Dead Spot Pitpro 125cc

[Tonner]

Guys I've got a small problem I hoping you may be able to shed some light on. My son has a Pitpro XR125, Jailing engine I think, anyway since new the thing dies from idle if you screw the throttle wide open quickly, slow it down a bit and its ok. It has a china Mikuni on it but I have also tried a Molkt carby as well with exactly the same result. I also noticed if you hold it wide open it stutters a bit at full revs.
Runs sweet as midrange, will idle all day and as I said will rev fine from idle if your not to quick on the twist. I have tried leaning it up and also made it a bit richer to no avail, any advice would be appreciated.

 

[byh0005]

do you mean open the throttle quickly if so my bike does the same thing and i would like to know how to fix it and maybe jetting

 

[Tonner]

Yeah buddy, thats exactly what I mean, I have tried different carbies and still have the same problem with the motor stalling if you crank it open real quick.....I dont know that the full throttle splutter was on both carbs though it has only come into the picture since I fitted the Molkt carb today. This could be a jetting problem as it came off a 160cc, I cant find a number on the main jet but it has a larger hole than the Mikuni main which is a 95. The slide is heaps bigger, diameter wise, on the Molkt so I would like to get this carbs jetting right and use it from now on. ( much easier to tune with the mixture screw being accessable & hopefully better performance being larger )
Hopefully someone can tell me what size main jet as a starting point on the Molkt and shed some light on the other problem with the dead spot.

 

[byh0005]

i have had the same prob since new with the stock carb so if someone knows a solution please tell

 

[sean01]

ya cant expect to swap carbs from one bike to another and the settings be spot on...

play with the needle height in the slide and change the main jet if needed..

 

[Tonner]

Gday Sean, I realise I will need to play with the Molkt but I have the same problem with both carbs, that is the original Mikuni and the recently fitted (today) Molkt...thinking it may not be the carb. Also after a starting point with the Molkt as there is no number on the main jet. With the problems I have should I go richer or leaner on the main jet? Do the jets interchange from the Mikuni to the Molkt ?


Needle jets mainly affect low to midrange which is fine so I dont think the problem is here, Hence my questions

 

[byh0005]

they might just dont force them in

 

[thump*140]

tonner generally bogging when cracking the throttle is caused by slightly lean needle jetting, or a pilot that's too small...
You should have a #20 pilot, and 92main... try moving the needle to the first clip off the bottom, and see how that goes.. The Fakuni carby is reknowned for not liking being opened too quickly...

 

[sean01]

yep, take the opportunity to check ya valve clearances too

 

[Tonner]

Thanks Guys I'll give it a go next weekend, I have done the valve clearance already to try to reduce the possabilities....still a bit strange to have the same problem with two carbs I reckon but then again stranger things have happened. I will let you know what happens next weekend.

cheers

 

[DvDRip]

the molkt is a bigger carby so will be more likely to bog if you don't have good throttle control.... most bikes will bog off idle if you crack the throttle too fast

 

[Tonner]

Cheers for the advice.... any thoughts on the stuttering at full throttle with no load, I have replaced the plug and tried with it running rich and lean with no change ...... tried another CDI and coil...no change....maybe the correct jets will help I guess. Will a 92 main and 20 pilot also be a good start with the Molkt carb or is that only for the Mikuni? I am in Brissie so where is a good place to get the jets from to suit the two carbs I have ?

 

[Tonner]

Okay so I have fitted a 95 main jet (Mikuni jet fitted) mainly because I had one and re-tuned the carb, that has made the spluttering issues at full throttle virtually disappear so I have ordered a 92.5 main to fit as suggetsed by Thump140. I think with this size jet will be running sweet as.
I also moved the clip on the needle but with no change so I guessing I need to get the #20 pilot jet, problem is I cant find anyone who sells them. If anyone knows where to get them from or if a pilot from another carb thats easier to source jets for will fit please give me the heads up. I am going to muck about with the needle a bit more to see how much difference it actually makes.

 

[Tonner]

Changed the needle to a middle setting to see what would happen and just how much difference it made, ran like crap at idle and stalled midrange so I put it back on the bottom position. Bike idles nicely with good midrange response on the throttle. So based on this setting on the needle do I need a larger Pilot jet? The only issue I still have is bogging down if you crack the throttle to quick which I expect the correct Pilot Jet will fix. Cant tell what size it has now as I cant see a number on the damm thing, am I better off getting some jet drills and drilling out one size?
Any advice is welcome and would be appreciated, Im no expert by any means.

 

[sean01]

here ya go mate...mikuni jets
DHZ Mini Moto

 

[Tonner]

Thanks Sean 01 but I really need to find out about the pilot jet...are they the same for Mikuni and Molkt? If they are I can source them reasonably easily......I dont know maybe no-one knows

 

[thump*140]

well if you have a mikuni and a molkt side by side, pull the pilots out and check them.. if they're the same, you should be fine to swap and see..
failing that, post some pics of them up, someone might recognise them...

 

[DvDRip]

nope molkt n mikuni are different

 

[Tonner]

Thanks DvDRip think i'll just go back to the Mikuni and forget the Molkt

 

[Tonner]

Okay Guys heres what I am after, assuming the picture bit works ok, the jet on the left is what I require in a #20 and dont know where to get them from. I am in Brisbane but anywhere is Aus is fine.