Suzuki DT85 won't slow down

[dekman2001]

I recently purchased a 1985 Suzuki DT85 for a very low price. When I first ran it, it would only run on 1 or 2 cylinders. When I tried running it with wide open throttle, it would of course run lousy, but it would have difficulty returning to an idle speed. Even after returning the throttle to idle position, the motor would continue to run at high RPM's for a long time if I let it (I've let it go about 30 seconds before shutting it off). <br /><br />Since then, I have rebuilt all 3 carburetors (which were filthy by the way). It now runs quite well on all 3 cylinders, but the throttle problem remains...its even a bit worse. After I return the throttle to idle position and the carb flaps close, the engine continues to run at high RPM's for a long time. <br /><br />Any hints? Could this simply be a carb ajustment problem? Do I need to buy a timing gun and mess with that (I borrowed someone's gun, and the timing appeared to be only slightly off from the factory norm)? Could it be anything else?<br /><br />Thanks for your help!

 

[jim dozier]

Re: Suzuki DT85 won't slow down

The idle speed is set with a bolt on the ignition timing lever arm. It modifies the timing to change the speed. The carb butterflies should be closed at idle. You have to synchronize the carb linkage with the ignition timing linkage if you haven't already done this. Set them to manual specs. The idle speed should be set in the water with the engine in forward gear. Don't set the idle in the driveway.

 

[dekman2001]

Re: Suzuki DT85 won't slow down

Also, I did not trust the oil injection system on this motor. I crimped off the oil intake and began running a 50:1 mix instead. Would this cause any of the effects I'm seeing? It won't harm the engine/carbs, will it?<br /><br />I did set the idle in the driveway...perhaps I should take it out to the lake and set it as you suggested.

 

[jim dozier]

Re: Suzuki DT85 won't slow down

The Suzuki oil injection systems are very reliable if maintained. I would recommend keeping it after you have checked it out. The oil lines need to be checked for cracking and should be replaced if they are old. You can check the pump output with a syringe and some extra tubing. Get a manual for the specs. Oil is injected into the reed block not the carb so a lean carb won't stop the oil injection system like it will premix. Use premix until you verify that the system is working if you decide to keep it.<br /><br />Yes you should put it in the water and see where your idle is. Without the backpressure of the water and the drag of the prop in gear the engine will idle high. If you got it to run at the proper rpm in the driveway it would conk out in the water in gear.

 

[dekman2001]

Re: Suzuki DT85 won't slow down

I spoke with a guy that works at a Suzuki repair shop. He informed me that the reason the boat remained at extremely high idle speeds after I reved it in neutral was that too much gas enters through the carbs and continues to power the motor. The engine is not meant to be reved at such high RPM's in neutral. I had even disconnected the battery, and the thing continued to run! I had to remove the gas line and wait for it to run out of gas. He said it wouldn't do this in gear in the water, so I am no longer afraid to take it out on the lake. <br /><br />On running without the oil, he recommended 50:1. He also recommended removing the rod that drives the oil pump so that it would not seize up or get damaged over time.