should I go 50cc or 70cc two stroke cylinder kit? By nobodyspecial (Read 4,139 times)

[nobodyspecial]

Ok I nipped up my 50cc Minarelli piston and cylinder (12mm pin) and need to replace it.  I'd like to go 70cc and need to hear from people who have done it.

I have blown one up previously (70cc) when Scootercraft sent me the wrong too tight piston for my stage 6 kit so I want to be careful this time.

My concerns are this.  I have heard I should go aluminium instead of steel cylinder for cooling.  Do I need to ditch the oil pump feed and go premix, if so, what ratio?  Ideally I'd like to leave the pump in and add oil to the fuel tank as well.  Also jetting, where do I start with a main, I will have a 19mm Mikuni with a 70# main standard for the 50.  Any other concerns issues I should watch out for? As usual any help is appreciated!!!

[Alleyoop]

I guess you found out pretty quick. Without a pipe and or under size MAIN JET it ran LEAN AND MEAN and you seized the sucker. It should have given you a warning it was running to LEAN by the MOTOR SOUND so you could have backed off the throttle. But most do not know the motor sounds when there is trouble in river city and they blow their motors.

Just a tip bud a #70 main is to small for a 70cc you need at least and #80 maybe even a little bigger than a #80 all depends on the motor and what it is putting out. They all run different and produce different power. But to make sure it is not running lean you always want to ERROR ON THE RICH SIDE never on the LEAN side because first WOT RUN you do will most likely kill your motor.
Alleyoop

[jct842]

Way better to ditch the pump for oil and add oil to fuel. The pump would be fine for a new stock engine, but once you get modifying you want to control exactly the oil you are lubing with. As an example if you depend on 1/2 the oil to come from pump what happens when the pump craps out? If you just add oil to fuel along with what the pump puts out now you will have smoke and spark plug fouling. 2 strokes have been run for a million years by lubing the fuel why change a good thing.

[kevinharrell]

Mar 28, 2016 12:33:28 GMT -6 jct842 said:

2 strokes have been run for a million years by lubing the fuel why change a good thing.

How many times do you need to be told not to exaggerate? (Perhaps two million times?)

But, on point. The last time I kitted a 50cc two stroke I started with an 86 jet and then went to an 84, but, that was going with a 65cc kit not a 70cc kit. You may want to start with an 88 jet and see where you should go from there.

[czmdiver]

Mar 28, 2016 3:19:49 GMT -6 nobodyspecial said:

Ok I nipped up my 50cc Minarelli piston and cylinder (12mm pin) and need to replace it.  I'd like to go 70cc and need to hear from people who have done it.

I have blown one up previously (70cc) when Scootercraft sent me the wrong too tight piston for my stage 6 kit so I want to be careful this time.

My concerns are this.  I have heard I should go aluminium instead of steel cylinder for cooling.  Do I need to ditch the oil pump feed and go premix, if so, what ratio?  Ideally I'd like to leave the pump in and add oil to the fuel tank as well.  Also jetting, where do I start with a main, I will have a 19mm Mikuni with a 70# main standard for the 50.  Any other concerns issues I should watch out for? As usual any help is appreciated!!!

Ill address the Alum.(plated) vs Iron Sleeved Cylinders.
The best thing for Iron is a Frying pan or the back yard grill. Iron holds heat, has horrible heat dissipation and thermal expansion property's. I try to avoid Iron if I can.
Aluminum Plated cylinders have superior heat dissipation and thermal expansion qualities over Iron bores.
Many have blamed a piston on a seizure but it was the Iron cylinder sleeve that expanded into the Piston causing the seizure.






I know the are both four smokers but one is plated and the other iron.


If ya want to go the pre-mix route thats cool Please use good quality mc synthetic oil. I'm not going to pick a ratio for you but you can go pretty darn lean upwards of 50:-1.
Please stay away from the no name two smoke outboard oil at the gas station.
An if you change ratio like Add More Oil, you have Leaned out you air fuel mix so be careful. More is Not better.

[czmdiver]

Mar 28, 2016 12:33:28 GMT -6 jct842 said:

Way better to ditch the pump for oil and add oil to fuel. The pump would be fine for a new stock engine, but once you get modifying you want to control exactly the oil you are lubing with. As an example if you depend on 1/2 the oil to come from pump what happens when the pump craps out? If you just add oil to fuel along with what the pump puts out now you will have smoke and spark plug fouling. 2 strokes have been run for a million years by lubing the fuel why change a good thing.

Ill tell ya exactly why.
The industry has lost complete faith the Joe scooter can properly mix his fuel to the correct ratio every time.
If you add Oil to the Fuel in addition to the Pump you will drastically Lean out the Engine and she will most likely Seize unless you Up-jet to compensate. Be careful!

[Alleyoop]

To much oil it will not even start.

[czmdiver]

Have your piston to cylinder clearance properly checked.
As the final assembler its your responsibility. know it and note it.

[Alleyoop]

No need to go through all that, these are not race engines that have to be precise and that get re-built after ever short run. All that is needed is not run them lean after installing them.
He just happened to be to eager and ran the sucker without a pipe and lean. Happens to many of them
because they did not come on a forum and ask some questions.

By the way CZMDIVER what are you riding put a picture of your ride we like to see what everyone is riding.
Alleyoop

[czmdiver]

Apr 4, 2016 20:00:43 GMT -6 Alleyoop said:

No need to go through all that, these are not race engines that have to be precise and that get re-built after ever short run. All that is needed is not run them lean after installing them.
He just happened to be to eager and ran the sucker without a pipe and lean. Happens to many of them
because they did not come on a forum and ask some questions.

By the way CZMDIVER what are you riding put a picture of your ride we like to see what everyone is riding.
Alleyoop

Oh I gotchya.   as the piston guy Im compelled to address the "too tight piston".
Wait. did we just agree?   just funnin






The Carolina fleet, Sunny 150, late model CBR1K, 986 Porsche, daily driver P-71 Interceptor.

My other toy. street strip 91 Silverado, long rod 385i mouse motor

[czmdiver]

[Alleyoop]

Just lack of lubrication is all no luby luby it goes

[czmdiver]

Apr 4, 2016 20:00:43 GMT -6 Alleyoop said:

No need to go through all that, these are not race engines that have to be precise and that get re-built after ever short run. All that is needed is not run them lean after installing them.
He just happened to be to eager and ran the sucker without a pipe and lean. Happens to many of them
because they did not come on a forum and ask some questions.

By the way CZMDIVER what are you riding put a picture of your ride we like to see what everyone is riding.
Alleyoop

ya know, I rethought this and I need to disagree, cuz thats what we do.  just funin don't ban me.
I'm finding Little if any of the current product usable out of the box.
Il point out a few things.
Here is the very popular 61mm No case Bore NCY cylinder on the left. Perfect Circle Off- Center. Junk.




Here is the popular 61mm NCY piston to with that cylinder, supposed to be clearance for a stroker, Oh ok, They Cut the Skirt off with a Cut off Saw instead of properly millling a scallop, Unreal, Unusable Junk.



Here is a proper skirt design properly clearance for this 2.2mm stroker.


Here is the High End Taida 61mm supposed forging. ok They Forgot to Drill the Pin oilers. Nice tuff snit no warranty no guarantee nada. The left put a machining process and tuff stuff

The Fake stuff.
Big Valve heads right? big sellers huh? ya they have big valves dumped in Stock Size Seats. Huh? how many bolt it on a go thinking theree high perf now?
I have actually had a good time and a laugh exposing this junk

i
Any scratching around with the ports would have been a wast of time. ( I won't call it porting).


This is good, NCY Ti Valve Springs, NCY's own label states this, yes a couple vendors have a correct description.
Since when is Ti magnetic?


Now I know this market segment just doesnt have the measurement equipment and experience, just irks me the Low prices and vendors and private labelers Know there selling unusable junk.
Here is a proper skirt design clearance for a stroker.

[Alleyoop]

BAN you for what, your Opinions!!!
Anyone can disagree with anyone, but you have to know your audience and not come on with over the top stuff that nobody gives a crap about. I am VERY MECHANICALLY INCLINDED and can go against the best, I can also spot a WANNABEE from a mile away.

I notice and know WHO GIVES GOOD ADVICE TO ACTUALLY HELP FIX A PROBLEM and who just puts out B.S because they really do not know. Sometimes I have to post to correct the bad info in a way that does not offend the poster of the bad advice and or bad info. I do that so the One looking for advice on what to do does not take the bad advice and info and make things worse.
To give good advice one needs to know each system and what each part in each system does to properly diagnose the problem. Also for each their are some tests that can be done to find the problem child and not waste their money buying parts that are not the problem.

Just so you are up with this stuff HUNDREDS and I mean hundreds if not thousands on here and ITSTHERIDE have bought and slapped in the BBKSt no special tools no measurements, just take the old crap off and slap in the BBKs. Button them up adjust for more fuel and away they go. Most are not very mechanically inclined and some IMO never had a screwdriver in their hands(HAHAHA).

So just remember when giving advice, they are on here because they just want to get their crap running and do not really care for any advice that requires special tools and or precise measurements. They are not racing on the track for big bucks and by the way they do not have big bucks. So advice given think cheap easy and fast.
Alleyoop

[czmdiver]

Apr 5, 2016 12:04:50 GMT -6 Alleyoop said:

BAN you for what, your Opinions!!!
Anyone can disagree with anyone, but you have to know your audience and not come on with over the top stuff that nobody gives a crap about. I am VERY MECHANICALLY INCLINDED and can go against the best, I can also spot a WANNABEE from a mile away.

I notice and know WHO GIVES GOOD ADVICE TO ACTUALLY HELP FIX A PROBLEM and who just puts out B.S because they really do not know. Sometimes I have to post to correct the bad info in a way that does not offend the poster of the bad advice and or bad info. I do that so the One looking for advice on what to do does not take the bad advice and info and make things worse.
To give good advice one needs to know each system and what each part in each system does to properly diagnose the problem. Also for each their are some tests that can be done to find the problem child and not waste their money buying parts that are not the problem.

Just so you are up with this stuff HUNDREDS and I mean hundreds if not thousands on here and ITSTHERIDE have bought and slapped in the BBKSt no special tools no measurements, just take the old crap off and slap in the BBKs. Button them up adjust for more fuel and away they go. Most are not very mechanically inclined and some IMO never had a screwdriver in their hands(HAHAHA).

So just remember when giving advice, they are on here because they just want to get their crap running and do not really care for any advice that requires special tools and or precise measurements. They are not racing on the track for big bucks and by the way they do not have big bucks. So advice given think cheap easy and fast.
Alleyoop

Il back peddle. I'm just busting your chops.
I did not disagree with you as if you do not know what your looking at, I know you are them Man over here with the Best illustrations and directions to help this market get there scoots going BAR NONE!
I am aware of your life long past of hot rodding and was it a Firebird you used to drag race? all cool
I agree I see horrible parroting advice given and they have a owner with no experience tearing his engine apart when all he needed to do was adjust the valves or had a vacuum leak to fix.
I am very aware with what type of market Im dealing with and there skill level.
Yes I have seen tons of these bbk builds and see many under-performing or far below expectations.
I suppose thats were i get a little over the top with some technical details to look at. they don't have to read it or care but maybe just learn something and take there next build to the next level. if not , fine its there scoot.
I can also spot a Phony a mile away, I hope we are not going down that road again of "Im a Snit Talker who Doesn't Know Snit" thats why I like to post Lots of Pictures. I can say I have a very good reputation in the Motorsports industry and would not have lasted as long as I have and worked with some of the best talking wannabe snit.
hers some Free HP. No fancy measurement equipment just a Dope scale from the local Head shop.HAHAHA
I think you know who I am or was anyhow.nhahaha