1975 70hp Johnson not firing on #1 cyl

scruffo

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Dec 6, 2008
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Hi all

Top site & have found it very informative but can not seem to pin point what is going on with my motor.

I have just recently purchased this boat & motor & have been having issues every time i put it in the water go's ok at first then would stall as soon as i put it in to gear tho seemed fine on the muffs at first but now when i put my hand over #1 carb the engine doe's not change & the carb starts to flood in the venturi with fuel & when i do this to no 2 & 3 carbs it near stalls the motor.

Has good compression 118psi on # 1 & 3 & 115psi on # 2 has very strong blue spark on all 3 cyl

Since owning it the carbs have been completely striped & cleaned including the removal & replacement of the small welsh plugs in the carby & floats reset.

New power Pack
3 x new coils as the old ones the leads were that short they only just reached the plugs & at $30 each thought i may as well replace the complete coils with leads
New plugs champion QL77JC4
New fuel pump after kitting the old one & not being able to stop it from leaking
Have done link & sync

I have swapped reeds & carby from #3cyl to #1 cyl to see if the problem change to no 3 cyl & it did not make any difference when putting my hand over the carby,at the moment i don't have a socket big enough to remove the fly wheel to check the stator.

Engine is a 1975 70 hp Johnson 70ESL75E 1975.

Any help in giving me some ideas on what else i could check or test would be appreciated.

Regards Shaune
 

tashasdaddy

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Nov 11, 2005
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51,019
Re: 1975 70hp Johnson not firing on #1 cyl

if you have blue spark on all 3 no need to check stator. you have great compression, so the only thing left is that the carb on # 1 is not delivering fuel to the carb, stuck float, clogged jets, sucking air.
 

scruffo

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Re: 1975 70hp Johnson not firing on #1 cyl

Hi

Thanks for the reply

I have swapped #1 carb & reed block with #3 carb & reed block as an elimination process #3 cly still ran fine with #1 carb & reed yet #1 cyl still had no response with #3 cyl carb on it when i put my hand over it.

Hope this make sense.
 

tashasdaddy

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Re: 1975 70hp Johnson not firing on #1 cyl

remove the fuel line from # 1, have some try to start motor, see if you are getting fuel as the motor turns over.
 

scruffo

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Re: 1975 70hp Johnson not firing on #1 cyl

Will give it a try in the morning it's 11pm here in Aus at the moment may p1ss the neighbours off if i try turning it over now lol.


after i do put my hand over #1 carb fuel comes out of the front of it,so i'm thinking the bowl has fuel in it .
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: 1975 70hp Johnson not firing on #1 cyl

it sounds like the float needle may be sticking. did you change the needle and seat, and adjust the float? you have fixed jets so nothing to adjust except the float. http://forums.iboats.com/showthread.php?t=244013


another thought, have you changed fuel lines to alcohol resistant lines? the ethanol deteriorates the inside of the old lines, causing carb problems.
 

scruffo

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Dec 6, 2008
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Re: 1975 70hp Johnson not firing on #1 cyl

Thanks again for your replies

Have replaced all fuel lines only a week ago

I replaced all 3 needle & seats & set the floats

I don't think it is carb (but then again outbard are all new to me) as i can put swap top & bottom carby & the problem stays in the top cylinder.

I have sprayed aero start around carb & manifold gaskets & don't notice any changes in the sound of the motor.

From what i can gather when i had the reeds out,top & bottom pistons look like new underneath when shining a torch through the inlet ports where as the middle cylinder has certainly had more use & every gasket on the engine tells me this motor has not had much use since being apart/rebuilt & i'm beginning to wonder if the they sold the boat not being able to hunt down this gremlin within number 1 cylinder.
 

scruffo

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Dec 6, 2008
Messages
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Re: 1975 70hp Johnson not firing on #1 cyl

It appears to be an air leak between the plate that the reed blocks attach onto & the manifold gasket near #1 cylinder.

Is there any trick to sealing these as i have tried 2 sets of new gaskets & still can not get it to seal & now #3 cylinder is leaking between the same gaskets as well & has no effect when blocking the carb with my hand.

Is there a torque setting for the manifold bolts & a certain sequence to doing them up,i have been working my way from the center outwards & cannot find a torque setting for these bolts in my manual or online.

I have been working on cars for over 15yrs & re-building my sons sprint kart engines for nearly 4yrs & have never had so much trouble trying to seal gaskets tho this is my first boat motor i have ever worked on.

I have had a straight edge over both reed plate & manifold including the crankcase where it all bolts onto & it all seems fine.

Shaune
 
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