[1bad69]

Just changed the valve springs on my 781's from 924-16 comps to Straub Industries springs... unfortunately, it didn't change a thing... it does not run good at all, and it is fouling the #2 plug. This thing should be all over the road and eat tires like no one's business, but it doesn't... it falls flat on it's face before 4000 rpm. I have the anti pump hyd roller lifters I believe they are Morel. I have them set at 1/2 turn past lash for preload. It starts fine, but fouls the plug #2 immediately. maybe not foul, but it is VERY black, and the rest of them are nice milky brown. It is a 850 HP Holley. I have it jetted at 78/84's with 3.5 power valves (new) I did add a new ignition system and it does have a rev limiter, but I have the rev limiter set at 6800 or so... It is a Mallory Comp 9000 and Hyfire IV. It has to be something simple. I'm to my wits end... My mechanic friend thinks it may be in cam timing... Wouldn't it not start well if it was in the cam timing? I ran it straight up and it is a Big Mutha Thumpr, which is not the most desirable camshaft, but I would think it would run better than 4000 rpm...especially now that I have good valve springs... Thanks Chris!:beers:

Good Guys is less than 2 weeks away, so I don't want to do anything drastic as it runs and drives, just falls on its face...

 

[Stokerboats]

I wouldn't use a comp 924 on an ink pen.

 

[Stokerboats]

I use a 6.5 PV on my Dominator. (primary) plugged in the rear. I NEVER have had the carb load up. Are your spring heights set correctly? Seals on correctly? Vacuum leak?

 

[1bad69]

I use a 6.5 PV on my Dominator. (primary) plugged in the rear. I NEVER have had the carb load up. Are your spring heights set correctly? Seals on correctly? Vacuum leak?

Yes... set at 1.9" No vacuum leak, as far as I am aware of. Seals, I don't know... I have not had this issue until this motor. Same heads on 3 motors.

 

[sschevellefan]

cam timing and ignition timing is different. Ignition timing will have a effect on starting but cam timing wont. Did you degree the cam or just put it dot to dot? Ive heard the thumper cams are hard to tune.

Is the plug gas fouled or oil fouled? Whats your fuel system like? How did the valve seals look when you replaced the springs?

 

[LS6 Tommy]

Dual plane or single plane intake? Stock BBC heads are notorious for needing different mixtures on the individual ports. You may need to stagger jet the carb...

Tommy

 

[1bad69]

cam timing and ignition timing is different. Ignition timing will have a effect on starting but cam timing wont. Did you degree the cam or just put it dot to dot? Ive heard the thumper cams are hard to tune.

Is the plug gas fouled or oil fouled? Whats your fuel system like? How did the valve seals look when you replaced the springs?

Gas fouled... fuel system is stock 3/8 line from tank to hi flow Jegs mechanical pump. I didn't degree camshaft, I just ran it straight up.

 

[jeff swisher]

anti pump up lifters with 1/2 turn past lash?

My understanding of the anti pump ups for years was ZERO preload.

This i have found to make a cylinder have black sooty plug..
LOW OR NO COMPRESSION..
which can happen if the lash is not correct.

 

[OLDED]

Did you run a new full 12 volt wire from the ignition to the hei dist. Set up? The dist needs full 12 volts to run correctly. Ed

 

[mfret1970]

anti pump up lifters with 1/2 turn past lash?

My understanding of the anti pump ups for years was ZERO preload.

This i have found to make a cylinder have black sooty plug..
LOW OR NO COMPRESSION..
which can happen if the lash is not correct.

My first thought too. What method was used to run the valves?


Sent from AutoGuide.com App

 

[1bad69]

My first thought too. What method was used to run the valves?


Sent from AutoGuide.com App

EO/IC 1/2 turn past zero lash

 

[1bad69]

Did you run a new full 12 volt wire from the ignition to the hei dist. Set up? The dist needs full 12 volts to run correctly. Ed

I ran the power wire directly from the battery.

It was fouling plugs with my HEI as well...

 

[1bad69]

anti pump up lifters with 1/2 turn past lash?

My understanding of the anti pump ups for years was ZERO preload.

This i have found to make a cylinder have black sooty plug..
LOW OR NO COMPRESSION..
which can happen if the lash is not correct.

I am going to do a compression test, but leakdown tested fine. Also.. this is the only plug that is doing this, and all of the rest are good and milky brown. Same lash method.

 

[Bluegoose1970]

Dead cylinder. I take it you have already swapped plug and wire on the cylinder and leak down passed, sounds like too much preload on lifter. The lifter on that cylinder could have been collapsed when you adjusted it.


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[1bad69]

just tested compression on #2 cylinder. 175 lbs....

 

[OLDED]

Cracked porcelain on that plug?

 

[1bad69]

Cracked porcelain on that plug?

No... I put a brand new plug in, gapped it at .045" it fouled it at startup, I believe. Put another in it, fouled it in 2 minutes. I think why the 2nd didn't foul immediately was that the motor was warmed up a bit with the new fouled plug, and I didn't have to give it gas to start it. I kind of think it is in my carburation, but it is only the one cylinder... BEATING HEAD UP AGAINST WALL! I would like to just change the carburetor and see if that fixes my problem.. but I don't have anything large laying around. I have a 600 cfm Edelbrock on the shelf, but I don't think I would find anything out in that small of a carb, and don't want to damage the engine, as it is brand new with 200-300 miles on it.

 

[Blownchevelle68]

Cant see how one cylinder would be effected by your carb, could be wrong though. I'd sooner think more than one would have a issue if that is the case.

Did you test spark on that wire? Check the underside of the dist cap to see if there is a crack or if the tab is gone?

 

[1bad69]

Cant see how one cylinder would be effected by your carb, could be wrong though. I'd sooner think more than one would have a issue if that is the case.

Did you test spark on that wire? Check the underside of the dist cap to see if there is a crack or if the tab is gone?

I know it is getting spark.. I don't know how good of a spark. I can't find my spark plug wire pliers, but I did start it without the wire on, and it did run better with it on. I never even thought about maybe the dist cap or rotor... I did buy the system used, but barely used. He had it in the car for very little use. Motor blew, so I bought ign system. I'll see if anyone around town sells the cap for the Comp 9000. I'll change both cap and rotor. It does have new Moroso 8mm wires.

But I did have this problem before with my Accel HEI distributor...

 

[Blownchevelle68]

I know it is getting spark.. I don't know how good of a spark. I can't find my spark plug wire pliers, but I did start it without the wire on, and it did run better with it on. I never even thought about maybe the dist cap or rotor... I did buy the system used, but barely used. He had it in the car for very little use. Motor blew, so I bought ign system. I'll see if anyone around town sells the cap for the Comp 9000. I'll change both cap and rotor. It does have new Moroso 8mm wires.

But I did have this problem before with my Accel HEI distributor...

Just for curiosity sake, flip-flop wire #2 and #4 to eliminate the wire. Not sure who around town, other than Karl Performance, will have a new Comp cap. Might be a Craigslist search if your trying to do it today...??