TOPIC: 88 Johnson 150 high altitude jetting help

Hey guys I could really use some help with this. I have been struggling with this Johnson outboard that came on a recently purchased 89 Larson runabout boat. I primarily operate this boat at attitudes ranging between 6 and 10,000 ft. I use high octane fuel only , rarely ethanol free ,as it is difficult to obtain in my area. I do get it once in a while though. I pre mix Walmart outboard oil at 16 ounces to 5 gallons. It usually starts ok, however once in a while really struggles with it. It also struggles at idle, which it doesn't like to do for too long before getting a bit of throttle. I must shift quickly to just past where 1st gear starts to avoid stalling. From there , if I try to accelerate much past this point it wants to and often does stall. The trick I've found to keeping it running is to push and hold the key in for a second or two just as it's about to bog out. This opens the choke solenoid which injects gas directly into the cylinder. This tells me it's running lean. Once it's past this crucial Rpm range (between 11 and 1300 Rpm) it's fine. Cruises at full throttle just fine, and when I back off, it's also fine at low speeds. It's just accelerating through this small range. I have another thread detailing all of these issues called " 89 Johnson" (before I figured out it was a 88). Another member on here "chinewalker" advised me to pull down and clean up the carbs. Last week I completely disassembled all three, removing every jet, and cleaning them with carb cleaner individually before reinstalling​. I was skeptical as they seemed pretty spotless upon disassembly. Nonetheless cleaned em well, put everything back together and took her out this past weekend. It ran pretty much exactly the same. I have been suspicious about the carbs needing different jets for high altitude. However I learned that high altitude jetting usually involves actually down sizing the jets, which would result in a ever leaner condition ??? Information about the jets is difficult to obtain. I have called several marine shops here in Colorado and none have had an answer for me. Any help would be greatly appreciated. Thanks

No response yet.....either the post was too long for anyone to read, or nobody here can help with this particular problem. Is there any other sites I should attempt to get help ?

aomci.org/forum/viewforum.php?f=2
forums.iboats.com/forum/engine-repair-and-maintenance/johnson-evinrude-outboards

Thanks silver bay, I didnt find anything directly relevant to my situation in the thread you linked. I found out that johnson does not recommend changing the jets in these engines for high altitude. The problem has persisted. It is definitely fuel starved at the specific rpm range I mentioned. The primer bulb is difficult to get hard and doesnt stay so. High altitude jets are usually smaller, that would make the problem worse. The only way to keep it running is with the primer/choke solenoid, which injects fuel directly into the cylinder I am starting to think the problem may be somewhere other than the carbs. Would a bad fuel pump still work good at high rpm, but struggle at most other speeds ? Really hoping for insight here.

Both links were ideas on other places to ask, both have large populations of old hands (some who are on both sites)

If the fuel pump is keeping the carb bowl(s) full, I'd THINK the primer bulb should stay hard, since the pnly thing that keeps the bowls from overflowing is the float valve closing off the inlet (the same thing that makes the bulb hard to pump), so maybe it is a weak pump....

thanks silver, finding a replacement pump for my exact model number has been difficult. Unless there is a cross reference, it doesnt look available. What else could be causing this besides the fuel pump ? Some have mentioned a clogged fuel line, but again , I would think the problem would be apparent at all speeds. Since the nearest shop that can work on it is about a 2 hr drive and charges 96 bucks an hour shop rate , and is backlogged for 3 weeks.... it might be best to just throw some money at it . I am thinking of starting with the pump..if I can find one. The only other parts I can think to replace would be the primer bulb and hose....or the fuel pickup in the gas tank. Suggestions please ?

I am no mechanic, but feel your pain. If fuel line with primer has some years on it, why not start easier and cheaper and replace first. It never hurts to have a good one before any hose does start failing. If that doesn't solve it, no great loss yet. Then maybe pull that tank pickup and check for anything including looking in tank. I can only do these simpler things, but at least that is 2 tries that don't cost too much. This is where I have to rely on professionals for further repairs as I have not learned further skills. Wish I could help more. Is your tank vented without restriction? Are any hoses pinched or kinked? You have probably done all of this and more... I am just reaching at this point. Maybe your tank pickup is near the front of the tank and the tank is lower on fuel so when you are planing off, the fuel runs to the back until you plane off. Ok - I am reaching at this point and am way out of my wheelhouse. Good luck. Hope you get better advice than mine!!

Thanks dr.go. Great advice sir ! those are all some possibilities I have not looked into. I am not sure about the tank ventilation. There is a vent below the filler cap, I noticed when I overfill the tank, gas leaks out here.

Could I get the model number of your engine? They built a GT version & just a 150 in those years. Each has its own size carb. You are correct to assume that if the engine will run at WOT (wide open throttle) then the fuel pump is putting out adequate pressure for idle speeds in most cases. You are also correct that at altitude jets (high speed jets) are usually reduced in size to lean the engine since there is less air for the engine to breathe. The confusion comes from the fact that the low speed (idle jets) in this motor are air bleed jets. That means in order for them to make the engine run richer (more fuel) the jets have to be smaller in number (smaller hole). Restricting the air makes more fuel enter the carb throat. Now this brings up another interesting point? Air leaks become a very important consideration. Your carburetors have a top cover on them with a gasket under it. Did you put new carb kits in when you cleaned the carbs? It is important that these gaskets have a good imprint to show that they are sealing in all areas. The tiniest leak will cause the motor to run lean. Does the engine lean spit when it dies? Do you trim the engine up level until you get ready to take off. This can help get you past that point. You will notice the motor will run smoother trimmed up (top of motor cover) level with the water while idling around in no wake zones. You may have some other issues, but let's start there for now.

I posted a link to this thread on the AOMCI forum in a members-only area (which may have brought t2 over) and another trusted veteran (who also posts on iboats, and worked professionally on OMC engines) wrote (his emphasis in bold):

Well since I live at about one foot above sea level, I'm no expert when it comes to 10,000 feet. But my first thoughts are check the synchronization between the carburetors and spark advance (link & sync)---by the book. If the carb butterflies do not close completely and start to open at the correct time, nothing else is going to work. Related to this is the timer base sticking and moving late, a notorious problem, caused by old sticky grease.

Hello t2, and welcome to fiberglassics ! Thank you for joining in, I need all the help I can get here. Additionally thank you for all of the great information you just provided with one post, so many great questions. First off the model # J150TLXCA.

As far as the carb kits go, no I did NOT replace those gaskets nor any other parts in the carbs(no kits used). However the gaskets looked like new. The problem didnt change at all after I cleaned them. A member here "chinewalker" advised me to just pull em apart, clean up everything, especially the jets, and put it all back together. They were all very clean upon disassembly.

The engine usually (I dont think always) makes a spitting noise when it dies. I have tried starting with the engine trimmed up and down, It doesnt make much of a difference with this problem, it IS more difficult to get her through that rpm range while trimmed down, but does the same thing with it trimmed up, just gets through it a smidge better.
Thanks again for the helpfull insight

silver-bay wrote: I posted a link to this thread on the AOMCI forum in a members-only area (which may have brought t2 over) and another trusted veteran (who also posts on iboats, and worked professionally on OMC engines) wrote (his emphasis in bold):

Well since I live at about one foot above sea level, I'm no expert when it comes to 10,000 feet. But my first thoughts are check the synchronization between the carburetors and spark advance (link & sync)---by the book. If the carb butterflies do not close completely and start to open at the correct time, nothing else is going to work. Related to this is the timer base sticking and moving late, a notorious problem, caused by old sticky grease.

Thanks again silver bay ! Really appreciated. I have looked over that section of the manual (link and sync) it looks like a PIA ! I hope the issue isnt there. The timer base thing sure would suck too !!

I got your message (email). For the good of all we will go over the details here as to how to proceed. If you don't have it off already remove the front cover from the carbs. The black plastic cover. I know there are a lot of screws & the bottom three are tough to get too, but you can leave it off till we get this figured out. This takes a little time, but is not hard to do. Get you some round wooden tooth picks. Any restaurant usually has them. Look up into the mouth of each carburetor. You will find two low speed air bleed jets in the top roof of each carb body. These are little 8 X 32 brass jets. According to the parts books they should be .030 in size for your model engine. You may be able to see the number on the face of the jet? If you have a small mirror it helps. Take a tooth pick & stick it into one of the jets. It will stay in the hole if you push it in. Start the motor as normal and warm it up. Remember to keep the engine level. We are going to be putting the tooth picks into the various jets randomly. It's OK to put in more than one tooth pick at a time. You may want to put a pair in one carb? Give the engine a minute to respond. If you start to notice a difference then trim down and try to accelerate ahead. Caution! Do not take off enough for water to come over the back of the boat & go into the motor! Just goose it a little to see if it is better. Idle around to see if it idles better. By blocking the jets off with the tooth picks you are making the low speed circuit of the carb go full rich. The motor should load up some, but stop sneezing when you find out which cylinder (cylinders) are lean? I have different jets you can change to here that I can send you. We are not going to leave it full rich. If it takes a totally blocked jet to make it run correctly you have an air leak somewhere else. We will go looking for it. Like I said this can take a little time to accomplish, but better you do it than a mechanic @ $95/hr! Some won't even do it!
Let me know when you have an idea where you stand. We will proceed with the next step.

Dan in TN

Wow ! Thanks t2 , some great stuff there. Hope it helps others out as well. Sorry for the delay in posts. I took her out for a run last week before I read this. She ran much better but still suffered similar issues. Most notably when pulling a skier.
Unfortunately I ended the day by clipping the dock on the way in. Left a decent sized hole in the side, way above water level, but I still wanted to deal with it ASAP. Sooo ...I spent the better part of the last week first researching fiberglass work, then over the last few days, dealing with the repair. Not fun, but I'm just about finished with it,so now it's on to figuring this motor issue out ! A few weeks ago I removed all the carburetors for cleaning...while doing so I also removed all 6 jets in each of the 3 carburetors. I noted the jet sizes. The low speed/idle jets you mention are a size 31, not a 30 as you also mentioned. Next time out I will bring toothpicks to try to isolate the issue further. Perhaps using the 30 jets would help... either way I will report back after I have done the toothpicks test. Thanks again Dan

Sorry you ran into a dock. Nothing is more irritating than a motor that won't idle consistently. If you still have the carbs off you could check one more thing while you are there. Sorry I forgot to mention it. There are six check valves on the manifold. Two under each carburetor, one for each cylinder. You need to make sure the hoses are in good shape (not split) and the valves are not blown open or clogged. Take them out and you can clean the valves with brake clean. They check away from the manifold. You can blow into them once they are clean. The part #392988 expensive ($35.99ea), but I may have a couple or check Ebay.
A #31 jet instead of #30 jet is not going to be your problem. It usually takes 4 or 5 sizes to make a difference on an air jet. Fuel jets are a lot more sensitive. Keep in mind just the least bit of air getting into the system will make the engine lean. Easier to move air than fuel.
Keep me posted as to your progress. I know this all takes time, but we will get it!

Dan in TN

Thank you so much for all your help here ! The carbs are on the motor, I only had em off long enough to disassemble, clean, and then put em right back on. As I mentioned, this had little to no effect on the problem. I wish I had known to check out those valves before I pulled the carbs....not too worried though, I'm confident that with your excellent guidance we will get this sorted. Whomever worked on the motor before did some hack work...many of the bolts on the air cover are different sizes, a few are missing. One thing I'm curious about; the air cover has a deal at the bottom on the starboard side that holds the throttle and shift cables in place. With that cover off will the cables still operate ? Logic tells me no....but you would know better than me. I'm planning on attempting to try the toothpick test next time out. I will let you know how it goes.....if it goes ! Hopefully I can get a pic or 2 or maybe some video to post to give you a better idea of what she's going through

Only the black plastic cover needs to be removed to perform the jet test with the tooth picks. The base (aluminum) has the cable attachment points. You should not run the motor with the cable anchors disconnected. The screws that hold the black plastic cover on should be 3/8" headed screws with a flat washer under the head. I think there are 10 of those? People (mechanics) have a tendency to leave the bottom center one out as it is a pain to get to. Fuel & oil residue will end up in the lower pan & water if the bottom bolts are excluded in the assembly. Be sure the gasket is in place. The base plate that holds the anchors for the shift & throttle cables is retained by 6 - 7/16" headed screws. You may find that those bolts have been swapped around. The 7/16" headed bolts don't fit well in the plastic cover. I have plenty of correct hardware if you should need any?

Dan in TN

Dan, Im not sure if my engine has 2 black covers. I am near certain it was only 1 black aluminum cover...but it did have about 10 bolts, and the cable anchor is part of that assembly. I will take a pic today to confirm. Thanks again

Alright...it is as you described ...my memory had failed. So I removed it today. It is missing all 3 bottom bolts. And there is a bit of oil in the pan. Not a ton , noticable though. I left the plastic cover and bolts in the boat so I can reinstall after testing with the toothpicks.

Finally ! I got to try the toothpick test. The closest lake to me is about an hours drive , over 2 mountain passes, so it took me a bit to get this done. This particular lake is the highest elevation of all of the lakes I go to, its sits at right around 10,000 ft above sea level. However it is the closest, most of the others I go to are about 20 minutes more drive. I was alone on the boat so there was no load. She started pretty easily, but really didnt want to idle. Every time I tried to put it in gear it would just stall right out. Finally I managed to get her to run, but she really struggled, especially when trying to get here to plane, just didnt want to do it. I removed the cowl and started with the upper most carburetor, inserting the toothpicks into the idle jets, one at a time. Upon getting the first 2 in the top carb, I did notice a very slight improvement, so I continued and blocked the jets on the middle carb, there was no noticeable difference, I moved on to the bottom most carb, this is obviously the most difficult to access, again not much noticeable improvement. I cruised around a bit and tried to "goose" it through the point at which it normally stalls, it still wanted to stall out, although it didnt make the same "spitting" sound. I managed to keep it running for quite a while, after putting around slowly (toothpicks blocking all idle jets the entire time), and not trying to increase speed for quite a while... I was able to accelerate to plane, however I still needed to press in the key to prime enough gas to make it happen. wasnt easy, but once she got moving she was screaming ! Putted around good for a bit after, then she stalled as I was docking. Sorry for the lenghty description but I want to make sure you have all of the details here. Im not sure what to make of this, or how to proceed next ? Should I repeat the test at lower elevation, I do notice a difference at the lakes that are lower in elevation. Is there something else I should test or check out ? Thanks again for the great help here, I really hope it benefits others

Sorry, I have been gone for a few days. So the top carb seemed to show some improvement you think? That would be the easiest one to work on. Your in luck! Take the top cover off & look at the imprint of the gasket with regard to the the carb body. See if you see any light spots where it doesn't look like the gasket is making good contact. Those are the areas that could be leaking air. It is very easy for air to get by. Since the other carbs did not react we will assume they are not leaking for now.
Did you remember to trim up lever with the water any time you were off plane? That is very important. You will notice the motor will idle better at this attitude. Especially if the recirculation valves are in bad shape? You can try a test by just warming the engine up with the motor trimmed up level them trim it under. Watch you idle go to heck! Trim it back up level & it will come back if it doesn't stall before it clears out. If you find this is happening you will have to go back in to clean, inspect, & replace some of the recirculation valves. Let me know if this is the case. I have a couple. They are pricey now!
What temperature is this motor running at? Should be uncomfortable to keep your hand on the top of the cylinder head at idle. 125 degrees minimum. That is important to minimize the amount of unburnt fuel left for the recirculation system to handle. All the system does is move that junk around till the next time you run WOT & consume it.
Do you have a timing light?

Hey y'all ! Sorry once again for another delay in the progress of this thread, which I really hope helps others as well as myself to deal with these issues.

To briefly answer some of the questions t2 posed. I did not pull the top cover of the carb off again yet. I just got back from a week on lake Powell with the boat. I have paid attention to the trim while going on and off plane, as well as starting. It does make a big difference. If we are going slow , and I have the trim down, she is not happy. Trimmed up at slow speed works great ....but I found that to take off from low speed it helps enormously to trim down. We launched at Powell with the boat loaded down heavy, possibly beyond capacity. 3 total passengers , but we had tons of gear for camping for 5 nights. 2 huge coolers and one medium sized one, tents, bags, wood , water, portable toilet (required at Powell) , 6 extra 5 gallon fuel cans full, plus tons of other stuff.
Shortly after setting out I realized how big the lake is. And also how inconsiderate most other boats out there are. Huge 100 ft long vessels to 40 footers and smaller all going full tilt at all times , many passing closely with no regard. The wakes were dangerous. With our boat so weighted down I wanted to find a camp spot asap so we could unload all the gear.
I attempted to bring it up to plane, it made a revving sound but didn't pop on plane. This is the exact same thing that my old boat did before it died ( would start but not move) . So we cut the throttle and recentered our wieght. After that it planned fine, took a moment with all the weight, but was fine.
The really important thing to mention is that the boat (even while weighted down with over 1200 lbs ) was able to plane WITHOUT having to do the " key " trick (priming) . The entire 5 days out there I was able to drive the boat as if it were normal ! I could easily throttle through the entire range with no stalling issues.
To clarify further, lake Powell is at 3700 ft above sea level. I live and operate my boat at more than twice this altitude !
However , the boat did also start a bit easier, but still took a few tries every time. Getting it out of neutral without stalling was the same as it is at my altitude. It requires having the rpms around 2k with the warm up lever, then quickly shifting out of neutral , going just past the detent for second gear immediately after the warm-up lever is depressed. Trying to just shift into "troll" /1st will end up in a stall. Once out of neutral (after goosing it past the 45 %) the throttle can quickly be worked back to slow speed .
We did have one crazy moment worth mentioning. While heading back to our camp spot from exploring a side canyon about 12 miles our site we got caught in a super intense squall, called a microburst. It produced 6 foot crashing swells ! My wife was at the helm I grabbed the bow rails and guided her through a feild of houseboats as we attempted to make it to the closest marina. Can't believe how hard the houseboats were getting tossed by the waves ! We are really lucky it didn't last to long. The next day dozens of boats and 2 houseboats were sunk in a similar storm. We had just escaped. Thankfully my boat made it home safe and sound. Now to get her to run like she did down at Powell !
Wondering what you make of this t2 ? Could it just be I need much smaller jets for my altitude, or perhaps those check valves are clogged up, or there is a airleak in one or more of the carbs. I will pull off the carb top covers again asap. They looked pretty perfect when I had em off before, but will inspect again anyway.
Thanks again, sorry for the super lengthy post.

Well we are almost live time here now! Your post being 36 minutes ago. Lots of information here, but let's get a few things straight before we proceed. I'm not fussing or berating you, just concerned? Your boat (what brand, size, rating hp?) has a lot to do with how it might idle off plane. Since it is a 25" model motor I had not given that much thought before. Those boats would normally have plenty of free board. When the boat is floating in the water normal load trimmed under, where are the exhaust relief holes (two 1/2" hole at the bottom of the cowling) in the center rear of the engine. With regard to the surface of the water what height are they at?
If you keep revving the engine in neutral & slamming it in gear to get going the gearcase is going to give up! Got to get this figured out before you do damage to an expensive part. When I talk about trimming out to improve the idle you should stay that way while you get going (above 1500 RPM) and trim down at that point to get on plane. Your boat sounded like it was definitely over loaded, but those cross flow motors have plenty of bottom end if propped correctly. What does your motor turn with a normal load at WOT trimmed out? I know it would not run normal with the load you had on it that day.
Still going to have to take this in steps. Get me some more answers to these questions. The motor should be richer at altitude than at sea level! Idle or WOT. Obviously WOT is effected more as the engine needs a lot more air at WOT. IF you take the carbs off definitely take a look at the recirculation valves while you are there. Clean them with brake clean & make sure they are checking. If they are blown open then they are the same as air leaks. Keep me posted.

Dan in TN

Hey Dan, Im back from the winter hibernation and ready to get this Johnny up to par ! Im hoping you can still help guide me to get this SOB running smooth this season. We had a very mild weather this winter here in CO, so that usually means we will have some winter weather during spring and early summer. Nonetheless I am excited to get wrenching on the boat. I havent "dewinterized" yet, but did get her all uncovered earlier this week.
To answer the questions from your last post the best I can :
The boat is a Larson Delta conic citation 17.5 ft. Its rated up to 150 hp, which is the rating of the motor. The exhaust relief holes generally sit pretty high above the water line, never took an exact measurement though.
Although its tricky getting out of neutral without stalling, I wouldnt say that I "Slam" into gear, the rpms come down quite a bit before the gears engage, never felt abrupt it just has to happen quickly to not stall. Still not a good scenario to keep playing out.
That day at Lake Powell with the heavy load, the boat was probably even more loaded down than I geussed, I bet it was quite a bit more that 1200, with only 3 of us on board, but enough food, drink, gear and gas ( 30 extra gallons in cans) for a week in the wilderness. I wont be doing that again !
I cant say exactly what rpms im at during wot, but I seem to recall it being around 4,500. Likely irrelevant but I do notice while towing a wakeboarder at the most ideal speed (not sure what that is since the speedo isnt working) rpms are best between 2700 and 3200.
I figured that taking the carbs all back off to get a look at those valves (didnt notice any last time I had them off ) would be the next step, but I will wait to hear back from you for now.
Thanks again Dan !

I know this thread is old, but I hate leaving things unfinished. Finding "unfinished threads" drives me nuts ! So Dan from TN aka T2 stroke had helped me along in this thread. I ended up going on the AOMCI site where I got more help from a nice fella from Rhode Island, Don aka fleetwin. He helped me sync everything. However the problems persisted. So I went ahead and did the compression test. Man I REALLY wish I had done this first. All cylinders tested right around 60lbs, with the exception of the #1 cylinder, which came in at just less than 40 lbs. I retested several times and got the same results. Don had to break the harsh reality to me. I had been sold a lemon. His recommendation was to replace the powerhead with a rebuilt one. I have not been able to find a rebuilt for less than 2900. If by some miracle, someone out there happens to have a decent used one to sell PLEASE chime in here. Otherwise the final prognosis is that this was a damaged motor from the get go. Thanks everyone that jumped in here to offer help, I appreciate everyones input here. I miss my Merc !