40 HP Yamaha Bogging down still

[rnellie4]

I have a 1997 40hp Yamaha percision blend 2 stroke. The motor will get up and go then slowly lose speed after 2 minutes. Then,you back off the throttle, punch it down again...It will get up and go again then slow down again after 2 minutes. Compression is fine(100,100,100). I put this post up about a month ago, but didn't get any responses. Since then I have done the following: carb job, replaced gaskits on carbs, changed gas,run sea foam, changed plugs, checked fuel filter, new fuel line and prime bulb and new fuel line connections. The bottom carb did have a little trash in it. Myself and the kind people helping me are completely out of ideas. I would greatly appreciate any advice on this issue. Thanks!

 

[Arny]

Re: 40 HP Yamaha Bogging down still

Have you tried to change the fuel pump + gaskets?

 

[aj584211]

Re: 40 HP Yamaha Bogging down still

Please let us/me know if changing the fuel pump solves your problem because I've got the exact same situation with my 2002 50HP and have gone thru the same clean out/fuel source replacement procedures with no luck...
Looks like the fuel pump is a fairly straightforward replacement, but I'll let you tell me.
Thanks for any response

 

[rnellie4]

Re: 40 HP Yamaha Bogging down still

will do...I have actually turned the motor into a mechanic and he is also at a loss. I will let you know when he figures out what the broblem is.

 

[rnellie4]

Re: 40 HP Yamaha Bogging down still

aj584211 - I didn't forget about you...the motor is still at the mechanic's and now he can't figure it out. Any update on yours? Thanks

 

[Scott/Tampa]

Re: 40 HP Yamaha Bogging down still

Good Afternoon! By any chance, did you ever figure out what was causing your problem? We basically have the same problem except our will run great for several minutes then bog down. Idles fine.

 

[DIXIEEGG]

Re: 40 HP Yamaha Bogging down still

I am having the same problem. After rebuilding the carbs and after pulling them several times have noticed the manifold bolts were loose. I tightened them and hopefully that will correct the problem. I will advise on Monday. You may need to check the carbs to see if all the screws are tight on them as well and gaskets are sealing the parts together. 02 50hptlrz

 

[Blue_Dog09]

Re: 40 HP Yamaha Bogging down still

Hi people

has any one found the problem too this it seems too be a comon prob iv been reading forums and theres alot of people with this problem and no 1 has reply to fixing the problem. iv got the exzact same stuff going on with my 1992 yamaha 40hp oil injected
iv have done every thing iv cleaned carbs iv got new fuel tank, fuel lines, fuel filters,fuel pump,spark plugs, iv even tryed pulling the wires off to the handle the sensor wire still made no diffrent iv got a macanic lookin at it in 2 days time ill keep use inform on the out come .

ps.. im thinking some fuel + match = barbie Q

 

[Blue_Dog09]

Re: 40 HP Yamaha Bogging down still

finaly found the problem its FIXED im as happy as pig in sh*t

well the wife isn't cost me $420 bucks aussie bucks that is and thats second hand new price i nearly had to change me pants :redface: any way the problem was a bloody BLACK BOX knowen as a CDI ignition box !!!
so all u pple with this problem it isn't bloody fuel probs its that stuiped little BLACK BOX that sits on the side of your motor with about 20 wires coming out of it .
hope this saves pple lot of time and money on trying to frind the problem as it cost me a arm an leg on replacing every thing to do with fuel ,at least it has all brand new the fuel system now and a good second hand BLACK BOX