So your bike is 4 stroking...

66cc

66cc

Member
Hello All,

This topic is most probably discussed elsewhere.
I would like to bring new light to some problem areas for which I was unable to find solutions on this website.

Ive had many 2 strokes in the past, and haven't experienced 4 stroking like I am with this 2014 grubee gt5 kit.

Currently over 500kms on the engine since August 2014.
Experienced 4 stroking after first tank refill from 16:1 to 20:1
Currently on 32:1 ratio.

I cleaned out air filter, and added a ram air to increase air in the mixture, this didnt make much of a difference.

yesterday I moved the needle from 2nd to 1st most leanest position and the 4 stroking got worse, and there is a considerable LOSS OF POWER.

now im thinking of moving the needle back and then maybe increasing the amount of oil in the mixture to lean out.

or make a hole in the air filter.

rejetting is not on the table as sometimes randomly when the bike is on a long trip the 4 stroking seems to dissappear even at WOT.

PLEASE ADVISE. :/

so far best kit, was a no name 2011 kit in my 2012 trail ride and night ride videos. no problems whatsoever for the life of the engine and still going strong!

I want that kit again!!! :D

https://www.youtube.com/watch?v=46Eigr5-6xY
(WHAT FOUR STROKING SOUNDS LIKE)
:-||
 
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if 4-stroking low speed and high speed and leaning didn't help it may be something else like a clogged muffler
 
UPDATE:

so I moved needle back to 2nd notch, cleaned out the air filter, i was able to pry the air filter inlets to wider, and the performance is way better, I was able to reach 53km/h on a long stretch of smooth tarmac.

So the bike 4 strokes all the way up to about 44km/h and then it just changes into 2 stroking i believe at that speed the forced ram air system pushes more air or something and it sounds so good and the power is like nothing else.

plug chop is chocolate brown, and it only 4 strokes under load, when clutch engaged, when I pull the clutch it freely revs to redline.

Any ideas?

thank you.

xct2
 
If you started with 16:1 mix pull your exhaust off and see if you can blow it out, chances are it's gummed up with oil, a quick check is ride it around the block with the pipe off and see.

Regardless I highly recommend you get an NGK 5944 (BPR7HIX) Iridium spark plug for it, you'll feel the difference.
 
so a clogged exhaust could cause 4 stroking?

Can someone please explain the mechanism as to how that would occur?

Also, when the exhaust cap fell off, it was still 4 stroking??

Thanks for the input guys!
 
clogs often happen at the top of the muffler where the honeycomb section is

exhaust prevented from leaving chamber can foul the next fire cycle
 
66cc said:
Also, when the exhaust cap fell off, it was still 4 stroking??
Click to expand...
The stock exhaust is not hollow.
Depending on the kit it has a combination a catalytic converter and silencer in there.

If yours fell out when the cap came off and it's hollow now then it's not your exhaust other than it is now not providing any back pressure, that's not good either.

A tuned exhaust can actually give ya 1/2 a horse or so.

Expansion Chamber Exhaust.
You can liken an Expansion Chamber exhaust to a reverse turbo charger.
To understand how this works you need to understand how a 2-cycle motor works.
They say a picture is worth a thousand words.
An animated picture is worth a whole book so here you go.

expansion_chamber.gif


The way 2-cycle motors work is to try and do the exhaust and intake in the same up/down/up cycle of the motor so it can fire on each top visit, and because of that a lot of unburned (green) fuel goes out the tailpipe.
An Expansion Chamber (on the right of that animation), named for its peculiar looking fat section, is tuned to push that unburned fuel back into the cylinder, thus giving each cycle an extra Boost of fuel.
~$60 to ~$80.


One more simple thing to do is make sure you have no settled oil in the bottom of your crankcase, pull the plug out and with clutch out pedal it up the street and back, you'd be surprised how puddled fuel in the crankcase can mess with your new atomized gas/air mix.
 
UPDATE: "she purring now"

Bike is only four stroking and low speeds at low to mid throttle. THANK GOD.

Remedies:

-Full Carb over haul
-Air filter cleanse
-Increased number of holes (10+) on the filter cap (drilled 3/8inch holes at bottom and where rain or water would be able to seep.)
-Cut off the intake tubes
-oil mix from 32:1 to 40:1

Thank you all for the help.

Next project would be an exhaust rebuild and cleanse.

xct2brnotdance1
 
crassius said:
clogs often happen at the top of the muffler where the honeycomb section is

exhaust prevented from leaving chamber can foul the next fire cycle
Click to expand...

How can I remove the catalytic converter or honeycomb thing without cutting?

or is cutting the only way?

I plan on making a muffler after gutting it.

These new catalytic converter mufflers are garbage!
 
AFAIK, they have always had the converter inside - I have a drill bit that is 18in long that opens them a bit when needed
 
All of my builds in the past three years or so 4-stroke terribly. I thought it was kinda normal seeing as how none of them were 2-strokes. Does this sound right?

I really try to make them 2-stroke but nothing seems to work.....:D

Should I reverse the polarity?

:-||
 
66cc said:
How can I remove the catalytic converter or honeycomb thing without cutting?

or is cutting the only way?

I plan on making a muffler after gutting it.

These new catalytic converter mufflers are garbage!
Click to expand...

I've already done this on my bike and noticed huge gains.

First of all, the plates inside the muffler aren't catalytic. They are just thin metal discs welded around the main pipe which has holes on the sides. So the exhaust gases have to hit the end of the inner pipe (which is capped off) and then travel out the little 1/4" holes in the sides of the pipe and then pass through the plates to get out of the end cap. This quiets the motor and makes it really wimpy.

Option 1:
In order to gut the muffler and turn it into an expansion chamber, you have to make a cut with a hack saw near the top of the expansion chamber (only cut until you hear the inner pipe fall inside). Then you can remove the end cap and the inner pipe and discs will come out with it. Simply unbolt the end cap from the inner pipe and weld it back onto the expansion chamber and weld up the previous cut at the top of the expansion chamber while you're at it.

Keep in mind that your bike will be loud as &%^*. Mine registers at 104 decibels at idle.

Option 2:
If you don't have a welder, I'd recommend cutting the cap of off the inner pipe and leaving the end cap off of the expansion chamber too. It's only 10 decibels louder and you'll have way more power.

Either way, here's a picture for your reference. If you are a welder, don't judge. :) This was my first time wire welding and this metal is really thin.

WP_20141219_004_480x640_zpsffef7e25.jpg
 
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pulsar2121 said:
I've already done this on my bike and noticed huge gains.

First of all, the plates inside the muffler aren't catalytic. They are just thin metal discs welded around the main pipe which has holes on the sides. So the exhaust gases have to hit the end of the inner pipe (which is capped off) and then travel out the little 1/4" holes in the sides of the pipe and then pass through the plates to get out of the end cap. This quiets the motor and makes it really wimpy.
Click to expand...

The reason being is you have the old style non-catalytic type pipe.....there is a diff.
 
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