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Author Topic:   1991 Yamaha 50-HP Stalls
USAwhaler posted 09-03-2013 06:32 PM ET (US)   Profile for USAwhaler  
I have a newly-acquired 1988 SPORT 15 with a 1991 Yamaha Pro 50.

[The 1991 Yamaha 50-HP Pro model] starts rapidly, sounds good, then dies in a very short time. [Recently I installed] new [spark] plugs, [checked and found] good spark; [I also] replaced the main fuel line to fuel pump.

I did notice the 703 remote control fast idle lever does not feel like it does anything--no resistance. I tried pumping [the primer] bulb on fuel line without positive results. When I took it for a ride prior to starting the project, [the 1991 Yamaha 50 Pro] ran fine, and compression tested okay. [An infrared] temperature [gun] said 102- to 105-degrees-F, [which] seems a bid cool. [The] oil light on dash stays on all the time but, [the 1991 Yamaha 50 Pro] smokes like it is getting oil.

I just finished re-doing the boat interior, moving battery under console, and lifting the console to 27-inches. I thought I was ready for a test run and the engine dies. Thank you for your help.

jimh posted 09-04-2013 08:45 AM ET (US)     Profile for jimh  Send Email to jimh     
Describe how the engine stalls. Does the engine stutter and slowly stall out? Or does the engine just stop, like you had turned the ignition key switch to OFF?
USAwhaler posted 09-04-2013 09:31 AM ET (US)     Profile for USAwhaler    
It just stops.some times it run a bit longer than other times but stops rather fast. I did dump all the oil in the tank since I did not know what type and replaced with Yamalube, also checked for clean oil tank filter. Thank you.
dg22 posted 09-04-2013 11:05 AM ET (US)     Profile for dg22  Send Email to dg22     
Possibly your fuel filter just before your fuel pump is dirty/restricted.
USAwhaler posted 09-04-2013 11:21 AM ET (US)     Profile for USAwhaler    
OK, I retested this AM to verify how it dies after start. It starts instantly every time I turn the key. Runs for a very short time, does a very, very short shutter and stalls. This happens every time and it will also stall if I accelerate. I still need to find why I do not have any action or resistance on the fast idle neutral throttle lever at he 703 remote control but it seem like it should still run without the neutral lever up since it starts instantly.
I was planing on removing the Yamaha filter and replacing with new inline car type that lets you clearly see the fuel. Will this cause any problems?
Thank You.
USAwhaler posted 09-04-2013 02:47 PM ET (US)     Profile for USAwhaler    
Additional testing results: Replaced Yamaha filter with clear automotive in-line fuel filter. It did not improve the stalling. Again, It starts very fast, runs at 2000 RPM for a very short time, drops to about 900 RPM again for a very short time, the stalls. I did notice a very small cough in the prop exhaust but not every time. Thank You
USAwhaler posted 09-04-2013 05:27 PM ET (US)     Profile for USAwhaler    
New discovery: found that number 3 (lower cylinder) is going for a free ride. I pulled the plug wire and had no change in RPMs. All plugs do have strong spark. So it seem that I am not getting fuel to #3 cylinder? Can the problem be the lower carb? Than You


jimh posted 09-04-2013 07:48 PM ET (US)     Profile for jimh  Send Email to jimh     
If the engine stalls out with a slow stutter, the cause is probably a fuel restriction, with the carburetors losing fuel.
dg22 posted 09-04-2013 10:31 PM ET (US)     Profile for dg22  Send Email to dg22     
Pilot jet passages may be plugged on that carb. Also, check to see that the carbs are in sync. The carbs should open and close exactly the same on all cylinders so they run the same. You may need a service manual to adjust the linkages.
Tom W Clark posted 09-05-2013 10:48 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Too bad it has a good spark.

If you are not getting fuel to the lower carb, that means it is also not getting any lubrication. That is very bad. You may now have a scored cylinder.

USAwhaler posted 09-05-2013 08:29 PM ET (US)     Profile for USAwhaler    
Thank You all for the great information. I will not try to start it again until I remove and rebuild the carburetors. I need to find a better book than the Clymer manual. It did not even explain what cylinder to use for finding TDC. Since I noticed the timing mark is on a slider and I can see that it has been moved I need to confirm TDC. The Throtlle linkage adjustment and CDI advance indicators also show completely different image than my 91 Pro 50. Do the rebuild kits for all three carbs include the needed gaskets or seals to the block?
Thank You very much for all your help
dg22 posted 09-06-2013 09:38 AM ET (US)     Profile for dg22  Send Email to dg22     
Check eBay, you should be able to find a Yamaha service manual for your specific motor. Below is one on CD for $7.99.

http://www.ebay.com/itm/Yamaha-40-50-HP-2-Stroke-Outboard-Motor-Service-Repair-Workshop-Manual-CD-/181161521366?pt=Motors_Manuals_Literature&hash=item2a2e1170d6&vxp=mtr

mcole posted 09-09-2013 09:12 AM ET (US)     Profile for mcole  Send Email to mcole     
Sir I also have a Pro 50 and recently repaired the exact same symptom.

This is how I trouble shot my engine.

Does the engine run longer or rpm increase when you hit he choke switch?

If so check this: remove engine hood and on the right side of the carbs is the choke linkage. It links all three choke plates. Remove the two metal rods linking the lower, middle and upper carb choke plates. Start the engine and one at a time with your hand close each choke plate one by one and notice if the RPM increases momentarily . Do this for each carb.

If the RPM increases on any cylinder then that carb has a blocked or restricted idle / pilot circuit in the carb.

This is very easy to fix and actually required no parts.

Let me know what you find. I can guide you through the rest of the process.


Mike

USAwhaler posted 09-09-2013 03:27 PM ET (US)     Profile for USAwhaler    
Thank You. I already did a rebuild kit on the 3 carbs. The kit was a 3 pack so It seemed proper to do all 3 at the same time. It was very easy. It took longer to get them off than to do the rebuild. Yes, I was slow on the take off but I wanted to make sure I had picture off all placement. I pulled the 3 oil injection lines to the back of the carb since they looked like they really needed replacing. Did all fuel lines, fuel pump,and fuel filter.
Does anyone know the proper way to clean the check valves on the oil injector lines? How do you confirm that they work?
Can I use carb cleaner or will that break some parts down? Also, the return check valve to the top of the oil tank is clear without any oil inside, is that proper or should oil flow flow in the return? My thought is no but not sure. That return check valve points to the "T" connector on the top-left side of oil tank.
I sure hope this all works and the engine give me a few good years for some retirement fishing. Will post images of the interior modifications when done. Thank You.
USAwhaler posted 09-09-2013 03:29 PM ET (US)     Profile for USAwhaler    
Thank You. I already did a rebuild kit on the 3 carbs. The kit was a 3 pack so It seemed proper to do all 3 at the same time. It was very easy. It took longer to get them off than to do the rebuild. Yes, I was slow on the take off but I wanted to make sure I had picture off all placement. I pulled the 3 oil injection lines to the back of the carb since they looked like they really needed replacing. Did all fuel lines, fuel pump,and fuel filter.
Does anyone know the proper way to clean the check valves on the oil injector lines? How do you confirm that they work?
Can I use carb cleaner or will that break some parts down? Also, the return check valve to the top of the oil tank is clear without any oil inside, is that proper or should oil flow flow in the return? My thought is no but not sure. That return check valve points to the "T" connector on the top-left side of oil tank.
I sure hope this all works and the engine give me a few good years for some retirement fishing. Will post images of the interior modifications when done. Thank You.
mcole posted 09-09-2013 08:03 PM ET (US)     Profile for mcole  Send Email to mcole     
It does not matter if you did carb kits or not! Carb kits do not unblock jets and passages you cannot see. You mentioned it took longer to get the carbs off than it took for the kits. All of the circuit in the carb must be checked to make sure they are clear. You don't just change the jets and float and call it good. Please just do the procedure i mentioned above and get back to me. I have 20 years experience repairing outboard engines. Dealers call me when they can't fix problems. The problem is always very simple. There are several passages in your carbs that are difficult to see if they are clogged. For example there is a crossover port just under the main jet that connects to the idle circuit it could easily be blocked.

Mike

USAwhaler posted 09-11-2013 05:34 PM ET (US)     Profile for USAwhaler    
Will Do Mike. I ran into some medical problem but should be back very soon. Thank You.
mcole posted 09-11-2013 10:08 PM ET (US)     Profile for mcole  Send Email to mcole     
Hope all is well. I have the same engine that had the exact same symptoms as you described. Basically what you are doing by closing each carbs choke plate is momentarily dumping fuel into that cylinder to counteract a lean mixture ( or no fuel) condition. A cylinders rpm should not increase if you add more fuel at idle without adding more air by opening the throttle plate. If you hit the choke the engine should stumble and stall. The reason the rpm momentarily increases is that by closing the choke plate you are sucking fuel directly from the float bowl via the main jet, RPM increases and then decrease because you are now over rich or flooding that cylinder with fuel.

Another indication of the idle circuit being clogged is that you cannot get an rpm change in that carbs cylinder when you adjust the idle mixture screw. You should always be able get get an rpm change if you close the screw.

My lower carb had a blockage at the cross over port between the main jet and pilot jet. This is located just under the rubber plug on the idle jet side. The crossover runs horizontally in the carb housing. My idle jet had a restriction and the passage way under the idle jet that leads to top of the carb near the idle mixture screw was clogged. All though not the recommended way of cleaning a carb I use brass wire to fish all circuits of the carb.

Feel free to email me directly with any questions.

Mike

USAwhaler posted 09-14-2013 04:52 PM ET (US)     Profile for USAwhaler    
Not a good day for positive results. All carbs increase RPMs if each carb throttle is increased very,very slightly with linkage disconnected. Butterfly stays closed on all carbs all the time. If I try to open them it stalls. Laser head temp is 146 to 148 on all cyl.
Fast idle lever now works. It was of it's track inside the 703. Fresh non-E fuel, fuel bulb gets hard but does not stay hard? I does run much longer now the I did kits on carbs, fuel pump, replaced all oil injector and fuel lines and vacuum line. No leaks.
Does any one know a good outboard mechanic on the north side of Lake Norman NC. I am the one running out of gas... Thank You
USAwhaler posted 09-14-2013 04:52 PM ET (US)     Profile for USAwhaler    
Not a good day for positive results. All carbs increase RPMs if each carb throttle is increased very,very slightly with linkage disconnected. Butterfly stays closed on all carbs all the time. If I try to open them it stalls. Laser head temp is 146 to 148 on all cyl.
Fast idle lever now works. It was of it's track inside the 703. Fresh non-E fuel, fuel bulb gets hard but does not stay hard? I does run much longer now the I did kits on carbs, fuel pump, replaced all oil injector and fuel lines and vacuum line. No leaks.
Does any one know a good outboard mechanic on the north side of Lake Norman NC. I am the one running out of gas... Thank You
mcole posted 09-15-2013 10:16 AM ET (US)     Profile for mcole  Send Email to mcole     
Sir did you open the throttle blade or close the choke. The test I mentioned was closing the choke. The choke plate is the outer plate closest to the air silencer. The choke plates are linked on the starboard side using two pieces of wire rod. The throttle plates are inner and closer to the engine. They are linked with with an assembly of wire and plastic ball and socket clips .

I you want to give me a call I can talk you through the procedure.


Mike
781-706-3365

mcole posted 10-06-2013 11:39 AM ET (US)     Profile for mcole  Send Email to mcole     
Just checking to see how you are making out and if the problem has been fixed. After speaking to you on the phone I am curious to know what the issue was.

Mike

USAwhaler posted 04-04-2014 03:37 PM ET (US)     Profile for USAwhaler    
Late reply, was out with medical problems.
I still had the same problem after the third time rebuilding the carbs. I did find i pinched one of the oil injector line behind carb 2. That should not have made any mayor difference? I when i took the carbs off to clear the oil line i did put new O rings on the fuel enrichment pump due to a very minor but still noticeable fuel leak.
It starts fast and runs fair. carb one and two react when i place my palm in front, #3 not so much?
Now a new problem has arrived from the deep...

As soon as I start the motor the Tach pegs all the way to MAX. It just pegs out. Turn key off and it goes back to 0.
I only worked on the carbs so no idea on why the tach problems. I checked all connection and all are good.

Thank You for all your help and hope to get on the water as soon as the tach is back on line.

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