[solg]

I could use some help.I an installing the 50s style exhaust system on a 2008 500cc Iron barrel with an ACE Air canister.Can some help me with  a good jetting starting  point. From past posts I am guessing a 127.5 main jet & a 27.5 pilot jet would get me started but, what about the needle jet & needle position?

[The Garbone]

What type of carb?   

[single]

That should be ok for low altitude.You will probly only need to set the needle at full rich or in the last notch toward the pointy end.Mine was too lean with the stock needle and needle jet,but could hardly detect it.So watch for that,do plug chops.It feels like you are playing with the throttle or the timing at a steady 50+ mph.But the exhaust note doesn't change noticeably.I was running a 130-30 combo.62 mpg.I don't know if it would have ever hurt the engine but I could not ignore it any longer and rather than fix it decided to switch to 34 Mikuni flat slide so I cannot tell you what the fix would've been.

[ace.cafe]

In many cases, you can get away with the 27.5/127.5 combo, and the needle all the way up.

If you have hiccup problems at smaller throttle openings during accceleration, then you need to get a richer needle jet like a P0 or P2.

Make sure that your intake manifild hose is not leaking air, and that you don't have any exhaust leak around your header pipe at the the head.

Do plug chops at a variety of throttle positions to make sure the plu looks okay.

The bike will run leaner in cold weather, so keep an eye on it if the temp drops.

[solg]

Thanks for the input fellas!I am running the stock VM28 Mikarb at aprox 600' above sea level . so I will try raising the needle all the way and take plug readings. Or would I be better off switching jet needles right off the bat? does the needle need to be changed as well?

[ace.cafe]

Thanks for the input fellas!I am running the stock VM28 Mikarb at aprox 600' above sea level . so I will try raising the needle all the way and take plug readings. Or would I be better off switching jet needles right off the bat? does the needle need to be changed as well?

The needle will usually work out fine in the richest slot.
It's the needle jet that might need changing if there is a 1/4-throttle-1/3-throttle hiccup.
Needle jets are only available at CMW because they are not interchangeable with any Mikuni needle jet.

[solg]

Alrighty then. I'll put her back together,taker for a ride, read the plug & watch for hiccups on acceleration at low throttle. Now I read recently the P 2 needle jet may be no longer available. will a P 4 work for my application?

[GreenMachine]

I have the exact setup that you have and what ace suggested with the stock needle all the way up/needle clip on the lowest setting. Ace: I get the 1/3 hipcup every now and then. If I let her warm a wee bit longer or take off gently and nurse it  bit it seems to be done and over it after about 1/8 to 1/4 miles down the road.  Its never been any real problem but I can assume if I do as you suggested then the occssional hipcup/carb thingee should evaporate.

[ace.cafe]

Alrighty then. I'll put her back together,taker for a ride, read the plug & watch for hiccups on acceleration at low throttle. Now I read recently the P 2 needle jet may be no longer available. will a P 4 work for my application?

Sol,
The P2 needle jet that is discontinued is for the Mikuni TM32 flatslide.

The P0, P2, and P4 needle jets for the 28mm Mikarb are all available at CMW, and they are specific to the Mikarb
Mikuni needle jets will not work in the Mikarb.
So, you can get any of the richer needle jets you might need from CMW. They are all available.

[ace.cafe]

I have the exact setup that you have and what ace suggested with the stock needle all the way up/needle clip on the lowest setting. Ace: I get the 1/3 hipcup every now and then. If I let her warm a wee bit longer or take off gently and nurse it  bit it seems to be done and over it after about 1/8 to 1/4 miles down the road.  Its never been any real problem but I can assume if I do as you suggested then the occssional hipcup/carb thingee should evaporate.

Green Machine,
The 1/3-throttle hiccup is definitely needle jet territory.
If it is a very mnor hiccup, and goes away after warm-up, it is probably ok.
However, it might get worse in cold weather, because the denser air causes the carb to run leaner.
You might try a P0 needle jet, and see how it goes for you.
If it's too rich in the summer with that, then just use the P0 needle jet for your winter jetting, and go back to the O8 needle jet for hot summer.
It's not unusual at all to need different jetting in winter and summer.

The needle jet is a critical jet, because it controls the mixture in the throttle range that is used the most in normal everyday type riding.

[GreenMachine]

ace u right on the money...i usually don't drive in cold weather but we do get a few good days in the winter...i'll probaby just order that p0 just to have it..cheers

[solg]

Ace, Mea Cula. I guessed that the post was refering to the flat slide mikuni right after I posted. Now, going by Green Machines info. if I were to start w a P 2 jet w. needle all the way up and found it too rich,i  could  just lower the needle no?

[ace.cafe]

Ace, Mea Cula. I guessed that the post was refering to the flat slide mikuni right after I posted. Now, going by Green Machines info. if I were to start w a P 2 jet w. needle all the way up and found it too rich,i  could  just lower the needle no?

Sol,
Probably.

[solg]

Ace ,what I meant to say was Mea Culpa .Cula is something else. I do feel more confidant though with the info I've just received to have a go at it.Thanks!  I just finished installing the exhaust. I used  copper high temp silicone on the pipe at the heads & rejetted the carb w a 127.5 main & a 27.5 pilot jet. I will raise the needle all the way and start with the stock needle jet until I see if the P-2 needle jet is needed. The weather was perfect today but I want to give the silicone overnite to cure.

[solg]

well, took the bike for a ride today.51deg.& sunny.It starts up just fine w the choke on but it wont idle for nothing till its good and warm.choke ,or no choke. Once warmed up it will idle, sort of. (still  dies at stop lights if they are too long)I have the Idle set about 1k rpm .I took it for a ride down I-88 speedo reads 80mph at full throttle. thats 10mph  faster than when stock. Did plug chops at ,1/3, 1/2 , 3/4 & full throttle. The plug reads a milk chocolate. I am happy with the plug readings but would feel better if I could get it to run better on the idle circuit. I went with a 27.5 pilot jet air screw is 2.5 turns out I am wondering if a 30 pilot jet will help. Now for a new development after getting the bike home I noticed oil leaking from between the head & the jug on the timing side.