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87MCProstar
06-29-2010, 03:36 AM
and seems to be running rough when it just in gear, but then smooths out as you put the hammer down though the smell of gas coming out of the vent in the motor box doesn't go away. and we went through 2 gallons of gas yesterday running the boat for at most 15 minutes at 25 mph. seems real high to me. so i wanted to adjust the fuel mixture but not sure about how to go about it, i don't want to touch anything other that the fuel screws and want to make sure I'm turning them the right way. i found (through a search) that in is lean and out is rich, but i couldn't find a picture of the screw on the carb. i have a 4160. thanks

airdrew99
06-29-2010, 11:17 AM
If it has been running fine up until this point, it shouldn't need much change in the mixture. It could be that your choke it stuck. This will cause increase fuel consumption and a rough idle. Also, you could have a float valve that is not closing off completely. This will cause the same symptoms. Usually, if you have to adjust the mixture or re-jet the carb, it is from an altitude change or a drastic weather change (really hot to really cold). Hope this helps.

Drew

thatsmrmastercraft
06-29-2010, 11:25 AM
Good call on the stuck choke airdrew99.

If thats not it, next most likely thing is a blown power valve. Could be a float stuck or an obstruction in the needle and seat keeping it from closing. Sunk float will give the same symptom too.

If you don't find the choke stuck, sounds like you are in for a carb rebuild.

87MCProstar
06-29-2010, 11:40 AM
The boat is running fine, but have been smelling the extra fuel for awhile now its not something that just popped up. But I'll definately check the choke to see if its stuck. Thanks guys.

thatsmrmastercraft
06-29-2010, 11:49 AM
1. Smell fuel from running rich: carb, plugs, distributor cap & rotor, plug wires, plugs.

2. Smell fuel from fuel leak: Fix ASAP before your boat blows up.

Luv2Ski
06-29-2010, 04:09 PM
Change your PCV!! It is a $2.50 part that can cause rich idle conditions if the check valve is closing off too much during idle. Few owners change them as often as they should and just cause you can shake it and hear the valve move does not mean it is flowing as good as it should.

If you can turn your idle screws all the way in and the engine does not die, your power valve is toast. You will need the 2.5 and can probably order it from any local parts store, just ask them to get out their Holley catalog as it seams none of the employees at those places know what a PV is.

Otherwise, all the other tune up suggestions are good to follow if you have not done them for a while.

87MCProstar
06-29-2010, 05:31 PM
Thanks Luv2ski, i'll look into that too, everything else other than adjusting the carb are all brand new

oldairboater
06-29-2010, 05:45 PM
Everything listed above could cause your problem. You need to find the cause of the fumes. Especially if it is new. I have personally seen someone blown out of a boat that was having fuel problems. He was sitting on the engine cowling while they were trying to start it. The cowling hinged at the top and was clipped at the bottom. I always wondered if his weight kept the rest from being burned as bad. One of them you will not believe what I saw moments. Flying through the air and multi layer burns on the arms is nasty.

SugarLake
06-29-2010, 05:45 PM
I recently purchased a remanufactured carb from www.flyingfishcarburetors.com and had a real hard time getting it to idle smooth. It always smelled rich and the idle mixture screws didn't seem to have much effect. I also had issues with surging when trying to hold a steady speed between 1500 - 2000 RPM and noticed some gas dripping from the venturis. After doing some research on here and elsewhere on the internet I learned that a power valve with too high of a rating can flutter open too soon, even at idle. When I opened up the carb this weekend I found it had a 7.5 instead of the normal 2.5 for my engine ('88 351W, 4160 carb). I replaced it with a 2.5 and the problem was solved.

joecarew3
06-29-2010, 06:18 PM
Try not to poke to much fun... I don't have a teacher to help with the same issue. I have pulled the carb, rebuilt it, cleaned it, put it all back together and it works but have the same issue, doesn't want to idle all the time, put a load on and it dies unless you goose it. Also after its warm I have to hold the choke down to start. I know I will be replacing the electronic choke, and distributor with an electronic ignition. Wondering if you guys recommend anything else? -Sorry for the thread jack!

Luv2Ski
06-29-2010, 06:47 PM
If you determine that your PCV and power valve are good, here are some tips on adjusting the screws themselves. There are a few ways to do it, methods I have tried include 1) tuning for max RPM, 2) tune for smoothness, and 3) tune for max vacuum. In reality, all three methods are related and should lead you to similar results.

I like to start by turning the screws all the way in with the engine off, counting the turns so that I can always put it back to where they were set when I started. Do not over-tighten them, this damages the seats. Then set them back to where they were, start the engine and warm it to operating temperature.

I initially try to start tuning with both screws in the same position so I will adjust one or the other such that they are the same number of turns out. I will then lean one screw until the engine runs rough, then switch directions and screw it open until the engine smooths out. I do the same to the other screw. That gets them both close and then it is just a matter of very small moments to optimize both screws, one then the other and back again.

As others have indicated, that fuel smell is a bit of a concern and indicates a pretty rich condition. That is what leads me to believe there is more going on than just the idle screws. Even if you find another cause, there is nothing wrong with optimizing the idle mixture.

Luv2Ski
06-29-2010, 06:54 PM
Try not to poke to much fun... I don't have a teacher to help with the same issue. I have pulled the carb, rebuilt it, cleaned it, put it all back together and it works but have the same issue, doesn't want to idle all the time, put a load on and it dies unless you goose it. Also after its warm I have to hold the choke down to start. I know I will be replacing the electronic choke, and distributor with an electronic ignition. Wondering if you guys recommend anything else? -Sorry for the thread jack!

There is a very high chance your rebuild kit came with the wrong size power valve. Even the kits recommended by Holley for a specific carb list number will come with the wrong power valve. My 4160 kit came with a 5.5, so I put the original 2.5 in when I rebuilt. The number represents the vacuum at which the valve opens, so the higher the number the earlier the PV is dumping extra fuel into the circuit. Again, replace the PCV. Adjust your idle mixture screws.

Luv2Ski
06-29-2010, 06:56 PM
One last thought for both of you, a vacuum leak will cause lower manifold vacuum and create a situation in which the PV opens to early. Check for vacuum leaks by spraying starter fluid or carb cleaner around the base of the carb. If engine RPM increases, you have a leak.

thatsmrmastercraft
06-30-2010, 12:13 AM
Try not to poke to much fun... I don't have a teacher to help with the same issue. I have pulled the carb, rebuilt it, cleaned it, put it all back together and it works but have the same issue, doesn't want to idle all the time, put a load on and it dies unless you goose it. Also after its warm I have to hold the choke down to start. I know I will be replacing the electronic choke, and distributor with an electronic ignition. Wondering if you guys recommend anything else? -Sorry for the thread jack!

Could be a leak at the carb base gasket. With the engine idling, spray some carb cleaner along the base gasket. Use some care here as this is potentially a fire hazard. If the engine speeds up while you are spraying, you found your leak.

joecarew3
06-30-2010, 11:22 AM
Thank you guys! I will let you know what I find. I really appreciate it!