I have had the ufo's for two years now and have yet to install them. I would like to this year but I really do not want to burn down my engine. If anyone has setup suggestions for this engine I would appreciate it. I actually put them in for one night before a trip, Couldn't get it to idle right so I took out the jets and put it back to stock. I believe i have an engine where I have to drill the base where the needle jet goes, anyone done this. Another concern is that I want to put a 501 rotary valve, short intake boots, and maybe port it, How would these affect the ufo's? This has been a project sled for the last year for me, mainly suspension but now I want to get into the motor. Thanks

TOI, a friend of mine had the same sled and never could get the idle thing figured out so after a winter of dickn' around he took them off.

do you know if he drilled the hole at the base of the carb?

as far as i can remember the trick was to drill the hole in the bottom of the slide not the carb. could be wrong as it was not my sled . you know how it goes.

Don't drill your slide. The hole your refering to is drilled in the needle jet,at the bottom of the carb. Picture your slide at closed position,you'll put a #55 hole at the lowest spot in the needle jet to provide a air bleed hole.This leans out the pilot jet setting allowing a bigger pilot jet to be used,and will help your gas mileage.The pilot jet feeds fuel threw out the throttle range.The u.f.o creates alot of vacuam in the carb but the bleed hole lessens it to some extent,bringing back better mileage.

motor'n, do you have these installed in a 670. I know where to drill the hole, they have a picture in the directions where to drill. I am looking for anyone who has had a setup like this, what worked what did not. If I were to put them in and not drill, my sled will not idle correctly. Will everything else work OK

No there not in a 670.If you decide not to drill the needle jet you'll end up with a very small pilot jet,which can be dangerous.The air bleed hole allows you to up the pilot feeding more fuel at the lower midrange position.With a tiny pilot (10-15) theres not much fuel to keep things safe.Your sled will need a very small pilot without the air hole,to idle properly.Your "jet needle" will also need to be tuned,by moving the clip."REMEMBER ALWAYS START RICH".Some 670 actually changed the needle jet to make it run.UFO's take a lot of time and tuning to make them work but when they are set up you'll be impressed.Sorry I don't have the exact set for your sled,but I will say be cautious,parts are expensive.UFO's are not a bolt on and go product.

I ran UFO's for 5000 miles (est.) in a 96 formula SS 670. I found the unnessary
and even though got them to work they are unnessary especialy for a high torque engine such as the 670 rotary valve doo. For trail riding I'd tightened up the secondary (throttle response is directly related to clutch setup) and get it jetted good (safe for the gas you will be using). Just my experience.
I am running a 600 triple cat without APV valves and I clutched around ALL the BOGG these engines are known for.

i dont have a setup but i did read to also drill the hole in the ufo out to 5/16 (where the neddle goes through. as well as drilling the needle jet. my brother inlaw has them in his ac 500 and likes them good milage and power but lots of tunning

I have UFO's on my 643 with overbored mikuni 44's now being 45.5 mm.

I had a lot of trouble with over rich idle and midrange (even with the 12.5 pilot jet) until I drilled a 1.5mm hole in the needle-jet shroud along the bottom of the carb "floor". This procedure is explained on thunder products' web page and solved all problems at once.

Suddenly the engine responded to the air screw, and the needle settings.

I have never run the engine without the UFO's so I don't know how it would be without them but I think the throttle response is very impressive!

Lynx, did you have to go back up in pilots after drilling the hole ? I am currently down to a 20 pilot and still can't get the air screws to work. Thanks

No I still use the 12.5 pilot jets, the 1.5 mm holes made the difference from hardly driveable to OK!
(Actually I don't use any jets anymore, the engine went to pieces last weekend due to a cracked piston as it seems... :-( )

Originally posted by team old iron@Dec 24 2003, 01:25 AM
motor'n, do you have these installed in a 670. I know where to drill the hole, they have a picture in the directions where to drill. I am looking for anyone who has had a setup like this, what worked what did not. If I were to put them in and not drill, my sled will not idle correctly. Will everything else work OK
A friend of mine had ufo:s in a 670, with 12,5 pilots and it still was to fat at idle.
BUT THIS WAS BEFORE THE RELEASE OF THE HOLE DRILLING!!!
there newer was any hooray i got so mutch more power feeling do.
Other wise that set up was ok....except that in desperation to get it working at idle he raised the needle clip to much an a piston blow...
Drill the hole in the needle jet (as motor'n says, ther is a picture on the home page) jet it right and be weary happy.
But if your not willing to spend some hours tuning, skip the ufo:s and leave it stock.
I bet there is more to gain faster in fine tuning the clutch system.
(and the chance of engine disaster is not precent in that tuning)
Lars