1988 120 HP V4 - Bogging at WOT

Hello to all you guru's.. thanks for taking the time to look at this post. I recently bought a this 1988 Seaswirl with 120 HP Johnson. It had been stored for at least 3 years. Not knowing much about engines, I at least checked compression - all cylinders around 120 psi, good spark. It starts up pretty good, steady stream from Telltail.

Filled it up with new gas and took at out for a drive. I started slow for about 3 minutes, then decided to open her up. It went solid for about 30 seconds, then cut rmp's to at least half. It would not exceed I guess around 2000 rpm, no matter what I did to the throttle. Stops and start just fine, good water stream, but no power. Sound like it occasionally is mis-firing.
I took her out the water, look around... thought intitially something wrong with the lower end putting some kind of drag, but found nothing. I put her in the water again after a few hours of resting and was able to open her up again for about 3 minutes, but then the same thing.

So, I'm thinking it's related to heat - or power unit sending the (don't know what the term is) SLOW command. I also noticed a lot of carbon on top starboard cylinder spark plug, thinking maybe not enough spark or fuel issues. (could have water in tank) If I'm getting good flow in the Telltail, how do I know if it's passing the thermastats and getting to the engine?

Also, after ready some great posts here, I'm know I should replace the water pump (and I just did the plugs and fuel filter) Does the hot and QuickStart sensors go out? How do I check for that? I'm not a mechanic by any stretch, but I'm not afaid of getting the hands at little dirty. If anything jumps out at you, please let me know.

Re: 1988 120 HP V4 - Bogging at WOT

if it sat that long you will want to do a few things..

1) Spark pugs
2) Feul filter
3) feul water seperator
4) primer bulb (if need be..since there is Ethanol in gas now..)
5) Last but not least..Carb job.. I would rebuild thecarbs with some nice new kits..I think around 20-30 bucks each..you will need 4

As far as your issue it sounds like the high speed jet (s) could be getting clogged with gunk..this is why a carb rebuild is very good practice when any motor sits that long.

Regarding the carbon..some recommend doing a decarb on the engine..basically mix gas with seafom in a container..take plugs off spray in there, then attach the feul line to the rest and run the engine..it will caough and start to die but you can keep her going for a bit,,, then wait 20 minutes and start her up... she will smoke like you caught the house on fire but will clear up (carbon burning off).. Idealy you should take her to the water and run her to clean her out... then do again if you think its needed...(you can do all of this on the watr if you want...

PS..buy the manul for your engine..its worth every penny..get an OMC repair manual....not seloc or cramers...

Re: 1988 120 HP V4 - Bogging at WOT

Thanks for the reply. Would the fact that it ran fine for a few minutes be explained with the direct injection into the heads, and that bypasses temporarily the high speed jets in the carb? Also, when it boggs, I can put it in nuetral and rev it to high RPM's. Is that because it doesn't use the high speed jets unless there is a load?

I did put new plugs today, also replaced the thermostats (both were stuck open - not sure it that is the default possition) Ran motor in a tub of water for about 7 minutes... good water stream comming out of telltail, and warm. Starts right up, but does mis-fire at time during idle, but does better when warm. I plan on testing on water tomorrow. If everything is pointing to carb rebuild, then I'll be doing that too.

Re: 1988 120 HP V4 - Bogging at WOT

ccranda said:

Thanks for the reply. Would the fact that it ran fine for a few minutes be explained with the direct injection into the heads, and that bypasses temporarily the high speed jets in the carb? Also, when it boggs, I can put it in nuetral and rev it to high RPM's. Is that because it doesn't use the high speed jets unless there is a load?

I did put new plugs today, also replaced the thermostats (both were stuck open - not sure it that is the default possition) Ran motor in a tub of water for about 7 minutes... good water stream comming out of telltail, and warm. Starts right up, but does mis-fire at time during idle, but does better when warm. I plan on testing on water tomorrow. If everything is pointing to carb rebuild, then I'll be doing that too.

Click to expand...

Yes and no... when you start the engine you usally choke it by pushing in the key...what this does is (choke solenoid) shoots gas bypassing the carbs to start (this only happens after you have primed the bulb hard)..after that the feul pump takes over... so, if it ran for a bit then cut out you may have used the feul in the carbs and you were not replenishing it.or not enough..so back to carbs and/or feul pump..or just general feul issues..

High revs in a tub doesnt really tell you a whole lot.. it confirms it starts and runs but you really want to do treu testing on the water if you can.

I had an issue with my feul pump (vro)..that ran great on muffs, not that great in the water and under a good load it wasnt keeping up with feul supply.. in the driveway i could idle all day long and you would never know there was an issue...

Re: 1988 120 HP V4 - Bogging at WOT

Well, I added a water/fuel filter, replaced fuel line and bulb to engine, new plugs, and did a very basic carb spray with the air cover off, and opened up the carb bowl drain plugs. Didn't have time for the full carb overhaul... but took her out for a spin on the lake and she cruised like a charm. I was super happy. Then, I took her on a quick vacation to another lake and my high speed acted up again. I didn't have the power in the over 2500 rpm's range. So, I have some time now and bought a carb kit to hopefully do it right. Any suggestions? Was reading posts about old fuel lines... should I replace all lines inside the engine too? How about fuel pump, any good way to check that? Thanks for your advice.

Re: 1988 120 HP V4 - Bogging at WOT

ccranda said:

Well, I added a water/fuel filter, replaced fuel line and bulb to engine, new plugs, and did a very basic carb spray with the air cover off, and opened up the carb bowl drain plugs. Didn't have time for the full carb overhaul... but took her out for a spin on the lake and she cruised like a charm. I was super happy. Then, I took her on a quick vacation to another lake and my high speed acted up again. I didn't have the power in the over 2500 rpm's range. So, I have some time now and bought a carb kit to hopefully do it right. Any suggestions? Was reading posts about old fuel lines... should I replace all lines inside the engine too? How about fuel pump, any good way to check that? Thanks for your advice.

Click to expand...

you can check the pimp by taking the top hose of and having someone to crank the engine while you catch what shoots out of the elbow.. you should get good consistent rushes of gas..if it tappers off there could be an issue thee..

if its acting up at WOT..then it points to high speed jets inside the carb bowls..just behind the drain plugs.. after you pull the drains..you should squeeze the bulb and lets gas flush bak.. if its not clogged then you may be able to get whatever is in there out.

yes the gas lines of old are not taking the ethanol well..many will tell you to replace them all..and i agree.. I will be doing mine as well.. inside and out..but i think i will try and find te clear hoses so i can see fuel flow as well..