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Honda Four 90 HP 1998

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Buzzftl

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I have a 1998 Honda 90 Four It was running great until a day ago. Now it runs but coughs and is rough at idle Just before that started it had a kind of ether smell from the exhaust. Could a valve be stuck or not operating properly ? It ran at 5000 RPMs and was strong until the smell . The oil is clean and I put in new plugs. The old ones looked good.
 
Hope you did not feel neglected....

First of all..that motor should run up between 5500 and 6000 rpm with the proper propellor.

Second...

If this motor came into the shop, I would check the following...

-Check fuel for quality and water.
-Check/change fuel filter if it looks really bad.
-Run the following tests on shop fuel tank
-Perform cylinder drop test to see if problem is limited to one cylinder
-Activate choke on each carb individually (after removing linkage) to see if motor speed changes
-Check compression
-Check spark plugs and probably change them if they look suspect
-Check spark
-Check timing marks
May not even do all these tests depending on what is found along the way.

Can not explain the smell (unless maybe oil is too high).
If a valve is stuck open, if will show up in a compression test.

It is probably just a gooed up carb or water in fuel.



Mike
 
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I took the boat to the honda shop around the corner after I changed the fuel/water sep. It ran alot better. I emptied the old sep in a pan and found the fuel a little cloudy with some specks in it. I don't think it was rust. Rust looks like sand but darker. The dealer said $700. to rebuild the carbs. I said it was running better and I would like to run it a little more before doing that again. The carbs were rebuilt in Jan. 09 and I had some other stuff done. Anyway I have screwed the adjustment screws on each carb and I don't know where they started. Are those air or fuel screws and is screwed in more or less air or fuel ? They are each about 2 turns out of closed . The dealer said it smells like unburned fuel at idle.
 
The initial position for the idle mixture screws for the 90 are 2 1/4 turns out. The more turns out, the richer it is.

The other screw on each carburator is the vaccuum balance screw. Do not adjust any of the vacuum balance screws without vacuum gauges attached to the intake manifold.

If it is running rich, you should be able to tell by looking at the spark plugs.

Mike
 
Thank-you for the information. I will try them at 2 1/4 out and see if it idles smoother. Changing the fuel filter seems to have helped a lot. I just need to run it some more . I have a long way to go to get to somewhere you are allowed to go fast. I was certainly willing to pay for an adjustment, but he was insistent on a $700. carb rebuild. Thanks again. Buzz
 
Given the "ether" smell and the junk in the fuel-water seperator, it sounds like you have bad gas that has experienced phase seperation - i.e. the ethanol has seperated from the gasoline. The dark reddish stuff that looks like sand, but is not as hard is made by a bateria that eats on the alcohol.
 
Thanks for the information. I use the boat monthly and add new gas when it gets low. How long does it take for the gas to separate ?
 
If you don't use a stabilizer like Marine Stabil, it actually starts destabilizing right after the ethanol is added. But it does not become noticeable until later. I don't know any particular time frames. I do know that if E-10 gas is stored for over a month without stabilizer, the separation becomes noticeable in terms of both smell and appearance of the fuel, this is especially true when it is not in a sealed container, and of course your boat tank is not sealed.
 
I started it again today and it is running well at idle. I don't know about the vacuum balance adjustments. I would like to have someone tweek the adjustments but not for $700.00. I need to go out and run it some more. Thanks for the info on stabilizer. Is it OK to put that in regularly ?
 
You can use the stabilizer IAW instructions for every fill up. However, I would consider using Valvtec which has both a fuel stabilizer and a decarbonizing cleaner. Here where I am, on the Chesapeake, several of the marinas sell gas pre-blended with Valvtec, which is actually cheaper than buying it retail and adding it yourself.

I assume you are using a fixed tank in your boat. If you are, then you probably need to drain out the remaining gas, and start with fresh. Here is the procedure I've used to drain a boat tank. I'm sure there are other methods that work just as well, if not better.

I purchased an aftermarket 12V electric fuel pump from an automotive parts store and rig up a plastic hose on the intake side that will reach to the far corners of the tank. I remove the plate that has the fuel pick-up hose connected to it. (Be sure to clean the screen on the end of the pick-up.) Then I raise the bow of the boat and tilt it slightly to one side so the fuel will accumulate in one corner of the tank and pump the fuel out through a standard, clear, inline fuel filter rigged up to the outflow side of the fuel pump. That filter will show you how much crap you are getting out. You will likely need to clean it out often. Also, pump the first several quarts of fuel into a clear glass container to see if there is much water and junk are in the bottom of the tank. You can use the remaining fuel (less the water) in your car or truck. Then put in a couple of gallons of new fresh fuel, drop the bow and slosh it around in the tank as best you can to pick up remaining debris. Raise the bow again, and pump that out, using the same procedure. That will get almost all the crap out of the tank and the external Racor fuel-water seperator will take care of the rest.

By the way, that electric fuel filter can be used for many other tasks around the home, like draining lawn equipment tanks, and transferring other fuels. It's relatively slow, but works consistently and safely.
 
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