The 81 lives!

The compression test was done with the throttle held wide open. He set the timing and checked the valve clearances before the carbs went back on since there was no point if the head had to come off due to a bent valve or some other problem. Once the compression had come up after putting the stuff down the holes he decided it would be worth trying to start it. So we mounted the carbs. After we couldn't get it started we verified the timing was right and it was getting spark. Then we started investigating why it was firing but not starting. This was when we discovered the firing order must have been off... or the compression was simply too low to allow it to start. When we changed the firing order by swapping the coil wires it started instantly. Ran it for a while to warm it up, checked the compression again and came up with the same number. At this point he suggested the tester may have been off because he didn't think it would start that easy with the compression that low.

So would it start and run well on 85 PSI? If so, assuming the valve timing is right what else could be the cause of low compression?

The engine from ebay was apparently tested at 150 across the board so its a good way the test the tester once it shows up. I'd check the compression on that when it came anyhow to make sure it is as the seller claimed.

Buy a new tester for what they cost worth having in your workshop, you can then conduct a basic health check whenever for whatever vehicle you have.
Example Ebay 191153672373

As for low compression if the valves are good- your only other options are stuck rings or (gulp) bent rods. Still, if all six are low, but pretty much even, this last possibility probably isn't it.

How long has the motor sat before you ran it? You may see those numbers come up as you ride it. Even if they don't, if it runs well I wouldn't worry too much about it.

Lucien-Harpress wrote: As for low compression if the valves are good- your only other options are stuck rings or (gulp) bent rods. Still, if all six are low, but pretty much even, this last possibility probably isn't it.

How long has the motor sat before you ran it? You may see those numbers come up as you ride it. Even if they don't, if it runs well I wouldn't worry too much about it.

This has been sitting since mid/late last summer. Before that it sat for at least a year according to the previous owner, maybe two.

I'm not going to be riding this one. After it failed I stripped some of the best parts for the 79 and I'm not going to expend my efforts on two 1300s. The exhaust is also in bad shape so it would cost too much to make it sale worthy in its current condition. Once I verify the engine compression add I'll be yanking it out and selling it. I'll part out anything else I don't want to keep for the 79. I have pretty much a brand new top end, big bore kit and pistons should the new motor ever need them, or I may sell them as a package. Pistons, rings, bug bore cylinder and reworked head.

if your going to break it up i would be interested in the complete rear light. :whistle:

I will keep that in mind. I'm not sure what components I'm keeping as of yet but if I let the tail light go you have first dibs.