View Full Version : The mighty backfiring saga (Well hopefully not a saga!)
quallman1234
19th May 2008, 18:21
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 :innocent:.
Would send it up to pete sales and cheat but im racing 125gp bikes this year so minimal money.
Any ideas appreciated.
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
19th May 2008, 22:04
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
19th May 2008, 22:11
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/Listing.aspx?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?
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.
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.
magneto still needs a trigger, either points or hall effect or whatever.
Don't worry points aren't that scary!
quallman1234
19th May 2008, 22:20
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
19th May 2008, 22:23
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?
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
19th May 2008, 22:26
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
19th May 2008, 22:32
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
19th May 2008, 22:39
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 :shutup:, 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 :).
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
20th May 2008, 10:26
One last thing - check that the zorst header fits snugly on the exhaust port spigot thingo (technical term).
Yeah its really odd system.
Um we went leaner than stock but also we had more fuel coming in the barrel with the bigger inlet port.
So youve got less fuel coming in and differnt chamber and itl be on the edge of running to lean
Str8 Jacket
20th May 2008, 15:30
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.
*ahem* we're not talking about my A100 are we?! I am gonna get around to looking at it. At the moment I am busy but I refuse not to be involved in the fixing up of the A. I think it may be the crank seal OR the carb. It could also be a multitude of other things but I would like to do it myself..... I'll let you know when I want to pull it apart again and you can come and help me/us out. Thanks for the offer of help though! :D
Anyway, back to your bucket prob Kyle!
F5 Dave
20th May 2008, 17:13
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.
Just a point, these suzi coil/cdi units are pretty susceptible, RG50 ones died often.
But backfiring is often wet/stuffed plug or timing way out. Have checked timing with TDC matches flywheel pointer?
quallman1234
20th May 2008, 17:33
But backfiring is often wet/stuffed plug or timing way out. Have checked timing with TDC matches flywheel pointer?
Funny you say that i think the plug was a bit wet.
Will try a new one next round.
Thanks for the help!. Don't have time at the moment (VMCC and Uni exams coming up!) to have a look at thing's will post up with an update next weekend sometime.
quallman1234
20th May 2008, 17:34
Nevermind going to the garage now will post up later with my finds etc.
quallman1234
20th May 2008, 17:59
Updated ===
Things found what i should of looked for before the weekend anyway (rushed)
-Spark Plug Cap, had electrical tape around it because half of one of the sides was missing. Result - Replaced with a NGK spark plug cap what looks good
-Took the plug out.
The plug looks very very gray! and is slightly wetish for a couple of threads.
looking at this http://www.skunkworks.net.nz/Spark_plug_reading/index.php (thanks skunk)
it appears to look like number 27 Woo! - Too hot or lean / pre ignition range.
also the plug was a B9ES (the colder type)
Going to whip the flywheel cover off and check the timing out now.
Just a thought.
The chamberrunning through there couldnt be evaporating fuerl once the carby etc got hot could it?
Skunk
20th May 2008, 18:17
Well, the advice here is helping me with my issue. Thanks F5 Dave and Ivan.
Which coil is the stator coil? There's two in mine one big and one small...
Well, the advice here is helping me with my issue. Thanks F5 Dave and Ivan.
Which coil is the stator coil? There's two in mine one big and one small...
Ok the one going directly to the igntion up to the coil should be black with Red stripe thats the wire you want and the coil you want but there will be another coil with wires that belonged for lights etc thatwont be hooked to anything thats the one you remove that coil.
quallman1234
20th May 2008, 18:23
Just a thought.
The chamberrunning through there couldnt be evaporating fuerl once the carby etc got hot could it?
Maybe, however the picture's a little misleading.
Update ==
Timing appears to be fine as ivan said he didn't touch it.
However i did find that the clutch push rod was bent
and
There were only two screws holding the flywheel cover on.
Mmmm maybe i should of done this when i got it. Oh well!
Maybe, however the picture's a little misleading.
Update ==
Timing appears to be fine as ivan said he didn't touch it.
However i did find that the clutch push rod was bent
and
There were only two screws holding the flywheel cover on.
Mmmm maybe i should of done this when i got it. Oh well!
So most likely a bit of jetting then.
Try a tad richer but if your saying plugs wet then thats a bit rich anyway.
Remember a slight tanned look is just right as youl learn on the 125's
But its odd your saying when it gets hot thatit plays up thats why I thought of the fact that fuel could start heating up to much from direct heat source around as the chamber would be getrting that area of the motor fairly hot.
Just try with going richer on the main jet
THen you can always adjust from there
Skunk
20th May 2008, 18:38
Ok the one going directly to the igntion up to the coil should be black with Red stripe thats the wire you want and the coil you want but there will be another coil with wires that belonged for lights etc thatwont be hooked to anything thats the one you remove that coil.
That would be the small coil then. That's the one I used...
Str8 Jacket
20th May 2008, 18:51
Well, the advice here is helping me with my issue. Thanks F5 Dave and Ivan.
Which coil is the stator coil? There's two in mine one big and one small...
Stator = Stationary.
Rotor = Turning.
As Ivan says two stator coils in yours.
Slingshot
20th May 2008, 19:26
Mmmm maybe i should of done this when i got it. Oh well!
It's fucked...give it to me :)
Skunk
20th May 2008, 19:33
Stator = Stationary.
Rotor = Turning.
As Ivan says two stator coils in yours.
Nah, Ivan saying one is lighting and the other is the ignition stator.
Nah, Ivan one is lighting and the other is the ignition stator.
Yip a lighting coil and a stator coil.
Lighting is not needed and is putting extra drag and weight on bike you dont need.
I know you know this SKunk its for any one else who is confused as to why you would bother.
They are both stator coils, one for lighting and battery and one for coil.
Doesn't really matter anyway, aslong as u get it sussed!
Updated ===
Things found what i should of looked for before the weekend anyway (rushed)
-Spark Plug Cap, had electrical tape around it because half of one of the sides was missing. Result - Replaced with a NGK spark plug cap what looks good
-Took the plug out.
The plug looks very very gray! and is slightly wetish for a couple of threads.
looking at this http://www.skunkworks.net.nz/Spark_plug_reading/index.php (thanks skunk)
it appears to look like number 27 Woo! - Too hot or lean / pre ignition range.
also the plug was a B9ES (the colder type)
Going to whip the flywheel cover off and check the timing out now.
Another important point!
The plug will look "lean" as you put it because it is running HOT!
Plug colour isn't just an indicator of mixture strength; it is basically a measure of HEAT, excess heat can be caused by lean mixture AND/OR incorrect timing.
Therefore you are correct and prudent to be checking both aswell as other things that could make it run hot such as air leaks after the carb or whatever.
quallman1234
21st May 2008, 14:41
Now where would i get different size jets from? Preferable in stock? Im going to start by riching it up by 2 - 3 jets. Also is there a way i can measure what jet is currently in there or do i need a special tool?
Thanks for ya help
Cheers
Kyle
Now where would i get different size jets from? Preferable in stock? Im going to start by riching it up by 2 - 3 jets. Also is there a way i can measure what jet is currently in there or do i need a special tool?
Thanks for ya help
Cheers
Kyle
Yeah man.
They numbered and youl soon tell thebigger the number the bigger the hole in it but sometimes it can be theother way round take it out either 6mm or8mm will do the trick go to TSS or what not and say can I get a jet richer than this grab a few while your there they only like 50 cents or something they aint much then youve got more to muck around with it
$11.50 from TSS (as new parts) a couple of weeks ago.
I think motomart have a decent selection in stock because they do dyno tuning and the like but I think if you go to the parts counter and ask for them they will order them in as new parts and thats why they cost alot. not sure on that.
I think there is someone selling them on atrdme for $5 each or so.
Your carb will probably be a mikuni (but may not be) but there are a few different types of those with different jets.
Remember there is more to it than just main jets aswell, they are only for full throttle operation.
Also remember they may be numbered as "130" but actually be drilled out to more like 150 or somthing.
Drilling is somthing that you can do to try it cheaper BUT ,in short, it ain't as good or accurate.
Pull the carb apart and see what the jets are like and write down all the numbers on them. I may have a few you can try to start with to get an idea where the jetting is at.
Remember if you are running premix on a bike intended for injection (yep!) the jetsize must go up aswell.
The jets will probably be causing it to run lean but still check the timing first and make sure that is all set to original spec so you are only dealing with one thing at a time.
Start reading... (http://www.sudco.com/mikunijets.html)
quallman1234
21st May 2008, 16:00
$11.50 from TSS (as new parts) a couple of weeks ago.
I think motomart have a decent selection in stock because they do dyno tuning and the like but I think if you go to the parts counter and ask for them they will order them in as new parts and thats why they cost alot. not sure on that.
I think there is someone selling them on atrdme for $5 each or so.
Your carb will probably be a mikuni (but may not be) but there are a few different types of those with different jets.
Remember there is more to it than just main jets aswell, they are only for full throttle operation.
Also remember they may be numbered as "130" but actually be drilled out to more like 150 or somthing.
Drilling is somthing that you can do to try it cheaper BUT ,in short, it ain't as good or accurate.
Pull the carb apart and see what the jets are like and write down all the numbers on them. I may have a few you can try to start with to get an idea where the jetting is at.
Remember if you are running premix on a bike intended for injection (yep!) the jetsize must go up aswell.
The jets will probably be causing it to run lean but still check the timing first and make sure that is all set to original spec so you are only dealing with one thing at a time.
Start reading... (http://www.sudco.com/mikunijets.html)
Cheers man. Im going to the take the carb down to motomart now. See what they can do for me. It only occurs at full throttle btw. Im just going to go wild and see if a couple jets higher will do the job. Problem a dump idea but they are cheap as.
quallman1234
21st May 2008, 17:05
Ok ive gone up 3 jets richer. That should be a good place to start from.
Ok ive gone up 3 jets richer. That should be a good place to start from.
Awesome.:niceone:
quallman1234
29th May 2008, 23:15
update, When skunk stole my stator we noticed that the clipy thingy slidy thing what u line up shit with (Forgot the name completely out of my head!) what keeps the fly wheel on straight and lined up, was just a piece of metal, will have to try find one.
That could lead to the timing being out....
Skunk
30th May 2008, 09:03
It had a thin piece of steel metal that wasn't big enough in it. WTF!? The timing was either out or moving all over the place I reckon because the flywheel wasn't tight either.
It had a thin piece of steel metal that wasn't big enough in it. WTF!? The timing was either out or moving all over the place I reckon because the flywheel wasn't tight either.
Damn! That is crazy shit!
I have a vivid imprint in my brain of a big backfire out of the carb, a shitty sheetmetal key would do that!
It does sound like the mainjet was woefully inadequate ASWELL as the timing being shockingly shit.
Should be a decent bike when it is sorted right.
quallman1234
30th May 2008, 11:57
My memory is back.
Wood Ruff key.
Slingshot
30th May 2008, 13:13
Schrodoco have a selection of them. You'll have to measure the width of the slot then take a guess at the height that you need.
Would be a good idea to lap the flywheel to the shaft with some valve grind paste too (that's an F5_Dave tip) as it's not the woodruff key that stops the flywheel spinning on the shaft, it's the taper of the shaft.
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