Good afternoon Fellow Riders, First time posting and it's a question I'm sure has been answered lots on this and I've tried lots ...this may be long winded so bare with me.

Bike: Tomoto 150cc GY6 automatic Fwd/Rvs ATV

Background: Bought bike as a project, was told it sat for years and was not running, figured easy peasy bad gas, bad carb and a good cleaning.

Bought new carb, changed oil, changed spark plug, drained old fuel(it was green....yuck) cleaned out tank, new fuel lines and oh yeah used a new battery I had for my 90cc. BAM some starting fluid and it ran ok at idle but Bogs under any throttle no matter if it's in Fwd/Rvs or N. Noticed after it idled for about 3-5 mins it started smoking that blueish white smoke for telltale bad rings
Compression check done and it came back with 80psi, really low.
o purchased a new cylinder, piston, rings, gaskets etc to install. pulled the head off and the combustion chamber was caked with carbon and valves were bad too, figure I'd clean them up while it's apart. installed new parts removed and cleaned up the valves, seated them with my lapper and compound and reassembled. Set lash on Intake to .004 and Exhaust to .005.

What happened next boggled my mind. Setting timing on this thing is where I may be lost....

Using the guides online and such I attempted to set the Timing MULTIPLE times. If I set the bike to TDC using the marks on the flywheel I cannot get the cam gear to line up with the 3 holes in the right orientation. If the flywheel is on the line next to the "T" the 2 holes that line up with the edge of the head the most rear one is hidden and when it's tightened done the marks are more on the "F'" when aligned.
Similarly if I line the 2 holes up on the cam gear with the edge of the Head the flywheel is about 1cm away from the "T" mark in the other direction from the "F" ie ___X__| T F Where X marks where the flywheel would align to.

I've actually tried timing on both marks.....neither changed the problem of bogging. Question here is WHICH is more correct?

So I've also tried 3 different Carburetor's, including buying a "race" one with top feed cable driven throttle versus the standard vacuum designed electric enricher one that came on it.

I also thought it might be an issue with CDI so swapped it out and no change.

I have a feeling it might be a timing issue but for the life of me I cannot match the diagrams I see online to make it work.

Suggestions on places to look?

I have a spare complete wiring harness which may be my next item to try but that involves changing out the Stator etc...

compression test after the new piston/rings shows 125psi with throttle closed, not sure opening it up full will really change it due to it being vacuum driven

Any help greatly appreciated.

 

Your problem has probably always been the carb. The Chinese replacement carbs may be plug and play or they may not. Usually cleaning out the original carb is the best way to go as it ran right on that carb before the lay up. Have you tried another plug, the new one you fitted could be a dud. Check that something isn't seized in the transmission OK at idle but saps the power once the transmission is engaged. I have written on here before about a problem I had with a bike that had been laid up for 2 years, waiting for a top end rebuild. Had same problem as you after the rebuild and it turned out to be a blocked silencer, how it had come to block whilst being laid up, I don't know, rodents?

A long time since I did a GY6 engine but you can only get as near as 1 tooth on the timing chain. If it is midway between two teeth when T mark and dots on cam sprocket are lined up, I go for having the non adjuster side of the chain tight and set it so as the chain stretches it will get nearer the T mark and dots lining up.

 

So minor update on this, After 3 different carbs, including a "race" carb with external choke there was no change to the engine what so ever. Had good spark, good Fuel and good compression/air. Or so I thought. I decided to start checking electrical components and seeing if there was any change.
Coil, CDI, etc all swapped out and in without any change.

THEN, I decided to look at the stator, did a voltage test while running......getting 8-9v which is low.....I unplugged it and noticed that 2 pins were effectively bent into 1 pin in the harness, straightened it out stuck back together and no real change so figure I'd replace it. replaced with new stator and engine fired up and ran well, still hard to start(likely a compression issue I think). Ran really well for a good 2hr ride one day.

Now a month later with strong battery(although small and may be not enough CCA to run the machine) it won't start at all. I can get it to bumble after about a min on the starter but that's it. It is cold here now, like 0-5 degrees Celsius(like 35-40F).

I've swapped plugs
I've tried quick start
I've tried unplugging and plugging in all electrics etc.

Is it just a warm weather machine?

 

Check what compression is like now, check valve timing again and valve clearances, check the choke is working properly, in fact try one of the other carbs.

 

I did install a new head gasket set and piston/cylinder after only getting about 80psi of compression. Then after that I was seeing around 120psi. I'll check it again but it's hard to get accurate readings with these machines with the vacuum based throttle assemblies. I may swap out the electric enricher carb for a traditional one with a choke etc just to see if it helps.

Thanks!