weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong running?

[ctravis595]

i have a weird issue with my (i think 1988) johnson 48 spl. i bought the boat used and i'm thinking the previous owner couldn't get this issue sorted out, explaining why he wanted to sell the boat

he said he replaced the impeller already, so i don't think the engine is getting overheated at all. it shoots a steady and strong stream of liquid

but whenever im out on the water, i start the boat and it usually needs a little throttle to stay running under load. i don't have a tachometer so it's hard to know exactly whats going on with the rpms. it idles, but if i dont have some throttle going then it will die when i put it in gear

it will run for a while (at least 15 minutes) at full throttle, runs great actually and i was somewhat impressed with the speed this little old 48 hp can get to with my 17 foot center console but after running full throttle for a little bit it will start to run really crappy, like it's only firing on one cylinder instead of two and only barely idling along... sometimes i can get the boat to kick back up to full throttle after a few minutes of playing with the throttle. pumping the gas bulb doesn't help and niether does spraying starting fluid in the intake

i tried taking apart the carbs to see if i could find anything that looked wrong but everything looked okay? i did my best to clean them out and blow out anything that could be clogging it up but it didn't really help

i've noticed non ethanol gas helps it run better/dies out less

i'm assuming my issue is my high speed jet carbs, my question is - should i just buy a rebuild kit or a whole new carb assembly? i'm new to working on these outboards but they seem extremely easy compared to working on my cars and bikes. how do i know exactly what parts i need to order for my 48 spl?

any help is awesome and would be greatly appreciated!!! would be cool to get the boat running for summer!

 

[carholme]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

If it is a 1988, it would be one of these models:

VJ48ESLCCC

1988 Johnson/Evinrude 48 - OMC, Johnson & Evinrude Parts Lookup or

J48ESLCCC

1988 Johnson/Evinrude 48 - OMC, Johnson & Evinrude Parts Lookup

Here is a link to the condensed version of the Clymer manual to help you get started. Download it soonest to your computer as the link is short lived.

Small Engine Repair Reference Center Home: OUTBOARD MARINE CORPORATION - EVINRUDE AND JOHNSON TWO-CYLINDER MODELS 40 H...

Gerry

 

[ctravis595]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

some more info

just checked the coils, they look like they were recently replaced. the spark plug cables look new and so do the spark plugs. the primer bulb feels somewhat stiff after pumping but not "hard as a rock" like some would claim. upon doing more research i've read that my thermostat could have gotten gunked up because i use the boat in saltwater? do i have to open the actual engine up to get to the thermo? seems like it would be underneath the plate where the spark plugs enter the cylinders but i'm not sure.....

edit; after some thorough reading of the manual you linked i was able to figure out the thermostat is indeed under the cylinder head cover

 

[ctravis595]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

If it is a 1988, it would be one of these models:

VJ48ESLCCC

1988 Johnson/Evinrude 48 - OMC, Johnson & Evinrude Parts Lookup or

J48ESLCCC

1988 Johnson/Evinrude 48 - OMC, Johnson & Evinrude Parts Lookup

Here is a link to the condensed version of the Clymer manual to help you get started. Download it soonest to your computer as the link is short lived.

Small Engine Repair Reference Center Home: OUTBOARD MARINE CORPORATION - EVINRUDE AND JOHNSON TWO-CYLINDER MODELS 40 H...

Gerry

much appreciated!

 

[carholme]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

See the thermostat as item 12 under CYLINDER & CRANKCASE

Gerry

 

[ctravis595]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

im in the process of reading the service manual you linked to me and i'm having trouble differentiating whether or not my engine is an 88 or an 89...

they say only the '89 has a remote ignition, which i'm assuming refers to the fact that it is started using a key somewhere such as the center console (please correct me if i'm wrong)

but according to the manual, on these 89 models it has a S.L.O.W system which is designed to limit the engine to 2,000 rpms when it gets over 203 degrees. perhaps my engine isn't getting flooded and it's getting overheated somehow?

if this is the case i'm really leaning towards the thermostats...

still have some more reading and troubleshooting to do though

 

[ctravis595]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

service manual also recommends replacing the cylinder head gasket when i check on the thermostat

for anybody who wants to help troubleshoot here is some useful info regarding overheating directly from the manual -

"overheating may be caused by damaged thermostat, damaged relief valve, exhaust cover gaskets leaking, head gaskets leaking, and faulty water pump/water passages"

 

[ctravis595]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

forgive me for my ignorance and inexperience, but i'm self taught as a wrench(and 21 years old) and have learned through ordering very expensive car parts that you don't want to buy anything that isn't broken. is it common practice to just order and replace all suspect parts since they can be found relatively cheap? i'm asking because i'm not sure if i should just go ahead and order a carb kit and new thermos when the actual problem may not lie in either of these components...

 

[carholme]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

No it is not a good idea to spend money on parts until you are sure what the problem is. However, carb kits and thermos are routine maintenance change items and are not going to break the bank. Take the thermo out and test it in boiling water. You will be able to see if it is gunked up from saltwater ops. As a mechanic, you know that carbs are great when they are working but with the types of orifices, floats, needles jets, etc., it only takes that one spec of crap to foul your day.

Take the carbs apart, clean them well, ensure the float heights are set correctly and give them a try. Without a tach, it is hard to know if you have the carbs setup correctly.

You say you are worried about the thermostats but for the moment, that does not seem to be your biggest problem. When you start the engine, the telltale should not be visible for a bit until the engine heats up to allow the thermos to open. Presumably this is happening as you say you have a good telltale and it ran very well for 15 mins.

Time to just do the basics and see where you stand. Do a compression test, check that you have spark. ensure that you don't have any fuel or air leaks, check the filter and the diaphram in the fuel pump to make sure you don't have a problem there.

Have you determind yet which model engine you have?

Gerry

 

[ctravis595]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

No it is not a good idea to spend money on parts until you are sure what the problem is. However, carb kits and thermos are routine maintenance change items and are not going to break the bank. Take the thermo out and test it in boiling water. You will be able to see if it is gunked up from saltwater ops. As a mechanic, you know that carbs are great when they are working but with the types of orifices, floats, needles jets, etc., it only takes that one spec of crap to foul your day.

great advice on testing the thermo, i've yet to break one on any of my vehicles so it's not something i'm entirely familiar with but i will be sure to do that

Take the carbs apart, clean them well, ensure the float heights are set correctly and give them a try. Without a tach, it is hard to know if you have the carbs setup correctly.

i've tried cleaning them (service manual says not to overnight soak them, use aerosol spray) but i never had a chance to properly set them up according to the service manual as i've never had much luck finding one until you linked me (which is highly appreciated)

You say you are worried about the thermostats but for the moment, that does not seem to be your biggest problem. When you start the engine, the telltale should not be visible for a bit until the engine heats up to allow the thermos to open. Presumably this is happening as you say you have a good telltale and it ran very well for 15 mins.

Time to just do the basics and see where you stand. Do a compression test, check that you have spark. ensure that you don't have any fuel or air leaks, check the filter and the diaphram in the fuel pump to make sure you don't have a problem there.

Have you determind yet which model engine you have?

Gerry

when i take apart my thermos i will compare my engine to the schematics in the service manual to try to figure out what year i have exactly

i hate to belittle your expertise (As it seems you very well know what you're talking about) but i read elsewhere that the engine should be pissing ALL the time(as the water is constantly running through the engine, hence why you shouldn't start the engine out of the water or without muffs)? because my motor definitely pisses the entire time it runs (which i thought was normal)

if this isn't the case then i think perhaps my thermo is stuck open? causing my engine to not heat up to proper operating temps (and if the compression isn't 100 percent) then the metals aren't expanding like they should in the engine, causing a blow by scenario (therefore explaining how it only fires on one cylinder)

if this is the case i should have oily plugs correct? i will check these also when i tear nto the motor later today...

you've been a tremendous help in getting this whole thing in perspective mentally. i'm kinda exhausted project wise as i've been working on an engine and transmission swap in my car for the last few weeks

 

[ctravis595]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

i keep finding different opinions as to the proper behavior of the pisser...perhaps it's a constant slow stream but picks up and shoots a lot faster when the thermos opens? i just don't understand how an engine designed to have water flowing through it would have intermittent operation, although i am new to these older style engines

or perhaps the previous owner removed the thermos altogether to keep the engine from overheating (hiding another problem altogether) because it does look like they tried the usual troubleshooting methods already

 

[carholme]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

Well. as you say you are tearing in to it soon, you will see if there is a thermo in there or not. Whatever happens with it , good luck and let us know what you find.

Gerry

 

[ctravis595]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

Well. as you say you are tearing in to it soon, you will see if there is a thermo in there or not. Whatever happens with it , good luck and let us know what you find.

Gerry

so after tearing into it, i've found not only does it have the thermostat, but the thermostat is functioning correctly (watched it open up in a boiling pot of water)

at this point i'm leaning towards either a coil pack overheating or the power pack

i have little use for a compression tester besides testing this engine and want to keep some sense of blind faith in this engine if it does indeed have rough compression. would have no problem with going through more spark plugs than normal if that's all it means (call me ignorant or arrogant or whatever but shall be it). i just have faith in the fact that it runs great when it does run properlyso that's good enough for me

im gonna try to pull the spark plugs next to see what they look like, crossing my fingers

 

[ctravis595]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

i also cannot determine if this model is a 88 or an 89....ive tried comparing photos to the ones in the service manual but im not having any luck

 

[ctravis595]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

after very extensive reading i'm almost sure my symptoms are congruent with people having issues with their power pack. seems common on 1980's johnsons.

the only issue i see with this theory is whatever caused the power pack to fail the first time, will possibly make the pack fail again. i guess the only way to figure it out is to try it. i will report my findings for anybody else having this issue. if anybody has any advice it is welcomed

 

[ctravis595]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

edit:was able to use to cross reference part number from existing power pack to find a new one, if anybody has any opinion on whether or not this power pack is the best fit for my engine then let me know as it seems there are a few different versions that could be used

and i'm leaning towards my engine being an 1988

 

[carholme]

Re: weird 48 spl issue, rough idle/dies at full throttle after 15 mins of strong runn

If it is VJ48ESLCCC or J48ESLCCC, see item 21 under IGNITION SYSTEM

0586800 KIT | eBay

Gerry