Yamaha 40 rough idle / stumble when accelarating and yes I have cleaned the idle jets

[littletunny]

2 stroke.

cleaned thes carbs twice. Got all the holes, even pulled out the main and idle jets and soaked them.

Did the lync and sync.

Seems like it will idle then load up and stall. If I try to throttlw thru it it will stumble and run rough.

Maybe i didnt link and sync correctly?

HELP

Little update. I let the boat sit for 30 minutes. It cranked and idle right up awesome for about 25 seconds them it stumbles and stalls. Every subsequent start it stumbles. The carbs are "loading up" but how do i prevent this?

 

[Inducted]

Re: Yamaha 40 rough idle / stumble when accelarating and yes I have cleaned the idle

What year is the engine? always give a complete model #!
In order to prevent loading up double checking your float setting is always a good idea.. How does your engine (choke) choke plates? enrichment valve? prime start? Prime start the needle is (open) when cold so fuel can flow it closes thru the electrical connections. If it does not close, to rich, and engine bogs down.
Also if your engine is a 95 40hp then it has a magneto control rod as part of the linkage so you do need a manual to set the linkage adjustments properly. Are all the throttle plates closed at idle? There is also a throttle cable adjustment! ANYWAYS check your enrichment system first that will cause your carbs to load up.. Also if the carbs were crapped up they may need another cleaning. Good luck

 

[littletunny]

Re: Yamaha 40 rough idle / stumble when accelarating and yes I have cleaned the idle

What year is the engine? always give a complete model #!
In order to prevent loading up double checking your float setting is always a good idea.. How does your engine (choke) choke plates? enrichment valve? prime start? Prime start the needle is (open) when cold so fuel can flow it closes thru the electrical connections. If it does not close, to rich, and engine bogs down.
Also if your engine is a 95 40hp then it has a magneto control rod as part of the linkage so you do need a manual to set the linkage adjustments properly. Are all the throttle plates closed at idle? There is also a throttle cable adjustment! ANYWAYS check your enrichment system first that will cause your carbs to load up.. Also if the carbs were crapped up they may need another cleaning. Good luck

1. 2004 40TLRC
2. will check the carb float
3. motor has the prime start will check
4. all the throttle plates are closed at idle

Why are there 3 settings on the Prime start?? Normal, emergency and one other setting (forgot what it was called). Can someone explains how it operates??? Its not even in the manual.

THANKS!!!!!

 

[99yam40]

Re: Yamaha 40 rough idle / stumble when accelarating and yes I have cleaned the idle

The third position is off. This will stop any fuel going through the enrichment system if the enrichment diaphragm is leaking and flooding motor.
emergency is for just that, for an emergency. When you can not start motor because of carb jets are plugged or the enrichment system is not functioning properly
Your owners manual tells you all about it and how to use it in an emergency to get back to dock and have it fixed

Sounds like your carbs still have a plugging problem and as soon as the fuel enrichment of the prime start system ends then the carbs cannot keep the motor running.
Would be a good idea to monitor the timing as when starting the CDI advances the timing until the motor is warmed up(or for a few seconds if the motor is already warm) and then retards the timing to the normal idle timing setting (7 ATDC). Then advances the timing as the throttle is applied, if the timing is not doing it's thing then it could bog down the motor under load.
But my guess is you still have plugging in carbs

 

[robert graham]

Re: Yamaha 40 rough idle / stumble when accelarating and yes I have cleaned the idle

Maybe check your fuel pump operation for possible bad diaphragm causing raw gas being sucked into a cylinder causing wet/rich fuel mixture spark plug fouling....Easy to just run the motor a while and then remove/inspect plugs for fuel wet condition. Good Luck!

 

[littletunny]

Re: Yamaha 40 rough idle / stumble when accelarating and yes I have cleaned the idle

Thanks Guys. The fuel pump is brand new. I am going to delve into the prime start. I can only clean the carbs so many times!

 

[99yam40]

Re: Yamaha 40 rough idle / stumble when accelarating and yes I have cleaned the idle

Have you tested the timing like I said??
mine was off at idle and I had to replace the CDI

compression, spark, and timing are easy to test using the proper equipment(tools).
If all that is good the you are left with the fuel.air mix

 

[shaman 2]

Re: Yamaha 40 rough idle / stumble when accelarating and yes I have cleaned the idle

hello,

I have a 2006 F40 TRA that just recently is difficult to start. I think it's the prime start as it used to "click" when the key was pushed in. The engine will start eventually but sounds like it's startin on 1 cylinder then smooths out after a minute or so.

Is there a way to test the prime start? I disconnected the bullet connectors at the prime start & checked with a volt meter w/key in on position but got nothin. Is there a fuse/relay or anything inline? Called a yamaha rep but the guy didn't know much.

thanx for any help.

 

[99yam40]

Re: Yamaha 40 rough idle / stumble when accelarating and yes I have cleaned the idle

shaman 2 you need to start you own thread as this one is not about a 4 stroke, and prime start does not do anything when pushing in on key only electric choke does

 

[littletunny]

Re: Yamaha 40 rough idle / stumble when accelarating and yes I have cleaned the idle

Hey guys,

Bout got the problem licked.

It basically the ethanol clogging the idle jets.

The boat runs like a scalded dog but wont idle for nothin. I cleaned the carbs for the third time and it remedies the idle, then after about 30 mins of run time, idle jets get clogged again.

It looks like a gel and also a white chalky substance inside of the carb.

I dont know where the crap keeps coming from.

 

[99yam40]

Re: Yamaha 40 rough idle / stumble when accelarating and yes I have cleaned the idle

It comes from the fuel tank and the rest of the system. Your fuel has gone bad. Get rid of it and start over with fresh stabilized fuel.

It is not the ethanol that is plugging things up it is the plastic and rubber from the deteriorating lines and tank the ethanol is attacking and it is the water the ethanol has sucked up and separated out leaving the rest as bad fuel also

You will need to drain and clean the tank, fuel pump,primer,and all lines or best just replace them. That stuff will hide in them and end up in the carbs every time you crank it up and run it.
or clean the carbs again and again and again.
Cut a small piece of fuel line off and then split it open to look at the inside of the line, see if it is coming apart from the ethanol.