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Author Topic:   OMC 90 hp carb rebuild
knothead posted 03-19-2002 04:50 PM ET (US)   Profile for knothead   Send Email to knothead  
A friend of mine just bought a 1988 Montauk with a 1988 Evinrude 90. The boat is in great shape(garage kept) but the motor will only rev up to 4000-4100 RPM's at WOT. Prop is 13.25X17. Mechanic says carb's need to be rebuilt, high speed jets are probably gummed up from boat sitting with no stabilizer in the fuel.
Question is, how hard is a carb rebuild on this motor? My friend is very familar with auto carbs (old MG's and Corvettes)but like myself, is somewhat intimidated by outboard motors. What special tools, gauges, etc. are needed for this job? We both realise that you can destroy a 2 stroke engine with bad carb settings. Should we try the rebuild or just take it to the dealer? He wants about $300 to rebuild, but if it's similar to an auto I know we can do a better job.
Eagleman posted 03-19-2002 05:02 PM ET (US)     Profile for Eagleman  Send Email to Eagleman     
Why doesn't your friend get a can of carb. cleaner and run it through. It would be quicker, less expensive and probably effective to in getting those high speed jets cleaned up. Good luck
knothead posted 03-19-2002 05:53 PM ET (US)     Profile for knothead  Send Email to knothead     
Mechanic says that there is no "magic bullet" when it comes to carbs. He says that too much spray carb cleaner washes the oil off the cylinder walls and causes galling because of inadequate lubrication between the pistons and cylinders. I know that carb cleaner will work in cars to a certain extent, I just don't know about these 2 strokes.
David Ratusnik posted 03-19-2002 06:24 PM ET (US)     Profile for David Ratusnik  Send Email to David Ratusnik     
$300 well spent. .03 David
David Ratusnik posted 03-19-2002 06:33 PM ET (US)     Profile for David Ratusnik  Send Email to David Ratusnik     
My point illuded me. If you just bought it and thought you got a deal--then, as you point out trash a cylinder with a bad carb, where are you in $$'s.?? If oil is not being fed into the engine you are looking for big $'s trouble. Spend the $300 and get a good night's sleep. Then, again, it may not be a carb prob at all. Could be a coil or two. .03 David
clanton posted 03-19-2002 09:09 PM ET (US)     Profile for clanton    
The 2 carb kits are 32.00 US and change,and flatrate should not be over 3 hours. You need a float guage and jet tool to remove the jets. You can pass on the float guage and make the jet tool from old screwdriver. There is more if you decide to do the repair.
May not be carb problem, Compression test first, spark test second, and after you get it running check the VRO2 pump and oil tank.
WHALETEX posted 03-19-2002 09:38 PM ET (US)     Profile for WHALETEX    
If you are comfortable with auto carbs then theses will be no problem. The usual keep track of what you take off to put it back on particularly with the linkages. Remove airhorn cover and airhorn. Carbs are held to motor with 2 allen screws each. Remove the float bowls and there will be a pair high speed jets behind the drain screws comming in from the side of the bowl and some low speed jets in the bottom of the bowl. These jets are threaded so remove them. Remove the float, needle and seat from the carb body along with any other plastic parts like the linkage snaps. Remove the vent cover on the top. Put the carb body and the metalic jets in one of these gallon cans of carb cleaner with the basket inside. Do not put any plastic parts in this stuff. After 20-30 minutes pull the parts out and rinse with water and blow all passages clean. I use a can of spray cleaner on any deposites in the bottom of the plastic bowl. My bet is your floats are set ok so I would just verify both carbs have the same setting and reassemble. The gaskets in these carbs are really high quality and with care during disassembly you will be able to reuse them.
WHALETEX posted 03-19-2002 09:44 PM ET (US)     Profile for WHALETEX    
Oh, to verify you have gummed up carbs just pull the drain screws from the sides of the bowls and pull a couple of the high speed jets. They will either be clean or varnished up with that bad gas smell. If the are gummed up go ahead and pull the carbs down and do the full cleaning since other parts of the carbs will also be gummed up. You don't want to take a chance on running the engine lean by just cleaning the high speed jets.
ratherwhalering posted 03-20-2002 01:06 AM ET (US)     Profile for ratherwhalering  Send Email to ratherwhalering     
Hi Knothead. I have a 1987 Johnson 90, and also had a similar problem. I tried Merc "Powertune" and got an additional 500 RPM from the engine. It worked great with just one problem...the base plate started leaking started dripping out the lower cowel. I also have experience with auto carbs, and opted to pay my mechanic to service the carbs. It was about $280.00, with parts. Best money I ever spent, it runs like a champ. My mechanic did the final adjustments in a water tank, with the engine in gear to simulate low idle. I honestly wouldn't have thought of that...just an example of what paying for a little experience brings to the table.
Bigshot posted 03-20-2002 09:44 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I would take all these posts and pull info.

1) Do compression test....worth the 10 minutes, hate to spend $$$ to find out you have a dud cyl. testers are $25.

2) To see igf carb is shitty either A)tap the choke when running and see if she picks up or bogs. If picks up, carbs or fuel related. If it bogs, try squirting fuel into each carb and see, if it picks up....

3) $300 is a bit high if he is removing, installing , and adjusting it is OK. If you remove and install then it should be about $75 per carb. It might be worth the $150 due to the "synch & Link" you need to do. These carbs have no idle adjustment per say, you need to adjust butterflies to get the idle and can be tricky.

4) If not carbs I would venture to say a coil breaking down or maybe some schmuck messed with the timing. Last but not least could be the lower unit but highly doubtful.

ratherwhalering posted 03-20-2002 12:11 PM ET (US)     Profile for ratherwhalering  Send Email to ratherwhalering     
A quick update after looking at the invoice.
Parts- $35.70. Labor about 2.5 hours, including removal, tear down, cleaning, reassembly with service kit, linkage and idle adjustment. The Labor is an estimate, since the invoice included lower end removal, inspection, and replacement.
where2 posted 03-20-2002 12:38 PM ET (US)     Profile for where2  Send Email to where2     
Anyone who can dismantle and clean an MG carb, and a Vette carb can certainly handle the 2-Stroke carb on a 90Hp Evinrude. No accelerator pumps to fiddle with! Just a bunch of linkages to connect back up.

The in the tank idle adjustment just allows you to have adequate back pressure. I always end up tweaking my 70Hp's idle after I relaunch it unless I use the garbage can to simulate back pressure. It idles much faster on earmuffs w/o back pressure.

knothead posted 03-20-2002 01:19 PM ET (US)     Profile for knothead  Send Email to knothead     
I appreciate all the information. We checked the compression at lunch 130-130-125-130, so that looks good. Checked the plug wires, and will put in new plugs. Thursday night will run a can of OMC carbon removal through the fitting on the carb, let sit overnight and take it out Friday to "blow out the carbon" Stay tuned, no pun intended.
Bigshot posted 03-20-2002 01:43 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
You are on the right track. Bring a squirt can of gas/oil mixture and leave off the flame arrestor so if still sluggish, try the squirt down the carb throat trick.

Check your fittings by sqeezing the ball. Any gas leaks correct them. Take a peak at pump but I doubt that as well.

SuburbanBoy posted 03-20-2002 03:19 PM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     
You might want to put some 50:1 mix in a portable tank... Just in case the oil injection is malfunctioning. Better than a siezure.


knothead posted 03-24-2002 04:57 PM ET (US)     Profile for knothead  Send Email to knothead     
Put the OMC carbon remover thru the carb last night as per the directions, took the boat out today (Sun.)

The motor ran great. Started, no problems, ran 5300 rpns WOT-42.5 mph. Ran a full tank thru this afternoon with nary a hiccup.

In retrospect, it was either a loose plug wire or just carbon, we changed too many things to be sure. At any rate, we think the problem is solved. Great boat, and if the motor holds up for the next couple of years it will be a good deal.

Thanks to all for your suggestions.


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