1972 Mercury 1150 (tower of power) carb questions

[Mooredom91]

So I been working on my boat/engine trying to get it going after sitting for 2-3 years and fixed a couple of problems using valuable info from previous posts I made and read.
After I got her started I wanted to test the electric choke and realized something was stopping choke cover from covering the 2nd carb. I took the black screen off and saw a broken Black plastic piece that sat on the bigger/thicker jet pointing up. It had 2 wings to hold it in place but one of mine broke off. Because I can’t find it I think the broken wing went into the engine.
I’ll post pic of the piece.
What is the function of this plastic piece?
How important is it piece and can I use the engine without it for just 1 season?
I just had the carbs rebuilt before putting it in storage.
How bad is it that the broken piece went into the engine and how likely is it that it made it out?
Or melted somewhere in the engine

 

[jimmbo]

That is a Booster Venturi, it creates a stronger Vacuum Signal at the Main Nozzle. Carb will not work properly without it. Check with a Mercury Dealer to see if it is available as a service part. You may need to replace the Carb. Look inside the Reed Block, if inhaled, it probably would not have made it past the Reeds, due to its size. A more likely Scenario, it fell out of the carb when the engine was tilted. Who rebuilt the carbs?

 

[Mooredom91]

I personally did not rebuild the carbs. But when I went to Mercury today to order an ignition switch and choke button I found out that those are not the original carbs to that engine. Those carbs came from a later model (6000 serial number range).
That small plastic Venturi is a serviceable part that COST $30. No way I want to pay that if I don’t have to. There is a cheaper way for me but because of covid-19 the American lifestyle sucks right now and the place is closed.
It may not run correctly without the Venturi but will it run enough for me to go from spot to spot?
What are the symptoms for a missing Venturi on 1/3 carbs?

 

[jimmbo]

It might run well enough to cause a lean condition at times to burn out a couple of cylinders. If the part wasn't required, Tillotson would not have used it

Since the carbs are from something else, were you able to find out what engine it was, as to HP and Year?

I remember looking up one a couple of Years ago, it was about $27(can) then

 

[racerone]

$30 is not an outrageous price for a part for a motor.----Certainly cheaper than the damage that can be caused with it missing !

 

[Mooredom91]

The carbs came from a 1978 115 hp.
I finally broke down and bought the Venturi.
Thanks for the knowledge.

 

[jimmbo]

The newer carbs will likely have the Back Drag(black hose in picture) feature on them.It was a feature added in about 1975, in an attempt to get better fuel Economy out of these engines. Simple and it did work, by lowering the air Pressure inside the Fuel Bowl under Crusing speeds at part throttle thus leaning out the Air-Fuel Mixture.. However todays gasolines have Oxygenators added and this will cause a very lean condition when used on engines with these carbs
If you want the engine to survive on Today's Gasoline, Plug the hose on each carb. it can be removed off of the Fuel Bowl fitting, but once it is plugged, the other end must remain attached to the fitting on the carb body.

 

[Mooredom91]

72 1150 mercury carb questions AGAIN

Been searching for a Venturi for my middle carb and found out that the 1972 carb did not have them from factory. Thought the carbs came from a newer year same model so I searched engine serial numbers until I found a motor with a Venturi. Found it in motors serial numbers starting with 6000. So I ordered it but it was def way to small compared to the ones I got. My carb part number is 1399-3682 so I took that to the mercury and they couldn’t find it under 115hp. Did a little more digging and I think these carbs came from a 90hp not sure though.
Can anyone help me identify which engine year and model a mercarb 1399-3682 came from?
Does wmk have a part number that is equivalent to (1399-3682)?

 

[Faztbullet]

Look on carb fuel chamber...should have a WMK-XX number on it.

 

[jbcurt00]

https://forums.iboats.com/forum/eng...different-carbs-on-same-motor-72-mercury-1150
closed duplicate topic

 

[Mooredom91]

Can I replace the center carb which was wmk 3 with a wmk 2?
There’s a difference in the Venturi size, will that have some type of negative effect to how the motor run?

 

[GA_Boater]

Since you insist on starting new threads and replying in all, now have been merged into one, except the duplicates which were deleted.

 

[Mooredom91]

Ga boater Thanks for clarifying how it work Was a little confused at first. But why does it say this post is closed and will I get any reply if they see that in the thread?

 

[Faztbullet]

No all three must be same series....

 

[Mooredom91]

Does the Venturi have to be the same style?

 

[GA_Boater]

Ga boater Thanks for clarifying how it work Was a little confused at first. But why does it say this post is closed and will I get any reply if they see that in the thread?

No one can reply to a closed thread. That's what Closed means. It's like a closed store, you can't buy, but you can window shop.

This thread is not closed.

 

[Mooredom91]

Finally found the Venturi I was looking for with explanation. The reason I couldn’t get a part number or find the part in the manual itself is because mercury did not offer the Venturi as a separate part back then (according to Mercury).But to replace it I had to get the main jet screw out which was glued in. Put some work getting it out so I bought a new screw.

Why is that brass flathead on the bottom of the carb and others glued in and Is it a must to glue it back in?

I ask because my Gunk parts cleaner says no plastic pieces which means I’m prob have to struggle/replace the brass screw with the other 2 carbs as well.

 

[jimmbo]

You have the broken Booster? Soak it in the carb cleaner to see if it dissolves/softens

 

[Mooredom91]

It’s been in there a day.as I assumed for that short time nothing. But I will leave it soaking consistently n I’ll post when the integrity of the booster is compromised.
is there a certain length that parts should not be in there?

 

[jimmbo]

What does the can say?