'58 - 348 Tri Power

Fathead Racing

Well Known Member
Supporting Member 7
872 block with 971 heads

I'm hoping for bad plug.

And will do a check on the cranking compression for that cylinder.
What are you thinking re: if the compression on that cylinder is off? and how would it be resolved?
Do you mean 791's? That would be the 1958 head without the cooling holes for the spark plugs. Also that block is not correct for the heads as it does have the cooling holes. Someone must have modified the block to seal off the steam holes.
 

'37-4D

Well Known Member
Swap the plugs as you said, then run it up to temp even take it out on the road if you can. After that pull # 6 again an see what it looks like.
Did exactly that and took it for a spin. I'll pull the #6 spark out again in the morning and see if it fouled.
Couldn't tell about the sound....I think i'm loosing it now, I can't tell anymore....Lol
I think it sounded different. hard on my ears, this thing is loud even with the main headers blocked and dumping out back.
I wear plugs :)
 

'37-4D

Well Known Member
Do you mean 791's? That would be the 1958 head without the cooling holes for the spark plugs. Also that block is not correct for the heads as it does have the cooling holes. Someone must have modified the block to seal off the steam holes.
They do seem a little dark all of them. How can you help?!!! :bow
Yes, sorry type-o, meant 791 heads and yes it's an 872 block with the holes.
I had mentioned that in the first page of the thread when I came on and informed Don.
I didn't see the steam holes! so yes. (roll eyes)
 

Fathead Racing

Well Known Member
Supporting Member 7
They do seem a little dark all of them. How can you help?!!! :bow
Yes, sorry type-o, meant 791 heads and yes it's an 872 block with the holes.
I had mentioned that in the first page of the thread when I came on and informed Don.
I didn't see the steam holes! so yes. (roll eyes)
Can't tell until we see what your jetted now. Who did the carbs? They should know.
 

DonSSDD

Well Known Member
Supporting Member 2
10 km rides do not heat up the fuel delivery system on a carbed vehicle. Imho you could take this for a 20-30 mile highway run and see then how those plugs work.
Others here are way more expert than me on this but short drives around the city at low revs with a lot of idling and 3 carbs will mean you need to have some good long hot runs once in a while to keep this thing running good.
 

Don Jacks

Well Seasoned Member
Supporting Member 3
I agree with Don.That engine needs about an hour run at 100 km[60 mph] at part throttle inorder to check the plugs and be sure where your jetting and or plug heat range settings need to be.
 

Fathead Racing

Well Known Member
Supporting Member 7
10 km rides do not heat up the fuel delivery system on a carbed vehicle. Imho you could take this for a 20-30 mile highway run and see then how those plugs work.
Others here are way more expert than me on this but short drives around the city at low revs with a lot of idling and 3 carbs will mean you need to have some good long hot runs once in a while to keep this thing running good.
I agree with you in regards to the short hops not being good for the engines well being overall. Further, I will assume that the carbs are in a progressive linkage mode. Only the center carb will be open until 60% throttle opening, only then do the front and rear carbs start to open progressively. If jetted correctly you should not see such fowling unless the choke were not functioning correctly.
 
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'37-4D

Well Known Member
Thank you all.
I did build this for long haul rides up to the farm!
I haven't had much time with it!!!
This morning I did check the plug (#6) and no fouling, but as you all said, need to get out there for a long cruise.

Yes to progressive linkage, no choke. I was aware of the centre carb only running until I hit higher speeds then the other two open up :)
I have to give some credit here to the guys that built it as far as jetting amongst all other items mentioned!
That plug was bad, pretty sure!
Let's see if this one fouls!!!!
Next ride will be a long one and on the highway :)
 

Don Jacks

Well Seasoned Member
Supporting Member 3
His engine builder dyno'd the thing before he got it back to install so I'd think the jetting at WOT would be close.Hopefully a couple of long cruises will let that little engine settle down.
 

Fathead Racing

Well Known Member
Supporting Member 7
Also, there is a power valve in the center carb that acts off a spring like the Edelbrock Rod system. It is vacuum sensitive. If you are running with less than say 10" of manifold vacuum that valve will be adding fuel in that instance. When I modified my three two system I also modified that spring so it would not add fuel until the vacuum was less than , I'm guessing, 8".
 

'37-4D

Well Known Member
His engine builder dyno'd the thing before he got it back to install so I'd think the jetting at WOT would be close.Hopefully a couple of long cruises will let that little engine settle down.
You did also mention that as far as the sound is concerned, it's what happens when you block off the heat cross over port in the intake manifold on these engines.
 

'37-4D

Well Known Member
So here is a photo of the swapped plug in #6 after a spin yesterday evening!
Wasn't a long ride by all means and at city speed.
Not sure if the fact that the side terminal is wet and black a bad sign or simply shows that I need to take it for a descent rip to see?

 

Fathead Racing

Well Known Member
Supporting Member 7
You did also mention that as far as the sound is concerned, it's what happens when you block off the heat cross over port in the intake manifold on these engines.
Yes, the exhaust note is not the same when the crossover is blocked. When the crossover is open under the intake the two exhaust banks are connected sharing pressure at the head. The exhaust note is distinctly different.
 
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