75hp is very slow

[bigbz28]

I have a 1974 Chrysler 75. It starts quick, idles normal and run fine at slow cruise speed about 4mph. If I try to go any faster it bogs down and cuts off. When not in water or gear I can rev the engine at the carbs and it has good throttle and rev response. I tried reducing the oil ratio and different gas with no luck

 

[Frank Acampora]

Re: 75hp is very slow

Try replacing the fuel pump diaphragm and gasket. Check all fittings for partial clogs. Clean the carbs and set the float level. You may have a sticking float or inlet needles.

 

[bigbz28]

Re: 75hp is very slow

I'll take a look at those things. In the meantime I am also gonna service the gear box and replace the water pump

 

[bigbz28]

Re: 75hp is very slow

Replaced the fuel pump and that didn't change a thing. I'm on the lake now trying to figure it out. Engine runs good out of the water but in the water, meaning it is now under load, it still has no power

 

[roscoe]

Re: 75hp is very slow

compression and spark test.

examine sparkplugs for differences.

 

[bigbz28]

Re: 75hp is very slow

Well, compression is 150, 155, and 160. Put new spark plugs in but I don't think the old ones were the problem. It seams to be fuel related. While on the lake I noticed that the primer bulb didn't get firm like it used to, so I removed it but that didn't change anything.

 

[81 charger]

Re: 75hp is very slow

try getting a new primer bulb. Mine has done that be for and it was the primer bulb. Pull the carbs and give them a good cleaning. lots of carb cleaner and compressed air along with checking floats will help a bunch.

good luck

 

[bigbz28]

Re: 75hp is very slow

Ok, I replaced the primer and put a see-through fuel filter on it. Bulb gets plenty hard and fuel fills the filter. Took it out on the water last night and it ran good and had power for all of 30 seconds before returning to the same slow condition. I squeezed the primer a couple more times and floored the throttle only to get an even shorter burst of power. Let it idle and worked the thottles in nuetral while watching the filter. It reved ok and the filter stayed full. Then it died... The igntion switched had failed on my. At this point it would crank and then stall when I let go of the key so I had to hold the key in "start" position to keep it running long enough to get back to shore. I was wondering if it could be the check valve in the pickup tube in the gas tank... Although it doesn't matter which tank I use and I did check it and the ball felt to be moving freely inside the pickup tube. About to try it back on the water after replacing the ign switch and then about to give up.

 

[MickLovin]

Re: 75hp is very slow

You said you replaced the fuel pump? did you replace the diaphragm? Do you have the filter in between the fuel pump and the carbies?
Also you haven't mentioned what you have done to the carbies, have you checked float height, and have you cleaned them.
After cleaning them and blowing them with compressed air, do a test too see if you are receiving fuel by taking your plugs out and hold a white cloth about 2 inches away from the hole, crank it and make sure you have fuel on the cloth, do this to all of your carbies.

Make sure you check Frank A's link and sync sticky at the top of this forum.

 

[jerryjerry05]

Re: 75hp is very slow

If the squeezie is hard. The diaphragm is probably ok.
Changing the pump usually changes or means changing the diaphragm.
The fuel lines might be delaminating.
The ethanol we use weakens the internal core of the hose.
I found a hose that the inside actually collapsed from the pressure of the suction of the pump.

 

[bigbz28]

Re: 75hp is very slow

All new fuel lines. The filter I installed is between the tank and fuel pump. I took apart the carbs and they were clean. What is the spec height for the floats?

 

[Jiggz]

Re: 75hp is very slow

Move the clear filter between the fuel pump and the carbs. Which tells you if it is full when the motor bogs down the fuel pump is delivering the fuel required as designed and also tells you the problem is downstream of the filter, i.e., carbs not set right, carbs floats not set properly, clogged needle port, etc. But if it is not even 3/4 full then it tells you the fuel delivery problem is upstream of the filter, i.e. fuel pump, hoses, pick up tube, tank vent, etc.

The fact you were able to get power for 30 seconds last time you tested it, it is obvious the problem is fuel related. And this is really not that hard to troubleshoot if you have the clear filter between the fuel pump and the carbs.

 

[bigbz28]

Re: 75hp is very slow

Ok I moved filter to after the fuel pump and it empties when I throttle it so this most mean a problem with the pump. I replaced the diaphragm last year though. Guess I'll take it back apart and see what I did wrong

 

[bigbz28]

Re: 75hp is very slow

Fuel pump diaphragm seams fine. Inside the pump is clean. I did notice that there is some black crap coming out the weep hole in the lower unit whatever that means

 

[MickLovin]

Re: 75hp is very slow

See if you can find a junker and swap some parts around, that's how I found most of my problems with my 80 and 76 model 75's.
Could still be your tank or your tank vent or your tank pick up or even a air leak from the tank onwards.

 

[bigbz28]

Re: 75hp is very slow

If it was the tank it would have emptied the filter when I had it on the feed hose from the tank

 

[MickLovin]

Re: 75hp is very slow

Thought you repaired the fuel pump and diaphragm?

 

[bigbz28]

Re: 75hp is very slow

I did but after putting the see through filter between the pump and carbs it empties when I rev it up

 

[MickLovin]

Re: 75hp is very slow

Which means you either have a leak or your diaphragm in your pump is fail, for the cost of a diapragm and gaskets, get one. Also look out for a junker doesn't have to be the same hp as these fuel pumps were used on many others, my 100hp had the same pump.

 

[MickLovin]

Re: 75hp is very slow

Black crap is usually un-burnt fuel, which can be from a an over rich mixture, air/fuel mixture too rich or excess fuel entering through the fuel diaphragm, it only takes a pin hole.