Chrysler 55 hp rpm problems

[jmk]

What could cause my 1971 Chrysler 55 hp out board motor run slow rpms while in full throttle? The thrrottle body is wide open but the boat only goes 10 mph. It idles and runs smooth, but does need some throttle to start. I have rebuilt the carb.

 

[eurolarva]

Re: Chrysler 55 hp rpm problems

If it does not over rev and go slow I would rebuild the fuel pump if it over revs and goes slow your prop hub is spun. Rebuild kit for the fuel pump is 18-7806 and Iboats sells them. Usually it is just the diaphragm and the main gasket that need to be replaced in the fuel pump.

 

[moparman]

Re: Chrysler 55 hp rpm problems

might also want to check your advance to make sure its moving with the throttle. A little history on the boat also would help[any work done to it before this happened, ect] Post us back with your findings,and or history . MOPARMAN

 

[jmk]

Re: Chrysler 55 hp rpm problems

I bought this boat in the spring and it would only run with the choke fluttering so I rebuilt the carb. This a Chrysler 1971 55 hp outboard. It seemed to be running well. I had also rebuilt the water pump. Anyway, all seemed good so I took it to the lake. It wouldn't start. I found that the gas tank vent was closed and the pressure build up was real high with air expansion. The primmer wouldn't pump up gas either. Then I noticed that the tube inside the gas tank fell off. After getting a different tank I could prime the plunger up and get gas to the carburetor. It would only start in full throttle. I had to let it run in full throttle for ten seconds or so before the rpms picked up. Then it would idle, but took full throttle to get it to about 10 mph. It ran smoothly but slow. I did check the advance and it is advancing with the throttle from what I can see outside of the flywheel. I wanted to get the flywheel off to look at the points and electronics, but I need to get a flywheel puller. I am not sure what the advance is doing inside. My original thought was that the pressure in the gas tank sitting in the sun with the vent closed had built up pressure and stretched the diaphragm in the pump. Can that happen? I closed the vent so water wouldn't get in the tank from rain. Is it bad to have the tank hooked up with the vent closed? I had left the vent closed for about one month while I made seats for the boat. Another thing too, does the gas tube inside the tank have a check valve? I was wondering if the tube came off from pressure in the gas line? This is one of those portable red plastic tanks that lay down flat.

 

[eurolarva]

Re: Chrysler 55 hp rpm problems

On your list of things I did not see you rebuilding the fuel pump. That would cause a lot of the problems you are seeing and is about the cheapest thing you an do for the motor. The diaphragm can be distorted, ripped or have pin holes in it. Cant give you a good answer on the gas tank. Glad my boat hangs out in my garage. I only close the vent on the gas can during transport or if I have to take the gas can out of the boat to refill. I know when my plastic gas tank sits in the sun with the vent closed the tank turns into a balloon.

 

[jmk]

Re: Chrysler 55 hp rpm problems

I ordered a fuel pump rebuild kit from iboats. It will be here soon. I hope this will fix the problem. I was thinking that this was it, but I wasn't sure if a fuel pump gone bad could still work like this. The ones that have gone on me before were bad to the extent that they wouldn't even run. I will replace it and let you all know if it fixed the problem. Thanks, jmk.

 

[jmk]

Re: Chrysler 55 hp rpm problems

I am sorry I forgot that I had made a seperate post about the gas tank. I didn't meen to make a double post by asking about it on this one. I figured out where the pick up tube failed. It cracked and broke off right at the brass nipple elbo that goes through the tank. I unscrewed the elbo and now know how to fix it too. It was a clear tube like snowmobile gas line. It must have been brittle and broke off while going down are bumpy road with the gas sloshing around.