2008 Yamaha F40TLR runs badly

[Gary13]

Purchased 2008 Yamaha F40TLR 4-stroke in June. Boat was delivered with fuel lines full of water, which consequently ended up in carbs. After the initial no-start, the dealer drained carbs, engine started and idled fine. I ran it for 3 hours for break-in before an ignition coil went bad. Coil repaired, headed out again and after 2 hours, engine lost power all the way to idle. Took back to dealer who said they pulled and cleaned the carbs, which according to them, was full of ?junk?(the inline filter was clean). Had them install a Racor 10 micron fuel/water separator. Motor runs now but very poorly. Idle is rough, and during acceleration (slow...I don't do hole shots )there is a flat spot that will shut engine off, and at higher rpm?s there is constant surging. Engine is never run above 75% throttle so I don?t know about WOT yet. Fuel is fresh, tank is totally clean, spark plugs look normal and gapped correctly. Any thoughts?

 

[nabeel]

Re: 2008 Yamaha F40TLR runs badly

We (a sailing club) have similar problems with our 2004 F40TLR. One of us -- a shade tree mechanic but a very meticulous and careful one -- has rebuilt the carbs 3 times since we bought the engine. Each time the engine starts running more and more poorly. And each time he dissembled the carbs, he found an orange deposit had built up on the surfaces that is easily removed by alcohol. (Of course, we suspect ethanol in the gas but have no proof. Our other fuel injected 2005 F75 has no issues.)

Most recently, after the engine starting running poorly again, we took the engine to a Yamaha dealer -- we had worn out our welcome with the shade tree mechanic member of our club. The pro mechanic disassembled and reassembled the carbs, syncronized them, and replaced missing float check balls. Plus, we switched to a strick regime of using a fresh gas every weekend and at the end of the day disconnecting the gas and running the engine until it stalls so that no gas remained in the engine from one weekend to the next.

Still the engine does not run right. The transition from idle to part power causes the engine to stall unless someone with a the right touch is operating the boat.

I'd appreciating hearing if you solved the problems with your engine and how it was done.

 

[rodbolt]

Re: 2008 Yamaha F40TLR runs badly

to start with this motor does not like an easy touch on the throttle, the desighn of the accelerator pump needs a rather rapid opening action to work.
ign coil failure on the F40(non-merc desighn) I have never seen.
if the tech,especially a shade tree does not have a tech-mate vacum mate tool or similar manometer its simply impossible to set the carbs.
tech mate gets about 650 dollars for the tool.
I own one.
occasionally due to various reasons the air/fuel mixture screws have to be removed,cleaned and reset. again this procedure requires the use of a manometer but now its simply technician understanding of how multi-carbed 4 stroke gasoline engines work as there is no written procedure.
the brass EPA tamper proof plug will have to be drilled and extracted prior to removal/adjustments.
this motor MUST be propped to turn 5800-6000 RPM or its not happy.
this motor also likes to run above 4000 RPM or its not happy and extra maint will be required.
the orange deposits sound like ethanol is dissolving the residual fuel solids from our previous gas blends.
not a yamaha issue, its a fuel issue.
stalling on acceleration indicates an issue with the accelerator pump diaphram assy ,mis adjustment of said assy or low fuel level in the fuel bowls.

 

[nabeel]

Re: 2008 Yamaha F40TLR runs badly

Thanks! This gives me something to discuss with the tech. Unfortunately, it sounds like this motor is not the best one for us. We do lots of low speed stuff, moving marks, pulling people out of the water, towing boats, etc.

 

[rodbolt]

Re: 2008 Yamaha F40TLR runs badly

and that motor will do it flawlessly if set up correctly with a trained tech and the correct tools.
just remember at the end of the day it really wants to be run at or near its max RPM for about 30 minutes.

 

[nabeel]

Re: 2008 Yamaha F40TLR runs badly

Thanks for the suggestion. I'll try to make it a standard end of day procedure to run the engine for a while at high rpm.

Talked to the Yamaha tech today who rebuilt the carbs over the winter. He says this:

1) synchronization mainly (only?) affects idling. But he has all the necessary tools anyway. He kind of shrugged me off so I don't know whether he has the equivalent of the techmate vacumate. However, the motor does idle fine. By the way, I cannot find that tool by googling its name.

2) he said he cleaned the carbs multiple times in an ultrasonic cleaning bath but he can't get access to the circuit where he believes some sludge must be blocking a tiny passageway. He mentioned drilling out the carb to get access and then plugging it with a float bowl drain plug. He's never done it but he has heard of it.

I still may take it in and ask him to check the accelerator pump linkage. But to check the diaphram would require removal and dissembly, wouldn't it? (I don't want to ask for an unreasonable amount of follow-up work.)

Would the drilling out procedure allow access to that circuit with the carbs still on the engine? In other words, would it allow us to clean things out occassionally without complete removal and dissembly?

I guess I'm searching for the most sensible next steps...

 

[rodbolt]

Re: 2008 Yamaha F40TLR runs badly

look carefully at the carbs.
on the aft end near the top you will see a brass plug about 14" in diameter.
use a 9/64th bit and drill in the center. try to stop before the bit hits the screw and drives it in.
then use a self tapping #10 screw, thread it in the plug tillits snug, then use a pair of vise grips on the screw and pop the plug out.
its against the law for me to tell you to leave the plug out.
now you can adjust the A/F mixture and clear the passage.
part number I have is vacuumate 08-0251 made in s africa.

if you hit the screw and drive it in remove it and make sure you did not damage the tip.
then set it about 2.5 turns out from lightly seated and adjust from there while observing the vacuumate.

 

[Gary13]

Re: 2008 Yamaha F40TLR runs badly

UPDATE: Sorry it took so long to get back to the forum but wanted to give update on motor status.

Yamaha had a factory tech work on my motor that had been having problems since purchase. The tech played with it from 4 Nov-12 Dec 2008, rebuilding carbs, ultrasonic cleaning carbs, finally decided to replace all 3. Boat now running fine (but not for long). Installed a 10-micron water separator.

Changed prop...would only turn 4900 rpm at WOT. New prop brings it up to 6100 rpm WOT

Finally, oopsssss.....back to same problem again and its only September. Took to dealer Friday. Will be interesting again

So here we are again. Motor is 15 months old, been in the shop more than 6 months of this time, and has 41 hours on it. My canoe looks better every day.

 

[jeffreydoctor]

Re: 2008 Yamaha F40TLR runs badly

Go back to your dealer and politely ask them to exchange it for a new one. I work for a Yamaha shop and I had two warranty repair jobs that saved my customer $2100 and the other $3200 both motors were damaged due to neglect, abuse and both were out of warranty. Yamaha knew about the whole situation. They will definitely give you a motor if you ask.

Yamaha has a good will warranty if you aren't covered. If you're near the bay area I'll get you a motor.

The smaller engines like the 40 have passages in the carb that are too small to clean. If dirt or **** gets in them they clog for life and you need to buy a new carb.

Jeffrey