My Mods on 250B in progress..UPDATE-NEW PHOTOS By ScooterRider (Read 2,197 times)

[ScooterRider]

OK, installed all new stainless steel High Performance exhaust and the air intake, and upon recommendations, with it I have installed Main Jet 125 and Pilot Jet 40 ( Keihin Carb).
On the center stand, am trying to see how it all runs. So far, can't pass the 6800 RPM, and am only at the 3/4 of the throttle. When twist pass the 3/4, it starts acting like is bogging down and the RPM dropping below 6,000. Am puzzled, because before the re-mods, I was riding it up to 83 M/H pass 7,000 RPM. Any idea what's going on?

Thank you the input

[scootaway]

I think 125 is too big, what is the elevation of Missouri. Johannesburg SA is about 6000vt above sea level where the oxygen is thin and I am running a 118 main and 7000rpm is possible with a little throttle left. I would rather lower the needle one notch.

[ScooterRider]

Update- swiped Pilot Jet from the new 40, to the original 38.
Lowered the diaphragm needle to the lowest position, after the trial at the middle groove.
The results- increased the RPM to 7300(on the center stand) but, still is bogging down at ¾ throttle on the road and top speed reached was around 53 m/h. While puttering at speeds of 30-40 m/h, noticed inconsistent power and the feel of like something was holding me back or pushing. I suspect a vacuum leak at the connection of the tube coming from the fuel pump to the “Y” connector. I have replaced recently the original flimsy tubes with the thicker 3/16” I.D. tubes the connector felt a bit loose.
Am I a the right track?
Also, thinking to go back to the original Main Jet-115, instead of 125. Hoping to regain the power AND the speed, and put this puppy back on the freeway
Any thoughts?

[ce]

Too much exhaust, not enough back pressure. Change the Y's, the stock ones have too small ID.
I'm running a 40 pilot with a 125 main, 42mm filter stuck in the airbox, and stock exhaust at 75 miles an hour at 5,000 feet elevation with 6,000 RPMs from 12/16 sliders in the CVT.

[ScooterRider]

I have relocated the clip upwards, to lower the needle, to reduce the fuel flow. ( I used a posted diagram as the guidance)

[scootaway]

Scooterrider one of the fundamental rules when messing with jet settings is to do one thing at a time. If you don't follow this rules you will eventually run in circles and get horribly confused. That feeling you describe of something holding the scooter back is actually the engine bogging down and is mostly because of too little fuel ie. too lean. Also it is not good for an engine to be pushed to 7000 rpm when on the stand. That will achieve nothing because the engine is not really working, only on the road will a problem show up. Drop the clip notch by notch and go for a ride. After ¾ it is the main jet that takes over (which is what jrryan means when he says smooth transisiton. Sort out the needle first and if all is ok up to ¾ but not there after then tackle the main jet. Can you tell us what mods was done to the air intake, that could hold the key here?

[ScooterRider]

Thank you for the input Scootaway,
I will take some pics of the equipment I have installed and post them. I should make a correction here. I meant to say an air filter, rather then intake.
After my first road test after the re-mods, 2 spark plugs( I have exchanged after I stalled on the freeway) were completely black and covered with soot. I have cleaned them since then.
I ran an other test ride(before the last Dr. JR and your suggestions) After the needle clip relocated to the middle grove and I dropped in Main Jet -120 and put back original Pilot Jet -38
Result: improved power(some) but was able to reach only the top speed of 63 m/h.
I did not check the condition of the spark plug yet. Still felt the bogging at full throttle.
I will re-adjust the clip again and see what happens?

[scootaway]

True what jr said just nibble at it. With the new air filter did you actually increase the airway? The sooted up sparkplug is a clear sign of over richness. I believe that is as a result of the needle setting and not so much the main yet. 120 can do but in the mid range your needle is critical. I would suggest you put the clip at its highest mark (dropping the needle) and test from there.

[ScooterRider]

Dropping the needle was my next step. I haven't check the spark plug for the color, after the last test run. Am very curious if there is any change.
A side note here, with the main Jet 125, I could smell the fuel when getting started. This makes me think, that I was running Super Rich.
Well, back to the drawing board (sort of speak) ..lol

[scootaway]

Ja with a pilot of 40 you will want to go leanish on the needle. The fact that you smell gas on start up tells me that either your pilot and or needle is rich....not so much your main as the main only operates around ¾ throttle. Remember you can also lean out the pilot via the mixture screw.

[ScooterRider]

...thank you guys for the input. Will attempt to do some work on it, this coming weekend. The Autumn is here and the weather is great!

[ScooterRider]

here are the photos of some of my mods:

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[ScooterRider]

...more photos...

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[ScooterRider]

New Road Test Results:
After dropping the diaphragm needle to the lowest point and resetting the mixture screw from the dead end to 1.5 rotations.

1.No more bogging down.
2.Smooth run.
3.On the freeway was able to push RPM to 8,000 !!!
4.On the down side- max speed only 65 m/h @aroud 6,500 rpm

After the engine got to normal operating temp., it had tendencies to die, had to rev up to keep it going at the stop lights.
Am thinking that I may need heavier weights in the vario, to push the belt up on the pulley?
Is my thinking on the right track? One more thought. I did not check for the possible belt slippage

[ScooterRider]

Hey DR.JR
The high rpm were unintentional, I just wanted to see how fast it can run, so I cranked it up. High rpm and not so fast ...lol
The vario is not the original one. It's the J.Costa, it supposed to give you up to 10 m/h faster with more power. I am suspecting, the shipper gave me underrated model (with lesser weights). I need to weight 'em and see.
It seem, I rev too high while just cruising