new guy here, new to small 2 strokes. jug head question.

Jimmy Bloodmaker

Active Member
Nov 24, 2018
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i have a new 2 stroke kit, bought off amazon. great little engine, nice low end torque right out of the box. it is a 66/80cc china made ( y'all call 'em china dolls or girls? i think?). it has a one piece jug/head, slanted spark. piston looks pretty flat from the spark plug hole. i was wondering if i can buy any 8mm head and jug to replace the factory. i'm not looking for more power, it's got plenty, right where i need it. it's hilly around here. this is a daily driver in spring and summer, but it gets hot!! i only want more cooling that this small thin finned factory set up. any advice on what jug and heads i can use? are the pretty much universal for the head/jug bolt size?
 

junglepig

Member
Oct 28, 2018
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Georgia
To the best of my knowledge, you are correct. There are several geometries that consist of slightly longer strokes and a "long" or "short" rod, coupled with two basic piston types with a low type "A" or high type "B" wristpin position, all with the same 47mm bore. Even though this changes the port timings slightly, you won't see multiple types of jugs for sale on eBay, except possibly from companies that make modified engines. You'll be safe going with any generic eBay jug for 8mm studs. (I'm no expert, but I asked basically the same question about a week or two ago.)
There are lots of aftermarket heads that offer more material and fins than the stock slant head. The "Fred head" is popular. Other members can give better recommendations than I can.
 
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Jimmy Bloodmaker

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thank you for responding so quickly. i had a feeling they we most interchangeable, sept a few special cases. this is my first bike and i want it to last a long while. i plan on buying other engine to tinker with. i just want some aftermarket cooling ability on this little guy. i was told my engine would run like crap at first. nope, runs great actually. doesn't have a lot of top end go, but i'm in a hilly area, so i don't need it. i think the slant head/jug design of this particular company adds all tht low end torque in. i will find out when i buy another engine to modify. i know i can buy fully built engines tht just need tuned, but wheres the fun in that. the key to this little gal i have now was simply adjust the main jet just a bit leaner than factory setting.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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The stock head actually works (& cools pretty well).

The three best aftermarket heads (IMHO) are the Fred Head, Jake Head & the Shark Head.
Keep in mind that these heads will raise the compression (& cause more heat), & in most cases will make the engine run different until you re-jet the carburator.
 
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Jimmy Bloodmaker

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do you know of any sellers that has close to a factory performance or even factory 2 piece( i'm not sure if im a or b yet)? all i've done is polish the ports a bit, to remove uneven surfaces. i'm not trying to make a fast bike just yet. i like where this one develops most of it's power. it's not really to fast, but has nice pull to top speed, good on most hills. i just pull the clutch in and let it idle down hills. i'm trying to keep this one at the band it is in. since these motors are so easy to swap in an out ( 10 mins), i am gonna build my racer engine to swap in and out as needed or as wanted for use. my main goal in this first engine is longevity and street riding. when i was saying it gets hot, i mean it gets real hot sometimes going up hills. i have adjusted my fuel as best i can. these tiny fins leave a lot to be desired.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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I've never tried this one, but the 8.0 Fred Head might be close to what you're looking for...
https://shop.crmachine.com/product.sc?productId=81&categoryId=15

Also.... when doing the re-jetting, keep it as rich as possible (large jet) without it feeling 'sputtery' when fully warmed up.
If you jet too small, it will feel more powerful but it will make a lot more heat (& quickly blow up the engine)
 
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Jimmy Bloodmaker

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i'm gonna have to try tht head. i'll do it when i get another motor to tinker with. the kit i bought was so cheap ( can build a bike for under $200, bike and all), i'll pick up another. i've head some bad things with these cheap kits, but i'll tell ya, i'm impressed. im not a pro at 2 strokes, but i understand them. only thing i didn't really like was the single piece jug/head. it's really small too. i backed off the c clip on the needle valve so it is one rung from the top, would load up the plug where factory had it. that an i was eating gas like my truck, lol. idles great, only sputters when it hits way to high an rpm. i'm guessing i run it around 4.5k- 5.5k rpm while cruising, little bit of throttle left. only when i hold it in WOT at the top end will it sputter, and shake like Salinas did in 89. an let me tell ya, i was there in 89. lol
 

junglepig

Member
Oct 28, 2018
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i'm gonna have to try tht head. i'll do it when i get another motor to tinker with. the kit i bought was so cheap ( can build a bike for under $200, bike and all), i'll pick up another. i've head some bad things with these cheap kits, but i'll tell ya, i'm impressed. im not a pro at 2 strokes, but i understand them. only thing i didn't really like was the single piece jug/head. it's really small too. i backed off the c clip on the needle valve so it is one rung from the top, would load up the plug where factory had it. that an i was eating gas like my truck, lol. idles great, only sputters when it hits way to high an rpm. i'm guessing i run it around 4.5k- 5.5k rpm while cruising, little bit of throttle left. only when i hold it in WOT at the top end will it sputter, and shake like Salinas did in 89. an let me tell ya, i was there in 89. lol
I missed the part of your original question where you stated that you had one of the new one-piece jug/head engines. It didn't really change what I said now that I reviewed it. Did the kit you bought say anything in the description or pictures to let you know that is what you were getting?
 

Jimmy Bloodmaker

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Nov 24, 2018
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I missed the part of your original question where you stated that you had one of the new one-piece jug/head engines. It didn't really change what I said now that I reviewed it. Did the kit you bought say anything in the description or pictures to let you know that is what you were getting?
oh yeah, the pic showed it as a one piece. all the reviews said it was 8mm head/jug bolts. they are bhcs, at 5mm allen. which does mean an 8mm thread area. i work at an industrial hardware supplier as their fabricator, so i have access to make my own head stud etc. i also have some machinery like a welder, grinder, etc at home. so making support piece for my motor is no problem. i just figured i could get a jug and head at a later date ( when i get another motor to tinker on), an just make my own head studs. i had to ask about the jug/head cause a local guy tht builds bike said i could only use factory, but everyone else i talked to about it said otherwise. my first thought was, " if they have the same center space, im golden. if not, i would just have to get a different block. " i do eventually plan on building a racing motor, just not yet. still breaking this boy in, lol. seems to get stronger with each ride. i have around 600miles on it so far. i was pleasantly surprised on my third tank, bout half way through, it took off like a rocket when i goosed it. been riding tht way ever since. the smoke got less and less with each mile i put on it too. my only problem is, it get real hot sometimes. running more oil or richer on the carb just burns up fuel when im not at high rpm ( still burns at high rpm, but im going somewhere, lol). i don't run it all tht hard, i try to keep it humming, instead of screaming. im just wanting to have it run a bit cooler than it is. now it is winter, well i dont have heat problems. in the midwest, so summers aren't super hot.

addition: it is on a 24" roadmaster 18 speed mountain bike. so i know my top end is gonna be lower, but im in it for the torque. lots of hills around here and tht extra torque is so sweet when going up a steep one. 44t back sprocket. an if you are wondering, i can pop a mean wheelie on it. lol
 

Jimmy Bloodmaker

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Nov 24, 2018
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so i took the advice and went with larger jetting etc. she runs mean and great. a lot cooler than the stock jet. thanks guys!! she's running 30 degree's cooler at full speed now. it four strokes a bit on take off, but soon revs up, i can live with tht though.
 
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Jimmy Bloodmaker

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Nov 24, 2018
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oh and the stock jet was a #68, so i plugged in a #70, #71 was four stroke all the time, #72 was super chug chug. #69 gave me awesome power, but still way to hot for my taste. #70 is great power, not as good as #69, but 30 degrees cooler. i was running at 390 or so after a long run with stock jetting. she's down to around 350-360 with the #70. stays stable at that temp on long runs of over 2 miles at 3/4 throttle.
 

Jimmy Bloodmaker

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Nov 24, 2018
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one last thing, if it wasn't for y'all, i never would have realized i was tuning the main jet way too lean. would have burned my baby up. the plug gave me nice color, i thought the head was the heat issue problem. you guys rock!! my next build i'm gonna try one of them fred heads like venice recommended. thanks again biker brothers, ride on!!
 

Jimmy Bloodmaker

Active Member
Nov 24, 2018
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ok i have been studying up on oil ratio's. what i have found is pretty contradictive to what a lot of people say on here. i've notice a lot of people run a really lean oil mix ( higher fuel to oil ). yet what i have been finding in the books i've read is tht more oil is better. i've also experimented on my bike and found if i jet properly, i'm getting more power with more oil, to a point. i was expecting more smoke, but i'm not getting a lot more, a bit more yeah. i found if i run a #73-#74 jet with a oil ratio of 16:1-20:1, i get some pretty sweet power and lower cylinder temps. a lot of post say less oil ( more fuel) is more power, but tht is exactly opposite of what my experimenting has found. can anyone explain to me why or how they are getting more power with less oil? isn't that wearing the parts faster and causing the oil to burn off rather than seal the rings better? i do get some spooge when i run the lower oil ratios ( more oil), but i don't mind with all the power it creates. besides oil is pretty cheap. now if i toss in a #78-#79 jet with an 8:1 mix, it smokes to high heaven and doesn't really give me any more power than a 16:1, plus it really spooges out the muffler. i'm not to versed on 2 stroke engine, but have quite a bit of 4 stroke experience. i just can't figure out why they are running so lean on oil, and saying they get more power. isn't the oil part of the ring sealing factor on these engines? how do they get away with running so little oil and not wearing out the ring fast? or for tht matter, the bearings. any insight would be greatly welcomed.
 

chmn22s

New Member
Jun 8, 2017
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"simply put, gasoline has more potential joules of energy than does oil, so more oil in the mix reduces the power of the burn. modern MX'ers commonly run 50:1 or higher even, to try and safely squeak out any iota of hp to be gained without melting something and still be lubricated"
I copied that from dirtbike magazine. but these arent dirtbikes built good an peple always tell me break it in 20:1 then go 32:1 after a few tanks and u can feel when it wakes up more when it's broke in full but u cant tune it much b4 that and dont use the cheap out oil.