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Discussion Starter #1
I just tried to fire up for the first time since rebuilding. First attempt, I had the pick up coils swapped. It didn't go well. Fortunately someone here had the same symptoms, so I knew what it was. Also good news, I was able to pull my stator cover post tuxedo mod, so that's a win! Anyways, on to the reason for writing.

Second attempt it started up, but only the back cylinder is firing. The front is just popping. What could this be?

https://youtu.be/d_ouWOocKrY

Also I have a Google Photos album of all the work. I have photos of the cam timing. Unless I misread it, they are spot on.
 

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Discussion Starter #2 (Edited)
Correction, front is fine. Rear is bad. I unplugged the front plugs and it doesn't run. I unplugged the rear and it runs on only one cylinder, but no popping.
 

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Maybe do a compression test on both cylinders to compare,?

Sounds like it's popping through an exhaust valve, maybe. Thinking one may be leaking, but not sure.
 

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Discussion Starter #4
I am working on getting a compression test kit and a leak down test kit. In the meantime, I pulled the spark plugs to see if there is anything obvious there. Keep in mind, I never got the engine warm.

The front plug is very black and sooty, but I was running with the choke full on. The rear is dark brown and dry. Note, this is after sitting overnight.

I took one more picture of just the rear plugs after running about 30 seconds. Still dry, and not even warm.

The carbs sat without fuel all winter, so I don't think anything is gummed up. Heavy throttle doesn't help (thinking that perhaps the pilot is clogged).
 

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Discussion Starter #5
Using spare fuel line and vacuum line, I made my own makeshift leakdown tester. I ran compressed air into the rear spark plug hole with it at TDC. I also tried rotating 360 degrees.

In both cases, I hear the air coming out the exhaust. I guess I'm glad it isn't out the coolant or crank case...

SHOOT I JUST HAD A THOUGHT!!! Maybe the exhaust camshaft I bought on EBay was actually for the front cylinder! I only compared the lobes, not the timing mark. I think that's the only difference between front and rear exhaust cam shafts.
 

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Discussion Starter #6
I went through the positions that the cam shafts would have to be in. The rear intake should be pointing up towards the rear at about 45 degrees, and the rear exhaust up towards the front at about 45 degrees. If i put a front camshaft into the rear position, the timing marks would result in that cam pointing down towards the rear at 45 degrees. My pictures show it in the right spot.

However, is it just me, or is the left exhaust rocker out of position in this picture? I don't have the heads off to look again.

https://photos.app.goo.gl/PYhgkVgf4R9c31gb8
 

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On the left, that spring steel retainer looks bent, maybe? It's sticking up more than the short one on the other side.

Some way, it sounds an exhaust valve is open as the cylinder fires. So a leaky valve or valve stuck open, or the cam opens it at the wrong time. Sounds like you're sure you have Cams in right.

Did you do anything with the valves, like lapping or remove them at all?

If the rocker is actually out of place, there's a chance it could be holding the valve open if it's jammed against the valve stem. Like maybe the rocker rolled onto it's side between the valve stem and cam.

It's hard to see where the rockers actually are in the pic.

Shane the valve covers won't come off without moving the engine.
 

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Also, the plugs won't tell you much since it was just started briefly, and the choke was on.

This might be one of those times when a cheap bore scope could be used to look at the exhaust valves and rockers. Can go through the spark plug holes to see if a valve is hung open. Not sure if there's a route to peek under the valve cover.

It needs an endoscopy,!
 

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Discussion Starter #9
I outlined the rockers. The lower left looks more straight than the lower right.

The first two pictures are the same picture during reassembly, only one has red lines drawn on it. The last two pictures are from disassembly, one with red lines on it.
 

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I outlined the rockers. The lower left looks more straight than the lower right.

The first two pictures are the same picture during reassembly, only one has red lines drawn on it. The last two pictures are from disassembly, one with red lines on it.
I'm having trouble making out the red marks, but I think I found them using the computer instead of phone.

Which cam is the exhaust cam in relation to the pics, top or bottom?
 

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Ok, flipping quickly between the first two pics, it looks as though nothing has moved out of place, just your red lines pop into view.
 

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Discussion Starter #12
I used my "leakdown tester" on the front cylinder today, just to compare. First try, it blew air out the exhaust just like the rear. I spun the engine 360 degrees and it held the air. I definitely have a leaky exhaust valve.
 

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Have to watch, sometimes the air pressure will cause the piston to move enough to open a valve.

Edit: Will be interesting to see what the problem is.
 

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Discussion Starter #14
I was able to get the cover off without fully removing the engine. I pulled all three mounting bolts, the bottom of the radiator and the front bevel, but I had just enough clearance to get the cover off.

Sure enough, the right exhaust rocker wasn't seated on the valve and was holding it open. Good news is the timing is correct. Using a screwdriver, I pushed it over and it popped onto the end of the valve.

It looks like it put a little bit of wear on that cam. I couldn't see any missing material, just a bit shinier on that lobe. I don't think it's cause to replace the cam/rocker/valve.

I'll do another leakdown test before putting it together.
 

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Discussion Starter #15

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Was able to look at the pics on a 60" tv.

Working with the last four pics,... Are there any of those Mark's that you can catch a fingernail on? If not, then I think it will be ok.

In the third from last pic... Which lobe had the rocker out of place? Looking at a possible gouge mark on the one to the left. Can you catch a nail on that mark?

If any of the wear Mark's catch, will a scotchbrite pad polish them away? They don't look too serious, especially if they're just 'images' and not piled up metal.

Never saw that sort of retainer arrangement before. Nor the wear patterns beyond the pad of the rocker, but that looks like it's normal in this case.

Quite a collection of pics!
 

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Discussion Starter #17
Nothing deep enough to catch on my nail.
I decided I'm going to run it as is, and maybe check it at the end of this season.

I did another leakdown test and the cylinder holds air now!
Now time to put everything back together and fire it up!

:grin2:

Thank you very much!
 
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