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motor will only run at just above idle speed
|Author||Topic: motor will only run at just above idle speed|
posted 08-28-2001 09:36 PM ET (US)
I have a 1987 70 hp Johnson. I have not really used it that much since I bought the boat, but it always starts and idles great. Up unti this last trip it would also run full throttle without a problem. The last time we went out, launched, idled out to main part of lake, throttled up, and crusied on up the lake at full throttle. Getting good stream of water from the pump not too hot and thinking everything is fine. Then, motor drops down to just above idle rpm even with throttle in full position. With throttle in full position, motor ran slow but seemed a little out of sync. If I pulled the thtottle back, motor ran slow and just as smooth as ever. We motored back to the ramp, even started and stoped to check under the hood. Loaded up and went home. There was some stuff in the motor in line fuel filter, but it did not look like enough to cause a problem. I have not taken off the canister fuel filter and changed it yet, but I am going to. I know it could be a lot of things, but I just wanted to seen if someone has had a similar experience. Can the problem be poor fuel flow from the gas tank, or is it something else? I don't really want to just turn it over to the shop cause I am thinking about a new motor anyway, but if it is something simple I would like to keep using it. Kelly
posted 08-28-2001 10:05 PM ET (US)
Well, the first thing I would do is check the fuel flow - clean the in-line as you did and change the canister filter. ( when was it last done ? ) Also check for any blockages / kinks in the fuel line etc. Vent opened on tank if applicable ?
Just out of curiousity, would the engine rev up when out of gear ?
|Tom W Clark||
posted 08-29-2001 01:05 AM ET (US)
I'm not surer about the 87's but the VRO OMC motors of the 90's had a S.L.O.W. (I think that's what it was called) engine protection system that would limit engine speed to something like 2000 or 2500 rpm if any of several conditions were present like lack of oil in the reservoir, over heated motor, ect. Is this a VRO motor?
posted 08-29-2001 05:01 AM ET (US)
Either it is your motor over heating or you need to replace your temperature sender to the updated sender. This is the little rubber looking deal that sticks into your head (near the spark plugs)with a brown wire sticking out. Be careful not to break the bolts off if you have ever used it in salt water. If the bolt doesn't come out freely, use a torch and heat it up and slowly turn the bolt back in forth until it comes out.
posted 08-29-2001 06:16 AM ET (US)
Check the throttle linkages! All three carbs are linked via a rod held in place with plastic socket clips.. this rod can come loose and bingo, no throttle response at all.. just a hunch... happy Whalin'.. clark
posted 08-29-2001 08:58 AM ET (US)
Tom, It is a VRO, but the line is plugged, and I run premixed. It was that way when I bought it. I wondered about the SLOW mode, because it ran very consistently at the lower rpm. The water stream did not feel very hot, just warm, so I would be surprised if it was overheating.
Airborn, I will try the temperature sender. The way it went from working fine to not working fine almost instantly makes me think that it might be a broken wire or something like the sender. We were in some pretty choppy water, lots of boats on a pretty day, and something could have broken loose. The boat was in salt water before I got it so some corrision of connections may have occured.
Clark, I wondered about the throttle linkage, but it seems to be responsive in the low rpm range and if you push the thottle past the maximum (slow) rpm that the motor is running at, it is like it is getting more fuel but the spark is not advancing or something. It keeps running, but just not a smooth as when the throttle is pulled back to where it should be for he slower rpm.
Soho, I will do the fuel line thing first since it is the easiest for me and needs to be done anyway. Hope that is it.
I'll let you know what I come up with.
posted 08-29-2001 10:03 AM ET (US)
If it's the SLOW kicking in, it will run
fine up to 2000 RPM, then buck and kick
and splutter. (Been there.) That doesn't
sound like your description.
posted 08-29-2001 01:14 PM ET (US)
Also see my post at "Johnson VRO Bogging Down." I get the same intermittent problem but usually goes away if I pump some gas in. Still wondering if I once in a while forget to open the tank vent all the way. Also could be some older gas still in the bowl.
Mine's a 1986 has the oil thing working. I will try some of these suggestions and post after this weekend.
posted 08-29-2001 02:59 PM ET (US)
I have the same problem sometimes. One time the cooler shifted an crushed the bulp pump. Move the cooler and gave it a few squeezes and all was fine.
posted 08-30-2001 01:09 PM ET (US)
Ahoy, Kelly. Have you verified that all three cylinders are making power? Your symptoms are those of an engine down one jug.
Try pulling your plug wires one at a time, if it drops rpm that is a good cylinder, if no change, that is a dead cylinder.
If you find a dead cylinder, see if the plug wire for that jug will produce a 1/2" arc to the block. No fire? Ignition problem that can be isolated by swapping parts between cylinders. Got fire but not making power? Fuel problem, most likely in that carb.
Let us know what you find.
Red sky at night. . .
posted 08-30-2001 01:28 PM ET (US)
couple things. I am almost positive the 70's did not have SLOW in 87 because my 1990 did'nt. Check compression first. Then check spark if comp is ok. If you have spark then remove the airbox in front and squirt gas in each carb while running. If it bogs good. If it picks up, you have a fuel problem in that carb(my guess). Usually the bottom carb gets clogged first. Even on 2 cyls it should almost plane so you might have another issue but start somewhere. i would do a comp test before I started messing with stuff.
posted 09-01-2001 08:52 AM ET (US)
Check Compression!! ,I had same problem on my
40hp Evinrude and the compression was 125psi vs 110psi ,removed head cover, broken piston and scored cylinder = $$$$,hope you have a diferent problem.
posted 05-13-2002 10:15 AM ET (US)
I'm just wondering if you solved your problem. Just put in this last weekend and had nearly the same problem with an 80's vintage VRO. Going into the shop Friday....
posted 05-13-2002 11:32 AM ET (US)
Check your fuel line and primer bulb. If the check valve in the bulb is shot or the hose is leaking (fuel out or air in), you may not be getting enough fuel to the carbs. It happened to me a few miles out in Monterey Bay, but fortunately I had a spare fuel line and bulb.
posted 05-13-2002 01:04 PM ET (US)
Following the easiest things first approach, I installed a new fuel line. The old one was shot. The bad thing is that I have not had the boat out since. I will be thrilled if that fixes the problem. Kelly
posted 05-15-2002 11:20 AM ET (US)
Thanks for the advice. I'm hoping for the same kind of problem; however, I had a spare tank and line which I changed to and the problem remained so I am preparing the checking account for a new Merc 60HP EFI just in case....
Kind of hoping I have to repower, but don't tell the wife...
posted 05-16-2002 07:10 PM ET (US)
I have a 93 50hp evenrude VRO that runs great, except, shifting into gear, forward or backwards cuts off. Have to be very quick to get a chance at keeping it running, even when it's very warmed up. I'm thinking it might need a slight idle up adjustiment. Might as well try and adj. it, if i screw it up, then take it in to the shop. It's only a problem when leaving the ramp or returning to the ramp. Has anybody had this problem
before, any ideas ?
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