02 MTN CAT 883 jetting and clutching?

PwderJnkey · Sep 30, 2012

In the process of rebuilding a 2002 MC 800 carbed to a Wiseco 883cc big bore. Will be running twin D&D pipes, and cold air intakes. D&D's website said to use a staggered PTO/MAG 490/500 main jets for the 900 application. Now I believe the 900 actual engine size is 862cc. So thats a 21cc difference....I've had some guys telling me to just go 1 or 2 sizes above the 900 chart.
Other than that, I haven't been able to find any information on what to do for the over bore setup in regards to CORRECT jetting or primary clutching. Even the local dealer/ mechanic just shrugs and says, "get bigger jets and check your plugs religiously". :face-icon-small-fro
Also heard that AV gas is good for cooler cylinder temps.

Some wisdom is greatly appreciated

motocrazy2006 · Sep 30, 2012

Start with something around 900 charts. Best to do is install egt guages in each pipe and if it runs HOT your lean. Fatten it up. Have used digital infrared temp guage to help jet with quads and bikes before

PwderJnkey · Oct 2, 2012

Yeah egt sensors is deffinitley a good idea. I was planning on installing them for this mod aswell. I guess the 883 kit just wasn't a very popular mod. Tech Info is pretty difficult to come by for this application.

01ZRTCAT · Oct 2, 2012

I have been told the same on jetting up!
Not much help ...

Arctic Thunder · Oct 2, 2012

I would start out with 400/410 mains, the same as I ran with the slp twins on my stock 900 motor.

One thing to really watch is the running compression on the sled. the stock 900 with SLP twins increased the running compression just enough that it would detinate if pushed below 5000'. So you might start out with a shot of av gas for protection. I don't know how close the squish is on the 883 or the running compression of the pipes you are running.

Tough to read plugs with Av gas. But you need to watch it really close. I am sure the mid range will be lean like every other cat.

Install some EGT's and keep it under 1150 with the probes 4" from the piston skirt.

Thunder

Idcatman3 · Oct 2, 2012

PwderJnkey said:
Yeah egt sensors is deffinitley a good idea. I was planning on installing them for this mod aswell. I guess the 883 kit just wasn't a very popular mod. Tech Info is pretty difficult to come by for this application.

The 883 wasn't terribly popular, because it's not a big upgrade over the stock 900, so why not stick with stock because it works and parts are cheap?

I'd guess you'd be good to go with a main jet size larger than is recommended for the same setup on a stock 900.

Meatman · Oct 3, 2012

Idcatman3 said:
The 883 wasn't terribly popular, because it's not a big upgrade over the stock 900, so why not stick with stock because it works and parts are cheap?

I'd guess you'd be good to go with a main jet size larger than is recommended for the same setup on a stock 900.

good advice. but you have to remember that even though it is not a big upgrade, you are still increasing the volume of flow and combustion so I would recommend going extremely fat, the only reason is because it is now a different motor, and going to have completely different settings. Your mains are for higher RPMs so I would run on the fatter side. Your base for your mains has a lot to do with elevation. (don't forget that the mains run on 3/4 to WOT.) so you can start fat as hell (in a safe zone within reason.) and still be able to get some readings.

I have no idea what elevation you are running, or any other mods to the motor so i can't give you a starting point.

Start with something around 900 charts. Best to do is install egt guages in each pipe and if it runs HOT your lean. Fatten it up. Have used digital infrared temp guage to help jet with quads and bikes before

Absolutely no offense at all but this is not good advice. EGT gauges are a tool for identifying problems AFTER they have been calibrated to the motor. The mounting point has everything to do with what the temps will show you. Before you use an EGT gauge as a fail safe you need to figure out @ what temp are you are satisfied with the plug color and piston wash.

PwderJnkey · Oct 4, 2012

I usually ride around 5k - 7K. Typically 15*F-30*F. And occasionally a warmer spring ride. 40's to 50's. Engine mods will be: D&D twin pipes and silencers. Cold air intakes. STM exhaust valves. 162" challenger and 19/43 King cat 900 gearing. Will prob run some AV gas this year as well.
Ok so, the Main's control WOT RPM's
Then the 'Jet Needle' kicks in from alittle over 3/4 throttle to alittle before 1/4, and the 'Needle Jet' from over 1/2 to about idle, and the Pilot for idling obviously. All over lapping jetting coverage. This info was taken from "Hi-Performance engineering" by the way. From what I've been reading so far the main problem areas for fuel mixture is from around 1/2 to WOT....So Jet Needle, and Needle Jet sizes and settings are pretty critical, as well as the Mains.....right?

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02 MTN CAT 883 jetting and clutching?

PwderJnkey

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01ZRTCAT

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