The mighty backfiring saga (Well hopefully not a saga!)

[quallman1234]

The engine is an AX100 btw.

Well i had some problem's with my old bucket of shit on the weekend. Managed to fix most of them including making a better mount for the tank (well kinda) with the help from koba and the currie brother's.

However the engine seems to be running like crap, it handles mildly ok, however with no feel. I want more power!

Now the symptons are

Backfiringness?! On a 2 stroke, well that isn't good.
It seems that it runs OK at the start of the race.
Please note i have done these thing's recently.

Since ivan had i did a pistion in it 0.5 OS, New chamber what is a wee bit more suited too it, but no where near perfect.
Bought a Stock Head and Barrel (Stock porting etc) for 30$ to suit the pistion instead of reboring and still having the questionable porting on it.

Now i have a feeling its the main jet size as ivan set it up for god know's what?
Anyone got any idea's? I need more power, once its sorted ill jump in to the back off the A group just to be fair .

Would send it up to pete sales and cheat but im racing 125gp bikes this year so minimal money.

Any ideas appreciated.

[koba]

Any ideas

How does the timing work?
Points magneto?
Find out how it should be and make sure it is all set up correctly.

It was backfiring out the carb when you pulled over in the 2nd point race (thanks for that BTW, another 2nd for me!)

A proper fuel tank is a must because if that is causing fuel starvation or somthing from the tiny line and size it may confuse the issue.

[Slingshot]

From what I gather, 2-strokes shouldn't backfire...unless the timing is out.

I'd check that the flywheel is tight and the the woodruff key is still in place.

[quallman1234]

How does the timing work?
Points magneto?
Find out how it should be and make sure it is all set up correctly.

It was backfiring out the carb when you pulled over in the 2nd point race (thanks for that BTW, another 2nd for me!)

A proper fuel tank is a must because if that is causing fuel starvation or somthing from the tiny line and size it may confuse the issue.

The fuel line wasnt that tiny, it was actually too big for it and had to use make shift hose clamps (Zip ties just like everything else) too prevent it from leaking. However the line was super long.

Going to buy one of these and building a bracket for it above the chamber (in the tank cover)
http://www.trademe.co.nz/Browse/List...x?id=156066340
if its got enough clearance.
Will check the flywheels in place etc, Luckily ive just rebuilt my RG150 (Bottom end) twice so i know some stuff down there, can't be much different now can it?

Also note that when it finally happens happens like before it completely shits itself, it still works ok down low. I ended up trying to save the engine from shitting it self in the later race's by short shifting a bit.

Thanks for the help keep it coming! will keep ya updated.

Good news quick search tells me its got a magento etc instead of points (So much easier!). Confirm andrew?

[koba]

Nice!

Do check the main jet then but Timing is suspect at the mo.

The electrical side is almost the same but will probably have points. They need to be set to the right gap aswell as clean and flat. Skunk will know more about the AX so he should know the right gap an correct timing setting. (easier than trail and error!) If you get stuck give me a yell.
Even If it aint causing the problem directly it is worth checking coz they do need adjustment every now and then for best performance.

[Ivan]

Just to confirm we wnet through this at tech these are cdi ignition with the CDI being located inside the coil.

Down there in the bottom end there will onlybe the stator coil the lighting coil has been removed to take less drag off the flywheel.

I havent altered ingition timing at all but it may be out I had that beast up to 110kph lol being chassed by my mate in his Galant lol

Also check the earths are fully clean and that it isnt being caused you to poor earthing or bad contacts.

Also you say youve changed the expansion chamber and head since I had it jetted which will alter the jetting again a differnt pipe will require differnt jet but also the difference in head compressions will need altering.

[koba]

magneto still needs a trigger, either points or hall effect or whatever.
Don't worry points aren't that scary!

[quallman1234]

Nice!

Do check the main jet then but Timing is suspect at the mo.

The electrical side is almost the same but will probably have points. They need to be set to the right gap aswell as clean and flat. Skunk will know more about the AX so he should know the right gap an correct timing setting. (easier than trail and error!) If you get stuck give me a yell.
Even If it aint causing the problem directly it is worth checking coz they do need adjustment every now and then for best performance.

Sweet as, ill check the plug, even tho it was yesterday. I wouldn't be surprised if its the jetting. If it is ill probably just go a few jet's richer than standard as it has a slightly more chunky chamber instead of a straight pipe like stock.

Haha, im a bit redulcant about points! Something to do with watching you struggle for a couple hours!

[quallman1234]

Just to confirm we wnet through this at tech these are cdi ignition with the CDI being located inside the coil.

Down there in the bottom end there will onlybe the stator coil the lighting coil has been removed to take less drag off the flywheel.

I havent altered ingition timing at all but it may be out I had that beast up to 110kph lol being chassed by my mate in his Galant lol

Also check the earths are fully clean and that it isnt being caused you to poor earthing or bad contacts.

Also you say youve changed the expansion chamber and head since I had it jetted which will alter the jetting again a differnt pipe will require differnt jet but also the difference in head compressions will need altering.

Thanks for that ivan. Clears that up! I thought they were cdi's (Ohhh Futureistic!). Ill clean / crc all the contacts (There's not that many at all so thats easy).

Its stock standard with reference to porting. I bought a barrel and head for 30$

Do you remeber what way you jetted it verus stock? Richer leaner?

[koba]

Haha, im a bit redulcant about points! Something to do with watching you struggle for a couple hours!

Still havn't worked out what is up with that thing!

Dont think it is the points tho...

[quallman1234]

Still havn't worked out what is up with that thing!

Dont think it is the points tho...

My money's on the crank seals have given in. Easy fix. just means you gotta spilt the cases. If your in the mood for it one weekend give me a yell ill give you a hand.
Maybe a full looking over is the best way to isolate the problem in that case.

[Slingshot]

it still works ok down low.

Main jet might be blocked/too small.

or

Could be your float bowls aren't filling with fuel quick enough.

Wouldn't cause it to do a proper backfire...but might blow a little back out the carb as it's stalling.

[quallman1234]

Main jet might be blocked/too small.

or

Could be your float bowls aren't filling with fuel quick enough.

Wouldn't cause it to do a proper backfire...but might blow a little back out the carb as it's stalling.

Sounds like a possibility as i wasn't quite sure if i had a breather in my "tank"/the fuel line was long. and it only happened after running the bike for a while. The bike ran "fine" at the beginning of the race's as the B group found out , and then after it kinda felt like it was running out of petrol. would run ok at low rpm's however it would die when i tried opening the throttle like it was starving.
It only "backfired" once or twice one was quite loud.

Sounds good! Ill check everything as well however .

[koba]

That scooterparts tank looks just the ticket for balancing carbs and the like, much better than an old milk bottle!
You have also made me think about using a small tank and plastic cover like the Aprilia when I finally get around to making mine, I could use the NSR tank to make a fibreglass fake cover.

[vifferman]

One last thing - check that the zorst header fits snugly on the exhaust port spigot thingo (technical term).