No more vroom vroom?

[Project_Mayhem]

I've been chasing my tail on this issue since I launched. My little two stroke inboard engine doesn't have any power and the RPM's are far lower than they should be. RPM's vary a bit at idle but it otherwise runs ok at low speeds. It starts as expected as well. I posted this on another forum but I think a set of fresh eyes would help.

Symptoms:
-Engine typically lacks RPMs. Top speed is 2200-2800. Engine is rated for 3700
-Severely lacking power. I get a top speed of about 2-3kts
-Engine is more likely to exhibit issues after it's been running for a little bit
-Cooling water is lacking a bit. I may have received an incorrect part as there are multiple part numbers
-Varying RPM's at times with occasional surging. I did find a vacuum leak yesterday

I did some testing and inspection this week including:
-Stator/trigger testing and disconnected the rectifier per CDI troubleshooting guide
-Verified engine is running on both cylinders by disconnecting one coil at a time. Engine nearly died both times
-Tested fuel pressure after the mechanical pump. A little hard to read the gauge since it was made for fuel injected engines but it looked like it was putting out 2.5psi at mid to high RPM's
-Inspected the leaf valves. They looked beautiful. You could tell me that they are new, old stock and I wouldn't doubt it. I'm guessing it was replaced during an engine rebuild back in 2003
-When I removed the leaf plate, I discovered that one of the vacuum lines was a bit too big for the nipple so there's a small vacuum leak. I'll get some new hose

To recap, I did the following prior to this most recent work:
-Rebuilt carb. I adjusted the float so it was level with the carb body when held upside down. With the float hanging (body right side up), I measured 1.55". Specs are different depending on which service manual you look at. Since I have the carb out at the moment, I'll try adjusting it to 1-1/8" per my printed manual
-New power pack
-New coils
-Test tank with clear tubing and bulb
-Attempted to spray for leaks. I don't think this was very successful since the can sprayed a stream. I can try this again with a spray bottle and the silencer/air box attached
-Swapped low speed mixture needle with a used one from a reputable source
-New plugs at the beginning of the season. I did not gap them. I will check them
-Check head and/or exhaust temps in the rare case when it does have power

Up next I plan on doing a compression test, checking plug gaps, fresh gas in a test tank, replace vacuum line, possibly spray for more leaks. Is it possible that the head gasket is holding at lower RPM's and leaking at higher? Aside from that I'm running out of ideas.

 

[Timm R Oday25]

Did you replace any of the carb needles ? Sounds like ,from here anyway a carb issue . The carb body may not be snug against the reed valve plenum . Vacuum leak possibility number 1 . It sounds as if the motor is starving for fuel . A worn main jet will cause the conditons you describe .
worn sliding components inside the carb are also suspect.

 

[jssailem]

Sorry, I do not have much experience with your gas engine.

My troubleshooting technique is to identify a timeline of events (changes I have made to the system) when stumped. Then, I identify when on the timeline the change occurred. At this point, I look for the simplest answer that identifies the change and attempt to reverse the change (Ockham's Razor philosophy).

 

[danooxnard]

Make sure the exhaust path is clear and not plugged with carbon or old marine growth.
Best of Luck Dano

 

[Project_Mayhem]

Did you replace any of the carb needles ? Sounds like ,from here anyway a carb issue . The carb body may not be snug against the reed valve plenum . Vacuum leak possibility number 1 . It sounds as if the motor is starving for fuel . A worn main jet will cause the conditons you describe .
worn sliding components inside the carb are also suspect.

I replaced the low speed needle with a used one from a reputable source. No change in performance. When I rebuilt the carb, I pulled it out to replace the seal. I found that the needle was a bit bent. I straightened it out as best I could. Still no change.

I currently have the intake "manifold" off after I inspected the valves. I'll remove the old carb gasket and replace it with a new one. Who knows how old the current one is.

Multiple people have said that the engine is starving but the strange thing is that the plugs are usually soaked like they always have been on this motor. It also bogs down instead of improving when I spray starter fluid in the intake which leads me to believe that it's not running rich but perhaps that's way too much fuel for the engine. The specs state that the engine should have 1.5psi min at WOT. I'm seeing 2.5psi before WOT. This measurement was taken between the mechanical pump and the carb

Sorry, I do not have much experience with your gas engine.

My troubleshooting technique is to identify a timeline of events (changes I have made to the system) when stumped. Then, I identify when on the timeline the change occurred. At this point, I look for the simplest answer that identifies the change and attempt to reverse the change (Ockham's Razor philosophy).

Make sure the exhaust path is clear and not plugged with carbon or old marine growth.
Best of Luck Dano

 

[rgranger]

Make sure the exhaust path is clear and not plugged with carbon or old marine growth.
Best of Luck Dano

... or mud daubers

... that is one chase that took me all day ....

 

[higgs]

You don't say how little your engine is or its brand. If you have been using ethanol gas (premium now has ethanol) it is very possible that fuel has clogged ports. You should be using Rec 90 gas. Small engine carbs have very small ports and sometimes the answer is a new carb. Also be sure your connections at the engine and tank are not letting air in. How old are those connectors?

 

[Project_Mayhem]

... or mud daubers

... that is one chase that took me all day ....

I was considering disconnecting the exhaust before the muffler and sticking the (new) hose in a metal bucket. I can also put an inspection camera in there. If it was the exhaust, wouldn't it consistently have low RPMs?

You don't say how little your engine is or its brand. If you have been using ethanol gas (premium now has ethanol) it is very possible that fuel has clogged ports. You should be using Rec 90 gas. Small engine carbs have very small ports and sometimes the answer is a new carb. Also be sure your connections at the engine and tank are not letting air in. How old are those connectors?

-It's the notorious OMC Saildrive. It's a detuned 25hp power head on a hull mounted leg. It's a high torque 15hp motor
-I only use ethanol free from the marina. It currently has some from the yard that came out of a 55 gallon drum. I'm not sure how long those drums sit before they are used up. I always use a stabilizer during storage. I plan on running it off of a test tank when I fill up on gas soon
-New carbs aren't available. Only used and those are hard to come by
-Fuel lines are all new. I also tested with a test tank.

Is there any reasonable way to test to see if the engine is running too rich or too lean? I think that would be a good way to see what direction to head

 

[Timm R Oday25]

Here the color of your sparkplugs is your friend . Install new ones . Run for 10 minutes at full throttle , or as close to it as you can get . Shut off the motor quickly . Allow the engine to cool off . Pull the plugs and check the color

 

[Project_Mayhem]

Here the color of your sparkplugs is your friend . Install new ones . Run for 10 minutes at full throttle , or as close to it as you can get . Shut off the motor quickly . Allow the engine to cool off . Pull the plugs and check the color

In gear or neutral?

 

[kappykaplan]

In gear or neutral?

I'd want a load on the engine at full throttle, so in gear.

 

[Project_Mayhem]

I'd want a load on the engine at full throttle, so in gear.

Got it. That's going to be limited to about 2200RPM due the current issue at hand. I'll do in and out of gear at WOT

 

[kappykaplan]

I'll do in and out of gear at WOT

That will be hard on the transmission, etc.

 

[Project_Mayhem]

Engine is still in pieces but I did manage to find a used carb. Next up will be to put the motor back together (3/4 of this engine is like that last PITA spark plug on a cargo van. Unnecessarily difficult at every turn), a compression test, adjust float on current carb, rebuild the new carb with a Chinese kit as a test. Is air in a can powerful enough to blow out a carb? A compressor is a bit cumbersome on a dinghy

 

[Crazy Dave Condon]

What model and manufacturer

 

[Project_Mayhem]

What model and manufacturer

OMC Saildrive. Essentially a 25hp power head tuned down to a high torque 15hp. I got the new carb. I'm hoping to try it out tomorrow

 

[Crazy Dave Condon]

Thank you for sharing