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  #1 (permalink)  
Old 02-07-2010, 04:05 AM
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350 small block wont start after warming up

[IMG]ok here goes lol
i have a 1981 pontiac trans am that origionally came with the 301 turbo i swapped in a small block 350 i built myself, the engine block was from an 84 corvette, stock crank, rods, pistons. i put on a set of edelbrock performer heads with 10.5-1 compression, a comp cam 280H cam with .480 .480 int ext lift. hydraulic lifters. .100 long push rods, comp cams 3.5 roller rockers, edlebrock performer intake, with dual four barrel 650cfm performer carbs. i have a full up mallory ignition system to include a hyfire6A ignition box, an Ecoil, and a mallory magnetic breakerless distributor, 8.5 mm mallory spark plug wire into accell short header spark plugs , and a set of hooker full length race headers 3.5 out let.

ok lol now onto the issues at hand when i start the car cold it fires right up if i let it sit and run or go drive it around after i shut it down it will not fire back up until the water temp is almost completly cold, if i loosen the distributor and quickly advance the timing while the engine is being cranked over it will fire up, which brings me to issue #2 timing, i know for a fact that my timing gears are properly lined up and my valve train was adjusted properly but i cannon seem to get this engine to run right for the life of me it sounds like it has very subtle misses through the exhaust when at idle and when in gear it has no bottom end really at all, but once moving takes off like a bat out of hell but starts popping and not running smooth under load,

so hopefully someone out there can help me iv been working on this car for a very long time and im bout ready to call it quits thanks
*rob*
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Old 02-07-2010, 06:11 AM
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To me it sounds as if you have timing as well as ignition issues.
I would get rid of the accel plugs, I won`t run nothing with accel written on them.
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Old 02-07-2010, 11:11 AM
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Quote:
which brings me to issue #2 timing, i know for a fact that my timing gears are properly lined up and my valve train was adjusted properly but i cannon seem to get this engine to run right for the life of me it sounds like it has very subtle misses through the exhaust when at idle and when in gear it has no bottom end really at all, but once moving takes off like a bat out of hell but starts popping and not running smooth under load,
Ayuh,... You're confusing Valve timing with Igntion timing...
While they're both derived from the cam gear, they're also pretty much Unrelated...
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Old 02-07-2010, 11:16 AM
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Quote:
Originally Posted by UPandComing
[IMG]ok here goes lol
i have a 1981 pontiac trans am that origionally came with the 301 turbo i swapped in a small block 350 i built myself, the engine block was from an 84 corvette, stock crank, rods, pistons. i put on a set of edelbrock performer heads with 10.5-1 compression, a comp cam 280H cam with .480 .480 int ext lift. hydraulic lifters. .100 long push rods, comp cams 3.5 roller rockers, edlebrock performer intake, with dual four barrel 650cfm performer carbs. i have a full up mallory ignition system to include a hyfire6A ignition box, an Ecoil, and a mallory magnetic breakerless distributor, 8.5 mm mallory spark plug wire into accell short header spark plugs , and a set of hooker full length race headers 3.5 out let.

ok lol now onto the issues at hand when i start the car cold it fires right up if i let it sit and run or go drive it around after i shut it down it will not fire back up until the water temp is almost completly cold, if i loosen the distributor and quickly advance the timing while the engine is being cranked over it will fire up, which brings me to issue #2 timing, i know for a fact that my timing gears are properly lined up and my valve train was adjusted properly but i cannon seem to get this engine to run right for the life of me it sounds like it has very subtle misses through the exhaust when at idle and when in gear it has no bottom end really at all, but once moving takes off like a bat out of hell but starts popping and not running smooth under load,

so hopefully someone out there can help me iv been working on this car for a very long time and im bout ready to call it quits thanks
*rob*
You have dual 650 cfm carbs on this 350?
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Old 02-07-2010, 03:51 PM
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Quote:
Originally Posted by S10 Racer
You have dual 650 cfm carbs on this 350?

loll yes dual 650's properly tuned and jetted doesn't run rich, the heads are SB-Chevy 302-400Ci Performer RPM Aluminum Cylinder Head
185cc Intake Ports
70cc Combustion Chambers
2.020''/1.600'' Valves
1.460'' Valve Springs, .575'' Max Lift
3/8'' Rocker Studs
Straight Plug

^^as per the description from jegs


also i think i just made my words a little confusing on the timing portion up there, my cam to crank gears are properly aligned, my valve adjustments are right, when i drop the distributor in i make sure the #1 cylinder is tdc compression stroke and that the rotor points to the #1 cylinder, the engine fires right up...while warmed up i set the idle speed to 800 rpms and advance the distributor until all detonation ceases then tighten distributor, when snapping the throttle i get instant response with no back fires from intake or exhaust, car sits in gear fine at a stop with no signs of dying, the car takes off from a stand still but not enough to break the tires loose, once moving it seems to be all top end power but for some reason it sounds like its backfiring constantly under load through the exhaust but still maintains the throttle response, could that be the result of running headers with cherry bombs and nothing else? then when i shut the car off i have to sit around and wait at least 2 hours for the engine to cool to the point where it will start again, and if im in a rush to get it running again i have to loosen the distributor and retard the timing while cranking then rapidly advance the timing to get it to fire up. i hope i was able to clarify a little bit better

Last edited by UPandComing; 02-07-2010 at 04:52 PM.
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Old 02-07-2010, 03:52 PM
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oh and the pic in my first post is of the engine i did have to crop it down for the forum though
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Old 02-07-2010, 03:55 PM
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I think it's a combo of the timing / carb adjustment / and i bet the starter is getting hot in the process also. JMO


Cole
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Old 02-07-2010, 04:14 PM
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Quote:
Originally Posted by eloc431962
I think it's a combo of the timing / carb adjustment / and i bet the starter is getting hot in the process also. JMO


Cole
good call on the starter, i had suspected that as well but i run a high torgue min starter so it has plenty of spacing from any heat sources such as the headers plust the engine spins over very nicely at least 300-400 rpms
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Old 02-07-2010, 04:35 PM
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Good cam, doesn't totally kill your bottom end and sounds good too. What is your idle speed? Are you using a progressive linkage on those carbs? What did you set your base and total ignition timing to? Do you even know?
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Old 02-07-2010, 05:39 PM
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Quote:
Originally Posted by Blazin72
Good cam, doesn't totally kill your bottom end and sounds good too. What is your idle speed? Are you using a progressive linkage on those carbs? What did you set your base and total ignition timing to? Do you even know?
idle speed 800 rpms, yes on the linkage, base timing if were talking the same thing i have the dot on the cam gear lined up with the dot on the crank gear, and the total ignition timing if once again we are talking about the same this is 35 degrees advanced at idle speed
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Old 02-07-2010, 05:58 PM
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You got a leaky spark tube...
 
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Base timing is the initial ignition timing with the engine at idle, nothing to do the cam, cam gears or anything related to it. 35 degrees at idle is way too much. 35 degrees is closer to what you should see with all mechanical advance in at whatever RPM it is set to come in at. Some will tell you that you should be running as much as 18 degrees at idle with that cam, I never ran that much. I stuck to initial timing around 12 degrees when I had that cam and even after I swapped to the Comp 282S.
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Old 02-07-2010, 06:35 PM
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Quote:
Originally Posted by Blazin72
Base timing is the initial ignition timing with the engine at idle, nothing to do the cam, cam gears or anything related to it. 35 degrees at idle is way too much. 35 degrees is closer to what you should see with all mechanical advance in at whatever RPM it is set to come in at. Some will tell you that you should be running as much as 18 degrees at idle with that cam, I never ran that much. I stuck to initial timing around 12 degrees when I had that cam and even after I swapped to the Comp 282S.

k but how do you set the timing on a distributor that has no vacume advance and has magnetic pickup?
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Old 02-07-2010, 07:38 PM
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Wrap the starter to keep the heat of the headers off of it,and put a ford solenoid on it .Run on the rear carb, and pull the front carb in with progressive linkage. Check the springs in the counter weights in your distributor. All of your timing should be in a 3000 rpms, Set your total timing at no more than 38 degrees Oh yea, and lose the accel plugs.
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Old 02-08-2010, 06:35 AM
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Quote:
Originally Posted by UPandComing
k but how do you set the timing on a distributor that has no vacume advance and has magnetic pickup?
The hard starting could very well be caused by excessive initial timing.

If you don't have either a dial back timing light or a degreed damper, MAKE A TIMING TAPE.

If you want to be sure the pointer and damper mark is correct for TDC, DETERMINE TDC.

The initial timing- that is the timing at idle, w/o centrifugal or vacuum advance added in- can be anywhere in the 8 to 14 degrees BTDC range. This is a rough estimate- the actual timing will vary from engine to engine depending on a multitude of factors.

TOTAL timing (centrifugal plus initial timing) should be in the area of 36 degrees BTDC, all in before 3000 RPM.

Why are you not using a vacuum advance?
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Old 02-08-2010, 11:27 AM
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[QUOTE=
Why are you not using a vacuum advance?[/QUOTE]


iv gone through a bunch of distributors from points to hei, to the one with the infared breaker, dual point , now the magnetic breakerless they all had vac advance accept the magnetic breakerless and it seems to run best
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