Setting Idle mixture screws

[foilled]

Do I set my idle mixture screws in idle or forward gear? On a side note I set rpm in forward gear right?

 

[Scott Danforth]

you set your idle mixture to get proper idle. I use a propane torch (not lit) to check idle mixture. if adding a bit of propane speeds the motor up, your lean. if adding it just starts to slow it down, your about right.

you set your final idle speed in gear at idle (I do it on the trailer, or in open water)

 

[alldodge]

Do I set my idle mixture screws in idle or forward gear? On a side note I set rpm in forward gear right?

Without knowing what motor and guessing its a 4 cyl, then yes

 

[foilled]

you set your idle mixture to get proper idle. I use a propane torch (not lit) to check idle mixture. if adding a bit of propane speeds the motor up, your lean. if adding it just starts to slow it down, your about right.

you set your final idle speed in gear at idle (I do it on the trailer, or in open water)

I can just use vacuum gauge in nuetral for idle screws correct?

 

[kenny nunez]

A good starting point with the mixture screws most times is 1.5 turns from lightly seated. Either with propane or a vacuum gauge 1/4 turn either way will be the setting. If the timing or dwell is not set right or a worn out distributor or an internal engine problem you will be wasting your time. If you use a vacuum gauge to set the carburetor while idling in the water the readings will be different than on land because of the back pressure of the water.

 

[Scott Danforth]

vacuum is erratic at idle, and as kenny pointed out, different on land and in the water

also, the other thing, unlike cars, there is no easy place to connect a vacuum gauge to a boat motor. you may or may not have a plug in one of the intake runners that you can pull, find a fitting, etc. where in 3 seconds I have the propane torch handy.

 

[foilled]

A good starting point with the mixture screws most times is 1.5 turns from lightly seated. Either with propane or a vacuum gauge 1/4 turn either way will be the setting. If the timing or dwell is not set right or a worn out distributor or an internal engine problem you will be wasting your time. If you use a vacuum gauge to set the carburetor while idling in the water the readings will be different than on land because of the back pressure of the water.

Should I set it in water or on land then?

 

[alldodge]

My opinion, which in many cases means very little, but give the motor what ever it needs to idle/shift smoothly. If it runs a tad rich or lean, it really doesn't matter unless you spend all day idling around. Tune it on the hard, then drop in the water and adjust more if needed

 

[foilled]

vacuum is erratic at idle, and as kenny pointed out, different on land and in the water

also, the other thing, unlike cars, there is no easy place to connect a vacuum gauge to a boat motor. you may or may not have a plug in one of the intake runners that you can pull, find a fitting, etc. where in 3 seconds I have the propane torch handy.

I’m about 2.5 turns from lightly seated. Is that to far?

 

[Scott Danforth]

do you have your spark arrestor in place?

 

[foilled]

do you have your spark arrestor in place?

Yes I do. This is the vacuum port for my gauge under the bowl. Is this correct?

 

[foilled]

Just increased idle rpm a bit and I was able to have engine idling smooth around 1.5 turns backed out.

 

[Scott Danforth]

Yes I do. This is the vacuum port for my gauge under the bowl. Is this correct?

zoom out and take a pic of the carb with the spark arrestor off. Marine carbs do not have vacuum ports. only the automotive carbs have vacuum ports

they also do not say holley performance on the bowls - that is specifically saved for the automotive carbs.

 

[foilled]

zoom out and take a pic of the carb with the spark arrestor off. Marine carbs do not have vacuum ports. only the automotive carbs have vacuum ports

they also do not say holley performance on the bowls - that is specifically saved for the automotive carbs.

Here you go. You can see one port where I need to hook my fuel pump overflow and in the back we’re ive been hooking up my vacuum pump to that’s temporarily blocked with a drill bit as original cover was leaking air through it

 

[foilled]

[No message]

 

[Lou C]

I actually set my QJet today using my engine analyzer tach using the lean roll/rich roll method, I go rich till it slows down then back in till it’s running it’s fastest. A clean carb responds much better than one that needs cleaning. I think the Holley I tried (for sure a marine carb) did say Holley Performance on the bowls...

 

[Scott Danforth]

the J-tubes are for marine, however they appear to be crooked

the two colors of plating have me thinking someone played frankenstein with your carb.

there should not be a vacuum port going to the carb base as marine carb bases are not drilled out for vacuum ports, however they are machined for o-rings on the throttle shafts.

 

[alldodge]

marine carb bases are not drilled out for vacuum ports

Agree for Merc but what about VP?

Also I don't see if it was changed, I don't see how a vacuum port will cause any real issues so long as there is not a large vacuum leak

 

[Scott Danforth]

doesnt matter if its merc or VP. Holley marine carb bases are not drilled out for vacuum ports. at least none of the ones I have ever come across from the mid 70's to the mid 2000's 4150, 4160, and 4175's

agreed, if plugged, shouldnt be an issue. however not sure what the OP has as the two different chromate plating colors indicate someone played mix-n-match parts.

 

[foilled]

Agree for Merc but what about VP?

Also I don't see if it was changed, I don't see how a vacuum port will cause any real issues so long as there is not a large vacuum leak

I’m seeing about 1.5 in. Hg +- fluctuation with my idle vacuum. Is that normal? It’s seems to be in a good range of about 16 in I still have a little playing to do with it though.