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Discussion Starter · #1 ·
Hi

I've had a niggling feeling lately that my 79 isn't feeling as torquey low down in the rev range. It seems to pull ok in the top revs but is a bit sluggish gettin there.
I've done my valve adjustment about 5 times just to be 100% sure its not a sticking valve.
Tried a compression test today after a good ride and on the rear cylinder with WOT I made 130psi after about 7 or so kicks which is good I think. When I tried the front cylinder I got it up to 130 also after around 10 kicks but the weird thing is, on the front cylinder the kicker just feels slack with no effort needed to kick it. Whereas the rear I need to give it some weight, the front I could do with my hand?
If I put the rear spark cylinder plug back in tight while I'm testing the front I get a bit of compression back to the kicker? Is this supposed to happen?
 

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id bet its time for a valve job... loosen the pushrods and put air in the cylinder to find out if the valve is leaking or if the rings are gettin whipped..130 is good for a stock bike but ten kicks is a lot.
 

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Discussion Starter · #3 ·
Yea I did think it was a few kicks to get it there. I'll have to find a compressor to do a leakdown on her. I don't think its the piston rings because I haven't got oil on my plugs and it aint blowing smoke out the pipes. Valve job easy enough to do with basic tools?
 

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Did you do your valve adjustment, cold or hot? If you did it cold, you need to warm it up first, and then do the adjustment. These old ironheads have iron everywhere, except the pushrods. The expansion can affect the adjustment sometimes. I assume you did the compression test dry? I would readjust the pushrods, loose, and with the covers still loose, do another compression test. As for the loss of power at the lower end, that sounds more like a tuning problem or low voltage on the ignition system. have you ever had your advance unit out and inspected the weights and springs? Points or IE? Did you hold the throttle wide open when you did the compression test? I think the factory book, says 5 kicks. So do 5 kicks, and see what the difference is. The leakdown will tell you the easy way.
 

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Discussion Starter · #5 ·
I did the pushrods with the engine cold as that's what all my manuals say to do?
The carb is fine I have tuned that so my plugs are golden brown and the bike doesn't bog down or stutter under full throttle so I don't think its a tuning problem.

Compression test was done with a hot engine, plugs out the holes and out the wires. Throttle open and choke open.

What I noticed just doin another test there is that if I leave the plugs in their wires but grounded against the cases, both cylinders make 110 psi, take them out completely and I can make 130psi both cylinders with 7kicks on each. The weird thing is that the kicker is noticeably weaker on the front cylinder?
 

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Hard to say with out a tare down, you will have to put air to the spark plug hole some how, even with a rubber tipped air gun, listen to the exhaust and intake for leeks.

Could also be the rings in the front barrel are lined up.......
 

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Discussion Starter · #7 ·
Forgot to say bike is on points, and starts up pretty good so I'm confident timing is ok.
Yeah I'm thinking I'll try and get an airgun somehow and try test for leaks but may resort to whipping the front head off for a quick look. Would a valve problem still keep compression in the cylinder but not at the kicker?
 

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Forgot to say bike is on points, and starts up pretty good so I'm confident timing is ok.
Yeah I'm thinking I'll try and get an airgun somehow and try test for leaks but may resort to whipping the front head off for a quick look. Would a valve problem still keep compression in the cylinder but not at the kicker?
Without a leakdown tester, which is a simple contraption to fab from a old spark plug, a "t" fitting, good pressure guage and a hose connection to hook to compressor. With out that, you will probably have to remove the heads. I would go for both, just to be sure they are both good. The compression will be directly related to the kicker, but only if the clutch is slipping, only on the front cyl. I would say not. Roach may have it, with the rings on the front cyl all lined up, But usually, that causes smoke on that cyl. Could be "something" failing, that is still runnable. Like a scuffed piston, that the rings are still holding pressure. It sounds like the valves are in pretty good shape, or you would not be getting that good of a compression reading. Nobody on here is as good, as you taking it apart and looking. We all guess, from what input you provide. If when you get it apart, you still do not see the problem, post closeup photos of the working parts, pistons, rings(both installed on rods) cylinder walls, valve chambers, springs and rockers(detail shots) and anything else you think could be wrong. But I bet, when you dissasemble, you will see the problem.
 

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Due to the curiosity on here, make sure you post what you find. Because like the "National Enquirer", we all want to know.
 
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