Exhaust I drove it without an exaust pipe for about 4 miles...

[azbill]

no, if you rode it too much with no pipe, you hurt it.

I rode my deviate for approx 200 miles with just a 1" stub till I got an exhaust

I agree, it sounds like carb to manifold or manifold to engine leak 8)

 

[saylor]

http://www.oldengineshed.com/twocycthry.html

I guess we disagree

I maintain that it is taking in air via the exhaust port, when it should be drawing gas/air from the intake manifold only, thereby allowing excess air to come in to the gas/air mix in the cylinder, and "leaning" it out.

so what happens if you run an engine lean too long? Does it get hurt?



a lean engine runs hot.

then what happens?

you warp or crack the head.

and read that in the past tense, , ,it TOOK in air... not "is taking",, as he has put the pipe back on since... I forgot myself there a bit.

 

[Dockspa1]

Think about it for a minute. The cold air being directly in contact with the piston after a hot engine, is definately not good. Expansion and contraction on the piston, head or even the inside jug walls is bound to resize itself with or with out cracks and warps.
It's just like having an overheated car engine and you turn it off and then add cold water, KAPOOTZS! KABAM! It's history.
Doc

 

[Guest]

Guys- remember that when the air/fuel mixture comes in throught the INTAKE, it is fairly cold.

This doesn't hurt or sieze the engine.

The exhaust on a two stroke doesn't suck air as when the piston is traveling downward, it pushed the (cold) intake mixture out of the crank case and into the cylinder. If anything some of the fresh mix gets pushed out through the exhaust, unburnt. That's partly why two strokes have "dirty" exhaust.

Also saylor, a couple of things- these engines don't employ reed valves, or even rotary valves, they are piston port timed engines.

If you read that web page, the incoming (cold) air pushes the exhaust out of the port via positive crankcase pressure. It doesn't suck in the mixture.

 

[saylor]

Well, hopefully the original poster will fix his motor and then tell us what the problem was.

 

[saylor]

BikeGuy Joe -

in your previous post - you mention

The exhaust needs to be on there for a couple of reasons, which I won't go into now.

No exhaust = no low end power and will cause lean running conditions.....really bad.

Put it back on.

Then - in another post, you say

I ran a mac 101 kart engine for a whole summer with no exhaust, just the open port- no damage.

Engines don't "need" backpressure, but work better with it, especially on the low end.

Maybe you could go into those details of why the exhaust needs to be on there? Obviously there is confusion in the forums, so we need an expert to set us straight.

 

[gone_fishin]

just checking in...we're pretty careful 'round here about friction...this is a tech/mech topic, aren't we supposed to be trying to help someone?

take the differing opinions & personal jabs PM or start a new "debate" topic.

the OP is fogg4444, and he's moved on to the next step.

fogg4444: your last post leads me to again advise you check head/jug/intake gaskets & carb-to-intake.

 

[saylor]

I'm not trying to create any friction - he said he had explanations that were too detailed to go into, but it's obvious that we in the forums need the detail as we're all just guessing as to what the problem is... so I was hoping he would share... it may make one of us think of something else that could be the problem.

Anyways augi - point made - this is a tech forum, and let's keep it that way. I appreciate that comment.

And Joe - no hard feelings. I'm just trying to help the guy, just like you are. We both could be right, or we both may be wrong and his spark plug is hanging halfway out and THATs the real problem... I guess we just don't know until he updates his post

 

[Guest]

BikeGuy Joe -

in your previous post - you mention

The exhaust needs to be on there for a couple of reasons, which I won't go into now.

No exhaust = no low end power and will cause lean running conditions.....really bad.

Put it back on.

Then - in another post, you say

I ran a mac 101 kart engine for a whole summer with no exhaust, just the open port- no damage.

Engines don't "need" backpressure, but work better with it, especially on the low end.

Maybe you could go into those details of why the exhaust needs to be on there? Obviously there is confusion in the forums, so we need an expert to set us straight.

No, it's cool.... You kind of answered the questions yourself there.

Engines don't need back pressure, but they run better with some, especially at lower rpm's. The kart I ran was run at WOT most of the time, and so the open port gave max output at a very limited rpm range. The engine was jetted properly to be run at WOT with no pipe, so it wasn't running lean. However, if you loose your exhaust on an engine jetted to run properly with it, it will go lean and that's a bad thing.

Also, the exhaust needs to be there for a couple of reasons- one more obvious one is noise suppression. The other is tunablility over a wider rpm range.

Class dismissed!

 

[rcjunkie]

Back pressure improves low end torque but at the expense of all out power at higher rpms.

Anybody who has a motorcycle with an aftermarket knows the hassle of having to rejet their carbs due to the free flowing exhaust over stock.