Down on power after engine rebuild

I like to run mine at 10* advance, i would check the carb, and look for vacuum leaks, What distributor are you running?

I stand corrected, I was actually at 12 degrees at 700 rpms in gear. I backed it down to 8-9 degrees. Must've been running lower rpms in the driveway initially.

I'll check compression tomorrow. I must've checked the spark plug wires about 10 times during install but it's very possible I was misreading or misthinking so I'll check them again tomorrow.

I want to say the distributor is a mallory but can't remember for sure. It has the Prestolite electronic conversion so no points.

There is a paperclip trick to tell if the secondaries are opening. It's described somewhere on the site, a search may find it.

Thanks, I actually found the paperclip trick last night and plan to try it today.

I did reuse the old lifters and they were put back in the same place they came from. I shimmed accordingly to get the proper preload on each valve. The push rods were also put back in the same place. The rocker arms weren't because the shop doing the valve job threw them all in a big box which I didn't appreciate but he swears it doesn't matter where they go.

One free check, make sure nothing is funny with the throttle cable. In other words, make sure the cable is operating such that if full opens the carburetor throttle.

It wouldn’t hurt to check if the distributor is advancing correctly. I assume you have a timing light, right?

Procedure:

Ignore steps 1 thru 4 if your harmonic balancer has timing marks that go up to 34 degrees (or close to 34 degrees).

1) Find out the diameter of the harmonic balancer. I think it’s 6.375 inches.
2) Calculate the tape cut length according to the below equation:

(harmonic balancer diameter) x 3.14 x 36 / 360 = tape cut length in inches

For example: 6.375” x 3.14 x 34 / 360 = 1.90 inches

3) Cut off a piece of masking tape (or electrical tape) to the length calculated above.
4) stick it to the harmonic balancer like the view below



One end of the tape will be at 0 degrees BTDC and the other end will be 34 degrees BTDC. With 12 degrees of initial advance, you should be getting approximately 34 degrees of total advance. If you want, you can do this on the trailer in neutral:

5) hook the timing light up
6) start the engine
7) point the timing light at the timing pointer.
8) slowly rev the engine to around 3000 RPM and watch the timing move. It should max out close to the end of the tape marked 34 degrees.
9) all the advance should come in around 3000 RPM. If it doesn’t, note what RPM it maxes at.

Post your results and we can discuss if something is wrong or not.

Mountain Man wrote: pull the spark plugs and look for any that are different in color from the rest - either wet with gas - or sooty - or oil soaked. ......... Steve

Your symptoms sure point to an ignition problem. The power surge at 3200 almost sounds like a fouled plug that is starting to fire intermittently. I'm curious on the results of the plug conditions.

Ok so here are the findings so far. I checked the compression and all cylinders are at about 118psi which seems really low for a fresh rebuild with GT40p heads. Should I be checking with all plugs installed or removed? I was testing with all plugs installed. All the plugs look normal and none look cracked, black, wet, or anything like that. Plug wires are hooked up correctly. I'm using 18456273 as the firing order with the distributor spinning counter clockwise. 1 being the front of the drivers side and 5 being the front of the passenger side.

I started the day running slightly weaker than yesterday and noticed the secondaries were not opening. The diaphragm appeared to be pulled in but could've pulled itself in when I pulled the cap off. Either way, there are no holes or tears and after hooking it back up, it opens fine. After a little while, the engine started sounding bad and wouldn't even rev to 3000rpms in neutral. It was really surging like crazy too. Turns out the wires I soldered for the prestolite electronic ignition had poked through the shrink wrap and were grounding against the engine. Fixed that issue and it runs a little better than yesterday with the secondaries opening but it's still weak and lacks a lot of power.

Engine vacuum at the intake manifold jitters between 16-17 in-Hg but I'm using a vacuum gage meant for composite work so I don't know if the jitter is a vacuum jitter or a vibration jitter from the engine.

The timing seems to top out around 25 degrees but that is a guess because once I pass about 1800rpms, all the numbers disappear. The numbers go up to 30 but after about 1800rpms, it just looks like the numbers got wiped and I'm guessing off of the stamping on the forward side of the harmonic balancer. Not sure if that's a timing light failing/can't keep up or whether that means there is some major timing issue.

-The firing order is correct for reverse rotation 351W.

-I wouldn't be too concerned on the compression readings. What would be more concerning is if one of the cylinders was 10 PSI (or more than 10) lower than the rest.

-You have to check all the plugs.

-That piece you show in the picture, looks like a magnet from the pick-up stator. There should be 8 magnets total. Pull your rotor off and you should see a black ring at the base of it (if its a pertronix kit). That ring should have no missing magnets in it. See the view below. It has red arrows pointing where the magnets would be.

To properly do a compression test you need a fully charged battery,warmed up,all plugs removed and throttle wide open. Why not remove the pertronix and reinstall the points and see what happens?

Waternut wrote: All the plugs look fine. The magnet was found on top of that black ring after pulling the rotor off. Do those magnets tell the coil to send spark?

Yes

If you are missing a magnet, one of your plugs is not firing. Did you look at the stator ring to see if any are missing?

The lower ring (pick up stator ring) comes with the pertronix kit. I know on mine (clip sytle distributor cap) the rotor is also part of the pertronix kit. The stock prestolite rotor will not pilot the stator ring properly.

Before you replace any parts, remove the cap, rotor and stator ring. Take pictures of all these parts. Also, take pictures of the pertronix ignitor. Post the pictures so we can see the condition.

Waternut wrote: ... The timing drift makes me think the electronic ignition (Pertronix Ignitor) is going bad.

I'm not sure if timing drift is a symptom of a bad ignitor or not. Maybe others could speak to that.

The first thing that comes to my mind is that one of the advance springs is broken. The springs are supposed to allow the weights to move out with increased RPM, thus advancing the timing. And, just as important, to pull the weights back in as the Revs go down, bringing the timing back down to normal.

Springs are in good shape and the weights move in and out properly. I checked that a day or two ago. They could be sticking but when I'm at the dock, the timing goes up and down smoothly. I'll lube them up to make sure they aren't getting stuck somewhere.

+1 seems like more than 1 has been bad lately