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Old 02 March 2012, 17:16   #1
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Odd 2 stroke issue

Hi,
Well started the old thing up again today and still noticing plug 3 is clean as a whistle while plus 1 and 2 are as they should be a little oily and sooty.

I am wondering if there is an issue with the reeds or card on cyl 3.

seems to run very nicley and revs freely with no lag or lumpyness.

Any Ideas??

ENGINE= Mariner 75 ELPTO 1991 2 stroke 3 carb.
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Old 03 March 2012, 03:33   #2
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Hi Jezza,

If it was the reeds I would expect some blow back through the carb i think, and it probably wouldn't run all that well. Have you tried pulling the lead on 3 and comparing the running of the engine when you pull 1 or 2? Compression test? Do you mix the oil in the tank or is it injected?

Questions questions questions

SR
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Old 03 March 2012, 04:21   #3
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remove the No 3 plug and have a good look at it and dont wipe it before you look at it ,does it glisten in the light? if so it could be the piston has picked up in the bore, now swop spark plugs to see if fault moves with the plug ,it doesnt move check to make sure the mixture screw hasnt screwed its self in, screw in until lightly seated then out for one and a half turns , is the throttles on the carbs still sycronized?remove the drain plug in the btm carb any crap come out if so remove carb and clean,you have to find out weather the fault is electric or fuel if it is electric i would also remove clean refit all earth wires, but it sounds more of a fuel problem, that lot should keep you out of mischief for a whill.
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Old 03 March 2012, 06:57   #4
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SR: oil injected and all seems well there. Not compression tested but starts first time every time and runs well out so think the compression is ok.
Not checked for blow back. but if a reed is stuck would it not get any fuel and run like a dog and have starting issues?

Uncle Al: plugs swapped still the same. yep does have a slight sheen on it as if it were getting fule/oil
If it picked up wouldnt it be ripping itself appart?
checked the mixture screws and all seem ok.
All clean when drains removed.
Sparks checked and on no3 its sparking properly.

How am I going to tell if its picked up without taking the head off?
not sure if the carbs are synced properly. its been a whiles since its been serviced as there doesnt seem to be anyone locally.
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Old 03 March 2012, 07:39   #5
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Ok, you say it's not been serviced in a while, I would definately start with a compression test, because its easy to do and can tell you alot. If thats all good then strip clean and adjust all carbs using the right rebuild kits. Then you'll be at a good starting point to diagnose further if it hasn't cured the problem.
But if you say it starts and runs ok, then needing a good service may be all the problem is!

If a cylinder has picked up then it's likely that the engine would run rough especially at idle. Compression test will tell you if theres a problem.

SR
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Old 03 March 2012, 07:47   #6
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Hi SR, just checked and no3 is clean as a whistle. Hmm.
carbs look clean and the jet looks ok. just adjusted no3 as per the manual. 1 1/2 turns out.
But is been some time since its had a service so could be the carbs out..
mau try put a vid on here.
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Old 03 March 2012, 09:58   #7
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as it is sometime since it had a service,this is what i would do,
remove strip and clean carburetors reassemble checking float hights
replace spark plugs
fit a fuel pump repare kit
replace fuel filter on the power head
i see you are on the site i will wait here for a while for a reply
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Old 03 March 2012, 10:33   #8
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Old 03 March 2012, 10:34   #9
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should be able to see and hear it running there
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Old 03 March 2012, 10:34   #10
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http://s1163.photobucket.com/albums/...t=PICT0002.mp4
Or here
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Old 03 March 2012, 10:43   #11
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i can see its a clam shell ,it doesnt seem a bad fault,(easy to fix)i managed to hear it now what i would do now is give it a service, go to a launch site run it on the trailer making sure that the obm stays in the water and doesnt push the vehicle and trailer back up the slope,run at quite high revs tickover to about 3500rpm in gear to make sure there are no flat spots if there is richen all carbs the same about one eigth of a turn on the mixture screws,remove spark plugs and look at the electrodes black to rich, white to lean then go from there
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Old 03 March 2012, 10:59   #12
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Thanks Uncle Al.

Sounds fairly good doesnt the old girl :-) for a 21 year old OBM.
now the starter is 100% she fires up in seconds.

I will take her down the coast and take your advice.

Its probably the carbs out.
reeds look ok or at least not stuck closed.

Thanks again
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Old 03 March 2012, 11:05   #13
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if it was reed trouble i would expect it to sneeze ,be carefull running it on the trailer as you havent got a dyno that is the next best thing , well better than nothing , i hope i sound as good as that when i am twenty one, dont nobody answer that
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Old 03 March 2012, 12:13   #14
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Well i'd do the same, a good service and a test run under load.

Let us know how you get on

SR
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Old 03 March 2012, 15:10   #15
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Quote:
Originally Posted by jezza2011 View Post
Hi,
Well started the old thing up again today and still noticing plug 3 is clean as a whistle while plus 1 and 2 are as they should be a little oily and sooty.

I am wondering if there is an issue with the reeds or card on cyl 3.

seems to run very nicley and revs freely with no lag or lumpyness.

Any Ideas??

ENGINE= Mariner 75 ELPTO 1991 2 stroke 3 carb.
You say it runs fine and revs ok, if it works i wouldnt be worrying about what the plugs look like. Its a 20 year old 2 stroke!!
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Old 05 March 2012, 07:35   #16
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Clamshell.....

Probablty a Q for Uncle Al or Turbo-D, but did the "needs a bigger jet in the top carb" thing carry through to the 3 carb versions? I believe the 50/60 Clamshells were prone to running a bit leaner in the top cyl?
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Old 05 March 2012, 09:54   #17
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9D280 The 75s dont need a bigger main jet in the top carb,that was only the 50/60hp clamshells cos they ran lean goodbye piston and if unlucky bore
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Old 05 March 2012, 10:28   #18
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I know!

I just wondered if the other clamshells suffered too, based on the top plug here......
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Old 05 March 2012, 11:18   #19
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NO just the damned 50/60s but once all the mods have been done i hate to say it they are not a bad obm, But still dont like them
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Old 06 March 2012, 04:30   #20
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They have been, and yes, the "no fitting does one job" thing is a PITA for servicing, but at 60Hp / 83KG I am not going to complain!

I guess we should stop hyjacking Jezza's thread........
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