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Old 02-12-2014, 04:08 PM   #1
bdawson OP
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Yamaha Riva 125 - problem starting

Bike:
1988 Riva 125 with ~2k miles.

Symptoms:
During cold starting, with the throttle held 1/8 open, the bike turns over for several seconds then starts briefly then dies. If I continue to hold the starter, a few seconds later it will cough again and then die again. The person who sold it to me said it always had trouble cold starting but ran great once started.

What I have done so far:
a) Cleaned the carb with carb cleaner and compressed air. All jets are clear, rubber seals show some age but look functional.
b) Verified the auto choke slowly extends with power on. Also measure resistance at 3.5 ohms.
c) Plug is good (clean blue spark)
d) Applied vacuum to the petcock and verified consistent fuel flow.
e) Tried to use starter fluid - no effect

Next steps?:
a) Check the valves (adjust if needed)
b) manually set the auto-choke in the "warm position" - try to start.
c) search high and low for any vacuum leaks at the intake manifold
d) ???

Any suggestions or experience with a similar problem? Anyone have a carb? Id love to have another carb for troubleshooting. Thanks,
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Old 02-12-2014, 04:26 PM   #2
gizmo309
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How old is the gas in it? I bought a 1995 Riva 125 last fall. It had 1100 miles on it. I used starting fluid to get it going. I rode the old gas out of it. The gas was in there for 2-3 years. It ran rough until I was able to get the old gas out. Sounds to me like whatever is in there won't burn. I take it you checked the air filter. Mine was almost a pile of 19 year old dust. I don't know how it ran at all. Once you get it sorted they are a fun scooter. Pretty zippy for a 125. I can't think off hand of what else it could be.

Bob
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Old 02-12-2014, 06:28 PM   #3
RedArrow
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bdawson ~

Sorry to hear about your starting issues. My 1984 Honda Aero 125 had some major idling problems when I first got her. I had to clean the carb 3 times before she'd finally run smoothly. Running an electric guitar high E string through everything along with SeaFoam finally did the trick.

My scoot is very cold-blooded and is very sensitive to flooding when first starting off. I don't open the throttle at all until I'm ready to pull out. I'm wondering if you are flooding your engine by opening the throttle while trying to start it? Is this the correct procedure for your scooter?

Checking the gas and the air filter is good advice. Another old bugaboo is vacuum lock from a non-venting gas cap, but I would think that something like that would only show itself after driving for a time. But, you could try removing the cap while trying to start it just for grins.

Is there a gas filter in line that maybe is old and clogged? Just a thought.

Good luck.
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Old 02-12-2014, 07:31 PM   #4
JerryH
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If you have completely disassembled and thoroughly cleaned the carb, I would remove the gas tank, and completely clean it out. The fuel system needs to be completely clean from one end to the other. That includes the tank, petcock, fuel lines, and carb. If it has a vacuum petcock, make sure that is working. Verify that you are getting plenty of new, clean fuel to the carb. IMO, this stuff is something that needs to be done anyway on an older used bike. If you still have starting/running problems, it is probably in what Yamaha calls the starter plunger assembly, which is what this carb uses as a choke, or enricher. I noticed Yamaha's design is a bit different than Honda's. The Riva also has a CV carb, which is more complicated.

If I remember correctly, the Yamaha Riva has a long history of being finicky as far as starting and running smoothly.


Here is another Riva 125 thread that you might find helpful. http://advrider.com/forums/showthread.php?t=791375
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JerryH screwed with this post 02-12-2014 at 07:38 PM
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Old 02-12-2014, 07:33 PM   #5
gogogordy
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Quote:
Originally Posted by JerryH View Post

If I remember correctly, the Yamaha Riva has a long history of being finicky as far as starting and running smoothly.
Carbureted.
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Old 02-13-2014, 10:29 AM   #6
Dabears
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http://motorscooterguide.net/Forum/v...1a103&start=15

http://motorscooterguide.net/Forum/v....php?f=7&t=678

Looks like someone else had same issue- not sure if resolved but think he found a solenoid that activates choke was bad.

Man i love the simplicity of a pull choke like on my Vespa. Hope you get it fixed soon!
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Old 02-13-2014, 12:56 PM   #7
JerryH
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I love the pull choke on my Stella too. And it is a real choke, not an "enricher". It also has a nice easy to work on non CV carb.
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Old 02-13-2014, 01:27 PM   #8
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There's nothing wrong with enricheners, I prefer them over a choke valve.

They are just a simple fuel-air circuit in the carburetor that is opened by a thumb valve or a thermo-electrical bistarter. It works without having to hold the throttle partially open, like with a manual choke, as it introduces additional air with the extra fuel.

Most 2 stroke motorcycles use them as do a few modern 4 stroke carburetored moto engines.
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Old 02-13-2014, 03:42 PM   #9
JerryH
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Enricheners are simple enough, but I have had 2 serious problems with them. First, the plunger that screws into the carb is always plastic. I have had a couple of them break off, and when that happens, the choke is "on" so to speak. So you are not going anywhere. I had to have my XT225 hauled 150 miles back home when the enrichener broke off. Many of them use a handlebar mounted lever with a long cable to the carb, and just the cable moving around is enough to eventually crack the plunger housing. I switched over to one that mounts directly on the carb, and so far it hasn't broken. But I carry a spare just in case.

The other problem is they use a vacuum diaphragm. These things are not cheap. My Vulcan 750 got to where it would not start and run properly, and I traced the problem to the coasting enrichener diaphragms. Both were melted. They were all gooey and sticky. I removed them, cleaned out the melted rubber, and replaced them. $100 later it ran fine again. Gasoline did not melt them, I suspect ethanol. A simple choke plate does not have these issues.

I also prefer non CV carbs. They have better throttle response. They don't deal with changes in altitude as well, but I would rather have simplicity and better throttle response.

On many newer bikes with carbs, simply rejetting them a bit richer can solve a lot of problems.

My old cars don't even have chokes. I removed them. They are jetted rich enough to not need a choke in AZ weather.
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Old 02-13-2014, 07:11 PM   #10
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If it won't pop with starting spray, then maybe your spark plug is not sparking. Check it out. These scooters can be hard to start as lots of things are controlled by vacuum, and the engine just doesn't generate enough vacuum when turning over. Be certain the battery is fully charged and the connections are clean.
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Old 02-14-2014, 05:00 AM   #11
Jim Moore
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I've never taken apart a Riva carb, but I'd try a new slow jet. It's almost impossible to clean those small orifices. That being said, I'd expect it to fire off with starter fluid no matter what.
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Old 02-15-2014, 11:56 AM   #12
JerryH
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If you have a good spark, that only leaves fuel and compression. I would suspect a fuel problem over a loss of compression, but I would check the compression first, if only to rule it out. I have been fooled a couple of times because an engine felt like it had compression, but did not have enough to run. I wasted a lot of time with the fuel system for nothing. Now if there is any possibility of a compression problem, I check it.

If you have a spark, it WILL fire on starter fluid if you have compression. It may not actually start, but it will fire. I kept a generator engine running for several minutes, with completely plugged carb jets, just by removing the air cleaner and continuing to spray gasoline into the carb with a trigger type spray bottle.

Be careful with starter fluid. It is ether, and burns very hot. I have seen pistons melted by overuse of it.
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2001 XT225, 2009 Genuine Stella
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Old 02-15-2014, 12:26 PM   #13
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Quote:
Originally Posted by JerryH View Post
Enricheners are simple enough, but I have had 2 serious problems with them. First, the plunger that screws into the carb is always plastic. I have had a couple of them break off, and when that happens, the choke is "on" so to speak. So you are not going anywhere. I had to have my XT225 hauled 150 miles back home when the enrichener broke off. Many of them use a handlebar mounted lever with a long cable to the carb, and just the cable moving around is enough to eventually crack the plunger housing. I switched over to one that mounts directly on the carb, and so far it hasn't broken. But I carry a spare just in case.

The other problem is they use a vacuum diaphragm. These things are not cheap. My Vulcan 750 got to where it would not start and run properly, and I traced the problem to the coasting enrichener diaphragms. Both were melted. They were all gooey and sticky. I removed them, cleaned out the melted rubber, and replaced them. $100 later it ran fine again. Gasoline did not melt them, I suspect ethanol. A simple choke plate does not have these issues.

I also prefer non CV carbs. They have better throttle response. They don't deal with changes in altitude as well, but I would rather have simplicity and better throttle response.

On many newer bikes with carbs, simply rejetting them a bit richer can solve a lot of problems.

My old cars don't even have chokes. I removed them. They are jetted rich enough to not need a choke in AZ weather.
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Old 02-15-2014, 01:20 PM   #14
scootrboi
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Quote:
Originally Posted by Jim Moore View Post
I've never taken apart a Riva carb, but I'd try a new slow jet. It's almost impossible to clean those small orifices. That being said, I'd expect it to fire off with starter fluid no matter what.
I cleaned the slow jet on my 125 Elite by pushing a single filament of copper from a piece of automotive wire. It had sat for 17 years and was gummed up bad. I used carb cleaner too.
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Old 02-15-2014, 08:01 PM   #15
fullmetalscooter
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A cheap Jewelry ultrasonic clean is 40 bucks . Does great job on single carbs and is worth the cost.
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