Carburetor swap

[nemer]

Does anyone know if I can put wh2 carbs on my 1979 v6 175 hp mariner. It has WH7 on it now? Will it require any modification. The carbs ar off of a 1978 150hp.

 

[nemer]

Thank you! you saved me some trouble for sure.

Probably not the venturi and jet sizes are probably different and the engine would be running too lean. It will cook the pistons and score the cylinders ? It is possible the 150 is just a detuned 175 you will need to see if it has the same powerhead and exhaust tube (inner) if it is the same engine then you will be lowering your HP accordingly.

 

[galamb]

Yes, just a detuned 200 (both the 150 and 175 in this case).

The venturi on both carbs is the same - 1.312

The WMH2 has a .064 main jet, the 7, .062

The 2 has a .044 progression (off-idle) jet, the 7, .034

The 2 has a .044 idle air jet, the 7 has a .040

and the 2's backdraft jet is .080 - the 7 has NO backdraft jet

(the backdraft jet, also called a bowl vent improves fuel economy at mid-throttle by reducing the air pressure in the bowl - so fuel is not "pushed" up the venturi. With this jet the motor may still function fine even though it was never included on your original carbs (or you could simply plug it - ???? never tried that)- obviously, the engineers feel it wasn't needed on certain carb models WMH 4, 6, 7, 8 and 10 to name a few)

You should be able to swap the jets (if serviceable) from your existing carbs to the (new) carbs.

If the price is right, I would certainly give it a try if your current carbs are toast..

 

[galamb]

I had a good look at the 200 - it has a different reed cage - the 150/175 share the same cage - so that alone would be about a 200 dollar "upgrade" on top of the cost for jets, gaskets etc.

Hardly worth it to gain 25 horses (14% power increase).

When a 50% power increase only results in a 15% top end speed increase, you would be paying upwards of 300 bucks for a 4% increase in speed (even if top end was currently 50 mph, that's barely 2 mph = $150/mph)

So in this particular case it's not a simple jet swap for the added horses..

 

[nemer]

Application

Should I try the 2's the way they are or swap the jets? Would the smaller off idle jet make it run richer? Might I get better Milage backdraft jet. Right now I suck gas like crazy. Would the timming be the same?

Yes, just a detuned 200 (both the 150 and 175 in this case).

The venturi on both carbs is the same - 1.312

The WMH2 has a .064 main jet, the 7, .062

The 2 has a .044 progression (off-idle) jet, the 7, .034

The 2 has a .044 idle air jet, the 7 has a .040

and the 2's backdraft jet is .080 - the 7 has NO backdraft jet

(the backdraft jet, also called a bowl vent improves fuel economy at mid-throttle by reducing the air pressure in the bowl - so fuel is not "pushed" up the venturi. With this jet the motor may still function fine even though it was never included on your original carbs (or you could simply plug it - ???? never tried that)- obviously, the engineers feel it wasn't needed on certain carb models WMH 4, 6, 7, 8 and 10 to name a few)

You should be able to swap the jets (if serviceable) from your existing carbs to the (new) carbs.

If the price is right, I would certainly give it a try if your current carbs are toast..

 

[galamb]

Here's my take on "if" you didn't swap the jets -

The smaller main jet would restrict the gas flow minimally.

The smaller progression and idle air jet would cut down the air intake (in line with the smaller main jet), so you probably wouldn't run rich simply because the jets are balanced respectively.

The backdraft jet certainly won't hurt as it's job is to prevent fuel from being forced to the reeds at mid-throttle (and two strokes sent a fair bit of unburnt gas right out the exhaust to start off with.

So, while it will probably run fine, you will probably 1) not get the same max rpms that you used to (which could mean a re-prop if you were already just in the WOT range and 2) you will not develop the full 175 horses you are capable of - you will effectively turn your 175 into a 150.

On that note, if you do tend to run at full throttle, it would have the effect of dropping your gph usage from somewhat north of 17 gph to 15'ish.

At rpms below full throttle you gas mileage would be the effectively the same since the displacement has not changed.

With either jets your timing should stay the same (19 deg BTDC at WOT but is set different if done at "cranking" speed in the driveway - 21 deg for the 150 carbs and 20 deg for 175 carbs) - idle timing can be anywhere between 0 and 9 deg ATDC, whatever gives you the smoothest idle.

 

[faztbullet]

It is possible the 150 is just a detuned 175

Depends on serial number.....

Yes, just a detuned 200 (both the 150 and 175 in this case).

Nope as the 200 is 2.4 liter and the 150/175 are 2 liters. Depending on serial number the earlier 175s had a bigger exhaust chest and the exhaust on bottom of block is 2 large "D" shaped exhaust ports(gasket 27-75909). If its the later model it is the same block with with exhaust ports raised .080 to give it a little more umph on top end.....

The venturi on both carbs is the same - 1.312 The WMH2 has a .064 main jet, the 7, .062

The venturi size is the same , the differences is the metering orifices cast into the carb and the main discharge tubes, that why different jet sizes...and the WH2 carbs will not work on your motor without a lot of trial and error in jetting.

I had a good look at the 200 - it has a different reed cage - the 150/175 share the same cage - so that alone would be about a 200 dollar "upgrade" on top of the cost for jets, gaskets etc.

The reed cages are the same on the 150/175 as they are 10 pedal vertical reed motors and the 200 is a 14 pedal horizontal reed motor. The intake and reeds off a 200 will not fit a vertical reed motor and to make it bolt up you would have to mismatch the front crankcase halves as they are the difference..

Should I try the 2's the way they are or swap the jets?

Swap main jets, idles should be find due to smaller idle tubes...

Might I get better Milage backdraft jet. Right now I suck gas like crazy. Would the timming be the same?

Doubt you get better mileage as the backdraft circuit only works in the mid range RPM (2500-3500rpm) timing will stay the same which is 18° BTDC or 20° at cranking speed as a 150 of the same year is 16° and 18° at cranking and make sure idle stablizer if still equipped are disconnected (removed is my choice)

 

[nemer]

Thank you so much. You are very helpful. If I could, I would buy you a beer. I do canvas work so if you ever need somthing sewn I would be happy to do it for you, no charge. Ship it to me and I will ship it back. I will buy the carbs and hope it straightens my motor out.