2004 40hp Yamaha four stroke opportunity

[nastyquedawg]

I have the opportunity to buy a boat with a 2004 Yamaha 40hp four stroke that has not been ran in a year fairly cheap. I have read the carburetor motors aren't reliable and the jets are notorious for clogging up. If I can get the whole package for $1000, is the carburetor issue worth the headache at that price?

 

[ondarvr]

If you rule out all motors that haven't been run in a year you will really limit yourself on the number of opportunities to get a good deal. The one year is a non-issue.

Does this mean you aren't going to see if it runs before you buy it?

 

[nastyquedawg]

I gonna definitely make sure it runs before I buy it. I just concerned about the carburetors. Don't want to find myself in a situation where I'm unclogging the carburetors every year.

 

[ondarvr]

Carbs aren't that big of a hassle, I clean mine every 10 years or so....maybe.

EFI will always run better, that doesn't mean the carb'd 4 strokes are bad though.

 

[99yam40]

the F40 does have small jets that plug easily from what I have read. I would guess you need a multi channel manometer to set them properly after cleaning also.

I did read where you can replace the jets with larger ones, but that will require some research on what size to use

 

[ondarvr]

I did read where you can replace the jets with larger ones, but that will require some research on what size to use

I don't understand that, unless the jetting was wrong when new, it would only run worse with larger jets. Some 4 strokes are jetted slighly lean at idle though.

 

[99yam40]

reasoning I heard was EPA forced them lean at all RPMs
so running a little richer helped

 

[Disschord]

I have yamaha f40 I clean the carbs every year my self it's a simple job.

When the carbs are clean she runs beautiful but as soon as the carbs start to foul up she becomes a pig to start and idles rough.

Some people change the jets to larger jets

 

[nastyquedawg]

Thanks for all the responses.

 

[Chilliman]

Hi
The F40 series of Yamaha outboards had their share of carby problems for a long time.
Having jets in a carby that are small is like saying the tyres on my scooter are small. They are meant to be .
Most filters do a good job at keeping particulate matter out of the carbies but will not keep out water.
Some outboard filters seem to be a little brave and not much more than rock catchers.
If your motor has the Keihin BCF carbies on it you may be in for some weird problems causing, flat spots off idle, a dead spot at around 2000rpm and surging at cruise RPM's.
I have seen a number of these carbies come out with oversized idle air bleeds, no main air bleed, and faulty accelerator pump mechanisms.
How they ran when new is surprising, but I have worked on a number of boats that have been to the dealers with only 80 or 100 hours on the clock and they needed a huge amount of attention.
I guess when you make a few hundred thousand carbies that are lemons, what do you do?
Blame the owner, or the fuel, then make them pay for new carbies that are no better at a cost of over $1000.
The carbies can be modified to solve all of these problems with very little work, but then you will need a set of manometers and someone who knows how to use them to syncronise them when the mods are done. Also not that difficult a job.
Pilot jet size is normally okay, main jetting is a little on the lean side to keep the environmental people happy, the idle air bleeds need to be hugely reduced in cross sectional area, and a main air bleed needs to be created.
Those three rubber hoses you see at the top of the carby stack is what the main system uses for air bleeds.
Way too big.
If you want more detailed info on exact sizes I found worked for my customers F40's I am happy to share that info with you by all means.
I also want to say there are millions of experts out there with a million opinions, and that this info is only the opinion of one old bloke in a dodgy old tin shed in the outback of Australia.
But I do have over 45 years of experience, specializing in engine work from the days when you had to know how things worked on a component level.
Not like today.
Go ask some young bloke to draw an illustration of an idle circuit of a carby and say how it works.
They will probably say, "dont need to know that. Everything is EFI now."
Have a good one mate

 

[ondarvr]

Good info.

Here in the states it is illegal to change or adjust jetting on anything newer than a 1998 model, so dealers have their hands tied when it comes to getting motors to run correctly. Plus the motors come jetted as lean as possible. Most of the issues are low at RPMs, hard starting, poor idle, shaking, cold blooded, etc. The dealer can clean the carb, or put on a new one, that's about it, and hope that it runs better.

The common practice by someone other than a dealer is to drill out the plug covering the low speed adjustment screw and richen it up if needed. I've never looked at a carb off of a 40 to know if this is an option though, and the ones I've seen ran well.