Rev Counter or Fueling problem?

[rdrider]

Afternoon all.
Although I have had my Mk1 RD125LC for 9 years, I am new to this forum.

So, I'm after a bit of advice, if anyone can help.

The Bike in question is a Mk1 RD125LC 1983 10W Full power Import.
Brand new Allspeed exhaust, made by Gibson for me in 2015
Brand new Standard 155 Main Jet in a 10W Carb and complete strip down and clean of the Carb.
New float - adjusted to the correct height and float needle / housing  plus new pilot jet.
Throttle Clip in position 3 as it states in the Manual for the 10W
New EBC Racing reeds formerly known as Hi Tech reeds (which apparently have now been modified to solid reeds instead of the "Petal" type)??

The issue in question is that at 7500rpm indicated on the rev counter it runs out of power. 
It doesn't "bog down" when it does this, it just won't rev any higher.

The Bike feels quite quick for a 125 and gets from the sweet spot of 4000rpm to 7500rpm extremely quickly.

Maximum power for the 10W model is at 9500rpm according to various sources, so I am baffled why mine tops out at 7500rpm.

Any suggestions would be greatly appreciated.

Many Thanks
Mark

[brigitte]

Hi Mark,

I experienced the same problem. My bike didn't rev as it should. Is your speedo showing about the right speed? Then go calculate primary transmission ratio, sixt gear ratio, chain drive ratio and rear wheel circumference. In my case, nothing was wrong with the engine, my tach was way off.

If you don't like doing the math, go to am*** and have a look for a small digital tach: www.amazon.de/s?k=drehzahlmesser+kleinmotor&__mk_de_DE=%C3%85M%C3%85%C5%BD%C3%95%C3%91&crid=34WBYW00DOHTE&sprefix=drehzahlmesser+kleinmotor%2Caps%2C113&ref=nb_sb_noss_2 I used such a thingy while my revcounter was (quite a long time) at the repair shop.

By the way: 80cc 30W has a different transmission ratio for the tachometer gear compared to 125cc 10W. They look the same but display different numbers.

Regards

Brigitte

[stusco]

Buy a £10 koso(fake ) digital tacho from ebay 10 min to fit it will give you the answer

[broughton]

the powerband normally starts at 7k so i would guess the rev counter is way off

[broughton]

i would also go up a couple of sizes on the main jet with the allspeed on but do plug chops that will tell you how the bikes running

[evochris]

Mark and I went out today on the 125’s, stopped off for a cheeky full English of course, he on the Rd and myself on my MBX125 and did some checking, the MBX at 60 mph was 6500 rpm, 70 was 7500 rpm, he was reading 5000 and under 6000 for 70, so we believe the rev counter is at fault. Giving the MBX some beans 9-10000 rpm through the gears Mark was always behind but never saw more than 7500 rpm. Time for a different rev counter me thinks.

IMG_3762 by chris tring, on Flickr

[museumman]

A few pointers from my experience.
I imported a lot of these bikes from 2005 onwards (I broke 60 bikes for spares) Many originals were great runners without engine builds, but now you might find the cases leak and effect performance, if they haven't been done, or commonly bodged.
The Allspeeds are overrated.
The original Rev counters have their grease melt and fall down onto the 'Dome' which makes the needle lag or makes them eratic. Also check the inner drive cable, and the metal drive in top of the gearbox.

[evochris]

Thanks Museumman, appreciate the pointers. The engine seems good and strong with no leaks at all. Sounds sweet too. It seems its a rev counter issue....needs a little TLC after 40 years I reckon .

[museumman]

Aug 23, 2023 9:50:50 GMT 1 evochris said:

Thanks Museumman, appreciate the pointers. The engine seems good and strong with no leaks at all. Sounds sweet too. It seems its a rev counter issue....needs a little TLC after 40 years I reckon .

Hopefully it will be ok with a clean inside.  I've improved a few like this. 

Be careful of the thin coiled spring in the middle and don't allow the dome to sit with the needle on the stopper as the needle can break as you put pressure on. You will need to hold the dome at say 6,000 RPM as you wipe the grease off, look underneath for debris, spider's webs etc.
(This is a part I don't sell anymore, I commonly replaced faded red lines or the damaged threaded boss)

[evochris]

Thanks a lot nice to hear from someone with experience. I will have a chat with Mark and make sure he see's this thread.

[rdrider]

Thanks for all the great idea's Guys.
As Chris said, the Bike is running great and goes really well for a 125 (and I reckon it's a bit quicker than his MBX 125 too lol) so think I will start with the Rev Counter, thank you museumman for the brilliant advice on the strip down too.
Will post back when I've fixed it with the details.

Oh, and thanks to Chris for reminding me that I have to use the Internet more often in my spare time.....