My 2 stroke is 4 stroking..

GoldenMotor.com

WaterDog

New Member
Sep 12, 2010
59
0
0
Miami / Fort Lauderdale, Florida
Ok, i 'assume' my bike is 4 stroking above 75% of throttle. Great pick up across the power band until i hit 65-75% of throttle. The sound changes like its missing every other stroke and the acceleration stops. Heres the deal..gas flow is fine, high performance air filter breathes great, no intake leak from the brake cleaner test, needle set on second notch from the top, spark plus is nice chocolate brown with no oil or white burns, exhaust is modified slightly and flows fine, 100 total miles on engine and using 40:1 synthetic oil.. now what in the world could cause my problem. Its still fun to ride and never fails to idle, start or run. Just wish i could figure out the high end problem to get over 23-25 miles an hour. Thx for reading this guys, any help is appreciated.
 

timboellner

Member
Apr 1, 2009
435
0
16
Towson Maryland
Yes it's too rich.
You can solder and re-drill the jet if you have the right bits.
Keep in mind that 3/100 of an inch difference in drill size can mean the world of difference how your engine runs.
Check this link and look just past the middle of the page to the Drill Bit Conversion Table.
Drill bit sizes - Wikipedia, the free encyclopedia

You'll have to experiment a little to get it just right but believe me it's going to make you smile when you get it dialed in.

Get yourself these 2 drill bits at a hobby store. I think I paid about $2 each.

#70 gauge drill bit (0.028 inches 0.711mm..... Usually close to the stock size)
#71 gauge drill bit. (0.026 inches 0.660mm. smaller than stock
Main jets are measured in millimeters #70 = .7mm
#68= .68mm etc.

Sick Bikes sell the jets but if you are handy you can save a little time and money doing it yourself.
#68 or #66 work best for me

Good Luck,
TIM
 

msrfan

Well-Known Member
Sep 17, 2010
1,808
120
63
Southern California
I discovered on teardown of one of my BGF motors that the seals are junk. They were flaking and looked used. I went to a bearing house and picked up some high quality seals and cured my problem. Most metric seals have the sizes molded right into them, like 14.8 27 5, and 14.8 27 7. My crank shaft measured 15mm, so the seals I ordered were TCM #15X27X5TC, and TCM #15X27X7TC. Metric seals use the bore, o.d., and thickness as the part number.
 

Nashville Kat

Well-Known Member
Apr 20, 2009
1,501
55
48
Jacksonville, Florida
I think you're too light on the oil mix- the plug should be darker- I don't know what the scales are- Does synthetic oil work in these things? Better more oil than less- at least the motor wont blow.

I got some results when I had this problem by closing down the petcock a bit- which seemed to indicate flooding. But then I added a little more oil and that seemed to help.

The sure fire best bet to stop four stroking is a billet intake from creative engineering or pirate cycles, if they have them in stock. I bought both a NTS 66 carb and a billet intake. I put the billet on first to see the effect. I've never got around to putting the 66 carb on the bike runs so well with just the billet.

I'll probably do it soon though, just as much for the extra shut off valve- and I'm putting a three piece alloy crank in.
 
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WaterDog

New Member
Sep 12, 2010
59
0
0
Miami / Fort Lauderdale, Florida
Good suggestion. I did notice that the stock pipe that the carb connects to has 3 or 4 slits in the end that the carb clamp is supposed to seal. Mine is far from precision and there was a leak there before. I just wrapped silicon tape around these slits and slid the carb back on. I thought i sealed it up but i should check again. Can you use permatec gasket sealer in the intake gasket? I used it on my head gasket and it sealed up a leak that was causing some compression loss.
 

FreeWheeler

New Member
Jun 22, 2010
240
0
0
Maryland
For the record:

After downjetting to 68, mine was still 4 stroking a bit much. I just tested my earlier plug gap theory. I'd tapped to about 024 before, so last night I pulled the plug. The condition and color was perfect. Put it back in after yapping to 032, and just now got back from a ride. No more four stroking at all (unless I back off the throttle, of course).

Science!
Are you going to say your plug was perfect chocolate color, but then post a pic of a crispy lean plug?

More seriously, I went the opposite direction on my plug and validates what your saying. I had no 4 stroking with the gap I used and then I closed it a bit and it breaks in and out unless a load. I felt the plug was a bit lean before and betting that improved. Have to pull it to see the color, but the gap affected 2 vs. 4 stroking.
 

FreeWheeler

New Member
Jun 22, 2010
240
0
0
Maryland
I was kidding about how this thread started with a perfect chocolate plug and some annoying 4 stroking, followed by well meaning suggestions based on those assumptions and then the truth. That's all. I dont doubt it when you say youre plug is good. :)

Sarcasm!