Yamaha LS 2000 (Port Engine Stall)

[Williamsjetboat]

Purchased my first jet boat a month ago and have been trying to figure this out since I first took it out

Starboard motor starts well with little to no choke, Port engine needs choke out whole way and needs gas to start, much harder to start then port motor. Once out with both motors running right one will stall almost like being shut off, starts right back up but will repeat problem any time it’s given gas or sits in idle more then 1 minute. 2 out of 3 sparks plugs will foul after trying to restart, problem with spark plugs seems to repeat itself as I’ve changed them 3 times. Original owner put an extra fuel pump to this motor because he had similar problem as he thinks it was starving for fuel but I eliminated this fuel pump after carb rebuild because I felt it was no longer needed

-What I’ve already done to try and fix
1. Changed spark plugs. Spark test came back good
2.Compression check (60 to 1 all cylinders) matches starboard engine
3. Rebuilt carbs
4. New fuel and oil lines/filters
5.New coil packs (All 3)

Really lost at this point and any tips or ideas are appreciated, next up on list to change is to run a hotter spark plug gonna go from an 8 to a 10 and try and switch ignition kill switches on back by cleanout ports
View attachment 99862View attachment 99864

 

[4x15mph]

Are you having problems with both engines? It can be a lot easier to diagnose if it is one engine since you can swap out different parts ....

1) I doubt it is spark plugs and I would not change them again. Use the type called for in the manual (BR8HES I think but double check).
2) If compression is 60 Psi, that is too low or your gauge isn't accurate. You want it to be the same across all cylinders and you should look for 100+ with 120 being ideal
3) who rebuilt the carbs? OEM Mikuni kits or other? Carbs are complicated for these with the pop off pressure, needles, springs, etc. Given your problems, it sounds like a possible fuel problem = carbs, filters, lines.
4) What kind of fuel filter did you use? Are the installed in the right direction? Are all pulse lines connected to the carbs and have you checked for leaks
5) Did you only do new coil packs for one engine?

 

[Gym]

Agree 60 psi compression seems pretty low. Did you take this out for a water test with the previous owner?

 

[the MfM]

He said 60:1 compression ratio?... not sure how he’s calculating that

Did the previous owner solve the problem with the extra fuel pump. Was it electric? Condition of impulse lines?

 

[Williamsjetboat]

Are you having problems with both engines? It can be a lot easier to diagnose if it is one engine since you can swap out different parts ....

1) I doubt it is spark plugs and I would not change them again. Use the type called for in the manual (BR8HES I think but double check).
2) If compression is 60 Psi, that is too low or your gauge isn't accurate. You want it to be the same across all cylinders and you should look for 100+ with 120 being ideal
3) who rebuilt the carbs? OEM Mikuni kits or other? Carbs are complicated for these with the pop off pressure, needles, springs, etc. Given your problems, it sounds like a possible fuel problem = carbs, filters, lines.
4) What kind of fuel filter did you use? Are the installed in the right direction? Are all pulse lines connected to the carbs and have you checked for leaks
5) Did you only do new coil packs for one engine?

Only having problems with one motor thankfully
1.Spark plugs seem to get fouled quite frequently, more then likely due to over choking while trying to get started (my fault)
2.I thought 60 psi seemed low, but when I ran same test on opposite motor that is running good came back at 60 psi confused me as well
3.Local boat mechanic rebuilt carbs for me using Mikuni triple carb rebuild kit
4.when mechanic rebuilt carbs for me he changed all fuel lines and filters for me not exactly sure what filter he used but I can see fuel is in them and running thru, no leaks have been seen
5.Yes I only replaced coil packs for problem engine

 

[Williamsjetboat]

He said 60:1 compression ratio?... not sure how he’s calculating that

Did the previous owner solve the problem with the extra fuel pump. Was it electric? Condition of impulse lines?

Sorry new to jet boat world and I thought that was ratio, When I ran compression test on all cylinders on port and starboard motor (port is problem motor) it came back 60-65psi for all cylinders, Previous owner had installed extra (ELECTRIC) fuel pump because he said the port (problem motor) was starving for fuel, when I took it to the mechanic he said this was due to carbs being gummed up and after rebuild it was no longer needed, Please elaborate on impulse lines? Any help is appreciated thank you

 

[Williamsjetboat]

Agree 60 psi compression seems pretty low. Did you take this out for a water test with the previous owner?

Sadly no, previous owner was a family friend that told me it needed some carb work but would run good afterwards, I purchased it during a time of much rain in our area and much flooding so unable to take out for water test, I Agree 60-65 psi seemed low to me but starboard motor that is currently running good came back with same results on pressure test so it made me unsure

 

[4x15mph]

1) 1st step is to borrow a different compression gauge so you can get some good readings. I suspect your other gauge is inaccurate since 60 is very low and may not even run. The important part is to have consistent readings across the cylinders but if you have 60 psi, you need to be doing rebuilds. That is beyond low
2) Does the local mechanic have experience with these engines? Are they involved or available to help with the problem given they did all the work and it is not running? If this is a non credentialed mechanic and someone from craigslist, you may not want to go back to them....
3) I don't think this is a spark plug issue. Just use new plugs or keep the new plugs that you put in and address what is probably a fuel issue.
4) who installed the new coil packs? Are they new?

My first step would be compression check. My 2nd step would be to swap the carb racks between the good and bad engine to see if the problem follows the carbs. That would cut your problem in 1/2.

 

[Gym]

He said 60:1 compression ratio?... not sure how he’s calculating that

Did the previous owner solve the problem with the extra fuel pump. Was it electric? Condition of impulse lines?

I don't know of any guage that measures compression as a ratio. I'm sure he meant 60psi.

 

[the MfM]

I don't know of any guage that measures compression as a ratio. I'm sure he meant 60psi.

True, he meant PSI.


I was just making sure he wasn’t trying to do some fancy maths and convert compression PSI from a spark plug gauge to a Ratio. Which can’t be done.

 

[the MfM]

Sorry new to jet boat world and I thought that was ratio, When I ran compression test on all cylinders on port and starboard motor (port is problem motor) it came back 60-65psi for all cylinders, Previous owner had installed extra (ELECTRIC) fuel pump because he said the port (problem motor) was starving for fuel, when I took it to the mechanic he said this was due to carbs being gummed up and after rebuild it was no longer needed, Please elaborate on impulse lines? Any help is appreciated thank you

Impulse lines are what connect the crankcase to the original fuel pumps on the front of each carb. There are three on the 1200 engines.

They transfer the “pulse” or pressure from the engine to the fuel pump diaphragm. If they crack or have a loose connection then the fuel pump won’t pump efficiently. They can also get soft or gummy and collapse when they warm up also limiting fuel flow.