Altitude Tuning/ Jet Size

[kntutt]

I have a 1977 or 1978 Johnson 175 hp. I am using a 14 1/2 X 18 prop. The powerhead was rebuilt in FLorida years ago but the engine does not have 100 hours on it. I live in Colorado and had it jets put in for high altitude. Today the boat would not start until I got back home. <br /><br />Now to explain. The boat runs fine at Lake Powell, aproximately 4000 feet in altitude. I live at 7000 feet and the resevoir (Ruedi) is 7800 feet. Got the picture! <br /><br />If I can get this running up there it often stalls at hole shots and often just bogs down. I am thinking jetting problem here. I can't find a chart that will tell me what size jets I need for this altitude. I would like to be able to run between 4000 and 8000 feet. <br /><br />I believe I have a 59C jet size in it now. A mcechanic told me I need 54C in this engine for this altitude. He sold me three. When I got home I was told that I need 6 jets. <br /><br />My question is what size jets should I use for this altitude, mostly 7800 feet, and how many do I need? Oh and where the hell on the net is the chart that I am looking for?<br /><br />Thanks

 

[ezeke]

Re: Altitude Tuning/ Jet Size

I think you need to call a J/E dealer on this because there is variation even within the 78 models: <br /><br />Clymer manual (page 288) says: <br />1977 6,000-10,000 feet = 54C;<br />1978 "Early" 6,000-10,000 feet = 54C; <br />1978 "Late" 6,000-10,000 feet = 52C. <br /><br />I've not found a chart on line but there are on-line dealers who will tell you if you email and give the dealer the model and serial #. <br /><br />Try our hosts.<br />web page

 

[kntutt]

Re: Altitude Tuning/ Jet Size

Thanks for your quick replay. Ok, I went out to the engine and although I am not sure where the serial number is I did see a nice big sticker that said "1977 175 hp Johnson Spark advance 28.." with a small "o" for degrees. How many jets do I need for this engine? <br /><br />I have a Seloc Johnson/Evinrude manual for years 1973-1990 and covers L3,V4 and V6.

 

[kntutt]

Re: Altitude Tuning/ Jet Size

What am I changing out here, the high speed jets? It seems that there are three carbs on here, am I placing one or two jets in each carb?

 

[R.Johnson]

Re: Altitude Tuning/ Jet Size

You can't get by with just changing the high speed jet's. You will need 6 low speed, 6 intermediate, and 6 high speed jets. My son lives in Denver, and I had to rejet his 150 for him. When I get to the shop I will look up the bulletin on this set up

 

[kntutt]

Re: Altitude Tuning/ Jet Size

Thanks for that info. According to my manual the 1977 has the type II carburetor and that only has the low speed and high speed orifice. <br /><br />I just took off the black plastic piece that covers the carbs and the metal piece underneath that. If you would like I will take pictures of the carbs and post them here.<br /><br />Remember your son is in Denver, you know the old mile high stadium. That is 5280 feet above sea level. I will do most of my boating at 7800 feet above sea level. Below is a picture of Ruedi Resvoir.<br /><br />

<br /><br /><br />Either way thank you for your time.

 

[R.Johnson]

Re: Altitude Tuning/ Jet Size

I will look up your carb's in the service manual, and try to find that high altitude jet chart. If someone else has one, please post it.

 

[kntutt]

Re: Altitude Tuning/ Jet Size

Here is a picture of the carbs. I am sorry about the size, but I am on a pc that does not have photoshop and can't figure out how to crop.<br /><br />

 

[ezeke]

Re: Altitude Tuning/ Jet Size

I can't be sure from the photo, but it looks as though you have only one drain plug on each float bowl. <br /><br />If that is true then you need only one high speed orifice per carb. <br /><br />If there are two drain plugs, one on each side, then you need two.

 

[kntutt]

Re: Altitude Tuning/ Jet Size

Ezeke:<br /><br />Here is a photo of the other side. It looks as if there are drain plugs on this side also. Do I need 3 or 6 jets? Where exactly do they go?<br /><br />Again thanks for everyones help. I have never been able to get this boat to run correctly at 7800 feet. <br /><br />

 

[ezeke]

Re: Altitude Tuning/ Jet Size

Six <br /><br />Directly behind the drain plugs on the float bowls. <br /><br />Its tough to do without removing the carbs but if you do remove the carbs, get new gaskets. <br /><br />If you buy the carb kits the gaskets come with them.<br /><br />Also, slide a rag from the front of the motor under the carbs as far back as you can. You are bound to drop something and it will make it easier to get it back.

 

[kntutt]

Re: Altitude Tuning/ Jet Size

Ezeke:<br /><br />Thank you.<br /><br />If I am reading you correctly I need 6 jets. I need to confirm the size. Are they 54C's for this altitude? I have three of the 54c's now I need to get three more. Are these standard jets or must I get them through an OMC dealer? I ask this because I live in a rural area and the closes shop is 50-75 miles each way.<br /><br />Beleive or not just around the first left mountain that you see is the Ruedi picture is the "Aspen Yacht Club". Yup, even skiers need a yacht club!!<br /><br />Is there any way that somone can post a Chart which will show jet sizes for various altitudes?

 

[kntutt]

Re: Altitude Tuning/ Jet Size

First thanks for the rag tip. I didn't drop anything but I can see that it could easily be done. It will stay there until the job is complete. It also catches the gas from the float bowl. <br /><br />Ok, here is where I am. I have taken out the three jets behind the drain plugs on the bottom picture side (from the back of the engine this is the right side) and replaced them with the 54C's. <br /><br />I assume that the jets higher up on the carb and that are behind the linkage don't need to be changed. Is that correct? Which jets are those? Are those the high speed jets or low speed jets? I know that these carbs have only high and low speed jets.<br /><br />I understand why you said it would be difficult to change out the jets without taking the carbs off. My manual says that I need a special tool to do so. I am adventures so I did the following. I was able to make a tool and use it to delicately get the bottom jet out and replace it. <br /><br />I cut the end off of a screw driver and ground it down to fit in the drain plug whole. I mated it to fit the jets by using one of the jets that I had removed. I was then able to put it in the drain plug hole, fit it on the jet and hold pressure against it with my finger. <br /><br />This is where it gets delicate. I snapped a pair of vice grips on it and gently turned it to loosen the jet. This took several delicate tiny turns. I took out the jet when it was loose enough to turn with the tool alone that I made. There was no damage to either the jet or the drain hole threads. I reversed the procedure and snugged up the new jet. Don't try this at home kids!!!<br /><br />Now to find another three jets and change them on the other side. I hope that my tool works there.<br /><br />Let me know that I am doing everything correctly so far. I am educable. Isn't that a strange word? But, it is the correct word for that usage. <br /><br />Thanks for your help so far.

 

[kntutt]

Re: Altitude Tuning/ Jet Size

The upper jets are a size 32. Do these need to be replaced and if so with what? These are apparently the low speed jets. <br /><br />They look easy to get off but as I look at them I see the person who rebuilt the motor stripped the screww heads. I am trying to avoid taking off the carbs.

 

[ezeke]

Re: Altitude Tuning/ Jet Size

Been at work so excuse the delay, please. <br /><br />The orifices you are changing are the high speed ones. The low speed ones are behind the screws just in front of the upper bolts that connect the carbs to the leaf assembly.<br /><br />I cannot find a single reference to the low speed orifices so I think you will have to decide if you want to try it out with just the high speed modification or take a chance on lowering the low speed orifices. I know that if you go too low you can damage the engine by running too lean.<br /><br />The important thing is that you bear in mind that the problem there is air, not fuel, and that you are reducing the fuel flow by reducing the size of the opening. <br /><br />You will need to choke less, but you need to know for certain that the chokes are fully synchronized and 100% closed electrically, so get someone to hit the choke switch while you watch.

 

[kntutt]

Re: Altitude Tuning/ Jet Size

Ezeke:<br /><br />Please, no apology necessary. I am exmtremely thankful for all of your help. I will leave the size 32 jets alone at this point, and simply change the primary jets. <br /><br />The size 32's that I am talking about can be seen in the second picture of my engine. If you look at the top carb, look just below the large piece of linkage to your left, closest to the intake manifold, and you will see a screw underneath it. The 32 jet is inside there. It is in the same place on both sides of the carb.<br /><br />At this point I spoke to a local mechanic and tried to find the jets. He is out of 54C's and only has 56C's at this time. I will look to see where I can find them. I paid $1.75 a piece for the three I bought about 8 years ago at a marina. He says they are now $5-10 each. Interesting that this country denies inflation. <br /><br />I was once told that you could buy the jets at an auto parts store. Is that correct or must they be OMC?<br /><br />He also said that I will have to change my prop size down to a 15 or so. I have a 14 1/2 X 18 at the moment. I think I will simply see how it runs once I get the jets changed and go from there.<br /><br />Your idea about not choking it so much is a good one. I actually was able to look at the what seems to be the mechanical choke on the top front of the engine. When I pushed in the choke at the key it did not move however. It stayed in the choke off postiion. <br /><br />I am thinking that the key choke must trigger an electric cold start valve similar to a Porsche 911. I might be wrong here. It is just a guess. <br /><br />After I get the jets I need to get a new primer bulb as mine is dry rotted. I tried buying one from Walmart but it is for a 3/8 ID hose. It was to big for my fuel line. I would think that a 175 should have at least a 3/8 inc I.D. hose. <br /><br />I am actually thinking of changing the complete fuel line out. On ebay I won a new female connector that goes directly in to the engine. I hope that it is not a 3/8 also. If it is I am going to simply buy a 3/8 line with a primer bulb already built in and add the fittings that I need.

 

[ezeke]

Re: Altitude Tuning/ Jet Size

The handle on the port side of the top carb is your manual choke. It has three position on, off, and electrically operational. <br /><br />The cylinder on the starboard side between the middle and lower carb and mounted at about 45 degrees is the choke solenoid. <br /><br />On the older controls there is a switch below the key for it, others had a dash mount and in newer models the key could be pushed in to activate.<br /><br />In any event, the manual switch needs to be in the middle position for the solenoid to do it's job. Once you set it there, you can move the rod in the center of the solenoid downward by hand to see if it will close the chokes. <br /><br />I think that you are absolutely right about the fuel line sizes, But I don't like the after-market bulbs. All of the outboard manufacturers' bulbs seem better built. <br /><br />I like the Yamaha, Merc and OMC bulbs, but I haven't used the others. I use a full sized in-line water-separator filter and I think that plus the demands of the engine is enough to warrant the larger line.

 

[kntutt]

Re: Altitude Tuning/ Jet Size

First off I really want to thank you as I appreciate your sharing your knowlege of engines with me. Understand that I grew up in Lower Middle Class America where my father was a machinist so anything I wanted I had to buy broken and repair. <br /><br />I took my auto shop course and rebuilt a few engines (car/motorcycle) before I decided to go the educational root. Now I am back to tinkering again and talking to you brings a lot back to me and it is fun. So do I both understand appreciate your patience. <br /><br />My choke switch is the push the key type. I did not see the the solenoid move the rods. I will check that out more thoroughly now that I have full acces to the carbs. Maybe that is why I am having trouble starting it.<br /><br />I think I will get a bigger line for this engine. I am not sure what "a full sized in-line water-separator filter" is. I can imagine from the name what it might look like and where it goes. and what it does.<br /><br />I am just getting back into boating and reviving what has been sitting in my driveway for years. I grew up in Long Island seven miles from the L.I. Sound. Needless to say I did some boating there growing up.<br /><br />The difficulty as I have explained is that livng in the middle of the Rockies, 20 miles from Aspen, you don't just go to town to get the parts you need. Most everything is a long drive or mail order.<br /><br />This is an old boat (1979) and I want to get it running perfectly so that I can see how much I want to continue this. The more I am into to it the more I want a 23 foot cuddy. That would be something I can sleep in at Ruedi and something that I can take to Lake Powell for a week or so.<br /><br />Now if I get that I'll probably have to get a new woman back in my life. You don't have any tips for that do you?

 

[ezeke]

Re: Altitude Tuning/ Jet Size

No tips on the women in your life. But, if you want to keep that motor running well, you should get the OMC model specific manuals for it. You can buy the whole set: owners, service and parts from several sources or set up ebay to email you when some come up for auction. NAPA parts dealers can get them and a most of the parts you will need, although you may need to educate them if they do not have much trade in your area.<br /><br />The model and serial numbers are either on the side of the transom bracket (+/- 1" X 3" plate)or on the welch plug (round convex plug)on the top of the block near the cylinder heads, or both.

 

[kntutt]

Re: Altitude Tuning/ Jet Size

I will look into seeing what I can get from NAPA today in terms of jets. If I can get the jets I'll test it out this weekend if possible. <br /><br />I'll look for the serial number and keep thatin my current manual. I'll let you know how it runns.