rpms drop to 2500

[dipstop]

just bought a 98 johnson 60 with carbs from a 70 installed. wot with one person is 6000 rpms. after about 20 min rpms drop to 2500. although no temp guage,moter doesn't seem hot. after shutdown it will run about 10 min before backing down to 2500. the pisser is pissing,the buzzer is not buzzing and like i said,it doesnt seem to get hot. Ive replaced fuel tank, fuel lines, filter,and had a mechanic take a crack at it. he checked carbs and fuel pump and I think thats about it. didn't help. outboard guys are very busy and it looks like i'm on my own on this one. my limited knowlage telles me that its a black box problem. is there a way to check the s.l.o.w. system? before i start buying parts in my replace and try out way of fixing things, i thought i could pick your brains.

 

[ob]

Re: rpms drop to 2500

rob ,First locate the tan/w/stripe temp sensor wire and with the key in the "on"position ,ground it to the block and verify whether the alarm buzzer is working.This will give us a starting point in determining whether the engine is going into the S.L.O.W. mode or if there is another issue.

 

[dipstop]

Re: rpms drop to 2500

yup-grounding the buzzer makes makes it buzz

 

[ob]

Re: rpms drop to 2500

Ok ,Try disconnecting both wires from the temp sensor and see if engine repeats symptom.If so your sensor is good and your problem lies in the alarm module or another issue exists.

 

[dipstop]

Re: rpms drop to 2500

ok- i do have one stupid question first. if i disconnect the temp sensor and it turns out that i do have a cooling problem, will i end up cooking the engine?

 

[ob]

Re: rpms drop to 2500

I'm thinking you already would have since the alarm didn't sound and you performed a test on it.How did you determine that the engine didn't seem to get hot?Did you remove the engine cover and feel the head covers or block?<br /><br />You can obtain a heat gun or a 163 degree thermo melt stik to take along with you on the water test to check for engine temp.<br /><br />Do rpms drop immediately to 2500 or is it gradual?<br />Thinking also along the lines of intermittent spark loss to one or more cylinders.

 

[dipstop]

Re: rpms drop to 2500

i wont be able to get the boat in the water until the weekend-this having to go to work really cuts down my free time. i did finally get ahold of the mechanic and got some facts that might help. he checked carbs, compression,fuel pressure,plugs and leads,fuel filter and ran it in his tank for an hour with little or no load.everything checked out fine. he also said that he didn't know what was wrong and he didn't (and won't for at least four weeks)have time to run the boat in open water. he pretty much left me with the impression that tracking down the problem was not something he wanted to spend time on. nice guy.

 

[dipstop]

Re: rpms drop to 2500

as far as the rpm drop, it dropped from 6000 to 2500 in about 3 seconds and i put my hand on the block and still have all my fingerprints