1972 20HP Chrysler Fuel pressure problems

[JKEP44]

Hi Everyone, I am helping my neighbor out on his Little 20hp outboard. The model is 204HD, serial is 1318, I think its a 1972 by the charts that I have been looking at. The motor had been in storage for quite some time when he purchased it. We cleaned the carb really well and got it running great on the stand. The problem is that when you take it out on the lake and run full throttle for very long the fuel pump doesnt seem to be pumping enough fuel and allows fuel to drain back into the tank. Here is a list of what we have done and checked:
Fuel hose connections (bypassed by installing barb fittings)
Fuel Primer bulb (verified direction and changed out with a new one due to cracks)
Fuel tank (Connected a different one with completely different hoses)
Fuel Pump (Purchased a rebuild kit, replacing gaskets and diaphragm)
Fuel pump (changed out with a spare)
Checked engine compression (118# on #1 and 120# on #2)
Replaced all fuel lines

The engine runs great when it gets fuel. If you hand pump the primer bulb the carb bowl stays full and the engine runs great.
One thing I noticed that I thought was odd... Both the fuel pumps we had have no spring inside them on the diaphragm. I dont see one on the parts diagram either. Is this a common thing on Chryslers to not have a spring?
Any help would be great. I need a new direction to try to go. The only other thing I can think of to do is hook in a gravity feed system and slowly work my way back towards the tank looking for something but at this point I think it almost has to be something with the pump.

 

[jerryjerry05]

Re: 1972 20HP Chrysler Fuel pressure problems

If it's feeding back through the check valves aren't working.
Post a pic of the pump along side of a ruler.
I might have some??
Yo assemble the pump right?? Pics?

 

[JKEP44]

Re: 1972 20HP Chrysler Fuel pressure problems

Hi Jerry, thanks for the reply. I wish that I could send you a pic but I am trying to get a jump on having a plan of things to look at when I get home. I work overseas and wont be back until two weeks time. I will contact my neighbor and have him send me some pics if he can. Im pretty sure that the fuel pump is assembled correctly, everything was indexed so it can only go one way. Hopefully he can send some pictures and you will be able to look at them and see something. The check valves that you mentioned... are you referring to the little metal ones inside the pump?

 

[JKEP44]

Re: 1972 20HP Chrysler Fuel pressure problems

Here you go, I realize its only external pics but that is all I have for now. I have read in other threads that there is another style pump that can be installed on some models that works better, is that true for this one?

 

[JKEP44]

Re: 1972 20HP Chrysler Fuel pressure problems

Crap, I forgot to tell him about the ruler.

 

[jerryjerry05]

Re: 1972 20HP Chrysler Fuel pressure problems

That's ok not needed.
Take it apart and see if there is any bends on the reeds?
They MUST fit absolutly flat.Maybe the reed plates backwards??

 

[JKEP44]

Re: 1972 20HP Chrysler Fuel pressure problems

I thought about the Reed plate being backwards, but the pump is not symmetrical, it can only go one way and the reeds can only go on one side. Is there normally no spring?

 

[JKEP44]

Re: 1972 20HP Chrysler Fuel pressure problems

Jerry do you know if there is supposed to be a spring in the pump or if the other style pump can be adapted to this motor. I cant seem to find a old enough parts diagram for it and the repair manual is a little less than vague on internals of the pump

 

[Frank Acampora]

Re: 1972 20HP Chrysler Fuel pressure problems

WOW! That's a new one on me. That fuel pump is a single stage pump and was usually used on engines up to 15 horsepower. It is probably right at its limit servicing a 20. There is no spring inside, just the reeds.. HOWEVER: there is a fine screen inside the inlet that may be partially clogged. The problem may be there. You do need to check that the small reeds are laying flat at rest. Any opening at rest will reduce pumping volume. Also be certain that the reed seats are flat and smooth.

Older Chryslers had a two stage pump that fit over the bypass covers. I don't know if your engine can be retro-fit. A couple of photos showing the whole side of the engine would be helpful.

 

[JKEP44]

Re: 1972 20HP Chrysler Fuel pressure problems

Great, thank you very much for the reply. I was unaware of the inlet screen. The reeds appeared to be flat when we rebuilt the pump. I didn't even look for an inlet screen. You saying that the pump is probably operating at its max makes me wonder if the inline filter between the pump and the carb might not have too much volume and limits the pumps ability to deliver fuel to the carb??? That is two more things to look at and gives me a new direction for when I return home in a few weeks. I will post if that fixes it or not. In the mean time, any other ideas would be great. Thank you again

 

[Nordin]

Re: 1972 20HP Chrysler Fuel pressure problems

In another thread with same kind of problem with a 20Hp we figured out that the fuelhose from tank was to long.
Check the length of the hose, 7 feet sholud be good enough.

Check the floatlevel in the carb. I have had similar problem with a 20Hp and replaced the fueldiaphragma but it did not solved the problem.
Then I checked the floatlevel and adjust it a bit........problem solved.
The level shall be parallel with the castingedge when you turn the carb upside down.

 

[Nordin]

Re: 1972 20HP Chrysler Fuel pressure problems

In another thread with same kind of problem with a 20Hp we figured out that the fuelhose from tank was to long.
Check the length of the hose, 7 feet sholud be good enough.

Check the floatlevel in the carb. I have had similar problem with a 20Hp and replaced the fueldiaphragma but it did not solved the problem.
Then I checked the floatlevel and adjust it a bit........problem solved.
The level shall be parallel with the castingedge when you turn the carb upside down.

 

[Nordin]

Re: 1972 20HP Chrysler Fuel pressure problems

Sorry, double replay..............computer hang up.

 

[JKEP44]

Re: 1972 20HP Chrysler Fuel pressure problems

Thanks for the replies. I didn't even think to look at the length of the fuel hose. That very well could be the problem or part of the problem. When we replaced the hose I think we replaced it at the same length as the old one.

 

[JKEP44]

Re: 1972 20HP Chrysler Fuel pressure problems

I checked the float level in the beginning and it was set to the instructions in the manual without me having to adjust it. I will definitely double check it if these other ideas don't work out

 

[grizzrider09]

Re: 1972 20HP Chrysler Fuel pressure problems

JKEP44 I am the one Nordin is talking about having the problem of the hose being to long. I bought a standard hose from walmart and my motor acted the same as yours. I cut the hose down to maybe 2.5 ft long and its running like a champ. I also got rid of the chrysler fuel connections and replaced them with Johnson. Hope that helps.

 

[JKEP44]

Re: 1972 20HP Chrysler Fuel pressure problems

That actually does help a ton. The fuel hose that is on it is from Walmart. That's most likely the problem then. I will get home and cut some off and see how it goes. That's not a conclusion I would have come to very quickly. Thank you very much.

 

[Geosh]

Re: 1972 20HP Chrysler Fuel pressure problems

Wow, I just bought a '79 20hp with the EXACT same problem!

Problem with mine was it was also running hot (was probably running lean and needs a pump replacement) so when air got back into the fuel line... BANG! Yeah, that was kind of scary. Fortunately no major damage was done, just a fuel hose exploded.

I've got new valves for the fuel pump (waiting on gaskets), I'll be sure to check that screen. Please let me know what fixes the problem for you! I've got a fuel hose from Walmart too, so if cutting that shorter fixes the problem let me know! Thanks!

 

[JKEP44]

Re: 1972 20HP Chrysler Fuel pressure problems

I will definitely post the solution. A little less than one week left until I go back home so I will take it out as soon as possible and let you know how it goes.

 

[Geosh]

Re: 1972 20HP Chrysler Fuel pressure problems

I rebuilt the fuel pump today and I noticed that whoever messed with this thing the last time had the diaphragm and the gasket backwards on the pump. I'm not a mechanic, but to me that seems like it may be problematic, possibly even the cause of the problem. After some new valves, new gaskets, and some careful removal of the ill-placed gasket remains with some very fine sand paper preliminary tests show no more air getting into the fuel line, so that's a good sign!

The carb had some things done to it too that were "out of spec", but I bought this thing cheap, so I expected to have to work on it. I'm learning real quick that a mechanic's worst enemy is the guy who worked on it before you did! Doesn't anyone ever read the manual anymore? :facepalm: