1985 Yamaha 40ETLK will not go past 2500 rpm wot please help i just want to fish

[Ryno57]

ok this one has me stomped I have a 1985 Yamaha 40ETLK 6H4L 551328 that is new to me that will not go above 2500 rpms on the water but at home in a test barrel it runs amazing. So for what I have done so far to try to fix the problem. I have cleaned all three carbs I have tried new premium fuel with ethanol treatment. I have manually tried to make it get up a little more from the engine it self by not using the remote and just using throttle control on engine with the same result as using the remote. So instead of just throwing parts at it none stop I could really use some help Thanks in advance Ryno57

 

[Silvertip]

An engine running on half it's cylinders may sound good to the casual observer in neutral in a barrel or on muffs. Fact is, there is no load on the engine, hence the problem when you try to push the boat with a sick engine. So 1) pull the plugs and inspect them and change them if necessary. 2) Check for spark on all cylinders/ 3) Check compression. Since you had the carbs off, did you perform a link & sync after reassembly. A service manual is your friend here. I don't know if that engine has a "fail safe or protection" mode if an overheat condition exists, but if it does, that's generally the rpm an engine is rpm restricted to. So it may be possible the ignition system protection mode may be triggered even if the engine is not overheating.

 

[Ryno57]

Ok I have checked for spark in all three cylinders which it has a great blue spark on all three I checked the plugs after I put new ones in and I have found the number 2 cylinder is not burning any fuel which is sending me back to that carb must not have cleaned it to good last time. I also ha E do e a compression test since my last post and I am not sure on the numbers I came up with #1 60 psi #2 60 psi #3 60 psi I am not sure what this motor should have in the way of compression .

 

[rickclark]

The actual reading on the cylinders doesn't matter so much since different gauges will give you different readings. What is important is the variation in values btween the cylinders. Yours look good since they are all the same, assuming you did the compression test correctly. Variation of 5 or more PSi between cylinders may be reason for concern.
You may want to check the fuel pump, gas filter and fuel lines from the tank to the fuel pump even those these may be unlikely since the issue seems to be with only 1 carb.

 

[Ryno57]

Well final result ended up being I pulled all three carbs off again and completely tore them down one by one and cleaned every little crevice and then reassembled them put them back on an synced them took the boat back out on a test run and it runs like a dream. So I then took it out over the weekend fishing and had no issues in 15 hrs of fishing thank you for all the help and pointers everyone that helped

 

[robert graham]

Consider installing a fuel/water separator type canister filter and regular use of a fuel stabilizer like Stabil, and drain each carb float chamber for any lengthy motor lay ups....to prevent plugged jets, poor running , possible lean mixture/burned pistons....preventive maintenance is always better/cheaper than repairs....

 

[Ryno57]

I always run stabil and run off full in arbs before leaving the water. I had purchased this boat and it had sat for a very long time so I was fighting all the problems that had developed from sitting so long without being prepared for long storage but thanks again for all the help and pointers I will look into a water separator for sure

 

[99yam40]

With motors with more than one carb there is a possible problem running the motor until it dies when disconnecting the fuel line.
All of the fuel in the bowls will not be sucked out just because of the way the jets and bowls are set up, which leases some to evaporate quicker and leave residue in bottom of bowls.
Also some of the upper carbs will run out of fuel before the bottom one, so the motor is running lean on the ones low on fuel before it dies. no fuel moving through means there is no oil also so no lubrication to those cylinders too.

Best to leave full of fuel and run often
or open the drain screws to drain the fuel