jetting and dome size

[fastforworddad]

Just got a question in regards to jetting and does the size of your domes having any correlation to the size of your jets.

 

Got a redline built 10mil serval with shearers and PWK35's.  Currently jetting is 158 mains, 50 pilots and DGK needles on the middle clip with K&N pods at sea level.  Temps are 70*-90*.  My domes are 26cc.  

 

Chopped the plugs at 155 mains and seemed just a tad rich.  Since that chop i put 12 paddle extremes on and it felt a little flat so i richened it up 1 size on the mains.

 

Went through what others are running for jetting and consensus seems that I may be leaner than most already.

 

Wondering if the dome size may have some correlation to final jetting sizes.  

 

For example,  will an engine with smaller domes require a richer jetting tune?

[fastforworddad]

Really guys, nobody has an opinion? 

 

Find that hard to believe on this forum.

[RadarRacing]

Absolutely , even a dome design with the same Cc size will work differently. You might get 20cc domes from one place that would run completely different than another. One may require a bit more or less fuel depending on design. I am decent on jetting by the seat but ultimately am often off by a couple jets. If it felt rich to you and the plugs looked rich I dont understand why you would go up one jet. 148-160 is probably in the range where you will find most 35pwks on a cub. Dont worry about what others are running for jets unless you are way out of the norm. One builders domes may be fine on jetting and another with a different dome of the same cc may be quite a bit leaner or richer. Needle ,dome , pipe, degrees of timing etc all are a factor in jet size.

[fastforworddad]

Thanks for the replies.

 

So if I swapped in 23cc domes and everything else was the same(squish and profile), it would require bigger jets and more fuel, correct statement?

 

The reason I ask is because it seems a little flat in the midrange until it gets on the pipe. Wondering if I would have to go down a cc or two to get more midrange.

 

Had been playing with the needle positions, went 1 step leaner on the clip, then 1 step richer on the clip.  Seemed to be lacking some "zing" 1 step richer, so wound up with the needle clip in the middle position.  Then went down from 160 main to 158.  Just think when going to WOT it should build r's a little faster on its way to getting on the pipe.

 

Compression test yielded me 135psi each side with 26cc domes and timing  set to +4.

 

My pilot is a 50 and carbs have been synced using the sync tool that FAST sells several times. My slides are #6.

 

 

Another question:

 

My method for adjusting the pilots is as follows----I turn each screw out equally until the bike achieves its fastest idle speed.  Then I count the turns and I am usually around 3 turns out on both pilots.  This leeds me to believe that I am rich on pilots, but I really haven't noticed any real change in performance with the pilots 1.5 turns out or 3 turns out.

 

One thing I have noticed is that when I start it at home when engine is cold, starts usually 1st kick with only occasionally having to use the choke.

Idle is good and solid, although when motor is hot and after stopping for a few minutes out on the dunes, again starts first kick but idle seems considerably "lazier" and somewhat lower.  My thoughts are it is loading up, but why doesn't it load up when its at home.  I have let it get to operating temp at home and the idle is rock solid.  Think I will just have to get a pair of 45's and 48's coming.

 

Any thoughts will be appreciated as always.

 

Thanks.