1999 DT85, RPM problem

[Stan Mathews]

Bought the boat last spring. Had problem with water in fuel tank, solved that. Installed new in line filter. Ran great for a while, then lost RPM down to 4800. Idled well and ran good below 2500 RPM. Seemed like fuel starvation. Drained carb bowls, installed new breather hose, blew all lines with compressed air. Ran good for a while, but then would lose RPM down below 3000, sometimes recovering, but eventually stalled and won't restart.

 

[James R]

Re: 1999 DT85, RPM problem

If it is a fuel issue then it could be an air leak somewhere in the fuel line, a blockage at the fuel tank pickup or the fuel pump needs repair. Other questions come to mind. Is it pumping a strong water flow and running cool. Overheat protection will cause the system to slow the motor or shut it down.Also if there is a problem with the oiling system this will cause the motor to run at low RPM.

 

[Stan Mathews]

Re: 1999 DT85, RPM problem

May not be a fuel problem. Checked compression on all three cylinders and had 120 pounds on bottom and middle, but 0 on top cylinder. Any suggestions?

 

[Yamajoe]

Re: 1999 DT85, RPM problem

Check top cyl again and do a leakdown test and post results. lets hope the carb problems have not caused No 1 to fry.

 

[Stan Mathews]

Re: 1999 DT85, RPM problem

Thanks! Will perform leakdown test this week and post results. Could there possibly be a blown head gasket between the water jacket and top cylinder?

 

[James R]

Re: 1999 DT85, RPM problem

I dont know where yamajoe gets the idea that a leak down test will do anything when you have said you have 0 Psi on #1. If the carb is complelely blocked then a good compression cylinder will give poor to no reading. Its my guess that #1 is blown. Removing the cylinder head will reveal all.

 

[Stan Mathews]

Re: 1999 DT85, RPM problem

Removed cylinder head, piston not burned through, but severe scoring on cylinder walls, with some aluminum buildup. Stopped right there, need advice on whether to rebuild or replace with rebuilt powerhead.

 

[James R]

Re: 1999 DT85, RPM problem

Without knowing what your experience is with regard to two stroke motors and your tool and shop capability it would be difficult to answer your question.
I rebuild Suzuki's and all the others and you really have to have the knowledge and tools to make a proper job of it. A manual is an absolute must.As it is you will need to check all the cylinders for size and out of round to determine what has to be done to the block.You wont know the condition of the crankshaft untill the motor is torn down. Only then can you determine the cost re machining and parts. If it is your own labor then figure on $1K.

 

[Stan Mathews]

Re: 1999 DT85, RPM problem

Made several calls regarding new powerhead and took to a local dealer. All estimates were well over $3000. NADA says engine is only worth $1600. I decided to buy new Suzuki 90 four stroke. Thanks for all your advice.