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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 14483
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have a 70hp , 2003 engine and it hesitates when you give

Customer Question

I have a 70hp , 2003 engine and it hesitates when you give it full throttle. it also bogs down when you go to drive the boat up onto the boat trailer. have just installed a water separator and cleaned the three carbs. adjusted carbs. iaw tech, manual. any ideas?
Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.
Hello my name is ***** ***** am I speaking with?
Is this a 2 or a 4 stroke engine, can I get model number please.
Next, how old is the fuel?
When was the last time it ran correctly?
Has spark and compression testing been done yet?
Customer: replied 1 year ago.
2 stroke 6h3 70 t l r b 2003yr
day old fuel. ran good one month ago. had water in carbs. removed and cleaned. used clean 6-gallon tank with new fuel. still had hesitation. no power to push boat on plugs. compression, 120, 115, 112.
Expert:  Jason replied 1 year ago.
Hi Henry. Have you done a spark output test with either a timing light, or an adjustable gap spark tester, do see if it was sparking on all 3?
Customer: replied 1 year ago.
all three cylinders show spark with a tester. they also show fire when the plug is removed and held against ground. Could it be that the plug wires are breaking down under a load?
Expert:  Jason replied 1 year ago.
It's possible. But let me ask you this. Is it just "bogging" down, or does it feel like it's dropping a cylinder?
Customer: replied 1 year ago.
when i put the boat on the trailer its bogging down at full speed ahead. .
Expert:  Jason replied 1 year ago.
Will the engine eventually make full power? What kind of RPMS are you getting with the boat at tops speed?
Customer: replied 1 year ago.
YES 4400 RPM`S
Expert:  Jason replied 1 year ago.
Is that all you get is 4400 rpms at full throttle?
Customer: replied 1 year ago.
Expert:  Jason replied 1 year ago.
The engine should be making 5k to 5500 at full throttle. So something else is wrong here. Tell me how you cleaned the carbs. Did you remove them from the engine and completely dissasemble them?
Customer: replied 1 year ago.
this engine has always run at 4400 rpms. 34 mph on my 15 ft. boat. in fact the first time I took the carbs. apart completely I went from 29 mph to 34 mph. the rpms didn`t change, 4400 rpms. I completely disassemble the carbs, blow them out and then spray all the holes out with carburetor cleaner, then reblow it out with air.
Expert:  Jason replied 1 year ago.
Do this next as a test. Get another fuel tank, a portable tank, and run the engine off of that and see if there is a difference. If there is a fuel supply issue and the engine is starving for fuel that would do it. Let me know what happens.
Customer: replied 1 year ago.
will do.
Expert:  Jason replied 1 year ago.
Your RPMS really should be higher than the 4400, so let me know what happens, if the rpms even come up by a little bit when running off of the auxillary fuel supply.
Customer: replied 1 year ago.
Jason, found one of the problems. I adjusted the timing linkage and the rpm`s went up to 5000 rpms. can`t get it higher. adjusted linkage numerous times with no results. adjusted carburetors needle valve in and out with no increase in rpm`s.
what now ?
Expert:  Jason replied 1 year ago.
5K is within spec. Let me ask you this, have you ever personally seen this engine run any higher than that?
Customer: replied 1 year ago.
can`t remember. tech. manual says 54 to 5500 rpm`s
Expert:  Jason replied 1 year ago.
Good morning. The reason why I had asked if you have ever seen it run any higher is because I wonder if you also have the wrong propeller. 5k is within spec but it is on the low end. 5500 would be ideal, and that can be fixed by a prop change. Does that make sense?

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