The right Jet??

Backwoods

New Member
Joined
Nov 21, 2021
Messages
8
Hello all, I am new to this forum and joined because I have found a wealth of information pertaining to these bikes specifically, and I am now the proud owner of one myself.

I had originally wanted to build one back in 2016, however i had too much trouble finding a reliable source that would ship the kit to my area (central TX). The idea was put off until I found them available on Amazon and quickly ordered a 66cc kit from Anbull.


My own background, I am 32, I have some college automotive education, about half way thru to an associate's degree.

I really like all things amsoil, the oil has treated me very well. I actually had an oil analysis done by Blackstone labs($25, they will mail you the sample kit free, send the sample with mail order, teller check, check and they email you the results and send a mail copy).

After 15,000 miles the oil still had a TBN over 12, ever since I was sold. No other company believes in their own product so faithfully. I have hats, stickers, pens, and they all come free from my local dealer, he just gives them to me because I buy so much of their oil. Obviously this engine is going to be given a healthy diet of Amsoil Synthetic 100:1.

It was initially difficult for me to make the leap of faith. I told myself that amsoil hasn't lied to me yet, and if they believe in it, theres no reason why I shouldn't either. I'm not more educated than the professionals over at the testing center. The engine loved it. There was zero signs of oil starvation.

Now about this engine. The cylinder was decked and the squish is now measuring at 1mm at the cylinder edge. The head is a DONSP1986 High compression head 5.5cc.

I replaced the top rod bearing with that high performance one off Amazon I forgot the brand, but it's much beefier than the stock and is clearly built better. Copper head gasket.

I put on the hub adapter and went to a 41T sprocket which is actually perfect for me (I weigh 220) the 44 was a hair low, I wouldn't want any higher than where I am at.

I can hit 30mph on most days and I'm more than happy with that. I usually cruise around at maybe 10 tops. It's what I'm comfortable with on this particular bicycle.

I bought the fat belly pipe, I did buy the Windowed piston and cheap reed, but it leaked puddles of gas and just ran like crap. So I have the stock piston in currently until I can correct the reed issue, on my own. I think it just needs better seals and carbon reeds, I really am afraid of a little piece breaking off and messyin' up my day, or week.

I bought a set of jets as well and thus far the tuning seems to have worked. Stock was really 4 stroking. Which is why I purchased the jets. I am at a 58, I tried nearly everything down to the 45. The 45 had perfect idle and all, it just cut out pretty quickly through the mid, and as I went up, the rpm that it would stop or bog at just got a little higher and higher, the idle characteristics were nearly identical between all the jets I tested. I was looking for a good plug chop, and i just can't seem to get what i would like to have.

Usually theres always unburned fuel on the plug and black. You'd think too rich. That's what led me to try jets so low. I never saw any white. Not even any light brown. Then yesterday it just stopped running. Volt meter said the magneto was good, so I replaced the cheap chinese plug with a champion copper and it fired up first pull. The plug looks a little better too. However even on the 58 jet, the plug still looks a little darker than I would like it to look. I know from testing that the 55 is barely, Barely enough to get into the high end range, which is why I'm using the 58. Is this normal? I do have access to ethanol free gas, it only comes in 87 though, dernit. The picture with the micrometer is the squish clearance.
 

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Backwoods

New Member
Joined
Nov 21, 2021
Messages
8
I also did shave the piston. It did not fully open the intake side as many have reported. I shaved about 1.5 mm off both sides. I originally had concerns about the exhaust side but got the "f*** its" and did both for weight purposes. Shaving the piston I believe really, I mean Really helped with vibration. It could be the combination of the shaved piston and performance top bearing.

It works well. I don't intend to do any type of racing. This is a hobby thing. I dont need to go 50 on a bicycle. I fulfilled a long-time childhood dream. Having an engine on my bicycle. No racing, but I find great pleasure in pushing little engines.

They continue to impress me. I'm just having an issue getting the jet size right with this one. Either the jet is not ideal or theres a weak spark issue. Things definitely felt better when I installed an American plug.
 

Street Ryderz

Well-Known Member
Joined
Oct 14, 2016
Messages
4,221
Doing a plug chop is a specific procedure of checking the main jet's burn, this is done at wot with a running temp engine and a new plug installed hot then run up to wot and held for at least 30 seconds and the engine cut at wot to get the true read. Start up and idle with midrange use will blacken the plug as idle and just above is usually pretty rich and will give false reading. Do you live at 8k ft because a #58 jet is very lean and at 100:1 is going to be very deceptive.
 

Backwoods

New Member
Joined
Nov 21, 2021
Messages
8
No I'm at sea level. I believe the issue is the carb not being large enough to supply decent air. Basics, the air is only going to flow as fast as the smallest opening in the pipe will allow. In this case it's the carb. It's the most restrictive point that I can see. I feel like with a wider carb i wouldn't have as many issues. I thought the 58 was lean myself. I tested the 62, 65, 68, then went down to the 58 because the bogging was increasing from being rich, my top speed was suffering. I tested them by running WOT. The 55 worked well but I still had a wet plug, I went as low as 45, crazy I know. It idled great, had zero top end, then I went up from there. 50, 52, 55, with each increase my top speed got a little higher, a little more rpm. Then I hit the 60 again going up and it started bogging more and 4 stroking. The 58 gave me the best top end and all around driveability. I dont want it too rich down low because it puts more stress on the drive components with more powerful pulses to the sprocket. So I believe the carb is just not large enough. Changing the spark plug did make a noticeable difference.
 

Backwoods

New Member
Joined
Nov 21, 2021
Messages
8
I hit 30mph today with the 58. Even just one size up or down and that top speed suffers a few mp's, from what I tested. I tried to test them all equally on the same road going the same way. Measured with a gps phone app.
 

Street Ryderz

Well-Known Member
Joined
Oct 14, 2016
Messages
4,221
No I'm at sea level. I believe the issue is the carb not being large enough to supply decent air. Basics, the air is only going to flow as fast as the smallest opening in the pipe will allow. In this case it's the carb. It's the most restrictive point that I can see. I feel like with a wider carb i wouldn't have as many issues. I thought the 58 was lean myself. I tested the 62, 65, 68, then went down to the 58 because the bogging was increasing from being rich, my top speed was suffering. I tested them by running WOT. The 55 worked well but I still had a wet plug, I went as low as 45, crazy I know. It idled great, had zero top end, then I went up from there. 50, 52, 55, with each increase my top speed got a little higher, a little more rpm. Then I hit the 60 again going up and it started bogging more and 4 stroking. The 58 gave me the best top end and all around driveability. I dont want it too rich down low because it puts more stress on the drive components with more powerful pulses to the sprocket. So I believe the carb is just not large enough. Changing the spark plug did make a noticeable difference.
Basics ? LOL this is a 2 stroke the carb is plenty big enough for what you have and it relies on atmospheric pressure rushing through it at it's given volume then that volume of air is what pulls the fuel up metered by the jet, this setup has gone 50mph stock everything and at sea level a # 58 jet is way to lean trust! Bogging is a sign of being lean not rich and you want a bit of four stroking as load is reduced or at sustained fix throttle when it's just maintaining a fixed speed. Also as good as Amsoil may be it's not good enough for 100:1 use in these engines!
 

Karl Snarl

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Joined
Sep 20, 2019
Messages
2,420
Just want to toss my two cents in take it as you will. I don't care if you have magical fairy juice, 100:1 is to lean on oil. Well that is if you care about anything you pilot. Black soot on the plug is an indication of running to lean. Soot is created at higher temperatures when the mix does not contain enough oxygen to form monoxides and oxides. I want to bet money that you are lean surging. A common issue with these bikes when the builder/owner has limited info on how 2 strokes run, but some or even large amounts of info on how 4 strokes work. These engines like fuel, and love their oil. Look for that air leak, and put a bigger jet in with more oil. Your engine will thank you with power and longevity.
 

noah9988

Active Member
Joined
Jul 3, 2021
Messages
144
I don't know what the point of skimping on oil is. Also think of it like this:

Less oil = more fuel = richer with same jet size.

More oil = less fuel = leaner with same jet size.

Oil is good. You want oil. It lubes. It cools. It helps seal the rings.
 

YetiWoodz

Well-Known Member
Joined
Dec 19, 2019
Messages
1,224
I personally have tried Amsoil synthetic at 100:1 in my fuel mix when I started and this is what my cylinder and piston looked like only after maybe 6 hours of total ride time or less. I was even running a 78 jet (very rich jet)
Screenshot_20211126-092124_Gallery.jpg Screenshot_20211126-092213_Gallery.jpg
Very low piston wash and I can't say with 100% confidence that the low oil caused chipping of my cylinder but it couldn't help.

I'd run 40:1 with high quality synthetic oil like that or 32:1 with anything else. 100:1 with Amsoil is the minimum for an engine with low load like a weedeater.

Piston wash with same Amsoil but 40:1 and a 65 jet.
Screenshot_20211126-094958_Gallery.jpg
 
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