Problem with Yamaha 40 twins

S

SEA3PO

New member
I have had a recurring problem....with my 2003 40hp. Yamaha twins.... they die when I change rpm... speed up or slow down... they start up easily just after they die...and they will free rev...to well over 5000rpm....but will not go up to power under a load....one goes to 4400rpm and the other 3800rpm...when they were new they easily ran up to 5500 under a load... I have had the carbs worked on three times...I have replaced both fuel filters in the motors...I have installed two Racors... so if it were only one tank or one side I would notice the difference....I get good fuel flow from the hoses...still low rpm... the motors have always had Stabil used and only have 325 hours....

IDEAS ?? Why do these things run so bad ? On the delta I ran lots of fuel cleaner through (2 tanks of fuel)...and I think it helped some...but still they won't come up to power......

I will never buy a carbureted outboard again !

Joel
SEA3PO
 
oh I concur and empathize. After struggling with this problem for the last two years (4 cleanings). I just had new carb kits installed. The floats were constantly sticking, needle valves stuck in the seats, high speed jets clogged etc... I went through the litany of preventive measures to no avail. These problems would recur immediately after having them cleaned. I should have installed the kits after the first go round, it would have ultimately been less expensive and infinitely less frustrating. Next time it strands me at the ramp though...Suzuki 115 injected!! :xnaughty
 
OK...Maybe it is just prone to dirty carbs.... I use several filters...and use Stabil...but guess the answer is just to pay again to have the carbs rebuilt.

Joel
SEA3PO
 
Joel

ETHANOL in your fuel tank???

Doubt the Honda 40 has any better carb set up then the Yamaha and with near 1200 hours on them they start up instantly every spring and run well. Run the motors dry with Stabil in the fuel then drain all the carbs and that's it for the winterizing except for making sure the fuel tanks are completely full of ethanol free gas. In the spring before starting change the racor and internal motor fuel filters.

Jay
 
Joel,
I think they have pretty small passages in those carburetors that why they are so good on gas I guess. Jay's advice is spot on, Even on fuel injected motors that have a common fuel rail it's recommended to drain the fuel rail as they have the same sort of screw arrangement at the bottom (brass Screw and a drain hose) as water is heavier than gas and will accumulate there. The bottom injectors at least on Yamaha's will have a higher failure rate do to the corrosion build up from the water laying down there over time because people are not draining that fuel rail.
Thanks for all you do for the Brats, I for one think you deserve to make a profit on the transactions for your efforts. Thanks Again
D.D.
 
Joel my friend , wish we were closer . They run bad because of the quality of fuel we get , Its far worse in longevity [the fuel] since Yamaha designed those motors . The Carbs worked great at the time they were designed . As stated ,gotta stabilize heavily [we like PRIG and Startron cocktail for really bad gas]and drain the bowls even for a few weeks storage to avoid problems .Its definitely not a flex fuel motor!
Marc
 
Checked that.... the only thing I can think other than the plugged carbs is the fuel pump..... I see both fuel pumps have a tiny bit of oil at the bottom of them....and I noticed my oil level has risen...making oil...not a good sign... ruptured diaphram ? before I tear the carbs apart, or spend a ton of money on the carbs... I ordered two new fuel pumps and I will replace those... then do a oil change and add some ring-free,,, THEN as a last resort, I will pull the carbs...and start cleaning them....

Joel
SEA3PO
 
Joel,

I experienced some similar problems to yours and I have '03 twin carb Yami 50's. After going through the same frustrations, I had both engines cleaned/ rebuilt and changed all fuel lines/hoses and cleaned both fuel tanks. I discovered both fuel pickups in the tanks were badly corroded which the disintegration could possibly have caused the carbs to plug. Since replacing the pickups, I have had no issues whatsoever after running for 100 hours. I religiously stabilize with Startron as cheap insurance. Good luck.

Vern
 
One last Major try to clean it out...before I rebuild the six carbruators....

As a shop teacher I used to teach fuel injection service ....and invented a do it yourself....pressure tank that took the place of the expensive tool needed to service fuel injection...the students could then buy cheap injection cleaner mix that with an equal amount of fuel and run that through the system.... it did a much better cleaning than the factory units because they only used a small pressure can that was already half fuel and half cleaner....

So today.... I will mix in a one gallon fuel tank.... two bottles of SeaFoam cleaner and a matching amount of gas....then take the boat out on the water and run it... if this does not clean the gunk out....nothing will...

Joel
SEA3PO
 
Joel, you should try a couple of portable tanks to rule out tank pickup problems. The portables would be easier to try different fuel/stabilizers also. Good luck. All these carbed 4 strokes have really small jet passages. Ron
 
After spending several hundred dollars to get the fuel system and carbs of the Yamaha 100 cleaned out, I now use a stabilizer and run the engine dry after each run. Sounds like emptying the carb bowls is a good idea. Can you provide some simple instructions for this procedure? Thanks!
 
As we all know, gas engines need three things to run. Those being compression, ingition, and fuel.

In my experience as a 2-stroke O/B mechanic, the symptoms can lead you to the wrong system. Hundreds of dollars can be spent rebuilding the fuel system, only to find out that a spark plug wire is bad!

We always checked compression and leakdown first, then ignition, and the fuel system last. The reason is that if the compression is bad, nothing else will help. After that, verify ignition, because if ignition is bad, the fuel system doesn't matter.

With the first two verified, go to the fuel system. In the shop, checking compression and ignition don't take much time, cleaning an rebuilding the fuel system takes a lot more time and money.
 
After spending several hundred dollars to get the fuel system and carbs of the Yamaha 100 cleaned out, I now use a stabilizer and run the engine dry after each run. Sounds like emptying the carb bowls is a good idea. Can you provide some simple instructions for this procedure? Thanks!


I found out the hard way, per usual, that just running the motor until she quits will not empty the bowls of fuel. In fact, this method ensures quick evap of the fuel left in the bowl and varnishing at the exact point it does most harm. Open the drains, or start it once a week.
 
Ugh...fuel stabilizers, sometimes take on the sound of magic potions and witches brew. Despite the best intentions and experiences of those making such recommendations, one just never knows what to believe...the variables are many.

RE additives - gathering legitimate information only gets worse. That being said, I'll toss out my glowing observations on a product, that are far from isolated...but feel free to give it a healthy does of "snake oil skepticism."

I've found BG 44K to be amazing stuff. I've used it regularly over the last few years in all of my cars...the minute I start noticing a little rough idling, I toss a can in and everything is back to normal within a tank full. Likewise, I had great success with it on the boat a couple years ago after old, untreated fuel was left in the tank for over a year. My BF90 was running like complete crap, even after draining the old fuel and adding new. I hooked up a portable tank with a double dose of BG 44K in it, and the engine cleared up in about 15 minutes of running - and has been fine ever since, albeit with no more lapse in fuel stabilization.

It's not cheap, but I'm sold on the stuff - I'll try it first in the future for anything that seems like a possible fuel/carb issue, before digging deeper for solutions. eBay is your friend for finding it - not many places carry it.
 
Bill-

I used to rep the BG product line years ago, and it is indeed a great line of products. Marketed to the automotive service industry, it can be hard to find over the counter, so to speak.

I was impressed with all of their products, and used them regularly. In fact I need to get some 44K in my car. Thanks for the reminder!
 
Yesterday I was really fed up with these motors....so I called Marc at Wefings..(several thousand miles away)..... he and Al his mechanic talked to me.... and gave me some advice.... I took all six carburetors off...and took them apart...and using my torch tip cleaner and four cans of spray carb cleaner rebuilt them..... I sure diden't find much gunk....did not look all that bad..

I just got home from my "road test" and it ran gang busters....perfect...better than they have run for a long time....
All that was wrong with them was some small gunk .....

I still would like to sell them and buy a set of HONDA 50's...
Fuel Injection is really the way to go.... maybe next time I go to Florida I will pawn en off on my friend Mark as a deposit on those 50's

Joel
SEA3PO
 
I have to say, if I get my way, we will repower with twin 50 EFI Yami's in the future, before retirement, so don't hold yor breath Matt, but it will happen.

I was impressed this spring. After a full fuel fill last fall, (October) and a strong dose of the blue Marine Stabil, running around enough to be sure it was worked up well through the engine and carbs, that when I wtarted the boat in May for the FH CBGT, the started on the first crank, and ran like a top all weekend. I have been using that at the higer dose with every fill for the last year. Maybe it is working.

From what I have been reading, I may add the Starbrite line anti ethanol additive as well. Also recomended by my Yamaha certified mechanics.

Harvey
SleepyC :moon
 
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