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Old 07-24-2012, 08:00 AM   #31
hayasakiman OP
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New fuel valve and starter clutch assembly

New fuel valve had arrived yesterday and was installed.



Also, new starter clutch assembly was installed along with new idler gear. Old units are photographed here.



Up close of old clutch, below. Could this be the reason for not working properly when hot? Or did some one tried to fix it without replacing parts? Other than this tool mark, the old assembly did not show any sign of malfunction or excess wear. Maybe it was lacking lubrication on springs inside the assembly. Not shown in photo.





I think I'll go for a long errands this afternoon and see if the scooter works good or not.
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Old 07-24-2012, 04:11 PM   #32
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Starter clutch works good

The starter clutch engaged every time even when the engine is hot.

But, I feel there's fuel starvation is going on. It's not like what I have experienced before. It's not like power surge as some Riva owners are talking about. I feel there's power loss when taking off from stop. I will remove inline fuel filter and see what happens.
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Old 07-25-2012, 09:01 AM   #33
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The reason for me saying the carb is not getting fuel is this, see below. With new fuel valve installed and along with in-line fuel filter, the fuel filter was dry, full of air, inside after yesterday's errands. The photo is before the errands.



So I think either new valve is not sending enough fuel or it is not designed to work with in-line filter installed.
Just to be sure that there's no restriction for fuel going into the fuel valve, I removed it from tank. The strainer of the valve was free of debris. But I decided to clean the inside of the tank. See below.





20 years worth of crud????

Now the tank is as clean as I can get, and the in-line fuel filter removed. I went out for a short test ride, less than a mile. The tube was filled with fuel before the ride. But when I came back there's air pocket as photographed below. The engine does not have a pep and stumbles at times.



What's going on with my scooter?? It had more power with in-line filter with no fuel valve installed. The fuel fresh and other equipments like leaf blower and pressure washer has not problem running with the same fuel.

The battle continues,,,,,,,
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Old 07-25-2012, 09:48 AM   #34
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As long as it is keeping the carb bowl full that shouldn't be a problem.
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Old 07-25-2012, 10:16 AM   #35
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That's what I think, too.
But the way the fuel level go up and down as engine is running at various RPM on the stand doesn't give me a peace of mind. And definitely, the engine doesn't have power now.

Later, I'll see what's up with the carb. By now, I can do this in less than 5 minutes.
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Old 07-25-2012, 10:41 AM   #36
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Most of my Riva's surge issues, but not all, disappeared with a vacuum line change to the petcock. There is still a bit of low power at times and once it had to idle for about 30 seconds to regain power. That change was 400 miles ago. The original vacuum line was collapsing and a test with a vacuum pump showed the valve would not hold vacuum on its own. The diaphragm is probably in poor shape, as yours was.
The ongoing low power/surge may be due to the jetting Yamaha chose back in the 80s, though. Ethanol wasn't a concern for them. I did get a tank of approximately 100 mpg 40-50 mph driving through southern Wisconsin over the weekend. With 125cc and a CVT, that tells me its very lean. My commuting MPG is 75 - 80.
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Old 07-25-2012, 10:59 AM   #37
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I can relate to that "regaining power" after 30 second of idle. Why does it do that? My theory is float/fuel level had gone lower than it supposed be during normal running previously. = Fuel starvation.

Yeah after I saw your post about the vac line, I paid attention to the line I have. Since I don't have vac pump, I sucked on the carb side end. As far as I can tell, there was no vac leak I could detect and fuel flowed into the in-line fuel filter I had installed at that time. And this was after the new fuel valve was installed.

In the beginning of my troubles with the scooter, I had sprayed carb cleaner to detect vac leak while engine was running. There was no RPM change I could detect. This does not mean the vac line is in good condition now, since I had it removed and installed countless of times. This is worthwhile thing to check, now.
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Old 07-25-2012, 02:43 PM   #38
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The test I used first was connected to the carb end of the vacuum line. Three inches vacuum applied, fuel stopped flowing as vacuum was lost after about 10 seconds. The next portion was done at the fuel valve connection. The same result was achieved. Since the vacuum line appears to go to a inlet vacuum source, I figured that should not be an issue. The problem continued, so I took the side cover off and noticed the hose collapsing. With the vacuum pump applied, it collapsed at 10 inches vacuum. I have not hooked a gauge to the inlet, but I bet at part throttle cruising there is lower pressure than that. The steel line replacement solved that. Since I've not removed the petcock, I don't know if there is a metered leak on the vacuum side of the diaphragm. If there is, a collapsing vacuum hose would cause the valve to shut off fuel flow. When the engine loses power when the bowl level gets too low, the vacuum goes away and the hose resumes its original form. The valve then reopens and refills the float bowl albeit slowly as the engine power is using the fuel at some rate slower than the supply.
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Old 07-25-2012, 07:57 PM   #39
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If the diaphragm has a hole, extra fuel will be drawn into engine, causing extra rich condition. You should be able to see that on the spark plug. Also, if you use "see through hose", you'll be able to see fuel flow into the hose as you apply vacuum.

I am not so sure about last part of your explanation.

I had replaced vacuum hose with new one made for cars and run a little test run. It performed somewhat OK. So I went out for my test loop run (7 miles). Well, I did two loops. It performed OK, no pep, with some power surge at partial throttle. There's unpredictable lack of power at times as I apply throttle when I'm getting out of turn. I'm not so happy.

Since the tank is almost full, I will burn it off before I try something else to see if I can improve on the performance.
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Old 07-25-2012, 11:11 PM   #40
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Not sure how the Riva vents it's tank, but one quick and simple thing to try would be to loosen the gas cap next time it acts up (listening closely for any in-rush of air from suction), and see how it runs then. A plugged fuel tank vent could be a possibility, from your description.
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Old 07-26-2012, 03:43 AM   #41
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Fuel tank vent tube is routed to a box which I think is a charcoal canister equivalent of a car. Since fuel supply to carburetor is by gravity there would not be that much of vacuum created. But your idea is worthwhile to check. I think I can run with tube to the box removed. I think I will check the operation of check valve as well.

Thank you for your idea.

================================================== ====================

After above post, I went out for another test ride. Blue sky, cool air, why not. The engine performed similar to how it was last night. Fuel level within the fuel line leading into carburetor is the same as in the picture a few posts above. Changing vacuum line had no affect to this regard.

Vacuum pressure when idling is supposed be 17-20 in-Hg. Ambient pressure is around 30 in-Hg or 15 psi. So, I could say the engine is pulling about 5 psi of vacuum when idling. Correct me if I'm wrong.
And as RPM goes up, the less the vacuum. At max RPM, manifold pressure is close to 30 in-Hg.

Since I did not see my vacuum line collapsing at idle speed, it is safe to say my old vacuum line was not collapsing as well as my new line.

hayasakiman screwed with this post 07-26-2012 at 05:43 AM
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Old 07-26-2012, 02:44 PM   #42
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I couldn't wait till fuel level is low in the tank. So, drained it and replaced fuel valve with the one with no diaphragm. The fuel flows out and goes into the carburetor with home made fuel valve as the only restriction.



The photo above is after couple of runs. There's no air trapped inside the fuel line, but there was before the run.
And how did the engine run????
It run the same as with normal fuel valve with vacuum operated shut-off. So, as least on my Riva, vacuum line as the source of ill running engine is out of window.

What I need to check now are fuel level in carburetor bowl and pilot screw setting.
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Old 07-27-2012, 04:52 AM   #43
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Pulled spark plug out this morning. I looks like the engine is running rich.
Last night, turned all the way in the pilot screw while engine hot and running, the engine kept on running = idling.
I didn't try ride it like that.

What I don't understand is that the scooter run beautifully, though, it was only a half of one leg of commute. I have not changed anything, any setting other than installing fuel valve.

hayasakiman screwed with this post 07-27-2012 at 05:24 AM
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Old 07-31-2012, 04:56 AM   #44
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The scooter has about 275 miles since cleaned carburetor was installed. This morning, throttle was very hard to twist for the first start up. It has brand new throttle cable, replaced in June. It can not be this tight I thought. Since I don't have side covers installed, I was able to see throttle cam movement as I twist the grip. Stiffness is from throttle valve, I can see. I was going to remove and inspect the carburetor anyways for on going lack pf power issue. But I am surprised to have the throttle this hard to twist.

As I ride few miles the throttle became easy to twist. It must be varnish build up or something. The scooter was struggling to build speed, more so this morning. I'll check it out later.
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Old 07-31-2012, 10:54 AM   #45
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Question OMG!! Sludge???!!! Varnish ????

See the photos below. This carburetor was cleaned in cleaning tank about 275 miles ago in last month.







What is this???? The piston was covered with sticky stuff and didn't move with finger. No wonder the engine didn't have power. Air was not getting in!! So, the carb was cleaned.





Now, fuel tank is drained. And it is filled with AVgas. AVgas is clean and free of varnish. With this fuel, it should be free of sludge build up. Test run the scooter and it is running great. It has that pep back. I need to go on my test run loop to know for sure but so far so good. Only time will tell.

Here are some thoughts.
The fuel it had was bought from Costco. I wonder if they have crappy fuel? Or, is this because of excess blow by with this engine that causing the sludge build up? I use the same fuel for my car, Gopeds, pressure washer and leaf flower. No issues found with these engines except the leaf blower.

The blower had lost its power couple of days ago, just like the Riva did. I sprayed carb cleaner and it regained the power back.

Now I would like to know where others on this forum buy their fuel =gas? Avgas is way too expensive to run on. I need to find alternate brand of gas!!! Give your feedback if you will please.

hayasakiman screwed with this post 07-31-2012 at 11:16 AM
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