rebuilt 140 doesn’t like to idle

[SSTKO81]

I feel like this post has kinda meandered so I’m going to update with as much info as possible.
The 140 was pretty much rebuilt over the winter. -reason was the number 2 rod bearing spun and it was knocking like a tractor with no oil pressure. Everything was removed cleaned and inspected; and replaced as needed with the exception of the camshaft, which stayed home. Crank, #2 rod and piston are out of a donor and have brand new bearings and rings. The engine was reassembled with all new bearings and clearances were checked w plastiguage before final torque. Engine turns over freely and while compression isn’t awesome, it’s between 110-120. Oil pressure is great at 40psi @ 1500 rpm.
This thing is a b!#¢* to get started. You have to pump the throttle (gas shoots out of the carb just as it should In a nice, tight stream; I will say one of the Venturi boosters is missing tho) it tries to start but unless I bury the throttle it just won’t fire.
Once it does fire you really have to feather the throttle to find a happy place where it’ll stay running. It seems to be best at 1500-2000rpm, runs smooth at that point, no misses or what sounds like detonation. If the throttle is backed off to say, 900-1100 rpm (if I can keep it running) it shakes violently and I can hear what sounds like detonation. -naturally I first went to the carb settings here and turned the mix screws in all the way and back out 2 turns. Upon adjustment the carb likes to run with both screws out about a 1/2 turn (would seem way too lean, but ok) idle speed screw is having to be turned way in to keeps the engine running. 900rpm is about as low as I can take it and it will begin to lug and sounds like detonation. But I can run it up to 3k and it’s smooth as butter.
So timing.... forget about it. Won’t do anything less that 12* try to move it to 6-8 where it should be and it’ll die before it gets close. So that’s where I’m at. Dizzy seems to be ok after replacing cap/rotor and wires. No miss fires, dwell is appropriate and plugs are new acdelcos. IDK....

 

[SSTKO81]

Maclin I fear you may have hit the nail on the head. A couple google searches (user beware) netted my exact symptoms
Re: What would the symptoms be of a retarded camshaft???


“If you've installed one a tooth off retarded, the engine will start well, but have poor power past 3000, and all your tuning efforts for normal running -- timing, etc., will fail.

If you have a tooth advanced, you'll note hard start, maybe spitting or backfiring from the carb if you are trying to set to run your normal advance, but one running, seemingly normal power but accompanied by a hot engine. Maybe some dieseling on shutdown.

Either way, your timing efforts are the clue, having to twist the distributor too far left or right from what you're accustomed.”

 

[TurtleTamer]

Compression seems low for a rebuilt motor (though maybe not enough runtime for the rings to seat properly). I would have a look at valve adjustment before yanking the motor or checking crank/cam timing. Having had things apart, it can take the oil a little while to get through everything and pump up the lifters, so it's not all that unlikely that lash could have been set on essentially shorter lifters and now that they're fully pumping up, the valves are partially held open, just enough to not fully seat. This would not be as evident at higher rpm because of the stronger combustion helping to seat the valves. A quick way to check for this is to put the compression tester in the spark plug hole and, while spinning the engine over, backing the rocker nuts off about 1/8" at a time. A starter button makes this process much easier. If compression suddenly improves, either the lash is off or the valves aren't seating correctly.

Was the head rebuilt as well?

 

[Maclin]

Lower compression than expected is another symptom of cam timing being off.

 

[Bt Doctur]

Are you positive you lined up the marks on the crank and cam gears?

 

[SSTKO81]

Are you positive you lined up the marks on the crank and cam gears?

I’m not positive of anything anymore. And the only way to check is to pull it apart... I can’t even remember if the cam and crank had marks on them to show where they line up

 

[SSTKO81]

Are you positive you lined up the marks on the crank and cam gears?

I went to the junk pile today and checked out the old crank that I had replaced and marked when removing.... lo and behold....

the yellow low mark represents what I apparently thought was TDC and proper alignment, but if you look closer you’ll see the dot that represents what’s ACTUALLY the correct alignment mark....

 

[Bt Doctur]

Looks like you found the culprit

 

[SSTKO81]

Yeah. Missed it by that much

 

[Maclin]

One tooth off will do that. Every time Good luck on that repair.

 

[SSTKO81]

Welp, one tooth off confirmed. I don’t know how I missed this! While I’m in here I’m consider just going ahead and replacing the cam gear. It’s pretty rough looking. Any tips before I pull this thing?

 

[Silvertip]

Valves properly adjusted. Would account for poor idle mixture screw behavior.

 

[SSTKO81]

Valves properly adjusted. Would account for poor idle mixture screw behavior.

Well I’ve already figured out that I’m a tooth off on timin. Which means that when valve lash was said it was probably off by that much.