big one and rejet

[Benman]

Am goint to be putting a big one ( fresco) full exhaust system on my MTX 125 later this week and was hoping for some advice. Will it be likely that i will have to rejet the carb?? has anyone else done this and if so what size jet would i need?? Am quite new to this so all help would be appreciated : I have currently got the silencer on and really strong smell of fuel all the time now.
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Ben1972

[Matt-]

Yes any 2 Stroke will need the jet's looking at if the Air Intake / Exhaust has been changed. Check your standard Main Jet then get a couple of jet's which are slightly bigger, so for a example: 138 Main Jet as standard, you would want to get jet's 140 & 142.

When Re - Jetting start rich and work downwards starting lean can be very dangerous for 2 stroke machines.

Good Luck

Matty
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RIP jack (wheelie king), you will never be forgotten.
Current Bike's - Road Legal TZR 125 Pitbike, Aprilia SR50R 2010

[P.addy]

If stock jet was 140, I'd be looking at 148 jet to start with.

See what the bike is like at that.

Bearing in mind an SR50 stock is 53 main jet, you can go to a 63/65 for an exhaust and matched rollers. Best to run it slightly richer during the trial period eh

[Benman]

Ok so I have found out that the standard jet is 112 so what is going to be the best size to try???
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Ben1972

[P.addy]

[Benman]

Got a couple of new jets. Apparently rule thumb is extra ten percent from standard. So got 120 and 122.5. Should be gettin it done tomorrow so will let ya know how I get on. Should mixing screw be set to factory setting before I start??
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Ben1972

[temeluchus]

Are they Keihin, Mikuni, Dellorto or Amal jets?
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Some shite cruiser. Now with guns and FREEDOM!

[Benman]

Keihin
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Ben1972

[temeluchus]

[Benman]

Will do mate. Cheers for the advice. How will I know when it is running "PERFECT" as you say. Don't have access to a synonym at anything like that.
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Ben1972

[temeluchus]

There are a few things to try out

In this order

Try full power in a mid gear, it should go to the redline cleanly without stuttering or stopping. This is an indication the mainjet is in the right ballpark.

roll on the throttle open at lower RPM in a high gear-if the bike stutters or the motor bogs down you will need to look at adjusting the needle.

If it is difficult to start, takes an age to warm up and stalls a lot at idle (at the lights say) the idle mixture can be made a bit richer.
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Some shite cruiser. Now with guns and FREEDOM!

[Benman]

Cool. Thank you. Will post after I have done it.
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Ben1972

[Benman]

Hey guys. So I put the big one silencer on couple of days ago. Haven't had time to put the pipe on yet as I am having problems getting the nuts to move and I've already sheeted one stud. Will get to it at the weekend. Any way. I have noticed that my bike now reeks of petrol all the time. I have checked all the pipes and there are no leeks. There is however lots of unspent fuel around the exhaust tip. What gives???
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Ben1972

[P.addy]

Bet your spark plug is blacker than your average board marker.

Running rich?

[Benman]

There is plenty of blue smoke and it does this weird thing when I start it from cold when I have to use the choke. It starts pretty easy but then the revs slowly increase yet when I give it any revs it dies. I have to let it run like that for a while before I can go anywhere. Then I have to take the whole off when I move or it stalls on me. Why has it done this. I only changed the silencer. Yet to put the expansion chamber on. The wadding in the silencer is filthy too but saying that its not a new system. Think it's a couple of years old.
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Ben1972

[P.addy]

Pull your spark plug out... what colour is it.

[Benman]

Greyish brown Not too bad
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Ben1972

[Pol Anorl]

[Benman]

Pic quality is shit. Cause of file limits. Is dry and dark. So?? Is it just a case of running rich because of changing silencer. Should I repackage with new wadding and back off half a turn on the mixture screw ? Didn't think changing that end of the system would make any difference. Have got a 120 and a 122.5 jet for when the other end goes on. Which one do you think?? Guy at shop said the bigger one cause when changing exhaust from a standard system to a sports you go up about ten percent. Sound right???
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Ben1972

[P.addy]

Perhaps you are running rich... or perhaps you have left it on choke for too long.

Give it a clean with a wire brush and warm the bike up, get it revving to help clear the guff!

[Benman]

Def not choke issue cause it won't run for more than a minute or it stalls and can't start moving without it. Have to be quick getting away and then take the choke off after bout ten feet or it dies. The more I think about it the more the running rich makes sense. Gonna drop it a quarter of a turn and see what that does. Just got to finish putting her back together. Been looking for leaks. Cause she reeks of fuel.
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Ben1972

[Benman]

Well I couldn't find any obvious leeks and I checked all connections to do with fuel and the carb was clean too. The plug was dry and according to the Haynes it means too much fuel in the mixture. So gonna reset the mix to factory settings ie; 1 1/4 turns from seated. Then get her running to warm temp and see where I am. The exhaust is blowing a bit and there is lots of popping when I let off the revs and what I can gather from the other threads about mixture this is also a sign of running too rich. Although I think I might just be hearing that more because the original pipe is blowing where the stud sheered off so don't know if that could be adding to the problem as well. Gonna clean the plug up and take her for a quick high rev ride as recommended once the kids are in bed. Lol
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Ben1972