idle made it difficult to properly check vacuum. Is the balancer removeable w/o removing anything else?

Also, I was trying to setup the choke. I noticed that with full choke, the valve is basically closed, which has been causing the engine to snuff out. How do I get the connector rod for that valve off so I can bend it a bit? I think once that is fixed, the choke should work like it is supposed to.

[RUSHNBOBO]

If the engine has a fairly radical camshaft it may require an excessive amount of throttle opening for idle and/or have low idle vacuum levels. Either condition can lead to poor levels of
adjustability and erratic idles.
• A fix for the above condition is to run as much spark advance as possible at idle. If the distributor is fitted with a vacuum advance unit, connect it directly to manifold
vacuum. If you are not able to employ vacuum advance for some reason, then the mechanical curve should have a low limit, which will allow you to use plenty of initial spark advance.
• Measure the manifold vacuum at idle. If it is below 7" Hg, there is a good chance that the Metering Rods are in the up (rich) position. When combined with a high idle air rate this can
cause the Nozzles to discharge fuel at idle. Use a weaker Step-Up Spring to keep the Rods down at idle. With some cams, a stiffer spring (pink or
silver) is necessary. Experimentation is the best way to determine which is best for your application.

[RUSHNBOBO]

Originally Posted by 1LowToy

Let me guess you power brakes don't work worth a damn either as you probably have a wopping 13 inches of vacuum.

Big mutha thumpr cam will pull between 7-9 in hg at idle on a good day

[chevy_skills]

Why is everyone set on his carb is to big. The stock Rochester Qjets were 750. Its not the carb size. Level headed and unbiased I would say start with watching the eldelbrock tuning videos if you haven't seen them yet. after that id make sure the chock is properly tuned. and Idle screws(again). If thats not your issue make sure your gasket isn't leaking.

[jdheff1982]

Originally Posted by RUSHNBOBO

If the engine has a fairly radical camshaft it may require an excessive amount of throttle opening for idle and/or have low idle vacuum levels. Either condition can lead to poor levels of
adjustability and erratic idles.
• A fix for the above condition is to run as much spark advance as possible at idle. If the distributor is fitted with a vacuum advance unit, connect it directly to manifold
vacuum. If you are not able to employ vacuum advance for some reason, then the mechanical curve should have a low limit, which will allow you to use plenty of initial spark advance.
• Measure the manifold vacuum at idle. If it is below 7" Hg, there is a good chance that the Metering Rods are in the up (rich) position. When combined with a high idle air rate this can
cause the Nozzles to discharge fuel at idle. Use a weaker Step-Up Spring to keep the Rods down at idle. With some cams, a stiffer spring (pink or
silver) is necessary. Experimentation is the best way to determine which is best for your application.

I can employ manifold vacuum; however, it will be shared with the tranny vac line. If that doesn't provide enough advance, how do I use the mechanical curve?

I guess I wil need to buy the calibration kit to find a good working setup.

Thanks for the tips.

[85gmc2tone]

it would help alot if u had your 4th carb stud and nut thats missing in your sig pics

[RUSHNBOBO]

Originally Posted by chevy_skills

Why is everyone set on his carb is to big. The stock Rochester Qjets were 750. Its not the carb size. Level headed and unbiased I would say start with watching the eldelbrock tuning videos if you haven't seen them yet. after that id make sure the chock is properly tuned. and Idle screws(again). If thats not your issue make sure your gasket isn't leaking.

Totally agree a 750 is not the ideal carb but at the worst you may give up a little low end torque do to lower velocities and poorer venturi signal. But it will run just fine.....a larger cfm carb does not "flood" a small c.i. engine with fuel.

Engines and carburators don't work that way, any given engine can and will only draw so much air no matter how big of carb you put on it. And any given amount of air passing through a venturi can only pull so much air/fuel mixture period.

A engine is just a air pump, you could put a properly jetted 850 cfm carb on it and it will still run smooth and pull in approx the same amount of air/fuel mixture. The difference being air/fuel mixture will be moving at much slower velocities when compared to a 600 cfm (this is where the differences become a liability) The engine may not be capable of drawing the full 850 cfm but will draw only as much as it needs.

I just read an article where they took a 383 sbc and just for comparison purposes they ran a 390, 600, 750, 850, and a 950 cfm carbs. Every carb could be easily be jetted to 14.7: 1 and tuned to run smooth. The main problem when running oversized cfm carbs are not fuel consumption or mixtures but a poor venturi signal and velocity especially at low and mid rpms.....this is where over carburation will kill your torque and hp numbers. The venturies become so large that the undersized engine cannot pull the air/fuel fast enough through the smaller diameter venturi. Greater velocity=the speed of air/fuel charge.

The highest velocity is what your after at your desired rpm range. Example if you were to never to exceed 4000 rpm, a 390cfm carb on a 350 ci. engine may show increased throttle response and hp and torque numbers over a 600cfm. Exceed into higher rpm ranges and the venturies now become a restriction, hp and torque will drop off, due to air/fuel requirements now being greater than the carb can deliver.

If your engine is running like crap it ain't cause your a little over carburated especially not a 750 cfm. Read my last post about big overlap cams with the Edelbrock.....that cam is giving you a very weak manifold vacuum which makes the carb act like your accelerating hard even though your at idle (low vacuum) so your most likely loading up with excess fuel. This happens on Holley type carbs with big cams on the power valve circuit.....most stock Holleys have a 6.5 in hg power valve vacuum opening point. If you idle at 6-7 in hg you can quickly see the problem.....the power valve may be open or partially open at idle, flooding the engine with fuel. Swapping to a 3.5 or 4.5 will usually fix this. I have a friend with the same cam in a Camaro and he idles right at 7 in hg and would load up quickly right off idle, fixed the power valve circuit and it idles and accelerates fine.

Read the articles on the Edelbrock website....they go into detail how to set up their carbs on radically cammed engines.

[RUSHNBOBO]

Originally Posted by jdheff1982

I can employ manifold vacuum; however, it will be shared with the tranny vac line. If that doesn't provide enough advance, how do I use the mechanical curve?

I guess I wil need to buy the calibration kit to find a good working setup.

Thanks for the tips.

What type of distributor do you have ?......if it's an msd type, like mine they come with a kit to limit the amount of mechanical advance so that you can now run more initial which will help clean up your idle and improve throttle response off idle. Remember, initial+amount of mechanical advance = total advance (this does not include vacuum adv. ;read below)
A large cam like yours will be happy with as much as 15-18 degrees initial, if you can add vacuum on top of that without detonation do it. Get your mechanical right first, "rate" (how fast it rises) and amount, then add vacuum advance a little at a time (use an adjustable chamber) if you use full manifold vacuum dial your chamber to the lowest setting and see how it runs, if you hear no detonation begin to add vacuum adv a turn or two at a time. You may have issues with your starter at this high of initial advance....but there are ways to fix that. You can run a start retard box MSD (their cheap) you could step up to a mini gear reduction starter (not cheap) or you may have no issues....I run around 16 degrees of advance with a direct drive starter and it's a little sluggish when i'ts hot, some of that is heat soak though. Any port below the throttle plates is full manifold vacuum and will work even with a tee fitting.

[rs72z]

Why d you need to remove the balancer? If you don't have a pointer go to the parts store and get one. Are you can do as the Rush said and bump the timing up a little at a time, it you here detination back it down a little. Are you running a HEI dist? If you are pull the cap and make sure the mechanical advance is working and not froze up. Turn the rotor and it should spring back when you let go.

[jdheff1982]

Originally Posted by RUSHNBOBO

What type of distributor do you have ?......if it's an msd type, like mine they come with a kit to limit the amount of mechanical advance so that you can now run more initial which will help clean up your idle and improve throttle response off idle. Remember, initial+amount of mechanical advance = total advance (this does not include vacuum adv. ;read below)
A large cam like yours will be happy with as much as 15-18 degrees initial, if you can add vacuum on top of that without detonation do it. Get your mechanical right first, "rate" (how fast it rises) and amount, then add vacuum advance a little at a time (use an adjustable chamber) if you use full manifold vacuum dial your chamber to the lowest setting and see how it runs, if you hear no detonation begin to add vacuum adv a turn or two at a time. You may have issues with your starter at this high of initial advance....but there are ways to fix that. You can run a start retard box MSD (their cheap) you could step up to a mini gear reduction starter (not cheap) or you may have no issues....I run around 16 degrees of advance with a direct drive starter and it's a little sluggish when i'ts hot, some of that is heat soak though. Any port below the throttle plates is full manifold vacuum and will work even with a tee fitting.

I have a stock dizzy. Upgrading it is a future plan.

[jdheff1982]

Originally Posted by rs72z

Why d you need to remove the balancer? If you don't have a pointer go to the parts store and get one. Are you can do as the Rush said and bump the timing up a little at a time, it you here detination back it down a little. Are you running a HEI dist? If you are pull the cap and make sure the mechanical advance is working and not froze up. Turn the rotor and it should spring back when you let go.

I do have a pointer. The issue is the outer ring on the balancer has moved and shows the timing mark at the 10 to 11 oclock on the passenger side.

I am running a stock HEI. I will have to try that tip to see if the advance is working.

[jdheff1982]

Originally Posted by 85gmc2tone

it would help alot if u had your 4th carb stud and nut thats missing in your sig pics

Yeah I know. The PO stripped out that hole so the stud doesn't fit. They used a standard bolt instead.

My 2 options are:

1.) Drill out the mounting hole on the carb to allow use of bolt or;
2.) Install a heli-coil

I think I will prolly do #1 until I replace the intake manifold altogether.

[jdheff1982]

Well, I think a dizzy is in order soon. When I pulled the cap and tried to turn the rotor, it was locked in place. I did check to make sure the rotor was secure, but it wiggles around a little bit. Like the shaft is loose. It wiggles enough to change the timing just a little. Not sure what would cause that.

Any ideas? Thanks!

[Redcap]

Originally Posted by jdheff1982

Yeah I know. The PO stripped out that hole so the stud doesn't fit. They used a standard bolt instead.

My 2 options are:

1.) Drill out the mounting hole on the carb to allow use of bolt or;
2.) Install a heli-coil

I think I will prolly do #1 until I replace the intake manifold altogether.

You just like doing things the wrong way...don't you?

[jdheff1982]

I do things within my knowledge and experience. It worked before, it'll work again.

[chevy_skills]

Id put the heli coil on it they work fine.

[RUSHNBOBO]

Originally Posted by jdheff1982

Well, I think a dizzy is in order soon. When I pulled the cap and tried to turn the rotor, it was locked in place. I did check to make sure the rotor was secure, but it wiggles around a little bit. Like the shaft is loose. It wiggles enough to change the timing just a little. Not sure what would cause that.

Any ideas? Thanks!

Sounds like your "dizzy" is in marginal condition at best....can't over-emphasize how important it is getting the timing and spark quality correct. You don't wan't to take a chance, even with all the best go-fast parts in the world....if the timing ain't right your going to give up a ton of power and or driveability.

Also with that cam, a spark amplifier box is a good investment, they kick up the 12 volts to around 300-450 on the primary side. Most also feature multiple sparks at lower rpms to help light off the fuel with high combustion chamber pressures caused by high static compression and big overlap cams. I run a MSD 6a on every vehicle I own.....even my Yota pickup has one.

Also good heli-wound wires and a good aftermarket coil (make sure it's compatible if you have a spark amplifier).....one more optional ignition component is a in cab "ignition dialback", this is a valuable device if you run your ignition on the edge of ping, no ping. It connects in the with the spark box and allows you to change your amount of overall timing on the fly....great when changing elevation or when running sub-par fuel.

[jdheff1982]

I think next payday, I'm gonna buy a new stock dizzy until I can afford the MSD 6AL setup. Or get the MSD Streetfire dizzy which isn't much more than the stock Accel.

[rs72z]

Next question on the dist. Does it have any wires going to it besides waht plugs into the cap? I see in one of the pics that there is a four wire weather pack connector tied up on the firewall. I believe this year model may have come factory with esc, if so the dist. will not have mechanical advance.
If not then the mechanical advance is froze up if you cant turn it by hand. So what ever intial is set at that's all the timing you are getting.

[jdheff1982]

Originally Posted by rs72z

Next question on the dist. Does it have any wires going to it besides waht plugs into the cap? I see in one of the pics that there is a four wire weather pack connector tied up on the firewall. I believe this year model may have come factory with esc, if so the dist. will not have mechanical advance.
If not then the mechanical advance is froze up if you cant turn it by hand. So what ever intial is set at that's all the timing you are getting.

I believe at some point in this trucks' life, it used to have an esc. there is nothing computer controlled at all on this truck. Even if the dizzy is advancing, it still bothers me that it has some wiggle to it.

I noticed that Jegs has the MSD Streetfire dizzy on for $119.00. I will def. get that ASAP. Pulling the dizzy seems pretty straight forward. I won't need to remove the hood will I?

Thanks!

[jdheff1982]

I just wanted to say that I appreciate everyone's efforts in helping to resolve my issues. I know it gets frustrating when you can't be here in person. I could really use someone in my area that has good knowledge of these things to help me out some. Having only a Haynes book and the internet to go by, really makes things harder than what it should be.

Thanks for all your help, I know we all can get my truck running like it is suppose to soon.