Orifice sizes 55 HP, anyone know?

[CorB]

Re: Orifice sizes 55 HP, anyone know?

OBJ,<br /><br />She was just born last tuesday, so a lot of new impressions. A lot more to do then just feeding <br /><br />The tach is climbing to a lot more rpm's (additional 800 to 1200) then the actual rpm's (I can verify that because of the TinyTach). <br />No gooo around/under the flywheel.<br /><br />I did paint it completely. Just a couple of weeks ago also new decals on the cowling. The whole thing is near to new, apart from the idling problem.<br /><br />

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[CATransplant]

Re: Orifice sizes 55 HP, anyone know?

Pretty boat. Pretty water. A very nice place to be, I would think.

 

[rayjay]

Re: Orifice sizes 55 HP, anyone know?

Cor,<br /> The .031 goes in the top carb. When I had the carbs off mine I looked in the reed cages using a streamlight for illumination. All the petals have plenty of tension against the reed block. I have not yet run it with the airbox cover off. One thing that is weird [ to me anyway ], when the motor is running if I open the throttle butterflys by hand the motor does not rev up. It acts really lean. Advancing the timing lever with the carb link disconnected revs up the motor just fine. I removed the flywheel to check out the bits under there and everything looked fine. The timer base has a 2002 date sticker on it and the manu is some aftermarket supplier [ sorry, poor memory ].

 

[CorB]

Re: Orifice sizes 55 HP, anyone know?

@CATransplant,<br /><br />Thanks for your comment. It's a nice place to live, most of the Americans who come and visit here say every thing is very small over here. It's just what you are used to I guess.<br /><br />@Rayjay,<br /><br />Ok, we have the same size and position of idle jets, that's for sure. There is a good chance we both have the original orifices or we both have the wrong ones, and thats why the idling is worse <br />Yes you are right, it doesn't respond to the throttle butterflys apart from the ignition advance. Same thing with mine. It's not scientifically proved, but my impression is that it doesn't respond much at additional fuel delivery @ idle. The ignition (timing) must be the key factor for proper running I guess.<br /><br />Since we have the same problem on the same motor, I'm curious if it is intermittent on yours, or is it constantly? Did it ever run right? It might be that some former owner tried to solve it by mounting a new timer base?<br /><br />[EDIT] I've also seen that you have 150 PSI of compression, isn't that an awful lot? Could the compression be to high? Since mine is rebuild and the cylinder head is milled I could have got a very high compression also. Maybe it's just getting too much fuel/air in this scenario?<br /><br />Lots to think about I guess

 

[rayjay]

Re: Orifice sizes 55 HP, anyone know?

I think 150psi is probably just fine for a cyl this big. <br /><br />The timer base was probably replaced because the motor wouldn't run at all although it could have been replaced to try and fix the idling prob.<br /><br />I think something is not right with the engine not responding to advancing the carbs separate from the ign adv. although 4 degrees at idle is not very much ign lead. There is a sentence in the factory manual that says screw in the idle screw [ the one on the adv lever ] until the motor idles at 700 rpm in reverse. This is after the 'Link and sync ' and after setting the idle timing and the full advance timing.<br /><br />After I get the motor running at the proper temp I am going to do some more experimenting. Some combination of idle ign timing, idle jet orifice size and throttle plate idle bleed air hole size WILL make the motor idle happily.<br /><br />The first thing I have to remember to check is a a possible core plug leak . I think I will fire it up on the muffs and after it warms up a little I will dribble some water on the core plugs to see if it gets sucked into the motor. If the core plug is leaking it would definitely make the motor run lean at idle. The upper core plugs on my carbs have been whacked on in their past . The core plugs on the side are factory. If they are leaking I think I will just put some epoxy on the seams.

 

[CorB]

Re: Orifice sizes 55 HP, anyone know?

Rayjay,<br /><br />I've read a number of times that these motors will not idle well if they don't reach the right temperature. Good chance that the pressure relieve valve is the cause.

 

[rayjay]

Re: Orifice sizes 55 HP, anyone know?

Yeah, you gotta have the heat to make the fuel vaporize when it hits the cylinder. Without enough heat you just have a bunch of large individual fuel particles and the flame does not propagate well. At higher rpms the turbulence in the combustion chamber and the heat in the piston crown takes care of the fuel vaporization. Should have the parts in a couple of days but the weather is not too good. Typical Dutch weather. Only thing is I live in Georgia USA.

 

[RPJS]

Re: Orifice sizes 55 HP, anyone know?

Hi CorB<br />Something I picked up on while reading thru this post. You say that the motor smokes a lot when the idle is bad, is this smoke white, if so it could be that you are getting a slight water leak into one of your cylinders when the motor is hot. Have a look at the plugs just after you have the problem with the idle, if one or both of them is very clean that would be a sure sign of water.

 

[CorB]

Re: Orifice sizes 55 HP, anyone know?

@Rayjay,<br /><br />Typical Dutch weather doesn't seem to exist for a couple of years anymore. We are used to rain that's true, but also to consistent rise & fall of temperatures. Last friday we had 88 F and sunday around 59 F. We might have switched weather who knows <br /><br />@RPJS,<br />I thought about that also a couple of times. It actually doesn't smoke a lot (yeah, what is a lot) but it gets more when it runs bad.<br />But you are absolutely right, I will check the plugs after it stalls. Hopefully next saterday I have some time to do a lot of checks.

 

[rayjay]

Re: Orifice sizes 55 HP, anyone know?

I finally got to run my motor with the pressure valve installed in the head and it does a LOT better. Will just about idle in gear once warmed up. When warming up you can hear the motor start to idle better as the heat builds. It still will not respond to just opening the carbs manually without moving the adv lever and I think it should at least pick up a few revs and not act totally lean. I may drill out the idle orifices a couple of thou' each and see what happens. If it is better then all is good, if worse then all I have to do is buy some stock sized jets.

 

[CorB]

Re: Orifice sizes 55 HP, anyone know?

Rayjay,<br /><br />Great for you, seems like you've got the problem solved.<br />I didn't have time to do the checks yet..... just too busy, hope I have time saturday.<br /><br />Thanks for your update.

 

[CorB]

Re: Orifice sizes 55 HP, anyone know?

Update,<br /><br />This post has been inactive for a while, been too busy, sorry.<br />To refresh memories: The problem I'm facing is an idling problem with a '78 55 HP Johnson. It only occurs after running for a while.<br />Anyway I've been boating yesterday. After trouble free running at approx 2000 RPM for 1 hour (no wake zone), it came back. I tried the choke by pushing in the key and it stalled, so you might think it isn't a fuel problem. Then I removed the cowling and moved the choke butterflies manually just a bit by bit and then it picked up great @ idle and ran smoother. So I assume I have a lean running / air leak problem, which occurs after running a while or after running @ WOT.<br /><br />One other thing I found out that a little bit of fuel is running out of both of the carb throats when tilting the engine (air silencer removed). is just a little normal or not? It might explain the oil puddling I'm facing under the air silencer.<br /><br />Cor

 

[rayjay]

Re: Orifice sizes 55 HP, anyone know?

I have not had the chance to drill out my jets yet. Maybe this week. I still want to check for air leaks at the core plugs and at the manifold to carb gaskets. I doubt this is a problem because the motor runs good from just above idle to WOT. If it was air leaking it probably would have seized by now <br /><br />I think the gas leaking when the engine is tilted up can't be helped. This is normally collected in the airbox and sucked back into the engine via the hose at the bottom of the airbox.

 

[rayjay]

Re: Orifice sizes 55 HP, anyone know?

I finally drilled out my jets [ in a thunderstorm Thankfully I have a covered slip ]. I drilled out the top to .035" [ #65 drill bit ]. I drilled out the bottom to .033 [ #66 drill bit ]. The motor now runs a LOT better. Before it would not idle and it had a lean flatspot when hitting the throttle. Also, I had to choke it repeatedly when starting from cold. Now it takes just a couple of hits of choke and it will just about idle in any situation. In neutral it does pretty good. In gear it will start to go dead after about 45 seconds of minimum idle speed running. Remember, this is with a 1/16th inch hole drilled in each throttle plate. With the throttle advanced just a fraction it will run forever .<br /><br />One negative side effect is a richening of the high speed mixture. The boat has lost about 3mph of topspeed. I did a plug chop with the new jets and the plugs did not look rich at all. Actually, to someone like me that used to race aircooled 2strokes, the plugs looked scary lean but you can run a water cooled motor much leaner than an aircooled. I never run the motor at WOT for more than about 10 or 15 seconds at a time and then I throttle back to 25mph or less so I think I will not try and lean out the main jet to get back the lost top speed. I have a tach that I need to hook up to check RPM. <br /><br />I think I will open up the holes I added to the throttle plates to get the idle speed up a couple of hundred rpm and then I will be done.<br /><br />Cor, I think you should drill out your idle jets or buy the corresponding size from your dealer and see what you end up with. It is strange that the numbered drills skip .034". I would have liked to went with .034" top and .033" bottom. Might have been best to go with .033" top and bottom but my motor acted very lean at idle so I went with the .035" for the top.<br /><br />Let me know how yours works out. If OMC had have supplied carbs with adjustable idle mixture screws I doubt we would be messing with this stuff. We could have just adj'ed the screws until the motor idled good and if that adj'ment was one full turn richer than the stock spec, so what ?!?!?<br /><br />PS. With the motor running, it would be interesting to plug the hose that sucks out spilled fuel from the bottom of the airbox. This is basically a metered air leak.

 

[CorB]

Re: Orifice sizes 55 HP, anyone know?

Rayjay,<br /><br />Great news. I might buy new orifices and see what happens. I also have 2 brand new carbs from a '77 50 HP. I don't know if they are exchangeable, but they have adjustable idle mixture screws. I need to find out if i can use these carbs first.

 

[rayjay]

Re: Orifice sizes 55 HP, anyone know?

If they are physically the same externally I would check the jet sizes, install the 55hp jets if necessary and put them on. The 50 hp carbs may have a smaller bore and/or venturi.