motor surges on high end speed

[madbiker]

PLEASE HELP I have a 1970 johnson 20 hp. Sat up in garage for quite a while so i did a complete tune up with new point, plugs, condensers, plug wire,fuel pump, and rebuilt carb. Runs perfect on low end and idles as smooth as silk but in open throttle high end it surges like it is starving for gas and if you don't throttle down it will even go dead. Any help with this would be great.

 

[fireman57]

Re: motor surges on high end speed

When it starts surging have a buddy repeatedly squeeze the primer bulb on your fuel line. If it cures the problem then your fuel pump is bad. I know you put one on but this will test it. Also make sure that your tank is vented. If these two things are fine you probably have picked up some more crud in the high speed jet. If you are running old fuel lines pieces break off and settle where you don't want them.

 

[kbait]

Re: motor surges on high end speed

Does pumping the primer bulb help when it acts up? If so, weak fuel pump or leaky fuel line from tank to carb.. possibly gummed up intake screen in tank itself. If it doesn't help, could be a mal-adjusted float level, or possibly partially clogged main jet in carb. I'm assuming you've tested spark on both leads and found 1/4" blue bolt in open air. You could also test spark with the motor in forward and throttle wide open to make sure it's sparking correctly at that throttle setting, to rule out a plug wire arcing to ground when the armature plate is turned fully advanced. Some stuff to check anyway.. Good luck!

 

[madbiker]

Re: motor surges on high end speed

When it starts surging have a buddy repeatedly squeeze the primer bulb on your fuel line. If it cures the problem then your fuel pump is bad. I know you put one on but this will test it. Also make sure that your tank is vented. If these two things are fine you probably have picked up some more crud in the high speed jet. If you are running old fuel lines pieces break off and settle where you don't want them.

i did everything but in the tune up but the carb first and it did the surge then i did the carb and still surg and the bulb pumping does not help i tried that

 

[madbiker]

Re: motor surges on high end speed

i guess it could be screen in tank i will have to check that i have the float set to level all around like the book says to do it

 

[fireman57]

Re: motor surges on high end speed

set the float level when holding the carb upside down.

 

[madbiker]

Re: motor surges on high end speed

set the float level when holding the carb upside down.

yeah i did that. do you thing there is a chance is may need to be a little more that level to allow more gas? maybe motor is a little picky....lol

 

[kbait]

Re: motor surges on high end speed

yeah i did that. do you thing there is a chance is may need to be a little more that level to allow more gas? maybe motor is a little picky....lol

I had to do just that to get one to run correctly at higher rpms (mid '80's 25hp). I still don't know why it wouldn't run properly at full throttle w/float set parallel, but it's hard to argue w/success. Give it a try.

Good luck!

 

[Silvertip]

Re: motor surges on high end speed

Are you certain it isn't getting hot?

 

[madbiker]

Re: motor surges on high end speed

I had to do just that to get one to run correctly at higher rpms (mid '80's 25hp). I still don't know why it wouldn't run properly at full throttle w/float set parallel, but it's hard to argue w/success. Give it a try.

Good luck!

I went back thru it again today. It was installer stupidity I had the carb float in upside down. Runs like a champ now. THANKS

 

[fireman57]

Re: motor surges on high end speed

good to hear it. Also nice to see someone admit their own mistakes. I've made plenty mostly when I get in a hurry or too many cold tasties when I am working on something.