4 cycling mystery solved!

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Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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up north now
I have been reading a lot of posts lately about engines that four stroke a lot, some all thew time. I have a bike here I built a while back, and have been unable to sell it due to the fact I couldn't get it to ever break into a clean 2 cycle.

I changed the stock plug and wire, tried every setting on the needle, soldered and re-drilled the jet to the proper size, ect.ect.

If I put the "C" clip on the top notch, it would STILL 4 cycle and have very little power, if I moved it down it would get more power on each lower setting, but the 4 cycling was still there, no better, no worse.

Finally, today, I said "I guess I'll just go run this one hard and see if it's a ring sealing issue, break-in problem, ect, I'll either cure it or kill it." (I was just a bit frustrated, having run this bike for 20 miles or more and still running badly with everything I'd tried.

I was doing my "pre-flight inspection" and noticed the throttle cable was a little loose. The adjuster at the top of the carb is all the way out, so I looked at the throttle assembly. Apperently, I overlooked a shoddy fit where the cable housing goes into a sleeve and into the throttle housing. I used my aircraft cable swaging tool to squeeze the sleeve down tighter, and pulled the slack out of the cable before doing so.

THIS WHOLE TIME, THE ENGINE WAS 4 CYCLING BECAUSE THE CABLE WAS ONLY PULLING THE THROTTLE 3/4 OPEN AT BEST!!!!! I never got a good carb setting due to an overly large jet to begin with, and then the throttle not opening all the way meant I never really had a shot at setting the carb right.....

Yeah, I feel stupid being the "Godfather of motorized bicycles" and all to have let such a simple, tiny problem cause me so much grief.

I'm gonna go ride.
 
BarelyAWake

BarelyAWake

New Member
Jul 21, 2009
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orly? o_O

*runs off to check bike*


actually, my 4 strokin probs seem to be behind me - but it can't hurt to check this lol
 
aquarianmonkey

aquarianmonkey

New Member
Sep 27, 2009
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sedona Az.
I have checked all of that on my bike. It will only 2 cycle when I climb hills. I was told that these engines only 2 cycle when they are under heavy load ? It would be nice to have 2 cycle all the time. I wish S&S would build a carb for these. They do wonders for old Shovles LOL
 
flybytaco

flybytaco

Metal Molding Madman
Oct 17, 2009
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mine 4 cycled only at top end everywhere else she was mint. I have a box of jets from all the streetbikes i've done and they are the same type of jet but were way too fat as they were for big bikes. I soldered and used a ss wire that is in my snapon electrical terminal removal kit. it has 3 sizes so I used them to make the hole int the jet. stuck it through and heated the jet fed the solder and pulled out the wire after it cooled I made the hole barley smaller than the stock jet and problem solved.plug chop was beautiful bike revs from dead slow to full revs cleanly no 4 stroking at all anywhere anymore.
 
B

bandito

New Member
May 22, 2009
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colorado
When a 2 stroke motor 4 strokes what is it doing. Dont call me stupid I already feel that way by not knowing please. I know what dieseling is on a gas motor!
 
BarelyAWake

BarelyAWake

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Jul 21, 2009
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Firing every other stroke, usually a sign of a too rich mix - most HTs will 4stroke until broken in, even then most continue to do it when they're not under load and/or cold.

Drove me bat**** insane tryin' to figure out what was "wrong" with my motor fer the first coupla hundred miles :p
 
Humsuckler

Humsuckler

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Jul 28, 2009
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4 stroking wont hurt a two stroke at all, from my experience it actually helps them last longer... i let mine 4 stroke when im coming down from high speed, it just sounds healthier!
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
63
up north now
bandito said:
When a 2 stroke motor 4 strokes what is it doing. Don't call me stupid I already feel that way by not knowing please. I know what dieseling is on a gas motor!
Click to expand...
Because these chinabuilt engines are piston ported, and old tech, they don't fully scavange out the old fumes/mix/exhaust very well. They will fire every other stroke because of the dirty rich mixture, hence "four stroking" or firing every other revolution as a four stroke engine does.

If you read old motorcycle reviews (like re-prints in Walneck's Cycle Trader or old magazines) a lot of reviews mentioned the amount a test bike four stroked. Also the control line flyers out there know how to tune one of those engines for the "2/4 break".

It's a fact of life with these, and normal. When properly tuned, the engine should break into a clean two stroke with the addition of throttle or a load being put on the engine such as going from flat to uphill. Too much four stroking will cause the engine to run cold, buikld up excess carbon and ruin a plug fast. Too little (none) and you are on the ragged edge of too lean and piston or cylinder wall damage at least.
*as a note, an engine tuned to two stroke all the time will generally show slightly better power, and crisper acceleration....don't be sucked into this you'll pay eventually.

The engine will naturally four stroke when de-cellerating or going downhill. HOWEVER you only do harm to your engine if you run downhill for prolonged periods with the throttle closed.

Pull that clutch!
 
Last edited:
Humsuckler

Humsuckler

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Jul 28, 2009
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Bikeguy Joe said:
It's a fact of life with these, and normal. When properly tuned, the engine should break into a clean two stroke with the addition of throttle or a load being put on the engine such as going from flat to uphill. Too much four stroking will cause the engine to run cold, buikld up excess carbon and ruin a plug fast. Too little (none) and you are on the ragged edge of too lean and piston or cylinder wall damage at least.


Pull that clutch!
Click to expand...
that is my point exactly, call me old school. I know what a smokers cough should sound like :D
 
F

freewheeling frank

New Member
Mar 10, 2009
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ridgway colorado
just a short one here hobby lobby sells a set of small i mean small bits for like 6 bucks i used the smallest to solder and re-drill my jets and man what a difference but i am at 7000 feet and was running super rich, good luck guys, and thanks to everyone here, been wrenchin all my life and still learn something new here everyday
 
flybytaco

flybytaco

Metal Molding Madman
Oct 17, 2009
1,170
8
0
seekonk MASS
Bikeguy Joe said:
Because these chinabuilt engines are piston ported, and old tech, they don't fully scavange out the old fumes/mix/exhaust very well. They will fire every other stroke because of the dirty rich mixture, hence "four stroking" or firing every other revolution as a four stroke engine does.

If you read old motorcycle reviews (like re-prints in Walneck's Cycle Trader or old magazines) a lot of reviews mentioned the amount a test bike four stroked. Also the control line flyers out there know how to tune one of those engines for the "2/4 break".

It's a fact of life with these, and normal. When properly tuned, the engine should break into a clean two stroke with the addition of throttle or a load being put on the engine such as going from flat to uphill. Too much four stroking will cause the engine to run cold, buikld up excess carbon and ruin a plug fast. Too little (none) and you are on the ragged edge of too lean and piston or cylinder wall damage at least.
*as a note, an engine tuned to two stroke all the time will generally show slightly better power, and crisper acceleration....don't be sucked into this you'll pay eventually.

The engine will naturally four stroke when de-cellerating or going downhill. HOWEVER you only do harm to your engine if you run downhill for prolonged periods with the throttle closed.

Pull that clutch!
Click to expand...
you say pull the clutch in because when the throttle is closed its not really lubing the motor right? and btw it fourstrokes a tiny bit now but toatally dealable I dont want to lean the heck out of it but i did go down one size. off topic but I just finished having the head milled on my starfire 50 I took the whole lip off the head
 
flybytaco

flybytaco

Metal Molding Madman
Oct 17, 2009
1,170
8
0
seekonk MASS
freewheeling frank said:
just a short one here hobby lobby sells a set of small i mean small bits for like 6 bucks i used the smallest to solder and re-drill my jets and man what a difference but i am at 7000 feet and was running super rich, good luck guys, and thanks to everyone here, been wrenchin all my life and still learn something new here everyday
Click to expand...
I'm a motocycle tech for 15 yrs now and same here I'm not afraid to take new advice.. love it here guys everyone is cool so far..
 
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