rs125 hesitant on full throttle

[mraraju1]

hiya,

my rs125 seems to hesitate on full throttle and starts to kangaroo when the throttle is open full!! however if it is half open it seems to pull fine and all the way o red line pretty much, altho it struggles to get over bout 80 mph!!

anyhow had a look on the forum and found that it may be due to the carb being incorrectly set, so how do i check the jets?? where are the jets?? how do they look like??

my bike is derestricted, it also has the powervalve which is working!! and cleaned etc!!! my bikes a 2003 rs125 and it has the pollini card on it altho i dont know how many mm it is where do i check????

any help will be great

thx

raju

[Gazdaman]

Although this carb is different to yours, you'll get an idea.

https://www.gaz-racing.co.uk/bike/TZR/website/22-8-05/DSCI0173%20(Small).JPG

The hex headed bronze thing in the middle is the main jet, which unscrews, make sure that's not blocked.

And you see the orangey pipe next to the main jet, that just pulls out. And in the hole you unscrew the pilot jet, make sure that's not blocked aswell.

Although it sounds like you havn't got the bike in the powerband.

If you're trying to get a highly tuned 2t 125 to pull from little revs, then it won't like it.

You'll have to work the clutch a fair bit off the line.

Gaz

[mraraju1]

the bike is definatly in the powerband!! it happens at any revs!! i can rev it up to about 7-8k, and then if i open the throttle wide open it starts to kangarooooooo!!!!! and this can happen all the way to red line, however if i do the same at about half throttle its fine!!??

so what are the reeds??? or jets?? that get replaced?? you kno the pins??? not quite sure!! thx for the help thio ill b having a look sum time today!! i take it just clean it with sum WD40 or sumthin?? carb cleaner???

[mchaggis]

Need a decoke?
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[Gazdaman]

Sounds like a blocked main jet, as that's where the fuel will be coming from on full throttle.

Gaz

[Kickstart]

Hi

Not so sure it is the main jet being blocked. Possible but not likely it would still be flowing enough for half throttle. Personally I would suspect that someone has upjetted the carb and fitted a main jet far too large.

This thread gives more info on the Dellorto phbh carbs.

https://www.bikechatforums.com/viewtopic.php?t=17124

All the best

Keith
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[mraraju1]

wat size jets are required for the bike???

if it is either the 28mm carb or the larger 34mm one?? its a pollini carb, thx, i am goin to be stribbing the carb today so will see how it goes, also goin to check the spark plug and HT lead!

thx

[Kickstart]

Hi

For the 28mm carb is is around a 120 main jet, for the 34mm carb it is around a 150 main jet. Actual size varies with the exact model.

All the best

keith
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[mraraju1]

hiya,

took it all apart yesterday, and cleaned it all up. but feel like a bit of a spoon its a delorto carb and its got 28 on there so im guessing its a 28mm. anyhow there seemed to be 2 jets on there which sed 60 on one and 70 on the other one. there also was a large jet where the needle went through but i wasnt sure what it sed on that cus i couldnt find any numbers!

there also seems to be something not connected up to the carb, there is pipe missing on either side, i am not sure if it jus overspill stuff or what but im gna see what it today hopefullly!! thx

[Kickstart]

Hi

The main jet is mounted in the large brass bolt that also hold the float bowl in place.

All the best

Keith
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[mraraju1]

well i cleaned the carb, chenged the plug, but my bike is still doin the same thing!! its seriously doin my head in now, can anyone tell me the size of the the jets on the bike?? im jus gna replace the wholes jets, along with the needle, the bike is derestricted and has the delorto 28mm carb on it!! thx

[Kickstart]

Hi

Aprilia owners handbooks can be downloaded here:-

https://www.serviceaprilia.com/Index_f.htm

However I cannot see the main jet size listed in the latest versions of the manuals.

Check what size of main jet is currently fitted.

All the best

keith
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[Worden]

Hello! I'm new here...just thought I'd add that I have exactly the same problem on my RS125 which I've only had about 3 weeks. Mines a 2000. Perhaps it is an inherant problem?

The way you describe it is exactly how mine seems to be. If I accelerate slowly I can wind it up to redline, but if I accelerate slowly or averagely THEN pull harder (not necessarily full) on the throttle, the bike will chug and jerk around the 6500-7000 area, and will only get through this zone smoothly if I let go of the throttle slightly and accelerate smoothly past 7000, then it happily whips up the revs.

Must be someone that has had this problem, hopefully! Seems funny that both our problems are identical, suggests something related to the model rather then a coincidence problem in the carb or whatever....any more ideas?

Cheers!

Pete

[simon1221]

^ Either youve got a flat spot, or the carb settings are wrong, so it is flooding if you dont go flat out (or not ebough fuel) , so when you do it just dies.
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DNA50 (sorry) ->> TZR125l >> GPZ500S

[mchaggis]

Is there an accelerator pump on the carb? If there is, it's possible that it's dodgy?
____________________
I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.

[simon1221]

What is an accelerator pump?
____________________
DNA50 (sorry) ->> TZR125l >> GPZ500S

[Kickstart]

Hi

No they are not fitted with accelerator pump carbs (not seen a 2 stroke fitted with them to be honest).

If the problem is between 5000 and 6000 rpm then it probably needs the cdi unit mod.

All the best

Keith

PS - Accelerator pump is a bit in the carb where a piston operates on a small chamber of fuel so when you are opening the throttle it squirts the fuel into the inlet. Loads of sporty carbed cars use these, as do some bikes such as large Moto Guzzis.
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[mchaggis]

[mraraju1]

hi ya guys,

just thought i should say the problems is still not sorted!! even when the bike is in neutral and i open the throttle full, it only revs to about 7000rpm, and it just stops there, almost as if it hits the limiter!!!!

any ideas???

Also had a look at what the powervalve does, and it seems to shut again after about 5-6000rpm??? should it do this?? should it just open and stay open?? or should it open and close?? any help will be great thanks.

raju

[Kickstart]

Hi

No reason it should stop at 7000rpm really. Will it go past that point with, say, half throttle?

The power valve should be open up to 2500rpm, then closed from there to ~8000rpm (varies with the exact model of Aprilia 125) where it opens again. It just opens at low revs so that round town it gets opened regularly so it avoids sticking.

Could be that your rev counter is miles out.

All the best

Keith
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[mraraju1]

the revs are definatly correct because at half throttle i could get it to redline, but if i get it to redline at half throttle and then open the throttle wide open, the revs coms back down to about 7k!! arghhhhhhhhhhhhhhhhhh wats going on???? the powervalve seems to be working correctly then!!

if the main jet was to small for wide open throttle would this sympton occur?? cheers

raj

[Kickstart]

Hi

Could well be the main jet. Take it out (on the large brass bolt holding the float bowl on with the 28mm phbh carb) and check it. Also check the bolt it sits in to ensure that is clear. Clean them out with carb cleaner and compressed air. DO NOT stick anything down the jet to clean it out as most things will scratch it and damage it.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[mraraju1]

i have already cleaned it all out with carb cleaner, only thing to dois replace it with the correct size jet, if it is the wrong size that is!!
anyhow will let you know how it goes!!

[Kickstart]

What size is fitted now?

All the best

Keith
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[mraraju1]

not sure to be honest, but i have done some reading and researching and it should have a 150 jet on, does this sound right to you?? i am going to check the size tommorrow!! although feel this will be correct!! but will see!!

thanks

raju