Honda 40 hp idle out under load

[yamp]

looking for ideas on my honda 40 hp long tiller 04 model, the problem is nagging me,the motor will idle smoothly out of gear but putting it in gear it idles ok but has a bit of a cough/slight miss about it,i can put if out of gear give it a squirt with the throttle and them put in back in gear and start trolling at lowest idle and it will idle nicely with no miss and them about 30 secs later start idling abit rough again,So far I have pulled the carbs apart cleaned with carb cleaner(they didnt look bad at all)replaced plugs, checked valve clearance,replaced t stat ,checked auto choke resistance,checked carb sync with carb sync tool to meet factory manual specs,adjusted idle mix screws above and below the factory setting about 1 either way which did not seem to effect the rough idle problem,thinking of pulling the carbs off again for ultrasonic clean?could be a waste of time I have also noticed some times trolling on idle speed when i disengage and engage the motor in gear the motor will idle perfecty in gear I wonders if the cable ajustments could have any effect on idle,I would like to thank spainard king (Gary )he has been great giving me a hand over the phone I thought I better give the poor Bloke a rest from me pestering him for a while any help greatly appeciated cheers Yamp

[Noelm]

you have tried the very simple things, like plugs and so on? it reads like you have tried all the hard stuff first.

[finga]

What's it idle at?
Is the idle rpm under spec?

It would not take much for a carbi or two to perform under their optimum. I haven't much faith in carbi cleaner doing a good cleaning job. Ultrasonic may give marginally better results but there's no result as good as a complete dis-assemble, clean and then re-assemble..

[yamp]

I have changed the plugs and checked the idle revs workshop manual 950-1150 with small dig tacho,I pulled the carbs apart and cleaned with aerosol carb cleaner, I didnt replace the little o ring gaskets that seat the jet tube into the carby thougth them seemed to be fine?I replaced the other gaskets needed to pull the carb set apart though,I have tried the idle setting at the high end and the low end of the scale but the rough idle seems to still be there not sure if there is a easy way to check for air leaks,I remember reading in a forum something about spraying something around the carb bodies that will increase rpms if there is a leak will have to try to find it again any other ideas cheers yamp

[finga]

Spraying any light oil such as Lanox around the carbs may find an air leak. I say may as there as places you can't spray.

Did you blow through all the jets and passages in the carbs to make sure there's no crud?
Never assume spraying with carb cleaner will clean them.

[yamp]

when I had the carbs apart i did not have compressed air so i was using the carb cleaner aerosol like compressed air to blow through the jets and tubes they looked clear but the holes are pretty tiny, finga thanks for the tip with the light oil might give it a go next time out on the water Yamp

[Spaniard_King]

I have changed the plugs and checked the idle revs workshop manual 950-1150 with small dig tacho,I pulled the carbs apart and cleaned with aerosol carb cleaner, I didnt replace the little o ring gaskets that seat the jet tube into the carby thougth them seemed to be fine? I replaced the other gaskets needed to pull the carb set apart though,I have tried the idle setting at the high end and the low end of the scale but the rough idle seems to still be there not sure if there is a easy way to check for air leaks,I remember reading in a forum something about spraying something around the carb bodies that will increase rpms if there is a leak will have to try to find it again any other ideas cheers yamp

This little part always seems to be overlooked. I would change all of the o-rings and reassemble using engine oil to lubricate the 0-rings. I still think you have a lean mixture. The other thing I would do is adjust the tappets and do a compression check to see your not waisting your time with the carbies.

[OPTI]

your wasting your time trying cleaning carbies without compressed air.as gary suggested do a comp test or even better a cyclinder leak down test.and go from there.

[yamp]

Been away for the weekend thanks for feedback Gary and Opti,I have checked the valve clearances were in workshop specs but a have not done a compression test ever or cylinder leak down test,i think I could do the compression test but not sure what a cylinder leak down test is.Gary I had a play with the idle mix screws again adjusted with the motor running at idle in drum of water instead of muffs,set to max idle speed starting at bottom carb working up adjusting idle speed back to 950 after adjusting idle mix screw, most of the carb ended set at around 4 to 4 1/2 out.I also found the idle speed changed when I put the motor in gear running in the drum,so i adjusted the idle speed to 950 in gear which runs about 1050 to 1100 out of gear is this normal?anyway I thinking about pulling the carbs off again and changing the o rings and cleaning carbs again good practice I suppose thanks Yamp

[Lucky 1]

I hope this doesn't come across too way out, but have you removed the prop, and looked for crap around the prop shaft ?

[yamp]

i haven't had the prop off in a while i will check it tommorrow cheers Yamp

[yamp]

Though I would raise this one from the dead,as I still haven't sorted this annoying idle issue,Since last post I have had the carbys ultrasonic cleaned and replace all the gaskets and o rings,i have taken the prop off to check for obstructions,all clear.I have had a look on youtube and their is a couple of clips with 50 and 40 hondas with near identical rough idle under load as mine,unfortunately no comments to fix idle.I have the exploded view of the carbs and was wondering if someone could explain the idle circuit?does it come though the emulsion tube up of the carby? or does it enter the throat of the carb somewhere else? I couldn't work out the set up from the picture.I notice that when knocking the motor in and out of gear sometimes if you ease in back into gear it will idle smooth as out of gear idle?like it should be.thanks for any advice in advance Yamp

[rooboy98]

G'day Yamp,

I have a 2000 model Honda 40 tiller and it used to do what sounds like the very same thing. Idle fine in neutral but when you put it into gear start to run rough at idle. It used to annoy me as I do alot of slow trolling for barra. Mine always started fine, rev'ed fine and reached max re'vs , just rough at idle sometimes when in gear. If I gave it a quick blast of the throttle, that seemed to cure it for a bit.

I had the problem sorted by a guy in Townsville during the motor's annual service. I know you said you have checked the carbies etc already but this guy simply carried out carbie adjustments (including a tune/carb sync) and got it purring nicely again. Just looking at the receipt now, he also did the plugs, water seperator element, fuel filter on engine, IGN timing plus the other usual stuff for an annual service. My motor has done about 1,300 hours.

Good luck with it.

Cheers,
Roo.

[yamp]

Thanks Roo
Your situation sounds exactly the same as mine slow trolling for barra annoying idle.I would take to get tuned by the local bloke but have no real confidence he would fix it last time it was( none of the carby jobs idle smooth only the EFI models)?when i got it back he had just increased the idle revs so you couldn't slow troll and it was still fairly rough. my motor has only about 150 hours on it cheers Yamp

[Spaniard_King]

Have the carbs been synced with vaccum gauges???

[yamp]

I did sync them with vacuum gauges that I bought online the all where within the tolerances if I took a video on my phone I should see if I can post it up some way