Idle surge

[bmstang]

I have a 78 235hp evinrude at idle the rpm's go up about a 100 and go wright back down. I'm wondering if it is spark related may be a weak coil or fuel related may be carbs.I just rebuilt both fuel pumps because they were spitting fuel but that didn't change anything. I tried squeezing the fuel bulb while running that did nothing almost stalled it any help would be great thanks.

 

[emdsapmgr]

Re: Idle surge

Probably easiest to check for spark first. An inductive timing light will show the quality of spark on each plugwire. Keep in mind that weak ignition components tend to fail when the engine heats up to normal operating temps-so check the spark after the engine is warmed up. Even better if you can check spark if it is under load, like when in gear, idling at the dock. You have two identical power packs on that engine (one for each head) which can be swapped for ignition testing purposes. Double check the idle rpm's. It should idle smoothly at a constant rpm somewhere between 650-750 rpm, when in gear, floating at normal level in the lake.

 

[191Seanymphstriper]

Re: Idle surge

It is 1 or 3 things or 4 but the 4th is expensive. Its not the fuel! Its a coil pack a wire from coil to spark plug a plug if its the 4th its the power pack and that sucks bc its the most expensive thing. Try hooking up a sep little tank of fuel with sea foam in it and run it a little. make sure you have full ball presure as well with the little tank. Burn up half a tank. If the prob is still there its not the fuel at all. But to be safe before you run the little tank drain all the carbs to be sure there no water in them. Then buy all new coils and all new plugs and just change them. There cheap enough and may need to be changed anyway if they havent been. GL!!!

 

[191Seanymphstriper]

Re: Idle surge

Also check those wires real good. If you see green build up it could be sending a short and grounding out somewhere!

 

[bmstang]

Re: Idle surge

Thanks guys i will look into those leads. I was looking at the coil packs one of them has a crack on the outer side of it does that mean it is bad. As far as replacing them there not that cheap there about $30 apiece and i have 6 of them looking at $180 plugs are new.

 

[191Seanymphstriper]

Re: Idle surge

Cheaper then a new motor. Buy all new coils and buy new plugs again and a set of wires. Im telling you she will run like a new motor after this! Its worth it!

 

[bmstang]

Re: Idle surge

Thanks i appreciate the info i will do that. The others are probably original except for one they have a square pack on one with 2 male spark plug terminals on that style but i checked spark and it has good spark. I wonder if i could use that style over the round ones i think they are cheaper and i have about 5 laying around from my 28 spl. I don't know where to get the ground wire for that pack that has the little right angle boot on it. Probably dealer item

 

[191Seanymphstriper]

Re: Idle surge

Listen. Before you go changing coils change your difram in your fuel pump! This can cause ruff idle and a or a serge as well. I just had a recent issue with idle and that was the issue. Hope it works for u and it was only a $3 fix

 

[emdsapmgr]

Re: Idle surge

Spark plug coils are pretty reliable. If you sense you have an issue with one, replace it. Does the engine appear to be lean sneezing? Coughing/missing every 5-6 rpm? That's a carb issue.

 

[191Seanymphstriper]

Re: Idle surge

Ok these are boats. We are on the water and somtimes offshore. Just get a rebuild kit for the carbs. There cheap and come with directions and is very simple if you can turn a wrench. But first. Replace all plugs cheap. And replace the diafram. If this dosent fix it. Move to the rebuild of the carbs but first run ( sea foam ) A product to clean carbs the best one there is. And see if that helps if not rebuild the carbs for piece of mind. If this solves it great if not. Start testing and replace coils They could be expensive but just because its sparking dosent mean its working. Could be lazy so listen and count the spark in a 10 sec interval. Replace any old fuel lines that look to be warn etc. And if its not that then its the stater. Or the spark plug wires are or could be bad. But you need fuel ignition spark and compression. If you have all these then she should run fine. So it may be a fuel or coil sounds to me. First I would get a rebuild kit for the fuel pump and get sea foam and new plugs. Start there. That should solve it!

 

[bmstang]

Re: Idle surge

Thanks guys i already rebuilt the carbs earlier i did have to rebuild the fuel pumps because one was spitting gas out the top hole. Rebuild kits cost me $15 i did the second one only because i thought it would just be a matter of time before that one started acting up. After i rebuilt the pumps it was still hunting i just changed the coils and wires and that solved the problem i got away from those round coil packs and went to the square ones with the double male terminals. Thanks for all the help.

 

[191Seanymphstriper]

Re: Idle surge

Great! Have fun on the water! Hope she runs great for another 35 years!

 

[bmstang]

Re: Idle surge

I wish i could did you read my other post about one head overheating. No sooner do i get one thing fixed another one pops up. I can't catch a break the life of owning a boat i guess i won't let it beat me though. Thanks for all your help