MCX 240 nytro stumble

[pelon]

My friends mcx 240 nytro has a bad off idle stumble. It actually pops pretty hard, but when he feathers the throttle a few times it clears up and takes off. No air/fuel gauge to look at. Only 400 miles on the sled.

I don't know Mcxpress, so any input is appreciated.

thanks

 

[up-high]

A/F would show lean IMO. Runs ok everywhere else? Just off idle should be handled by the stock FI. TPS ok? No codes? What does the engine idle at?

 

[pelon]

A/F would show lean IMO. Runs ok everywhere else? Just off idle should be handled by the stock FI. TPS ok? No codes? What does the engine idle at?

Runs like a raped ape elsewhere

No codes

I'll check idle today

yes I think its lean too

 

[BBNytro]

I would guess you need to increase the CO number.

 

[M5-]

It may also have a very small vacuum leak. My MCX Nytro can be a bit blubbery down low when it is first started, my A/F usually will be reading 10-11 when that happens then it'll clean up and lean out to 13 - 14 at idle once it's warm in about a minute.

M5

 

[pelon]

Idles at 1500

 

[Cpt.Ron]

as mentioned..

As mentioned above, check for vacuum leaks at all ports, check hoses for cracks or torn where pushed onto fittings. If all else looks good, then perhaps bump up your CO's through your multi function display unit.

 

[pelon]

So I took his nytro for a long ride today. Turns out the stumble occurs at 5500 to 6200 RPM depending on snow conditions. So it's stumbling upon boost (threshold) then it rockets out of that area up to rev limit.

As I said I am unfamiliar with MCX, so we went to the dealer where he bought it 2 weeks ago. They said he needs to contact Leipheimer Yamaha and purchase the control box that allows fuel adjustment.

We sled at 11,000 feet on average

thanks

 

[APEXXPRESS]

Give me a call 406-782-2318 New Number
Mark

 

[pelon]

My friend will call

Thanks

 

[BigFish BC]

So I took his nytro for a long ride today. Turns out the stumble occurs at 5500 to 6200 RPM depending on snow conditions. So it's stumbling upon boost (threshold) then it rockets out of that area up to rev limit.

As I said I am unfamiliar with MCX, so we went to the dealer where he bought it 2 weeks ago. They said he needs to contact Leipheimer Yamaha and purchase the control box that allows fuel adjustment.

We sled at 11,000 feet on average

thanks

just need a reprogram not a whole box,any dealer should be able to do that.

 

[pelon]

just need a reprogram not a whole box,any dealer should be able to do that.

Dealer does not do it.

Leip. said check for exhaust or intake leaks.....I can't find any so far

thanks

 

[Smoke Show]

two things I have seen recently. Fuel filter plugged slightly and a crack in the exhaust manifold. Look closely at the manifold i'd say. and it never hurts to change a fuel filter.

 

[pelon]

Bad wiring harness......go figure

 

[pelon]

Give me a call 406-782-2318 New Number
Mark

Thanks for helping him out so quickly Mark

 

[Duke]

Check vac leak, then try bumping fuel press up 1/4 turn at a time, may have back off fuel press a bit. Have seen it a couple times on MCX Nytro's.

 

[Mountain Bound]

Just one more thing, what kind of fuel is he running. I live in flat land country about 1700 feet. Years ago when I took my 240 to the mountains I was still blending some race fuel into the sled. This however was the problem. It ran very similar to what you are experiencing, pulled all fuel out and filled with premium and wa-la it was mint. Saying that I am still running premium even at home at -20 C and runs great. I thought I was being to sled with a little race fuel but it ran like ****. Just something to think about.
Cheers

 

[pelon]

Just one more thing, what kind of fuel is he running. I live in flat land country about 1700 feet. Years ago when I took my 240 to the mountains I was still blending some race fuel into the sled. This however was the problem. It ran very similar to what you are experiencing, pulled all fuel out and filled with premium and wa-la it was mint. Saying that I am still running premium even at home at -20 C and runs great. I thought I was being to sled with a little race fuel but it ran like ****. Just something to think about.
Cheers

91 octane.....it's plenty