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Discussion Starter · #1 ·
Well, after experiencing different symptoms with my 1972 XLCH, such as hard starting, flooding, popping out the carb, even with a new Mikuni, new battery, new Dynatek ignition, I did a compression check to find both cylinders reading 30 psi when warmed up, 60 when cold. I've adjusted the pushrods so thats not the culprit. The PO had the top end redone, so that is suspect. It starts fine when cold, hard as hell when warm.

Strange thing is, when it starts up, she runs fast and strong, with no smoking, although there is some oil spraying out the breather. How can this be?? I would imagine if I had compression that low, she wouldnt even start, much less run and idle good. It even takes all my weight to kick her over.

I've tried two different comp testers with the same result. I checked the cam timing and it looked fine:


Also, here's vid of me kicking her after I did the comp test.


This is driving me nuts. Any ideas??
 

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rings might be put in the wrong way. you should have waay more compression than that. on my 81 sporty the timing mark on one of my cams looked alittle off. could go either way so i tried one way. it ran like sheite so i changed it and it ran like a mofo. this was only on one cam mind you. and for the love of pete don't use that much sealer on that gasket when you put it back together.
 

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you might have to pull the heads ,sounds like valves not seating. had a shovel do the same with low comp,ran good cold then after warm could hardley keep it running,pop out the carb etc. just my 2cents
 

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sounds like a top end issue heads, rings, valves or may get real lucky and need head gaskets.
 

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lol it is possible, but the PO might not have annealed the head gaskets when putting them in making them sit incorrectly when the bike is up to temp or even warm. The way I read it was that it was both front and rear compressions tanking when warm. The front cam gear should only influence the front cylinder.
 

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Do you know what the over bore is on the cylinders? You said the PO had the top end done.

72-early 73 cylinders are notoriously thinwalled and can only take a few bores before you bust into the oil returns. I had a 72 and when I pulled the top end off, the oil returns were wide open all the way up the ring wear area.
 

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...Strange thing is, when it starts up, she runs fast and strong, with no smoking, although there is some oil spraying out the breather. How can this be??
Oil spraying out of the breather is consistent with poor compression. That is, if the rings are not sealing well, the expanding combustion gasses will blow around the rings and 'pressurize' the crankcase, causing it to blow some oil out. When you first start the bike, you are likely getting better compression than when the cylinder heats up. As it heats up the ring to cylinder gap increases, you get more blow-by and worse engine performance.

If this were my engine, I'd disassemble the upper end, check the cylinder bores and the rings, check the valves, then ensure that the cams are properly timed.
 

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Well, after experiencing different symptoms with my 1972 XLCH, such as hard starting, flooding, popping out the carb, even with a new Mikuni, new battery, new Dynatek ignition, I did a compression check to find both cylinders reading 30 psi when warmed up, 60 when cold. I've adjusted the pushrods so thats not the culprit. The PO had the top end redone, so that is suspect. It starts fine when cold, hard as hell when warm.

Strange thing is, when it starts up, she runs fast and strong, with no smoking, although there is some oil spraying out the breather. How can this be?? I would imagine if I had compression that low, she wouldnt even start, much less run and idle good. It even takes all my weight to kick her over.

I've tried two different comp testers with the same result. I checked the cam timing and it looked fine:


Also, here's vid of me kicking her after I did the comp test.


This is driving me nuts. Any ideas??
Those timing marks are off alot man. Roll tha pinion back a little c/clockwise to line it up better with number 2 and you will see it. Stock marks arent exactly opposite from eachother either. Check this out and tell me they are same as yours.
 

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Number three cam to number two looks to be a tooth off...

With your reading on the compression being low...Think I would do a leak-down test....This can be done with the pushrods out of the motor...

See what the test shows on where the compression is slipping by...
every thing drag says...to clarify, this SHOULD be done with pushrods out or loose...and if your gonna do it with the cam cover off be prepared as the motor may make a turn or 2...things will fall out..
 

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Number 2 and 3 cams do look off, like Dragstew says. If you're gonna check the cam timing again, recheck the oil pump timing while your in there. I don't see the timing hole below the gear, but it might be close to the notch and I'm not seeing it in the picture.
 

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Discussion Starter · #17 ·
and for the love of pete don't use that much sealer on that gasket when you put it back together.
I know, right? That was the PO.

If this were my engine, I'd disassemble the upper end, check the cylinder bores and the rings, check the valves, then ensure that the cams are properly timed.
Agreed. I rechecked the cam timing and made sure it was PERFECT. Ran the bike and had the same probs. Taking the heads and cylinders off next, then taking them to Baisleys Hi-Pro.
 
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