air fuel mixture adjustment?

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FishTastic

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My 1983 Suzuki DT30 run ruff at idle shakes and rattles the boat, think it is running rich, I can not find a mixture adjustment anywhere. I ran some sea foam through the last tank of gas and that helped. Still need to adjust air/fuel mixture. Anyone know about this motor, two stroke with Mikuni carb. Thanks.
 
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Mmfh

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If it is shaking at idle you might want to check out your ignition parts and make sure everything is good in that area.

Mm
 
Chromatose

Chromatose

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Some carbs have their adjustment screws covered. Look for a cap. Pop off cap and you will find your setting screw.


Common Causes:

* Dirty air filter
* Weak ignition spark
* Worn or fouled spark plug
* Improper carb adjustment


If a full tune up has been performed recently and the condition is only noticed when the engine is at idle, the problem is likely to be caused by trash in the carb or an improper adjustment. If equipped, the idle mixture screw is most often located on the side of the carb.

"""""""""Note that most newer engines will not have an adjustable carb."""""""""


Basic Idle Mixture Adjustment

With the engine warmed up and running at the recommended idle speed, locate the idle mixture screw.

* Step 1. Slowly turn the idle mixture screw in clockwise until the engine just starts to miss and/or the RPM just starts to "fall off".

* Step 2. Turn it back out until the engine again starts to miss, hesitate or "fall off".

* Step 3. Finally, again turn the mixture screw back in clockwise until you reach approximately between both extremes. Make final adjustments by turning the mixture screw no more than 1/4 turn (in or out) to reach the optimum adjustment.

While this may not be a perfect adjustment, it should suffice to solve a rough idle problem. Otherwise, if none of the other potential problems are found, you'll need to clean the carb and fuel system, paying close attention to the idle circuits in the carb.

Make sure your fuel filter is clean or new. If all else fails check your fuel pump diaphragm for cracks or warped. Replace. Then try again.

Good Luck to you.
 
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FishTastic

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hey thanks that's some really good information. No air filter on this that I can see anway, carb throat is open but there is a small circular baffle type thing spaced about 3/4" away from carb air entrance and open all the way around the sides, looks like three machine screws hold that piece on. i will for sure look for mysterious caps that may be hiding those mixture screws. Thanks for the tuning info I will use it! Thanks again:clap:
 
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FishTastic

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OH I forgot to say that I did install a new fuel filter and screen right from the start and it is still clean. I also ran a half a can of Sea Foam with 6 gallons of premium gas and that helped.
 
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FishTastic

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Chromatose- No I did not take the needle out of the carb, I am very suspicous of my abilities with carburetors, never been my strong suit:rolleyes: I don't know why but I always run the other way from carb troubles.:lol:
 
Chromatose

Chromatose

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Good.

I do not know what type of Mikuni you have,but the pdf I posted might be of some help
 
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SNDSLGR

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OH I forgot to say that I did install a new fuel filter and screen right from the start and it is still clean. I also ran a half a can of Sea Foam with 6 gallons of premium gas and that helped.

replace that fuel filter pronto! Its cheap and anytime you are cleaning the fuel system you want to change the filter a few times, every couple gallons. All the junk that is being displaced is getting caught by said filter.

Also, make sure the filter put in properly for flow direction, I have seen even mechanical genius' put them in backwards and have your same simptoms!
 
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FishTastic

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yeah for sure, this filter has a removeable cleanable screen and I have checked it a few times since flushing , but the tank and lines are new, the only old thing in line before the filter is the fuel pump, I put the sea foam in to try to clean out the carb and motor. I double checked it again quick and the filter is clean as can be and all is hooked up correctly to the directional arrows, this thing huals butt when I twist the throttle so it is not starving for fuel at least to me:lol: Thanks again.
 
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Mmfh

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Just thinking about that shaking at idle again. Is it making any noise? I'm wondering if maybe it could be a mechanical vibration as in something screwed up or ignition miss or possibly junk stuck on the mixture needle. If the needle has a cap over it and you are scared of carbs than maybe just keep adding seafoam once in awhile to see if it improves like it did the first time.

Good Luck!
Mm
 
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FishTastic

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Just thinking about that shaking at idle again. Is it making any noise? I'm wondering if maybe it could be a mechanical vibration as in something screwed up or ignition miss or possibly junk stuck on the mixture needle. If the needle has a cap over it and you are scared of carbs than maybe just keep adding seafoam once in awhile to see if it improves like it did the first time.

Good Luck!
Mm

Not making any noise, I doubt that it is a mechanical issue as these are relatively mechanicaly simple designed 2 cyl 2 stroke motors. I will keep adding the sea foam but I think my problem is deeper and needs a screwdriver type fix. Thanks for your input I will certainly keep it in mind.
 
Chromatose

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How did you make out?
 
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FishTastic

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made out ok, helps a lot when I REMEMBER to gap my spark plugs!:lol:

still making minor adjustments every time out, but much much much better. Thanks again.
 
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GDBrown

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Sounds like the problem I had with a Merc. Turned out there was a plugged hole that let the exhaust out above water line when ideling. Also check your fuel to oil ratio! Since most if not all gas nowdays has some alcohol in it there can be problems with things not getting lubed right. Might be worth a visit to one of the boating forums where they talk about motors and problems. That's where I found my answer!
 
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FishTastic

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Sounds like the problem I had with a Merc. Turned out there was a plugged hole that let the exhaust out above water line when ideling. Also check your fuel to oil ratio! Since most if not all gas nowdays has some alcohol in it there can be problems with things not getting lubed right. Might be worth a visit to one of the boating forums where they talk about motors and problems. That's where I found my answer!

Thanks for the info. I found out I needed to keep the fuel tank vent just ever so slightly cracked versus having it wide open, seems to run much better that way. Now I spun the hub in the prop, bought new prop from Suzuki but does not fit, think I might just sell it all and go back to fishing from the bank.:(
 
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GDBrown

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I see you are also in Hillsboro. Why don't you PM me and we'll see if we can hook up for an outing.

GD
 
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FishTastic

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UPDATE: OK so now I have put a new hub in my old prop and I am functional "for now". We will see how she runs this weekend.

GD Brown, I will PM you about an outing.
 
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