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Old 05-16-2012, 07:14 AM   #1
hayasakiman OP
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Joined: May 2012
Location: WPB, FL, USA
Oddometer: 159
Battle with My Riva 125

This year, 2012, I bought a very first scooter in my life, Yamaha Riva 125 with 22000 miles on it. High mileage scared me but it seemed have been well taken care of.
300 miles since I got it, the intake valve got stuck and it was bent.


Got new valves, in and ex, installed after the head was cleaned and inspected. There were cracks on intake valve guide which were visible. I thought it will be OK. 100 miles after new valves installed, the two valves decided to hit each other.


So, this time, I got used cylinder head with valves and other parts still installed. The intake valve shows un-even heat transfer.

The head was disassembled and cleaned before installation.

Now, the scoot is on the road and has two issues. Starter clutch does not engage on first try, on occasions when hot. It catches eventually, and I can be on my way home. I know this clutch should be replaced soon.

Second issue is the engine coughs when at steady speeds between 35 to 45ish miles. A few times, I had the engine quit on me when I was decelerating for stop light from 50+. At about 40ish, I lost engine and had to coast to stop. When this happens, I have to wait like 1 to 2 minutes before it starts again.

Does any one have any idea? Carburetor needs cleaning and adjustment?

hayasakiman screwed with this post 06-10-2012 at 08:44 PM Reason: Added pics.
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Old 05-17-2012, 11:01 AM   #2
hayasakiman OP
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The battle continues

Took the scoot for errands. The throttle cable broke prior to the last place for the day so I didn't make it there. Parked the scoot without shutting down and raised idle speed. Good thing I didn't have side covers installed. Doing this didn't give me enough RPM to roll on its own but I was able to limp forward with light kicks.

When there was not much cars, I was able to use my finger to open the throttle a little. Good thing the cam on the carb was on left side. Also, I had riding gloves on!!. The throttle cable guide on the grip was pinching the cable. The cable was flexing every time throttle was twisted instead of rotating on its bud end.


Now, I need to order a new throttle cable, adding to do list for the scoot.

hayasakiman screwed with this post 05-20-2012 at 10:17 AM Reason: Added a pic
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Old 05-20-2012, 10:28 AM   #3
hayasakiman OP
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Location: WPB, FL, USA
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Waiting for new throttle cable and new tube, I replaced gauge cluster.

Some one must have used wrong bulb.

This is what I got.

The scoot lost almost 9500 miles.
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Old 06-06-2012, 11:17 AM   #4
hayasakiman OP
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Heat wrap



Finally the throttle cable and throttle tube had arrived yesterday. Installed them today along with heat wrap on exhaust pipe. Took it for a ride. The wrap was white when installed. Smoked a lot. Now it is tan.

The starter clutch didn't engage when the engine was hot. It took like 10 tries to get engine started.

The battle continues.
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Old 06-08-2012, 03:21 PM   #5
hayasakiman OP
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Location: WPB, FL, USA
Oddometer: 159
Tire Recommendation?

My scooter's tires are in need of replacement. Currently the front tire is dry-rotted Bridgestone, Molas-8 and rear is worn Chengshin something. Riding with these on wet roads is like riding on icy roads.

I am thinking of getting Kenda K329 or Kenda K413 due to their price.

What are your thoughts and actual experience on these? Or, any others you recommend?

Thank you.
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Old 06-08-2012, 05:37 PM   #6
DudeClone
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Wow. I have no tire recs but I will give this a little bump with a BIG hearty 'thanks' for posting such clean, detailed pics of that engine and other things, as well as your explanation of what is going on and what went wrong.

Very interesting for this mechanical newb.
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Old 06-08-2012, 11:37 PM   #7
hayasakiman OP
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Thank you!! DudeClone. Your post on this thread is very first one made by someone else other than myself after about 650 views later. Although I started doing this for my own sake, I was beginning to think of abandoning it. I am pleased that you found this thread very interesting. It gave me some motivations to continue.

Now, the engine quitting problem is, I think, due to auto-choke not working properly. It has gotten progressively worse. Newly installed spark plug is removed when the engine quit. It is really black and wet. I will perform troubleshooting later.

hayasakiman screwed with this post 06-08-2012 at 11:58 PM
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Old 06-10-2012, 07:11 AM   #8
nedc
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ANY new tire will be better than what you have! i've had good luck w/ Pirelli and Michelin. They're all fairly inexpensive for the size you need.
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Old 06-10-2012, 04:19 PM   #9
hayasakiman OP
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Thank you, nedc. Just checked prices and reviews on one of on-line stores. Pirelli SL26s are $6 more than Kenda K413s. I think I'll go with Pirellis since they are supposed be excellent in wet weather. Also, they have your un-biased suggestion.

Checked the function of auto-choke today. Heat element is working as it should as per service manual. The cam is pushing the plungers. Took the carb apart to see if anything is clogged or something. Didn't find anything eye catching there except rusty crud on the bottom of the bowl and wear on needle valve. The scoot had in-line fuel filter installed when I bought it. So, I don't know if the crud was there and then the filter was installed. Or, the filter is not so effective.

Got other kind of filter from a local cycle shop. The shop owner says on those filters, there's something pass through the filters. . Really? Why bother installing it then? Why is he selling them many kinds and sized filters?

The carb had signs of some one being there before me. There's extra washer under the main jet. An O-ring is missing between the main jet and needle jet. A blank plug is removed for pilot jet.

The battle continues.
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Old 06-10-2012, 05:43 PM   #10
DualSportDad
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Good luck with the scoot. I miss my old 125.

Sent from my Galaxy Nexus using Tapatalk 2
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Old 06-10-2012, 10:03 PM   #11
Wentwest
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Tires: I use Kendas and they work fine. The price is right and the grip and appearance is OK, too.

Starter clutch: This is a problem with bikes generally. You have to go pretty far into the engine to get to the problem. I'm not sure how Yamahas work, because I mostly understand Hondas. There is a service manual at:

http://www.motorscooterguide.net/Man...ice_Manual.pdf
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Old 06-11-2012, 06:19 AM   #12
hayasakiman OP
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Thank you, Alex.

Thank you, Wentwest, for the link. The scooter came with service manual, but having it on PC come in handy as well.
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Old 06-13-2012, 02:09 AM   #13
hayasakiman OP
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How to adjust a CV carb ??

Put the carburetor together. The engine started fine and idled fine, too. Let it warm up, and revved engine. It seems good. So, I did test ride the scoot. It run fine for 10 minutes and then the old problem came back. The engine hesitates at speeds 30-45 mph. If I keep at that speed. The engine dies. If I accelerate, it runs good.

It seems like the pilot jet is clogged. So, I took it apart again and blow compressed air through it. Visually inspected. It seems fine. I am lost for now. I wish there's a detailed "how to" on adjusting this carburetor on the service manual. Float level and fuel level has been checked and adjusted to spec per the book.
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Old 06-13-2012, 08:27 AM   #14
nedc
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If it does indeed run fine for 10 minutes, the problem is not your pilot jet. It's got to be something that is related to heat. If you electric choke was malfunctioning, it would be apparent immediately after the scoot warmed up, sooner than 10 minutes. Maybe your valve clearances are slightly too tight and after the engine gets good and hot (10 minutes running or more) they are hanging slightly open. My $.02.

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Old 06-15-2012, 07:37 AM   #15
hayasakiman OP
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Joined: May 2012
Location: WPB, FL, USA
Oddometer: 159
Thank you for your input. Adjusting those clearances were really difficult for me because of their sizes, too small!!

I'll check on that sometime this weekend.

There's another Riva 125 up for sale. I think I will look at it on this weekend as well. Use this one as parts, or the one I have for parts,,,,,. It would bites if both becomes "dead".
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