2002 Yamaha C40TLRA Intermittent rough running

[deepwater52]

2002 Yamaha C40TLRA (2cycle) that I bought new in 2002. Well maintained and stored but was not used last year at all. Pulled it out this year and replaced all old gas with fresh. Started in driveway and idled a little rough but when bringing throttle up it would run fine then puff blue smoke and run rough every few seconds. Carbs removed, cleaned and rebuilt along with head gasket just for good measure. A bit improved but still same behavior of puffing blue smoke every few seconds. Any ideas what would cause this intermittent cough with a puff of smoke?

 

[99yam40]

lean sneeze would be my guess
go thru the carbs again and make sure you follow the link and sync procedures in service manual after installing the carbs.
anything in the fuel pump or lines can plug things back up in the carb if not flushed out and cleaned before putting them back on.

might want to check on the re-circulation check valves pressed into the crankcase . the lean sneeze can put pressure on fuel pump , check valves, and other seals on crankcase when it goes off like that

 

[atti_mac]

Deepwater52 , i almost have a same problem. Has a 2007 40 hp F40TLR..Bought a boat 4 weeks ago, yesterday I took it out first time. Had a little gas in it so I topped off with new and put stabil in it.
Motor starts , idle bad, shakes the motor, when i try to put it in gear dies off. Or even if I try to choke it.
After hours of research someone told me the jets are wrong size in carb by the factory! Because of their fuel efficiency...
Here is what he said:
"If you own a Yamaha 40hp you may experiencing acceleration issues and this is a factory defect . To solve the issue you must replace the jets. We are moving up from a #95 main jet to a #108 main jet then we are moving up from a #35 jet to a #45 jet. The part number for the jets that you need is 65W-14943-79-00 and 676-14948-05-00 and you need 3 of each jet. ********** is a good place to buy these jets"
So I will order it tonight.. Also I been told to replace the spark plugs to a NGK DPR6EA-9 !
I didn't mean to talk about my problem, and hijack your post, I believe we have a same issue. Also an other guy I found on facebook facing with a same problem.. Please let me know if you find out more. You welcome to call or text me as well. 713-884-552two
Here is couple of links:
http://www.*****************/boat-forum/showthread.php?220152-2008-Yamaha-F40TLR-4stroke-headache

​https://www.youtube.com/watch?v=UZLTH94Yvnk&spfreload=5

Looks like some of my info edited by this forum, text me and I will send you the full links...


​

 

[99yam40]

atti,
your motors are not even close to being the same he has a 2 stroke

 

[robert graham]

If it ran well before and now is missing/smoking then I wouldn't screw with the jets.....

 

[deepwater52]

lean sneeze would be my guess
go thru the carbs again and make sure you follow the link and sync procedures in service manual after installing the carbs.
anything in the fuel pump or lines can plug things back up in the carb if not flushed out and cleaned before putting them back on.

might want to check on the re-circulation check valves pressed into the crankcase . the lean sneeze can put pressure on fuel pump , check valves, and other seals on crankcase when it goes off like that

I replaced all fuel lines and the fuel pump and filter. When I rebuilt the carbs I had kits with new jets, gaskets etc. I used carb cleaner and compressed air and blew out every hole I could find. Would it be better to dip them in the carb cleaner and let them soak?

What causes this "sneeze" I have seen written about and why the puff of smoke?

 

[deepwater52]

Deepwater52 , i almost have a same problem. Has a 2007 40 hp F40TLR..Bought a boat 4 weeks ago, yesterday I took it out first time. Had a little gas in it so I topped off with new and put stabil in it.
Motor starts , idle bad, shakes the motor, when i try to put it in gear dies off. Or even if I try to choke it.
After hours of research someone told me the jets are wrong size in carb by the factory! Because of their fuel efficiency...
Here is what he said:
"If you own a Yamaha 40hp you may experiencing acceleration issues and this is a factory defect . To solve the issue you must replace the jets. We are moving up from a #95 main jet to a #108 main jet then we are moving up from a #35 jet to a #45 jet. The part number for the jets that you need is 65W-14943-79-00 and 676-14948-05-00 and you need 3 of each jet. ********** is a good place to buy these jets"
So I will order it tonight.. Also I been told to replace the spark plugs to a NGK DPR6EA-9 !
I didn't mean to talk about my problem, and hijack your post, I believe we have a same issue. Also an other guy I found on facebook facing with a same problem.. Please let me know if you find out more. You welcome to call or text me as well. 713-884-552two
Here is couple of links:
http://www.*****************/boat-forum/showthread.php?220152-2008-Yamaha-F40TLR-4stroke-headache

​https://www.youtube.com/watch?v=UZLTH94Yvnk&spfreload=5

Looks like some of my info edited by this forum, text me and I will send you the full links...


​

Its an aggravating problem isnt it. I have read a bunch of posts about these similar problems but different models may have different solutions. Sounds like yours may be a four stroke and you might have found the problem. My bad was I let the boat sit a little longer than normal last year. Even though I used all proper storing processes, the crap ethanol and salt water will get it sooner or later. I had this engine since new in 2002 and this is the first problem so I cant complain. Good luck

 

[deepwater52]

If it ran well before and now is missing/smoking then I wouldn't screw with the jets.....

Yes, for 14 years it ran great! Its probably carb crud that I missed first time around. I sure cant complain about the engine. Its been a gem till now and its probably because I let it sit a little over a year last year. Thanks

 

[deepwater52]

Also one more question. How long do reed valves usually last before they should be replaced. If the carbs are off it would be easy to do.

 

[atti_mac]

Sorry bud, I thought yours is 4 stroke as mine.