ADVrider (
-   Battle scooters (
-   -   The dreaded Riva 125 electric bystarter (choke) (

tbirdsp 08-27-2011 03:23 PM

The dreaded Riva 125 electric bystarter (choke)
I had some slight issues with my Riva 125 so I decided to clean the carb. Discovered some monkey messed it all up:huh
I can't believe this thing was even running! Multiple issues, but :

The electric choke is showing an open circuit - not good. Plus it looks as if someone took the black plastic barrel off the metal part and removed a pushrod with a beveled end that pushes on the cam which depresses the choke plungers. I don't know - never seen one before, but that's how it looks in the manual. There's a brass piston inside the plastic deal that looks like it's extended pretty far but no way it could contact the cam, plus the mating surfaces wouldn't match up.

I there any option other than buying the $200+ plunger assy from Yamaha? (I did find it for $159 at least).

Has anyone just permanenetly depressed the plungers and ran the thing with no choke function? Will it even start?

I'm on the RivaRiders Yahoo group but every single message has to be moderator approved:huh Takes forever to get any answers.

tbonestone 08-27-2011 04:26 PM

Jeez, for that price of $159 could you find a completely different carb to work with that Riva? Maybe some kind of GY-6 carb could do what you need. I'm having a similar problem-different scooter experience with my Honda Helix. I'm waiting on the chinese clone carb to land on my doorstep. I'd love oem but right now I need my scoot to ride since I cannot afford to feed my car.

tbirdsp 08-27-2011 05:01 PM

Some guys have fitted Mikuni carbs, but a lot of adaptation is required. I see the cheap GY6 carbs but most are for 150's and will probably need all of the jetting sorted out.

tbonestone 08-27-2011 07:18 PM


Originally Posted by tbirdsp (Post 16727130)
Some guys have fitted Mikuni carbs, but a lot of adaptation is required. I see the cheap GY6 carbs but most are for 150's and will probably need all of the jetting sorted out.

Forgive me for being snarky, but I come from the vintage vespa scene before I adopted my helix... All things need jetting sorted out. Nothing is perfect right away. Shoot... If i get jetting right the first time on anything you better hunker down in the apocalypse bunker.

tbirdsp 08-27-2011 07:55 PM


Originally Posted by tbonestone (Post 16727914)
Forgive me for being snarky, but I come from the vintage vespa scene before I adopted my helix... All things need jetting sorted out. Nothing is perfect right away. Shoot... If i get jetting right the first time on anything you better hunker down in the apocalypse bunker.

Thanks for the "help" :rolleyes

The stock carb is perfectly fine on these - if some stupid fuck hadn't have messed with it, and if the electric bystarter worked.

Would really like to hear from anyone who has dealt with this on a Riva 125 ( or similar 200, 180 is different).

tbirdsp 08-28-2011 03:14 PM


Explanation on page 4-4, carb section of the manual

I decided to just block the enricher in the "warm engine" position. If you look at the diagram on 4-4 of the manual - I removed the return spring that pushes the enricher plungers out. I then bent a piece of aluminum sheet in a "V" shape and wedged it on top of the cam to hold the plungers in.

As I said, I don't know how this thing even ran. The pilot jet was totally plugged and the pilot screw was full of crap. Float bowl coated with varnish. I think it was idling on the enricher circuit alone (which was stuck in the "cold start" position). The pilot screw was opened about 4 turns, book says 1 3/4. Since I will now be without a choke, I opened it another 1/2 turn to 2 1/4.

The old air filter is deteriorated so I have a new one coming. I installed the carb, pulled a vacuum on the petcock line to get the float bowl full, and then - she started right up, even better than before! And that was without the airbox/filter installed, so it will actually have more restriction = run richer. I didn't run it too long without the filter on but she seemed to rev out OK too.

I'll update when I get the filter and take it for a proper test ride. May be a bear to start in cold weather, but I'll take it for now.

fullmetalscooter 08-28-2011 07:39 PM

nice scooter but the carb set up is a nightmare . I know that the guys on the riva yahoo group can help you out.

tbirdsp 08-29-2011 06:29 PM

Got the air filter today (came pre-oiled, which was nice). Wow - now I know how this thing should have been running all along! Even without the auto-bystarter it starts fine. Much better than before I cleaned the carb. Also runs better. It had an off-idle bog that I thought was just the nature of the CV carb combined with the CVT, but it's gone now. I'm seeing better throttle response across the board and probably 5 mph faster. I actually had it reading 67 mph:eek1 (downhill with a tail wind of course). That was scary on 10" wheels with drum brakes:evil It pulls harder and loses less speed on hills and in headwinds though. Can't wait to see what my gas mileage is.

If anyone has trouble with these things, try to block the bystarter plungers in like I did before you spend $200 on a new one or try to do a carb swap. Remember - you can't just unplug the electrical connector because it will fail in the "cold engine start" position and be too rich once warm.

I may have problems starting it in cold weather, but it starts so well now I can't imagine it will be THAT bad.

YamaGeek 08-31-2011 10:13 AM

I'm not sure this would have helped, but the clone carb for an Elite 125 might have worked for you..

it has a series of front, back, and side views.

tbirdsp 08-31-2011 11:33 AM

Not sure if the diameters would match up, plus everything is on the opposite sides.

elovemer 12-13-2012 11:15 PM

this is a follow up on the riva 125 choke problem.
took out the spring in the center between the two plungers.

then put a small chip in between the end of the wax thing and the plastic pusher that it fits into.
the size of the chip was chosen so that when the choke is put back on and pushed flush against the body of the carb, it is just touching the plungers.

in other words, it does not push the plungers in any more than they are already. but is still touching them.
then put the spring back in between the plungers.

disconnected the wire connected to the wax thing.
when the wax thing is completely screwed in, the plungers are pushed in as far as they would be if there was no spring in there.
when the wax thing is unscrewed, the out pushrod is pushed away from the cam, while the plunger spring is pushing the plungers out.
so in effect, when unscrewed a bit, the position is in cold position.
when completely screwed in, the position is in warm position.

the result is a manual choke using the existing automatic choke which is shit to begin with.
if you still have trouble starting when cold, it is probably because the carb is not working well.

another method you can use to get from cold to warm is a hair dryer for a few minutes, blown onto the carb.

my experience is that my scoot refused to start anymore.
now, it still does not start when cold, but when warm, it runs great and starts easily whereas before it would not even start or run when warm.

my guess is that if my carb was in better shape, it would start when cold also.
it does not help that it is winter time in new york state.

if i was in a warmer climate, it might even start when cold.

anyway, at least it is not stuck in cold postion anymore. and by screwing and unscrewing the outer assembly, i can manually change it from cold to warm position on the choke.

and i did not have to buy a new choke or carb.
it runs great when warm, like it used to before the choke started to fail.

also, it looks a lot tougher, when the rear side panels are removed. : 0 )

also, disabled the ignition switch as part of the brake pedal by jumping the wires together. didn't take long to do that.
also disabled the side stand kill switch ..... just by unscrewing it and screwing it back on with only one side attached so that the stand does not touch it.

would like to move the foot pegs up towards the front to have a place to put feet while riding.
haven't figured that one out yet.

also would like to convert one of the switches to cut out the head lamp manually. any tips ?

also, would like to modify the bright switch to have a middle position which includes both low beam and high beam at the same time.
i think this might be as simple as removing a spring inside the switch.

i noticed that while riding, if i have the high beam on, if i move the switch toward the low beam, it can run both high and low at the same time, it provides much better visibility than either alone.

any tips ? i am thinking it must be something with a spring inside the switch.

also, would like to attach some kind of ratchet to the accelerator, so that it can lock into place and be sort of a manual cruise control.... so that you don't have to be constantly trying to maintain the same speed by hand.

another tip, my riva xc125 has a rear luggage box mounted onto a rack holder.
if you remove the luggage box, the scooter becomes a lot less stable on the road.

hayasakiman 12-14-2012 01:26 AM

Yes~~another Riva 125 rider on the forum!!

My choke works still and I have working spare wax thing just in case the current one stop working.

Not sure about mods you want to do, but good luck with them.

g-haad 01-29-2013 12:35 PM

I have one and have monkeyed with that damn carb too many times. Bigger problems now that I'm down on compression (10psi) ! So I'm gonna have to tear her apart anyways so I thought I'd ask the question:

How hard would it be to get it converted to propane?

cheap bastard 02-02-2013 02:34 PM

The 125 riva (in my experience) starts very poorly in sub 50 degree weather if it's allowed to sit for a couple days. My personal investigation has shown, at least on my scooter, with an in tact clean carb, the float bowl nearly dry by day three. There is very little vacuum at cranking speed and it is pulsing, of course. The vacuum petcock has little chance to supply enough fuel to the empty chamber, so cranking times are very long. My engine showed 160 psi during a compression test. Cranking vacuum peaked at 7 inches. Clear fuel filter installed, Fuel shows low flow when cranking. If a vacuum is applied to the petcock before trying to start the engine cold and dry, filling the float chamber, starting is easy.
Conversations with a couple guys that have used these machines for years has taught me that cold start issues are very common, at the least.
The Grizzly 125 ATV may have a related engine with a proper choke, but I came up with no supporting info. Changing to a different model's carb was more work than I wanted to expend on this bike, so I looked for other solutions. A "T" in the vacuum line, with a syringe and hose could provide a vacuum source for the petcock. A check valve in the carb side of that arrangement would be needed, but a way to defeat it would also be required to shut the petcock off as it would hold a vacuum after shut down. The other idea, the one chosen, was to port a hose long enough to route to a handy position. The hose was fastened over a nipple inserted in the air box. Starting fluid can then be sprayed into the air box without dripping it all over ones hands. There is a cap on the hose to avert having unfiltered air drawn into the engine.
One could also just start the machine every day or two and put a battery charger on it occasionally for maintenance.

Times are GMT -7.   It's 12:22 PM.

Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2015