Honda 9.9hp Fourstroke.

[Markrandles]

I have a 1991 Honda 9.9hp Fourstroke outboard which came with my boat. I started it up at home and it fired up and ticked over like a dream. When I try to rev it up it splutters and wants to die. It will rev out when the choke is out.
This engine has not had much use and stood unused for a good 18months. Would I be right in thinking that the problem might have something to do with the main carb jet? I am trying to save money by trying to do as much as I can myself.
£35 per hour is a bit much I feel!!!!!
Thanks.

 

[Talbot]

Buy some carb cleaner from Halfords, get the engine running , rev it up and spray the cleaner into the air intake (having removed the filter). Your problem is almost certainly sticky valve from evaporated petrol.

 

[Lakesailor]

I would say it is the residue from old fuel, but would go further than Talbot and suggest you dismantle the carb and remove the main jet which is on the side of the vertical tube casting in the float chamber area and also the main nozzle which is inside the vertical tube casting (you undo the brass plug screw at the bottom)
This carb doesn't have the slow jet and primary jet of the bigger engine carbs.
Then soak those two parts particularly in carb cleaning fluid, and the needle valve and pilot screw as well if they look manky.

DO NOT try to poke the holes in the jets out. Only blow through them (and I didn't say with your mouth, that's up to you)

I have a superfluous repair manual for Honda motors. If you're interested PM me..

 

[Talbot]

Whilst agreeing that this is the final solution, I always look for a potential easier way to try first - It may or may not work, if it doesnt then sure pull it all apart, but if it does, job done!

 

[andy_wilson]

I agree with Talbot. One caveat, have you got rid of the old fuel and bought fresh? Start with fresh fuel, then try Redex treatment or similar down the throat of the carb and in the fuel.

Start taking the carb to bits as a last resort. In fact if you are still struggling, I would take it off and fill it / soak it in solvent before stripping.

 

[andyball]

I must have fixed 100's of motorcycles/mopeds with the same problem after a long lay-up with fuel left in the carb' ( a business I ran).

Most every carb' cleaner is ( for obvious reasons ) kind(ish) to rubber seals & o-rings & doesn't shift the deposits left after fuel has sat & evaporated over a long period - esp inside the hole of a jet.

Iso-propanol does a pretty good job on this - but is not kind to many rubber seals.... don't use it unless the parts in question are removed from the carb' or it's stripped to remove rubber parts. A brief wipe with a cloth/isopropanol + drying afterwards is normally fine. Tape head cleaning fluid is usually the same stuff.

Even some "kind to rubber - safe to use" carb' cleaners & solvents will degrade seals if left to soak - a particular problem can be with the float chamber gasket 'growing' so it won't fit in the groove afterwards ( or will, but with extreme patience)

Your problem might not be the jets - but a sticking float due to the same 'gum' that can clog jets. This can cause fuel starvation and/or flooding & is most reliably cured by dismantling/cleaning.

sometimes you may clean enough from a jet to seemingly fix the problem, yet the jet hole is still smaller than normal due to gum. This may lead to problems only noticed under load, rather than in neutral.... & if you're really unlucky the resultant weak mixture can damage the motor if run at full load. ( rare - but I've seen it).

stubborn deposits inside jets 'can' be shifted safely using a soft, plastic coated wire or a closely sized brass or copper wire - but great care is needed. The brass wire will be same hardness as the jet, so minimises the possibility of damage.



I'm not dis-agreeing with other replies, but having seen it/done it many,many times - hope the info may be useful.

 

[Lakesailor]

Yep. Take it to bits. It's not rocket science.
-Don't do it on the stern. (at least in the cockpit, preferably on land)
-Do use precisely sized screwdrivers. Wrong size blades chew up jets slots.
-Do not over-tighten bits you are assembling.

As Andy says. The quick methods may not actually fully clean the jets and although it will run OK it could be weak.

Storing up trouble.