Alternative pilot jet for uncorked stock carbs.

[edfmaniac]

Just in case anyone else is having a hard time getting the Teikei #50 pilot jet for their 660, I found an alternative Mikuni jet that is readily available. The VM28/486 #40 screwed right in and made my Skorpion the happiest it's been since I've owned it. I can't believe I've been driving that thing around for about 8500 miles now with a sluggish low end and popping overruns. Why the #40 Mikuni runs richer than the #48 Teikei I have no idea. Maybe it has something to do with the slight difference in design but it works great for me and can be ordered or purchased at almost any cycle service center in the US. My local Yamaha dealer had one in stock. It cost me $40 worth of gas in the old Econoline to find the damn thing but at least my bike runs again.

Don't attempt to drill out the stock #48 unless you know exactly which size bit to use and/or already have a backup plan. I guessed wrong.

Here's a pic of the Mikuni. It's much longer and not as fat above the threads but works like a champ for me.

[Berniecal]

Nice work! I, too, was driven nuts by the erratic snatchy behaviour at low rpms, and reamed the pilot jet with a needle. That, and one notch up on the primary needle, transformed the low end behaviour. I now have the skorpion 3 years and expect to keep it for many more.

[den]

hi , can i jump on this thread,
what do you mean "uncorked" (derestricted maybe)How? , please tell
and what you say about curing the ride,My baggys stock untouched and rides like a dog below 50 kph,Its like trying to hold back a snarling rotweiller.Tiering to ride in town sometimes , If you look at my gallery photos you'll see i changed the exhaust which made a difference but still doesn't like low end speeds ,
Would you kindly post me a rundown of your setup so i could copy it to see if it cures mine
Many thanks

[edfmaniac]

Yes, by uncorked, I mean the snorkel is removed, K&N air filter element installed in stock frame, header welds ground down and Pro Circuit exhaust as well as the other usual stuff. Without taking the carbs apart, I can't confirm what main jets I'm running or the needle settings but I'm pretty sure it's what is most recommended here on the forums. Just pop that pilot jet in and give it a try. Remember what Bill always preaches too. Don't try to lug this engine around like an XR650. Keep the revs above 3000 unless you are pulling away from a stop, especially in higher gears.

The main difference that I noticed was getting the bike rolling. Instead of having to worry about the bike snatching and dying, it just pulls very smoothly until you get the rpms up high enough to give it the juice. I'm also running the primary carb only for about the first 1/8 of the throttle range(about 3 or 4 turns out on the adj. screw) and try not to open the secondary until I'm above 3000rpms.

A good test to see if you are getting the proper amount of torque is to get on flat ground with a nice solid idle. Put the bike in gear and slowly let out on the clutch without touching the throttle. Before the new pilot jet, my bike would just flat out die as soon as you put any pressure on the clutch. Now it takes considerable effort to hold the bike back without using any throttle. I'll try to remember to write down all of my settings next time I'm in the carbs.

[Bill Jurgenson]

sounds good.
hier from the Stocklist of the importeur here in Germany

VM28/486 Leerlaufdüse 2,67 €

or about 3$
can't do anything wrong there.

[basser23]

What Pro Circuit exhaust you running?
Make much difference?
Chip

[edfmaniac]

I'm running the Pro Circuit T4 for the XR650. I've been consistently finding more and more power almost every time I make changes so it's hard to say for sure but it sounds really good.

viewtopic.php?f=3&t=5477&p=27985&hilit=xr650#p27985

[den]

snorkle and header welds ???I thought it was just a shim between engine and carb?Whats a snorkle and who put the header welds there and why.

[basser23]

Den,
The snorkle is the top of the air filter housing,removing lets more air to the filter.
The welds mentioned are in the header pipes and are a result from manufacture.....not intended to be there but...slag from the welding process.

[basser23]

does that Pro Circuit can come with the mid pipe as shown?

[edfmaniac]

Yes. It comes ready to mount up. You just have to find your own mounting position as the stock one doesn't line up with the Pro Circuit. I drilled a hole in the existing down tube for the old mount and used my own little soft mount contraption(rubber washers basically). Ideally you would relocate the stock mounting system if you know someone with a welder as it has much better dampening in my opinion.

[Srinath]

I have a few of those lying around - GS500's post 01 use that same type of jet but a 20 size (the modded size up from a 17.5), and 89-00 bikes use a different type of jet but a 40 size. Some guys put the 40's in the 01 type and wonder why their bike dont run and send me the carbs.
Anyway My skorpion has a pipe and stock air filter with airbox and a DJ kit that seems to work quite well. However in a few days I am setting up to get into the carbs so I may try a swap.
Cool.
Srinath.

[Bill Jurgenson]

removing the snorkel does not let more air into the airbox. It changes the resonance of the box, what little there is.
Actually it destroys that resonance, so the powerband is quite a bit wider but the top is less.

[Srinath]

Just in case anyone else is having a hard time getting the Teikei #50 pilot jet for their 660, I found an alternative Mikuni jet that is readily available. The VM28/486 #40 screwed right in and made my Skorpion the happiest it's been since I've owned it. I can't believe I've been driving that thing around for about 8500 miles now with a sluggish low end and popping overruns. Why the #40 Mikuni runs richer than the #48 Teikei I have no idea. Maybe it has something to do with the slight difference in design but it works great for me and can be ordered or purchased at almost any cycle service center in the US. My local Yamaha dealer had one in stock. It cost me $40 worth of gas in the old Econoline to find the damn thing but at least my bike runs again.

Don't attempt to drill out the stock #48 unless you know exactly which size bit to use and/or already have a backup plan. I guessed wrong.

Here's a pic of the Mikuni. It's much longer and not as fat above the threads but works like a champ for me.

The pointy end of this jet would hit the carb body. Shave it ~2mm and its a perfect fit.
Cool.
Srinath.

[edfmaniac]

You could do that if you think it's necessary but mine has been working fine installed as is. There's an old saying I was brought up around, "If it ain't broke, don't fix it!", and mine ain't broke. LOL