Honda 4 stroke idling problem

[BEARCATJER]

I have a 2001 18 ft Starcraft pontoon with a 2001 Honda 40HP 4stroke motor. I bought this rig used about 5 years ago and during that time we havent used the boat as often as we expected we would.As a result I have had to have it "tuned up" several times and every time i do it seems that it doesnt last very long before it starts running ragged and stalling in idle gear.Unfortunately i didnt buy this boat from the marina on the lake where i live so the nearest Honda dealer is 30 miles away.I dont have a trailer because it stays in the water at my dock do getting it to a dealer is an expensive proposition. Four months ago i had the motor extensively tuned up to the tune of $500 by a local crackerjack mechanic.Since that time the motor has purred like a kitten and runs very well. This past weekend we got on the boat to take a cruise...hadnt used it for about 5 weeks. Motor started fine but after warming it up and putting it in idle ..it stalled. It would easily start using the choke everytime but would run ragged for about 15-20 seconds and then stall when i put it in idle. I dont use gas with ethanol and I do use the stabilizer my boat dealer recommended. Anyway, i got the boat in gear and took it out on the
big lake and ran it for about an hour.It ran beautifully, but when i stopped it out on the lake and put it in idle,it stalled just like it had at the dock.

I cant figure out why it runs so well but wont idle! Im not very mechanical but I'm not totally stupid so I figured that maybe if i could adjust the idle screw it must have somewhere to a higher rpm setting it might do the job.As it is when i put it in idle it runs at about 800RPM for a few seconds and then stalls.

I dont have a service manual for this motor.I took the bonnet off of the motor but couldnt figure out where the idle screw might be. Then i got the bright idea of asking the experts on this forum for some help or suggestions to solve this aggravating problem.

Any helpful advice would really be appreciated. This motor doesnt have more than 100 hours on it in 10 years.My ace mechanic says it is in excellent condition...compresion etc.

Thanks for your help.

 

[MinUph]

Re: Honda 4 stroke idling problem

Sounds like its time for a carb cleaning. Turning up the idle will make it shift hard and will wear on your transmission. Just adding a water separator/filter to mine made a big difference. Mine was not idling well. While it didn't stall it would idle at 800 to 1200 and back and forth. I had it looked at and the mechanic adjusted it and I put a filter on, it now idles well. You gotta use these motor. Also try the additive route. It does help. Gas sitting in a tank absorbs water. More so on a boat and more so on a not full tank.

 

[isaksp00]

Re: Honda 4 stroke idling problem

Might be a clog in the low speed (idle) jet. Don't know the 40HP at all, but my Honda 8HP has had those symptoms, and every time I pulled the idle jet and cleaned it, it smoothed it out. On the 8, it is easy to unscrew that jet from the outside of the carb - you don't have to remove the whole carb.

Also, various gurus here have recommended unhooking the gas line and letting the engine run itself out of gas every time you stop for the day. I have done this so far this summer, and the clogged jet has not recurred. Evidently, the Hondas (maybe all brands?) have a very small idle jet hole, and it varnished easily if you leave gas in.

 

[BEARCATJER]

Re: Honda 4 stroke idling problem

I actually had all three carbs removed and rebuilt completely 4 months ago and also added a water separation filter,too. I guess i will go up to where my mechanic is and talk to him to see what he says since he did all the work on it. I live on a small lake where about 20 of my neighbors have pontoons and most of them dont use them as often as I do and dont have the trouble i have had with this Honda outboard.

Sounds like its time for a carb cleaning. Turning up the idle will make it shift hard and will wear on your transmission. Just adding a water separator/filter to mine made a big difference. Mine was not idling well. While it didn't stall it would idle at 800 to 1200 and back and forth. I had it looked at and the mechanic adjusted it and I put a filter on, it now idles well. You gotta use these motor. Also try the additive route. It does help. Gas sitting in a tank absorbs water. More so on a boat and more so on a not full tank.

 

[BEARCATJER]

Re: Honda 4 stroke idling problem

Thanks for your feedback. What do you mean by "additive"? Is that the gas stabilizer i already use or something different?

Sounds like its time for a carb cleaning. Turning up the idle will make it shift hard and will wear on your transmission. Just adding a water separator/filter to mine made a big difference. Mine was not idling well. While it didn't stall it would idle at 800 to 1200 and back and forth. I had it looked at and the mechanic adjusted it and I put a filter on, it now idles well. You gotta use these motor. Also try the additive route. It does help. Gas sitting in a tank absorbs water. More so on a boat and more so on a not full tank.

 

[BEARCATJER]

Re: Honda 4 stroke idling problem

is there any product you can buy which could be sprayed to clean out an idle jet, if i can find it on this motor? I have seen mechanics in the past use some product to spray into the carbs to "clean "them out without having to do a total carb rebuild. wondering if whatever that is might work on my problem?l

 

[bobhol]

Re: Honda 4 stroke idling problem

I just purchased a Honda 15 from a fellow .It was in storage for 7 years ...he hooked it up and ran it for me and I bought it and took it home ...it also had idling problems...I used Mercury Power Tuner which comes in a spray can and it worked wonders....I have used it before on my 3.0 litre I/O
...it now idles a tad lower than specs 950 vs. 1100 rpm ...just follow the directions on the can...regards,Bob

 

[toyota3l]

Re: Honda 4 stroke idling problem

I actually had all three carbs removed and rebuilt completely 4 months ago and also added a water separation filter,too. I guess i will go up to where my mechanic is and talk to him to see what he says since he did all the work on it. I live on a small lake where about 20 of my neighbors have pontoons and most of them dont use them as often as I do and dont have the trouble i have had with this Honda outboard.

I've found, after wasting much time and headscratching that you can't get multi carb. engines to run smooth unless you syncronise the carbs using vacuum gauges to each carb. remove the blanking screw on each induction tube and plumb the gauges in there, you can buy kits complete with adaptors from flea bay.

 

[frankhjr]

Re: Honda 4 stroke idling problem

I'm seeing multiple threads on Honda 4 strokes having idling problems. I've always run mine ('97 9.9hp purchased in '04) on 93 octane, with fuel stabilizer, never had an issue. Last fall I started having this idle problem and cannot figure it out! I'll be taking the carb apart again today. I have a factory service manual - it's OK, but it's light in my opinion on detail, no troubleshooting to speak of, and diagrams are so-so. Best diagrams for any of these motors is **********, I needed those to remove my lower unit. Under the "choke" section of Honda outboards - I saw this:

"1. I have an 8HP Honda that is probably about 3 to 4 yrs older. I had a similar problem that was caused by a clogged low speed jet. There was one difference that isn't easy to explain though - mine was hard to start and would not idle well, if at all, but this persisted even after it was warm. It tended to stall at idle whether in neutral or in gear, and I had to throttle up to even be able to shift, which obviously wasn't too good for the gears.

My carb has a low speed (idle) jet that is accessible from the carb without removing or disassembling it. It is on the top, on the side of the carb toward the outside of the engine (on mine, that would be the left side). It looks more or less like the top of a bolt, with a slotted head. It is easy to unscrew and remove (just don't drop in the drink!). Once out, it has a thin tube (hole) up the center and one or two, I can't recall, across its diameter. Clean it out with something soft, like a very thin plastic "string". I use a floss threader, if you know what that is - drugstores sell them. I have been told not to use any wire, even a thin copper strand, to avoid scratching the inside of that orifice. Also use some sort of solvent like spray carb cleaner. That may do the trick. When you screw it back in, there is no adjustment - it just goes in until seated, just don't tighten so much you kill the threads.

If not, I am no mechanic, though somewhat handy, and I disassembled my carb and cleaned it and put in new gaskets. It isn't that hard, though I'd invest the 30 bucks or so in a factory manual from Honda. This site may sell them, if not, you can find others online (or if you are lucky enough to be near a dealer, go there). "

 

[frankhjr]

Re: Honda 4 stroke idling problem

I'm seeing multiple threads on Honda 4 strokes having idling problems. I've always run mine ('97 9.9hp purchased in '04) on 93 octane, with fuel stabilizer, never had an issue. Last fall I started having this idle problem and cannot figure it out! I'll be taking the carb apart again today. I have a factory service manual - it's OK, but it's light in my opinion on detail, no troubleshooting to speak of, and diagrams are so-so. Best diagrams for any of these motors is " boats . net " , I needed those to remove my lower unit. Under the "choke" section of Honda outboards - I saw this:

"1. I have an 8HP Honda that is probably about 3 to 4 yrs older. I had a similar problem that was caused by a clogged low speed jet. There was one difference that isn't easy to explain though - mine was hard to start and would not idle well, if at all, but this persisted even after it was warm. It tended to stall at idle whether in neutral or in gear, and I had to throttle up to even be able to shift, which obviously wasn't too good for the gears.

My carb has a low speed (idle) jet that is accessible from the carb without removing or disassembling it. It is on the top, on the side of the carb toward the outside of the engine (on mine, that would be the left side). It looks more or less like the top of a bolt, with a slotted head. It is easy to unscrew and remove (just don't drop in the drink!). Once out, it has a thin tube (hole) up the center and one or two, I can't recall, across its diameter. Clean it out with something soft, like a very thin plastic "string". I use a floss threader, if you know what that is - drugstores sell them. I have been told not to use any wire, even a thin copper strand, to avoid scratching the inside of that orifice. Also use some sort of solvent like spray carb cleaner. That may do the trick. When you screw it back in, there is no adjustment - it just goes in until seated, just don't tighten so much you kill the threads.

If not, I am no mechanic, though somewhat handy, and I disassembled my carb and cleaned it and put in new gaskets. It isn't that hard, though I'd invest the 30 bucks or so in a factory manual from Honda. This site may sell them, if not, you can find others online (or if you are lucky enough to be near a dealer, go there). "

The web location I found excellent parts diagram can't be posted here. To find it, take the "i" off this website name, and switch from ".com" to ".net", there's no forum there, but the diagrams are very helpful. You get save pieces of them by doing a PC Screen Capture. Key strokes: hold down Alt then press PrtScr (print screen) then paste that image onto a document or slide (Ctrl & V).