Yamaha RX125

[boars]

Ok, that makes sense ...

Some models just don't make it over to here. There may have been an RD125 in the states but I don't believe so. I know there was never an RX model (in the states) from at least 1973 and up, all RD's..

Your bike appears to be pretty much a half of an RD 250 in excellent condition. I miss my old 1975 RD350, (an old man turned left in front of me in 1977, totaled it and almost took me out indefinitly when I was 19)

It's seemingly in pretty good condition, just a couple of quibbles really. Heck, it's probably in better condition than the similar 80 I had 20 years ago.

Yikes on the crash, lucky it didn't end up worse.

Anyway, hopefully get the wheel back so I can put her thru her paces on the weekend... and sort out any (hopefully) minor issues

 

[turbid]

maybe the throttle spring (or whatever its called) at the carburettor is sticking a bit causing this strange power delivery. check the magneto contact points as well and check the ignition timing is correct, check also that the cables are moving freely and not sticking or anything. my kawasaki is the complete opposite, it does not want to take off unless i apply half throttle in 1st gear! i,m taking it to a mechanic as im not very good at engines/carbs

 

[boars]

maybe the throttle spring (or whatever its called) at the carburettor is sticking a bit causing this strange power delivery. check the magneto contact points as well and check the ignition timing is correct, check also that the cables are moving freely and not sticking or anything. my kawasaki is the complete opposite, it does not want to take off unless i apply half throttle in 1st gear! i,m taking it to a mechanic as im not very good at engines/carbs

I have next to no idea what I'm doing... that's why I'm not commuting on this beast. It might take me a while to sort thru these seemingly minor issues... but the intention is to learn on the way

 

[degake]

Hi Will,

If you want to tinker a bit more with your new bike, take a look at the attached manual

View attachment 41064

Grtz,


Degake

 

[TownsendsFJR1300]

what power are you saying is fluctuating? the engine's or the headlight? the headlight needs some revs for the magneto/coil to give it some juice to be half decent. the batteries die almost daily on these bikes, you need to have a 6v charger handy and give it 2hr charges. yeah clean the fuel tank if its rusty and the carb otherwise it wont run well. check engine timing is spot on as well as it will foul the spark plug

i have a 79 kawasaki kh100 very similar to yours that im restoring and trying to use it as my daily commute, but i,m afraid to use it for work... if it doesnt start in the first 3 attemps it floods the carb and it wont start no matter what, petrol starts spewing out of the float chameber, then the battery dies and no indicators and horn can be used. i smashed its fuel tank last saturday with frustration! ( i have to fix it or buy another one)

Sounds like your float level is bit on the high side.

As I recall, that bike should have CDI ignition and a rotary valve on the right side to time when the lower end suck fuel into the engine...

If the crank seals are original, hopefully they are still functioning as they should. If there's a vacuum leak on the bottom end(seals aren't sealing), it about the same as a vacuum leak on the intake tract of the FZ...

 

[TownsendsFJR1300]

maybe the throttle spring (or whatever its called) at the carburettor is sticking a bit causing this strange power delivery. check the magneto contact points as well and check the ignition timing is correct, check also that the cables are moving freely and not sticking or anything. my kawasaki is the complete opposite, it does not want to take off unless i apply half throttle in 1st gear! i,m taking it to a mechanic as im not very good at engines/carbs

If that engine is like the RD, it has a round, slide throttle and just a push back return spring. There is no vacuum slides to deal with.

It too, should also have a non adjustable, CDI ignition (Yamaha starting eliminating points around 1973 and as I re-call, is not adjustable (I may be wrong).

That engine should have reed valves (for the intake) and its not un-common for the bike to not have much power on the bottom end and kick in higher in the rev range. All that is dependant on the factory porting in the cylinder when it was designed..

 

[turbid]

Sounds like your float level is bit on the high side.



how do you adjust the float? thx for the insight townsends. i was really on the verge of getting rid of this bike, but when i stop to look at it i start to like it again. it was in a sorry state and i brought it to half decent shape so its kinda grown on me.

 

[boars]

Hi Will,

If you want to tinker a bit more with your new bike, take a look at the attached manual

View attachment 41064

Grtz,


Degake

Thanks Degake, that's a fair amount of reading right there! :thumbup:

 

[TownsendsFJR1300]

how do you adjust the float? thx for the insight townsends. i was really on the verge of getting rid of this bike, but when i stop to look at it i start to like it again. it was in a sorry state and i brought it to half decent shape so its kinda grown on me.[/QUOTE]

It would help if you had a shop manual.

I would pull the carb and check the needle and seat of the carb and make sure it's not worn (horizontal groove on the needle, worn seat).

You can check to see if the float is stopping fuel fully by hooking up a fuel line to the carb body, hook up an auxilary gas tank and fill it with water (you can use gas but obviously a lot more dangerous). Move the float up and down from full droop to up fully. You want it closed (no flow) at about the center of the travel...

I don't know what your fuel level measurement is however as a general rule, once the carb is off, you'd flip it upside down. Let gravity shut the float closed. It should be pretty much in the center of fully closed and fully open (with the bowl on).

Clink on this site and find the bike closest to yours if not yours and bring up the parts fisch of the carb: PowersportsPlus.com - OEM Powersports Parts from Honda, Kawasaki and Yamaha at discounts up to 80% off MSRP

This is a link to a 32mm Keihin CVK carb(used on a Kawasaki KLR 250). The lower end (float area is generally the same) and will give you an idea whats under the float bowl: Keihin 32CVK Disassembly .

I brought up a 1979 Kawasaki 100 carb on the above mentioned parts fisch. As I thought, its strictly a slide throttle, no vacuum slides/diaphrams, etc, quite a bit simpler.

You might find the float height after doing a search on the internet.

If you find the measurement, its usually checked/adjusted by measuring off the the flat base of the carb body while held upside down. IE, if the spec is 17mm, you would bend the small tab (very, very gently) on the float (what actually touches the needle) until the flat part of the carb body and the bottom of the float(now upside down) is 17mm. Make sure you have NO LEAKS in the float by either shaking it and listen for liquid inside or hold under water and look for air bubbles coming out..

Hope this helps, kinda hi jacked the thread but the procedure for the RX is the same..

 

[boars]

So got some new road tyres and also replaced the front tube due to the previous owner trying to put a 2 inch tube inside a tyre that well... isn't. Some interesting creases on it when it expanded without the room it required :spank:

Pulled the breaks completely apart, gave the piston a bit of a light sand as it had some surface gunk/rust(?) - seemed to be extremely minor but figured I'd clean it all up while I had the wheel off.

Took considerable effort to get that bastard back in! Not to mention getting it out in the first place, the pads were together and needed some serious prying to get them to push the piston back in... anyway short of it is, it's done and I've learnt how they work :thumbup:

Got a fairly average brake bleeding kit... does the job... the tube connection on the bottom of the RX leaves a little to be desired tho... makes it hard to tell if I'm sucking air from the system or from around the not quite as tight as it should be fitting pipe.

Pushed it about a bit to test and all seems ok... think I might get some braided brake lines and do it all again in the not so distant future.

Anyway fired the old girl up (started first kick :rockon... took it for a test ride..

RX125 - test ride - YouTube

and the brakes functioned... ok... not as nice as I'd like... though that was the least of my problems... refer to 2mins 50 secs or so...

Engine just stopped firing, continued to turn a few strokes and stopped and I rolled to an ominously quiet stop 2 rides on the RX so far and 2 times I've had to push it home. Luckily I wasn't overly silly... and was just riding local streets... yeah I was squiding it up a bit there, no jacket... all the rest of the gear... I half expected murphies law to strike...

A couple of oddities... the horn went off for a brief moment by itself two times on the ride. Wont actually go off when I press the button tho. Thought maybe the battery was dead... indicators and brake light still seem to function, headlight wont seem to turn on...

Checked battery ... looks newish ... water level looks fine too.

What are anyones thoughts as to what is going on? Spark plug? Battery? Should I just replace both and be done with it?

 

[turbid]

that's great you got it running. i still have to watch the vid as i dont have acces to youtube at work.


on a sidenote. thx for the precious info townsends. i checked the float and it was punctured!! i had to change it and it runs like a clock now!

i have to change the clutch as its worn but anyway i m happy with the progress. thx townsends:thumbup:

 

[Nelly]

I found some info on the Yamaha owners club.
This was posted by a member called Roscoe:
"Otherwise, the rx only sold in Arg, Australia and New Zealand. And in Brazil and Uruguay of course".
I just re-read this and realised it don't make sense. So to clarify it would seem your bike is not an RD.
I haven't been able to find a manual, the YOC is a subscription club:spank:
Good luck Nelly

 

[boars]

that's great you got it running. i still have to watch the vid as i dont have acces to youtube at work.

Well it ran for about 3 mins... then all ignition ceased... :spank:

Hopefully get time to work out why this weekend... Was a perfect day for a ride the other day and tonight the rain is bucketing down It'll no doubt rain all weekend :Flip:

 

[boars]

The source of all my recent problems... :spank:

Had to seek help from a mobile mechanic but hey, he taught me a few things in the process! Much better than dropping it somewhere, then having them fix it, give you a bill, then leave you wondering if you could have done it yourself.

Mick rocked up, explained what he was doing, showed me as he noticed things and commented on all manner of interesting bike things :cheer:

After diagnosing the problem (the smashed Crank Woodruff key you see stuck on the magnet there) he let me know how to fix it myself, since I was keen on getting my hands dirty.

Had a great yarn, learned a thing or two and hopefully I'll get the RX out on the road again this weekend :thumbup:

Much kudos to: Mobile Motorcycle Repairs | Break Down Service | Brisbane, Queensland | Wizard Motorcycles