6th gear bog

[banshee07]

I have a 4mill long rod, 66.5mm ported(not sure how much), 22cc, +4timing,fmf fattys,

Before I did the crank,timing,head all was good but after I did those mods when im going thru the gears WOT 1-5 is good screams. But when I hit 6th it will scream for a second then it comes down a little and then back up to screaming. It's like half way thru 6th I let off the throttle a little bit but i didn't. I would say it feels like the lower rpm/bog comes in on the powerband. Is it possibly my stock carbs can't allow enough air? Any ideas? TIA

[Sandking]

What jets are you running

[banshee07]

290 and a 310 2000feet. Both plugs are the same brown colour. But I never thought but when I tuned it couple years ago I tuned holding it pinned for a bit then shut the bike off. Thinking I should be jetting it in the power band? I'm use to jetting snowmobiles that are at there peak hp at the top rpm.

[sheerider11]

Sounds lean.

[Sandking]

Try 330

[Strm Trpr]

330 minimum on a ported 4mil!

Stock carbs have made over 80whp!

 

And while we're at it, check your float heights too.

They should be 20+/-1mm.

And for shits and giggles, what groove are your needles on and what pilots are you running?

FMF pipes like fat pilots, so you better have 30's in there.

 

http://www.fmfracing.com/RiderSupport/JettingCenter

[Zillaguy]

Wait, you're running different jetting in each carb?! Not a very wise choice. Keep the carbs synced with identical jetting.

[uman1030]

Wait, you're running different jetting in each carb?! Not a very wise choice. Keep the carbs synced with identical jetting.

Its a snowmo thing i think! seen many snowmobiles with a larger main jet on the pto side carb.

 

but yea fix that keep them the same.

[trickedcarbine]

 

Its a snowmo thing i think! /quote]

So, leave it for the snowmobiles!

[J-Madd]

I have a 4mill long rod, 66.5mm ported(not sure how much), 22cc, +4timing,fmf fattys,

Before I did the crank,timing,head all was good but after I did those mods when im going thru the gears WOT 1-5 is good screams. But when I hit 6th it will scream for a second then it comes down a little and then back up to screaming. It's like half way thru 6th I let off the throttle a little bit but i didn't. I would say it feels like the lower rpm/bog comes in on the powerband. Is it possibly my stock carbs can't allow enough air? Any ideas? TIA

 

What size tires and gearing?

[Glorfindel]

Sorry, but a fine tuned 2 strokes doesnt have the same jetting on each carbs. Put egt sensors and see by yoirself guys... If you tune it by egt, you will not have the same main on each side.

[trickedcarbine]

Thank you for that Jennings era info.

[J-Madd]

But was yours tuned by EGT? On alky we commonly have to open a power jet more than the other, but it's not always on he same side. Jetting sounds way lean as mentioned.

[Glorfindel]

Thank you for that Jennings era info.

Sorry, i don't understand what you mean.

[Strm Trpr]

What elevation are you at?

Stock pilot seems a little small for WETF "Sport Ported" means.

K&N in Airbox w/lid removed or K&N Pods on the carbs?

To start, I'd make sure the carbs are sync'd and the floats are set to 20+/-1mm.

 

When jetting any motor, always err on the side of caution, meaning rich first.

Lower the needle clip one groove to raise the needle and fatten up the entire fueling circuit and see if the top of 6th gets better.

 

If it get's worse, take note how it behaved, then go the other way with the needle.

Move the clip up two grooves to be in the 2nd goove from the blunt end of the needle.

This will lower the needle and lean out the entire fueling circuit.

I seriously doubt you need to lean it out, but I've been wrong less times than I've been right...