I bought an '03 Vmax with the UFO StreetPro 4-2 on it. I've got the carbs apart to clean them because the bike felt and sounded like it was running on three cylinders at 5000+ rpm. (It's fine at light/moderate throttle below 5000.) I noticed the main jets are 170s. I'm concerned those may be too big. I had a '98 with drilled stock exhaust and a 155 was too big for it--I ended up going back to stock and shimmed the needles a little. I'm sure the StreetPro flows more than the drilled stocker, but 170 seems like a really big jet. Thoughts? Thanks!
170 main jet with UFO StreetPro 4-2 and otherwise stock bike?
Help Support VMAX Forum:
Rusty McNeil
Well-Known Member
You need to determine if that's a 170 Mikuni or a 170 Dynojet.
If it's a 170 Mikuni then it is WAY too big, like stupid big......
If its 170 DJ then its probably ok but bigger than I'd run for that setup. If it's just an exhaust I would stay stock or smaller on the mains, making adjustments elsewhere to fine tune it...
A DJ 170 is just slightly smaller than a Mikuni 160 and slightly bigger than a Mikuni 157.5
PATMAX
Well-Known Member
You may have enough adjustment on the needles but I'm not sure the overlap of the fuel circuits but I'm not sure offhand if the 5k range is covered by needles. DannyMax would know offhand I bet.
Rusty McNeil
Well-Known Member
What is covered by what at a certain rpm is also dependent on throttle opening....
Example, if your running down the highway cruising at 5000 rpm then your certainly "on the needle"
If you wacked it open 100 % starting at 2000 rpm by the time you are getting to 5000 rpm your starting to go off the needle and more on the main.
If you wacked it open 100%, without downshifting, while cruising at 5000 rpm your probably going to be on the needle for a while as the engine catches up with the throttle opening....
So it's all really subjective, all this stuff overlaps, a lot.
And you're really never completely ON one thing and OFF another thing, they all contribute to some degree, even the needle open 100% at WOT still pokes into that hole some and its size and setting will still have an effect....
In general the slide opening is really more related to throttle opening than it is to rpm...although sudden throttle changes leave the slides trying to catch up,
Most recommended practice is to jet from the top down, until the mains are right don't even worry about the needles etc. It has such a big play in all the ranges that doing it last will just make you end up chasing your tail..
Example, if your running down the highway cruising at 5000 rpm then your certainly "on the needle"
If you wacked it open 100 % starting at 2000 rpm by the time you are getting to 5000 rpm your starting to go off the needle and more on the main.
If you wacked it open 100%, without downshifting, while cruising at 5000 rpm your probably going to be on the needle for a while as the engine catches up with the throttle opening....
So it's all really subjective, all this stuff overlaps, a lot.
And you're really never completely ON one thing and OFF another thing, they all contribute to some degree, even the needle open 100% at WOT still pokes into that hole some and its size and setting will still have an effect....
In general the slide opening is really more related to throttle opening than it is to rpm...although sudden throttle changes leave the slides trying to catch up,
Most recommended practice is to jet from the top down, until the mains are right don't even worry about the needles etc. It has such a big play in all the ranges that doing it last will just make you end up chasing your tail..
adambweird
Well-Known Member
Hell, i run a 165 mikunki w/a streetpro 4-2 and it runs great! Any smaller and i start having problems on the top end.
Thanks for the responses, guys. I'm pretty sure I found the problem. The carbs looked nice and clean inside, but when I blew carb cleaner through the jets, I got a lot of brown soupy stuff out. I pulled the lid from the airbox (I had removed it without taking off the lid) and found that there was a puddle of filter oil--someone had gotten seriously over the top when oiling the K&N. That extra oil had partially clogged up some of the breathers.
I also noticed that one of the vacuum slides isn't moving as smoothly as the others. After cleaning the bore and the slider thoroughly, it moves almost as smoothly as the others, but not quite. I'm going to switch the slide to another carb and see if the slight stickiness stays with the carb or follows the slider. I'm just about positive that the slider not opening is what was causing the bike to run on three cylinders when at or above 5K rpm.
I'm not sure what brand the 170 jets are. The previous owner said someone named John Cornwell or Crowell (I think) had sold him the exhaust and the jets and that they were expected to work well together. So adambweird may be on the money with his 165s.
I also noticed that one of the vacuum slides isn't moving as smoothly as the others. After cleaning the bore and the slider thoroughly, it moves almost as smoothly as the others, but not quite. I'm going to switch the slide to another carb and see if the slight stickiness stays with the carb or follows the slider. I'm just about positive that the slider not opening is what was causing the bike to run on three cylinders when at or above 5K rpm.
I'm not sure what brand the 170 jets are. The previous owner said someone named John Cornwell or Crowell (I think) had sold him the exhaust and the jets and that they were expected to work well together. So adambweird may be on the money with his 165s.
PATMAX
Well-Known Member
Jon Cornell or UFO is who supplied those parts/advice.
thor_eyerdhal
Well-Known Member
Mikuni jets have tapered holes, not DJ ones.
Very easy to see
Very easy to see
veebooster
Well-Known Member
Whats your air intake setup? With stock needles, morley air box, HMF Headers (similar to UFO) I needed mikuni 170s to work up top. If you're using the stock airbox this would be to big for sure. Use stock mains 152.5 with stock air box and UFO headers. Maybe 1 size down.
Dale
Dale
sdt354
Well-Known Member
A 170 is a mikuni. And it's huge. Dyna andmikuni make different sizes. I'm running a 165 Dyna in a hybred stage 7 setup. #30 FP needles stock springs and normal vboost. i'm still getting 115 to 120 miles beforre the fuellight comes on. A little popping on decelleration,but she flys. ❤ her.
correction-170 can be either.
correction-170 can be either.
Last edited:
I got a reply from Mike at UFO over the weekend. Here's what he had to say:
Dave
We run a 165 main in all the customers bikes normally buy I run a 175 in all mine so I think you would be fine with the 170's. We set the needle in the 4th position down from the blunt end, turn the pilot fuels out 2.5 turns off the seat,make sure the air correctors are in the top of the carbs and the slides are drilled with a #19 drill. We also run the stock slide springs here or we get a flat spot in the mid range. This is the tuneup we run here for our Elevation depending on where your at you might have to do some slight adjustments for your Elevation but this should get you close. If you have the stage 7 make sure the vboost is still in place and closed ( plugged in ) before syncing the carbs. Once the sync is good un plug the vboost in the open position. You should do this for stage 1 or 7.
I hope this helps my friend.
MIKE/UFO
Dave
We run a 165 main in all the customers bikes normally buy I run a 175 in all mine so I think you would be fine with the 170's. We set the needle in the 4th position down from the blunt end, turn the pilot fuels out 2.5 turns off the seat,make sure the air correctors are in the top of the carbs and the slides are drilled with a #19 drill. We also run the stock slide springs here or we get a flat spot in the mid range. This is the tuneup we run here for our Elevation depending on where your at you might have to do some slight adjustments for your Elevation but this should get you close. If you have the stage 7 make sure the vboost is still in place and closed ( plugged in ) before syncing the carbs. Once the sync is good un plug the vboost in the open position. You should do this for stage 1 or 7.
I hope this helps my friend.
MIKE/UFO
Rusty McNeil
Well-Known Member
Awesome to get a DETAILED and meaningful response in jetting questions from anyone, kudo's for that.
Are the 170's he's referring to DJ or Mikuni?
They're the experts but for internally stock motor 170 Mikuni seems huge.
DJ 170 sounds about right though.....
I replied to Mike that I'd thought I'd found the culprit--whoever had installed the K&N filer had overoiled it so excessively that it had leaked a small puddle in the bottom of the airbox and sucked a bunch of that junk into the breathers.
I disassembled the carbs did and did a pretty thorough job getting them cleaned out There was no scale to speak of; the only problem was the brown gunk that fcame out at high speed when carb cleaner was shot through the breathers. I hit up all of the breathers until none of them spat out anything ore than carb cleaner.
While reassembling the carbs, I noticed that the diaphragm had a .160" hole drilled in it The needle was chipped two away from the top and three away from the bottom part. The mains are definitely 170s.
So, what happens is this:
1) with tboost set to stock, and the rider accelerating at 1/4 - 1/3 throttle, once the tach gets to about 5000rpm, the bike starts sputtering and losing steam. If I recall correctly, the sounds come from the left side exhaust which should go to th right side front and the left side rear. If I accelerate very gently up to 6000+ rpm. the problem doesn't seem to crop up.
INteresteingly, if I have the Tboost turned on, the hestitation and spitting at 5500rpm are pretty much gone. That's all well and good, but it's not fixing the original problem, and that's what id like to do.
Something else strange I noticed--tonight I removed the two left side vacuum slides and they were both damp to the touch with fuel. I presume the fuel came in through the 0.16" home at the top of the cylinder. Not a lot of fuel, just enough to be a little damp to the touch.
The rear left carb was the one that was giving more some grief about moving smoothly until I cleared it out, and now the side seems to move just about ask fast as the other three slides to when closed. The other three go "thWAACCK"where as the last one goes thwaacckk" in a slightly politer fashion.
I disassembled the carbs did and did a pretty thorough job getting them cleaned out There was no scale to speak of; the only problem was the brown gunk that fcame out at high speed when carb cleaner was shot through the breathers. I hit up all of the breathers until none of them spat out anything ore than carb cleaner.
While reassembling the carbs, I noticed that the diaphragm had a .160" hole drilled in it The needle was chipped two away from the top and three away from the bottom part. The mains are definitely 170s.
So, what happens is this:
1) with tboost set to stock, and the rider accelerating at 1/4 - 1/3 throttle, once the tach gets to about 5000rpm, the bike starts sputtering and losing steam. If I recall correctly, the sounds come from the left side exhaust which should go to th right side front and the left side rear. If I accelerate very gently up to 6000+ rpm. the problem doesn't seem to crop up.
INteresteingly, if I have the Tboost turned on, the hestitation and spitting at 5500rpm are pretty much gone. That's all well and good, but it's not fixing the original problem, and that's what id like to do.
Something else strange I noticed--tonight I removed the two left side vacuum slides and they were both damp to the touch with fuel. I presume the fuel came in through the 0.16" home at the top of the cylinder. Not a lot of fuel, just enough to be a little damp to the touch.
The rear left carb was the one that was giving more some grief about moving smoothly until I cleared it out, and now the side seems to move just about ask fast as the other three slides to when closed. The other three go "thWAACCK"where as the last one goes thwaacckk" in a slightly politer fashion.
Rusty McNeil
Well-Known Member
Fuel damp on left is pretty normal in my experience. Side stand effect.
thor_eyerdhal
Well-Known Member
With butterfiles closed, the A/F ratio is richer on the midrange.
If it is way too rich =>sputtering and power loss
Had the same issue with S7 and 175DJ mains.
It was too rich with Vboost opened but ok, and way too rich with Vboost closed...
Change for 147.5 and i can ride it closed or opened without any problem.
jwood
Well-Known Member
This is the exact setup I am running.. I still have a slight what appears to be a lean condition just off idol.. What can be "tuned" for elevation? I have tried to shim the needles to 4.5 and it is way to rich and the lean spot is still there but getting better... I did the shotgun last week, again much better! But still there...
fmcandrew
Well-Known Member
Running a Morley kit with stock needles, Sean suggested 165 mains to get me close. With the Stage 7 needles the main drops off considerably as the Stage 7 needles are very agressive in the transfer from mid to top
Last week, Mike left me a voicemail. (He's in Eastern and I'm in Central, and I wasn't up yet!)
I sent him the following reply, which explains my findings:
"Hi Mike,
I got your voicemail last week--thanks for the call. I took your advice and raised the needle clips to the #3 position (changed from the #4 position, making it richer) and that helped a tiny bit but the misfire was still present. I pulled the top off the airbox and noticed that one of the diaphragms was mostly stuck. I took the bike for a short ride and confirmed that it wasn't moving smoothly like the other ones. I pulled it, cleaned it and lubed it with WD40 but it's still not sliding the way it should, so I'm going to order a replacement. I'm confident that will fix it.
On a side note, the bike would not rev past 4000rpm with the airbox cover off, whereas when I had the cover on, it would rev to redline even with the misfire. The stock airbox must be a HUGE restriction if the bike runs too lean to rev past 4000rpm with it off!
Thanks again for your assistance!"
So, I'm going to order another diaphragm and that ought to make my Max healthy!
I sent him the following reply, which explains my findings:
"Hi Mike,
I got your voicemail last week--thanks for the call. I took your advice and raised the needle clips to the #3 position (changed from the #4 position, making it richer) and that helped a tiny bit but the misfire was still present. I pulled the top off the airbox and noticed that one of the diaphragms was mostly stuck. I took the bike for a short ride and confirmed that it wasn't moving smoothly like the other ones. I pulled it, cleaned it and lubed it with WD40 but it's still not sliding the way it should, so I'm going to order a replacement. I'm confident that will fix it.
On a side note, the bike would not rev past 4000rpm with the airbox cover off, whereas when I had the cover on, it would rev to redline even with the misfire. The stock airbox must be a HUGE restriction if the bike runs too lean to rev past 4000rpm with it off!
Thanks again for your assistance!"
So, I'm going to order another diaphragm and that ought to make my Max healthy!
Are you sure the needle/needle jet isn't the issue?
I moved the slide to another carb and the problem followed the slide.
The problem isn't the diaphragm--it's in sound shape, nice and flexible with no tears or holes. When I move the slide with my finger, it doesn't move smoothly--it feels like it's binding.
The problem isn't the diaphragm--it's in sound shape, nice and flexible with no tears or holes. When I move the slide with my finger, it doesn't move smoothly--it feels like it's binding.
