I have decided that I'm going to get a new carb and cam to help turn my 96 Sportsman 500 into an HO+. I know some of you are thinking just trade it in... that's not one of the choices, so please don't say anything if that's what you're going to say.

www.aaenperformance.com has 3 flatside carb options for me...

-36mm
-40mm
-42mm


My question isn't really as much which one will make the most horsepower, as I think we all know that the 42mm will make the most flow, and give the most power. One of my uncertainties comes from the the fact that I live in Denver,CO. What does high altitude do to a carb? Do I need a bigger carb to get in more air since the air it's getting isn't as dense, or do I need a smaller carb at higher altitude because I can get more of the less dense air through the smaller opening anyway. I can see it both ways, and one's not right. I talked to the tech at aaen perf, and he said that the 36mm flat side flows like the standard 40mm on the HO. So if I just want to be as good as an HO, then I can do that and be good... but who said that would be good enough [img]i/expressions/face-icon-small-wink.gif[/img]. I guess the answer really comes from the answer about altitude. I'm not going to be racing this, I'm just used to my 400cc bike on the trails, and I think any quad is going to be a dog compared to that.

On to the cams...

Again, they have several choices for cams.

-HO Update Cam
-Long Duration Cam

They claim this about the long duration cam. "We tried several cams during development. Some produced more power, but at higher RPM's and with a loss of bottom end torque. This cam has 10 degrees more duration with stock lift and improves both midrange torque and top end power with only a 200 RPM increase."

According to their dyno chart... you don't lose any torque anywhere along the power band. http://www.aaenperformance.com/Power500.asp

The question about how things behave in higher altitude is also going to answer which cam would be better I would think.

I do plan on running all the way up to 13,000 feet, and know at least one trail up to 14,000 feet here. So although I'm normally going to be at 9,000-11,000 feet, I'm gunna do it all, and I don't want to screw myself by getting power hungry.

Oh, I'm also going to do a high-compression piston to bring compression up to 11:1 at the same time, but I don't think this has any impact on the other decisions. I'll probably do a little head porting down the road, but I can't afford to right now.

Anyone care to help me pick out my toys?

Thanks for your time...

Mike

 

thumper, i ran the long d cam in my 500 scrammy for a while. it pretty much does what they state. one thing about it though, you prolly wont be pull starting anymore so make sure you always got a good battery. the decomp is taken out of the cam lobe. another thing that will help is a good hi comp piston such as wiseco. as far as the flat slide carb tried it and didn't like it was really dead off idle and throttle response was lacking, a better choice imo would be the 40mm off scrammy 500. altitude will affect any carb you choose, youll just have to jet for it. a dial a jet may help.

 

thumper, one more thing. there are clutch mods for hi alt also, such as lighter weight, different spring and such. this will help whatever set up you decide to go with

 

I just installed a heelclicker clutch kit tonight. I didn't have the new belt yet, so I can't test it yet though.

The tech at aaen told me that they sell the flat side carbs because they're supposed to have better throttle response and aren't sensitive to air box mods like the factory carbs are. I'm probably not looking at any airbox mods, so I don't really care as far as that goes, but for what I'm doing, throttle response is key. I want more power, but don't want to lose all trailability.

 

I would have to agree with jeffroe. I ran the 42mm Aaen carb on my Scrambler for a while and ended up getting my money back. Aaen was super to deal with and some of the claims on the carb were true, but it is not for the casual rider. It was a pain in the neck as for jetting. It was very sensitive to altitude. Get the larger boot and carb off a Scrambler.

 

yeah aaen told us the same when we bought our 42mm, then tried to help rejet, change needles, etc to get off idle response. its sitting on a shelf in the box at the shop, unless it got stuck on ebay. word of advice on the mods, build the motor first and then clutch. you may have to change what's already done depending on what else you change for power. just what ive learned in the past. good luck!

 

FST(four stroke tech) makes a 600 stroker kit for the Scrambler. I don't see why it won't work on a Sportsman. I am now saving money towards that. I think, for me, it will be money better spent. The only thing that may get you is the age of the Sportsman, but I think most the specs are still the same. They have their own cam they use with the kit.

 

Thanks for the info! Do you think it's all flat side carbs that would have this problem, or is it just that the 42mm was just too big? Would the 36mm flatside be better than than the scrambler carb?

Quick question about head porting while I'm here... Is there a downside to head porting other than cost?

 

The way I understand the porting for the 500 motor is a waste on a nonmodified motor. Even then it's gains are marginal. The problem, as I understand it, is not that they don't flow enough, but that they flow too much. Throw a hi comp. piston and a stroked crank and that changes somewhat.

Now as for the carb, your guess is as good as mine. It just may be the wrong application. If you were dragging or racing and had time to tweak for every heat etc.. it can make sense. I think it was slightly faster on top end. I always had a flat spot when first accelerating. If you were on a line and reving a bit it was not a problem. They were aware that this was an issue. It was just a characteristic of this carb. Next I broke two throttle cables off right as the cable leaves the carb. They replaced them with no problems, but that's when I sent it back. That is not reliable and I was lucky to have a tow back when it happened.

 

If you are trying to keep the normal, low rpm characteristics and rider friendliness in tact on that motor, I would recommend bumping compression (since you lose cranking compression with altitude). The 600 big bore kit would probably be a fantastic idea too. I would only go with a slightly more agressive cam if you feel the need to replace it. At altitude you are pulling very thin air through the carb and I don't know if you would see any benefit to swapping the carb. I think you would totally kill your low end response if you went to a bigger carburetor. If I am not mistaken your stock carb is a constant velocity type. If this is the case, there is no way I would swap it out. That CV carb will do a nice job of keeping good flow at low rpms and that will be more necessary as you get to those sky high altitudes. As far as head porting you probably don't need it since you are not maxing out it's flow capabilities in any way (especially at 12000 feet).