ATC 110 and 200s - low compression and spark issues

[webbch]

I recently picked up 3 trikes, only one of which was actually running, and 2 have low compression:

'84 ATC 110:
Didn't run when I got it...I thought it was only because of a no-spark condition. The exciter coil had an open (infinite resistance), so I replaced that (now has 240 ohms), and am now getting a tiny spark (but haven't replaced the plug yet either). Pulse generator/pickup coil ohms out at 90 ohms, manual says it should be 20-60. Would 90 ohms be a problem? I thought they normally failed due to low resistance. However, I just hooked up my compression tester and am only getting about 60-90 psi, which I suspect will make running it nearly impossible. To make sure it wasn't valve timing, I put a bit of oil in the cylinder, and compression went up to about 140 psi - I think that means it's time for a rebuild, no? Only other thing would be a leaking head gasket I would think, but that should be pretty obvious when I go to disassemble the motor I"m assuming.

'84 ATC 200s:
This one ran when I got it, but pull starter wasn't retracting the rope (and PO had installed a cable instead of rope), so could only bump start it. Ran very poorly and wouldn't idle at all. After fixing the pull starter, I could start it with the pull-starter....barely...it took dozens of pulls. I cleaned the carb (disassembled, soaked in carb cleaner, cleaned out main and pilot jets, blew them clean, adjusted pilot screw...after replacing missing o-ring and washer) and got it going a little bit, but it really wanted the choke in the middle position in order to run, even with the pilot screw adjusted 2-1/4 turns out per the manual specs, so I thought air leaks right? I also replaced the air intake boot because it had a bunch of cracks in it. No improvement. On a whim, I put my compression tester on it and was getting about 90 psi (with decompression lever disconnected). My heart sank as I put oil in the cylinder and watched the pressure go up to about 140 psi as well. Argh!! It appears that my "air leak" is from the cylinder, not the carb. BTW - it's the stock carb, but an aftermarket air cleaner, and the airbox lid is missing. I haven't investigated the muffler for blockages yet, but the compression is a pretty critical item I think.

My 3rd trike is an '83 185s and has decent compression (about 140-145 psi). It's not currently running either, but for reasons I haven't yet tried to diagnose. At least ONE of them has good compression!

All the trikes turn over just fine - I want these to be good runners for a number of years. Is it reasonable to expect a cylinder hone/new rings, and lap the valves and ?? to achieve this, or does the cylinder need to be bored and an oversized piston installed for that? I'd appreciate any advice.

Also, given that I haven't done a rebuild on a small engine since high school (I'm 34 now), what kind of special tools are needed for this job? piston ring compressor, valve lapping tool, and ridge reamer are on my list. Anything else?

[barnett468]

make sure the valves have clearance, if so

remove head

put carb cleaner in port.

look to see if it weeps out around valve, if it does vakve is leaking.

remove cyl, if you feel a ridge it needs a bore, if not measure accurately with in 2 positions 90 degree apart and at top middle and bottom of cyl.

if there is a total of more than around .003" between the 90 degree measurements and the top to bottom ones it is bad and needs a bore.

you do not need a ring compressor, the bottom of the cyl is tapered.

if bore is good, hone and install new rings.

[webbch]

Thanks. I'll do those checks. I just pulled the 110 motor last night. I'll pull the 200s motor tonight (have to work on the trikes at the neighbors house at night so kids don't see their x-mas present :)

Do you think 90 ohms on the pulse generator/pickup coil is likely to cause spark problems? Spec is 20-60 ohms in manual.

[barnett468]

Do you think 90 ohms on the pulse generator/pickup coil is likely to cause spark problems? Spec is 20-60 ohms in manual.i think its ok. tell them to never remove their feet from the pegs while moving they might run themselves over.

[webbch]

Is a cylinder leakdown test on these motors valid? I set the crank to top dead center on the compression stroke and installed my leakdown tester in the spark plug hole. At 80 psi of inlet pressure, I was only holding about 40 psi in the cylinder. I was getting a MAJOR leak coming out the intake port in the head. I was not expecting that - I thought my previous test of squirting some oil in the cylinder resulting in higher (peak) cylinder pressure was a dead giveaway of it leaking past the rings.

I tried rotating the crank until the cam was about +/- 30 deg off TDC to see if the timing was just off real bad, but there was no "sweet spot" where the cylinder would hold more pressure. Am I correct in thinking that my problem appears to be with the intake valves? Maybe I just need to focus my efforts on the head....

[webbch]

Update:

Got all 3 running so far.

110:
I took it apart, bead blasted the head, lapped in new valves and put in a new stem seal (there's only one stem seal on this model), installed new cam chain, cleaned the carb (soaked in carb clean and blew out the jets), and timed it. Also de-rusted the fuel tank, put in fresh gas and a new spark plug. Runs like a top. Very happy with this one (so are the kids).

200s:
Same stuff at the 110, except also had the cylinder bored and honed because it appeared to have been run without oil. Also replaced carb intake boot. Running well enough to ride around a little bit, but still a little rough. I haven't fiddled much with the carb yet though. I just set the pilot screw to 2-1/4 turns out. It seems to hold onto a high rev unless I leave it in gear and come to a stop, then it pulls the idle back down. Doesn't that normally point to an intake air leak?

185s:
After cleaning the carb and fuel tank and putting in fresh gas and a spark plug, I got it running. However, I suspect spark issues because in addition to running rough, I notice a severe lag (1+ sec) from the time I give it throttle to the time I get a corresponding increase in rpm, in addition to some backfiring in the muffler it sounds like. The kill switch is stable in the center position, so I don't think it's grounding out. I need to take a timing light to it to verify, but if it is indeed an intermittent spark issue, I'm planning on swapping in a different CDI unit to see if that helps resolve the issue.