Help Diagnosing engine issue

[cubaniche]

Hi guys. First time post. Bought an LS2000 that had both engines replaced about a year ago. After a little TLC (replacing oil lines, performing compression checks which showed 118-120 on all cylinders, replacing fuel filters, new plugs, installed primers into the fuel lines to manually prime before start, took exhaust apart and broke it down to the three parts and cleaned all the gunk and buildup that was in there and put back together with new oem gaskets, and a few other maintenance items on the boat) both engines start and run. Cooling is great.

The issue I have is with the starboard engine. Its not as smooth as the port and doesnt rev as high as port. Not going to go into too much detail there to prevent mis-diagnosis. Basically, I think I've confirmed that the #3 cylinder isn't achieving combustion. I thought it was spark at first but testing that showd spark arcing if I grounded the spark plug to metal while turning over the engine. I also tried disconnecting the boot from the plug as the engine ran and there was zero discernable change in sound or rpm or anything but if I pulled one of the other two boots off a cylinder (1 or 2) it was definitely noticeable. If I put one of the other wires from 1 or 2 on 3, nothing happens. I started the engine on one cylinder, first on 1 and then on 2 only but when trying 3 only, all it does is turn over. Using one of the other cylinder plug wires results in the same no start using only #3.

Pulled the plug from #3 and its sparkling new, no steel of fuel or anything. The other two, while only a month or so old, have a nice brown/black tinge to them. This is when I tested spark btw and confirmed #3 has spark. If I adjust the low end screw the engine does not respond in any way but if I adjust one of the other two I can get the engine to change rpm.

So, my question to you all is, does this confirm that fuel isn't reaching this cylinder and if so does that make this a carb issue specific to this cylinder and carb? Is there an "easy" way to test this? Like, is it OK to pop the flame arrestor cover off and dribble fuel down into the carb with the oil that dribbles down or would that cause some sort of backfire? I just want to see if I get fuel in there, does the engine respond in any way, and if so, then I know its that carb.

Any help is appreciated!

 

[cubaniche]

Quick update. I started the engine with the arrestor open and dribbled some fuel into the carb, and the engine responded with rpm increase. So, I think that confirms it for me.

Since this carb is the one closest to the rear of the boat, I was able to remove the metal plate to expose the black diaphragm. Fuel spilled out. What does that mean? That fuel is making it in but not through the carb to the jets? Or clogged jet? I've never worked on these before so its all new to me.

 

[rkluck]

I am not familiar with these boats but I do tinker with engines in general. From what you described you are not getting fuel to that cylinder. It sounds like you have checked and fuel is reaching the carb. From what you are describing I assume you have a carb for each cylinder. If that is the case I would rebuild/clean that carb. If you have gas in the bowl then either the carb it is not pumping the gas or the jet(s) is clogged (gummed up).

 

[cubaniche]

I am not familiar with these boats but I do tinker with engines in general. From what you described you are not getting fuel to that cylinder. It sounds like you have checked and fuel is reaching the carb. From what you are describing I assume you have a carb for each cylinder. If that is the case I would rebuild/clean that carb. If you have gas in the bowl then either the carb it is not pumping the gas or the jet(s) is clogged (gummed up).

Thanks for the reply. Yeah I'm familiarizing myself with these carbs. I ordered genuine mikuni rebuild kits, and new gaskets. I didn't order new needles and seats because from what I've read, those technically shouldn't need replacing. We'll see once I pull it apart.

Hopefully the rebuild goes well. I'm mechanically inclined but like to be well informed going into something I haven't tackled before.

 

[the MfM]

Have you checked compression on the #3 cylinder recently?

Each of the three carbs have an impulse line to the crankcase. They are hard to see but if it’s not connected (rotted, loose etc.) the #3 carb won’t be pumping fuel.

Good luck. Probably worth rebuilding the carbs if you don’t know the history of them.

 

[cubaniche]

Have you checked compression on the #3 cylinder recently?

Each of the three carbs have an impulse line to the crankcase. They are hard to see but if it’s not connected (rotted, loose etc.) the #3 carb won’t be pumping fuel.

Good luck. Probably worth rebuilding the carbs if you don’t know the history of them.

Yep. New engine, compression is at 118 to 120 acros all three. The vacuum lines are all connected. I got the carb off. Took the needle side apart, the one with the black diaphragm in it, and pulled the seat and needle. The seat was completely plugged up on the other end. Rebuilt kit is on its way. I'll tear more into it tomorrow, see what else I find.

 

[the MfM]

Well that would do it. If you rebuild all the carbs you’ll probably find you don’t need the primers you just installed. I did mine last year and it went from a PIA to start the boat every weekend to the engines would fire the first or second time turning the key.

As an aside, it sounds like keeping the oil injection system in place likely saved your #3 cylinder? A clogged carb running premix could have been worse.

 

[dabomb6608]

Well that would do it. If you rebuild all the carbs you’ll probably find you don’t need the primers you just installed. I did mine last year and it went from a PIA to start the boat every weekend to the engines would fire the first or second time turning the key.

As an aside, it sounds like keeping the oil injection system in place likely saved your #3 cylinder? A clogged carb running premix could have been worse.

Exactly what he said times 100!

Definitely go ahead and rebuild all carbs and not just that one. I stay away from primer kits because a 2 stroke ski or boat that is hard to start means its due for carb rebuilds. The primer kits are just a cover up to the real issues...

And the oil injection system saved the day for you for sure. When running premix you risk any 6 of those fuel pumps to fail and no longer supply oil or fuel to that cylinder/crank bearing.

 

[cubaniche]

Thanks. Yeah compression is good. Rebuilt carbs. Reinstalled everything with new gaskets all around (both intake manifold and each carb to mounting plate). Fired right up. Still won't go over 4k rpm. I tested the engine on just the #3 to make sure and it runs on that cylinder alone now, as opposed to before when it didn't leading to the no fuel diagnosis. So I know there's fuel, oil, compression, etc now.

The port engine has no problems going past 4k on the hose out of the water. I adjusted the hi/lo screws on the STB engine carbs after rebuild as per the manual on all three. I really really don't think its the temp sensor but I'm going to swap the port sensor to stbd and test again.
Anything else anyone else has to offer in way of troubleshooting, I'm open for ideas.

 

[the MfM]

If that’s not it you might check that the pump liner isn’t binding with the impeller.

 

[cubaniche]

If that’s not it you might check that the pump liner isn’t binding with the impeller.

I checked both pumps before, and replaced both intermediate bearing assemblies (not rebuilt, new, $$$). As for the impeller and liner, these don't have that. Its factory yamaha bare metal housings, no liners. With the engines running, I'm not seeing any wobble or impeller contact and no more noise than you would normally hear from the pump units out of the water. I would think if that was the problem, the RPM limit wouldn't be so precise and consistently at 4k. Wouldn't it be less consistent and vary more (sometimes 3k sometimes 4, sometimes more or less) if it were a mechanical issue like 'wobble' or impeller contact?

 

[the MfM]

Doesn’t sound like it’s the problem but the wear ring/housing has been known to “swell” and push against the impeller.

Behind the helm there are a bunch of quick connect electrical connectors, one set for each engine. You can swap port and starboard and see if the RPMs change. Maybe just a problem with the tach.

 

[the MfM]

@4x15mph any suggestions?

 

[4x15mph]

You could swap carb racks to see if the problem follows the rack. This would cut the problem in half (fuel). I also like the idea of checking the temp sensor first. That would be the easiest

if it’s not the carbs, you should consider new plug wires and I think jetskisolutions can help there.

 

[cubaniche]

Upon rebuilding the carbs with the mikuni kits and testing the boat out on the water, I noticed I now have dribbling fuel from the venturi on all 3 carbs which tells me I used the wrong spring. The kits came with two, a shorter one and a longer one. I used the shorter one as it seemed to resemble the one that came out, the most.

However, upon researching this, I found that two causes are: 1) spring is too weak so popoff pressure is way down from where it should be so it just dribbles fuel from the venturi, which I guess is where the high needle fuel flows from, or 2) the high is open too far, or 3) the return line is clogged in some way.

There was no issue with fueling like this before, common sense tells me its popoff pressure due using the wrong spring. I didnt touch the carbs in any other way. Im going to replace the springs with the taller one to see what happens. I don't have a tester, and I already took the carbs off so I'm just going to do that for now. I also was able to test this by closing the hi on the back end (PTO?) almost all the way and was still seeing fuel dribble when I ran the engine for a few seconds. So Im positive its the spring. But I'm not an expert and don't fully understand the workings that go into popoff pressure other than the spring weight.

I read the springs are slightly different colors (gold, silver, dull) but I can't tell for the life of me. From my understanding popoff should be in the 50s for these engines in these boats.

As for the 4k limit thing, I'm going to swap the sensor over from the port side to see what happens. I also ordered new bearing housing, bearing kits for both intermediate and cone, new impeller and new impeller housing. After double checking, the impeller does sound like its scrapping the housing. Its definitely louder than the port side.

I took it apart again but like last time, I couldn't get the shaft to budge free from the shaft coupler (even with a ratchet strap and I'm not willing to try the pull it off with a truck method and risk damaging the transom in some way) so Im just going to cut my losses and cut the shaft in half to pull it out from the bearing side. The bearing housing needs to go anyways as the rubber isolator the shaft coupler passes through that the bearings sit it is loose.

We'll see how it goes. Parts arrive in a few days. For now, getting to fixing this carb situation.

 

[4x15mph]

We'll see how it goes. Parts arrive in a few days. For now, getting to fixing this carb situation.

You are digging in deep and I had all of the same issues at one point or another. With the carbs, I rebuilt them myself with non mikuni kits, then mikuni kits, and then one rack leaked like yours. I threw the towel in and sent my one rack of carbs to jetskisolutions. They rebuilt and restored them to like new! Sort of expensive but not really when you figure how much the parts are, time, and the cost to redo these. You have more experience than me with the popoff, springs, etc. I have attached a few references manual that may help

I also had to cut off an impeller shaft. Actually I had someone else changing out the impeller and they ended up cutting it. I installed all new impeller housings (replaceable inserts), impellers, and even a jet pump bucket. Expensive when all that was said and done.

Keep us posted and I will be watching for your updates!

 

[the MfM]

Here’s the thread when I was rebuilding the carbs on mine.

https://jetboaters.net/threads/carb-pop-off-pressure.22114/

The last person to rebuild mine used extra gaskets that weren’t required and some in the wrong order I think...with the mikuni kits there is an extra insert in the instructions for the early vs late versions of the carb. We have the late version.

I set everything back to stock and ~50-55 pop off.

 

[dabomb6608]

Generally it is best to reuse the old springs when rebuilding these carbs. BUT that doesn't hold true when you don't know history of the ski/boat and they could have been changed out previously by other owners.

Point in case, I've got a Exciter 135 at the shop currently that I am replacing shift cable on and rebuilding carbs. Whoever rebuilt the carbs last used Non-Genuine kits and also replaced the springs. I ended up having to replace the springs with the lighter (grams) of the two that come in the kits because pop off was WAY high (higher then my pop off gauge even reads). Now pop off is right around 50-55psi.

On my LS2000 this year I rebuilt carbs on port motor and followed groupk's suggestion on switching to the 115 gram springs to reduce dribbling/loading up on long no-wake zones. I ran it for the first time this season 2 Saturdays ago. That motor is very crisp and responsive now regardless of time spent idling. I turned out low speed and high speed screws 1/8 turn from factory settings to help compensate for the higher pop off. I plan to make the same change to the starboard motor before the next outing.

 

[cubaniche]

Keep us posted and I will be watching for your updates!

Thanks for the reply and info! The boat had been neglected for sure. I only paid $1500 for it so fixing it up was part of the plan.

Here’s the thread when I was rebuilding the carbs on mine.

https://jetboaters.net/threads/carb-pop-off-pressure.22114/

The last person to rebuild mine used extra gaskets that weren’t required and some in the wrong order I think...with the mikuni kits there is an extra insert in the instructions for the early vs late versions of the carb. We have the late version.

I set everything back to stock and ~50-55 pop off.

Yup! I saw that in the Mikuni PDF and instruction sheet included in the kits. When I took mine apart, I just followed what I had seen in videos online specific to the LS/LX rebuild and the carbs themselves that all used the one gasket and plastic sheet, and not 2 like the sheet showed for the 44. I also read that the kits going out by Mikuni lately, the higher gram spring thats supposed to be gold, is actually silver now. Which makes sense because there were no gold springs in the kits I purchased for the Super BN carbs.

Replaced the springs last night. Will reinstall today with the hi/low settings suggested in the manual and go from there. Thanks or the reply!

Generally it is best to reuse the old springs when rebuilding these carbs. BUT that doesn't hold true when you don't know history of the ski/boat and they could have been changed out previously by other owners.

Point in case, I've got a Exciter 135 at the shop currently that I am replacing shift cable on and rebuilding carbs. Whoever rebuilt the carbs last used Non-Genuine kits and also replaced the springs. I ended up having to replace the springs with the lighter (grams) of the two that come in the kits because pop off was WAY high (higher then my pop off gauge even reads). Now pop off is right around 50-55psi.

On my LS2000 this year I rebuilt carbs on port motor and followed groupk's suggestion on switching to the 115 gram springs to reduce dribbling/loading up on long no-wake zones. I ran it for the first time this season 2 Saturdays ago. That motor is very crisp and responsive now regardless of time spent idling. I turned out low speed and high speed screws 1/8 turn from factory settings to help compensate for the higher pop off. I plan to make the same change to the starboard motor before the next outing.

Exactly. I don't know the history except for what I was told by the previous owner. It supposedly had two rebuilt engines. Checking compression proved that to be true as all 6 come up at 118-120. But they used all the old stuff to bolt back on to them. Both shift cables broke at the linkage at the buckets after the first few times I tried to actuate them. So those are new too and shift smoothly.

The port engine is good and happy. This stbd engine has been the headache, and it's the one that has a whole new long block. The oi lines were pinched under the flame arrestor compartment, lines were leaking at the oil pump, fuel filter had rubbed a hole into itself and was leaking, the #3 carb was clogged and not getting fuel, etc etc. Im so happy i didn't lose this engine during all the troubleshooting.

I appreciate all the comments and helpful/knowledgeable suggestions.

After all the mechanical work and getting the boat 90% of the way there to running right on the water, i finally tackled the visuals department:

 

[dabomb6608]

Definitely a clean boat! You did slightly better on price then I did when I bought mine. But mine came with a blown motor lol.