PE28FL: Name That Tune!

[bigdano711]

Since so many of us own this carburetor, the idea with this thread is to simply sound off with your tune and maybe your model of bike, altitude and/or time of year you tuned it. This would be to give those of us who have no clue about what we're doing some kind of starting point. Here's where I'm at now, but will likely change to a 40 pilot...back where I started.

Bike: Hawk 250
Main Jet: 108
Pilot Jet: 40
Needle: one down from middle, or position 4
Altitude: 6000'
Attempting to tune in November, below freezing conditions, probably a mistake.

Right now my issue is a lean bog when I crack the throttle from idle. I'm pretty sure the 38 pilot is too small, but will test again to make sure. I still get the lean bog with the 40 pilot, but I have a feeling it's the right jet and can be fixed by moving the needle to a richer setting.

As for the air mixture screw, my manual tells me clockwise = rich, counter clockwise = lean. Can someone confirm this?

[Texas Pete]

Ah, the old chasing the lag or bog off idle when really you crack the throttle wide open when you don't have an accelerator pump throttle design tuning game.

Here you go, enjoy the process. As stated in the video it's a long game, 17+ attempts and testing results, to get closer to a solution.

As far as air-fuel mixture screws remember the basic tenent. If it's on the air box facing side it meters air volume amount, if it's on the engine intake side it meters fuel volume amount. Closing the screw reduces the amount of what's being metered. Opening the screw increases the amount of what's being metered.

[bigdano711]

I had a feeling this would be a lesson in pain. I decided to go back to what the carb came with, knowing if anything it would just make things rich. Then, I decided to check the needle and, 'lo and behold, it was at position 4!!! The manual said it is set to position 3, or the middle. I moved it back to where I thought it was supposed to be, 3, and therefore leaned it. I will likely have to move it back. Seems the base setting they shipped the carb with was best, although a bit rich. So here's where I'm at now:


Main Jet: 115
Pilot Jet: 40
Needle: Position 3, or middle


The air mixture is turned almost all the way in, I believe it's 1/2 turn out. Does it make sense that when I move the needle to position 4, or richer, I will likely have to turn the air screw out to lean, and therefore hopefully be within the 1 to 2.5 turns out sweet spot?

[bigdano711]

I went to position 4 on the needle and as I suspected, I had to come out on the air adjustment screw to lean it and now the low end is totally dialed.


Top end is another story. At WOT, as soon as it hits a certain RPM, it starts to bog. I thought it was lean so went to a 120 main and it got worse, so I'm going the other way, down to a 105.

[Bill Hilly]

On the PE28FL the mixture screw is an idle fuel mixture counterclockwise is richer, clockwise,leaner. I know you're at higher elevation than most of us. I can't remember if your exhaust, and breather us stock, but the 38 pilot would be plenty if you are still running it pretty much stock. I would say about a 110 main,or 105, but I think my Nibbi came with a couple of less common sizes, like a 112.5, or a 108. If you have a 108 it should be pretty good, as well. I get confused when people take about the needle clip position using numbers, but if it doesn't do well with the clip in the middle try moving the clip up towards the blunt end one position. If the bike was doing well with your other carb, then the main jet in it may be the size you need now

[bigdano711]

Originally Posted by Bill Hilly

On the PE28FL the mixture screw is an idle fuel mixture counterclockwise is richer, clockwise,leaner. I know you're at higher elevation than most of us. I can't remember if your exhaust, and breather us stock, but the 38 pilot would be plenty if you are still running it pretty much stock. I would say about a 110 main,or 105, but I think my Nibbi came with a couple of less common sizes, like a 112.5, or a 108. If you have a 108 it should be pretty good, as well. I get confused when people take about the needle clip position using numbers, but if it doesn't do well with the clip in the middle try moving the clip up towards the blunt end one position. If the bike was doing well with your other carb, then the main jet in it may be the size you need now

Are you sure about the air screw? Is the manual wrong?





https://cdn.shopify.com/s/files/1/05...g?v=1669022780


I decided to try the 108 and it's just a little rich. It will bog if I come off the throttle too aggressively from WOT, but if I roll off the throttle, I'm good. Gonna go with the 105. Then my jetting will be exactly the same as the stock carb.

Yep, running mostly stock. I will be doing the exhaust mod next. My neighbor will be welding it back together.

[Bill Hilly]

Originally Posted by bigdano711

Are you sure about the air screw? Is the manual wrong?





https://cdn.shopify.com/s/files/1/05...g?v=1669022780


I decided to try the 108 and it's just a little rich. It will bog if I come off the throttle too aggressively from WOT, but if I roll off the throttle, I'm good. Gonna go with the 105.

Yep, running mostly stock. I will be doing the exhaust mod next. My neighbor will be welding it back together.

I might be thinking about a different carb, but either way just set it by ear. Get your bike idling at proper sleep, about 1400-1500 rpm, and slowly adjust it in small increments, and if it speeds up the idle, turn it back to proper speed, and then fine tune it to get the best idle. Then you know you are right about were you need to be, and if you want to try a small bump in either direction, then you can. I have noticed that when I would either be just slightly over jetted, or have my needle set just a hair high, the bike would still seem to accelerate ok, but it would stumble just a little bit as I would roll off of a full throttle.

[XLsior]

How does the idle behave when the bike is up to running temp...?


If you turn the idle adjustment knob fully out does the rpm go under 1000rpm or lower and konk out?



1/2 turn out on the A/F mix from seated is a bit under spec the ideal window is between 1 to 2 full turns.


Seems the air density at 6000ft does have quite an effect... Most of us low landers under 1000ft seem to be on the 40/125 mid clip baseline for stock CG250 specs.

[bigdano711]

Originally Posted by XLsior

How does the idle behave when the bike is up to running temp...?


If you turn the idle adjustment knob fully out does the rpm go under 1000rpm or lower and konk out?



1/2 turn out on the A/F mix from seated is a bit under spec the ideal window is between 1 to 2 full turns.


Seems the air density at 6000ft does have quite an effect... Most of us low landers under 1000ft seem to be on the 40/125 mid clip baseline for stock CG250 specs.

That question seems to be something to try? I will try that tomorrow and report back. I should update where the carb is at:


Main Jet: 105
Pilot Jet: 38
Needle: Position 3 or middle
Air Screw: 1.25 turns out


I have been busy making some vids:

[Zapkin]

I apologize if you've already seen this, if not, its worth a watch:

[bigdano711]

Yes.


Answer to the question: "If you turn the idle adjustment knob fully out does the rpm go under 1000rpm or lower and konk out?"

[XLsior]

Good to confirm. Sometimes people try to tune/jet carbs with the idle screw over done.

[“IAmYourFather”125]

Did you get it all sorted? If not, I have a few tuning basics I’d suggest.

[bigdano711]

Mostly. Went back to the 40 pilot, 38 was too lean. Now I'm onto the mid-range or needle adjustments. Have been slacking on it. Rode it the other day. She fires up fine in freezing temps. I'm close on the low end but it's still a little lean.

[ughmas]

Nothing too constructive to add that hasn't already been said, but I have been having a bit more trouble than expected tuning mine at around 700 FT above sea level.. will be doing some more experimenting this week - following along