I have a 1983 Yanmar 3GMF in a 1983 Hunter 34. Since I bought the boat three years ago I had to replace a broken throttle. Before and after the replacement the engine has never been able to exceed 2600 rpm's. It runs well, usually just a puff of smoke when it first starts up. I'm wondering if the tach is wrong and will test the hull speed against the GPS soon. If she can't hit hull speed what should I do? Thanks.
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HULL SPEED
Leave it alone, the engine is 21 years old and how many hours, why blow a connecting rod.
Leave it alone, the engine is 21 years old and how many hours, why blow a connecting rod.
Check RPM's
What rpm's are you getting on the motor? Maybe your governor (on the engine throttle lever)is set too low. Or if the mechanic used an incorrect, too short cable, there could be a problem.
What rpm's are you getting on the motor? Maybe your governor (on the engine throttle lever)is set too low. Or if the mechanic used an incorrect, too short cable, there could be a problem.
3200 rpm,s
Mine runs 3200 rpms wide open at 7.7 knots with glass water..... 86 hunter 34 with 3gmf
Mine runs 3200 rpms wide open at 7.7 knots with glass water..... 86 hunter 34 with 3gmf
Throttle cable
Make sure the throttle cable isn't slipping. Is there a lock down screw and clamp on the front of the pedestal. (Merriman pedestal) Is it tight? Try operating the throttle by pushing the throttle at the engine. IF you get full throttle there, then the cable is slipping or is not in the clamp. Take the compass off and you can see down inside pedestal, the fix should be easily seen. Good luck!
Make sure the throttle cable isn't slipping. Is there a lock down screw and clamp on the front of the pedestal. (Merriman pedestal) Is it tight? Try operating the throttle by pushing the throttle at the engine. IF you get full throttle there, then the cable is slipping or is not in the clamp. Take the compass off and you can see down inside pedestal, the fix should be easily seen. Good luck!
Should be able to get more than that
My 3GMF in my H34 will easily run at 7 knots ( by the GPS) on smooth water on the lake ( even at not so smooth)at 2600 rpms onthe tach. I can get up to at least 3200 without a problem. This was withthe 15X12 2 blade. Will see what I can do this summer with the same prop with non slip tips added this winter from Bay Prop- almost worth the money just to havethe prop back all shiny and new looking!
My 3GMF in my H34 will easily run at 7 knots ( by the GPS) on smooth water on the lake ( even at not so smooth)at 2600 rpms onthe tach. I can get up to at least 3200 without a problem. This was withthe 15X12 2 blade. Will see what I can do this summer with the same prop with non slip tips added this winter from Bay Prop- almost worth the money just to havethe prop back all shiny and new looking!
Joe, do the following test to determine...
where the problem is. First warm up the engine in neutral, about five minutes. While still in neutral run the engine up to full throttle or maximum RPM. Check your engine manual for the max rated RPM; it should be around 4,200. If the engine will not reach its maximum RPM in neutral then you need to trouble shoot the problem. With the engine off check your throttle linkage to make sure it runs stop to stop. You may want to check this before you do the above test. If the throttle runs its full course then you might have either an exhaust flow blockage (clogged mixing elbow), air flow blockage (clogged air filter), or fuel flow blockage (dirty fuel filter). Each of these need to be checked. Contact yanmarhelp.com for additional assistance in trouble shooting your problem. Let us know what you find out. Terry
where the problem is. First warm up the engine in neutral, about five minutes. While still in neutral run the engine up to full throttle or maximum RPM. Check your engine manual for the max rated RPM; it should be around 4,200. If the engine will not reach its maximum RPM in neutral then you need to trouble shoot the problem. With the engine off check your throttle linkage to make sure it runs stop to stop. You may want to check this before you do the above test. If the throttle runs its full course then you might have either an exhaust flow blockage (clogged mixing elbow), air flow blockage (clogged air filter), or fuel flow blockage (dirty fuel filter). Each of these need to be checked. Contact yanmarhelp.com for additional assistance in trouble shooting your problem. Let us know what you find out. Terry
Good advice Terry
Two more points. First, his engines' governor setting is 3600rpm max. The other point is, his prop might be over pitched.
Two more points. First, his engines' governor setting is 3600rpm max. The other point is, his prop might be over pitched.
On a 3GM30...
...you should get 3600 rpm WOT. Of course, your normal high rpm's would be 2880 rpm (3600* 80%). So, given that everything is running properly - as Fred said, your prop may be over-pitched (or in need of reconditioning). But, if you are overpitched, you would also be generating black smoke from overloading.
...you should get 3600 rpm WOT. Of course, your normal high rpm's would be 2880 rpm (3600* 80%). So, given that everything is running properly - as Fred said, your prop may be over-pitched (or in need of reconditioning). But, if you are overpitched, you would also be generating black smoke from overloading.
Fred, he could be over propped, but he needs...
to rule out the other issues first before he attempts to change the pitch on his prop. Terry
to rule out the other issues first before he attempts to change the pitch on his prop. Terry
Another simple check
With the engine running and warm, activate one compression release lever at a time to be sure you are running on all three! When you open a valve the engine should shudder, but may not stop, if you lift the lever and it does not shudder, or stall, that cylinder is not firing. We had a carbon build up on the valves in #2 cylinder from the previous owner not running the engine at high enough RPM's. Three diesel mechanics checked it out and could not find the problem. A simple carbon job and valve surfacing solved it.Best of luck!
With the engine running and warm, activate one compression release lever at a time to be sure you are running on all three! When you open a valve the engine should shudder, but may not stop, if you lift the lever and it does not shudder, or stall, that cylinder is not firing. We had a carbon build up on the valves in #2 cylinder from the previous owner not running the engine at high enough RPM's. Three diesel mechanics checked it out and could not find the problem. A simple carbon job and valve surfacing solved it.Best of luck!
Check the exaust
My buddy just had a similar problem. Turned out to be the elbow of the exhaust which had rusted inside and in turned started blocking the free flow of exaust fumes. The mechanic said that it is not all that uncommon of a problem on 20+ year old Hunters. The next symptom will should be that it won't start due to the back pressure. Had the exhaust elbow replaced, runs like a champ.
My buddy just had a similar problem. Turned out to be the elbow of the exhaust which had rusted inside and in turned started blocking the free flow of exaust fumes. The mechanic said that it is not all that uncommon of a problem on 20+ year old Hunters. The next symptom will should be that it won't start due to the back pressure. Had the exhaust elbow replaced, runs like a champ.
Yet another check
All good advice, but my 2gmf had a similar issue two years ago. After an exhaustive search, I found that the uptake in the fuel tank was half blocked off by algae deposits. It wasn't showing up in the filter or separator, and I had algicide additive in the fuel, but it had built up over time, probably with the last owner. It ran fine untill I asked too much of it, then it would lose RPMs. A friend of mine cut his intake so it hangs about 1" above the tank bottom. I just cleaned mine.
All good advice, but my 2gmf had a similar issue two years ago. After an exhaustive search, I found that the uptake in the fuel tank was half blocked off by algae deposits. It wasn't showing up in the filter or separator, and I had algicide additive in the fuel, but it had built up over time, probably with the last owner. It ran fine untill I asked too much of it, then it would lose RPMs. A friend of mine cut his intake so it hangs about 1" above the tank bottom. I just cleaned mine.
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