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Missfire at 1/8 throttle on 485 banshee


lt1bird

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Guys, this misfire is driving me crazy... 485 trinity setup... runs great at 1/4 throttle up... for the life of me I cannot fix the what im calling a misfire...  at 1/8 throttle it seems to sputter a lot....I lean it out and you can feel it get a big boggy as you would think, but the sputter is still there....seems to be there if im rich or lean...does not matter..again, everyplace else seems just fine...If it were ignition I would think it would do it under more of a load as well...  any help would be awesome, im lost at this point and ive built a bunch of these LOL

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carbs are clean, no power valves as they are blocked off.

Ignition...its all new, timed etc but ill put a timing light on and see if its misfiring via the spark plug wires... you don't think jetting would do this? air leak...guess I could check the reed block gaskets etc...

Edited by lt1bird
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its a 485 with trinity PV cyl's... blocked off.... stock porting....155psi compression...  setup for pump gas...ignitec ignition...24 total timing... 38mm keihin carbs..  pipes are midrange pipes... v force reeds,

158 mains

65 pilots

#6 slides

DEQ needles

 

Ive tried leaner slide, richer slides....different needle dia etc to try and clean up 1/8 throttle... im starting to wonder if there is a leak in the exhaust.. so its sucking air in at lower throttle settings... think that could do it?

 

whole new setup so its never been dialed in...  well, 1/4 throttle up was and I rode it like that for a little bit...now im making a big effort to make it smooth... and its just not good.... don't get me wrong...you can ride it like this but it should not be doing that at 1/8 throttle, you should be able to put along at 1/8 throttle steady cruise without is misfiring/sputtering...

Edited by lt1bird
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The porting is stock.... the PV block off plates I cut to fit so they matched the port perfect...full open. Even with the power vavles installed it was going the same thing....maybe a bit worste..

I have tried pretty much all the pilots from 50 up...

Edited by lt1bird
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tim from titan made them...they were exactly what I wanted...  positive quish unlike the negitative squish angle on the trinity domes.

 

The DEQ needle.... the Q is the diameter, and its the leanest I can find.... that's why I went to a leaner slide...the leaner slide most definatly leaned out the idle as well... so the slide leaned from idle to 1/4 throttle... and it still seems to misfire like its rich... even the EGT seems to drop when it starts to miss at 1/8 throttle... drops to 290-300C from high 300's   This is the second motor ive had do this...I had a 535 do the same thing... but I never spent much time to fix it.....whole different motor, pipes etc... with power valves... im just wondering if im being to picky? maybe a built in issue with the stock cylinders? I would imagine not many quads would be staying at 1/8 throttle lol   I might take a day and go trhough the setup and check for leaks, comprssion, leakdown etc... check timing... just to make sure....

 

 

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