Yamaha 07 Rhino 660 Muzzys good performance gains!!


AZ's Finest - UTVUnderground Approved
First let me say thanks to Scott at XMF for hooking up my buddy Price with a set of Muzzy Duals for his rhino 660. Most people don't know that XMF is a Muzzy dealer.

This started with my friend Price calling me looking for a pumper carb for his Rhino. A friend of his had a shop put a Kiehn FCR 41 on his Rhino last dune season and they liked the performance gains, so Price wanted to try something. I can get Mikuni carbs much cheaper than Kiehn so we decided to try a Mikuni HSR 42 rather than the 45 most people use. It seems to me that on a mostly trail, sometimes dune rhino the 42 would probably perform better.

Price had a stock pipe and carb on his rhino at the start of last weekend. Price pulled the header, the welds were ground out and he installed a bung for the AFR sensor. He put it all back together and brought it over. We installed a Mikuni HSR42 pumper carb with a K&N X-Stream filter and no airbox. With the bung in the stock header we could get the jetting spot on with the NGK air fuel meter I bouhght from Hunterworks a couple years back (best investment I have ever made by the way). It took some time, basically all last weekend and we could never get it to run as good as we had hoped for. Thinking maybe the sensor on the AFR meter was bad as I use it on my race rhino with leaded gas all the time, we went to autozone and got a replacement. Found a suitable bosch 5 wire and hooked her up again. Ran out of time last weekend and just never liked what we accomplished.

Jump to this weekend, Price found an exhaust gasket in the bottom of the rhino...oops!! It had a pretty big exhaust leak at the header, throwing our readings way off. He came over again and put new exhaust gaskets in and we started the jetting process over. Believe it or not, it ran 12.5 to 1 air fuel with a 135 main. Sure seemed small, but thats where it ran. Throttle response was great but it really didn't improve the top end. I have long been a believer that the intake wasnt the restrictive part of the rhino, but the head pipe was, so I finally convinced Price to try the Muzzys. He didnt want ron wood loud, but did want performance gains. I was skeptical as most quiet pipes dont make power (gibson, Yosh with quiet cores), but it's worth a try.

It took us about 90 min to change the pipes. Lucky he doesnt have a bed in the way. We left the quiet tips in and added the supplied spark arrestors. A quick run and it was definatly lean on top, 14.5 or so to 1. Changed the main from a 135 to a 140. 12.5 to 1 again. No other changes were necessary. Throttle response is better, timed acceleration to a known mark is better (used to be 40mph at that spot, now 45mph). Top speed is up 4mph over the stock pipe. Needles to say, Price was very happy with the results.

In the end we had a 140 main, 25 pilot, Y-4 needle jet, 97 needle 2nd clip from top no shims and a 50 pump nozzle in the HSR 42 carb. This maintained a 12-13 to 1 AFR throughout any throttle setting and any load.
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