Overcarburated 200

[RammaR]

My buddy has a 1989 Johnson 200 GT that has been missing and flooding out on an idle and has just discovered that it actually has 225 carbs on it. He bought it used and the previous owner must have made the swap.

One option is to look for carbs from a 200 and go back to the original configuration, but that's 6 different carbs. Any suggestions for alternative options - like a new manifold, etc to ease the pain and get it running better?

Thanks

 

[Bosunsmate]

Re: Overcarburated 200

Hows he know they are 225 carbs?
i thought they were the same as the 200

 

[RammaR]

Re: Overcarburated 200

He got tired of trying to troubleshoot the way it ran and took it in to a local (reputable) marine shop and they said that on the 200 "GT" it should have the 200 carbs. They should have a narrow through versus the 225's wider throat. It's an '89, so maybe they made a change to the same carbs later? I don't know. We've got to get the actual model number off the engine - and were going to look up the drawings at marineengine.com and see what they say is the proper part / carb number.

The other thing that we do know is different on the boat is that the original mechanical fuel pump was replaced with an electric. Not sure of the pump model, but we're suspecting that the carbs could be correct and that the fuel pump is putting to much flow.

Does that sound more plausible? Suggestions to check?

Thanks,

 

[ezmobee]

Re: Overcarburated 200

Some doofus put 140HP carbs on my 90HP at one point. My mechanic diagnosed it and recommended I try to find a set of 90 or 115 carbs however he was able to get mine jetted so that it runs perfectly even with the larger carbs. I've not been inclined to mess with it further!

 

[Bosunsmate]

Re: Overcarburated 200

Yes it does sound plausible if the electric pump is too powerful for the float.
You could bypass the fuelpump and hand prime using primer bulb to see if that corrects it.

This next part is a morning time guess but i dont think a wider throat would cause more fuel to be sucked in as the volume of air would still be the same because the vacuum created by the pistons would still be the same volume. All that would happen is that the density and speed of flow would be less on the wider throat as there is more of a throat for more air to pass through. I would of thought the narrower carbs would make for a more densely fuel charged mixed and more likely to cause an overly rich mixture.

Same principle with choke butterfly valves, or putting a playing card over the top half of a carb throat. Reducing the flow intake size of carburettor opening enriches the mixture

 

[pn]

Re: Overcarburated 200

maybe one or more of your six float needles are sticking. tilt your motor down, try pumping your primer to see if it gets hard and if it doesn't look to see where the fuel spilling out. 225 and 200 sounds like pretty much the same number to me.

 

[jimmbo]

Re: Overcarburated 200

Some doofus put 140HP carbs on my 90HP at one point. My mechanic diagnosed it and recommended I try to find a set of 90 or 115 carbs however he was able to get mine jetted so that it runs perfectly even with the larger carbs. I've not been inclined to mess with it further!

Port the block , add the 140 heads, the exhaust bubble back and its internals, exhaust tuner, and tada you have a 140

 

[metriccrescentwrench]

Re: Overcarburated 200

The other thing that we do know is different on the boat is that the original mechanical fuel pump was replaced with an electric. Not sure of the pump model, but we're suspecting that the carbs could be correct and that the fuel pump is putting to much flow.

A couple of things on the fuel pump. You should be getting around 5 psi out of the pump, much more than that and it could overpower the float valves.

ALSO, unlike auto engines which have an oil pressure switch which turns off the fuel pump when the engine isn't running, there's no such provision on 2 stroke outboard engines. Therefore you've got the possibility that the fuel pump will keep supplying fuel even if you really really really don't want it to, like in some sort of upset or engine failure. At a minimum that electric pump should have a provision to shut it off with the engine safety kill switch.

Finally, you can look at www.shop2.evinrude.com and see what part number carbs were used on which engines.

 

[RammaR]

Re: Overcarburated 200

Thanks for all the excellent feedback. I've got a gauge, we should be able to try to measure the fuel pressure. How confident that much over 5 PSI is an issue? He's gotta pick up the boat from the mechanic to get the actual model number - then we can check the carbs at the link.

 

[RammaR]

Re: Overcarburated 200

Just to close it out -- we found that with the cover off it ran perfectly. The baffles in the airbox were very restrictive - so he basically gutted the airbox internals and put the cover back on and it runs great. The carb numbers seem to check out that they are correct for the engine. He found another post somewhere about the airbox being part of the difference between 200 and 200GT's. So we're thinking the covers may have been accidently swapped at some point in the past, but for now the problem is solved.