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Lean running 2.6 225 Yamaha
https://hpbc.ca/viewtopic.php?f=19&t=2941		 Page 1 of 5
Author:  J.Kimmerly [ June 30th, 2015, 4:43 pm ]
Post subject:  Lean running 2.6 225 Yamaha
Im having issues with my engine running lean. It has Nikki carbs 34mm. From what ive read its the main air jet in the top of the carb that effects higher rpm the most, like above 4000. Just want to make sure im on the right track here.

Some of the guys on here are familiar with this engine, used to be OneCycles. Its ported with cross milled intake and tight heads. The gas jet is a #180. The air jet is #240.
Author:  DoktorC [ June 30th, 2015, 11:09 pm ]
Post subject:  Re: Lean running 2.6 225 Yamaha
It's probably easier to add fuel through the main jet...how lean is it? If you find bigger jets don't do anything you may need to drill the needle and seats.

You are correct about the air jets on the top of the carb.
Author:  idvette [ June 30th, 2015, 11:33 pm ]
Post subject:  Re: Lean running 2.6 225 Yamaha
Doc's the guy to talk to on this motor
Author:  J.Kimmerly [ July 1st, 2015, 12:25 am ]
Post subject:  Re: Lean running 2.6 225 Yamaha
Lean enough to do damage. The plugs are showing up brown, seemed ok to me. The exhaust temp on the pyrometer was climbing up to 1150 F. at 5900 rpm and was starting to surge. Put a new piston in it tonight, one of the lower ones.

How much bigger do i drill the jets?
Author:  DoktorC [ July 1st, 2015, 11:57 am ]
Post subject:  Re: Lean running 2.6 225 Yamaha
J.Kimmerly wrote:
Lean enough to do damage. The plugs are showing up brown, seemed ok to me. The exhaust temp on the pyrometer was climbing up to 1150 F. at 5900 rpm and was starting to surge. Put a new piston in it tonight, one of the lower ones.

How much bigger do i drill the jets?


Until it stops blowing up lol.

How tight are the heads??
Author:  Jeff Yammer [ July 1st, 2015, 2:16 pm ]
Post subject:  Re: Lean running 2.6 225 Yamaha
As mentioned above.

What drill size jet are you running currently ? What holes are showing as hot ?

When it comes to EGT they can be misleading at times but if it's burning up then ..... All other possible block / intake leaks checked for passing gaskets etc etc ? Fuel pump checked for consistent pressure throughout the rpm range ?
Author:  J.Kimmerly [ July 1st, 2015, 2:41 pm ]
Post subject:  Re: Lean running 2.6 225 Yamaha
Top and bottom cylinders are showing very little piston wash on the crown, mid cylinders look like they are getting lots of fuel. Drill #49. 73 thou on the main jet. Running the stock pulse fuel pumps. Not sure how to check pressure on those.
Author:  J.Kimmerly [ July 1st, 2015, 2:44 pm ]
Post subject:  Re: Lean running 2.6 225 Yamaha
Heads are HT 8200. It compressions at 110psi. Id imagine thats cause the exhaust is ported so mush higher than stock.
Author:  ONTBULLET [ July 1st, 2015, 4:22 pm ]
Post subject:  Re: Lean running 2.6 225 Yamaha
Owned the motor long?
Author:  J.Kimmerly [ July 1st, 2015, 5:07 pm ]
Post subject:  Re: Lean running 2.6 225 Yamaha
A year.
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