no gain after big bore installation

[wbradshaw6]

I recently had a big bore kit installed on my 50cc 2 stroke XMC Americano. The mechanic told me that it was a 90cc kit. After the install and a 100 mile break in period, I cant notice much of a difference. Maybe a little bit more power, but top speed is the same. I am wondering why this is. The mechanic rejetted my carb so I know it is not that. Could it be that my carb needs more air? Should I try installing a uni pod air filter? If I do, is all I have to do is remove my air box and clamp the pod directly to my carb? Also, it looks like it will not fit without an elbow or something, where can I find an elbow for it. Someone let me know because I am a little mad that I spend money on the big bore kit and I did not get any gain.

[stepthrutuner]

Not really familiar with this scoot. Most, if not all, 50cc 2 stroke motors cannot be modified to 90 cc without enlarging the crankcase opening where the cylinder mounts. The crankshaft must also be replaced with one that gives a longer stroke. Having someone do this most likely would cost at least $700 and more likely more than $800. Most likely you have had a 70-72cc cylinder installed.

Your problem could be intake track restriction and a cannister or cone style filter will help a lot. You will need to go up in main jet size to somewhere around 85-95 most likely to compensate for the loss of vacuum in your carb throat due to the free-flowing filter. Sometimes stock exhausts have a restriction at the header/exhaust flange mating area, so you could check for that too. Of course a performance pipe, in addition to the free-flow filter, would help too.

[stepthrutuner]

Check your exhaust for the restriction before you do anything else.

[wbradshaw6]

thanks for the advice. The mechanic said that he derestricted everything that he could find, something about matching the exhaust manifold to fit something, I was lost with what all he said he was doing. For the pod filter, do I just remove the air box and clamp it directly onto the carb? Also, I dont know if it will fit so is there some type of elbow or something I can get to make it do a 90 degree bend like my air box does, or something I can get at the store to ghetto rig a bend? And I am not sure of what to get, especially what size. Below is a link to the filter I am planning on ordering, let me know if this is the right one. Also, the mechanic rejetted my carb when I got the kit installed, should I put on the air filter and give it a test run before I rejet it again? You know, just to make sure that it is not running rich now and the air filter will just even it out. My elevation is at 3500 ft and I got the kit installed around 1000 ft, so maybe the change in elevation had something to do with it.

Pod Filter:
www.scootercatalog.com/air-filter-unipod-scooter.html

My scooter is the same as a Strada RX8 or Zip, just different body style. It has the 1E40QMB engine, the same that is on pretty much every chinese scooter you see.

[90GTVert]

Yeah, the pod filter would either attach directly to the carb's mouth or via an adapter like you mentioned. If you use an adapter, try to keep the diameter at least as big as that of the carb's mouth and the ID of the filter. You can make one up, may take creativity, or try using part of the stock airbox maybe. Here's one I made from a few things from Ace...

49ccscoot.proboards.com/index.cgi?board=carb&action=display&thread=369

Take a look at your plug and see if it's black like it's rich. You need less fuel at your elevation because of the thin air than he would have needed to tune it at 1000ft. I'm in a flat area so I'm not used to elevation changes, but from what I've seen you would probably be 1-2 jet sizes richer tuning at 1,000ft compared to 3,500ft. The idle mixture setting would be rich as well.

[wbradshaw6]

Just checked my plug, extremely black, almost looked wet. I am thinking that when the mechanic upjetted the carb, he didnt do anything to increase the amount of air getting in. I checked my carb and it is a 19mm, I didnt realize it came stock with that. Also, I couldnt get a good measurement of the air intake side of the carb, looked to be around 37-39mm. Is the pod filter that I have a link to the right size? Seeing as how I am going to have to ghetto rig something to work as an elbow, should I get a wider one so that it is not to small. The website that I am looking at has either 38mm or 44mm, let me know which one I should get. Also, does anyone know of a site to order main jets from for my carb, again it is a 19mm 2 stroke carb. Thanks for all the advice, this is really helping me out!

38 mm filter
www.partsforscooters.com/Uni-air-filter-for-full-size-scooters-169-71?sc=2&category=76416

44 mm filter
www.partsforscooters.com/230-33-Uni-air-filter-for-full-size-scooters?sc=2&category=76416

O yeah, does anyone know of a good place to buy materials to make the elbow? I live in a small town so all we have is a Lowes Hardware, any good materials there? PVC? Metal tubing?

[wbradshaw6]

I got the materials covered, I didnt see the link in the previous response. So now I just need to know if I shouid get the 38mm or the 44 mm. And also where to get main jets. Thanks

[2strokd]

You can get jets here www.jetsrus.com/..
You probably have the common Mikuni VM18mm on your mina.
Most came with those or a clone of one. Not all did tho.
I need to know what kind of carb for sure to tell you what jet you need.
I can tell you that there is no REAL benefit to running an open air filter on a slightly modded scooter. It will just make sound, like two exhausts . You will need jets for sure if you go with one though!



Edit, Is it a Minarelli engine? :stars:

[wbradshaw6]

I looked up the carb online and it says that it is a "Carb is a PZ19JB-2 QJ brand. Its a 19mm carb so that's a plus. Jet head size is 6mm, length 10mm with 6mm thread. Standard jet size is a 61." I do not know what size the mechanic put in but I am guessing it is already too large because my spark plug is blacker than night. Plus, I live at 3500 ft so according to previous posts it does not need as much fuel. So I am hoping that the air intake will just even it out. But to be sure, what size jets should I order. I figure I will get a couple, so maybe 75, 80, 85, 90? Which one should I start with?

[wbradshaw6]

Nevermind, that was wrong. It is actually this:

Identification: PZ19JB
Venturi:19mm
Main Jet Size:#80
Pilot Jet Size:#57.5
Neddle position: 3rd groove from top
Idle air adjusting srew: open 1 1/2 tp 1/2 turnout counter clockwise
Float Hight: 13+-mm

And again, it was already upjetted to something, so maybe I should be shooting for the 95 range for the main jet?

[90GTVert]

The info you're giving us sounds an awful lot like a minarelli, but it would be nice to know. Do you see 1E40QMB or soemthing similar on the case? Should be near the back of the case, up top, by the CVT cover. If that's what it is, it probably is the Mikuni VM11/22 main jet style. Here's another good spot for those jets...

www.rockymountainatv.com

At your elevation, the stock 80 might do it with the stock airbox. Might even do it with a pod filter. I dunno. I'm at a mere 40ft above sea level and I use a 90 witha stock airbox and the snorkel removed for a 70cc sport kit with a pipe. Like 2strokd said, the aftermarket filter really won't do much. It's going to make the scoot much louder though. I love 2Ts, and even I'll tell ya it can be an annoying tone sometimes with a pod filter.

[Fox]

Raise the needle clip position a notch or two and then check the plug color after a little ride. Raising the clip will lean out the high speed mixture a little w/o changing the filter. You may see a few more RPM's. Try it in all positions. Brown plug means you're there.

[stepthrutuner]

That pilot jet is huge (57.5). Is that the stock pilot jet? This could be part of your problem. Wish I could talk to your mechanic and ask him what exactly he did. I'm down to a 30 on my Derbi to get the off-idle response clean.

[wbradshaw6]

As far as I know that is the size of the pilot jet. My engine cover does say 1E40QMB, so I am pretty sure I need to get the jets you are talking about. I went to lowes hardware today and got the same setup to build an elbow for my pod, j pipe and pvc. The intake should come in the mail in 2 or 3 days so I will let everyone know how the install went. If this doesnt fix the problem, does anyone know of a good scooter mechanic in central or western nc? I have been to 2 shops so far and have not been impressed with either, seems like they just want to do it quick and move on to the next bike, I need to find someone who will take the time to do it right!

[90GTVert]

Check on your local craigslist. You might have more luck finding folks working from their homes for some spare change that are more likely to spend the time they need to make it right, and probably charge less hourly than the bigger shops.