difference between wh40 and wh48 carbs

T

tracker88

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Aug 7, 2011
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Hi,
I have a 1988 mercury 150 that is the 2.0 version. I bought it used it is mounted on a tracker 1800FS. It runs really well WOT but really struggles at taking off. I got a Seloc manual and went through all the timing and it was off quite a lot. It runs better now but still bogs down taking off. So I started going through the carbs and have found something that isn't correct by the repair manual. The top carb is supposed to be an WH48 but all three are WH40 and all jetted the same. Do I need to try and find a WH48 or just re-jet the WH40. It smokes a lot at idle.
Any thoughts would be appreciated.
Rod
 
DamianJP

DamianJP

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Mar 25, 2008
Messages
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Re: difference between wh40 and wh48 carbs

I not sure exactly if you can just re jut that spec carb *BUT* I went thru the same thing with my 1989 Black Max XR4 150hp. Alot of my out of the hole was due to a worn fuel pump , might have been some of the carbs fault but Im unsure. Because I fixed the fuel pump before I got my right carbs.

I needed WH-41

Motor came with
TOP 41
MID 27 jetted like a 41
BOT 27 jetted like a 41

I bought a set of 41's off ebay for $100 and rebuilt them and jetted them the right way (%100 stock jetting). Havent looked back since, the motor has been alot better in every area, Idle, out of hole Med/High RPM range.


I would say get a set of carbs that you know %100 belong to your motor. Now if a Merc GURU comes here and checks everything out and says yes you can jet them because that is the only difference okay but until then I would set the motor up how it came out the factory.


With the smoking, do you stil have the oil injection still on the motor? Or is it blocked off and you premixing?
I took my oil injection off (Due to multiple reasons) and premix 50:1.
What plugs and gap are you using?


DamianJP
 
J

Jlawsen

Master Chief Petty Officer
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Apr 22, 2012
Messages
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Re: difference between wh40 and wh48 carbs

First off you need to get rid of that Seloc manual and look at the Merc Shop Manual. The fat block 2.0's 88-91-1/2 can run just about any carb you want for a 135 or 150. Right on up to the WMV Series. You don't need to jet the cylinders differently but you do need to jet them right. You can usually jet them per the manual and they'll run well. If you use a carb after 1995-96 it will be a 2.5 litre block and the carbs will have diferent jetting on 5 and 6 usually. Those cylinders and sometimes 3 & 4 run a little leaner on the 2.5 so you have to fatten them up to keep them from leaning out. Thats not a problem on your block.

The WH-20 is the carb of choice if you can find them. They will produce the most HP and are the simplest to work on. Parts aren't easy to come by but if you know the right people you can get them.

As a side note, if you are looking to make that engine run like a fine watch, drop down to a set of 135 small bore carbs. You'll loose a little HP but not much and it will idle like a dream. The hole shot response will be good and it will be smooth all the way to the top. I wouldn't do that to a fresh rebuild because it would be a waste but on an older motor it can be an amazing change and engine life extender of sorts.

FYI, I can make that motor turn 8,000 rpm easily and produce nearly 200hp. It was one of my favorite "Let's see what this does" blocks.

Oh, if you change to a carb after 90-1/2 you'll need to change the linkage and the throttle cam. If you find a set on Ebay ask the seller to include them.
 
Faztbullet

Faztbullet

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Re: difference between wh40 and wh48 carbs

he top carb is supposed to be an WH48 but all three are WH40 and all jetted the same.
Click to expand...
That is correct as the WH48 is used on 1989 and up motors, you should have .048 in idle circuit and .080 in mains.
drop down to a set of 135 small bore carbs.
Click to expand...
Wifes tale as no such thing as a small bore carb anymore(WH1-WH8), the only difference is the idle and main emulsion tubes pressed into carb body, the throat diameter, venturi size and throttle plates are all the same and throttle plate have different size metering holes in them and linkage differences. The WH 20's use all the same gaskets,floats needles as the WH40 only difference is the venturi in carb body and emulsion tubes
 
J

Jlawsen

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Apr 22, 2012
Messages
810
Re: difference between wh40 and wh48 carbs

Wifes tale as no such thing as a small bore carb anymore(WH1-WH8)
Click to expand...

Glad you qualified that with "Anymore" hes not going to find a new WH or WMH anything "Anymore" either. What did you think or just misunderstand (again) that I meant he could go and buy new 88-90-1/2 135 carbs. Seriously...
 
T

tracker88

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Re: difference between wh40 and wh48 carbs

So Faztbullet just to clarify, are you saying I need to find a wh48 or use the wh40 as long as it is jetted the way you say? All 3 are jetted the way you say. My book says the top carb should be a WH48 and be jetted .044 in the idle circuit. Also my motor is an 88 model and calls for the wh40 in positions 2 and 3 but he wh48 on top. serial number OB313715. I live at about 3000 feet should I jet differently for that?
 
Faztbullet

Faztbullet

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