Orifice sizes 55 HP, anyone know?

CorB · May 23, 2005

Hi, Continuing idle problems with 55EL78S, did check a lot of things following the various advices I've been reading here, but no solution yet. I want to check if the idle orifices (fixed orifices) are the ones that originally were in there, but I need a cross reference from part no. to orifice size. I have different orifices in the upper & lower carb. Upper: According to parts catalog: no. 318823, found in the carb: size 31 Lower: According to parts catalog: no. 317473, found in the carb: size 30 Anyone knows if these part numbers and sizes match? Thanks, Cor

OBJ · May 23, 2005

Re: Orifice sizes 55 HP, anyone know?

Yes Cor, the PN match. Most likely the jets are different to improve idle characteristics. You can do this with most carburated engines if you have the right test equippent to measure idle air flow. Is your engine idling OK or were we just curious?

CorB · May 23, 2005

Re: Orifice sizes 55 HP, anyone know?

OBJ, Thanks a lot for your response. No the idling isn't ok. When I start it it idles kind of ok between 1050 to 1250 rpm (on TinyTach). When I put it in reverse gear (tied to the dock) it idles around 750 RPM, but is having a very hard time to keep running. Out of gear it will return to approx 1050 - 1150 rpm If I just start it cold and run it until operating temperature it will idle all day. But when I'm leaving the dock, and run it at different RPM's including WOT and head back at "trolling speed" it won't keep running at idle at the end (while manoevring etc..) it doesn't even anymore when not in gear. I knew the part number of the jets match my outboard, but what I meant is if the part numbers match the actual orifice sizes. In other words, maybe the jets in my carbs aren't the original ones. The powerhead is rebuilt with Wiseco pistons, runs strong (5800 rpm with 17p prop) and has no hickups above approx. 1300 RPM. I've (thoroughly) cleaned & rebuilt the carbs numerous times, I've exchanged the powerpack with a new Sierra powerpack, renewed the spark plug wires and spark plugs (QL77JC4 gapped at 0,040"). Idle timing is around 4 degrees (lower runs a bit worse), performed Link & Sync dozens of times (but I have the feeling, Link & Sync adjustment only affects the way it picks up from idle until higher RPM's, assuming that the throttle butterflies should be closed @ idle) I've tested the rectifier per Joe Reeves procedure and measured the primary & secondary circuits of both coils. I've tested the sensor & charge coil (if I remember right) for resistance and they measured ok, but I have no equipment (DVA peak reading meter or so) to measure the output from the timer base. The spark of both coils jump a 7/16" gap, but it is a small, kind of continue blue-white lightning-like spark. If I pull one spark wire it stops rightaway, it will not run & start on one cylinder, cyl 1 and cyl 2 don't make a difference. I've decarbed it regularly. It has a new fuel pump, the tank vent is open, if I prime the bulb it will make no difference and if I push the choke a little it will not pickup better. It doesnt make a difference if the yellow/black kill wire is unhooked. I didn't do a compression check (yet) because I trusted it after the rebuild. (but it starts with the touch of the key) It has a fairly new t-stat and I have a temp gauge which reads approx. 176 F at trolling speed and approx 90 F at WOT. It never ran ok @ idle since the rebuild, but after searching for the cause I found a lot of things that pointed in the direction of a cause: forgotten crankcase/crank seal, airleak between carb and intake manifold, spark plug wire that came loose from coil, inaccurate tachometer and play on ignition timing mechanism (plastic bushings) There are a couple of things that are not 100% ok, but I don't know how much harm it could do: - The crankshaft dimensions/diameter are just within spec, but there is a little feelable play at the flywheel, a couple of guys over here said earlier it would be ok. - When it's running worse the motor starts to shake and there is is a kind of "clunking" sound, I think caused by the crankshaft play @ low rpm's - After the rebore, I've chamfered the ports just a little with a dremel and small ball shaped tool. - There is always a green puddle of oil under the air silencer, I think it's coming out of the crankcase ventilation hose when the motor is tilted up. - When it's idling worse the onboard Faria tachometer (connected to the grey wire) is acting a bit wacky und jumps and there's also more smoke out of the exhaust. There is a difference between the faria tach and the tinytach, sometimes a difference of 1000 RPM and sometimes 200 RPM and very rare are they equal. No matter which pole setting I use, they are most of the time not consistent with each other (but it could be the faria's fault). - The battery charging voltage isn't very high, it 's around 12,6 to 13 volts @ 2500 RPM, but it never left me with a dead battery in the last three years. I don't know If I'm facing an Ignition, fuel or another problem here, but I do know it's intermittant. Sometimes it runs like a dream, but that's not very often.

rayjay · May 23, 2005

Re: Orifice sizes 55 HP, anyone know?

Did you replace all 3 main brgs and the upper and lower seals ? I have a 77 55hp that wants to stall at idle also. 150 psi of compression on both. It also has a little horizontal play at the flywheel but no vertical play. On 2stoke motorcycles you can do a crankcase pressure test. You put a rubber cork in the carb spigot, and attach an adaptor to the ex port and then pump in 3psi of pressure which the motor should hold and then 3psi of vacuum which the motor should hold. hard to replicate this test on a boat motor due to the layout of the ex. Any play in the main brgs is going to make it tough for the crank seals to do their job. I looked into the parts costs to freshed up my main brgs. Over $600 worth of parts and this is using the old pistons and rings. Upper brg $71, gasket set w/out head gasket $101, etc. 1977 motor is not worth spending the money on. I am increasing the idle speed ign adv and experimenting with an idle bleed hole in the throttle butterfly. I saw some OMC carbs on ebay that appear to have come from the factory with the holes. Good luck

CorB · May 23, 2005

Re: Orifice sizes 55 HP, anyone know?

Rayjay, Thanks for your response. Yes I replaced all bearings and seals. The crank seals (between the cylinders) are no rubber seals and not replaceable. They seal because they get "filled" with fuel/oil mixture, thus creating a seal. I can understand the play makes sealing harder, but I'm not sure how much effect it will have. I tried to experiment with the ignition advance, but the problem is that it doesn't always keep the rpm's high enough and at different times it revs at 2500 RPM @ idle. I know it's an oldie, but I got it nearly for free and used it as a "learning project". I assumed that I could get a "near to new motor" after spending time, money and replace the moving parts. It's in great shape now, also visually, except from the poor idling unfortunately.

rayjay · May 23, 2005

Re: Orifice sizes 55 HP, anyone know?

I really like my motor if I could just get it to idle consistently. I like the simplicity of twin cyl motors [ I used to race a BOTT { Battle Of The Twins } Suzuki GS500 motorcycle ]. Mine pushes my 14' bass boat at 30 mph indicated on the speedo. I normally run it at 25 mph to lessen the strain on the motor. I thought about trying Boyesen reeds but am tired of throwing money at this motor. I bought a 1996 Nissan / Tohatsu 40hp twin to eventually replace the 55hp evinrude. The power difference will probably be negligible. The older motors were rated at the powerhead and the newer at the prop. Plus the Nissan is at least 40 lbs lighter. I'm still going to keep messing with the Evinrude. I have not had the chance to lake test the holes I put in the throttle plates. I started out with 1/16" { 1.6 mm I think }. I don't like the Evinrude carbs. It is stupid to not have adjustable idle mixture. The older ones and the newer ones do have mixture screws. I got spoiled working with Mikuni and Keihin slide/needle motorcycle carbs. I do think that these engines being twin cyl does make them more susceptible to idle problems. 2 big cylinders going thud thud instead of 3 or 4 smaller ones.

CorB · May 23, 2005

Re: Orifice sizes 55 HP, anyone know?

I don't even care that much about idling consistently, it just needs to stay running, that 'll be enough for me. Apart from the idling it runs terrific, I can reach 37 MPH top with a 14 feet Glastron, but I want to lower the pitch a bit to get more holeshot for skiing. What's the purpose of the holes in the butterfly, it seems to me that you get more air and don't get more fuel, or am I looking at it the wrong way? Assumed that the problems are caused by leaking seals, could an adjustment of the idle mixture help in this scenario? End If so, then slightly bigger jets could also help maybe?

rayjay · May 23, 2005

Re: Orifice sizes 55 HP, anyone know?

The holes in the throttle plates are to allow more air in. It would be like screwing in the idle speed screw on a Weber automotive carb but these evinrude carbs don't have any true idle speed adjustment. At the top of the throttle plate there is a cutaway that supplies the idle airflow. The idle fuel outlets are in the same area. If for some reason your motor will not idle with the original settings then you have to improvise. I really have no idea how the idle circuit works on these carbs. I guess that the fuel is fed from the bowl via the small dia tube and goes through the jet into the chamber just above the idle and transition holes in the top of the throttle bore. I don't know if, where or how any air is mixed with this fuel to create an emulsion before it enters the carb bore. If you go down on the low speed jet I bet you would need to richen the high speed jet to compensate. Most carbs draw some fuel through the low speed orifices even at wot. I also think the reed valve is too large for the displacement which would decrease the intake velocity and lead to poor low speed running. I have a 250cc Suzuki MX motor that uses an 8 petal reed similar in size to the Evinrude 55. The Suzuki makes 35+hp at 7900 rpm versus the Evinrude's 26.5 at 5500. The Evinrude could probably get by with only 6 petals and possibly only 4. This would have allowed the intake tract to be downsized increasing intake velocity and increasing crankcase compression. Both are good for smooth running.

CorB · May 25, 2005

Re: Orifice sizes 55 HP, anyone know?

Rayjay, I think you are right on track, about how it works. I'm curious how your experiment with the holes in the throttle plates work out. I didn't have time so far to investigate further, I got a baby just two days ago.

CATransplant · May 26, 2005

Re: Orifice sizes 55 HP, anyone know?

"My motor is acting really lean at idle." I'm sure it is. You drilled holes in the throttle butterfly. That will lean out the mixture at idle, and could cause idle RPM hunting. Nothing wrong with the design of the carbs on that motor. You're trying to fix something by altering the design of the carburetor. That's a sure-fire way to cause problems, not to fix them. The design of that motor and carburetor are well-proven. The fixed idle orifice is that way because it works. Drilling holes in the butterfly ain't going to improve things, I'm afraid...only make them worse.

rayjay · May 26, 2005

Re: Orifice sizes 55 HP, anyone know?

Congrats on the new child. Boy or girl ? I ran the motor earlier in the week with no improvement. I really need to run it hard for a few miles but the wind had the lake really stirred up, too rough to get much over 10 mph. The last time out my wife ran it at very low speed following me in the houseboat so the engine is a bit loaded up. My motor is acting really lean at idle. I am beginning to think that some prior owner has taken out the thermostat. I guess I will pull the head cover and check it out. Outboards run cold anyway which plays havoc with fuel atomization.

rayjay · May 26, 2005

Re: Orifice sizes 55 HP, anyone know?

So what is the solution to Cor's problem ? If the carbs are so good why did OMC go back to a carb with adjustable idle mixture screws ? Why did they go from chokes to primers ? Why do some later OMC motors come from the factory with holes in the butterflies ? Why does it seem that OMC was regularly issueing service bulletins requiring the tech to drill out the idle orifices in the carb body?

CATransplant · May 26, 2005

Re: Orifice sizes 55 HP, anyone know?

I don't know the answer to his problem, but here's the deal. At some point, that 55 hp motor idled OK, I'm sure, complete with the no-holes butterfly. Now it does not. I don't know about service bulletins for that model, but it's a long time since 1978, and lots of fuel has run through that engine, so apparently the design worked OK. Cor want to redesign the engine, change the reed design and ventilate the throttle butterflies. That's fine, but at some point he's going to lose the design that works. My point is this: OMC designed the engine to run properly. For most of its life, it probably did. Now it doesn't. In my humble opinion, the goal should be to restore the engine to proper operation as designed. Anything else is tinkering with someone else's design. That's fine, but should be done by someone who can do that successfully and who doesn't need to ask repair questions on a forum like this one. Was there a service bulletin for THIS engine that recommended drilling out those orifices? I don't know. If there were, that would result in richening the mixture, not making it more lean. Drilling holes in the butterflies is going to make it more lean. If you read Cor's long description, the motor idles fine until it is fully warmed up and has been run at WOT for awhile. Then it idles poorly. That's the starting point, not the throttle butterflies. If it idles OK before being used hard, then idles poorly, the problem is not a design problem...it's something else. Now that the holes are drilled, it will be even harder to diagnose and fix, you see.

CorB · May 27, 2005

Re: Orifice sizes 55 HP, anyone know?

@Rayjay, It's a Girl named Robin, thanks for asking. @CATransplant, I have an older Glastron also, a 1966 Skiflite. Nice boats aint they? Just to be sure: I didn't change anything so far on the design and I didn't drill the holes in the butterflies. I was just curious how it turned out with Rayjay. The motor idled fine before I rebuilt it, so I guess something went bad after that. It would help a lot to have a clue if it is an ignition or fuel/air mixture problem. I thought I had found the cause a couple of weeks ago, because I didn't measure resistance anymore on the secondary circuit of coil no. 2 Turned out to be a loosened spark plug wire. I reattached it and after that I let in run in the water for 45 minutes. It idled low but never missed a beat. I revved it a couple of times to 3000 RPM and it returned nicely to idle rpm's. Is there anyone who can describe the behaviour of a motor with leaking labyrinth seals between the two cylinders in the crankcase? There could be an intermittent leaking situation because of the play on the flywheel.

CATransplant · May 27, 2005

Re: Orifice sizes 55 HP, anyone know?

Cor, After I wrote that, I realized that it was Rayjay who had drilled his butterflies. Sorry for the confusion. I do like my Glastron, even though it's the low end of the model line. It seems sturdy, despite its age and performs very well with my old 35hp. My first lake test, with a friend alongside with a GPS, I clocked 23 mph. After I've run the boat a little more, I repeated it and came up with 25 mph. I can't imagine that I could do any better with the ancient 35hp motor. Best of all, I can cruise in this trihull at about 10 mph with the boat riding nice and flat in the water and almost no wake. I fish small lakes, and there's usually no need for WOT runs on them. The slow cruise mode also doesn't bother the other fishermen on the lake. Good boat. From your description, I'd think fuel before ignition for your poor idle. I wouldn't worry too much about the labyrinth seals, to tell you the truth. Since the low-speed idle mixture isn't adjustable, it could still be some minor clogging in the low speed circuits on one or both carbs. Pain in the butt...but another round of carb cleaning might be in order, complete with a good blowout of the passages with compressed air. Since the symptoms show up mainly when the engine has been run quite a bit, it could be something else, too, I guess. You might take another look at your carburetor to manifold gaskets, and check tightness of the bolts that hold the carbs on the engine. Also, check for any other places where you might have an air leak, like the line that goes to your fuel pump from the crankcase. Think about things that warm up after the engine has run awhile and that might cause air to go where it's not wanted. Beyone that, I don't have any more useful advice, I'm afraid. Just look for the little things to find your problem.

CorB · May 27, 2005

Re: Orifice sizes 55 HP, anyone know?

CATransplant, Thanks, The carbs have been apart three times so far, and they are cleaner than an operating room in the hospital. I'll do a check on the area's you suggested.

rayjay · May 27, 2005

Re: Orifice sizes 55 HP, anyone know?

I pulled off my head cover plate and guess what ??? Good working thermostat but no pressure relief valve so I got all the bits on order. It will be interesting to see if a bit of engine heat helps my idle problems. The thermostat starts opening at app 130 degrees and is fully open by app 140. I also tested the overheat switch and horn. Cor, I know what you are saying about clean carbs ! Mine are spotless. If getting the engine temp up to snuff doesn't do it I do have a set of Jet Drills that go up to .039. The stock idle jets are .031 and .030 I have several 1977 Evinrude parts catalogs and the 55hp is one of the few engines that year that did NOT have air bleed holes in the throttle plates. I am also going to make sure that the core plug above the idle fuel chamber are not leaking air into the chamber.

OBJ · May 27, 2005

Re: Orifice sizes 55 HP, anyone know?

Hey guys.....let's go back to CorB's post. We are having idle problems, the engine has been just rebuilt. One thing that I look at is the symptoms and what we are seeing. Cor said he sees' a puddle of oil under the air silencer. All though this could be a little left over from the carbs, it could also be a sign of a bad reed. A bad reed will blow back through the carb and leave the residue at the bottom of the air silencer and cause a nasty idle problem. Ignition problem? Maybe. I would take a timing light and when the problem arises, put the light on both spark plug leads and see if the spark is consistant. Charging problem....associated with the idle problem....not likely. The charging system only cares about charging the battery...not keeping the engine running...may be a separate problem. If the sync and link are in order, the throttle plates are in sync, the carbs are clean, the fuel hoses are tight, and you have a consistant spark to each cylinder, I would look at an internal leak or bad reed. I have to agree with CA....drilling out the holes in a butterfly plate could probably make a problem worse. And...the orifice changes came about with rope and electric start models. Probably a little richer mixture for rope starts. Mid model changes are not un-common. Found a couple. Even with the later models, changing an orifice would make a difference....so we can't really say that all the changes imply inadequecy with the OMC engineeers.....not really wanting to cause an uproar...just a point of view.

CorB · May 28, 2005

Re: Orifice sizes 55 HP, anyone know?

@Rayjay, Ok, one thing we know now is that we have the same size of idle jets. Which one was in the upper and which was in the lower carb? I might have mixed them during the numerous rebuilts of the carbs. Core plug is also a good idea, going to check these too. @ OBJ, Good analysis. There is no visible blowback from the reeds while running. I have tilted the engine once without the air silencer on it and found out the oil then ran out of the hose which is connected between the crankcase & the air silencer. What are you saying, would an oil puddle in the bottom of the air silencer cause an idle problem? Or do you mean the oil puddle is a reason to suspect a different problem which leads to an idle problem? How about running it without this hose connected, thus preventing oil puddling in the air silencer? About the charging problem: I didn't see a connection also, but the funny thing is that the tachometer starts acting funny when it's running worse, and it also starts to smoke more by then. I did check with a timing light, but only on cylinder 1, so cylinder 2 could be suspect to problems. I would like you to know that I'm very thankful that you are helping me out here, but I'm very busy with the baby right now, so I don't know if I'm able to always respond & do the motor checks in a timely fashion, but I do really want to solve this problem.

OBJ · May 28, 2005

Re: Orifice sizes 55 HP, anyone know?

Gotta' take care of the baby Cor...how old? Boy or girl? The engine...I was saying that the puddle may be and indication of a problem. Sometimes you may not see the blow back but can feel it...at idle especially. I use a piece of tissue...a strip. I hold it in fromt of the carb. If it sucks in, reeds ok....if it blows out and in, problem with reeds. I'd recheck both cylinders with the timing light when the problem is occuring. It's possible the problem is heat related....meaning that one of the ignition components is being effected from the heat of the engine causing the rough idle. A good test is the ole' hair dryer test. Grab the wifes hair dryer and start the engine. While it's cold, play the hair dryer on the individual ignition components. If the engine starts running rough from a miss, you could have found the problem. The erratic tach may be pointing the way. Just to be sure, are you saying the tach goes crazy or is it just bouncing around with the poor idle? If it's crazy, the stator may be going out and taking the charge coil with it. The charge coil supplies the initial charge for the power pack. Is there any gooo laying around under the flywheel? OK...we'll let ya' give all that some thought while feeding the baby....

Post when ya' can...good luck with the baby! By the way....nice looking engine....did you paint it? EDIT: One more thing...make sure the nipple the drain hose from the air silencer connects to on the block is open. This is supposed to keep the drippings that end up in the bottom of the silencer from accumulating.

Orifice sizes 55 HP, anyone know?

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