Suzuki DT85 Rpm Trouble

paul_sheets

Recruit
Joined
Feb 21, 2002
Messages
2
I have a suzuki dt85. I bought this engine last year. the engine is a 1985 I think. When I get out on the water the engine starts and runs fine. When I give it full throttle and run for 5 to 10 minutes it is like some one starts turning down the rpms it will just get slower and slower. If you keep it at full throttle it will die after a while. Some times just turning the key off and starting the egine back up will cure it for a little while some times just letting it set cures it. any suggestion? Thanks for any help <br /><br /> paul_sheets@yahoo.com :)
 

12Footer

Fleet Admiral
Joined
Mar 25, 2001
Messages
8,217
Re: Suzuki DT85 Rpm Trouble

Welcome to the forum,Paul. The next time it does this, check to make sure you are not overheating first.<br />If head temp is ok, loosen the cap on the fuel tank. If it improves, your problem is a clogged tank vent.<br />If it does not, then pump the primer bulb to see if RPM's pick back up, and to see if it is soft in the first place. Also note whether it has collapsed or not.<br />It's not a definite fuel-starvation problem,but it's 90% possable.<br />Let us know how your tests come out, and we can probably narrow it down to one or two items as the cause.
 

paul_sheets

Recruit
Joined
Feb 21, 2002
Messages
2
Re: Suzuki DT85 Rpm Trouble

Thanks for all the help. I will try it when it gets warm enough to get on the water. I have been working on the boat all winter. Doing a little TLC here and there. I have the lower unit off now replacing the water pump. It had one broken fin and one cracked. Thanks again for all the help. :p
 

Jackschellack

Recruit
Joined
Jul 7, 2009
Messages
1
Re: Suzuki DT85 Rpm Trouble

Hi guys,

I am new at this, so bear with me if I don<t click the right button :)

I also have/had the same problem as Paul last year with my Suzuki DT 85, year 1984, where it would slow down by itself at high speed. I would turn the key off, wait 10 second and restart and it would go fine for 15 or 30 minutes and slow down again.

It finally stayed at the 5 mile/hour speed when going full trottle all the time.

Since then, I've been going nuts trying to figure out the problem !

I changed the diafram of the fuel pump since it was accelerating when my buddy was feeding gaz directly in the troat of the carburators. However, it did not improve with a new diafram.
I then changed the primer bulb and both hoses attached to it, no change.
I tried a seperate gaz tank (original built in under floor), no change.
I did a compression test and the first carb had 115lbs, while the other 2 had 135lbs.
I dismantled and cleaned the 3 carbs, soaking in gaz for one week. I checked the needle valvs (OK), inspected the gaskets (OK), I air dried all passage ways in carbs and re-installed them.
I did not check the float clearance though. The idle in neutral is still rough and uneven.

I then discovered that gaz was pissing from the fuel line connection at the motor, I then connected the fuel line directly to the gaz filter inside the motor.

The motor seemed to be running smooth afterwards, but after 5 minutes of idling and reving in forward, my friend discovered that I had forgotten to replug the arm which connects to the oil injection mechanism, because I had checked the gaz hose under that arm !! After I replugged the oil injection arm, the motor would idle rough again. I tried to lower the oil consumption a bit, no change.

This was all tested outside the water with a water hose connection.

I also tried to check the ignition timing which was inconclusive because I could not adjust to the 23 degree mark on the advance timing, and the reading is way off and cannot adjust further in neutral. My shop manual says to test the advance timing in neutral at 1000rpm, same as the retard ??? Can that be ? Or should it be tested at full trottle in forward gear ?

After reading the above posts, I realize one of my problems might be the impeller, as the motor was very hot after 5 minutes of operation.
I am buying a new impeller today and will inspect and replace if needed.

Could you confirm the advance timing procedure and advise if you think other gaz problems might be occuring, or is my motor shot aand should be scrapped !

Thanks for reading my novel ! Your suggestions, advice are more than welcome.

merci,

Jack
 

70Chevelle

Cadet
Joined
May 31, 2009
Messages
6
Re: Suzuki DT85 Rpm Trouble

I have a 1985 DT75 and I have had the same problems mentioned above. The motor would start and run well at full throtlle for about a minute and then it would sound like it was starving for fuel. I rebuilt the fuel pump and cleaned the carbs and still had the same problem. I took the fuel pump off again and I removed the plate that it bolts to on the #3 cylinder. The O-ring was shot and the fuel pump was not getting enough compression from the motor. I cleaned up the "backing plate?" put a new O-ring in and now it runs great.
 
Top