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rpm up and down at idle.

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48tony

Regular Contributor
Well after a long battlle trying to get this 1970 60 hp to idle and run good i have lost. I did a full rebuild on this motor bored cylinders 30 over new piston and rings all new internal bearings and seals. new crank shaft. all new ele parts stator,amp cdi,rectofier,coil,points,new plugs gapped 30 thousents. gapped points at 10 thousents good strong spark. my problem is in carbs. New boyson dual stage power reeds. Full rebuild on carbs removed all plugs cleaned out passage holes new floots ,new needle valves.link and synk carb likage.after all this the motor runs like a champ after 2,000 rpm,s Butt at idle it is eratic with the rpms going up and down.It will start right up when cold.and idle smooth on the muffs all day. take it to the lake do a few laps and it starts to idle up and down.I have messed with the slow speed adj I have adj it every possible way ran it rich and ran it lean to only get the same idle with rpm,s jumping on the tackometer.Again after 2,000 rpm,s it runs great no stumble no missis a nice steady purr right up to 5,000 .I am unsure if this could be do to the middle carb throttle plate being slightly out of sink i found that this plate was a bit open at idle I took a long screw driver and pushed on the carb plates to find the middle plate ever so slitely open. the rpms did drop when i pushed it shutt. I did a mc guyver move with a spring to keep it closed .Then adjusted the 3 throttle plates together.I think these carbs even though rebuilt may need to be replaced.can some one step in on this rpm problem.I need some input on what else it may be.Or it may be the carbs are a bit worn causing this. i am at a loss please help
 
Hi,All.After posting this rpm problem last night I was wondering if it could be a vacume leak.Today I ran it on the muffs and it ran great.Butt i no if I took it to the lake and ran it with a load on it the rpm,s would act up.The motor will run good at the lake for a while, it acts up when it gets to temp.This makes me think that a vacume leak is causing the rpm problem.Butt i have let it run for allmost 45 min on muffs water out of pee hole up to temp so why does it only do it with a load on the motor in the lake.I figure a vacume leak would cause this rpm flexuation all the time. help needed please
 
I could really use some feedback on this problem. please someone.Just put on some carbs from e-bay 1972 65 hp. did a rebuild on them to find I still have the problem.checked for vacume leaks on the old carbs thinking that was the problem.At carb base to intake the mid carb seem to have base leak.And the throttle plate linkage that goes through the carb casting allso .Sprayed carb clean arond all and found the motor to die out when sprayed in those spots.I am at a loss trying to get this thing correct.Could the gas pump be acting up really need some insite to fix this.Thank you tony
 
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