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High Altitude Carb Adjustment

840 Views 16 Replies 7 Participants Last post by  Ridgway81432
I have two 04 & 06, 660's and live in North Alabama, I'm taking them to Colorado in July for 3 weeks of riding, has anyone had any luck with Thunder products "Dial a Jet" that leans/rich the carburetor? A lot of people change the jets to accommodate for altitude, we will be riding 6000 up to 12000 ft. Thank you in advance.
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I have two 04 & 06, 660's and live in North Alabama, I'm taking them to Colorado in July for 3 weeks of riding, has anyone had any luck with Thunder products "Dial a Jet" that leans/rich the carburetor? A lot of people change the jets to accommodate for altitude, we will be riding 6000 up to 12000 ft. Thank you in advance.
Welcome from Colorado.
I don't think we have many members left that remember re-jetting carbs or using different brands of adjustable jetting, you may wait a long time for someone familiar with Thunder products to chime in.

I'm not sure if you've ever brought a 660 to elevation to have experience with what happens and why. In theory what you're going to deal with is an engine top-end that can handle the amount of gas provided with stock carb jets, if the air pump can provide enough O2 to burn the gas.

I'm luckier than most because I can make a carb change, go for a ride and not screw up an entire vacation. I can go back into the garage and make another change and take another quick ride to test the results; visitors to the area may not want to spend their entire vacation testing to then go back home.

When I was changing the carb jets for my area trail conditions/requirements and riding style I learned that when lowering the amount of gas delivered for the O2 available sucked in the performance department for my 660. I don't remember the different jet combinations I tried, maybe I was looking for tooooo much unlike wgc and his recommendation.
I've ridden many miles with wgc and his stuff works for how he likes to ride, so maybe you want to highly consider your trip using his jet recommendation. He's been a member here a long time and I would trust anything he says (except 'We can get to the gas station in Silverton'), he's been there, done that so knows. He was making less than a 3% change in amount of gas delivered, I ended up adding @200% more air by drilling the air box lid.

As for opening/drilling the air box lid for more volume, I did it because a new lid can be had for 22 bucks if I didn't like the results. As the lid is under the seat only dust is ever found on top of the lid. I do carry a roll of tape in the event I need to cover the holes to cross deep water. In your case if you got home and didn't like the holes, epoxy can be used to fill them later. Years ago I calculated the increased opening as compared to the stock snorkel, the holes allowed close to two more times the volume of air, and the stock filter works great to this day.

So you know most dealers back in the day changed the jets before the bike was delivered new to the first buyer, not because it worked but because the dealer could then changer more $$$ for the bike.....it was a profit center for the dealer. Years ago I had a few buddies bought used 660's because of mine and theirs sucked in the performance department, all we had to do was give them a full tune-up and install stock jets then give'm more air.

As for the tire p.s.i., depending on your tires be prepared to experiment for the area you pick. I added taller tires and the added sidewall required me to go up to 11 p.s.i. in the radial tires.
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Thank you all for your help, much appreciated. I'm 60 years old, have been to Colorado off and on most of my life, great state, lots to do. With that said we are planning a 10 day four wheeler trip in July, looking a Taylor park and surrounding areas. Thanks again for helping the old school carb guy here.
Taylor park isn't very tough, I rode that area without problems when the Griz was new before mods. The worst part about that area is the road riding, thus breathing the dust.
As for the tire p.s.i., that depends on your tire diameter/wheel combination in the trail conditions you find your self traveling. With my set-up I have 12" wheels with 14.5"s of total sidewall and with the radials there was a lot side ways darting at speed with the tread following the wandering grooves while the machine wanted to go in a straight line. This caused a back and forth shifting I stopped with higher p.s.i. and the added pressure helps keep the wheels out of the rocks. Maybe many think there's a problem with much higher p.s.i. so I post what I do for others to take or leave as they decide.
Here are a couple pictures of my tires/wheels to show the amount of sidewall and wheel rubbing riding my area, notice the wheels still get slight dings so with 5 p.s.i. there might be more problems.
https://flic.kr/p/hWZubM https://flic.kr/p/hWZvXT https://flic.kr/p/hWYyNB
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What areas of CO do you recommend riding? I know there's a ton but I've got 10 days to kill, I'm dropping off my twins at Philmont Scout ranch in NM, going riding with a buddy, we go twice a month in Tennessee looking for intermediate to "some" hard trails, any recommendations on areas with some milage?
I live at the northern base of the San Juan Mountains 10 miles from Ouray so most of my riding is in this area, there are hundreds of miles of old mining wagon roads in this area, the trick is to plan day rides from different trail head unloading areas as we have a lot of box canyon areas to ride with passes over the top to the next town and these towns don't allow a.t.v.'s to travel through for riding loops combining different trails. You can ride many miles say between Ouray unloading just above town to ride over just above Telluride but then have to ride back the same way, riding that area in the morning to then load up and trailer 7 miles to unload at Ironton Park heading toward Silverton.
Most of this is moderate riding but there are also forks leading to 'Oh My God' stuff, which you can look at then turn back if needed after feeling the hair on the back of your neck :)
Also in this area west of Ridgway you can unload on the south end of the Uncompahgre Plateau which is 92 miles long and ride for days up to 11,000ft. with the south end mostly timbered with the north end mostly desert conditions. The north west side of this Plateau is the area much of the Uranium ore came from for the Manhattan Project...this area is very unique, make sure you have plenty of gas if you want to run end to end while going side to side :)
As you mentioned areas with some milage, this area will teach you why c.v.t. mods are great to learn and install. The stock 660 on stock size tires indicates traveling 26 miles when the true distance traveled is 20 miles. I suggest you confirm how far your 660 actually travels on a gallon of gas so you don't get caught short, or have to turn around before reaching your intended destination.
I say that because most think their 660 get's 15 to 17 m.p.g., so if you have 5 gallons in the tank and 6 gallons extra in roto pax containers you might think you can go 17x11 miles or 187 miles buy the odo. Then if your odo is off 23% like mine was on stock tires your distance for 11 gallons is actually 144 miles. You might think you can ride from one end of the Plateau to the other to then learn during your trip you have a problem covering true distances.
Over the years many members have visited this area to ride and many times they have the trails planned before leaving the trail head so I know the distance to be traveled that day. Then I can look at their tires and ask which c.v.t. mods they use if any to then know how much gas will be needed for the day for all bikes combined.
Another thing to plan on is lightning causing you to think about changing trails used to miss (go around) a bad storm. I carry good rain gear all year and have grip mitts in the box to keep my gloves dry all year, I've enjoyed having heated grips in August here too. In most of my summer riding videos you'll see heavier coats and/or coveralls tied on the front rack just in case.
In my rear seat box I have several quarts of water along with cheap clean white hand towels in a zip-lock bag from Walmart and a roll of duct tape to stop bleeding.
In this S.W. area of Colorado we're out of cell service 3 miles from most towns so we have to 'get out of' what we get into.
Any mod you do to your 660 to ride here will make it better in other areas of the country, the mods I have on my 660 now are listed in my signature and they're there because of need, not want :)
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Wow, awesome information, thank you so much Ridgeway you have helped immensely! Lots to consider for sure, yes milage, gas, weather and a very well planned trip is key. Great Intel on gas millage, I haven't modified much except tires to SunF and 25's all around. There's not much my stock 660 won't do, it's a beast for sure. Thanks again!
Have you measured the circumference to know your 25" advertised tires are actual 15"s true? If they are 25"strue you speedo is off, reading high 3 m.p.h. at an indicated 20 m.p.h. and 6 m.p.h. high when reading 40 m.p.h. This how you can run out of gas after a few hours in this area if you're not careful.
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