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Yamaha 50 hp 2 stroke acceleration problems

armjr

New member
I have a 2003 Yamaha 50 hp 2 stroke. I bought it new. Until recently it has worked perfectly barring a few minor issues, water pumps, etc., never any fuel related or mechanical issues.

Recently it has begun to die out on acceleration past 1100 rpm. When I get to 1100 rpm and attempt to go faster it bogs down and dies. If I the choke lever to "emergency" it will run but not very well. If I then immediately switch to "Run" position it will run great. When I stop it is back to dying out.

I have replaced all the fuel lines, spark plugs, and oil lines in addition to cleaning the carbs as best I can without removing them. It is firing on all cylinders and will run on any one of the cylinders by itself.

My next move is to take it to the shop.

I'm not inclined to do that just yet.

Any suggestions?


Alan
 
.....in addition to cleaning the carbs as best I can without removing them.

No such thing as "cleaning carbs without removing them"....sorry bud.

No doubt the issue is fuel system related because of the reaction you get from the engine when applying choke. Carburetors have jets. The opening of these jets are incredibly small. Fuel runs through these jets. Over time, whether your using ethanol or non ethanol, sea foam or yamalube, the jets will get partially or completely clogged with debris. And since the jet opening is soo small, it doesn't take much debris to clog the flow of fuel, thus it doesn't take much debris to inhibit engine performance.

The carbs must be pulled to access the jets, soak, and clean them so they are completely clear. And while you're in there, check the float heights are to spec. And while you're in there, replace the kit. Especially if it's been quite awhile since you last replaced.
 
Since I replaced? We may have found the problem. I was really hoping for a miracle cure..... I hate messing with carbs, primarily because I don't know what I'm doing. It won't be the first time in my 63 years I was forced to learn something new.

Guess I need to surf the youtube offerings and find one that is informative yet not irritating.

Thanks for the reply. I kinda figured it was going to come to that but,.... as you said, the Sea Foam didn't work.

Thanks,

Alan
 
I'm going to order these two items. Is there anything else I should get for replacement while I'm in there?

Your response is the best info I've gotten all week, including from the Yamaha dealer who sold me spark plugs as the fix.

Thanks again.

Alan



Yamaha Outboard New OEM Carb Carburetor Repair Kit 6H4-W0093-03-00 40hp, 50hp
1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
$73.94$73.94
Yamaha New OEM FUEL PUMP ASY 6E5-24410-03-00
1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
$35.94$35.94
 
To answer your question about needle having a rubber seat,most do,but I also repair mowers and I have seen needles with out rubber seat,the rubber was in the seat not on the needle itself
 
Yes, that's what I meant. The first time I cleaned the carb on a lawn mower I blew it out with air. I didn't know the rubber seat was in the hole and it is now somewhere composting out in the back yard someplace. It took tearing down another carb to figure out what I had done. So, now I know what to look out for. There is likely more rubber seats in the kit.

Thanks for the reply.

Alan
 
Thanks. I was going to try to do that. I appreciate you saving me the trouble. Carb kit and fuel pump should be in next week. Just got to find some shade to work in. 95 here today.

Thanks again for all the help. I'll keep the progress posted. I've got some obligations tomorrow morning but may start pulling things apart in the afternoon.

Alan
 
I think I located the problem area. It's a wonder the engine would run at all. Thanks for all the help. I'll update after I get back on the water. I shut it down today. Will soak everything in Acetone tomorrow and put in the new kit.

Alan



IMG_1100.jpg
 
Man, I scrub and soak, soak and scrub. Every time the acetone dries there's still gunk caked on the carb body. I don't want to get too aggressive with it but I do want it clean. Most of the green stuff came off but what appears to be oxidized Aluminum is still caked on.


Alan
 
Last edited:
Everything is clean and back together. I put a few squirts of oil fuel mix in the cylinders and ran the starter for about 5 seconds with no plugs to lube up the works until I was sure I was getting gas. New fuel filters and water separation filter. I opted not to put on the new fuel pump right now and won't unless it won't run tomorrow. I started it and let it idle for about ten min (with water hooked up of course). It started on the first click.

We'll see. I'm just thrilled right now that I got it all back together and running at all!

Alan
 
I'm back in the saddle again! Ran as good as new. There was a little miss abut once a minute but I figure it's air working its way out of the system. Started perfectly and accelerated perfectly, over and over again.

Thanks to everyone who gave me advice and links to instructions. I really appreciate everything.

Alan
 
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