1985 evinrude 20 hp backfiring/running rough

[ballsout]

Hey I had my motor out for the first time today since i bought it late in the fall last year and shes running like poo. I did a carb kit and replaced the fuel pump over the winter. When I was out for the short amount of time tonight it was not idling smoothly and would hesitate and cut out under load. I took the cover off while on the water and it was backfiring and no matter how i adjust the carb it isn't helping at all. My mix of fuel is 100:1 and it has fresh 91 octane in the tank with johnson/evinrude outboard oil.
where should I be starting to figure out this issue, i need the motor running A1 in a couple weeks because we rented a cottage on an island.

it seemed to struggle when under stress like hitting big waves and it sounded like I was messing with the throttle when going full out. The motor starts and runs well when I have the flusher on in the driveway.
should my fuel tank vent be closed or open? I tried both and there was no difference.
Once again the motor is an 85 evinrude 20 hp.

 

[nwcove]

Re: 1985 evinrude 20 hp backfiring/running rough

avoid the 100:1 and go with 50:1, did you clean the carb or just add the parts from the kit? if you just added new parts you need to actually clean the carb. ( top secret file at the beginning of this forum) . sounds like its running lean . tank has to be vented.

 

[Daviet]

Re: 1985 evinrude 20 hp backfiring/running rough

First off, you need to use a 50:1 fuel/oil ratio.
The static setting for the low speed needle valve is 1 1/4 turns out from lightly seated and then fine tuned in the water in gear.
The tank vent should be open.
Is the engine backfiring through the carb or exhaust?
If it is backfiring through the exhaust, it sounds like a lean sneeze and the engine is running lean.
If the engine is backfiring through the carb, check the reed valves and see if one is broken or split. Make sure there is nothing stuck under a reed valve holding it open.

 

[ballsout]

Re: 1985 evinrude 20 hp backfiring/running rough

it seems to be backfiring through the carb and why not the 100:1 that is recommended? im just curious. I will check the reed valves tomorrow when i get a chance to open it up.

 

[Daviet]

Re: 1985 evinrude 20 hp backfiring/running rough

They found out that 100:1 was not protecting the engines, there was a bulletin about changing to 50:1 on the engines labeled 100:1.

 

[ballsout]

Re: 1985 evinrude 20 hp backfiring/running rough

avoid the 100:1 and go with 50:1, did you clean the carb or just add the parts from the kit? if you just added new parts you need to actually clean the carb. ( top secret file at the beginning of this forum) . sounds like its running lean . tank has to be vented.

carb was thoroughly cleaned with carb cleaner and torch tips in all the openings to get all varnish out. I was running anywhere from 1 turn on the carb to 3 turns and anywhere after 3 turns she wanted to quit on me.

 

[ballsout]

Re: 1985 evinrude 20 hp backfiring/running rough

update- I was out again today to try and tune the carb and nothing I dis helped full throttle performance. What I discovered though. at half throttle in forward it runs perfectly smooth with no backfiring. At idle it is a lot better today and not backfiring anymore. at full throttle it slows and seems to miss quite a bit. I replaced all the small lines off the primer over the winter because I wanted to have all new clean fuel lines and to fit on the nipples on the primer and the T fittings i needed to use larger fuel lines from a chainsaw. I can see a lot of air moving through the lines at all times. Could the air in the primer lines be causing the miss at full throttle? Should i try and get a hold of the small harder lines that came on the motor?
Also I changed the fuel mix today to 50:1.
Also the motor starts very easily (only half a pull and it fires) but i need to pump the primer on the front of the motor 5 times or so for it to get fuel into the carb.

 

[ballsout]

Re: 1985 evinrude 20 hp backfiring/running rough

bump

 

[nwcove]

Re: 1985 evinrude 20 hp backfiring/running rough

not 100 % sure on your engine, but air in any fuel line can be an issue. do you have access to a different tank for a try?

 

[ballsout]

Re: 1985 evinrude 20 hp backfiring/running rough

tank is good (used it today with a different motor) its the lines only from the manual primer to the top of the carb.

 

[nwcove]

Re: 1985 evinrude 20 hp backfiring/running rough

mentioned that because ive seen issues in tanks, when an engine would idle well, run midrange well, but get air at wot. i put the fuel line directly into the the tank ( open end) primed it and it ran great. the pick up line in the tank rusted out in two years! other than that, your motor sounds like like you have a lean condition at high speed, .....carb? or you need to narrow down the air leak? jmo

 

[ballsout]

Re: 1985 evinrude 20 hp backfiring/running rough

update...back out today, replaced all primer lines with smaller ones and primes a lot easier and seems to now create a vacuum and is better for that. Still same issue at high speed though.
What i did was pull the connector off the end of the fuel hose and same issue with cutting out at high speed. What I did discover though is if I am driving at full speed and am sqeezing the primer bulb it runs fine and will not bog down....so it is narrowed down to a lack of fuel supply I believe. With the connector on the end of the fuel line hooked to the tank normally it is fine if I am pumping the primer bulb at full speed.
So all I can think of is that I have a bad fuel pump....but my fuel pump is a brand new BRP one so before I go out and buy a new fuel pump again again is there anything else that can cause this issue?

recap
-cuts out at full throttle and bogs down
-starts and idles perfectly
-runs fine at full throttle while pumping the primer bulb
-fuel pump is new from BRP (opened up and screens are spotless and diaphragms are good)

please give me opinions i need it to be running ok by next weekend as we have rented a cottage on an island and need the boat for getting back and forth.

 

[ballsout]

Re: 1985 evinrude 20 hp backfiring/running rough

bump

 

[nwcove]

Re: 1985 evinrude 20 hp backfiring/running rough

still sounds like you have an air leak on the tank side of the pump, and supply is not keeping up with demand at wot. dont rule out a bad pump tho..new parts arent always good parts.

 

[AlTn]

Re: 1985 evinrude 20 hp backfiring/running rough

once the engine is warm, is there a way to plug off the cold start primer side of the fuel feed to rule out an air leak within that manual cold start primer?....thinking that by manually squeezing the fuel line primer you are also able to exert enough pressure that fuel and not air may be by passing any worn orings within the primer system

 

[ballsout]

Re: 1985 evinrude 20 hp backfiring/running rough

once the engine is warm, is there a way to plug off the cold start primer side of the fuel feed to rule out an air leak within that manual cold start primer?....thinking that by manually squeezing the fuel line primer you are also able to exert enough pressure that fuel and not air may be by passing any worn orings within the primer system

so would kinking the fuel line from the primer to the carb work to do this test?

 

[AlTn]

Re: 1985 evinrude 20 hp backfiring/running rough

I've used hemostats with some rubber tubing over the clamping ends to prevent damage to the fuel line for this, but any method that blocks it off should work just as well

 

[ballsout]

Re: 1985 evinrude 20 hp backfiring/running rough

I've used hemostats with some rubber tubing over the clamping ends to prevent damage to the fuel line for this, but any method that blocks it off should work just as well

awesome, i have nice pliable new fuel lines on the primer so they will be easy to clamp off without damaging it. Thank you very much for the help....this sounds very logical and I am having trouble believing it could be the fuel pump as it is a brand new OEM piece and I checked all the internals and they are perfect. fingers crossed this is the issue and I will also tighten and check all the hose clamps from the tank to the carb.