Brainstorm 2-stroke bogging with me....

Pablo

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Dec 28, 2007
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First clear your mind of everything, last night's beer, women, house payments, etc

OK now: Say you have a new 2 stroke engine that starts happy as a lark with full choke when cold. But is very cold blooded. Takes 10 minutes to get warm and runnable, but choke still needed. Seems to have sufficient power, but is still breaking in.

Runs fine for 30 minutes at almost full open choke, but still need to be ginger with the throttle. Then when engine is hot, can not go to full throttle or engine bogs and drops right off.

Am I too rich or too lean?
 

deacon

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Jan 15, 2008
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Is this multiple choice... LOL someone a lot smarter than me will have to guess. Usually they say look at the plug to tell which. Are you sure you don't have an air leak. Seems like you are cutting off the air with the choke to compensate for air leaking into the system, but hey I make no bones about not knowing what the heck I'm doing.
 

Bikeguy Joe

Godfather of Motorized Bicycles
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Sounds like you have an air leak somewhere fo' sho'.

You can have symptoms of an air leak if your base gasket is leaking too.
 
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deacon

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Check the carb screws for tight as well as the bolts on the manifold. Don't forget that pesky the connection between the carb and the manifold.
 

Pablo

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I think you guys are correct. Unless there is something defective about the main jet the engine should do fine at full throttle, fooling with the needle won't or should not change full or near full throttle behavior.

All bolts are tight, gaskets look good.

Before I go messing with anything else, I'm gonna seal the carb to manifold interface with automotive RTV and get a better clamp.

Bikeguy Joe said:
You can have symptoms of an air leak if your base gasket is leaking too.
Please explain "base gasket".
 

deacon

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If you haven't sealed that connection with either an o ring or sealant then it's the most likely place for an air leak.
 

Bikeguy Joe

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Base gasket is the gasket at the bottom of the jug, kinda like a head gasket, except it's a little lower and made a little different.
 

Pablo

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Base gasket is the gasket at the bottom of the jug, kinda like a head gasket, except it's a little lower and made a little different.
Got it - I was thinking that, but wanted to make sure. Looks OK from the outside.

Weather report: Raining like crazy.

OK so NOW I also know what you guys are talking about when suggesting adding an O-ring. I pulled the carb and sure enough, yes indeed I put a 5/8"x13/16" O-ring from my trusty O-ring kit inside carb and whilst pushing the carb on to compress said O-ring, I tightened the clamp. IT MADE A LARGE DIFFERENCE!!

But, Weather report: Raining like crazy.

It started right up and SOUNDED way more healthy. Reved OK, still cold.

Weather report: Raining like crazy.

Back in the garage, no Automotive RTV in stock. Why?

Even with the O-ring, the four splits in the carb flange and the general out of roundness of the manifold and the carb flange allow air leakage.

Weather report: Raining like crazy.
 

deacon

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That o ring at the end of the manifold tube was all mine needed. Norm does his with sealant instead of the oring. The oring is set at the very back of the manifold tube and seems to stop everything for me.
 

Pablo

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That o ring at the end of the manifold tube was all mine needed. Norm does his with sealant instead of the oring. The oring is set at the very back of the manifold tube and seems to stop everything for me.
I hear you, but even with the o-ring I could "see" air passages.....besides, I can be anal if I want.........:D

Anyway I got me a 1.5 oz tube of this: Permatex #2 and sealed that dude up. My little Firefox weather dohickey show sun tomorrow!!!!
 

Norman

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Jan 16, 2008
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Yea you will be able to see the slots cut in the carb when you use the silicone but it will seal better than an o-ring its got to have pressure against it to work ( the o-ring) and if it comes lose your engine will eat it might not hurt but if it snags on a port and breaks a ring your going to be in deep poo. The silicone works for me have not had a single leak and its very easy to use and clean off but I'm not going to try and talk you all out of your favorite way if you want to use an o-ring just letting you know what can happen if they get lose and wreak your bicycle motor then you will not be able to ride your motorized bicycle until its repaired. something to think about.:confused: rotfl
Or drive you all crazy wondering will it come lose or not.:D got you wondering yet?! To check for a leak free seal spay the area with carb cleaner or starting fluid you could use a spray bottle of water if you have to all will change its idle if there is a leak most likely it will die when sprayed and its leaking. do not spray the intake as it will die making you think you have a leak when you don't
Norman
 
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deacon

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I think the best way to check is to slap a thick coat of axle grease on the joint and if it runs okay clean it off and fix it lol.
 

Pablo

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I sealed it all up and it runs better. But is still bogs.....dang it!!

I can feel it has more power, that's for sure. I can rev it pretty good when there is no load. But still, even when warmed up full throttle under load, it goes into bog mode.

What the heck should I try next?
 

deacon

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It is possible you got all there is out of it. Mine going up hill does that, it just gives all it's got and it ain't quite enough so it just moves at its own pace. course you could move your needle again. Try to adjust it that way. They also say you need to run them a while to break them in and they will perform better when they are broken in better.
 
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Pablo

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OK I just came in........arrgg.....this is getting fun.

All the outside fiddling hasn't helped. It started to backfire through the carb every so often (clue Norman?) so I decided to attack the beast.

First of all I took the carb off and took it apart. Pretty simple really (yes Norman the O-ring was still there). The main jet appeared clear. I didn't mess with this:

http://motorbicycling.com/attachmen...le-carburetor-install-rebuild-carbpict014.jpg

Should I try messing with the float???

Put the carb back together. Then I took the manifold off. Found a big oops there....I didn't realize how lousy the gasket matched the engine. A big portion of the ill fitting gasket was being pulled into the engine. So I carefully cut the gasket to fit.

I put a new O-ring in and buttoned it all up with a little sealant.

It fired right up, sounding really good, nice midrange power....but go for full throttle and BOOOOOOOOOOOOOOOGGGGGGGGGGGGGGGGGGGGGGG......

Dern.

So far I didn't mess with the needle.

deacon said:
It is possible you got all there is out of it.
Something is fundamentally wrong.

Try one notch lower on the needle clip and see what changes.
I just did and it made it worse. That should make it richer. Indeed it did. So next I will try the top notch, I guess.
 

thatsdax

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Feb 22, 2008
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bogging

Check your Gas Cap. If there is no hole drilled, then you need to drill one. A gas cap that seals too good and has no vent hole will cause the very problem you speak of. Thanks..Enjoy the ride... Titan is coming.....