Unexplainable loss of mid range [Archive]

noobi

12th November 2009, 17:51

What reasonable explanations are there for a sudden loss of mid range power.
it started last Sunday when the bike wouldn't run properly, it was either throttle wide open or idle. nothing in between. just burbling, i changed the plug, same problem. i checked for blocked jets, same problem, i dropped all the fuel and rinsed tank and carb with meths to disprove water, same problem
. cleaned air filter, same problem. replaced fuel with different fuel/oil mix. same problem

the only thing i can think of is reeds, but i cant check them because the reed block is bolted is with a bolt with no head :blink:
the pipe is cracked but its been like that for a while and the loss of mid range is new

I'm going to get the pipe welded and the muffler re packed.

the jetting was fine last summer.

before you say oh its a gasgas, the carb is made by keihin, same as ktms :innocent:

klx kid

12th November 2009, 18:03

i had a similar problem.....i ended up taking the kill switch off and it went fine. so i put the kill switch back on and it started to fell my plugs and have no mid power. i ended up leaving it off my bike 4 a while and then i put a new coil and kill switch on and now im back at moto-cross going hard haha...:woohoo:

(oh and my bikes an 07 so its not like it had a hughe amount of use to burn out the coil or anything)

noobi

12th November 2009, 18:28

K6K

12th November 2009, 18:33

Is it loss of midrange or loss of mid throttle position? If it is throttle position it points to the needle jet fuel circut.

klx kid

12th November 2009, 18:37

did you unplug the switch and just connect the 2 wires together?

u mean the switch wire and the main 1 it connects to? if so yes but it had to be repositioned so that it would work.... it might not be grounding on ur bike either?????? that was part of the problem with mine...

cheese

12th November 2009, 18:41

It could be a stuck power valve, check its moving freely. Also check the reeds.

noobi

12th November 2009, 19:13

It could be a stuck power valve, check its moving freely. Also check the reeds.

checked the pv, it moves freely, but also found that there is watery oil splashed up onto the pv cover. so i dropped the g box oil and its just like new, which it is, less than 1 hour old. :blink: i have no idea how to check the reeds as one of the bolts has not head to undo :blink::blink:

K6K, im not sure which it is, as the bike wont run on either.
i checked the carb, cleaner the pilot jet, which did have some crud in it. but it still wont run properly.

noobi

12th November 2009, 20:20

Also check the reeds.

checked the reeds, still carbon fibre and mint. a little bit of scuffing on the top reed but otherwise seal well and un chipped

very quickly running out of things it could be :crybaby:

vazza

12th November 2009, 20:26

GG's aye.. Cant trust 'em :P

flyingcr250

12th November 2009, 20:34

GG's aye.. Cant trust 'em :P

ha ha i didnt want to be the first one to say that lol:sweatdrop

rossrc

12th November 2009, 20:37

I had the same thing happen to me with a KTM 300, but that time it was the PV - screw came loose so the mechanism wasn't engaging. Can you run it with the covers off and see it's actually moving?

noobi

12th November 2009, 20:37

GG's aye.. Cant trust 'em :P

your electric start broken yet?

vazza

12th November 2009, 20:38

Nah mate its working 100% sweet. I love e-start. Was riding up a tree and I stalled, lucky I had the e-starter!

:sweatdrop

noobi

12th November 2009, 20:41

I had the same thing happen to me with a KTM 300, but that time it was the PV - screw came loose so the mechanism wasn't engaging. Can you run it with the covers off and see it's actually moving?

i took the l/h side cover off and watched the pv open and close when the engine was revved. i think its a jetting problem as the bike runs fine at idle and just above idle and it will run WOT as long as its revving like crazy.

although i already cleaned the pilot jet out. time to strip it down i guess.

rossrc

12th November 2009, 20:41

one other thought - if the ignition doesn't advance properly, I think it would give a similar issue... afraid I don't know how to check that though

noobi

12th November 2009, 20:45

one other thought - if the ignition doesn't advance properly, I think it would give a similar issue... afraid I don't know how to check that though

i guess with a timing light, but i have no idea where it should be firing at. just before TDC would be my best guess...:sweatdrop

koba

12th November 2009, 20:51

If it has a battery make sure it is all good.
Also check air filter and exhaust and make sure the are clean and functional.

cheese

12th November 2009, 20:58

Hmm is your crank seal leaking? is it really smokey?

L Rider

12th November 2009, 21:06

Hmm is your crank seal leaking? is it really smokey?

When my crankseal went i had no power, mind you mine came right out & had oil pissing out

noobi

12th November 2009, 21:20

Hmm is your crank seal leaking? is it really smokey?

doesnt have a battery, exhaust is pretty sad, ill sort that out. but wouldnt think it would make as much of a dramatic difference as the problem is.

doesnt seem to be excessively smokey, ill pay more attention to it tomorrow though. i pulled the flywheel cover off and there was no oil in there, but again i could check it again. not sure how to check the crank seal

tommorth

12th November 2009, 23:16

possibly the best way to check your crank seal leakdown tester
http://www.kawasakimotorcycle.org/forum/kawasaki-motocross-offroad/104809-make-leak-down-tester-about-20-a.html

split manifold or leaking base gasket maybe?

krad_nz

13th November 2009, 00:17

You don't have an inline fuel filter do you? Running out of things to suggest.

Pay to do a quick compression test.

t3mp0r4ry nzr

13th November 2009, 07:22

Have you changed to summer jetting yet?
is the mid throttle area too rich or too lean? its been humid of late, possible running it rich. do you just need to raise the needle clip one position to lower the needle?

edit: on reread of your post, you say it "burbles" in mid range - too rich? if it bogs, its lean. if it is indeed too rich and you have no other obvious causes, try raising the clip one position.

noobi

13th November 2009, 16:40

Stripped the carb completely and soaked the body in terps for an hour. Rfitted everything, same problem.

Got the cracks in the exhaust welded, same problem.

Checked the reeds, they don't seem to be sealing particularly well, some of them are letting light in when i look through the reed block. that could be it
but id have thought that reeds would effect the bike everywhere in the rev
and throttle range.

Its not smokey.

I cut the wires to the kill switch no difference.

I'm now more than ever thinking its an electrical problem, although it may be i dont know how to clean carbs properly. but the jets are definitely not blocked, so maybe a blocked carb passage or something

:crybaby:

tommorth

13th November 2009, 16:51

bike with stuffed reeds may still go fine up top as the reeds barely close at high rpms good luck with the hunt

camchain

13th November 2009, 16:54

noobi

13th November 2009, 17:17

Been pondering your prob today. Would the old fulla's carb fit on yours for a quick try? (36mm)

Just checked the EXC125/200/250 jetting chart, all 36mm carbs on ktms. Jet size not much diff, main diff is needle so swap your needle into 250 carb for a quick try.

that might work, if dad lets me pull his 20 hour old carb to bits....
just put my jets and neddle into that carb.
i think the gasser 125 uses a 35mm carb though, worth a try i guess

if the reeds were the problem id expect them to be problematique everywhere and not just in the middle. id expect idle to be super rich

:crybaby:

camchain

13th November 2009, 18:10

Mmmm, if yours a 35mm carb, may not be worth trying to jam a 36mm onto your intake and risk an air leak/seize during test fanging up the road. 1mm diff not much though and outer part of carb possibly the same, just bore size different? Check with a vernier while it's on bike before taking carb off. It might easily let you rule out any carb prob if you can try it.

I reckon you're correct with reeds, worn petals would likely be rough running off the bottom and fine in the middle revs & up. Mine don't seat closed perfectly.

Pinch that nice 20 hour old coil and try that? Pull all the connectors on your main wires and check for dirt/corrosion. Soldered joints can look fine but still be dodgy, sweat them up again with soldering iron to be sure. Clean the earth connections up on frame as well. Don't quote me but I've heard ECUs can test OK but still be a problem.

Was thinking the same as cheese as well, maybe have another good look at that power valve. A power valve malfunction would probably have a big effect on a 125. Sounds like it's moving OK though.

Hope you can sort it for Sunday.

cheese

13th November 2009, 18:39

Burn it. ...........

noobi

13th November 2009, 18:44

at the moment im getting very good at pulling the carb off the bike...

i wouldnt be very popular if i started pulling the ktm apart to sort out the gasgas, i did ask, the answer was no :blink:

ill have a good look at all the connections i can find.

i watched the pv open and close. but i guess i could actuate it my hand and look in the exhaust port to see if they both open. otherwise i have to pull the barrel off to actually get at the moving parts.

if its not sorted iv got a back up bike jacked up from a good mate

noobi

13th November 2009, 19:43

Burn it. ...........

nah, its sweet now

flyingcr250

13th November 2009, 19:48

nah, its sweet now

still burn it...........

howd you sort it?

noobi

13th November 2009, 19:51

still burn it...........

howd you sort it?

burnt it.....

nah, cleaned some electrical connections and tightened one up. still managed to find a wire that doesnt go anywhere???

flyingcr250

13th November 2009, 19:53

burnt it.....

nah, cleaned some electrical connections and tightened one up. still managed to find a wire that doesnt go anywhere???

its always the simplest fix:yes:

xen

13th November 2009, 19:55

burnt it.....

nah, cleaned some electrical connections and tightened one up. still managed to find a wire that doesnt go anywhere???

good shit, not for a headlight?

Rupe

13th November 2009, 19:55

burnt it.....

nah, cleaned some electrical connections and tightened one up. still managed to find a wire that doesnt go anywhere???

Good on you for working it out yourselves, go enjoy.

noobi

13th November 2009, 20:00

good shit, not for a headlight?

nah it comes out of something next to the stator. meh

Good on you for working it out yourselves, go enjoy.

thanks. the next thing was to start taking parts to a shop.

cheese

13th November 2009, 20:16

Pull of the flywheel and check the coil packs, there normally is two of them. My IT175 had a high rev problem that was related to one of the coil packs. Also check all the wires running to the CDI.

its weird that its only mid revs....

rossrc

14th November 2009, 07:24

nah, cleaned some electrical connections and tightened one up. still managed to find a wire that doesnt go anywhere???

Is it a yellow one that stops around the airbox? That's for the tacho and isn't connected as standard