1969 Chrysler 55hp intermittent backfire and low rpm.

[bvsteamer]

I have a 1969 55hp outboard with CDI. I have replaced all the fuel lines and filter, cleaned the tank, installed a new primer bulb, correctly vented the tank, new plugs and checked the electrical system (not my first post). Also rebuilt the fuel pump and carb. The motor runs well, except after a couple hours will backfire/miss and attempt to stall. When I give it throttle, it revs up and the backfire/miss will go away and everything runs normal for quite a long time. Yesterday it did this and it also wouldn't rev over 3100 rpm at full throttle under load (maybe to too much load - I had 7 people in the boat). Anyways, after I rebuilt the carb, the idle needing adjusting to keep it running, and now when it warms up it will sometimes stall due to low idle as well.....any ideas? It seems to be a carb adjustment issue I think.

Bob

 

[bentle]

Re: 1969 Chrysler 55hp intermittent backfire and low rpm.

Sounds like carb issues but have you done compression test yet? Also older motors
Used points and condensers. May be another place to check.

 

[bvsteamer]

Re: 1969 Chrysler 55hp intermittent backfire and low rpm.

Compressions good, as is the ignition system. The problem (idle especially) seemed to begin after the carb rebuild.

 

[bentle]

Re: 1969 Chrysler 55hp intermittent backfire and low rpm.

Ok. Make double sure the primer bulb stays firm after priming. Check pickup tube inside of fuel tank. Double check for any loose fuel lines or cracked lines allowing air into fuel. Make sure the choke or outer butterfly on carb is all the way open while at idle. Check your float in carb for proper operation, the float may not be allowing enough fuel into fuel bowl. In fact if you can pump the primer while running and recover rpms then you are not getting enough fuel to the carb bowl to maintain rpms. Did you adjust your air fuel mixture? May be to rich and loading up. Number of people in boat will only slow you down. Shouldn't effect rpms just mph.

 

[bvsteamer]

Re: 1969 Chrysler 55hp intermittent backfire and low rpm.

Yes you can pump the primer and it will recover.....for almost an hour actually. I did all the fuel line stuff and checked the butterfly. Didn't touch the mixture screws or anything else when I rebuilt the carb. Sounds like I need to check the float adjustment......all this seems related to the carb rebuild.....as I said earlier, after the rebuild, it would not idle until I adjusted the idle adjustment on the engine. The RPM is also still an issue.

 

[jmulz824]

Re: 1969 Chrysler 55hp intermittent backfire and low rpm.

You might check the fuel pump screen too, it gets clogged from the fuel pump to the carb, you may not be getting enough gas.

 

[fucawi]

Re: 1969 Chrysler 55hp intermittent backfire and low rpm.

Air vent on tank OK ?

 

[bvsteamer]

Re: 1969 Chrysler 55hp intermittent backfire and low rpm.

Yes, I checked the fuel pickup and vent line for the tank. I also notice that there is a lot of gunk (lack of a better word) seeping out the two holes at the bottom of the lower end. Is this a over rich indication? The motor starts right up and seems to run fine otherwise.

 

[bentle]

Re: 1969 Chrysler 55hp intermittent backfire and low rpm.

Yes that's a good indication of running to rich. Need to adjust fuel mixture on carbs and
One other prob you may be having is your fuel recirculation may be clogged. What this does is collect and recirculate any unburned fuel and oil from any low spots in the crankcase. It then is transferred back to the intake side to be burned. If not working properly your motor can experience
poor low speed,poor acceleration,spark plug fowling,stalling or spitting (backfire) at idle. Excessive smoke on acceleration. This is sometimes one of thoughs places that goes unnoticed and unmaintained for years.

 

[bvsteamer]

Re: 1969 Chrysler 55hp intermittent backfire and low rpm.

Where are the fuel recirculation components located?

 

[bentle]

Re: 1969 Chrysler 55hp intermittent backfire and low rpm.

If any it will be located on the port side. What you prob. have are some hoses
that run to a tee then a hose that runs down to the lower leg. Back then chrysler wasn't to worried about pollution in the lakes or so i'm told. Just make sure thought hoses are not clogged by blowing air through them.