HONDA CT125 Big Bore Kit

[RustyRodder]

Sam, whats your full setup besides the 143/efie/S238? Wonder where yours differs from the others

 

[Happy Campa]

You can get the Finbro Big Valve Head, its a 2 valve. I got one on my 143 with takegawa n15 CAM and everything clears.

Originally I was going to go bigger than the 143 so i got the big valve head but decided to do 143 and avoid all the supporting mods that are suggested for the bigger BBKs. It probably helps around redline but im not sure it helps a whole lot in the rest of the rev range without the displacement.

Great info, Thanks! What is your top cruising speed? My aim is to pull 55 mph even with some wind.

 

[Happy Campa]

Here is the 2nd piston with 65 miles.
Felt great until it tried to seize at the 60 mile mark.
The last piston that did this, it was also at about the 60 mile mark…

View attachment 5716View attachment 5717View attachment 5718

WOW! It looks like its burning super lean.

Check this out if you haven't already.

 

[Samg7]

Sam, whats your full setup besides the 143/efie/S238? Wonder where yours differs from the others

S238 cam, PCX150 injector, EFIE @ 225mV, Yuminashi 143 kit

edit: After 1st seize, spark plug changed to CR8 plug.

I need to understand why this happens at ~60 miles both times. It could be that’s when I start to get on it, but after the first 20 miles I start to ride it like normal, just making sure to not rev it too high or downshift to aggressively.

 

[Samg7]

@Happy Campa it doesn’t look super lean to me but could be wrong

 

[Happy Campa]

@Happy Campa it doesn’t look super lean to me but could be wrong

The lack of carbon deposits makes me think its lean. What does the spark plug look like? It could have gotten hot and burned anything off, coupled with being new. Did you check the ring gaps before install?

 

[JPMcGraw]

Great info, Thanks! What is your top cruising speed? My aim is to pull 55 mph even with some wind.

55 is easy @ 1/4-1/3ish throttle. Ive done it with my SO on the back too.

This is my grocery getter and ride the dog around the neighborhood bike so 45 is where the bulk of my riding is. I have done the 9 miles to work and 9 back at 50-55mph before and it did fantastic. It was 60* outside though. I don't know that id be cruising 50-55 in summer heat for prolonged periods but that's my anxiety talking.

You should be able to do 55 with the stock head so unless you get the itch to fiddle id skip it.

 

[Samg7]

Got the bike back together again. This time with the spare 143 cylinder and piston from @Lazy Dog Productions I had laying around. Different piston with a different design.

Decided to disconnect the EFIE just to eliminate unknowns.

Did the first heat cycle last night on the stand, just warming it up varying the RPMs. I looked at the plug this morning and it looked much more rich than all the times before. Recheck my EFIE connections and voltage setting… all was good. Here is a pic of the EFIE setup in case I’m colorblind. White to O2 and Green to ECM

 

[dmonkey]

Got the bike back together again. This time with the spare 143 cylinder and piston from @Lazy Dog Productions I had laying around. Different piston with a different design.

Decided to disconnect the EFIE just to eliminate unknowns.

Did the first heat cycle last night on the stand, just warming it up varying the RPMs. I looked at the plug this morning and it looked much more rich than all the times before. Recheck my EFIE connections and voltage setting… all was good. Here is a pic of the EFIE setup in case I’m colorblind. White to O2 and Green to ECM View attachment 5727

What voltage did you set the EFIE to?

 

[Samg7]

225mV checked it a few times throughout and it was always 225-230mV.

I know the CT throws a check engine light if the O2 is disconnected, so doesn't seem possible that there was a bad connection.

Although I wonder if there was a bad connection and the O2 signal wasn't getting through, but the EFIE was sending the ECM 225mV, what the ECM would think...

But I did check all connections for continuity after install

 

[Samg7]

First 30 miles down. Feels ok, sounds ok, smells ok.
Here is the plug

 

[Happy Campa]

First 30 miles down. Feels ok, sounds ok, smells ok.
Here is the plug
View attachment 5760

What do you guys think? Here is a spark plug reference on engine conditions. Mayhaps a tad lean? Just my interpretation of the tea leafs.

 

[Samg7]

Here is a picture of @SLO‘s plug

 

[Happy Campa]

Here is a picture of @SLO‘s plug

View attachment 5782

Now that one looks like it's burning with a good air fuel ratio. Not too lean / hot. The center electrode is free of carbon build up, but not bright white from running hot.

 

[m in sc]

looks good. fyi, bottom of piston crown, under it, is best way to check motor heat. im serious. white, ashy or discolored gray, too hot.

 

[SLO]

Here is a picture of @SLO‘s plug

View attachment 5782

I did over gap the top two rings , the first by a few thousandths,not intentionally. It was the coating on the rings that I was removing,and a couple strokes with a file was too many. I put the gaps
in the rings 180 degrees apart as opposed to what is normal. I swear I believe the gap when installed was at least 14 thousandths on both of them. If it does smoke a little,it stops as soon as it warms up,does not use oil as far as I can tell,but I change it pretty often. ????? I will send a video of the Red Rocket if requested.

 

[Samg7]

Seized it again.

After 20 miles of 1-5% grade at 45-50mph. This is with the Thai 143cc kit, not Yuminashi, and without the EFIE. Safe to say the EFIE and Yuminashi kit are not the problem.

Luckily I can recognize it quickly now and put in the clutch. Let it cool off, and rode 20 miles back home with no issues or piston slap noise.

Did the borescope, minor 4-corner scuffing but will continue to run it. Drained the oil and switched to Castrol 4T 10w-40 Synthetic.

Does anybody know the numbers on their injector? @x29Saab your video showed the 5HT to be the Takegawa 115cc…

Just want to make sure my injector is what I think it is. It was given to me by a friend in Thailand, so I am unsure.

What I think is a PCX-150 injector reads “LJ06 5HT” and is a 6-hole.
For reference, my stock injector reads “KJ07 VFT”, also 6-hole.

 

[RustyRodder]

If you have a 115cc injector, that may be the cause of the issue. under fueling capability

 

[Samg7]

I really hope my issue has been the injector all along.

I’ve got a real PCX150 injector on the way, along with the Yuminashi 170cc/min.

 

[Happy Campa]

I really hope my issue has been the injector all along.

I’ve got a real PCX150 injector on the way, along with the Yuminashi 170cc/min.

I'd put money on it helping. I just ordered a PCX150 injector as well. Now I need the cam and bore kit!