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  Merc Carb engine (90hp 4 stroke carb)????

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Author Topic:   Merc Carb engine (90hp 4 stroke carb)????
Feejer posted 03-08-2007 05:09 PM ET (US)   Profile for Feejer   Send Email to Feejer  
I had a rude awaking after the dealer faxed me the spec sheet on a Dauntless I hoped to get. It never crossed my mind because I never had large outboard with a carb. It terms out the 90 on the boat is a 4 stroke carb. I know nothing about them. I have read many post on so called problems with them however. Gummed up carbs, needs to warm up before running, running rough. Is any of this true? My last to engines were Yamaha's EFI. Never had any problems with over 200 hours on the last engine. Turn the key and go. Am I making too much of the carb engine?


swist posted 03-08-2007 05:50 PM ET (US)     Profile for swist  Send Email to swist     
I have the same engine on a 2004 170 Montauk and have not had any of those problesm. It's smooth as silk.
Griff posted 03-08-2007 08:36 PM ET (US)     Profile for Griff  Send Email to Griff     
I am a Merc certified technician. The EFI and carb both, idle/run very similar. You really can't tell which engine it is once it is running. There is the key running. In normal applications (warm temps and ran recently) the carb start fine. It has 2 enrichener valves that allow more fuel to the engine during cold starts. This is an open loop system. They automatically open, allowing fuel to flow (like a choke). As the ignition key is “on” the valve get warn and closes slowly (normal operation). This happens without any input from the engine and its temperature. The EFI system compensates for the ambient air and engine temperature.

You must first understand that cold air is denser than warm air. Each stroke of the piston pulls in a consistent quantity of air (and fuel on carbs). However the colder the air the more it expands during combustion (changing the fuel to air ratio). Therefore on carb motors the fuel to air ratio changes depending on air and engine temperature. It must also be understood that a lean ratio spells trouble. This cause the factory to “jet” the engine a little rich so during cool running it is not too lean. Of course this means that during warm applications the engine runs a little fat (rich).

Bottom line is an EFI system is much better at cold starts, fuel economy and engine longevity. I will also tell you that the #1 issue I have seen with this engine is carb related. Think about it, 90 ponies with four carbs dictates very small fuel passages. The smaller the opening the easier the clogging. I’m not in sales, but I think EFI is a $1,200 - $1,800 option. This pays for itself in just a few carb rebuild jobs.

Not to spend more of your money, the 115hp has a shift interrupter switch making the shifting smoother.


Feejer posted 03-08-2007 09:35 PM ET (US)     Profile for Feejer  Send Email to Feejer     
Yea right, I only wish it was a $1200-$1800 price differenc. This is a left over 2005. Today I talked to 5 Whaler / Merc dealers in 3 state. Three told me I could'nt give them the engine for free. The other two would do a swap for a 115hp 4 stroke EFI but will only give me 3K for the left over 90hp. and will sell the 115 for 10K installed. That leaves another 7K I need to come up with. So now I'm back up to 30K for a 16ft boat. Thank you very much but that deal don't cut it with me.
Feejer posted 03-08-2007 09:40 PM ET (US)     Profile for Feejer  Send Email to Feejer     
For 33K I can get a 2007 with the 115 EFI, fishing package and alum trailer. If I buy the boat I'll end up putting a 115 E-tec on it a few years down the road
jimmy c posted 03-08-2007 09:48 PM ET (US)     Profile for jimmy c  Send Email to jimmy c     
I have a 2005 170 Montauk with 90 carb.Merc 4 stroke
I installed a good 10 micron fuel/water filter.I buy brand name fuel at gas stations on the road.
absolutely no problems.
I prefer carbs over least I can fix it if ever needed.
Barney posted 03-09-2007 11:48 AM ET (US)     Profile for Barney  Send Email to Barney     
I have a 2004 carbed 90. After I installed a good filter and going thru the carbs once, the problems have reduced to just a small miss after inital starting. This goes away after warm up. The junk left in the clear filter bowl shows why I had problems before. Jim
WT posted 03-09-2007 02:16 PM ET (US)     Profile for WT  Send Email to WT     

Buy the leftover 2005 Dauntless for $5000 less than you were going to pay for it. Run the 90 carbureted motor for a couple of years you might like it. If not, do a motor swap later.

Problem solved.


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