C2 compression check and carb tuning

[hatdragracer]

Now that my wiring is sorted out thanks to Geeks65 and Vetzs,

I currently have a holley 650CFM vac secondary, R43 plugs, Pertronix electronic ignition (points replacement)...and was having a lot of driveability problems at low throttle. Engine is a 327/300

I pulled the plugs last night and did a compression check (cold)
Cyl 1: 155
Cyl 3: 155
Cyl 5: 150
Cyl 7: 150
Cyl 8: 148
Cyl 6: 133
Cyl 4: 140
Cyl 2: 145

My overhaul manual says that if your max psi is 155, your min should be 117. My other overhaul manual says that the cylinders should be within 10%, meaning cylinder 6 is out of tolerance. I added oil to cylinder 6, the reading came up to 140. It also bothers me that the RH bank has altogether lower compression than the LH bank. I would love to know the forum's thoughts.

The plugs had lots of dry black soot, and last time it drove, would backfire through the carb at low throttle, timing as set at 10 degrees at idle (sorry I don't know total timing yet). I have ordered an Edelbrock carb as I am tired of messing with Holley's, I replaced a massive doublepumper with this vacuum secondary Holley and still cannot get it to run right. Vacuum readings were hunting between 15 and 18 on both carbs, idle was rough, and no power below 1500 rpm's.

What spark plugs should be used now that she is running on unleaded?
Any advice on carb tuning would be greatly appreciated, I thought I knew how but apparently I don't!

 

[allcoupedup]

Hi -


R43s are way too cold for the street. My motor fouled the 43s and runs like a champ on the R45s.


One bank of cylinders could be higher than the other for a few reasons:
1. One head milled more than the other and therefore more/less combustion chamber volume
2. One deck has more piston/deck clearance - could have come like this from the factory - my block is .010 higer on one side so I used a head gasket .010 thinner to equalize


cyl 6 is just a little low for that bank of cylinders- sqirt a teaspoon full of oil in the cylinder through the spark plug hole and try again - if the number comes up by more than a few PSI you have a ring sealing issue. Be sure to do any subsequent teting under the same conditions (battery charge, all plugs removed, throttle plates open, etc....).

I wouldn't sweat these numbers too much unless you have a bad idle.

Brian

 

[Mikey1]

Yeah....I use R45s as well and they are fine.

I would not bother about the no 6 beeing some 12% off.....this is not causing your problems. As described before...one bank off a little...compared to the other is not a problem as well.

So you really need to check out if your balancer is

a) the right one for the engine and year
b) if the mark on the balancer is truly #1 TDC

...because a wornout balancer can cause the timing mark to move...

Best thing is to remove the spark and to turn the engine by end. With the finger you should be able to feel the piston....if you are not Popeye...

Have you checked for intake manifold vaccum leaks already ? Do the same with the exhaust manifolds.

If this is ok....go and look for the distributor....a worn out or incorrectly assembled unit can cause lots of problems. check for the plate to me moving if a vaccum is applied (by a Mityvac...) ...check for the weights to be able to move...dimple in drive gear aligned to runner contact....how much endplay (axial) does it have ?

....you have to sort it out step by step. I personally do not believe that this is an elementary carb problem from what I read. I would leave the carb alone for a while and sort out everything else....if these things are all correct....then you have to go carb.

 

[hatdragracer]

Update, while spark plugs were still out from the compression check, I put the #1 cylinder into firing position...or so I thought. The balancer was off!

I replaced the balancer, set the timing, re-torqued the intake manifold bolts, kept the old carb, she pulled 16" vacuum at idle and ran like a champ with the old Holley carb. Installed new R45 plugs.

Took her on the shakedown run, I drove and drove and drove (in the rain I may add!) It felt good to have it running that good. It pulled strong clear through 5000 RPM's. Stopped in at the BP down the road and enjoyed the attention, the car looked great with it's fresh paint under the lights!

Sorry to ramble, this was my first time driving Grandad's vette more than a block without a backfire or electrical meltdown! It was a good day today!

 

[odqlesz]

Backfiring through the carb. Had the same problem.
My plugs were fowled. I replaced them with R45's ran like a champ.
I thought you could clean fowled plugs and they would be ok. Wrong.