75hp Chrysler dying at full throttle

[Moxit]

Today I replaced the fuel pump diaphram,fuel line and clamps,Spark plugs,thermostat and impeller.The old fuel line primer was deteriorating on the inside and I could see all of the black particles in the clear inline glass filter,I also removed the fuel filter on the fuel pump housing and it was pretty clean.Here is the problem.The engine idle's fine and runs great at wide open throttle for the first 10 minutes but after that it will bog down after about 20% throttle.Anything under 20% throttle and idle still work fine.Also if I close the choke about 25% while full throttle is given,it will almost run at full power and stay that way as long as I keep holding it.After the engine sit's for a few hours it does the same thing again(runs great for 10 minutes ect..) Someone mentioned to me today that it could be that the vent on the fuel can could be partially clogged causing this,I haven't tried removing the cap yet but will.Any other suggestions?

 

[Moxit]

Re: 75hp Chrysler dying at full throttle

Oops forgot something =) When checking the timing sould it be checked with the engine in neutral and at wide open throttle by moving the throttle linkage by hand?The manual just says wide open throttle and a friend of mine seems to think that it should be in gear so that the timing advances before checking it.<br /><br />Motor ID# 756h2J

 

[Oldsaltydog]

Re: 75hp Chrysler dying at full throttle

If you have found small chunks of rubber in the gas, your carbs may need a good cleaning. As for timing, you can do "static" timing by using your starter and in neutral gear. For "dynamic" timing, the boat would have to be in the water, in gear, running at full speed, the boat perhaps tied to a dock or hanging into the water from a trailer. You could check the SEARCH feature under synchronization.

 

[Moxit]

Re: 75hp Chrysler dying at full throttle

Thank's EBG,I will clean the carbs the next chance I get.I wanted to add something else though.Today I took the boat out and noticed that when the motor bog's down if I pump the primer bulb very hard and continuously the motor will run perfectly at top speed.Sometimes while pumping it would get soft like air was getting in.Also when I primed it when first starting up today I noticed a very small amount of fuel spill from the connector that connects to the fuel tank,after I turned the connector end a bit it didn't leak anymore.Is it possible that air is getting sucked in through that connector and causing this problem?It's an old style connector which I don't think is used anymore or perhaps it was a homemade setup so if I do change it out,I will need to replace the one on the line and the one on the tank.Thanks for your help!!

 

[rbruce63]

Re: 75hp Chrysler dying at full throttle

I would bet my 1969 Chrysler 20 that your problem is in the fuel pumps! This happened to mine. I had to replace the diaphragms and this solved the problem.

 

[Moxit]

Re: 75hp Chrysler dying at full throttle

Already replaced the fuel pump diaphragm and it still does it =(

 

[eurolarva]

Re: 75hp Chrysler dying at full throttle

Sounds like you have a air leak from someplace. It could be you have a defective fuel bulb. Even new ones can be bad. When you had the fuel pump apart did you check the valve seats to see if the gaskets were good? The center one with the scews is easy. the two press fit ones are almost impossible to get out without breaking. I would order two along with new gaskets and replace them. They are about 5 bucks each and the gaskets are almost free. Make sure the screws on fuel pump are tight Inspect nipple at fuel disconnect and verify you are getting a good seal. If you have a portable gas can you might want to take it apart and check the filter in the gas can. When you put it back together use teflon tape on the threads.

 

[Moxit]

Re: 75hp Chrysler dying at full throttle

Found and fixed the problem =) It ended up being the quick connect fitting on the fuel line that connects to the fuel tank.One of the o-rings was torn and it was sucking air.So I replaced the connector for $3.50.Thank you all for your help,I am once again a happy boater!!