PDQ OWNERS FORUM

I have a 2004 Yamaha 8hp on my dinghy and I can't get it to idle without the choke on. I would be surprised if the motor has 30 hrs on it, and I know that it has never been run hot. The last few years it has been mostly stored in our shed. It's been idling worse and worse over the last couple years until this summer it constantly stalled (I replaced the plugs which made little difference) since I could keep it running between accelerating and the choke I figured that the carb was gummed up from storage.

I rebuilt the carb, completely disassembled and dipped, with new gaskets, blew out all jets, float setting is correct (which usually controls the low speed circuit). It does run much better but still won't idle. The motor starts right up either with the choke or at a fast idle (if warm). It runs OK at a fast idle, and accelerates fine, let it slow down to idle and it will get rough and eventually stall. I have a new diaphram for the fuel pump but it does not seem like a fuel delivery issue. Our model has a separate fuel pump from the carb.

I would think that the Yamaha 9hp are pretty close to the 8hp model and I would think that there is experience in this group. I haven't done a compression test, but with the low hours feel that this motor is barely broke in.

Will appreciate any ideas or suggestions...

Mike

Mike,

I and others have had similar problem in the past with the 9.9 . There are a couple VERY fine passages which may still be plugged. Suggest you concentrate on the carb. I would remove it again and find the idle jet. Remove it and blow out the passages from it to the carb throat with a pressurized can of Gumout carb cleaner. Alternatively, if you can borrow a carb from an identical engine you could verify if yours is indeed the problem!

Chet
Allezcat 36010

I run two 8's in Page 83. I think Chet is right, there's still some ethanol gunk in the carb. Its over-kill maybe, but recheck the idle circuit. I dipped my disasembled dinghy carb in a very expensive gallon can of solderseal (tm) GUNK carburetor part cleaner (with basket) for about thirty minutes (before reading the part about removing all plastic parts) and we are back to starting and idling on the first pull. I found about a tablespoon full of amber colored jelly in the bowl, tubes and crevices. I would like to have a private conversation with Mr. Ethanol. Let me see, I'll need a tennis ball, some really scratchy 1/4" manilla three strand, duct tape and, oh yes, the big soldering iron!

Thanks guys,

That makes sense, adjusting the air mixture screw really has no affect. I dipped it overnight, apparently that wasn't enough - I think the carb dip stuff they sell at Advanced Auto is not the same strength that used to be available.

- The manual says to replace the float and needle valve (and not to adjust it). I'm thinking since I'm pulling apart again next week to go ahead and order one - any thoughts? $50 for a $10 unit is highway robbery but it eliminates another possiblity in the low speed circuit.

Mike

Sandy,
This is the second time I've broken my cardinal rule - "never own an outboard heavier than you can easily toss overboard". I had a Honda 9.9 that ran rough, the prop was so sensitive on the Honda that a small nick kept our 10' rib from getting on plane, this Yamaha 8 won't idle and is so heavy that our Zodiac 9' fast roller sit's in the water doing a wheely. Before that with 2 and 3hp direct drives never a hiccup... The joy of recreational boating.

Thanks folks,

That took care of it - dipped it again for a few hours, then blew it out and went over all of the jets and passages with Gunk pressurized carb cleaner. The idle circuit works pretty well now. The only thing I'm noticing is that if you accelerate slowly it works fine, but on a quick acceleration from idle the engine falters a little, then catches. I may need to to up the idle a little.

Mike

Basically a little diaphragm pump mounted on the bottom of the bowl. Because the suction line is low, it often gets plugged.

Its purpose is to supply a little squirt of gas on quick acceleration. You had to take the linkage off to get the bowl off.

Mike,

Thinwater is right. The accelerator pump squirts gas into the carb throat whenever the thottle is advanced. I use this feature to "prime" the engine during cold start but it is designed specifically to avoid the hesitation you are getting. As I recall there is a small O-ring that goes between the carb top and bottom at the accelerator pump. Check this, the pump operation, and the passages to and from it. You are now a Yamaha carburettor technician!

Chet
Allezcat 36010

Chet & TW,

I don't think the 2004 model has a separate accelerator pump - I attached the parts breakdown. I know that there is nothing drivien by the linkage, there is a nylon plug in the top of the carb body - it may be vacuum driven (part #19). Part #6 is simply a rubber plug over the jet port in the carb body. I did make a post on the Boats.net - that's a really good resource.

Thanks for the support, I'm glad that it idles now...

Mike

After a second dunk in the carberator dip tank (a full wee this time) my motor idles better now than it did when it was new. I guess the ethanol is a real issue and I'll need to use a fuel additive from now on. I'm also running the carb dry whenever it's going sit for awhile (a week or more).

Any recommendations for additives?

Mike

Stabil blue for ethanol.

I have two big fuel/water filters between the tank and the engines, but I still leave the same gas sitting too long in the tank. I'm using Startron's new Ethanol formulation; there's a big legal brewhaha going on between Stabil and Startron, but I'm not sure it isn't an advertising gimmick.

It could be advertising... I don't know which is better... just always used Stabil red until this stupid ethanol thing happened then I switched to Stabil blue. If any one has more experience, it would be nice to hear.

Thanks,

Next season I'll try the stabil blue - I put the motor up for the winter (I ran the carb dry first) and will probably run the rest of this seasons fuel in the lawn mower (it's not sensitive ).

mike

FYI: If anyone is looking for a dinghy combo - 2004 260 Zodiac Fast Roller (high pressure soft floor with keel) with a 2004 Yamaha 8hp motor bought new from Washington Marina. Has Zodiac fold down trim tabs, oar lock upgrades, and Dolfin for outboard. When we added the electric outboard to our Stbd hull we lost a foot of space between so this dinghy is a little wide for the space. Both have very low hours and are in very good condition (maybe 20 hrs of actual use) and have been stored inside most of the time (Dinghy Outboard combo 150lbs). Will only consider reasonable offers.