Strange engine performance?

[Jayjohnson]

I know I’m suppose to check previous discussions befor asking a question, so if this is already been discussed I apologize. I did look but I’m not sure how to word it in the search bar so I have found things about similar situations but not mine specifically

So I have a 2 stroke, not sure what kind. It’s a small silver engine. I got it used from someone. It starts up easy enough, but I run into issue with the bike only running with chime barely open. But I’ve been playing around with it and have discovered, once I hit certain speed the engine makes a hollow ratteling sound and acceleration stops. At this point I can open the choke a tiny bit more, and the normal sound returns, and I’ll gain a bit more speed and then it makes the hollow vibrating sound again. I can do this a few time, each time the engine goes a little faster untill I get to open the choke completely. With full open choke the engine will stop 4 stroking, accelerate very smooth, and goes fast, faster. But if I stop or even slow down enough, I have to turn the choke back on immediately, and basically repeat the process of opening the choke, accelerating, opening choke little more, accelerating, so on and so on. Any ideas?

 

[DAMIEN1307]

I know I’m suppose to check previous discussions befor asking a question, so if this is already been discussed I apologize. I did look but I’m not sure how to word it in the search bar so I have found things about similar situations but not mine specifically

So I have a 2 stroke, not sure what kind. It’s a small silver engine. I got it used from someone. It starts up easy enough, but I run into issue with the bike only running with chime barely open. But I’ve been playing around with it and have discovered, once I hit certain speed the engine makes a hollow ratteling sound and acceleration stops. At this point I can open the choke a tiny bit more, and the normal sound returns, and I’ll gain a bit more speed and then it makes the hollow vibrating sound again. I can do this a few time, each time the engine goes a little faster untill I get to open the choke completely. With full open choke the engine will stop 4 stroking, accelerate very smooth, and goes fast, faster. But if I stop or even slow down enough, I have to turn the choke back on immediately, and basically repeat the process of opening the choke, accelerating, opening choke little more, accelerating, so on and so on. Any ideas?

Sounds like it is running too lean possibly because there is air leakage around the carburetor, the intake manifold not being on tight with air leakage through the gasket or where it seats into the carburetor as well as the top four stud nuts on top of the cylinder head not being torqued down tight enough on the head which would result in a head gasket and bottom gasket leakage.

While your at it, make sure the exhaust bolts are also tightened.

You need to check out all of this.

Be very sure you tighten all of these areas ONLY when the bike is totally cold.

 

[GW's Motorized]

Yup, sounds lean too. Can you pull the spark plug after running it full throttle and not returning the choke? This will give a definite answer.

 

[Jayjohnson]

Sounds like it is running too lean possibly because there is air leakage around the carburetor, the intake manifold not being on tight with air leakage through the gasket or where it seats into the carburetor as well as the top four stud nuts on top of the cylinder head not being torqued down tight enough on the head which would result in a head gasket and bottom gasket leakage.

While your at it, make sure the exhaust bolts are also tightened.

You need to check out all of this.

Be very sure you tighten all of these areas ONLY when the bike is totally cold.

okay. So I had gotten the engine used, and there is what seems like black rubbery stuff around the spark plug, the exhaust port, and the carb/manifold. I think I was told it’s gasket maker. It makes it hard to get a wrench on any of the places you advised I check

 

[DAMIEN1307]

I think I was told it’s gasket maker.

I have never had to use "gasket maker" in any bike I have built in 10 years...Just the fact he used that much to oooze out and coat everything else makes me wonder...It makes me question the original builders abilities in building one of these to begin with and also makes me wonder if thats why he sold the bike, because he might not have been able to ever get it to run right and decided to sell off his "problem" to someone else.

 

[DAMIEN1307]

It makes it hard to get a wrench on any of the places you advised I check

Start scraping it off any of the bolts or nuts that "stuff" is on so you can get a tool on those fasteners to tighten things down...Freshman Introduction to Motor Mechanics, Room 101...You have to always be able to tighten things from time to time, no time like the present to start learning.

 

[GW's Motorized]

I only ever used gasket maker on my clutch cover because I accidentally ripped the gasket. A better alternative for gaskets is grease. It will swell cork and paper gaskets and it's not bad for the engine to consume

 

[robe]

I like to use grease on gaskets, I put that s*** on everything. On the exhaust gasket I put the Hi temp copper on the exhaust side only and once dry removed and a thin coat of grease on the flange side. I did the same thing in the intake side. Never a problem.

Also, everyone talks about locktite on everything, I put a little lithium grease on almost all my threads, the exception is the sprocket to hub gets locktite. I always have to take everything apart several times, so having it glued together is not good in my world. Don't have things come loose very often. I got the grease thing from working on boats that spend their time in the ocean.

Got rid of my last one a few years ago. 1952 wooden 32 ft converted fish boat with a 354 Perkins. Nice but a world of work. The best two days of boat ownership is the day you buy it and the day you sell it.

 

[DAMIEN1307]

The best two days of boat ownership is the day you buy it and the day you sell it.

I'm originally from New England and used to be sailing all the time and I know all too well what BOAT stands for...lol.

Break Out Another Thousand...lol.

 

[GW's Motorized]

I like to use grease on gaskets, I put that s*** on everything. On the exhaust gasket I put the Hi temp copper on the exhaust side only and once dry removed and a thin coat of grease on the flange side. I did the same thing in the intake side. Never a problem.

Also, everyone talks about locktite on everything, I put a little lithium grease on almost all my threads, the exception is the sprocket to hub gets locktite. I always have to take everything apart several times, so having it glued together is not good in my world. Don't have things come loose very often. I got the grease thing from working on boats that spend their time in the ocean.

Got rid of my last one a few years ago. 1952 wooden 32 ft converted fish boat with a 354 Perkins. Nice but a world of work. The best two days of boat ownership is the day you buy it and the day you sell it.

I just use high heat wheel bearing grease. The manager at the local NAPA will give me damaged oil and grease containers for free. He'll also give me the clearance quarts of oil for a buck a piece. I have a shelf full of oil and a couple things of grease.