Loss of high RPM spark?

[Norman]

Check the intake manifolds machined surfaces make sure they really are flat and true by using a steel straight edge to check for the surface being flat and true not warped, you will need to remove the studs for this, you can use a mill file to gently smooth the surface, don't go crazy with it, use the file in a gentle forward motion and don't let it tilt or rock when filing lift up the file for each stroke tap off the filings look at the files teeth each time as one little booger of aluminum still on a tooth will wipe out the work you have already done. You can see what is going on by looking at the marks your file is leaving. Poor boy machinist die the surface by using a dry marker and only smooth off the the surface to get the dry marker ink off, stop when it is off.
Another way around filing the surfaces is by using a slightly thicker manifold gasket and the dreaded silicone rtv and again don't slather it on use just a thin film on all gasket surfaces. assemble and check for leaks with the carb cleaner or starting fluid sprayed on the surfaces that you think are or were leaking if your intake/ air cleaner gets a whiff the spray it will speed up or die depending on how wild you get with the spray. I hope this will help.

 

[deacon]

I used gasket seal to fill in any imperfections. I used a lot of it actually just to be sure.

 

[Norman]

Be careful you don't want to rering it. If enough lose silicone gets in the engine it will be aww shoot it quit if it snags a ring.

 

[Pablo]

Check the intake manifolds machined surfaces make sure they really are flat ....

Well the intake port certainly was not flat. Not even close. Sort of concave, with some big casting marks on the bottom edge that would be a perfect path. So I plugged the port and gently filed it with my two best metal files....nice and flat. Then I vacuumed it all really well, pulled the plug out while vacuuming, then vacuumed and cleaned inside the port.

I still didn't get the gasket material. Tomorrow. I'm not sure this is the cure, but it certainly won't hurt. I've changed nothing else..........

I probably should mention that I took the studs out......

I'm torn on deciding if I should use sealant or not. What type?

 

[deacon]

I first used bearing grease but it still leaked so I bought some black gasket seal. Coated both sides of the gasket and slapper her on there.

Oh yeah, I tightened one sid a little then the other then back to the first. Memories of a broken goose neck on autos came to mind as I did it.

 

[Bikeguy Joe]

I'm torn on deciding if I should use sealant or not. What type?

I'd get some "Form-a-gasket" while yopu're at the auto parts store. Make a THIN coat and read the directions, they differ between brands.

 

[Pablo]

I'd get some "Form-a-gasket" while yopu're at the auto parts store. Make a THIN coat and read the directions, they differ between brands.

Thanks BGJ - I have the black Form-a-gasket #2 already. Should I give that a go? On the plus side it's fuel resistant, on the minus side it more or less doesn't set up (maybe a good thing) but does harden a bit with time.

OH and btw - THANKS for all the help.....I've got so many things going on sometimes when I get back to the bike I forgot where I left off!!

 

[paul]

lol i know how that goes pablo. look forward to hearing your bicycle engine is running like a champ. we are supposed to get up to a 10 inches of snow today so i have the shop heat on and my motorized bicycle is getting a complete makeover.

 

[deacon]

use what you got pablo is my opinion. All it has to do is fill the gaps not be purdy...

 

[Bikeguy Joe]

Yep, use what you have, it should work just fine.

 

[Pablo]

Well.........It's sealed tight. Still runs like crap. I mean now if I just think about coming off idle it bluuuuuuuuuuurps.....and dies.

 

[deacon]

How about the choke does that effect it at all. With the choke on does it die cause mine does if i try to run it with the choke on. I have to start it let it warm up and ease off the choke for it to run worth a crap. I don't really throttle up with the choke on cause it will bog down. did you take the breather off to check to see if the choke is working or is it stuck maybe.

 

[Pablo]

This is all with the breather off, so I watch the choke and the slide......even when warm (which takes awhile) it won't run with the choke off.....

 

[deacon]

If it wont run with the choke off when warm, I think you have to getting too much air with it off. the choke cuts off a large supply of the air so when you open the choke if it dies I think it means too much air. making the mixture too lean.

So we know you aren't leaking at at the manifold joint, or the manifold gasket,

You said you re tightened the head didn't you. Have you pulled the head by any chance. I suppose a leaky head gasket could suck air in. But that would be more likely to kill your compression and let air and fuel out of the chamber I would think.

Do you suppose any of the other ports are in as bad shape as the intake port you had to clean up. Lets see what norman or joe has to say. I didn't have a leak in the exhaust manifold so I don't know if that would do it or not. It still sounds like a fuel air mix problem to me.

 

[deacon]

I guess the other thing it could be is not getting the proper amount of gasoline. But you tried all the needle setting and they didn't change anything.

You have spark or it wouldn't run at all. I swear it sounds like a fuel air mix to me. One more suggestion here as a test.

How about pouring some gasoline down the top of the carb and starting it to see how it runs.you might be able to add it from a small bottle as it if were fuel injection and bypass the carbs normal system of throttle control.

 

[deacon]

My lawn mower wouldn't start yesterday and I tried about everything. I put some gas down the throat and it started. Whats more it didn't shut off. I guess something was stuck and the vibration of the engine shook it loose. i'll know next time I try to start it.

 

[Pablo]

I just took the carb apart and everything looked OK....indeed if an engine only runs while choked then somehow not enough fuel is being delivered....but when it gets warm enough to run with th choke almost all the way open - I give it throttle an it dies, and when it dies the engine is fuel soaked. Some times when it dies it back fires through the carb....clues?

hmmm head gasket.......the sucker seems to have hellacious high static compression....but maybe it leaks when hot....

 

[deacon]

Man I am baffled. Seems you have done about everything I know to do. That backfire should tell someone something but I don't know what causes that. I have had it happen when there is too much fuel in a car. Or out of time in a car but I have no idea if it is possible for a two stroke to even be out of time. I guess if the magneto was put on wrong it could be out of time. Seems norman had something to say about that recently something about a key on the crank shaft and the magnito. The key holds it in the right place I think.

 

[misteright1_99]

I have had instances where small engines will not run properly without the air filter (too much air/ fuel). I noticed you stated you have tried "this all with the breather off". Just a thought.....

 

[deacon]

That crossed my mind but I had no experiences with the breather off.... At this point I'm sure Pablo will try about anything. I know I would be...