Suzuki DT55 1985 lack of power after 30 secs of full RPM

geiz

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Aug 27, 2007
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5
Hellow,

We have already 2 years a problem with our Suzuki DT 55 2-stroke engine build in 1985.
At full throttle the engine runs fine and powerfull but after +/- 30 seconds the power / rev. drops down to a lower level (like it runs on 2 - 2 1/2 cylinder). When I release the accelerator to a lower level (1/2 throttle) for 30 seconds and gives full throttle again, it runs fine again for 10 seconds and again the power loss.

When I run the engine at only 1/2 speed, it runs fine for a whole day.

When I run the engine at 3/4 speed, it runs fine for some minutes, but after that it starts pendling between the normal rev./power and lower rev./power. (like it is digital controlled :D)

When I give full throttle, and keeps full throttle, even when the rev./power is going down, after a minute the power goes more down until it almost reaches the idle rev. speed.

The spark plugs and cables are replaced already, the carbs are cleaned several times and look very good, the fuel ball (hand pump) is hard and pushing it during the problems wouln't help, the fuel tank and lines and filter are clean.
During the "problem period" all spark plugs gives a powerfull spark.

Should it be an electrical problem? (ignition coil / CDI unit?)

The cooling water coming out was nice warm (could hold my hand under it without burning it), so I don't think it was overheated.

What I have seen is air bubles in the oil injection hoses (but always still oil in the lines) This air is not from the oil pump but from the cilinders. I guess this is normal, but is it really normal?

I hope someone haves a good advice for us, We can replace the ignition coils and the CDI unit without further testing, but when it wouln't fix the problem, whe have spend a lot of money for nothing ;)
 

deejaycee_2000

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Mar 28, 2006
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Re: Suzuki DT55 1985 lack of power after 30 secs of full RPM

Welcome to iboats :) ..... oil level float switch ....... or oil flow sensor ... no the bubbles in the oil lines is not normal .....
 

geiz

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Re: Suzuki DT55 1985 lack of power after 30 secs of full RPM

Welcome to iboats :) ..... oil level float switch ....... or oil flow sensor ... no the bubbles in the oil lines is not normal .....

Thank you for your reply.

I'll try to explain with pictures from the manual.

DT55-1.JPG

The "yellow" part is without bubbles in the oil.


DT55-2.JPG

The "red" part is with air bubbles.

Do you mean that the problem is not enough oil or the problem is, a sensor gives an fault message and the RPM is lowered by the CDI ?
 

captpn

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Jul 27, 2007
Messages
10
Re: Suzuki DT55 1985 lack of power after 30 secs of full RPM

Hi,
Sounds like a very similiar prob i had with a Yam 90 2 stroke...Fuel pump rebuild kit fixed it. (diaphram and gasket) took all of 10 mins...

Same symptoms as yours, and squeezing the ball while running during problem did NOT overcome the problem.

Basically fuel pump cant keep up with the motors fuel demand at high rpm... for 20 something bucks i would try it. good luck.
 

deejaycee_2000

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Mar 28, 2006
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3,447
Re: Suzuki DT55 1985 lack of power after 30 secs of full RPM

"""Do you mean that the problem is not enough oil or the problem is, a sensor gives an fault message and the RPM is lowered by the CDI ?""""

........... yes that is what I mean, it could be any of the 2, or can you say with certainty that the motor uses enough oil?
 

geiz

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Aug 27, 2007
Messages
5
Re: Suzuki DT55 1985 lack of power after 30 secs of full RPM

Hello,

The motor is using -I think- a normal amount of oil. I think we have to refill the oil tank ounce within 4-5x refueling with patrol (15-20 litres each time (3.3-4.4 gallons)). And then we put in, more than one liter, maybe 1 1/2 - 2 litres? I don't know it exactly, cause we don't sail every day with this boat ;-)

And about the diaphram, I will check it today!

To be continued ....
 

geiz

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Joined
Aug 27, 2007
Messages
5
Re: Suzuki DT55 1985 lack of power after 30 secs of full RPM

Hi,

I've checked the inner fuel pump, the diaphram and the gasket looks fine, no leaks.....

I think I will put now 2-swroke oil in the fuel ... look if it helps?
 

captpn

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Jul 27, 2007
Messages
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Re: Suzuki DT55 1985 lack of power after 30 secs of full RPM

opps double post...
 

captpn

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Jul 27, 2007
Messages
10
Re: Suzuki DT55 1985 lack of power after 30 secs of full RPM

My diaphram and gasket looked fine too, but it was the cure for me...i didnt have a leak either. did you hold it up to a light to look for a pin hole...sometimes they dont show any signs of wear, but old, they dont flex properly to keep up with the WOT fuel demands...1985 motor, i would change it. just and idea.

Running oil in the fuel will not prevent the sensor from reducing the rpm ...if thats the problem..but it could prevent potential damage until issue is resolved.


good luck
 

deejaycee_2000

Captain
Joined
Mar 28, 2006
Messages
3,447
Re: Suzuki DT55 1985 lack of power after 30 secs of full RPM

that sounds right ..... my suzuki 30hp did this the other day actually come to think of it ..... I just rebuilt the carbs, soaked a bit in carb cleaner and blew out with compressed air ..... then ran a couple of tanks with fuel system cleaner added to the fuel, perfect now .... runs better then ever ...
 

geiz

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Joined
Aug 27, 2007
Messages
5
Re: Suzuki DT55 1985 lack of power after 30 secs of full RPM

My diaphram and gasket looked fine too, but it was the cure for me...i didnt have a leak either. did you hold it up to a light to look for a pin hole...sometimes they dont show any signs of wear, but old, they dont flex properly to keep up with the WOT fuel demands...1985 motor, i would change it. just and idea.

Running oil in the fuel will not prevent the sensor from reducing the rpm ...if thats the problem..but it could prevent potential damage until issue is resolved.


good luck

But I think the buzzer have to beep when he have a oil flow / level problem?
Could the cooling water temperature sensor also have influence on the CDI / RPM "save mode" ??

I will order a diaphram and gasket now, put some 2-stroke oil through the petrol and check again. Still problems? I will try to measure during full load the sensor outputs.

I'll keep you informed about this problem / the solution
 
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