DT150 won't go over 2000 rpm's... help please!!

[Importkillerrr]

The last time I posted here my lower unit was broke, clutch dog I assume but I never got the bearing carrier out because the previous idiot owner welded it to the case instead of buying a new nut. Took it to 3 shops and they all refused to work on it, I grinded weld for days but still couldn't get it out so I just fished electric only reservoirs for two years.

My luck turned as I finally found a beautiful used lower unit close to me that wasn't selling for explain this to the wife money.

I put on a new water pump and slid the lower unit on. No issues at all, had to adjust the turnbuckle quite a bit in order to get her to shift correctly but I finally got er adjusted and she shifted in the test tank perfectly!

Drove an hour thirty to the nearest unlimited HP lake and was super excited to see my son's face as he experienced bow lift and running on plane for the first time!! I've owned Bass boats that would gps in the 90's before but never had a gas rig once we had kids and money was needed in other areas of life.. But now he gets to experience one of the greatest feelings a guy can have!!

On this lake there's about a 200 yard cove that's a no wake zone that you need to putter through until you reach the no wake bouys and can open it up. The engine started rough but ran good once it was warm, normal 2 stroke stuff. It shifted into reverse, then forward and it ran really well. We ran trimmed down at around 12-1500 rpm's at around 5 mph until we hit those bouys and then hit the throttle lever forward. The boat lifted the bow and started to roll over, you could feel the back pad lifting up onto plane but then just stopped right there and stayed at 2000 rpm. I returned to neutral and did it again and again and again with the same result... She would stop at 2000 rpm and 10mph and just stay there. We drove 4 miles and it never tried to surge past that mark. My son was able to reach back and squeeze the primer bulb whole we were at WOT, no change at all. The bulb wasn't hard but also wasn't sucked in either. He could feel fuel flowing through it and he was able to pump it a few times but the engine didn't rev or surge or die... Nothing changed. Ever time you would push the shift lever forward it would slide into gear and start to accelerate as it should but once it hit, say 10:00 if your looking at the shifter box from the side and neutral is 12:00 then it would click into forward at 11 and would accelerate until 10ish then stop accelerating. You can leave the lever there or continue to push it to it's max position but the engine wouldn't even to to rev any higher. If you started from neutral and pushed in the choke then shifted into gear with the choke pushed in you would reach that magic 2000rpm spot quicker on the clock image I described earlier but it still wouldn't go past 2000 rpm.

I went to an on lake marina and bought a new primer bulb, not because I thought mine was bad but it was the cheapest thing I could try that would allow the use of their dock. I changed the primer bulb and at the same time put the 3 blade Suzuki prop that was on the boat originally back on to see if the 4 blade prop I had on was just to big to spin. It shouldn't be, I'm not new to performance Bass boats and the 3 blade Suzuki prop that came with the engine is 14 1/4x24 pitch. The 4 blade I was running is 13 1/2x24 pitch. It shouldn't of made that big of a difference but was worth a try. I got the stock prop installed and left the marina. It ran at slow speed really well, I got into open water and slowly gave it throttle and BAMM... At around 1500 rpm's I spun the prop. It sucked that it happened BUT when it spun on its hub the engine also revved to 4 grand or more before it settled back down to an idle. That at least showed me that I didn't do something to the throttle linkage when I was in there adjusting the shift linkage turnbuckle. I limped back to the dock and switched back to the 4 blade prop and went on the rest of the day the exact same as before. She would jump out of the hole pretty good but would stop at the exact same rpm every single time. It was a brand new digital tach that I am considering returning because it sucked, I'm not 100% sure of it's accuracy but I know the rpm's always stopped at the same number, 2000. In real numbers it might of been 1850 or 2200,I don't know that but it was the same Everytime... That I know for certain. It also wasn't higher than 2500, I've been a mechanic for 25 years and I can hear rpm ranges and it wasn't much over 2 grand if at all.

Would switching to a twin stick fix this issue you think? Or did spinning the hub and bouncing off the rev limiter prove that it isn't a linkage issue? I would think that it did but I'm not sure yet. It only happened that one time. I know the motor has no issues at all revving like normal while using the throttle handle.

Any ideas fellas?!?

1992 Suzuki dt150 on a 1991 Ranger 397v Apache.
It's a carbed model. Two years ago when I blew the lower unit and knew she wasn't going to be run for awhile I removed the 3 bowl drain plugs on the carbs and got old gas out of the carburators. The engine lit off first turn of the key in the test tank in the driveway when I got the new lower unit installed. It must be something stupid. I read a 10 page thread on this forum last night from a guy named dk (I think) his engine was fuel injected though so not sure how much of the advice given to him effects me, some like the filters and such, which I'll check today.

Thanks for the help!!

[Importkillerrr]

Anybody?!?! I need someone to point me in a direction..., I'm out of ideas!

I'm sorry it's a long post but I've read a lot of posts on this forum and after putting up a shorter post asking for help people seem to always get told that they cannot be helped without more information, so I decided to post everything at once to avoid that problem.

So here goes.......

Today i replaced the fuel filter on the side of the motor, the housing had a pinhole in it and when you squeezed the primer bulb it would shoot out at you... Was kinda funny as it shot a perfect stream of fuel right between my eyes

I also replaced all fuel lines from the tank to the bulb and eliminated the big old water separator/filter that was on the boat from 1991. I had replaced the filter element last year when I restored the boat but, it wasn't needed so I eliminated it.

I put the other Suzuki 3 blade prop on and noticed something!!!! With the 3 blade prop on, the lower unit fit in my test tank whereas the 4 blade prop did not fit into the tank. The 4 blade was too big to fit by about 1/2-1" on each side... The 3 blade slid right in with plenty of room all around. The 3 blade says "Suzuki 141/4x24" the 4 blade I forgot what it was to be honest. It's stamped 26 pitch but has no diameter stamped, I measured it out to be around 131/2.

The engine started and idled great. I knew I wouldn't have that much time once I put it on gear before the water was splashed out of the tank and I didn't want to run the motor dry so I only had a few seconds once I put it into gear. I slid the shifter into forward and the prop started throwing water. I rolled the shifter forward and the rippems started to increase as they should. As before though.... they stopped at a little over 2k on the tach.

I shut it down and refilled the tank. This time I put it into gear and once the prop started to spin i put the shifter to the floor like I was trying to outrun a tornado and..... As far as I could tell... It stopped at around 2k.

I'M LOST!!!!

PLEASE HELP!!

[Murray]

I’m won’t be much help but I’ll ask a question. When you push the binnacle throttle forward to WOT are the throttle plates opening fully?(engine off) Try running without the prop in the barrel, gently since you have no load on the engine, see if you can get it past 2000rpm. Consider trying muffs? In post #1 you said “I know the motor has no issues at all revving like normal while using the throttle handle.” What are you saying? Manually opening the throttle at the carbs? Good luck, be patient there are members on here who have forgotten more than I’ll ever know.

[Importkillerrr]

Thank you for the help!!!

Sorry for the confusion... When I say throttle handle I mean the handle on the control box that only increases throttle, not the handle that puts it in gear while also raising the throttle as you go. While in neutral the engine has no problems hitting the rev limiter while using the throttle handle. I know enough to not bounce the limiter like a teenager with a Honda civic and a fart tube exhaust but as a test I was able to easily hit the rev limiter in neutral.

The reason I don't run muffs is that I've never had any luck getting enough water while using them. On this motor, while using muffs, the water flow alarms never shut off no matter what I try so I found using the tank is easier, quieter and doesn't smoke out the neighbors as much.

As far as the throttle plates in the carbs, yes they are fully opening as they should. That's why I assumed it was just too big of a prop because when I changed props and spun the prop on its hub the engine instantly bounced to the rev limiter. It revved from idle to rev limiter very fast and was strong, no spitting or sputtering at all. It took me awhile to realize what the hell was going on so I let it run at the higher rpm's for a few seconds while I tried to trim out of it... Then I realized I spun the hub and brought it back down to idle but there for a little while I thought I needed more trim

I'm being patient but the weather isn't... Water is gonna be hard in a few short months and it's gonna be a shitty winter if I don't get this thing to run at least close to WOT at least one time.

I dunno... I'm still leaning towards the prop being too big. I mean... It has to be..... Right?!?!?!?!

[Solarman]

There are several areas you should check.
Because it seems to stop at 2k rpms every time, hopefully you have a Suzuki service manual for this motor?
I am assuming that your heat sensors, and oil flow switch are not throwing the motor into safe mode?
I am also agreeing with Murray here, that the back throttle butterflies must be opening fully (motor not running) when throttle is pushed fully in the WOT position / forward?
The manual has a wiring diagram that should show you the "high" and "low" condenser charging coils in the magneto (under the flywheel). The "low" charging coil is for starting and low speed, below about 2500 rpms. The "high" condenser charging coil is for the higher rpms. Check this "high" charging coil (using wiring diagram for color of wires) per Suzuki manual to see if it's reading good? If it is within specs then we move to the throttle position sensor and check by manual. If the TPS is only working at lower range, then it could be dead at mid range and higher rpms? Also check the "gear counting coil" per manual, it has to read each tooth of the flywheel properly, it works with the TPS for proper timing.

Importk... you mention the motor runs fine up to 2k without surging, or acting like it's lacking fuel? is there a chance the carbs mid & high speed jets are blocked up? Do you use any fuel additives?

Is the oil injection system working on the motor?

Check out these areas and give us some info.

Good luck, post back on what you find out.

[cprice11]

Could it be the neutral safety switch ?

[Importkillerrr]

There are several areas you should check.
Because it seems to stop at 2k rpms every time, hopefully you have a Suzuki service manual for this motor?
I am assuming that your heat sensors, and oil flow switch are not throwing the motor into safe mode?
I am also agreeing with Murray here, that the back throttle butterflies must be opening fully (motor not running) when throttle is pushed fully in the WOT position / forward?
The manual has a wiring diagram that should show you the "high" and "low" condenser charging coils in the magneto (under the flywheel). The "low" charging coil is for starting and low speed, below about 2500 rpms. The "high" condenser charging coil is for the higher rpms. Check this "high" charging coil (using wiring diagram for color of wires) per Suzuki manual to see if it's reading good? If it is within specs then we move to the throttle position sensor and check by manual. If the TPS is only working at lower range, then it could be dead at mid range and higher rpms? Also check the "gear counting coil" per manual, it has to read each tooth of the flywheel properly, it works with the TPS for proper timing.

Importk... you mention the motor runs fine up to 2k without surging, or acting like it's lacking fuel? is there a chance the carbs mid & high speed jets are blocked up? Do you use any fuel additives?

Is the oil injection system working on the motor?

Check out these areas and give us some info.

Good luck, post back on what you find out.

Thank you for replying...I truly appreciate the help.


First off..I have removed the new tach that I installed before I took the boat out last week. I hate it and it bounced around way too much for my liking. I installed the trusty Suzuki tach that was in there, it's ugly but I know I can trust the numbers. I'll have better data next time I go out.

I do not have a manual but now that I have a working engine and a lower unit that actually turns I'll invest in one. The engine monitor gauge seems to be working as it should. The gauge has 4-6 round green lights in the center going from top to bottom in a row. There are also two round red lights, one on each side of the green row of lights. I believe the green lights are for oil level, all but the top light are lit. The red lights I believe are for water flow to each head. The alarm beep starts beeping with the turn of the key and will stop beeping once the water flow coming out off the tell tail is at its normal pressure. I've found that when using ear muffs the water flow isn't strong enough to turn off the alarm so I stopped using them after about 3 minutes and now use a large plastic drum as a test tank. I have never had any alarm go off while the engine is running. The alarm sounds at every key cycle and stops once the water pump starts to flow water.

I believe I have fixed the throttle handle issue and it was my fault. When I adjusted the turnbuckle at the throttle cam on the side of the engine I never thought that I needed to also adjust the turnbuckle going from the cam to the carb linkage and also the throttle cable from the control box to the cam. They were so far out of adjustment that when the throttle handle was rolled into forward the carb was at 50% WOT. When the throttle handle was at 50% the carbs were at WOT and the butterfly's were already fully opened! Rolling the throttle handle from 50%-Max throttle did nothing more than roll that cam on its spring... Doing nothing in reality because it was already at Max throttle. My bad... Stupid mistake on my part.

I reached out to the guy I bought the lower unit from and we talked for awhile trying to figure out what could be the issue. Turns out the dt150 he took the LU off of was on a 22' Boston whaler. Completely different hull design than my boat but similar in weight and overall size. My boat has less bow weight and more Stern but close enough to make a comparison. The 4 blade prop I was trying to spin was 13.5X24 pitch. The 3 blade Suzuki prop I switched to that spun the hub was 14.25X24 pitch. The other Suzuki that I was given when I bought the boat is a3 blade 14.25X26 pitch. The lower unit I'm running now was spinning a 3 blade14.25X18 pitch on a boat of similar weight. That's quite a big change in pitch going from 18 to a 26!!!

Last week on the water when I switched from the 4 blade wheel to the Suzuki 3 blade it backed up away from the dock and then shifted into forward really firmly with no slip... The prop grabbed and jumped up to 2-3k range very quickly, again it was on the crappy new tach and I am not confident in the numbers but it jumped from idle to the 2/3k range and felt like it was still digging past the rpm spot where the 4 blade was running. At that moment it spun the hub and the rpm's started bouncing off the rev limiter. That's why after thinking about it I'm now kinda leaning towards the issue being prop related. It easily and very quickly revved up from whatever RPM it was running at to hitting the rev limiter when that prop spun on its hub. I would think that if the issue was engine related that it wouldn't rev up to the limiter when the prop was spinning on its hub. I guess I'll see next time out.

I've read a lot online about removing the entire oiling system and going back to mixing the oil in the fuel. I can see the advantages of doing this, why rely on a 32 year old system that could destroy the engine if it fails. At the same time though, the system hasn't failed in the 32 years that it's been on the engine so why mess with a good thing? What's your opinion on this and if you feel like removing the system is the way to go, what do I do to remove the system and not have the alarm go off constantly?

Thanks again for your help. I will look into doing the tests you mentioned (stupid site won't allow me to scroll up to look at your reply while I'm writing this so I don't remember what they are right now). I'll start working on those things you mentioned tomorrow and post my results.

[Solarman]

First off, removing the oil system will cause complications because the system is connected to the computer. I personally would not remove the oil system. The Suzuki tach is also tied to the computer, the lights are for water temps and yes the ones in a line are for oil level. As long as you're using the same amount of oil for so much gas burned, you should stick with it.

Four blade props are for heavy boats, bass boats (unless long and too heavy for the dt150) generally will run 3 blades. If you want higher speeds you can try a good 2 blade prop, but you will lose the jump out of the hole with 2 blades, they start off slow but start grabbing about 20-30 mph then they go. The 3 blade is the best all around prop, but it too needs to be sized correctly for your boat and motor.

You should never change any of the linkage adjustments! All the carbs should be sinc'd together perfectly, so make sure you get them correctly adjusted, then leave them alone!

Good luck, post back on what you find out.

The only neutral switch you have is in the control box, from looking at parts book, it may not let you start the motor if out of neutral, and yes if it's stuck in the neutral position when shifting into forward it might limit rpms if it thinks its still in neutral?

Let us know something.

[Murray]

For a service manual in pdf form for $12US I have just the place for you. The owners of this group have it restricted so bad I can’t give you a self link but if you take the bold letters and fixer. After the last bold letter you need a period, after the period you then need the first 3 letters of the next word complete. Hope this make sense

[Importkillerrr]

First off, removing the oil system will cause complications because the system is connected to the computer. I personally would not remove the oil system. The Suzuki tach is also tied to the computer, the lights are for water temps and yes the ones in a line are for oil level. As long as you're using the same amount of oil for so much gas burned, you should stick with it.

Four blade props are for heavy boats, bass boats (unless long and too heavy for the dt150) generally will run 3 blades. If you want higher speeds you can try a good 2 blade prop, but you will lose the jump out of the hole with 2 blades, they start off slow but start grabbing about 20-30 mph then they go. The 3 blade is the best all around prop, but it too needs to be sized correctly for your boat and motor.
And also the can
You should never change any of the linkage adjustments! All the carbs should be sinc'd together perfectly, so make sure you get them correctly adjusted, then leave them alone!

Good luck, post back on what you find out.

The only neutral switch you have is in the control box, from looking at parts book, it may not let you start the motor if out of neutral, and yes if it's stuck in the neutral position when shifting into forward it might limit rpms if it thinks its still in neutral?

Let us know something.

I'll leave the oil system alone as it's functioning as it should. As far as the carb linkage, they are still in sync.

The linkage I adjusted is from the control box to the cam, looking at online schematics I think it's called the throttle cam or the throttle drum. So when I adjusted the turnbuckle going from this cam to the shift shaft it rotated the cam which threw off the adjustment of the throttle cable coming from the control box and also the linkage from the cam to the bottom carb. The turnbuckles and linkage that keep the carbs in sync haven't been touched.

So basically after installing the lower unit, it wouldn't go into forward, I then remembered that the old lower unit was so far out that I had to adjust it further and further to get it to shift into gear before it finally completely went kaput so with this newer lower unit it makes sense that I had to adjust it back to where it was to get the thing to shift correctly. I adjusted the shift linkage so that the control box would actually put the lower unit into gear, that in effect threw off the throttle linkage adjustment for the cable coming from the control box so that when the box was at 50% throttle the carbs were at at wot. The carbs are still as it was from the factory in 1991 and are in perfect sync. Once I readjusted the control box cable and the throttle rod, the control box is now in sync with the carbs and I have a full range of acceleration like I should.

My last 2 bass boats were a gambler and a bullet that both ran into 90's, the gambler was gps'd at 93 and the bullet 96. I've always had performance Bass boats that ran big 4 blade wheels that were custom cupped and pitched and would get every last mph out of the boat with hydraulic jack plates and custom built hydrofoils and low water nose cones, all the performance goodies!! Going to a older cookie cutter boat with a lower HP engine is a new thing for me so please excuse my ignorance. The 4 blade I had on the boat last week was actually the prop I had built from Nichols racing for my gambler which had a 225 Merc so thinking it would work on an older 150 was stupid on my part. Actually I wasn't even thinking about the prop until we were out on the lake, I was just so excited to have a working boat again that I overlooked things.... Guess even guys that have run high performance Bass boats for 20 years can make rookie moves lol.

When you say that the stock tach works with the computer, do you mean it cannot be changed or the engine will have issues? The Suzuki tach I have is a normal tach with 3 poles on the back, ground, power and ignition. That's it, there's nothing else on the gauge but a hole for a little light bulb and the setting dial with numbers 1-5. This one was set to 5 when I got it and I never changed it as it seems to read correctly.

I also don't think it has anything to do with a neutral safety switch. The switch in the control box works as it should, can't start the engine unless it's firmly in neutral. If it's clicked into forward or reverse it will not crank so I think that's working.

Also Murray, I don't know how to quote two different guys in one reply so I hope you read this. Thank you for the link...I completely understand your code

[Murray]

Stock Tachometer, from a DF90A 2009, yours would be similar or the same.

IMG_6294.jpeg

[Importkillerrr]

Stock Tachometer, from a DF90A 2009, yours would be similar or the same.

IMG_6294.jpeg

Hmmm.....That's not my tach. My tachometer is only a needle gauge, there isn't a check engine light or anything else on it. I've read a few posts on here and other forums about the tach after solar mentioned that changing it would effect the way the engine operated. My tach is only an old school rounds gauge with numbers and a sweeping needle. The back has no wires or plug on it. There are 3 threaded bolts coming out of the rear of the gauge with washers and a nut on each. One is labeled G and goes to ground. One is labeled I and goes to ignition power and one is labeled S and goes to the tach feed. There letters might be wrong, it's been a long day and I can't remember.... Sorry.

[Murray]

I can’t say what a 1992 2 stroke would have had for a OEM tachometer but I would ASSUME it would be something similar to the one above. My OEM tachometer also displays fault code’s should one of the sensors, or the engine, acts up. The link below is a list of fault codes.

https://www.suzukioutboardforum.com/...agnostic-codes

Last season my regulator/rectifier started acting up, it kicked out an overcharging code, I checked the voltage going to the battery and it was spiking at 17 volts. Likely saved me a battery.

[Importkillerrr]

I can’t say what a 1992 2 stroke would have had for a OEM tachometer but I would ASSUME it would be something similar to the one above. My OEM tachometer also displays fault code’s should one of the sensors, or the engine, acts up. The link below is a list of fault codes.

https://www.suzukioutboardforum.com/...agnostic-codes

Last season my regulator/rectifier started acting up, it kicked out an overcharging code, I checked the voltage going to the battery and it was spiking at 17 volts. Likely saved me a battery.

That would be cool... If I had one

After researching last night it looks like the tach in my boat isn't a Suzuki but I think it's a ranger gauge. I've seen it in pictures online of other older rangers that had mercs, Evinrude's and Suzuki's on the backs. Like I said earlier, they did install a Suzuki engine monitor gauge that covers oil level/pressure, water temp/flow, rev limiter and a check engine light. I'll try to attach pics of the tach and the Suzuki monitor gauge.

After further investigation of parts schematics online it seems that the water lights are not water temp sensors but are in fact water flow sensors, left light for the left head, right light for the right head. That makes more sense as the lights and the alarms stop notifying as soon as water starts to flow out of the tell tale. There's no way it could be a temp alarm as it stops beeping too soon for there to be any heat in the head yet. Upon looking it up though, it is definitely a flow sensor, that one had me confused for awhile

[Importkillerrr]

So after looking and looking one place has the water sensors listed as flow while others have it listed as temp. Are they maybe a dual mode sensor, flow and temp? My concern is that my alarm sounds and the water lights light up red on the gauge at every ignition key cycle but they turn off as soon as the water starts to flow out off the tell tale. The heads are still bone cold so I can't see how it can be temp and not flow at that point. If they are temp maybe mine are faulty because everything is shutting off (alarms) before there is any temp!?!? Just like a stuck open thermostat isn't great to run on your truck even though the engine will never overheat... It also will never get up to temp either which isn't a good thing.