1968 v4 carburetor differences

[tobinns]

If I put a 1968 85hp carb on a 1968 65hp engine do I turn the 65hp into an 85hp, or are there more differences to the motor internally?

 

[ondarvr]

Yes, so if you can get one off of 200 it will be even better.

OK back to the facts, typically there are other differences between motors and the carb is only one of the changes. You need to google a parts diagram and look at each part and see what the differences are. If the carbs fit, then even without the other parts (if any) you may see a slight increase in power, frequently it's not worth the cost, time and hassle.

 

[tobinns]

Your point is well taken, I didn't see the cid difference in the powerheads. But my question is, is there a cfm or jetting difference between the 2 carbs.

 

[F_R]

65hp is 70.7 CID and 85 is 89.5 CID---I think. I don't have the specs in writing for a 1968. But to attempt to answer your question, I an almost positive the 85 carb is larger (CFM)

 

[interalian]

65hp is 70.7 CID and 85 is 89.5 CID---I think. I don't have the specs in writing for a 1968. But to attempt to answer your question, I an almost positive the 85 carb is larger (CFM)

There's no replacement for displacement. Or so the old 'rodders always say.

 

[hemi rt]

You may gain a little more power but you'll loose fuel economy and in some cases you even loose power or damage the engine. The bigger carb, when adjusted to idle properly may be too lean at higher RPMs. Also remember that everything on the 65 was designed to operate with each other, changing one thing (larger carb) without changing the exhaust, intake and exhaust ports will over fuel an engine and may cause real problems, too much fuel - fouled plugs, washed cylinder walls etc.

 

[oldboat1]

Things aren't necessarily what you might expect. 85hp uses .063" orifice, PN 0328544, and 65 uses .072" orifice, PN 0328546. You should confirm.

 

[F_R]

What oldboat is saying here (and he is correct), is that the orifices are chosen by the engineers to feed the proper amount of fuel into the amount of airflow going through the venturi. The air flow is related to the displacement of the engine and RPM. More gas (bigger orifice) does NOT make more horsepower. It only changes the air-to-fuel ratio. The air-to-fuel ratio must be within a narrow range for proper combustion. Too rich or too lean will not run properly, or maybe not run at all.

 

[tobinns]

Things aren't necessarily what you might expect. 85hp uses .063" orifice, PN 0328544, and 65 uses .072" orifice, PN 0328546. You should confirm.

That makes no sense. I would figure, bigger orifice for the bigger displacement, but it's opposite. So I checked the 75hp and it uses a .056". Right between the other 2 but 75 and 85 have the same displacement. I'm guessing all three venturis flow differently. I'd like to set them all on a flow bench.

 

[F_R]

It is a combination of factors. Air flow rate, venturi size, air volume, and a bunch of other engineering speak. Bottom line still remains. It all comes down to fuel to air RATIO. Change one factor and the whole result changes.

 

[jimmbo]

The carb body, the carb body cover and the venture boosters are different too. As F_R said there is more to a carbs fuel curve than just the main jets