Suzuki DT85 Dies suddenly under load

[kwb74]

I just bought a boat with a early 90's DT 85. Prior owner was clear with me about the issue and price was right. He told me he had taken it to a guy and had the carbs gone through which I tend to believe.

It runs just fine at idle/neutral but put it in gear and put some load on it and about 20seconds later it dies suddenly. No sputtering like it is starving for fuel just stops like key is turned off.

Before I go chasing through the fuel system is there an electrical cause I should be checking on?

My plan is to get rid of the 2-stroke in a year or so when I find the right deal on a 4-stroke so I don't want to start firing the parts cannon at it. If I have a fatal (read expensive) fix on this engine I will accelerate the search for the 4-stroke.

Thanks in Advance.

 

[robert graham]

Sounds like a classic fuel system problem...should be fairly easy to check out....start at fuel tank pick-up tube and work your way towards the motor....might need a new fuel pump....

 

[99yam40]

sucking air from a bad connection maybe
or bad pump.

checking fuel pressure and vacuum might help locate a problem.

does pumping primer bulb help keep it going?

 

[ondarvr]

Check for spark when it dies.

 

[211libwtfo]

That damn anti-siphon valve is at it again. It's at the tank and hose connecting point somewhere.

 

[kwb74]

Completely bypassed the boat fuel system and went to a tank. Bypassed the filter on the engine. Inspected fuel pump. All good.

I haven't been able to put it back in the water but I have been able to get it to miss when on muffs at a faster idle (about 2500RPM - Tach doesn't work) the miss is probably big enough that it is what is killing it when in gear.

Does does this still sound like fuel or should I start looking for a CDI?

 

[kwb74]

I spent some time today on this - I went to a portable tank, bypassed the on engine filter, and inspected fuel pump.

I didn't get it in the water but I am getting a miss at a higher idle (about 2500 - Tach isn't working) when on the muffs. Along with the miss is a puff of smoke. I suspect if under load it would kill the engine so I will chalk today up as a win for being able to duplicate the problem.

Does this still sound like a carb/fuel issue or should I start looking at electrical?

 

[ondarvr]

If it dies like you turned the key off it's typically electrical, fuel issues tend to show up as surging or slowing down in a smoother way.

If you put a timing light on it you may be able to detect the misfire if it's due to spark, you will see it if you're on the water and it dies.

 

[kwb74]

delete

 

[kwb74]

I started playing with electrical.
All three plugs get a decent blue spark when cranking.
If I pull the wires while idling #3 does the least to how well it is idling
I tested Resistance on the three coils:
Cylinder Plug to + ... Plug to - ..... + to -
1............12.65K...........12.65K.........2.7
2 ...........12.64K...........12.64K.........2.6
3 ........... 7.03K........... 6.75K...........1.6

Looking at the parts callouts on this coil #3 has a different part number but my hunch is that it is due to the longer Plug wire and not so much an internal electrical difference. Can anyone confirm this?

I also noticed that it has BR8HS-10 plugs but as far as I can tell is they come gapped at .040 but are the same as a BR8HS which is the recommended plug with a .030 gap. I confirmed gaps are at .030.

The coil is ~$70 which is about as much as I am willing to spend on this thing to get a year out of it so I can shop for a good deal on a 4-stroke. I still have a few months before I need to have this thing ready to use.

I dug around the shop and didn't find the timing light so I haven't been able to check that - it has been years since I needed one (cars are reliable, big boat is diesel).

 

[kwb74]

New coil arrived - seems to not miss when I let it run a while on the trailer and pick up the RPM. Hopefully I can go do a quick sea trial tomorrow and put this to rest and start focusing on the other parts of sprucing this boat up.

 

[kwb74]

Well it was a cold and unsuccessful sea trial.

 

[kwb74]

I found a service manual online that had resistance values to check parts - looks like condenser charging coil is bad. It measures about double the resistance it should and as I warm it up with a heat gun it gets worse and worse. Another part on order.

 

[kwb74]

After a saga of getting the coil it is in, measure good and still sortof have the problem.

Before it wouldn't restart once it died. Now it will restart immediately. What I did find is that all of the other grounds for the boat were hooked to the positive terminal of the battery - explaining why bilge pump and nav lights showed no power when I was troubleshooting them.

Question is - could having all of that stuff on the positive terminal been causing the problem or does it still look like a CDI problem?

 

[kwb74]

I will add I looked at the plugs - it looks like #3 is wet and the other two have been firing.

Could I have a bad pickup coil causing this?

 

[99yam40]

easy enough to test
service manual and proper test equipment come in handy

also a leaking fuel pump can dump excess fuel into the bottom cylinder crankcase causing it not to burn properly

 

[kwb74]

Would the leaking fuel pump cause it to die though?
It restarts with a quick turn of the key, not like it ran out of fuel.

I don't have the box to test the CDI but I have been going through manual and checking everything I can. That is how I realized the main ignition coil was suspect when it ohmed out at double the spec.

 

[eddie haskell]

Ok, I got the same motor, went the same route you are.
It would run GREAT on the trailer, but not in the water, well, sometimes it did.

Two things, do this, and I'll bet you fix it.
First, the ground at the throttle sensor had a shop notice sent out years ago, its a crummy ground.
My had came loose, and it was never sanded down to get a good ground.

Next, pull the carbs, then apart, one at a time, clean, clean, and clean.....
Use air, and clean some more.

Put it back together.....adjust linkage if need be.

Mine runs great, but it took half a summer of doing what you are doing, when all it was is the ever so small debris that plays havoc in carbs.....