Is my KH100 possessed by an evil spirit?

I've posted the inane rantings of motorcycle noob here before. Safe to say it didn't got down t0o well so I'll keep this short and sweet.

This is my bike. It's my first. Yes that's an L plate on the back .



I got it in a much worse state and it ran but not very well. It didn't have the shiny decals and new paint either. It was a POS but I could see some potential and I like the idea of saving this thing from the junkyard. I also like the way it rides when it doesn't overheat. This is my problem, it goes great until 30 minutes in, gets jerky, loses power and wants to seize.

Things I, or occasionally my mechanic, have done to it thus far:
- New (old) fuel tank cap, fuel tap and hoses. The original tank cap had a venting issue that stopped flow and the tap leaked. All good now.
- Carby cleaned and adjusted. Runs perfectly well until it seems to get too hot... Plug shows a darkish tan. Maybe a bit rich.
- Timing checked. Spot on.
- New battery and rectifier. Charging just fine.
- Oil pump works. It is using oil and within the threshold marked on the pump itself.
- New top end including rings, piston, bearings and gaskets. Re-bored by a reputable firm I am 500ks in. It's been tumultuous.
- Today I de-coked the exhaust with caustic soda and got a heap of shit out of it using a coat hanger. Some jerk in the past decided to spot-weld the baffle in place so I did the best I could. After this it went like a bloody rocket.

With the exhaust de-coke I thought I had it solved. It was accelerating much better at lower revs and spinning freely right up there. It sounded better too. It was 33C today and I was riding for about 30 minutes and was sure this had helped the overheating. Until, around the corner from my house it starts getting jerky and wants to stop. I hit the kill switch.

What else do I do? Does the bike need an exorcist?

The bike starts first kick almost every time. Idles perfectly well forever. Rides really great, today it rode the best it ever has, I smiled when I looked back and saw that perfect little line of two stroke pollution flying out the back :)

Any ideas are most welcome.

You did not mention the rust in that 35 yr old fuel tank. Could have rust occasionally blocking fuel flow. If you are in the US then your ethanol fuel is causing water to be formed in that old tank. Once you clean the tank then try some Startron in every tank of fuel. You getting brown crud in the float bowl repeatedly? Have you looked?

Thanks for the reply. When I had the tank painted I'm fairly sure they did some kind of acid wash to the inside of the tank to clean it up. I've also been running with an inline fuel filter for a long time now. There is a little bit of rust accumulating in the filter every now and then but only a few specks.

However, I'm intending to lean the needle one notch tomorrow so I will take a look then. To be honest I have had zero interaction with the carb other than having my mech get it set right. I fear the carb. I've been periodically plug chopping to keep an eye on how it looks. At the moment it looks a bit rich.

I do feel that this problem is consistent in its timing. It seems to almost happen around the same time every time I take it out. I read this from here: "Most air leaks draw a very minute amount of air at low engine speeds. In fact it's very common for air leaking engines to start and idle very nicely. However when the engine is brought up to full temperature at higher rpms, the castings will begin to expand and deflect slightly in different directions."

It has made me wonder if it is in air leak that only appears after the engine is well and truly up to temp (the usual 25 minutes) as described.

Either one, or a combination of those things, may be your problem.

If the adjustment between new cylinder and rings is less than adequate, the high friction will overheat the engine, which will increase the friction even more.

If the exhaust is partially clogged, the same bad things will happen.
Chemical cleaning is seldom as effective as mechanical cleaning; I would eliminate those welded spots and dissemble the exhaust pipe for a deep cleaning.

Additional oil and reach mix should improve the overheating in the meanwhile.

There is no mystery or magic on these things.

You say you bored it? I'd try a jet then i'd clean the exhaust with some awesome cleaner (dollar general if you got one $1 there) it works great and is non toxic it'll deep clean and finish the job if theres buildup left from before. Btw VERY cool bike! Also look at your filter !

Sounds like it may be seizing. Did you check piston clearance AND ring end gap? Sounds like it is time to take the top end off again and have a good look for any scuff marks. BTW putting oil in the gas tank is not a good idea. You are actually keeping gas molecules/air mixture from going through the jets properly and actually LEANING your fuel mixture! You should be getting plenty of oil from the autolube system. Do not fix what is not broken.... I doubt it needs a jet change anywhere. More like a good cleaning of what you have in there. Check that float bowl for brown gas yet? How about an air leak where the carb bolts on also... Probably a 40 yr. old rubber boot manifold unless you replaced it.Aren't old bikes fun?

it is a hidden cover carb there is no reed valve boot :)

Its almost certainly seizing, due either to a poor quality piston, or badly done rebore. Take the cylinder off and have a look.

I feel I might be getting somewhere with the clogged exhaust. The first time I rode the bike after de-clogging the exhaust chemically and with a coat hanger (I am yet to remove the baffle because it is spot welded in and my hacksaw won't work) I had a hugely noticeable improvement in power and smoothness, though the engine did start to get hot after a while and it was a 33C day.

This makes me think that the exhaust, if not the only part, is a BIG part of this overheating/performance issue.

Today I commuted to my Mum's place, about 25kms across town (a bit of stop-start through the city and some sections at 60-70 km/h and about a 35 minute ride and it ran BEAUTIFULLY the whole way there and back. Admittedly it as a 21C day so much cooler than the other day.

But, this makes me think it possible (hope) it just might solely be the exhaust. It is finally running like a well-tuned machine. This week I'm going to get the baffle out and give it all a good physical clean. My fingers are crossed.

Here's the the little rocket with my house mate Steve.

There aren't ANY of these bikes around where I live (especially with paint and decals this good) so this little thumper really turns heads. I reckon it's cool too!

Should I have re-jetted the carb after top end rebuild? The bore was from 49.5mm(stock) out to 50.25mm I believe. Bit of a weird jump but the guys that did it, very reputable dudes, sourced all the gear for me and saved me waiting on overseas stock from eBay. About the same price, too.

I'm going to chop into the exhaust this week and get it all cleaned up properly and see if that does it. Ran perfectly in cooler weather today. Touching the cylinder along the way it was running noticeably cooler.

Will check filter too!

To be honest I just put the top end together myself without checking these things as I didn't have the gauges . I got the re-bore done by the same guys that sourced me piston, rings, bearings and gaskets, and they only bored after getting the gear in stock and checking for fit.

Also, I had a bit of a head gasket leak about 150kms into running it in (thanks to a dodgy borrowed torque wrench, I believe) and while I had the head off I had a good look for scuffs back then. If piston to cylinder clearance/ring end gap was an issue then would it show early in the running in?

I do understand that extra oil = leaning so I won't do that. Autolube is working fine and the exhausts a nice smelly 2 stroke fragrance.

It has become fun in the same way going out with a certifiably insane but really hot girl is. But also, as a complete noobie it has taught me many things and I'm enjoying learning

D

You always have to chk ring end gap when you put fresh rings in as they are usually slightly oversized....So that was likely part of the problem. Next time set the ring sets (both of them) in the bore an inch down from the top. Measure the opening(if there is one). If there is not one carefully file the ends of the ring(and the pin notch too) until you get the correct factory minimum setting. This is done because the rings expand with heat. Yes they will stop the piston from going up/down. They also can break and send a lot of nasty fragments into places you don't like. This was likely a big part of the problem.... A small but very important aspect of a rebuild.

Thanks for that buls4ever. I did the top-end after watching videos and reading forums on it and I don't recall coming across this part of the rebuild, which surprises me. I feel a bit foolish now.

You say "likely was part of the problem"... is this something that can correct itself by wear during running in? This not including the potential for scoring on the cylinder wall, and rings breaking and going into the bottom end?

I can't say that the exhaust has fixed it and there isn't other things happening, yet, but do you think I can conclude anything from a 25 kilometre/35 minute run on a 21C day with the bike running sweetly? I figure a longer run in warmer weather might be the truer test?

Nice little bike...but it needs a CAT scan to see what's wrong with it.

Unfortunately the only way to know for sure is to take the top end off and check out the spec for sure. It COULD clearance itself and they sometimes do........ Or they don't, and the ring ends jam in a port and break:eek1. Be very careful when you take off the rings working them only a little at a time and not TWISTING THEM.

I guess I'll get myself some new gaskets and lop the little jug off again and take a look

Unless, of course, after this exhaust clean up it is cured. About to head to an exhaust place now. I don't have the angle grinder and welder to muck around with these messy spot welds on the baffle, one of which is about 1 inch x 1 inch. Whoever owned it obviously didn't understand the importance of being able to clean out the pipe every now and then on these smokers.

Update:

So I talked to my mechanic and he seemed flummoxed as to what it could be and what to do next. I've almost resigned myself to a bottom end leak once it gets nice and hot (30 minutes or so) but until I find a way to test that and until I get my top end gaskets so I can check the piston ring end gap, I figured I'd check some other things.

I went and talked to the guys that did the rebore for a second opinion. He came back at me with some basic things: dirty fuel, check air filter, go RICH one notch on the needle, and dig into the left hand side of the engine and look for leaks/weeping/anything like that. He said if it's leaking on the otherside I'd know, (blowing smoke, fouling plugs, etc)

So this is far as I got today:

The filter looks fine to me. It's one of those paper ones. It seems clean, though it felt a little grimey/oily, is that normal?

I took apart the carb and float bowl to see how clean it was. There was a tiny bit of matter in the bowl but the fuel was otherwise clean. Here it is sans fuel. Thoughts?




Next stop was going richer one notch on the needle. I struggled to get this apart with any grace since I've never been into the carby before. Nevertheless it is apart, VERY apart.



I did find that the needle was already on the second to bottom clip which meant going richer will put me on the bottom? What does this mean? Adjustments across the carb?

Also, this half circle washer thingy on the left. What is it? It kind of popped out on me and I can't figure exactly how and where it goes. From what I witnessed it was on top of the slide below or above the bottom of the spring? Any advice on that one.



This is my first carb experience. Feeling a little :eek1

1. This carb needs a good hot dip and cleaning

2. The needle should be in about the middle pos....groove 3.

3. The needle is full rich right now. Remember this ditty about THE NEEDLE,'raise to richen, lower to lean".

4. I suspect you have a bad mag side crank seal. Did the crank play get checked also. A bad crank bearing will take out a seal right away. The engine should be pressure tested at the intake to see that it is holding pressure.

Oh, ....and that little clip with a lip goes between the needle clip and the spring. It holds the needle down by pressing the little c-clip and is pressed on by the spring. It usually only fits one side up properly.

Thanks heaps buls4evr for following along and helping out. I think'll get there eventually. I owe you at least . There should be a Paypal button for good advice. I'd buy you a pint

1. I've been trying to track down decent carb cleaner for soaking the whole carb in. Seems no one wants to dispose of it so no one wants to sell it. I have some carb clean in a spray can and I've heard good things about boiling the carb in either water, or believe it or not, lemon juice? Other ideas the auto parts guy presented to me was any kind of parts cleaning solvent. A decent drum of this stuff is $ though. Shall I carb clean from the can, spray with compressed air, give it a good boil, and see what happens?

2. That's the needle after I moved it one step richer immediately after taking it apart. I understand this is not desirable so I'm going to move it back to second to bottom (groove 4), the position it was in before I pulled apart the carb. Since this is getting down the needle, what adjustments can I make to bring it back middle? If anything, looking at the spark plug, I could go leaner from the current posi. Back to number 3. I imagine going leaner won't help me with my getting hot problem though?

3. Thanks for the ditty. I think I have my head wrapped around the relative confusion of needle adjustment now. :huh

4. When you say crank play, does this include con rod play? When I had the top end off I did note some movement in the con rod (something i noticed because it was my first time in ANY engine) but it was only vertically and only a small amount. There was no lateral play. I've heard this is normal. Once I clean this carb properly and reinstall it, then pop on the new pipe, I'm going to try and construct a tester or find some guys to help. I'm also going to see how far I can get into the mag side for a visual look about.

Cheers for the info on the clip with the lip. I was confused because it seemed to come loose from nowhere but it makes sense it was the clip holding it there. So, clip with the lip goes on top of needle clip with spring above. Makes sense.