Stumbling 302HO
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Stumbling 302HO
I just finished re-building an 86 302 HO engine with a Holly 600CFM carb and found that I had to shim the rockers .025 to get the valves to close all the way the vacuume is 14 lbs at idle ( I think it should be closer to 22 lbs).
The problem that I am having is that when I get on the gass from a dead stop the engine will stumble real bad and at times it has died
.
Any ideas as to what may be the problem?
Thanks for the help.
The problem that I am having is that when I get on the gass from a dead stop the engine will stumble real bad and at times it has died
. Any ideas as to what may be the problem?
Thanks for the help.
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From: peoria, az
Stumbling 302HO
O.K. back up. I'm lost here.You shimmed the rockers so that the valves would close?! Haven't heard that one. (not trying to sound harsh here) Something is wrong with that.Maybe wrong pushrods,worn rockers or something. But let's back up. This is carb'ed so is the accel pump working? How's your timing.Vacuum at idle should normally be 14"-18". 18" is hard to get. If you get 16 your doing good. I would look into the carb when you pump the gas. You should see a good strong squirt of gas going down the carb.Make sure your timing is correct. Check your vacuum advance and make sure it is hooked up to the correct source. (manifold vs ported) Maybe you can find something of value in here. I think I've been at it too long.
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From: Independence, MO
Stumbling 302HO
Originally posted by stepman
O.K. back up. I'm lost here.You shimmed the rockers so that the valves would close?! Haven't heard that one. (not trying to sound harsh here) Something is wrong with that.Maybe wrong pushrods,worn rockers or something. But let's back up. This is carb'ed so is the accel pump working? How's your timing.Vacuum at idle should normally be 14"-18". 18" is hard to get. If you get 16 your doing good. I would look into the carb when you pump the gas. You should see a good strong squirt of gas going down the carb.Make sure your timing is correct. Check your vacuum advance and make sure it is hooked up to the correct source. (manifold vs ported) Maybe you can find something of value in here. I think I've been at it too long.
O.K. back up. I'm lost here.You shimmed the rockers so that the valves would close?! Haven't heard that one. (not trying to sound harsh here) Something is wrong with that.Maybe wrong pushrods,worn rockers or something. But let's back up. This is carb'ed so is the accel pump working? How's your timing.Vacuum at idle should normally be 14"-18". 18" is hard to get. If you get 16 your doing good. I would look into the carb when you pump the gas. You should see a good strong squirt of gas going down the carb.Make sure your timing is correct. Check your vacuum advance and make sure it is hooked up to the correct source. (manifold vs ported) Maybe you can find something of value in here. I think I've been at it too long.
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Stumbling 302HO
Every thing is stock except the pistons ( hyper tech 9:1 .030 over) and the carb Holly 600cfm.
I shimmed the rockers to meet the valve lash requirments in the engine manual.
The accel pump is working great
I shimmed the rockers to meet the valve lash requirments in the engine manual.
The accel pump is working great
Last edited by jpourner; Sep 11, 2003 at 08:39 PM.
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From: Independence, MO
Stumbling 302HO
could you explain shimming the rockers to get the valves to close? how does shimming the rockers close the valves? DW
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From: Still under the hood in O
Stumbling 302HO
Crane sells shims that you put under the rockers (pedestal mount) to adjust for lifter preload, like these.
jpourner- A few ?'s
What I'm also wondering is, if the cam and pushrods are stock, why did you need to shim? Was there any head work done (milling)?
How is the accl. pump adjusted? You should have a little clearance between the cam and arm (I forget the recommended clearance). If this is a new carb you shouldn't need to adjust this, but if it's used someone may have in the past.
Have you tried adjusting the idle mixture screws on the side of the carb or the float levels?
Where do you have the vac advance running to, ported or manifold vac.?
Is there an EGR?
jpourner- A few ?'s
What I'm also wondering is, if the cam and pushrods are stock, why did you need to shim? Was there any head work done (milling)?
How is the accl. pump adjusted? You should have a little clearance between the cam and arm (I forget the recommended clearance). If this is a new carb you shouldn't need to adjust this, but if it's used someone may have in the past.
Have you tried adjusting the idle mixture screws on the side of the carb or the float levels?
Where do you have the vac advance running to, ported or manifold vac.?
Is there an EGR?
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From: Independence, MO
Stumbling 302HO
Originally posted by 90f150moneypit
Crane sells shims that you put under the rockers (pedestal mount) to adjust for lifter preload, like these.
jpourner- A few ?'s
What I'm also wondering is, if the cam and pushrods are stock, why did you need to shim? Was there any head work done (milling)?
How is the accl. pump adjusted? You should have a little clearance between the cam and arm (I forget the recommended clearance). If this is a new carb you shouldn't need to adjust this, but if it's used someone may have in the past.
Have you tried adjusting the idle mixture screws on the side of the carb or the float levels?
Where do you have the vac advance running to, ported or manifold vac.?
Is there an EGR?
Crane sells shims that you put under the rockers (pedestal mount) to adjust for lifter preload, like these.
jpourner- A few ?'s
What I'm also wondering is, if the cam and pushrods are stock, why did you need to shim? Was there any head work done (milling)?
How is the accl. pump adjusted? You should have a little clearance between the cam and arm (I forget the recommended clearance). If this is a new carb you shouldn't need to adjust this, but if it's used someone may have in the past.
Have you tried adjusting the idle mixture screws on the side of the carb or the float levels?
Where do you have the vac advance running to, ported or manifold vac.?
Is there an EGR?
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From: Still under the hood in O
Stumbling 302HO
Shimming the rocker moves the rocker up, preventing the too long pushrods from opening the valves too early. This was an option for me but I chose to convert to studs. I agree he does have something else wrong.
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From: peoria, az
Stumbling 302HO
O.K. I understand the shimming thing. What else could be looked at to cause this. Is it that this happens only when you romp it ? If you accel slowly does it do the same thing. I'm thinking not enough initial timing, not enough advance ( I'm assuming a new dist but I prob shouldn't do that) Maybe leaking vacuum advance. Carb opening up too fast. Just some things to think about.
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From: Independence, MO
Stumbling 302HO
first thing is you need to figur out this vacuum issue, if you have a vacuum leak, then you'll never get the carb to respond properly, once you have the vacuum issue resolved, stumbling off idle could be that you need a larger center squirter in the carb, possible a larger accelerator pump, or maybe just to adjust the cam on the pumt to give it a quicker shot of gas. Is this carb new, used,? whats the history on it? DW
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Stumbling 302HO
Sorry for stayng away to long Uncle sam called me to duty for a couple days.
Yes the head was milled and the machine shop did not grind the valve stims.
no there is not an EGR valve, the moron that I got the engine from pulled off the original EGR plate and carb and stuck on a rigged up 2 bbl adapter plate.
I installed a 1 inch riser that covers the EGR hole in the intake and allows the 600 cfm carb to operate.
The Carb is used but in good condition.
timming is set at 8 deg btdc.
The stumbling only happens from a dead stop and if I romp it.
if I am rolling even a little then every thing works great.
The vacuume advance is connected to the ported vacuume port on the carb.
The only thing I can think of is the 1 inch addapter does not seal the exhaust / EGR hole in the intake.
Yes the head was milled and the machine shop did not grind the valve stims.
no there is not an EGR valve, the moron that I got the engine from pulled off the original EGR plate and carb and stuck on a rigged up 2 bbl adapter plate.
I installed a 1 inch riser that covers the EGR hole in the intake and allows the 600 cfm carb to operate.
The Carb is used but in good condition.
timming is set at 8 deg btdc.
The stumbling only happens from a dead stop and if I romp it.
if I am rolling even a little then every thing works great.
The vacuume advance is connected to the ported vacuume port on the carb.
The only thing I can think of is the 1 inch addapter does not seal the exhaust / EGR hole in the intake.
