Engine only starts without exhaust attached?

S

snapshot

New Member
Hey, everyone.
I've been reading the forums for a while now. You all have helped me get my 2-stroke up and running!
This is my first post, as I cannot seem to find the answer to a problem I've been having. Any advice would be highly appreciated.

My 2-stroke wasn't starting for a few days after I bought it off a gentleman, who didn't know the first thing about these motors.
After a lot of problem solving, I was able to get the 2-stroke to turn over. It would turn over only when the muffler was detached.
"Well it must be the pipe! Perhaps it's clogged," I thought.

After making sure there was no carbon buildup in the engine block's exhaust port, I took the pipe and cut it with my bandsaw. Not even the slightest trace of blockage.

I've been riding the bike around town without the muffler, and it runs beautifully.

Recently, the new exhaust I ordered arrived, brand new. It's an expansion chamber/muffler, and was simple to install. But now the old problem returned with a vengeance. I can hear the plug firing the gas, but it won't stay running on it's own. Again, it runs perfectly without the new pipe attached.
Here's some info;
  • new spark
  • new gas and oil
  • brand new carb-jetted properly
  • gas line flows well
  • problem persists with choke on and off
  • spark plug has a nice gray color

Any help would be fantastic.
 
That's a new one on me. SHOULD not make a bit of difference except in noise.....
I'd be checking timing.
 
I know this is going to sound like an all too obvious suggestion but I have seen it happen so I have to ask...
There is a hole in the exhaust gasket isn't there?

I had a guy make his own gasket, install it, then brought the bike to me because it wouldn't run. He had made a gasket but he neglected to make a hole for the exhaust to get out. No kidding!!!

Tom
 
At the risk of sounding like an arse. How can you be jetted properly if you've been running without an exhaust? When you alter your exhaust, your jetting almost always has to change.

For example, when I took my stock pipe and dinked with it, I had to rejet after each modification. In my case, each thing I did, richened the air fuel mix, causing me to jet down. I opened up the manifold plate itself to an oblong shape to better match the port, I cut the stinger tube down, drilled holes in the cap too. All of that required me to retune.

From where I stand, you're running WAY to rich. Are you sure there's a jet in the carb at all? Is it tight? Is the tube? That's my two cents good luck.
 
assuming you have blown thru pipe to be sure it isn't clogged with packaging material, I'd next try leaving it on, but loose by about 1/8in to see what that does
 
Since you have tried two mufflers I doubt that's the problem, if it runs with only the head pipe you are probably too rich with the muffler attached. If the plug is gray it sounds like a rich condition, should be light brown.
 
If the plug is gray it sounds like a rich condition, should be light brown.
I agree with the light brown diagnosis. I always thought Gray /Light Gray was lean. Black is Rich. Correct me if I am wrong please.

I too have banged my head against a wall over a badly running bike. Most of last year I couldn't get the Sail bike to run well at all. Changing jets, Clip positions 3 different Carbs...Then I discovered the problem, Had everything to do with the Quarter size motor Exhaust port and the Dime sized (Not Stock) Muffler input. I hogged out the muffler flange with a dremel cutter/grinder and wouldn't ya know the Bike runs as good as the others.
 
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Spark plug color is a nebulous way to determine tune. I'm one of those weird-o types who run Opti-2 @ 100:1. My plugs are all shades of grey depending on how rich or lean. It has been discussed here before and the general consensus was that additives in gasoline vary from one area to another and might be responsible for the odd plug colors. This is especially true on a two stroke where different oils are used. One member displayed pictures of his plugs which were shades of red.

Chocolate brown is often used as a determining point but depending on other factors that color might not be possible to achieve.

Tom
 
If the o.p. responds maybe he can let us know more of what he has and hasn't tried. Tom posted about the exhaust gasket but since he has bought a totally different pipe I'm wondering if it were not carb related. Some carbs have hidden problems that are not easily found, I have a carb on the shelf that would not respond to jetting. I could not get top end speed with it, I change carbs and got it jetted right for that engine.
 
Thats a good one!
2door said:
I know this is going to sound like an all too obvious suggestion but I have seen it happen so I have to ask...
There is a hole in the exhaust gasket isn't there?

I had a guy make his own gasket, install it, then brought the bike to me because it wouldn't run. He had made a gasket but he neglected to make a hole for the exhaust to get out. No kidding!!!

Tom
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