Yamaha F40 Idle and Starting Issues

[Moburchette]

Here's a good one for y'all. I just bought a skiff with a 2003 Yamaha F40, my first trip out resulted in a tow back to the dock after a very short run. The problems are described below.

1) The motor stalled out (at idle)after about five minutes of operation and wouldn't restart at idle...just crank, sputter, and smoke little. The only way I could get it to fire up would be to give it more throttle in neutral, but it would stall when I had to throttle down to drop it in gear. A couple times I did manage to get it in gear and throttle up and it ran like a clock.
The boat had approx 1/2 tank of fuel when I bought it of undetermined age (it ran and idled just fine on muffs), before this maiden voyage I topped of the tank with E10 and added the proper amount of ethanol treatment.
Also, while scratching my head looking at my stalled motor with the cowling off I noticed a small amount of fuel puddle in the botttom, but was unable to determine the source.

2) The starting system problem: sometimes (most but not all) when I turn the key to the start position the starter clicks...makes about 1/4 weak turn and stops...still holding the key in start position for up to a full second...then it cranks away nice and strong and the motor fires right up.
The battery is brand new, I've checked the connections at the starter relay and motor, everything looks fine, I have noticed that after a couple cycles the neg battery post on the battery gets pretty warm.

I would like to avoid simply throwing parts at these problems, but rather systematically troubleshoot them...need some help getting started.
Thanks. Matt

 

[99yam40]

Re: Yamaha F40 Idle and Starting Issues

Good idea to do a leakdown test on all cylinders to make sure the are sealing properly and inspect the plugs when you pull them to see if you are getting some water into cylinders causing hydro lock keeping motor from turning over properly after running.

Those carbs are tough to clean and adjust properly, so need to take to an expert to do them.

Voltage drop test on cables while under load should tell you if one of the cables is going bad internally

 

[Moburchette]

Re: Yamaha F40 Idle and Starting Issues

Will check the plugs and do the voltage test on the cables. Not sure what a leak down test is...will google it.
Thanks for your response

 

[Capt Ken]

Re: Yamaha F40 Idle and Starting Issues

Remove the flywheel cover and rotate the engine over by hand. If there is no hard stopping other than compression on the cylinders, then the engine should be good. Check the oil for milkyness. If its clean then no water is coming in the cylinders. If the cable is getting hot, then that is where your drop in amperage is. Find the bad place and replace/repair it. But the leakdown takes special gauges and hoses and would be expensive for the layman to buy as with the vacumate to set the carbs up correctly. Probably time to take it to a Yamaha Tech.

 

[steelespike]

Re: Yamaha F40 Idle and Starting Issues

A compression test is easier to do and will give you a good indication of the condition.
The gas could indicate a flooding condition.Could be a problem with the carbs or a leaky fuel line.
You could add some Sea Foam to the gas probably won't solve the problem but could and it will preserve the fuel.
Observe the carbs next time you run it, one or more may be dripping fuel.
Could indicate a rebuild needed.When I have a leaking carb I like to tap carefully on the carb body near the fuel line connection.
About 10% of the time a not to badly abused carb will respond.

 

[Silvertip]

Re: Yamaha F40 Idle and Starting Issues

I can tell by your description of electrical checks that you simply looked at them. A warm battery post indicates a bad connection. Remove the battery cables, inspect the cable where it enters the terminal. If you see swelling at that junction, cut off the cable end and install a new one, or replace the cable. If that looks good, clean the cable ends and by that I mean shiny bright. Each cable has two ends so make sure you clean both of them. Then reattach securely. Does the alarm system on this engine work. If you don't know, read the manual to learn how it SHOULD work. It may be this engine is overheating and shutting down. If the alarm system isn't working you would not know that would you! Bad fuel, crud in the tank, clogged filters, bad plugs, gummed up carbs are all possibilities. Do the cheap stuff first and then seek professional help if you haven't resolved the issue.

 

[Moburchette]

Re: Yamaha F40 Idle and Starting Issues

Thanks everyone, will keep you posted..heading out of town for a bit so this project will have to sit.

 

[Hoosmatroos]

Re: Yamaha F40 Idle and Starting Issues

I owned a F40 2003 myself and had a similar problem. I cleaned the carbs and after that synchronized them. Worked out fine. Carbs are complex for this model but i have a small how to for this.

Attached two documents for cleaning the carb and synchronizing them. If you don't know what you're doing, please take it to a Yamaha specialist.

View attachment 1274438965-F40_Carb_sync_and_balance.pdfView attachment 1274438985-F40Carb_service.pdf

 

[Moburchette]

Re: Yamaha F40 Idle and Starting Issues

Well I finally got back to working on my little skiff. The idle problem seems to have resolved with a new fuel / water separator element and housing, as well as replacing a leaky fuel line connection at cowling.
The starter problem persists however...I have gone over all connections and they are pristine. Although I did find a place where the main leads had been spliced about mid way between battery and motor, I removed the tape / shrink wrap and cranked the motor and found these splices where getting quite hot. I cleaned them up and re-connected with bright shiny butt connectors. The problem was about 70% gone but not totally. I did notice the copper in these leads was quite black, shined up nicely with sand paper but still pretty black. In the following days the problem is pretty much returned as it was before I repaired the splice.??? Wondering if i'm focusing on the wrong thing.
Thanks.
Matt

 

[connemaraisland]

Re: Yamaha F40 Idle and Starting Issues

Don't fool around "fixing" the cables, just replace them they are not expensive in the context of boat repairs. In order to meet increased air quality standards Yamaha made special carbs for the 25/40hp engines that have 4 jets in them compared to the normal 2 jet system. This means that the intermediate jets are extremely small and easily clogged and they are not accessible because they are under blind holes in the carb bodies. Even if you normally clean them you will not be able to clear them out without an ultrasonic cleaner (thats what most dealers use now). Unless you are used to doing this take the engine to a GOOD Yamaha dealer. After you fix the problem instal the large fine micron filter kit and ONLY use premium fuel that does not have alcohol in it. Cost a little more but solves gas issues

 

[Silvertip]

Re: Yamaha F40 Idle and Starting Issues

You cannot adequately splice a battery cable because of the number of strands involved. Replace them. As I mentioned -- hot or warm connections are the issue.

 

[Moburchette]

Re: Yamaha F40 Idle and Starting Issues

New battery cables...starter problem resolved. Thanks!
Now on to rough idle and occasional stall problem. New filters and plugs on the way.

 

[Moburchette]

Re: Yamaha F40 Idle and Starting Issues

New filters and plugs did not solve idle and stalling issue. Just had a key Yamaha dealer tear down carbs and cook for 8hrs in ultrasonic cleaner...idle problem is solved. Motor runs great EXCEPT between 2300-3100RPM. If I try to go wide open from idle it will just stall...only way to get it past 3100RPM is to gentle stutte and stumble through the range, once past 3100RPM it will go wide open nicely. They claim to have run it on their tank and mine in the water without problems? Could it be a fuel pump prob? Any ideas? Should I let them touch it again?
Thanks! Matt

 

[enrique383]

ok guys I went thru the same thing with the f40 one year of frustration and so many arrogant stupid money hurger marine mechanics or so called,,,,, turns out Yamaha knows there s a problem but wont admitted it,to me that's low to put me thru that, kind of unknown frustration and so many mechanics that don't know really whats going on I finally sold the boat at a hugh loss of money to a eagar young man who thru the internet found out that the jet in the middle of the card was not sutable for the f40 and was replaced with the jet of the f40 .go to you tube look up eric edic and look in the f40 project he will explained the problem in a video I call Yamaha they would not help knowing they screwed up the only way you pay them back is to tell everyone I will not buy Yamaha again they should have stood by their product just shameful I was in contact with a rep from Yamaha his sugestion was take to a dealer ,,,,I don't think so ,,,spend more and more useless hundreds its was the f25 jets that fixed the problem I loss 2500 dollars,15 mechanics just shamefull industry they ruined it for the honest ones who really try to make an honest living this is the truth no bull here my friends ,

 

[handle]

enrique383, I am interested in you findings regarding this issue of miss jetting on the f40. Please elaborate.