Rough running 70hp

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dieselmekanix

Cadet
Joined
Jul 9, 2008
Messages
6
Have a rough running 1984 70hp Johnson at around 1500-2500 rpm, The things I have done so far are carb rebuild,fuel filter, new fuel pump, new plugs wires and coils, new cdi,new timer base, new head gasket,carb gasket, new exhaust manifold and gaskets,timing only at idle ok, compression tests around 130psi in all cylinders, the engine idles good and has power on the top end but seems to load up or loose a cylinder when cruising at 7 knots on my 14ft RIB. runs fine for about 5 min. when first starting out. bought the engine used and dont know the history, has any one had this problem? any help would be appreciated , bout ready to throw it in the drink.
 
W

wavrider

Chief Petty Officer
Joined
Nov 26, 2007
Messages
543
Re: Rough running 70hp

Seems like everything is correct. Heck it is al basically new.

Read Joe Reeves carb adjustment at top of engine page.

Also perform a very good link n sync. Critical on the 70 hp.

It is also possible that there is some trash in one of the jets or bowls.
Would not be the first time a piece of fuel hose broke off and found its way into a carb.

Also perform Joe Reeves timing located in the top of the engine page.
It allows you to chect WOT timing without running the engine.

It also could be as simple as throttle cable adjustments, the link n sync will find that out. Good luck.
 
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dieselmekanix

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Joined
Jul 9, 2008
Messages
6
Re: Rough running 70hp

Ok, thanks will check the timming again but would like to add, This engine originally came with VRO and was changed to straight fuel pump with 50:1 gas before I bought it, would that screw up the low end? will post results of outcome thanks .
 
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dieselmekanix

Cadet
Joined
Jul 9, 2008
Messages
6
Re: Rough running 70hp

Update, Checked all of the timing and sync, checked gap to plugs .040 , adjusted WOT timing was off -6deg. everything is ok. Idles pretty smooth but a little smokey, have good top end power but still seems like its loading up with gas at trolling speed, carbs were rebuilt(new jets,floats and needles) but may have missed something, has anyone had a problem with these carbs?
Will post results.
 
iwombat

iwombat

Captain
Joined
Jul 12, 2006
Messages
3,767
Re: Rough running 70hp

Might try putting a new set of idle jets. If someone cleaned them out by poking around with something harder than bronze they could be off spec. Wouldn't be the first time.
 
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dieselmekanix

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Jul 9, 2008
Messages
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Re: Rough running 70hp

Update, Removed carbs , cleaned and inspected, adjusted floats to close a little earlier and test ran, runs better than ever but not good enough, also checked if No. #1 cylinder at TDC was lined up with the flywheel TDC marks, will try to install new idle jets looks to be two in each carb, does anyone know if fuel is suppose to come out of the main jet infront of the butterfly valve at idle? maybe this is a problem. would like to add my first problem was water in the cylinders thats why I replaced head gaskets and exhaust manifold gaskets which stopped the leak and good to check everything out. thanks for the advice everyone.
 
Joe Reeves

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Re: Rough running 70hp

You mention "does anyone know if fuel is suppose to come out of the main jet in front of the butterfly valve at idle?"

This would happen if you neglected to install the small circular gasket on the center nozzle tube. Also, are the floats properly adjusted?

(Carburetor Float Setting)
(J. Reeves)

With the carburetor body held upside down, the float being viewed from the side, adjust the float so that the free end of the float (the end opposite the hinge pin) is ever so slightly higher (just ever so slightly off level) than the other end. And when viewed from the end, make sure it is not cocked.
 
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dieselmekanix

Cadet
Joined
Jul 9, 2008
Messages
6
Re: Rough running 70hp

Update, checked the carbs today, float setting good found one small round center nozzle gasket in the bowl to be cut so used an old one in good condition and put it all back together, still see some gas spirting out of the main jets at idle.
went for a boat ride , runs better but still surges and cuts out alittle like I am loosing a cylinder at 6knots, boat ran for 1.5 hours and didnt quit, plan on buying new carb gaskets and idle jets this week, Thanks Joe for the advice. will post results
 
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dieselmekanix

Cadet
Joined
Jul 9, 2008
Messages
6
Re: Rough running 70hp

Finally got her runnin right, figured out the butterfly valves in the carbs were not closing all the way and the low pressure was pulling too much fuel into the engine, this is an old engine so I just added some springs to assist the old ones to seat all the way, runs like a top now, too bad its snowing.
 
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