Won't run in the water....but starts up like a new engine on muffs

Gas Giant

Petty Officer 1st Class
Joined
Aug 8, 2010
Messages
239
Just when I thought I was ready! (I had a lengthy carburetor-related post awhile ago)

The engine is an '88 Suzuki DT75. It will fire up and run beautifully on the hose in my yard. Starts on the first try, and idles smooth as a sewing machine thereafter. Revs up great too. Its no harder to start than my car engine, except for having to prime the primer bulb.

Some background info, I JUST replaced the carbs, and when I did I went through the replacements and cleaned them really well. Every passage is clear, and the carbs were literally installed days ago. Spark plugs are good, and compression is 120 on each cylinder. Like I said, it starts and runs like a champ on the hose.

So, today I go drop it in the water, and it fires, runs for a few seconds, and dies. Does it a 2nd time, and a 3rd time. Then it won't fire at all. So I play around with the throttle and it fires up and runs at nearly full throttle - and I managed to get the stupid throttle lever stuck in my panic - so I shut it down and called it quits. Do note that the engine did stay running when it was revved up.

For reference, I was using the Fast Idle setting on the Idle Speed Switch, like I always do when starting it for the first time. (Changing the position of this switch didn't help at the boat ramp; I tried)

I haven't tried to start it on the hose again since I got home late and was very mad, but I believe it will start right up. Nothing changed between my house and the boat ramp except it wasn't on a hose anymore. Same battery, same 3-day old gas, same everything. In fact, only about 30 minutes passed between running it at my house and trying it in the water.

What I plan to do is fill up my plastic trash can with water and set the engine in the water that way, and try starting it. The only two things that I imagine are different are: 1) The exhaust has more backpressure when its submerged, and 2) it now has to suck water up through the cooling ports, instead of the hose gently pushing the water up for it. (I don't crank the hose up very high, and I'm sure this isn't the source of my problems)

So, any ideas on what I need to adjust? Most of the adjustments on this engine are controlled electronically, it seems like its starving for gas at idle - but only when its in the water. On the hose in my yard it seems to have all the gas it wants. Any suggestions would be appreciated; I had to take my manual back to the library and they aren't open on Sunday.


For reference, my starting procedure is this:

1) Prime the primer bulb until it gets hard.
2) Push the key in to close the choke
3) Crank the engine
4) Let go of the choke a few seconds after the engine starts

This works fine on the hose. Didn't have a change to try squeezing the primer bulb at the boat ramp, since it wouldn't run long enough for me to turn around and grab the bulb.

Thanks, and sorry for the long post.
 

crb478

Lieutenant Junior Grade
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Dec 6, 2006
Messages
1,036
Re: Won't run in the water....but starts up like a new engine on muffs

Just a guess here as I really do not know Yamaha's that well, but if your compression is good and your spark is as well then it is likely fuel related especially since you just replaced the carbs. It probably needs to be idled higher to run/start with back pressure than on the hose. Are your timing settings still the same as when it ran properly? I doubt that they moved on their own. Did you set the idle rpm on the hose? It should be set in the water. Hope this helps lead you in the right direction.
 

OUTTALINE

Recruit
Joined
Feb 26, 2009
Messages
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Re: Won't run in the water....but starts up like a new engine on muffs

One thing to check is the low pressure fuel pumps. I have Yamaha OX66 200 and had the same thing going on. Ran great on muff, in the water it would run for a very short time, restart and would run again and then not restart at all, back home started right up. One of the lp pumps had split, replaced and engine runs great.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
9,247
Re: Won't run in the water....but starts up like a new engine on muffs

RPM taking off like that may have something to do with your modifying the carbs to fit your motor, but who really knows from this side of the monitor.
You will have to try it again on the muffs to see about the starting and RPM out of the water.
I would be looking hard at the linkage
 

mphelle8vld

Petty Officer 1st Class
Joined
Aug 17, 2005
Messages
321
Re: Won't run in the water....but starts up like a new engine on muffs

Maybe the trip to the ramp stirred up some more debris in the fuel system, I'm sure you've seen the small idle mixture holes in the carb bores, takes almost nothing to plug them. Given your description of the condition of your previous carbs, you have the same dried up crap lining the fuel system from the filter to the carbs. Let us know if it runs at home on the muffs, if not, it's time to clean the carbs again, clean the filter and pump and replace the fuel lines.
 

lakensea

Chief Petty Officer
Joined
Jan 30, 2002
Messages
542
Re: Won't run in the water....but starts up like a new engine on muffs

RPM taking off like that may have something to do with your modifying the carbs to fit your motor, but who really knows from this side of the monitor.
You will have to try it again on the muffs to see about the starting and RPM out of the water.
I would be looking hard at the linkage

I would be looking hard at the fact that he does not have the correct carbs for that model year. -just because you can get them to bolt on does not make them right!
 

Gas Giant

Petty Officer 1st Class
Joined
Aug 8, 2010
Messages
239
Re: Won't run in the water....but starts up like a new engine on muffs

Disregard this post for now; I fired it up today and its running badly and backfiring, etc. I'm going to run a compression check to see if anything was blown up.
 

Gas Giant

Petty Officer 1st Class
Joined
Aug 8, 2010
Messages
239
Re: Won't run in the water....but starts up like a new engine on muffs

Ok, did a compression check. It somehow went from 120 on each cylinder to below 30. Engine is toast. I give up, posting the boat for sale on CL.
 
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