250 Carb Tuning By JR (Read 2,991 times)

[JR]

Today was a welcome day as far as the weather goes, it's been nice and cool but extremely dry in fact dangerously dry. But about 10:00 a.m. this morning a nice slow gentle rain moved in and my outside projects came to an end.

So I decided to do a little fine tuning on my wifes 250A and my 250B carb. Now we all know the Chinese are famous for setting things lean and I've read about several who have had good success with up jetting the 30mm carb on these two scooters but for awhile I've always wanted to know where the clip was set on my carb's needle so I started with the wife's 250A


Removed the top cover screws and out the diaphragm came and I'll have to say that I was very surprised at what I found.



This is the diaphragm and with this set up one has the little white plastic holder that locks into place instead of being held by a little screw. Just take a 7mm nut driver gently push in and twist and it'll unlock to give you access to the needle and be careful the plastic locking cap has a spring on it too.

Now here is what I was surprised at:



After removing the cap and pulling the needle out I found it set to it's lowest slot and one brass shim washer too! It came from the factory like that and I thought awe this is just an accident on this scooter but I found the same thing on my 250B! Whoever set this engine up richened it up as much as the needle slots would allow and shimmed it too!

So just for the heck of it I added one more brass washer on my wife's scooter because it has always been a touch slower than my 250B.

Slapped her back together and got a break in the rain and out on the road I went. The extra response and pulling torque was noticeable and even though we have a brand new highway here I didn't top her out on wet pavement but I did take her up to 70 with no problem.

Have done the same on my 250B and when the weather lets up we'll see how well she does.

This is a nice easy little upgrade that only takes minutes but remember you do need very thin and small washers to do this and preferably brass is better.

JR

[richardthescooter3]

JR, you said you added one more washer, I thought that if you want more gas you would just move the brass shim higher? I'm some what confused, because I want to check mine in the near future.

[JR]

Yes by adding a washer one raises the needle a touch which adds more fuel. The needle has 3 clip notches on it and on both of my 250's the clip was at the bottom notch and right under that a tiny brass washer which again would raise the needle. Raising the needle adds fuel, lowering the needle cuts back on fuel.

Again this really surprised me because it told me the Chinese knew it was way to lean like it came. So the easiest, cheapest and simpliest solution was one tiny washer versus rejetting to get more in the mid range with the needle. Here's some info on rasing the needle.

thescooterprofessor.proboards.com/index.cgi?board=carb&action=display&thread=196

If one wanted to they could remove the washer, raise the needle clip and put in bigger jets but both of my scooters run very well with what I done so why bother.

JR

[richardthescooter3]

JR, where do you get these washers?

[JR]

Any good ACE hardware should have them, I prefer bass but you can use others. I had a lot of washers from years of building up stuff, you know how that goes! LOl Mine have the right size hole was nice and thin but a little too big as far as the OD went so I just filed them down to fit.

JR

[alleyoop]

If you have a hobby store near you where they sell RC boats, airplanes trains etc, they will have small washers.
Alleyoop

[richardthescooter3]

Thanks JR, and alleyoop, you guy Rock:)

[speedracer]

JR, you have me confused. In your first post you said " After removing the cap and pulling the needle out I found it set to it's lowest slot and one brass shim washer too! It came from the factory like that and I thought awe this is just an accident on this scooter but I found the same thing on my 250B! Whoever set this engine up richened it up as much as the needle slots would allow and shimmed it too! Did you mean rich or lean? Because later you said the Chinese set the needles to run lean.

Thanks

[yoster]

does this work for us 244cc guys as well?

[richardthescooter3]

You know JR I had ongoing issuses with stalling, I thought I was running too lean, but I come to believe I was running too rich, I too put the needle out of carb, I found it set on the lowest slot like yours, I also have a mc54b, I moved it up one notch, I was amazed how much better its running.

Hey we got a person who is having the same issues here so I'll pass that on.

Mine seemed to have more power and top end set richer but just like with any scooter what works for one may not do well with another? They have a mind of their own sometime! ;D

JR

[JR]

Oct 20, 2011 16:58:12 GMT -6 speedracer said:

JR, you have me confused. In your first post you said " After removing the cap and pulling the needle out I found it set to it's lowest slot and one brass shim washer too! It came from the factory like that and I thought awe this is just an accident on this scooter but I found the same thing on my 250B! Whoever set this engine up richened it up as much as the needle slots would allow and shimmed it too! Did you mean rich or lean? Because later you said the Chinese set the needles to run lean.

Thanks

Sorry if I confused you but what I was trying to say is the Chinese are famous for setting the carbs up to run lean and when I opened mine up I expected the same thing that the needle clip would bet set at the highest slot which would be lean.

But to my surprise not only was it at it's lowest slot it was shimmed too! So it's running richer than I expected, this goes against nearly every Chinese scooter carb I've ever opened that was set by the factory. They have always had allowance to set richer but not the 250's of mine. So I added a shim washer.

JR

[JR]

Oct 20, 2011 17:25:42 GMT -6 yoster said:

does this work for us 244cc guys as well?

Who knows? The carbs are alike I do believe and for sure it just takes minutes to check.

JR

[speedracer]

JR how many slots should there be on the needle and where is the best place for the clip? I'm going to pull mine out tomorrow. I also am wondering if your's was set at the lowest setting, couldn't you just move the clip up to the next notch? Or am I so screwed up with this up and down part?

Thanks

Speedracer

[alleyoop]

They ususally have 5 slots and the CLIP USUALLY is in the MIDDLE slot leaving 2 above and 2 below.

If you move the CLIP DOWN FROM CENTER it raises the NEEDLE(RICHER). If you move the CLIP UP FROM CENTER it lowers the NEEDLE(LEANER).
Hope that explains it clearly
Alleyoop

[JR]

Well I don't know why Alley but this needle only has 3 slots and I'm sure that's why the shim washer because again both of my 250's were at the lowest slot.

Speedracer again I know it's confusing but when you remove the top and pull the needle out you'll see the slots along with the clip and "if" it's like the ones we have talked about here it'll have one tiny thin brass washer "under" the clip.

Now if this is what you find it is set at the "richest" possible setting "unless" you add another washer which will as Alley said raise the needle a hair more. When you raise the needle it adds gas= richer.

Now if you decide to do as Richard did and lean it a little simply pull the little clip and move it up one notch, this will lower the needle a hair = leaner.

JR