My wife is coming out of retirement to race the 125 this year so it has been freshened up with a much modified Dyna S CB750 ignition. Hopefully this will cure a miss fire above 12,000rpm.
Also building a new engine with lightened crank and maybe home made pistons.
I had a missfire at high rpm and found it was to weak a spark and it actually ran better with a smaller than standard plug gap!?
Isnt the standard max power at about 13,000rpm on the 125 twin?
I looked at one cb125 twin engine and it had inlet ports of only about 10-15mm; but I heard that some engines were of lower restricted power as the standard was about 16bhp, so did they make a restricted version with the small ports for smaller carbs?
@tpvalley I run Dyna coils and a total loss ignition system, big fat sparks until the battery gets below 10volts. See my comments above about rear wheel horsepower and rpms. The CB125TA was the non restricted version for the UK, later versions have small bore exhausts and a retard in the electronic ignition to limit power.
Honda claimed 16.5hp @ 11000 rpm. This was emphatically NOT at the back wheel, rear wheel hp was more likely 13.
Manufacturers claims of hp were based on crankshaft hp and usually optimistic at that Honda! For example they claimed 42 for the CB500T but when tested in 1975, actual rear wheel hp was 33.5! CBX1000; they claimed 103, actual 85.5.
nice, i had a 1971 cb100 honda (basically the same engine, it just revs even higher due to the lighter weight piston) that I ported intake and exhaust, turned a alum intake manifold, installed a 28mm dellarto carb, and a hand rolled megaphone. custom seat-tank-clipons-rear sets. I rode it 850 miles to Illinois for a motoguzzi rally
I am sure the CB125T was never imported into the USA (it's a twin cylinder engine). The CB100 was a single cylinder engine sold worldwide and also as a 125, sounds like you had lots of fun.
Safe engine revs are dictated in the first place by the stroke of the engine. The stroke of the CB100 is 49.5mm and the CB125T 41mm so the latter should be cable of revving higher. When I get around to making a new cam I reckon we can go to 14,000 occasionally before thing start colliding, we shall see.
@jonesjpthrower The CB100 was a single cylinder engine. The CT125T is a two cylinder with twin carbs. In standard trim it put out 17hp at 11,000rpm. The 100 cc engine was a single and was also available as a 125 and a 185.
Ported head and skimmed head, modified Honda 250 Hornet carbs, tuned exhausts plus stuff I can't remeber. You can find much more if you search for 'The Fang' and go to 'News 2008'.
very nice!
ijzerable 5 months ago
I hope to get onto the CB125T later this year. We are allowed 150 cc in F4 racing and I have a 150cc upgrade kit. My current single can be viewed at
I hope to get onto the CB125T later this year. We are allowed 150 cc in F4 racing and I have a 150cc upgrade kit. My current single can be viewed at
Search CB150 12500 (Can't seem to paste a link)
About 18.5 hp.
About 18.5 hp.
kiwiavi 1 year ago
Hi Kiwiavi,
Nice machine mate.
I love the little Honda engines.
My wife is coming out of retirement to race the 125 this year so it has been freshened up with a much modified Dyna S CB750 ignition. Hopefully this will cure a miss fire above 12,000rpm.
Also building a new engine with lightened crank and maybe home made pistons.
Kompins 1 year ago
@Kompins
I had a missfire at high rpm and found it was to weak a spark and it actually ran better with a smaller than standard plug gap!?
Isnt the standard max power at about 13,000rpm on the 125 twin?
I looked at one cb125 twin engine and it had inlet ports of only about 10-15mm; but I heard that some engines were of lower restricted power as the standard was about 16bhp, so did they make a restricted version with the small ports for smaller carbs?
tpvalley 1 year ago
@tpvalley I run Dyna coils and a total loss ignition system, big fat sparks until the battery gets below 10volts. See my comments above about rear wheel horsepower and rpms. The CB125TA was the non restricted version for the UK, later versions have small bore exhausts and a retard in the electronic ignition to limit power.
Kompins 1 year ago
your daughter has taste!
bravo3000pirate 2 years ago
Honda claimed 16.5hp @ 11000 rpm. This was emphatically NOT at the back wheel, rear wheel hp was more likely 13.
Manufacturers claims of hp were based on crankshaft hp and usually optimistic at that Honda! For example they claimed 42 for the CB500T but when tested in 1975, actual rear wheel hp was 33.5! CBX1000; they claimed 103, actual 85.5.
Kompins 2 years ago
Beautiful sound ... just excellent
OZLAVERDA 2 years ago
Yes it sounds wonderful, I would love to take it for a run around a race track but it would destroy the sound meter!
Kompins 2 years ago
nice, i had a 1971 cb100 honda (basically the same engine, it just revs even higher due to the lighter weight piston) that I ported intake and exhaust, turned a alum intake manifold, installed a 28mm dellarto carb, and a hand rolled megaphone. custom seat-tank-clipons-rear sets. I rode it 850 miles to Illinois for a motoguzzi rally
jonesjpthrower 3 years ago
I am sure the CB125T was never imported into the USA (it's a twin cylinder engine). The CB100 was a single cylinder engine sold worldwide and also as a 125, sounds like you had lots of fun.
Safe engine revs are dictated in the first place by the stroke of the engine. The stroke of the CB100 is 49.5mm and the CB125T 41mm so the latter should be cable of revving higher. When I get around to making a new cam I reckon we can go to 14,000 occasionally before thing start colliding, we shall see.
Kompins 3 years ago
@jonesjpthrower The CB100 was a single cylinder engine. The CT125T is a two cylinder with twin carbs. In standard trim it put out 17hp at 11,000rpm. The 100 cc engine was a single and was also available as a 125 and a 185.
Scootertuner1000 2 years ago
what did you do to the engine? port? big carb? pipe? ect?
jonesjpthrower 3 years ago
Ported head and skimmed head, modified Honda 250 Hornet carbs, tuned exhausts plus stuff I can't remeber. You can find much more if you search for 'The Fang' and go to 'News 2008'.
Kompins 3 years ago