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Discussion Starter #1
Hi guys ! Here is a good one for you all. My buddies car has some stange issues.
Last year we installed a 700 r4 and intstalled a new stock intake. Since then it has run terrible. We have done everyhing and nothing helps. Here is what its doing and what we did to attempt to resolve the issues.
Not firing on cylinders 4 and 5, we discoved this after putting in new plugs, it idles fine but runs rough and spits back from the carb when reved,other six plugs are firing, but 4 and 5 are dry and clean. when we removed plug wires from 4 and 5 no change.
All plugs have spark.
We first removed the ignition module and put back points, which did nothing.
Sent distributor to get rebuilt.
New plugs, new wires, new distributor cap, new rotor, compression test was good, vacuum test was also good. Rebuilt two barrel carb (Stromberg) played with timing about 200 times, checked valve lash, tried another carb, we put air pressure into #5 cylinder and turned engine over by hand and it does blow air out carb and turn more air out exhaust.Even added fuel down carb, The fuel stream in the carb is also splattey when reved. Also backfires at start up. I think I covered everything. We have done everything imaginable and we are ready to give up. any suggestions?
This engine does have an old paxton supercharger on it. No change to poor running with super charger off or hooked up.
 

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switch a good plug like plug one to the cylinder thats not firing. i get you got 2 bad plugs or you didnt gap them right. get a spark tester. it plugs into you plug wire and the to a ground and you will see the spark. make sure you have spark at the plug. if there is spark its the plug, if there is not spark then its the wire or the distributor and or rotor. make sure the contacts are clean. make sure the wires are not broke inside. put it on an ohm meter and should read OL that means its making a connection from one end to the other.
 

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Discussion Starter #4
Hi Rick, we checked the firing order and it is 1,8,4,3,6,5,7,2. The funny thing is it appears to spark late on the plug we tested, #5, but any change to correct the two miss firing plugs results in the engine stalling.
Like I mentioned we have spent many hours doing things that dont help, they should by all logics, but they dont.
We even tried moving wires around. Th efunny thing is the timing is way out to get it to run, any attempt to adjust the timing to proper settings kills the engine.
 

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Discussion Starter #5
switch a good plug like plug one to the cylinder thats not firing. i get you got 2 bad plugs or you didnt gap them right. get a spark tester. it plugs into you plug wire and the to a ground and you will see the spark. make sure you have spark at the plug. if there is spark its the plug, if there is not spark then its the wire or the distributor and or rotor. make sure the contacts are clean. make sure the wires are not broke inside. put it on an ohm meter and should read OL that means its making a connection from one end to the other.

We swapped plugs and they do fire on other cylinders, we even swapped wires and they also fire on other cylinders. Its a real stumper to me !
 

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Possibly distributor advance plate is stuck? Dissconnect brake booster line and plug it off. See idle changes. Spray brake clean or wd40 around intake manifold area and carb base with car running see if any changes. Don't spray in carb. RICK
 

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are you getting NO spark at ALL on those two cylinders?
pulled plug lead out and cranked engine over to see if you have spark??
might be distributor out 180*.
 

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Discussion Starter #13
you say it pops through the carb. almost a sure thing you have a bad cam with flat lobes. pull the valve cover and watch those two cyl wont lift as much as the others.
We did that too, valves are good, gap is correct, springs ok. Compression was good, vacuum was also good.
 

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Discussion Starter #14
be sure you put the distributor in right. cylinder 1 at tdc and point rotor at cylinder 1. it may be off a tooth or 2.
We did that many, many times too. When we timed it to specs it wont run, its not 180 out, it only backfires then. No matter what we do 4 and 5 dont fire.
 

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Discussion Starter #15
Possibly distributor advance plate is stuck? Dissconnect brake booster line and plug it off. See idle changes. Spray brake clean or wd40 around intake manifold area and carb base with car running see if any changes. Don't spray in carb. RICK
Funny thing is last year it was stuck, and mechanical advance was worn out, its now rebuilt and all is working fine when tested, but problem still exists. Like I said, we tried everything with no results.
 

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Discussion Starter #16
If you have to time it way off your distributor may be off. That will cause all sorts of problems.
Thats the problem, if we start where we should it wont start at all, to get it to run at all the timing is way out and 4 and 5 are not firing.
 

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Discussion Starter #17
Possibly distributor advance plate is stuck? Dissconnect brake booster line and plug it off. See idle changes. Spray brake clean or wd40 around intake manifold area and carb base with car running see if any changes. Don't spray in carb. RICK
We also did that and tested the vacuum, its high and steady, no leaks.
 

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Discussion Starter #18
are you getting NO spark at ALL on those two cylinders?
pulled plug lead out and cranked engine over to see if you have spark??
might be distributor out 180*.
yes, the spark is there, we tried the 180 and it wont run and backfires, this wrong timing position is the only way it runs the other six cylinders, but not 4 and 5
 

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have you by chance have the engine block numbered wrong?the cyls on chev are stagered from side to side.1357 on one side and 2468 on other this wouldhave your fireing order mixed up and distributor position outta whack..or mabe the plug wires on distributor in wrong rotating direction.
just a thought, hard to diagnose whithout the car actually in front of me
 
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