i have seen some talk about the 501 rotary valve i have an mxz 670 ho and want to get more out of it. is there a noticeable difference in performance, or any suggestions would be helpful. right now i have a goodwin clutch kit, 192 studs, roller secondary, and a b&b eliminator on it the last two things i'm not to sure if they were worth the cost but you live and learn

It depends what you like about your sled. If its torque you want leave it alone.At a minimumyou should *verify that the closing edge is set to spec or slightly past. If its peak power than the 501 is what you want. You lose a little throtle response but you can get that back by adding the short boots when you put in the RV.
Dont buy a new one just get a degree wheel and modify your existing RV.

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (H.O.RIDER @ Aug. 04, 2002, 9:32pm)</td></tr><tr><td id="QUOTE">Dont buy a new one just get a degree wheel and modify your existing RV.[/b][/quote]
The only problem with that suggestion is if you don&#39;t like the result you have to buy a new stock disc.

Just my 2 cents CDN http://www.snowmobileworld-s2.com/forums/iB_html/non-cgi/emoticons/confused.gif

If he wants to try a 501 he has to buy one anyway, so he might as well modify his first and if it works the way he likes than its money in the bank. If he modifies his own he can get the exact timing he wants, if you try to get a "501" to work he could be out by 4 deg or more no matter which way the valve goes in.

You&#39;re definitely better off to degree and cut your own. The 501 you buy is going to be off unless you&#39;re just plain lucky.

Hey H.O.RIDER,
Can you recall the exact degree setting you cut yours too, *on your H.O?

I put a 501 in mine and didn&#39;t notice a bit of difference. *This year i am going to do what H.O.RIDER suggests and custom cut my old one....

Check out this old post of mine, it has some numbers comparing the two valves.

http://www.snowmobileworld-s2.com/cgi-bin....hl=rave (http://www.snowmobileworld-s2.com/cgi-bin/forums/ikonboard.cgi?act=ST;f=3;t=983;hl=rave)

I think anything you do to an HO is a compromise. The motor was tweaked to get as much power out of it without the meticulous matching and massaging of a hand ported motor.
I found the best mod on my two HO&#39;s has been short carb boots, dne can, and ufo&#39;s. I ran the ufo&#39;s for a season and hated the mileage so i took them off. I loved the response and without them my machines could never properly pull the stock 53 deg start angle of the helix. I am trying them this year with a different setup that according to Lon at Thunder Products WORKS. I played with the RV but to be honest the stock setting works pretty well. Without the UFO&#39;s a straight 50 helix works better.

HO there was an article on this website about the UFOs. They said they were very difficult to calibrate. For the average rider not worth the effort. I don&#39;t know if the article is still up.

Yes I did read that article and many other re:UFO&#39;s. Lon is very certain that this setup will work as promised. I had great performance with them last time with poor gas mileage. I am still hoping for the performance with some better mileage this time. You really have to hear the throtlle response with a DNE can and the UFO to believe it.

I ran the 501RV, short boots, and UFOs on my HO last year and it worked well. *My mileage was still quite acceptable. *While these three things together did not make a huge difference I do think they helped a little. *I used the recommended set up for the UFOs and it worked well immediately. *The only place that I think it is off is in the first 1/8 to 1/4 throttle. *It is a bit rich in this area. *I am going to make some small changes this year to correct this. *670s still rule!

What did you run for pilots, e-clip position, mains, cutaway etc.

Did you drill the hole in the UFO to 5/16 ths?

I have a 99HO, where do you get the short intake boots, what did they come on? will i have to modify the air box ? and will i have to change jetting? Thanks

FAST used to sell them. You might want to try the Crank Shop in Essex Jct. VT.

In another topic,the guy said he got the short boots from his &#39;doo *dealer. Ask your parts guy if he can come up with the #s.

I am thinking the shory intake boots came on one of the early 670 mach 1&#39;s.

HO Rider,

I was afraid someone would ask that question! *I kept all of my notes on this stuff on my computer and then had a hard drive failure and lost it. *I will probably have to tear into my carbs to get this info back. *I did not drill out the center of the UFOs. *I drilled small holes in the hood of the needle jets (tubes). *I ground my slides to 3.5 cut-aways but they ended up slightly more than 3.5. *I will have to dig around for the size of the holes in the tubes, pilot jet size, and clip positions.

hey guys..shorty boots suc* carbs hit the oil pump and there not level(some of the time)to keep a constantfeul level....take your long boots turn them inside out ..an sand them on abelt sander to match your rotery cover and your carb...this works great if you tunnel port and bore the carbs!!!
PS...lonn was great help with my UFOs * make shure you have AA3 OR richer needle jets...

Im not sure which boots you are talking about but with mine the carbs certainly dont touch the oil pump and they sit as level as they do with the stock boots. The only issue some people talk about with the short boots is foaming of the fuel in the float bowl due to more vibration.

HO .. THE BOOTS I HAD CARBS HIT THE PUMP..THOUGHT ALL THE SHORTYS WOULD BE SAME LENTH.....GUESS NOT! http://www.snowmobileworld-s2.com/forums/iB_html/non-cgi/emoticons/biggrin.gif

ufo in 670
5/16 hole
#50 drill in needle jet hood
20# polit
3.5 cut away
aa3 or richer needlejet
whatever main you have run(310/290)???
I ALSOfeel1/8 to 1/4throttel is a little rich...but is does cool the EGTs when you get of the gas...
Hope this helps!!! http://www.snowmobileworld-s2.com/forums/iB_html/non-cgi/emoticons/biggrin.gif

Thanks for the info. Is that jetting for a regular 670?

670forever,

Yes, that is similar to the setup that I have and that is what is recommended by Thunder Products for the HO. The hole I drilled in the needle jets was slightly larger than a #50 because I could not find a #50 bit locally. *Also, I cannot remember if I ended up with #20 pilots or a bit larger.

One more thing! I did not drill out the center hole on the UFOs. *Thunder Products does not recommend drilling out the holes. *Also, many of the people that I have heard of having bad experiences with UFOs did drill out the centers of the UFOs but did not drill the holes in the needle jets.

I am running that on a non ho(dome pistons)42mm carbs short y pipe...
ANYONE TRY DIAL A JETS WITH THE UFOS???

Yes, I am running DAJ&#39;s with UFO&#39;s. *I consider them as cheap insurance with the other mods I have done. (Tunnel porting, 501, y-pipe, 42mm carbs, .060 squish) *I feel I am close to getting the UFO&#39;s/DAJ combination dialed in. *My fuel mileage is very close to where it was stock.

The current carb setup on my FZ 670 is:

UFO&#39;s / DAJ&#39;s
290/270 mains
#25 pilots (still slighty rich @ idle)
AA3 - center postion or #3
#50 hole in needle jet (did not drill the center of the UFOs)

I use one DAJ per carb ... the DAJ&#39;s were quite easy to tune, especially since I was on a pretty steep learning curve with jetting and consider them the extra insurance I need to keep me from doing something stupid. *

I did nothing really magical ... just started rich on the DAJ settings and worked down to the point where a main jet change was in order ... repeated the process until I got the EGTs/plugs/wash in line. ... little by little I feel am finally getting there. *What&#39;s nice is once you get the high speed circuit where it should be, I set the DAJ&#39;s up in the middle position to allow 2 settings richer and 2 leaner. *Allows for elevation/temp changes. Keeps things very crisp. The DAJ settings are a snap and you can feel the difference. *I am now tweaking parts of the carb circuit other than the mains (idle circuit).

The sled runs great. *A few more tweaks with the clutching and I think I am home. Spanks many bigger sleds hard in the 1000 to 1500 foot range and is very respectable on top.
All in all I would say if I was to do it again, I am very happy with the DAJ&#39;s and would likely run them again. *The UFO&#39;s are questionable in my mind whether or not they are worth the tuning headache.

Hope this helps

tjn

TJN.with out the dial a jets,with the 42mm carbs were yuor mains around 320/300(flatland and cold)?
Sound like we run close to the same motor mods,If you dont mind telle&#39;n what ramps ar you running?

I also have a similar setup on my 96 mxz 670:
shaved head 0.060
porting
carb bored 42.5
501 RV
air box gutted
Y pipe mod
cudney clutch kit
shorty boots
crank of a 670 HO
advanced timming
clutch weight and ramps are stock
1.18 full lug track
43&#39; widening kit
ETS-sc10
360-380 mains but didn&#39;t had time to tune it, only 300 klics last year on rebuild engine and didn&#39;t want too lean it too much.

If some of you guys have something to add, i&#39;m open to suggestions, I have UFO&#39;s but I am reluctant to install them because of all the bad things I heard about em and I don&#39;t have an EGT http://www.snowmobileworld-s2.com/forums/iB_html/non-cgi/emoticons/confused.gif

If you can do a head shave ,porting, bored carbs, rv timing, short boots, GUTTED AIRBOX,and advanced timing and dial that all in without an EGT I think you can handle the UFO&#39;s. LOL

670forever ... regarding my clutching ... I&#39;m running 297 ramps, 18.5 g, #2 clicker, 200/280 spring, 52/48 helix, 20 lbs preload on the secondary and stock gearing. *I tried the PX ramps for awhile ... they jam alot of power off the line, but I was trenching and spinning alot out of the blocks. *I like the trail manners of the 297 ramp alot better. *

I am planning this winter to go back to the 50 degree straight helix and compare it against the 52/48. *The belt is flying all the way to the top of the primary so I may also try to pull 1 more tooth on the top gear. Also plan to cut the 501 r/v @ 146° - 76° because now it&#39;s not that close to the desired mark.

As for the jetting ... after the carb/port job ... I think I bumped 2 sizes up from stock which would have been 330/310 ... keep in mind the DAJ&#39;s were richening things from there ... it was rich.

tjn