Suzuki DT85 idles to low

JMWilk

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Jun 19, 2005
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6
Hi,<br /><br />I am new to the forum... I own a 1979 DT85 very low hours that was heated garage stored for the past 15 years... I have taken it in to be unwinterized etc... I have had it out on the water 4 occasions an noticed that when switching gears forward and reverse from idle the engine stalls... Inorder to shift gears forward or reverse, I have to punch the throttle to prevent stalling... I have ordered a repair manual and read thru about 75 posts here but didn't see a problem/solution for this issue... Could anyone prescribe a starting point for troubleshooting this problem...?<br /><br />TIA,<br /><br />JMWilk
 

pmassey31545

Seaman
Joined
Jun 11, 2005
Messages
52
Re: Suzuki DT85 idles to low

Hey! I am new also and really don't know a whole lot, But I had the same problem with my DT85-1982model. I adjusted some on the carb linkage and also the idle screw and the problem seems to be fixed. If you're lucky it's something simple like that. It could be something more serious-dirty carbs or fouled/improper plug firing. But I always, as a do-it-yourself guy,start with the easiest and go from there. Hope this helps and good luck gettin' her goin'...
 

jafa

Petty Officer 2nd Class
Joined
Mar 10, 2004
Messages
172
Re: Suzuki DT85 idles to low

Your idle speed sounds like its too low.Should be around 750 rpm , in the water and in gear. When its on muffs and in neutral on the driveway it'll be around 1000 .
 

JMWilk

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Joined
Jun 19, 2005
Messages
6
Re: Suzuki DT85 idles to low

Hi, <br /><br />Paul: I agree with you 100%, I am more electronically inclined then mechanical so I always use that approach to start on these issues... Thanks...<br /><br />Rockhopper: I checked the idle speed both in the water and in the driveway... The idle speed hovers around 550 rpm under both environments... <br /><br />I will adjust that accordingly... Thank you both for your suggestions...<br /><br />One additional question I have is in regard to the propeller... I measured a 2-3cm exclusion in one blade of the prop... At WTO and at LTO, I am experiencing a slight vibration on steering...<br /><br />1) Can the exclusion in the prop be causing an imbalance therefore causing vibration...?<br /><br />2) Can the prop be repaired or does it need to be replaced...?<br /><br />3) After initial examination of the prop, I was unable to identify it by any type of markings... After reading the documentation that came with the boat, I was not able to clearly identify the prop pitch/diameter... As far as I am aware, the prop was the original prop that came with the initial purchaser... I have looked on a few of the prop websites for replacements; however, the diameter of the existing prop does not match the diameters represented on the websites for the DT85... Since there is no clear identification on the prop, I am uncertain about the pinch of the prop as well... I measured the lower unit... It looks like the prop can be 34.29cm in diameter max... However, I am questioning the pitch... Is there any way to determine the current pitch on the prop...? At WTO, the engine maintains 5000 rpm which is to spec...<br /><br />Would you have any recommendation for this as well...?<br /><br />Thanks,<br /><br />JMWilk
 
D

DJ

Guest
Re: Suzuki DT85 idles to low

JMWilk,<br /><br />As a precaution, get ready to rebuild the Mikuni carbs. on that engine. They are VERY sensitive, especially to sitting idle.<br /><br />Once that is done, post your wide open throttle RPM. That engine needs to be able to run at near 6000 to get the full performance of it.<br /><br />With your WOT RPM noted, we can help in prop selection.
 

JMWilk

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Jun 19, 2005
Messages
6
Re: Suzuki DT85 idles to low

Hi DJ,<br /><br />Would you have a recommendation for a rebuild kit supplier...?<br /><br />Thanks,<br /><br />JMWilk
 

jim dozier

Lieutenant Commander
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Jan 8, 2003
Messages
1,970
Re: Suzuki DT85 idles to low

The carbs proabably need a thorough cleaning and rebuild if its that old and hasn't been done in the last couple of years. As said above the Mikunis like to be clean inside. The idle speed is set by adjusting the the ignition timing stop on the throttle linkage. The idle speed can be affected however by the idle air mixture screw on the front of the carbs. Once you are assured that the carbs are clean, the idle mixture must be set to specs then the idle speed must be set which may in turn require fine adjustment of the idle mixture which may alter the idle speed. You may see where I'm going with this. All of this is best done with the manual specs and sequence.
 

JMWilk

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Joined
Jun 19, 2005
Messages
6
Re: Suzuki DT85 idles to low

Hi Jimd,<br /><br />Thanks for the response... I just recieved the shop manuals in the mail... Just started reading up on the engine... I did adjust the ignition idle stop to bring the idle speed to spec... That did take care of the stall problem... I did notice however that when running at 3000 RPM's in gear the engine will occasionally loose RPM's dropping down to 2500 RPM and then returning back up to 3000 RPM's... I will be cleaning the carbs first... If that doesn't work, I will definitely rebuild... Have you rebuilt these carbs before...? If so, is a carb balancer required...? Also, are there any tips you may have for the rebuild...? I have no experience with carbs > 1... That part might be interesting or tricky... <br /><br />Thanks,<br /><br />JMWilk
 

jim dozier

Lieutenant Commander
Joined
Jan 8, 2003
Messages
1,970
Re: Suzuki DT85 idles to low

I think you can get by without the carb balancer. Make sure that all carb butterflies close at the same time with the throttle off. There are linkages between the carbs to adjust this if necessary. The carbs are very simple, getting to them is harder than rebuilding but fairly straight forward. Rebuild consists of a thorough cleaning of the orifices with carb cleaner AND compressed air, replacement of the float valve seat, checking the float height, resetting the idle air mixture screw to specs and replacing the gaskets. While you are doing this you should replace the fuel pump diaphragm which is simple and inexpensive. Reinstall the carbs and set the timing/carb linkage according to the manual.
 

JMWilk

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Joined
Jun 19, 2005
Messages
6
Re: Suzuki DT85 idles to low

Hi Jimd,<br /><br />Can you provide a reference for the fuel pump diaphragm and carb rebuild kits...? The engine is 1979 vintage... I was only successful in finding the Mikuni.com rebuild kit(Carb and Pump)... The manual I have does not provide a part number or manufacturer for the pump as a cross reference... Should I assume that the pump is a Mikuni DF52-92...? Your help is very much appreciated...<br /><br />JMWilk
 

JMWilk

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Joined
Jun 19, 2005
Messages
6
Re: Suzuki DT85 idles to low

Hi jimd,<br /><br />Thanks for the reference... I ordered everything I needed...<br /><br />JMWilk
 
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