need expert carb tuning advice

[wanta86r]

I just put the top end of my 86 r back together today. It has a 67mm wiesco piston, esr porting, shaved head, rad valve, esr atc 5 pipe and a pj 36mm carb. Right now I have a 48 slow jet, and a 168 main. The carb is clean, and apears to be in good condition. The needle is in the middle position. and i have the air screw about 2 1/2 turns out. It starts in a kick or two , and i can get it to idle a little, but it seems to stutter in the higher rpm range. I have only starded to break it in, but have no idea where to go with the jetting. I live in mn-

[oddball3]

First break the new topend in, and then do plug readings.

[X2guy]

Try changing your plug. It could be fouled from running the engine slow for break in.

[Yamahondaman]

is it the OVAL or PWK Keihin or Mic. ?..The 250-r's Like the 39 mm PWK the BEST !! With the 55 Pilot,CEG Needle and a 175-182 Main...ESR Has them for 199.00 i Think ? or you can call SUDCO @ 1-800-998-3529.. They are good with Carb's !

[wanta86r]

anyone else have any ideas for me?

[OldSchoolin86]

If your just breaking it in the last thing you want is to be lean. Fatten up that main and then worry about bring it down when you got it broke in.

[wanta86r]

how long should the break in be, and how should i break it it?

[oddball3]

about 1 tank of fuel

[Mr. Sandman]

You'll get 20 different answers on how to properly break in a new top end. Some guys will ride it WOT as soon as they start it and if you've got an unlimited budget and like to rebuild top ends, that's fine.

The most common way is to just cruise it at 1/2 to 3/4 throttle and vary the RPM's and speed while riding. Don't ride for a long period of time at one speed and don't go wide open for any length of time. Once you have an hour or two on the motor let it cool down for a few hours or overnight, re-torque the head and then do a few plug chops with new spark plugs and jet from there.

[wanta86r]

i need to know more about what jets do what, and what the air scew adjustment affects

[MTS]

If your just breaking it in the last thing you want is to be lean. Fatten up that main and then worry about bring it down when you got it broke in.
i have to agree, fatten up your jets quite a bit till you get it broken in or you could be redoing your top end very soon

[TimSr]

"Breaking in" a top end just means the rings rub the cylinder walls until it makes a good flat contact fit. Wiseco used to include their break-in instruction with their pistons. This is what an old Wiseco instruction brochure says about a new 2 stroke top end:

1. Use the same gas/oil mix during break-in as you normally use. (Oil injected models ad 2oz. of oil per gallon in first tank of fuel.)
2. Allow 15-30 minutes for break-in of new piston and/or rings at varied rpm's.
3. Allow engine to cool down, re-torque cylinder head to factory specifications.

I happen to agree with Wiseco. Its okay and recommended that you give periodic revs, just dont hold it open. It should take no more than 30 miuntes tops. If you dont trust Wiseco and want to run a couple tanks of gas, about 7 hours on my machine, to make you feel good, go for it. I dont think youre doing your 2 stroke any good deed by putt-putting it around for hours at a time.
As for jetting, I wouldnt touch anything right now unless your plug is indicating a lean condition. You should probably run it for for 20 or 30 minutes before doing controlled plug tests as your readings may change, (plugs may look richer before rings have seated) but in the meantime, just keep pulling your plug to monitor the situation. Ride it a couple minutes, pull the plug, check it, put it back in and ride some more. Repeat. If conditions are dangerous, it will be obvious by the plug. You can always jet richer to be safe, but I just watch the plug. Then start doing plug readings with clean plugs after the rings have seated. Dont do any hammering on it until youve got a couple good top end valid plug readings.

[Wickedfinger]

i need to know more about what jets do what, and what the air scew adjustment affectsThis'll help you understand a bit better I hope ............

[OldSchoolin86]

TimSr: that's awsome, those instructions are perfect.

Wickedfinger: That chart is gold. I was looking for that the other day to show my nieghbor. One question though, should the main have a longer taper past the mid going into the 1/4 area?

[Wickedfinger]

TimSr: that's awsome, those instructions are perfect.

Wickedfinger: That chart is gold. I was looking for that the other day to show my nieghbor. One question though, should the main have a longer taper past the mid going into the 1/4 area?
Nope, the main only has its effect on carburation from 5/8 - WOT. In theory, the main jet is flowing fuel from 1/8 throttle on - however - in explaining tuning - the size, clip position, actual length and taper of the needle all are controllable tuning components of the carb and they are all critical in controlling the mid range by metering the flow of fuel through the main jet.

[OldSchoolin86]

Ahhh, that's what I thought but I remember someone else said it effected all the way from 1/8. Cool Cool

[wanta86r]

i have it broke in now i believe. I got best results jetting so far with a 58 pilot, 172 main, and the clip in the middle position. I had really good idle, good throttle response, but sputtered on the mid to top. I then changed the main with a 170. now it wont idle or really run at all. i am totally lost now, because i thought i had at least the idle and throttle response good, but its worse off now than its ever been. any advice or explanations would be great. where should i go from here

[Wickedfinger]

I would go back to the 172 main and see if that was really the cause .... I think something got knocked off kilter when you twisted the carb to do the jet change.