Honda 4 Stroke 8hp (Low Power)

[Smiley Starfish]

Floated the boat for the first fishing outing of the year this week. Motor runs solid at idle, but I've only got a 1/4 throttle. The first 1/4 of throttle opening works like it should, but after that there is no change in either speed of the boat, or RPM.<br /><br />I'm thinking that I've got a carb problem and as such intend to tear it off and give it a solid cleaning/rebuild. Is there anything in particular I should be looking for?<br /><br />Does anyone know of an online source for a schematic of these carbs?<br /><br />Later

 

[hondon]

Re: Honda 4 Stroke 8hp (Low Power)

Carb work may well be in your future,but generally, carb problems on these engines throw symptoms at you across the board.Your problem sounds much more like a fuel delivery issue.Also ,when was the last time those valves were adjusted?With these engines comes some maintenance that frequently gets ignored, and can cause exactly the problems you are having.

 

[Smiley Starfish]

Re: Honda 4 Stroke 8hp (Low Power)

Would the valves just go out of spec between the time I ran it last in October, and last week? <br /><br />I put the carb back together this morning and it's still not right. <br /><br />Course I got cabin fever in a bad way, and the weather is perfect and my motor isn't right...<br /><br />Here's Johnny...<br /><br />AARRRRRRRRRRRRRG<br /><br />Smiley

 

[Hooty]

Re: Honda 4 Stroke 8hp (Low Power)

I'm not familiar with that particular engine but some basic stuff to look at is the butterfly in the carb, is it opening all the way, what happens if you squeeze the priming blub when throttle is opened all the way. I think like hondon, you've got a fuel delivery problem.<br /><br />c/6<br /><br />Hooty

 

[45_red]

Re: Honda 4 Stroke 8hp (Low Power)

Do you have full travel of the throttle cable? The throttle hanle works by friction (at least on the older models).

 

[Smiley Starfish]

Re: Honda 4 Stroke 8hp (Low Power)

The throttle opens all the way, and the first thing I tried was to pump the priming bulb. That didn't do any thing. <br /><br />The really weird thing is that while it sits at WOT it sounds like it's bogging down, reducing the throttle back down towards the 1/3 it almost sounds like it's leaning out (ie rpms jump up just so slightly) All indications would point toward some sort of an airflow obstruction thats causing a fuel rich condition, but that isn't happening...<br /><br />Thanks for all the suggestions<br />Smiley

 

[Mufasa]

Re: Honda 4 Stroke 8hp (Low Power)

Smiley,<br /><br /> That motor has very small passageways in the carb. I think you overlooked something. Also make sure it is not over full on oil. If you transport it on its side you need to allow about 10 min of being vertical before starting. The valves should be checked and adjusted annualy along with the oil changed.

 

[Mufasa]

Re: Honda 4 Stroke 8hp (Low Power)

Smiley,<br /><br /> That motor has very small passageways in the carb. I think you overlooked something. Also make sure it is not over full on oil. If you transport it on its side you need to allow about 10 min of being vertical before starting. The valves should be checked and adjusted annualy along with the oil changed.

 

[Smiley Starfish]

Re: Honda 4 Stroke 8hp (Low Power)

Since I did the oil change myself I can guarantee that it is full to spec, as far as adjusting the valves are concerned, I just don't see them going out of spec since I had last used it in late october. <br /><br />As far as small passages through the carb would you care to elaborate? I can't think of any that are small enough to be impossible to visually inspect. I broke down the entire carb and soaked all the bits in solvent overnight, blew it all dry with compressed air and reassembled. <br /><br />Is there a good way to check spark advance?<br /><br />Smiley

 

[hondon]

Re: Honda 4 Stroke 8hp (Low Power)

How do we run with the motor cover off?

 

[Skull]

Re: Honda 4 Stroke 8hp (Low Power)

check the compresion in each cylinder by putting your thumb over the plug hole while u turn the motor over if one is low in compresion it could be the valves or somthing else in that cylinder

 

[DJ]

Re: Honda 4 Stroke 8hp (Low Power)

Smiley,<br /><br />I'm pretty sure you have a single carb. for both cylinders.<br /><br />I would suspect you're not "hitting" on both cylinders. That WOULD NOT be a carb. issue. <br /><br />Look at spark.

 

[Yepblaze]

Re: Honda 4 Stroke 8hp (Low Power)

On many Japanese motors you will find a tube above the main jet that protrudes up into the venturi of the carb. It.s called an emulsion tube and has tiny holes all around it allowing the fuel entering the intake stream to emulsify with air. Pull the main jet again and see if this tube can be rmoved by lightly pressing downward from inside the throat of the carb. Take a small wire from a wire brush and carefully probe the jet and tube till all passageways are clear when held up to the light and viewed.<br /><br />This may help. web page

 

[45_red]

Re: Honda 4 Stroke 8hp (Low Power)

I believe your motor has a manual choke, you can determine if it's running lean or rich by giving it a bit of choke, if it dies immedeatly it's rich, if it picks up rpm it's lean. When you pump the bulb does it firm up?