suzuki dt25 doesn't reach full rpm or speed at full throttle .

[jkirch]

I just had my first dt25 die on my after 20 years . I found another to replace it but it has been sitting for 7 years . I got it running and it sounds and feels better than my old one at low rpms . When I go to wot it will slowly get to about 4400 rpm and 10-12 mph. My old motor with the same prop would get 5700-5800 and 22-24 mph. I have hears that the third cylinder is only used for higher rpms . Could something cause it to not kick in ? I am a novice at wrenching on motors but I have been doing a lot of research and feel comfortable with tackling this myself . I have already cleaned and rebuilt the carbs ,fuel pump, and water pump . Does anyone have insight to my problems ?

[R. Reggae]

I have a friend with the same problem as jkirch. New 25 hp 4 stroke, will not reach optimum rpm. Reaches 4200-4500 rpm, Dingy will not plane off. Dealer changed prop saying they thought it was too big and not reaching high rpms. Did not help. Let me know what you find out.

[Solarman]

Jkirch, what year motor? First off, all three cylinders always work together, at all speeds. Unless the motor goes into safe mode, then you might have one cylinder drop out.
I would first check if all cylinders are firing by pulling plug wires, or using a timing light on each cylinder.
When cleaning carbs, did you soak them (each carb) in a carb cleaner solution for long enough, and did you blow each passage (all the litte holes in carb body) with plenty of compressed air? Each passage lets air, or fuel flow to cylinders (NEVER use wires/or anything else to clean jets or passages, only air pressure)?
when rebuilding each carb, the float level must be set just right. If float level is too low, that carb will run low on fuel at high speeds. If float is set too high, that carb will overfill (gas might run out of the throat of the carb, and flood that cylinder). And each carbs "low speed mixture screw" should be set exactly the same (per manual) for all three carbs.
If all three carbs linkages have not been changed (are all working identically) and all three cylinders are firing, and have the same/ proper compression, then the fuel to oil ratio (50:1) should make your motor run just like it should.

If not post back and let us know. Good luck.

R. Reggae, to start with, you have a 4 stroke motor with valves, nothing like a 2 stroke motor.
please start your own thread if you need some help?

[jkirch]

I switched out the throttle valve sensor from my old motor and now it runs as good as new. I read that they can be fickle or fragile . How do I know if the old one is bad or just needs fine tuning.

[Solarman]

Jkirch, the TVS changes the timing of the motor for different throttle valve positions, they can go bad. If your motor is running again after swapping that part with another, I would probably say the old one isn't good? Generally, the gear counting coil (counts the teeth of the flywheel), is usually the first sensor to start giving problems. So it's good you have a spare motor for parts, most parts for 2 strokes are not being made, as they're trying to phase them out.

Glad your motor is running again for you. Happy New Year.

Post back, if you have any other problems. Good luck.