Yamaha 50 problem...

[vallda]

Hi 2-stroke gurus ,<br /><br />I've got some problems with my Yamaha 50Hp -89...<br /><br />When idling (it runs on idle just a few seconds before it stops) it backfires through the carbs and when taking off it hesitates severly.<br /><br />To be able to take off, I have to give it a little choke (a few seconds). When picking up speed, there is no problem at all, I can lower the engine speed to approx. 2500 rpm and then give wot without hesitation. This fact should eliminate fuel delivery problems.<br /><br />First I thought it might be lean mixture (because of misfiring through carbs), but after some adjustments without response, I don't think that's the problem either.<br /><br />Then I tried adjust the timing. With the timing set very advance, the idle works better, but the hesitation in take off remains.<br /><br />I now suspect the reeds, but before I start disassemple the engine, I think it's worth a try consulting you on this forum, since some of you seem to have a lot of experience of this kind of problems.<br /><br />Hoping for help<br /><br />// Stefan

 

[rodbolt]

Re: Yamaha 50 problem...

hello<br /> I suggest a complete teardown and inspection of the carbs and fuel pump. you just described a blockage in the idle and intermediate circuits. you also may wish to run a leakdown test. the reeds can be inspected without an engine teardown.the backfire is a lean condition where the fuel mix is trying to ignite in the crankcase.<br /> good luck and keep posting

 

[vallda]

Re: Yamaha 50 problem...

Hi again, thank you for answering !<br /><br />I performed a carb inspection recently, maybe I was careless cleaning them... Well I'll do it again (and perhaps right this time!) <br /><br />What do you mean by "leakdown" test? How do I perform it?<br /><br />When I had the carbs down, I looked at the reeds at same time, I couldn't see anything odd about them though. Maybe because I don't know how they look when they are worn (are more used to 4-stroke engines...). I noticed one thing though, when opening them one by one (touching them gently) there was a slight "popping" sound as they left their seats. This sound could be heared from cyl.1&2 reeds but not from the cyl.3 reeds. Are any of them defect, and if so, which one? <br /><br />Thankfully<br /><br />// Stefan

 

[Ray Neudecker]

Re: Yamaha 50 problem...

If the reeds are intact and spring back to seal on the reed blocks, they should be OK. Take the carbs down completly and soak overnight in carb cleaner. Many times spraying at them will not get the job done. Make sure the needles are not sticking and the float level is set right before reinstalling. A factory service manual will be a great aid in getting everything set back the way it is supposed to be including the timing and sycn adjustments.

 

[vallda]

Re: Yamaha 50 problem...

Ok, I know what to do this weekend....<br /><br />Thank you very much for your advice!<br /><br />//Stefan

 

[vallda]

Re: Yamaha 50 problem...

Hi,<br /><br />I spent the (rainy!) weekend at the marina, tearing the carbs down. The fuel level was a little low in one of the carbs so I adjusted it. That eliminated the backfiring through the carbs. Then after 20 min low speed mixture adjustments it runs as smooth as never before!<br /><br />Thank you for all your help!<br /><br />//Stefan