Two stroke experts; A little help?

[bluegoatwoods]

I've got a 66cc. It's my first. They've all been 49s to this point.

It's doing a good job. It pulls me around reliably and with strength. But there's a few quirks that I don't understand.

It definitely seems to be slower than previous engines about warming up and getting to operating temp. If the temp outdoors is as warm as 50F (10C), then a noticeable warm up period is necessary. Perhaps a quarter mile of riding before it's clearly warmed up and can get some revs going.

I doubt that I'll be able to start it at all, as things stand, when winter comes again.

During this warm up time there is an extra exhaust sound. I've heard it before, but I can't identify it. It does sound a bit like metal to metal scraping. Maybe it could be called a high-pitched chirping. It also doesn't sound like it's coming out of the muffler. I suspect that it's leakage from the head gasket or the exhaust gasket. I haven't inspected these closely, but a brief glance doesn't reveal any damage.

It also seems to be running unaccountably lean. (I've inspected, and at one point remounted, my intake and carb-to-intake seal. I think it's okay. Maybe I'd better have another look, just to be sure) A while back I got the notion that it was a bit lean. I pulled the throttle slide. What I found was that the needle was on notch 4 of 5 toward the rich end. I went ahead and put in on notch 5 to see how it went. Since then I've had a look at the spark plug.

Spark plug color is almost where it should be by the rule-of-thumb measure. It's not quite the color of toast. It's a little more gray-ish than that. Maybe like soil that has some clay in it. But it's definitely not black or white, and it's not wet.

Reviewing these symptoms right now I'm still suspecting that she's a little bit lean for some reason.

But if anyone has any ideas to offer, I'd be happy to hear them. Thanks.

 

[2door]

Blue,
Start with the head gasket. Pull the cylinder head and inspect the gasket sealing surface. If it is leaking it will be obvious by a dark area. Check the cylinder head gasket surface. 'Paint' it with a magic marker and lighhtly run the head over sandpaper on a hard. flat surface. Glass works best. You'll quickly see if the gasket sealing surface is flat or if it needs a little lapping.

Replace the head gasket if it appears it had been leaking. If not re-use it and torque the head fasteners. 120 to 140 inch pounds, in an 'X' pattern. Replace the chrome acorn nut with hex nuts. Check the torque after a few heat/cool cycles.

Check the intake and exhaust manifold gaskets. The kit supplied gaskets aren't the best quality and are known for early failure.

Spark plug gap: .024 to .028 is a good starting point.

Crankshaft seals: Look for oily residue in the magneto cover and around the primary(small) gear on the right side.

Hope some of this helps.

Tom

 

[bluegoatwoods]

Yep, Tom, that will help. Thanks.

There's a few items on that list that I haven't thought of yet. In the case of the head, I ground off the caps on those acorn nuts and torqued to 120 in/lbs when I built the bike. But I haven't yet double-checked torque and gasket mating surfaces.

So that'll be a good place to start.

 

[2door]

It's always a good idea to re-check the torque after the engine heats and cools a few times. Usually you'll find that they have loosened a tad. Just don't exceed the torque values suggested. Some guys will go as high as 160 inch poiunds but I've never seen the need for that and you're pushing the limits of the threads in the case.

We typically recommend the needle 'C' clip be in the second groove from the top. Also keep in mind that the clip position has nothing to do with wide open throttle. From about 3/4 throttle and up, the needle is pulled almost out of the jet so fuel flow is a product of the jet orifice size, not needle clip position.

So many variables come into play with reading spark plug color it's hard to make an accurate determination with our little 2 stroke engines. Gasoline additives, type of oil used, how the engine was run prior to checking the plug are all factores that can have an impact on spark plug color. Obviously, if the porcelain is white or near to white you might be in that lean condition. However if the plug hasn't had a chance to accrue a coloration it might appear a light color. Checking a new spark plug with only limited run time won't tell you much.


I should add that often the flange of the exhaust manifold as well as those on the steel intake manifolds are warped from the welding process. The same method for checking the flatness of the cylinder head can be used to check the gasket sealing surfaces of both intake and exhaust flanges. A warped flange will result in gasket failure becuase no matter how tight you make the fasteners the warp will allow some leakage.

A leaking exhaust flange can give you a funny noise until it heats up and things expand enough to close gaps. Same for the head gasket. A leaking intake will give you all those symptoms you've seen described here many times; fast idle, hard starting, loss of power, etc.

Tom

 

[Davezilla]

Yup... what Tom said... I would also start with the head gasket since they do tend to settle in after a few heat cycles and will leak if not re torqued. I also at least lap the cylinder deck and head sealing surface before assembly or take the head and jug off a new engine to lap these 2 surfaces and reassemble since I've found many of them to not be perfectly flat...
if the bike is hard to start its usually the head gasket leaking or too much plug gap, but the other places I've seen them leak are at the intake,the base, the split line where the case halves meet, and the crank seals. All of these areas will usually have the tell tale oily residue around the leak at the failure point. One thing I do during assembly to help prevent this is either spray on a few thin coats of the copper gasket spray on both sides of the gaskets or brush on anything coat of Indian head gasket shellac which will help fill tiny voids that could possibly cause problems. Anaerobic sealant also works really well but a small tube can cost around $20. This stuff is nice because it doesn't glue its self to the gasket or the parts but it seals really well.

The best thing to try is re torquing the head, intake,exhaust, and also check the case halves since they can back out or sometimes they're loose to begin with.
Tom is exactly right too about the head surface and gasket and its best to replace the gasket if it was leaking.

 

[maniac57]

One thing I will add is that you NEVER see a china engine with stock jetting that is jetted too lean.
If you have a lean condition, look for air leaks or bad seals.
ALL china motors come jetted blubbery rich from the box to help reduce warranty returns.