pit bike 125 problems.

[locko90]

well managed to get it running sweet now, thanks for all the help my67xr

an there was a little bit of sand blocking the needle and seat hahaha was kinda satisfying to see that there was actually something in there causing it to overflow like that. easy fix

I have found that my little cut out water bottle ova the air filter helps make it run good, with out it it bogs and backfires.

I got the needle clip on the 2nd one down, mixture screw at about 1.7 turns out ( 1.5 turns and just a little bit more maybe a quarter more).

pilot jet is the old 15 (still yet to get the 20)
main is at 95.
and it runs awesome, its really got some torque down low rpm. 3rd gear accelerates really well its like surprising for a 125 haha.

next thing im going to do is check the valve clearance!

 

[locko90]

heres a pic of the little water bottle cover on air filter, makes it run better and also helps keep water off the air filter

 

[my67xr]

Good to hear it's all running better.
That cover for the air filter would be restricting the air flow a bit, it'd would be making it run a touch richer,
and making up for the pilot jet being too small, and no oil on the air filter

 

[locko90]

today I got the new #20 pilot jet and in installed it, carby mixture screw is at 1.5 turns out air filter hasn't got that plastic cover on it anymore and the needle clip is on the second one from the bottom.

It runs smoother at high rpm on and off throttle but it feels like it doesn't have the down low grunt it had before,
is this because ive tuned it back on the mixture screw and its not as rich as before?
would I be able to turn the mixture screw back to where I had it before and put the plastic cover back on to get that grunt back, cuz im seriously thinking about putting the 15 back in it was better, its pretty gutless now.

 

[my67xr]

Have you tuned the carby to suit the new pilot jet / lightly oiled foam filter ?

Warm the bike up, and let it idle, turn the idle speed screw in so it raises the revs about 500 rpm.
Now turn the mixture screw in till it start's to run rough.
Then turn it out till it reach's the highest/smoothest rpm
Turn it in about 1/8th of a turn.
Now Turn the idle speed screw back out till it idle's at a normal speed.

Take it for a test ride and see how it goes, it may need a touch more of a turn on the mixture screw to find it's sweet spot

 

[locko90]

I can't turn the mixture screw while running, the mixture screw is on the bottom of carb.
If its got less grunt then before would that mean that Its running more lean ? And turning the mixture screw out more will richen it ?

And yeah i got oil on the air filter now.

 

[my67xr]

Yeah, it's a Mikuni copy 22/26mm, i have worked on a lot of them
Do yourself a favour and find a small screwdriver bit like this on the left, i use a 4mm wide one
You can cut 6mm off the end if it need's a little more clearance too ( i had to do this for 1 bike i worked on)



now get some 5mm i/d tubing, like what's used for car windscreen washer tube, or clear stuff like this from bunning's etc

Cut a length about 150mm long and slide the screwdriver bit into the end (may need to warm the tube with a cig lighter)

This is the tool i use to adjust the mixture screw on china Mikuni copy carb's on pit bike's




I think it sound's like it's running a bit rich now, turning the mixture screw out will lean it off.
Also you said the needle clip is now on the second notch from the bottom in post #24 ?
Should be the second notch down from the top

 

[locko90]

Wow that is an awesome tool man that will make it so much easier dam ! I wish I thought of that. I have prob had that carb off 20 times and have gone bald in the process.
K well I'll get this tool made up and have a play around with it cheers for the post mate.

 

[china911]

with all this fine tuning don't dismiss the spark plug ... fresh plug and correct spark gap clearance does wonders

 

[locko90]

Yeah I've been meaning to get a decent spark plug keep putting it off. Prob should get a new racing cdi coil swell hey

 

[gottagetacheaperhobby]

Forget the racing cdis unless your running the tb one or better. More likely to give you problems than more power.

 

[my67xr]

Grab a new Ngk C7HSA (not the CR7HSA) from Repco, Burson's etc, usually cost under $5
Gap it to .7mm too


If you have a multimeter you could measure the resistance on your coil to check if it's ok too
Primary side should be around .7 Ohms measure with your meter set at 200 Ohms
Secondary side should be around 3000 - 5000 (3K- 5K) Ohms

To measure the primary side, put one lead from your meter to one terminal on the ignition coil, other lead from meter to the 2 terminal on the coil
If it only has 1 terminal then the second lead goes to the coil earth point

To measure the secondary side of the ignition coil, first unscrew and remove the spark plug cap off the end of the coil lead.
Set your meter to 20,000 Ohms (20k Ohms), put one lead the the positive terminal on the coil, other lead goes into the end of the coil lead to touch against the copper core.

To test the spark plug cap, use the same setting you used to check the secondary side of the coil
Put one lead into the spark plug side of the cap to touch against the clip that goes on the spark plug thread
And the other lead goes in the other end of the cap and touch it to the self tapping thread.
You should get a reading around 5ooo Ohms (5k Ohms)


If any of the measurement's are more than the reading's i mentioned, post them up here and i'll let you know what to do.

I have found these coil's to be pretty good-http://www.ebay.com.au/itm/Racing-Ignition-Coil-GY6-50-110-125-150-200-250cc-ATV-Trail-Dirt-Quad-Bike-BUGGY-/261302808644?pt=LH_DefaultDomain_15&hash=item3cd6dc7044
Or you could fit one of the NGK performace coil/leads- Racing NGK Ignition Coil Pack 110cc 125cc 150cc 250cc ATV PIT PRO Dirt Quad Bike | eBay
Or a Takegawa coil- Classic Honda 50's Australia

And these lead's really help to give your engine the best spark too, you can hear the difference - Performance Coil Spark Plug Lead CAP 50 110cc 125cc 250cc PIT Quad Dirt Bike ATV | eBay