1990 suzuki 85 losing rpm after 5-10 mins at full noise

tony.l

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Nov 22, 2010
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Hi there. I have a 1990 suzuki 85 outboard with a problem at full rpm around 5200rpm. The engine starts and runs fine then you get going at wide open throttle and runs like a dream for 5- 10 mins . Then it will drop anywhere from 500 to 1500 rpm and stay there. If i pull the throttle back to just above idle the engine sneezes a few times sparatically and comes clear again, sometimes with a vibration. If i turn the engine off and restart it the problem goes away and will run fine for anywhere from 2 - 10mins and loose rpm again.

I have already changed one coil on the number 2 cylinder earlier because then the problem first occured the engine would die but would restart straight away but apon engaging gear it would die. Also i noticed the tacho was way out and off the clock during the first lot of troubles. But when i changed the number 2 coil the problem was fixed.
Running the outboard under load on the trailer and removing the leads numbers 1 and 3 cause the engine to run rough, but when removing number 2 lead the engine note does not change, the spark does appear noticably weaker on cylinder 2 even after changing the coil.

I have checked the fuel system and it all looks ok even when the problem occurs the fuel primer is hard. And when the loss of rpm occurs sometime you do notice a vibration and when you throttle back to very little rpm the vibration is still there. Also no alarms sound during the problem occurance

I think maybe im looking at a electrical break down somewhere and it is intermittent. Maybe the black ignition box is on its way out? Any input would be greatly appresiated as it has really got me stumped. Have searched the forums and not found any othere problems similar to these. If anyone has any ideas ,diagrams or tests please feel free to post many thanks in advance.
 

waterlogged1

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Sep 15, 2010
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Re: 1990 suzuki 85 losing rpm after 5-10 mins at full noise

Have you performed a compression check recently? Sometimes a cylinder will "act" okay when started up cold but when warmed up it can have enough loss in compression to cause power loss. I've worked on various types of 2 strokes and have found this to be a problem. The compression may test within the factory minimums when cold but change (drop) at operating temperature.
 

tony.l

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Nov 22, 2010
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Re: 1990 suzuki 85 losing rpm after 5-10 mins at full noise

yeah i have done compression tests hot and cold all three cylinders are even. Im still convinced it is a electrical problem given the way it will appear then dissapear thanks for the input
 

waterlogged1

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Sep 15, 2010
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Re: 1990 suzuki 85 losing rpm after 5-10 mins at full noise

I have a '89 DT85. I'm hoping someone will jump in and possibly help with your problem, I'd be interested in knowing what's going on myself. Hopefully it's not your ignition box, Suzuki is extremely proud of those. I came across a spare parts engine a few weeks ago and snapped it up primarily because I know how much the new parts cost. Sorry I couldn't be of more help, I'll keep watch on this thread.
Reg D.

I found this thread that might be of help. Sounds like the same thing yours is doing.

http://forums.iboats.com/showthread.php?t=211152
 

tony.l

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Nov 22, 2010
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Re: 1990 suzuki 85 losing rpm after 5-10 mins at full noise

Yeah i hope its not too. Does not look like a cheap bit of kit!. Thanks for your input though i read through that article and will try some of those suggestions
 

waffles1

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Jul 15, 2008
Messages
260
Re: 1990 suzuki 85 losing rpm after 5-10 mins at full noise

Sneezing or coughing is a sign that you are running lean, not enough gas. I'd start by taking the 3 jet screws out at the top of your carbs and spray some cleaner in each. Turn the screws clockwise at first and count the turns until lightly seated. You need to find the specs for the correct settings of the jets according to the manufacturer but I believe it is 11/2 +-1/4 turns for that motor. If they are set incorrectly that could cause your issues also. Make sure you put the same jet screws back in the same carbs (not totally necessary but just my personal preference) and screw clockwise until lightly seated then back it out to the recommended turns. Clean the end of the jet screws with cleaner also. If that doesn't fix your problems then rebuild your carbs and look at your fuel pump diaphragms. Try pumping the bulb when you experience problems and see if that changes anything. Good luck!
 
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