More starting questions

[alehman]

Okay. I've been trying to get my 79 K started for the few months I've owned it. As I'm a student, I don't have a huge amount of free time. However, today I (finally) got around to running a compression test on the bike. It was a cold test, and I got 120, 105, 125, and 120 going from #4 to #1. I know the manual says something like 150 psi is what it should be, but what can we realistically expect for compression in bikes these old? What sort of readings do you guys get?

Moreover, do you think this would prevent my bike from starting?

A few facts about the bike:

clearances are good.
Carbs are cleaned and rebuilt.
Spark seems to be good. I suspect it might be weak but I have no idea what a good spark looks like.

[alehman]

I should also mention the bike didn't come with an airbox so I re-jetted and podded it. Would incorrect settings fully prevent my bike from starting though, or should it be able to start and then just run really badly?

[Re-run]

What hose did you use on the test, was it a thick rubber hose or a thin one, or better yet, a metal tube? The typical hoses will not read right since they are designed for cars. So check that.
Also, 1 cylinder is lower and that makes me wonder if you did not have a good seal or if it is something else.
Easy test would be to put a teaspoon of oil into the cylinder and take the readings again.
If no change and readings are still low with a good hose, then it would be valves.
If readings go up, then rings are the culprit.

Either way, those #s are not too low for engine operation. If you rejetted and put on pods, you are going to need to read your plugs to see if they are wet from fuel or bone dry.

One thing to remember is you have vacuum carbs and they don't like pods much. It can be quite difficult to get pods to work right on those.

[alehman]

I used a tester with a rubber hose about .5 inches thick. I was a little wary of the one cylinder with lower compression. I'm gonna test it again with the oil trick.

Yeah, everyone has warned me about the pods with CV carbs, but I'm pretty determined to get them right. I've seen a lot of DOHC bikes with carbs and the owners swear they've gotten them right. I should say that my exhaust is a little funky... it's a 4-4 system but two of the mufflers have been removed so the pipes are open. That'll mess things up. Because pods will send everything lean, should I put my pilot screws further in or back them out? I'm not sure which way will make the idle mixture richer.

[Re-run]

Do you have the service manual here? If not, grab it. I think your idle screws turn out though to go richer.

[robs750]

I bet the valves are leaking.
A leakdown test will show whats wrong.