fuel delivery problem over half throttle

[grizzlybars]

have a 65model 90 hp johnson. bought motor used. motor started up easily, but when i took it to the water it starves for fuel when giving it over half throttle. have replaced fuel pump diaghram, plugs, points and condenser, and replaced water pump impeller. bought 2 new plastic fuel tanks, with vents, new fuel line connecters on both ends, new hose, and changed primer bulb twice. tore down carbs and cleaned bowls and checked needle valves and seats- all in good shape. compression check showed 55lbs on all cylinders. was worried about this at first but have found out engine had lower compresion from factory and as long as they were all within 10% was good. engine doesnt miss or foul plugs and has no problems untill giving it over half throttle, has to be a fuel delivery problem or timing problem of some kind i hope. points are at .20 and timing belt is new and lined up. i dont have a manual to use timing light on this engine so any help would be appreciated. thnx

 

[steelespike]

Re: fuel delivery problem over half throttle

I hope you used a manual to do your carbs.<br />When doing the carbs you need to be sure all<br />passages are clean and clear.Float settings shouild be checked and free movement of the float and needle and seat.<br /> Does it help if you choke it when trying to open the throttle?<br /> Unhook line to carb(s) and carefully check the flow from pump as you crank the motor. Close the <br />kill switch so it wont run.<br /> Should be a strong pulsing stream.If not check<br />all fittings and connectors.Check the pulseport<br />be sure it is clear.

 

[strocker383ca]

Re: fuel delivery problem over half throttle

make sure that the mixture sreew are ok if they go it on those carb sometime the run to lean went the gaz change circuit in the carb and make the motor miss or shut off. may the engine go good at full throttle

 

[grizzlybars]

Re: fuel delivery problem over half throttle

thanks steelspike, i have done all that except manually disconnect hose and look at fuel stream. i did manually run a wire or probe into or through every port and passage in carbs, pretty simple setup. and i know better than to work on something without the manual, ase mastertech for 23 years on autos, but havent found one yet and was impatient to go boatin. thing just seems to not have enough volume at higher fuel demand rpms. thnx again, any ideas are appreciated

 

[grizzlybars]

Re: fuel delivery problem over half throttle

oh steelespike, it does seem to do a little better when first startin ,ie choke partially closed, and as i said problem goes away when someone sits by tank and pumps primer bulb. just cant find anyone willing to sit in the floor all day pumpin the bulb, ha ha

 

[pbailey]

Re: fuel delivery problem over half throttle

A freind of mine repowered his boat with a 96, 88 special. After a few months it develops this problem of slowing down and then quiting when running at WOT. <br /><br />We replace all fuel line, fuel pump and the tank pickup tube. Didn't help.<br /><br />I tear the carbs apart. Clean as a whistle. Floats check out ok. <br /><br />When I'm putting the carbs back on I'm trying to get some slack on the fuel line from the fuel pump so I can hook up the fuel line to the lower carb and find that it has worked it's way under the motor mount. Loosen the nut on the motor mount and free the line. Inspection of the fuel line showed that the motor mount had ben pinching on about half of the line.<br /><br />When full throttle was applied, engine torque would pinch the line. <br /><br />Try looking for this or other kinks in the fuel line.<br /><br />pbailey

 

[grizzlybars]

Re: fuel delivery problem over half throttle

for anyones info, problem is fixed. decided to inspect engine bolt by bolt, found missing bolt where block comes together behind starter. was sucking air into crankcase. replaced bolt, full power now with no starvation problems. thanks for the help