McXpress 240HP Nytro......idles bad!

w8nfsnow · Dec 21, 2009

Just finished up building an McXpress 240HP Nytro. Everything seemed fine on the first ride up and down my street. The last ride I took down my street I got into the throttle to build some boost. The boost shot up fast to 12-13psi at 50% throttle position although I only held it for 2 seconds. After that ride it seemed to idle different almost rough. Didn't sound really bad but I could tell something wasn’t right. I started by changing the plugs, checking valve timing and compression all good. I took it out to the lake yesterday to do some short blasts. The sled seems to work good under boost for the 3-4 seconds I held it. Throughout the day the bad low end miss and idle got worse and worse. No engine codes have been seen.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com

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Have read that the TPS sensors can cause lots of problems? Should mention that viewing my McXpress display shows my throttle position jumping around at idle from 12-15% back and forth.<o

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To me it seems like something from the factory didn't care to see 13psi boost and is failing? I bypassed the TORS for a bit and didn't help at all.<o

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Any help would be great.<o

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TBird · Dec 21, 2009

Have you been in DI mode and checked the readings from TPS?
Should be between 15-95

Washy · Dec 21, 2009

What are your CO settings? Try -15 and see if it helps idle. Seems like your issue maybe more than this though.

SPOOLED · Dec 21, 2009

did you check your valve lash clearance? on all the valves.

w8nfsnow · Dec 22, 2009

SPOOLED said:
did you check your valve lash clearance? on all the valves.

Just finished doing a rough check on the valve lash. Thanks for the tip I think you called it. One of my exhaust vales has zero clearence.......not good at all.

I noticed when I first got the sled running it had lots of ticking in that general area. The sled ran good until I hit first boost and the idle problem has gotten worse each time on boost. Should mention that the valve noise I was hearing is gone?

I had my local dealer do my head shim, could they have done something wrong with the valve spacers and retainers or somehting form the factory? I have only put 1 mile on the sled since the head shim and the sled has a total of 440miles.

SPOOLED · Dec 22, 2009

ya the dealer probably screwed up. when that happens the valves are most likely screwed, the keepers and valve tips as well as the shim buckets are going to show signs of wear. the shims were most likely not seated properly in the spring retainers.

0007 · Dec 22, 2009

Ouch
That's an inexcusable problem
First thing you do after cam install is check valve clearance, if your dealer put the cams in then...........
Dont run it, you may need to replace the top spring seat, maybe even the valve

Polarisrocks · Dec 23, 2009

when you pull the cams out to get to the head bolts, you can lift a valve bucket and shim and not even see that you did.... hence the reason to check it everytime. Yamaha doesnt spec thier cams that well either. I think it is better to have your cam specs towards the max side of the specs and not the narrow side. If you noise is gone you may have a big mess, bent valve, stuck broken valve, flat cam lobe. Either way you are pulling the head off or atleast the cams out. Did you do your cam timing when they did the shim?? Look to see it they slotted the intake sprocket.

w8nfsnow · Dec 23, 2009

They did the cam timing and I can see where they slotted the cam gears enough to turn the cams back approx 1mm on both. Looks like they did a nice job on the cam timing but as you say I'm pretty sure they didn't measure the valve clearance after the job. You can bet I'll be taking a quick peek at things before firing it up again. I'm new to these 4 strokes but I'm learning fast..........the hard way! Bringing the sled back to the dealer next Monday to check out the damage!

Do you think the dealer can get the valve retainer back in position and set the valve clearance without pulling the head? Will a leak down test verify the condition of the valve seats etc? I did a compression check and and all 3 cylinders came in at 150psi. I'm hoping I'm lucky and the exhaust valve just isn't opening enough to let the charge out......does that make any sense?

Polarisrocks said:
when you pull the cams out to get to the head bolts, you can lift a valve bucket and shim and not even see that you did.... hence the reason to check it everytime. Yamaha doesnt spec thier cams that well either. I think it is better to have your cam specs towards the max side of the specs and not the narrow side. If you noise is gone you may have a big mess, bent valve, stuck broken valve, flat cam lobe. Either way you are pulling the head off or atleast the cams out. Did you do your cam timing when they did the shim?? Look to see it they slotted the intake sprocket.

SPOOLED · Dec 23, 2009

i would not reset the retainers without looking at the retainer it self and the valve stem, if one keeper is sitting lower than the other than it is just rubbing on the stem, have a good look and dont cut corners just to save a gasket. it could cost you later. i would change the keepers and valves that are questionable they are not expensive at all.

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McXpress 240HP Nytro......idles bad!

w8nfsnow

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TBird

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Washy

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SPOOLED

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w8nfsnow

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SPOOLED

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0007

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Polarisrocks

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w8nfsnow

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SPOOLED

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