Wasted a day tuning a 48 HT

[Wildturkey]

I have always been lucky with my 70cc engine I guess. I spent the most part of today attempting to get a 48 to run well for a friend.

I have 2 here a Rock Solid with 1000kms and a leaking crank seal, and a Zbox that is about 1 hour old. As I have many carbys and plugs here I have been trying all combinations with no luck. I have tried jet swapping, mixture settings, swapped plugs and plug gaps. I just can't get these things to sing. The plug always reads OK but never any 2 stroke action, and never any bottom end power. At times I can get it to scream up high. Though I then turn around to go back home and it won't do it again? They start very easy and will idle.

The only thing I have not changed is the coil and plug leed? Could this be something to check out?

I am a mechanic by trade and can tweek most things. But these have me stumped?

Any clues????

 

[HeadSmess]

YEP GIVE UP

OOPS... capslock

i went fourstroke so the ht has been surplus...i tried starting it the other day...i say TRIED....

ill stick with my fourbangers now something about knowing theyll actually get you there and back...without carrying a full toolkit(usually!)

yeah, ok, doesnt help...

what can i say? can get one to scream one minute, the next your wondering why your pushing a motorised bike up a hill, when it doesnt have a flat tyre,nor is it out of fuel... conquer that hill, and it will haul up the next one, even steeper, without even slowing down... temperamental POS!

 

[Wildturkey]

They are great when they are running. I hammered my last 70 off road MX style for over 5000Ks rarely let me down. When it did it usually had something to do with me.

 

[motorpsycho]

check for an air leak at the carb, or at the intake tube.
try starting it with the choke on or your hand over the carb throat and see what happens.

 

[Wildturkey]

Tried all that Psyco. It idles well.????

 

[HeadSmess]

ok j, now its getting painful...

exhaust? what type? standard? saying they sing is like saying my dog has perfect pitch when it howls...i wish! get an expansion chamber could even just want a cleanout...

erm. leaks around the exhaust gasket can cause issues. youre rejetting, so id hope you know what youre doing (what? no computer? nope, cant service it!)


theres still one...two...three. three different mixture settings on these. jet size, needle size and position, and the slide bevel. all working together for ideal transition... oh, and the oil/fuel ratio plays a part!

anyways, getting in further... check crank seals, both sides...once they start going...bye bye! id peek at the engine that ran the longest...

oh. it is the one losing the crank seal...oops!

 

[Wildturkey]

Will do some more testing with a mate today.
A fresh set of eyes may do some good?

 

[motorpsycho]

Tried all that Psyco. It idles well.????

so did this help the problem or just make it stay the same?

 

[Wildturkey]

We rode allday instead of work on junk.

 

[Biker]

This worked for me,also the stock main jet was to big.
http://www.motoredbikes.com/showthread.php?p=286146#post286146