The Honda PCX / Forza / ADV150 / SH Forums

We all know that there's going to be inherent complications when you screw with the engine, particularly with those big bore kits. On the other hand, it's still good info to know how long folks can get away with it.


So out with it:
What kind of engine mods have you done(trans doesn't count), how long have you had it(preferably in miles/km), and what, if any complications/problems did it cause?

Could be changing a spark plug, going all the way with a Yuminashi 196cc big bore kit, and anything in between .

Scrubs like me might appreciate the ramifications of your engine melting down in 6 months after shelling out over $1,000 to replace all those OEM Honda parts .

Valiant wrote: Scrubs like me might appreciate the ramifications of your engine melting down in 6 months after shelling out over $1,000 to replace all those OEM Honda parts .

Chief say... "mess with engine bring bad medicine"

I am a big proponent of "If it ain't broke, don't fix it". A long time ago, a work friend got an almost-new Fiat 124 (a very pretty piece of machinery, but not, how you say... reliable). Since he was a MechE, he figured that if he took it apart and did his best to "blueprint" the engine, it would be fabulous.

You all know how that turned out....

I guess if I wanted a higher top speed, I would have chosen a different scoot, especially now that the Forza exists.

But I do love reading about all of our members' adventures messing with the guts of our little guys.

GeorgeSK wrote:I am a big proponent of "If it ain't broke, don't fix it". A long time ago, a work friend got an almost-new Fiat 124 (a very pretty piece of machinery, but not, how you say... reliable). Since he was a MechE, he figured that if he took it apart and did his best to "blueprint" the engine, it would be fabulous.

You all know how that turned out....

I guess if I wanted a higher top speed, I would have chosen a different scoot, especially now that the Forza exists.

But I do love reading about all of our members' adventures messing with the guts of our little guys.

!00%, nothing to add

As a counterpoint most of these bikes do low mileage or will have their useful life ended by something other than engine failure.

So fiddle away....

14000km with big bore and no piston melts or big drama so far. Has acelaration of 9sec to 60mph all day every day...I have to say it's fairly reliable so far.

Have about 700 miles on my Yuminashi cam, rockers, double valve springs, intake manifold, injector and throttle body.
So far so good ...better than vario and sliders alone, for sure.

Pcxdemon wrote:14000km with big bore and no piston melts or big drama so far. Has acelaration of 9sec to 60mph all day every day...I have to say it's fairly reliable so far.

What type of kit is it? IIRC, Mgalutia88 had an issue with his 170cc SP Takegawa kit with the gasket head getting worn out after 5000km. I'm also a little concerned that the kit doesn't include stronger valve springs, which I hear is necessary.

dasshreddar wrote:Have about 700 miles on my Yuminashi cam, rockers, double valve springs, intake manifold, injector and throttle body.
So far so good ...better than vario and sliders alone, for sure.

Is that a 175cc kit or the newer 196cc kit? Did fuel economy change at all? Did you need something to tweak the fuel mixture, or are those parts working well enough without remapping?

pcxdemon has the 164 Yuminashi big bore for the v.1 125 pcx...

I don't have a big bore kit, just the stock 153 and stock ecu with the Yuminashi head mods. works fine.
fuel economy is pretty much the same... not really sure/don't really care, but probably around 80+mpg.

Do you ride WOT often?

I normally get about 95+ mpg on the gauge, though today I went 38 miles almost entirely on WOT and got about 83 mpg.

If I understand it right, the trick is to gear it longer so you can cruise at the same speeds, but at lower rpms, and the big bore is just for torque and acceleration to get you up to speed.

I wot it most of the time..it's hard not to but it's not really hurting it so far. Remarkably I still get just over 200km out of the tank. If I would to gear it up, it would be even better than it is now, but I'm quite happy and content getting it fast to 135kmh on the speedo..it's fast enough!

Pcxdemon wrote:I wot it most of the time..it's hard not to but it's not really hurting it so far. Remarkably I still get just over 200km out of the tank. If I would to gear it up, it would be even better than it is now, but I'm quite happy and content getting it fast to 135kmh on the speedo..it's fast enough!

Really? That's quite the number there, about 84 mph IIRC. I can only do about 70mph on a bit of downhill with full transmission mods, air filter, and exhaust on my 150. It might simply be the island roads(almost no straights, low speed limits, heavy traffic in the day), but I typically can't go much faster without encountering one obstruction or another that makes me back off the throttle.

Pretty shocking that 11cc's can make that much of a difference. Did you also tweak the fuel mixture a bit?

For me, it's not quite about raw speed, but rather how fast I can get to that speed. Right now I'd say 0-50 is about 10 seconds or less, but anything past that takes forever to climb up to unless I'm going downhill. Unless I'm on a flat or downhill, a family sedan can still leave me in the dust on the highways.

I'm also thinking that if the WOT speed is 85 mph, but I'm only twisting enough to go 70, it would be much less straining on the engine, which I suppose might be an irony of an engine mod if my point was for reliability.

If the quality of the kit is good and the install is competently done, is there any anticipation of any problems? I presume if the fuel mix isn't too lean, damage to the engine itself shouldn't be expected?

I can't see any problems...for fuel mixture, just upgrade to bigger injector, no problems there..

Sounds scrumptious . I just need to pop Reggie an e-mail about when he'll have more 196cc bbk available.

Despite what I said, I'm starting to feel an itch. It's a bit sad to see the family minivan tearing ass past you on the highway Q.Q

Pcxdemon wrote:14000km with big bore and no piston melts or big drama so far. Has acelaration of 9sec to 60mph all day every day...I have to say it's fairly reliable so far.

dasshreddar wrote:pcxdemon has the 164 Yuminashi big bore for the v.1 125 pcx...

Wut? Wot? What?
http://www.hondapcx.org/viewtopic.php?f=9&t=796

If that's true, I might give Takegawa more consideration, as it is said that Takegawa is more conservative with their performance mods.

I won't "mod bash" but this scooter's performance even with my minor mods provides questionable long range or frequent freeway performance with me as a 150lb rider and no cargo.

I think if you're frequently encountering hills and since you wegih 200 and take 25-30lbs cargo...you can sweat it out over mods, or just get a Reflex and call it a day.

I'm usually all for modding, and modify every vehicle I own including my Nissan Leaf! Lol. But, these parts coming from Asia with no or poorly translated instructions, etc just have me a bit spooked. I dunno what to tell you, other than learn to live with a power deficit, or go through the mentally taxing task of try to research parts that are hard to find any sort of hard data, facts, or reviews on.

It's a shame the PCX doesn't have more bawlz, as it would not have been hard to do. If you can get someone with a reliable setup to help you through the mod process with a big bore kit, then great. But if not, I would just let it be. I want more power on mine, but am smart enough to know if I need more, to just get a bigger scooter. I've had plenty of 1000cc sportbikes and all. I was literally trying to get away with the smallest engine possible with my PCX. And, for me and my weight/needs...it works (just barely).

I totally agree with the "sketchy" Asian customer service on performance parts.
I can't say I trust Yuminashi stuff/customer service, however all my Yuminashi parts are doing fine (knock on wood).

But i'm all for Valiant being the guinea pig on a 196 big bore kit sounds awesome.
Until then I'm much more leaning towards a engine swap... probably a forza 300 with pod filter, custom exhaust and Dr.p sliders only.

Is there enough space to fit a different engine underneath the fairings? Because I figured that would be one reason why the BBK are limited as they are.


On the bright side, my scooter shop says such a mod(the Yuminashi 196cc kit specifically) would cost "at least $600", which is a very favorable rate given that my dealer charged me almost the same amount for an oil change and to change out the exhaust, belt, and vario.

My bad, it seems like it was pcxdemon and not Mgalutia88 who had the issue with the Takegawa BBK:

http://www.hondapcx.org/viewtopic.php?f=9&t=3414

Pcxdemon wrote:I have to say this...yuminashi big bore is better. Why? Well it's slightly smaller than takegawa in cc's and that will give you a safety margin regarding head gasket space between water jacket and combustion chamber. It means there is less likely a chance of head gasket failure and a leak. Point 2, it uses a single layer gasket like a Honda stock gasket which also means of less failure than a triple layer takegawa gasket. Point 3, because it's a single layer gasket, compression is higher which means it will be more powerful than takegawa kit.
However takegawa is good kit as well, but, when my head gasket failed after 5000km,their reply was 'head gasket is a consumable part and it's advised to replace gasket after 5000km...also,it's made for racing application so no warranty afterwards is given unless you have received defective product and they would replace it immediately..

I wouldn't be too thrilled at having to replace the head gasket every 3000 miles, especially since there doesn't seem to be availability for just that part on webike. Unless you can cross the Takegawa BBK with the head gasket from Yuminashi?