HONDA CT125 Big Bore Kit

[RustyRodder]

None,except check what the valve clearance is. It might change,or change what it is currently. Check after running a minute or two, let cool off to room temp,check. The valve adjusting screws
will work,but while ordering the 238 cam,order some longer ones. I put the cam in before the big bore kit,and noticed big improvement right away. I did not line up slot in cam with timing chain sprocket
before tightening,and the tab on the timing chain sprocket snapped off after about 15 miles. Loosen the timing chain tension as I did not,and it should make it easier to put timing chain back in place.
I think the 143 cc bbk install was actually easier.

Good to know- I may install this weekend! I should have ordered the longer adjusters...

 

[m in sc]

TBH aren't necessary. ive had zero issues with regular adjusters (and have a set of long ones on hand) set it cold, test ride it, and in a day or 2, recheck it when dead cold.

 

[selly]

I tried the high compression 125 piston as well, and it helped a lot. tried the tb cam, which is more top-end oriented, a stock grom cam, and then the yuminashi cam. all of this with a decatted stock exhaust, all on a stock injector. I didnt feel the need for the larger injector until i went to a 143 and a larger exhaust system, but it can't really hurt as long as you keep it reasonable.
If you look at x92saabs posts on his bike, the HUGE injector he had, i sent it to him. thats primarily for 180cc+ motors, too much for the 164 hes running. so, be careful with going too big as the injector may not be able to trim down enough, or perform poorly if its too large. Theres value in know 'whats too much' as well.
Im running a genuine pcx150 injector, 143, 28mm throttle body, larger intake (not an open pod filter) w larger filter IN the airbox, and aftermarket exhaust and it handles it just fine. .02

Hi m in sc I'm interested in your bbk conversion so wondered if I can ask your advice on a few things please sir. I first got inspired by x92saabs experiments, like yourself I've just done the yuminashi 243 with efie, bigger injector and a Koso afr meter to check how I'm running. I started out with a Yuminashi 155cc injector got too rich readings on the afr, moved down to a Yuminashi 140cc injector and I'm still getting the same too rich readings but the bike runs way better than with the 155cc. I'm running the efie at 250mv, the temperature on the Opmid, which I know is not a true head temperature, looks good at 248 f max so far. Do you think it's worth going down injector size to deal with the rich running or would it be better to trim the efie down to say 225mv and would that get me into a better air to fuel ratio? I'm currently running the stock air box with the filter removed but planning to rip out the paper filter and fit a replaceable foam in it's place. The rubber air intake hose in the airbox could be cut off within the airbox to retain the waterproof side of air intake but would that increase air flow ? What did you do to your intake? Thanks in advance
Selly

 

[m in sc]

yeah you can run it down a bit to 21mV~20mV. as far as the intake, i have a larger throttle body and a larger intake. the intake was sort of a pain, but i was committed to do it as after the exhaust, its the biggest restriction IMHO. its an nk unit.

you also have to modify the airbox , open the hole up a bit. i then sealed it with rtv and its fine. I also modified a stock air filter with a bunch of holes and a sheet of uni air filter material. (no pics to show of that)

you can def try the smaller injector. just keep an eye on it.

 

[selly]

yeah you can run it down a bit to 21mV~20mV. as far as the intake, i have a larger throttle body and a larger intake. the intake was sort of a pain, but i was committed to do it as after the exhaust, its the biggest restriction IMHO. its an nk unit.

you also have to modify the airbox , open the hole up a bit. i then sealed it with rtv and its fine. I also modified a stock air filter with a bunch of holes and a sheet of uni air filter material. (no pics to show of that)

you can def try the smaller injector. just keep an eye on h

 

[selly]

Hey thanks for your help. I think I'll see if I can get the 155cc injector running better with the efie down at around 210mv and see how that goes before moving on down to the 140cc injector as I've seen people having overheating issues with too small injectors. I like the look of that intake you have, what's the expansion chamber looking thing underneath it ? What was the main issues with fitting it ? Thanks

 

[m in sc]

its supposed to be a helmholtz resonator chamber. how effective it is on THIS is beyond me, but i left it alone. its supposed to keep the resonance frequencies from causing a negative reversion effect in the intake. In short, when the intake valve closes, it sends a wave up the intake tract thru the throttle body and can cause disruptions in flow, this is supposed to quell that. was it sized correctly for this? beats me. It was liek 50 bucks for the intake so i cant imagine there was a bunch of engineering going into it.

There was a fitment issue again, at the airbox, had to open it up. also, IN the airbox, it was a hair too long had to cut about 1/2? inch off the end. (hit the top of the box internally).

lastly, under the bodywork, there is a support that it rests right against, makes it hard to route. hard to explain... but its workable.

I would BET this was intended to run an open filter on the end of, even though the ad showed it going into an airbox.

the injector size really is dependent upon what the motor needs, obviously, and what duty cycle the injector is running. you want to stay under or no more than 80% at max useage. Unfortunately, w out a standalone ecm or a power commander (which still as far as i know a PC doesn't exist for this), you cant monitor the duty cycle. THAT was always the determining factor on dialing it in on the grom, etc. you could get correct afr but at wide open, it it was maxxing out at like, 40%, the injector was too big. If it was at like 95%, it was too small.

hope that makes sense.

 

[Happy Campa]

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[m in sc]

just stuff a genuine pcx150 injector in it, will be fine.

 

[selly]

its supposed to be a helmholtz resonator chamber. how effective it is on THIS is beyond me, but i left it alone. its supposed to keep the resonance frequencies from causing a negative reversion effect in the intake. In short, when the intake valve closes, it sends a wave up the intake tract thru the throttle body and can cause disruptions in flow, this is supposed to quell that. was it sized correctly for this? beats me. It was liek 50 bucks for the intake so i cant imagine there was a bunch of engineering going into it.

There was a fitment issue again, at the airbox, had to open it up. also, IN the airbox, it was a hair too long had to cut about 1/2? inch off the end. (hit the top of the box internally).

lastly, under the bodywork, there is a support that it rests right against, makes it hard to route. hard to explain... but its workable.

I would BET this was intended to run an open filter on the end of, even though the ad showed it going into an airbox.

the injector size really is dependent upon what the motor needs, obviously, and what duty cycle the injector is running. you want to stay under or no more than 80% at max useage. Unfortunately, w out a standalone ecm or a power commander (which still as far as i know a PC doesn't exist for this), you cant monitor the duty cycle. THAT was always the determining factor on dialing it in on the grom, etc. you could get correct afr but at wide open, it it was maxxing out at like, 40%, the injector was too big. If it was at like 95%, it was too small.

hope that makes sense.

That makes sense and thanks for taking the time answer my rooky questions. As you say without a measured way of knowing what the engine is demanding its a case of try it and see. You are running your ct125 on a pcx150 injector with a bigger intake and throttle body without issue so I'm taking from that on my bike just running the yuminashi 143 with takegawa exhaust and uni filter the same type injector (Yuminashi say 140cc - it's a Hehin VYT 8 hole new style PCX according to the seller) it should be able to give the engine the fuel it needs. My narrow band AFR is currently saying its running rich but I've not done many miles on it yet so assuming the ECU has yet to learn and trim the fuel down. Am I jumping the gun in thinking about running the efie at a lower mv setting to lean it out instead of allowing the ECU to learn and correct it ? These bikes are a whole lot of fun and as I've just found out tuning them is indeed a rabbit hole.....

 

[m in sc]

give it 50-60 miles. its a slow learner.

 

[Happy Campa]

give it 50-60 miles. its a slow learner.

Here is a snip from Yuminashi to back up "m in sc"

 

[m in sc]

one footnote to that. for the ecm to learn, a quick 5-10 second WOT hit in a lower gear while its learning wont cause damage, and it puts the throttle position/rpm in an area where it can learn. If you read the posts/reports, a lot has to do with 'i did a high speed run' or a 'sustained run' and it over heated/blew up. you need to hit wot gently to give the ecm a data point to refer to a few times in the learning process. .02

 

[Happy Campa]

I'm not sure, but I ordered a PCX150/150 cc fuel injector to couple with the Clipping Point cam I ordered. Hopefully it'll all come in by this weekend. I'll let you know!

May 26th - The cam is in and it seems to be running fine. Time will tell.

June 2nd - Adding to my own comment, yesterday while riding 50 miles back home in 90 degree temps wide open, my engine started stumbling. It was acting kind of like vapor lock, only it is obviously fuel injected. My guess is that with the new cam and hotter weather, my stock injector was maxing out on duty cycle and getting too hot. After dropping back on the throttle it stopped stumbling. I also checked the spark plug. It indicated that my engine was burning on the lean side. Last night I installed the PCX150 150cc fuel injector. Surprisingly it ran really well right off the bat. If this doesn't remedy the lean burn condition, I'll install the oxygen sensor mod.

June 5th - After running 60 miles on the new injector, it has been running richer. So far it hasn't been too rich judging by the spark plug. I bet it will level out as I ride it. I can tell it is using more fuel according to the gas gauge too.

 

[m in sc]

it might cure it, but you should really target a richer afr. fuel is a coolant.

 

[Happy Campa]

it might cure it, but you should really target a richer afr. fuel is a coolant.

Agreed. I'm taking it one step at a time and documenting the results. Hopefully these steps in testing can help others plan their builds. My opinion now for installing after market camshafts is to upgrade the fuel injector with it. Once the ecu settles on afr, I'll check the plug for a lean condition. I already have the Eagle Research gizmo and will probably add that later. I have to pull together some water tight connectors to do it professionally first.

 

[selly]

I'm still getting rich running readouts on my Koso narrow band AFR despite trimming the EFIE down to 205mv. I'm running the Heihin PCX150 injector sold by Yuminashi as the new 8 hole version of the classic 6 hole 140cc minimum, they say "on steroids". Am I right thinking the 6 hole and 8 hole is the same if its delivering the same 140cc? I've run out of ideas. I'm sure I'm hearing a tappet sound when getting on the throttle and it goes away off throttle. I've checked the valve gaps a couple times and all is good, any ideas ? Running stock cam, throttle body, intake, modded air filter in stock airbox, Takegawa sports exhaust and the Yuminashi 143cc kit. I'm planning a long moutainous trip from South Wales UK up to the North Coast in 2 weeks and I'm getting a bit concerned that the CT won't be dialed in for the trip.....

 

[JPMcGraw]

Depending on how rich we are talking I'd run rich on your trip in 2 weeks then fiddle with it when you get back. You aren't going to hurt anything being a little rich. The last thing you want to do is lean it out too far on a fun trip and have a headache to deal with.

Bring an extra sparkplug for piece of mind on your trip. Then when you get home and you didn't have to switch out the spark plug, you now have a spare on hand. You can use that new fresh clean plug to test out all the fiddling you will be doing when you get back.

 

[RustyRodder]

Agreed. I'm taking it one step at a time and documenting the results. Hopefully these steps in testing can help others plan their builds. My opinion now for installing after market camshafts is to upgrade the fuel injector with it. Once the ecu settles on afr, I'll check the plug for a lean condition. I already have the Eagle Research gizmo and will probably add that later. I have to pull together some water tight connectors to do it professionally first.

As of now, you have only the S cam and injector?

For connectors, consider some single-wire weatherpacks. Amazon sells them pretty cheap, and they are pretty easy to set up

 

[selly]

Depending on how rich we are talking I'd run rich on your trip in 2 weeks then fiddle with it when you get back. You aren't going to hurt anything being a little rich. The last thing you want to do is lean it out too far on a fun trip and have a headache to deal with.

Bring an extra sparkplug for piece of mind on your trip. Then when you get home and you didn't have to switch out the spark plug, you now have a spare on hand. You can use that new fresh clean plug to test out all the fiddling you will be doing when you get back.

Thanks good advice. On a related note is it necessary to do a ECM reset using a SCS DLC test mode plug ?, I've seen others have done this after doing engine mods.