Re: Johnson 5hp TD20 ignition timing facts & figures?

[legendre]

Alright, it seems that both of my TDs have the same timing geometry.. that is, they both fire significantly ATDC when at lower speeds. Full speed looks to possibly have some amount of advance BTDC but it’s not been measured. Someone apparently ‘borrowed’ my good degree wheel.. so all I can do is approximate.

And I’ll have to admit.. at the moment, I really don’t know what might be the trouble with this one. So here’s a thought, let’s try to rule-out the head gasket without throwing $20+ at it.

If the gasket is bad, it’s going to be having an effect on compression, among other things. What if I pull the head & gasket, goop it up with some decent sealer, and then re-install. Once it’s dry, I can take some compression readings and compare – if the readings come up, that tells me something, eh?

Re: Use of sealer on head gaskets – I generally would never suggest it, but in this case it will never have to hold more than about 80-100 psi so it should be fine (I don’t plan to run it that way). Sound like a reasonable diagnostic?

BTW – Do you or anyone else know of any sources for reasonably-priced head gaskets for these models? It’s not too intense.. really seems to be plain rubber / fiber about 1/8" thick or so. Not a composite design, no seals ’round the holes, just die-struck from plain sheet material.