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Evinrude 90 rough idle when warm

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realslimshady

Contributing Member
Struggling to get my '82 Ev 90 to run consistently. Carbs have been apart a few times, has new plugs, HT leads, fresh fuel. Only been in the water this year so not had a chance to try the motor before now.
Starts easily from cold and runs pretty well, but as it warms up the idle gets more and more lumpy until it stalls. Will then start again immediately, but once again won't idle. Will rev, but takes a long time to spin up.
Link to a short video-

https://youtu.be/4-xPqVE94RE

Any thoughts welcome.
 
3 years is a long time to sit around. How's the fuel bulb in the line, maintaining firmness?
Does squeezing it help the idle any?
 
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Have you performed a link and sync adjustment? Many problems with carbureted O/B emanate with the link and sync being off. Compression test, spark test, clean carbs, link and sync are a must to tuning up an O/B.
 
I did do a link and sync, as it wouldn't rev at first! Fuel system is fine, fresh fuel,no leaks. I will try the 'bulb squeeze' test on next visit.
 
No gooey substances or anything like that, but on my last visit had real problems keeping it running-and there was no pressure in the fuel bulb. Time to overhaul the fuel pump?
 
Before fuel pump, try the more basic items... sounds like it could be time for a new fuel bulb anyway. And make sure the tank vent is working, which can collapse a bulb and stop fuel flow. Try opening gas tank cap while running.
A clear inline filter between fuel pump and carb will let you know if fuel is flowing while motor is running.
Bubbles in the mix can indicate a bad fuel pump or pump diaphragm.
Good chance it's just a bad bulb...
 
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I took the cap off the fuel tank while it was running and it made no difference, so not the vent. The only way I could keep the motor running-and only at idle-was by squeezing the bulb, which I could feel pressurising the line. Surely once the engine is running the bulb has no function?
There is no inline filter in the system, just the one in the pump...maybe there should be...
 
realslimshady said:
I took the cap off the fuel tank while it was running and it made no difference, so not the vent. The only way I could keep the motor running-and only at idle-was by squeezing the bulb, which I could feel pressurising the line. Surely once the engine is running the bulb has no function?
There is no inline filter in the system, just the one in the pump...maybe there should be...
Click to expand...

Sounds like your ticking things off the list.
Do you have to squeeze the bulb to get the motor started when cold or will it start fine on its own?
Asking because you indicate the problem occurs when warm.
Maybe the bulb supplies fuel for a little while then is too weak to assist.
Try putting in a clear filter.
I don't want to get too caught up on fuel bulbs, but they do need replacing from time to time and can effect things more than we might think. This is an interesting read. Others will probably get something out of it too.
http://continuouswave.com/whaler/reference/primer.html
 
thanks for that link-an interesting read. Given me more food for thought! I think I may well go for a complete overhaul of the fuel supply system-replace all the hoses, overhaul the pump and change the primer bulb too! For the amount it will cost I think it's worth it.
 
Hey guys, sorry to revisit an old thread but I seem to be dealing with the same issue as above.

'84 E90 V4 this winter I replaced ALL rubber hoses and gasket in the entire fuel system. Overhauled the Carbs, Fuel enrichment/primer solenoid valve, and Fuel pump as per OMC manuals. Fuel tank was removed from the boat flushed out and the vent port was inspect and new vent hose was installed. New primer bulb hose kit was also installed. New spark plugs. New cooling system components. All of the tiny check valves in that cross feed fuel tubing system were checked and held pressure. That tiny fuel tubing itself was replaced.

I believe I did the carb throttle plate synchronization correctly? Starts very well cold or hot but struggles to idle and has a very lumpy idle. It can't idle down very well without stalling out during an idle. Very much like the original video the guy posted.

Compression has been checked twice. Cold all were close to 128 psi. Warm block all close to 118 psi.

Manually pressurizing the fuel system with the primer bulb during idle makes no difference. Using the enrichment/primer valve only bogs down the engine yet more with the extra fuel and does not improve the idle quality. Beyond approx 45% throttle run the engine runs smooth has good power and accelerates well in my opinion.

What I'm I missing? Any advice or direction would appreciated thanks!
 
I'll check that next. I have a very basic spark gap tester. The 3/8" gap is at a healthy starter cranking speed or engine idle? Would these CDI ignition systems be able to jump a 1/4"? gap and still fire the plug at the sometime during idle?

Thermostats and all related gaskets where replaced during the winter maintenance with new OEM BRP parts.

I appreciate your advice, I will head to the boat this weekend and report back!

Thanks,
Travis
 
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