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shortyx250
08-29-2011, 03:38 PM
I checked my sparkplugs and the front ones are leaner than the rear. Its a 1980 S&S with a new 351W. Any ideas? Maybe a leaking intake?

CantRepeat
08-29-2011, 03:45 PM
Could be a vacuum leak at the runner gasket?

shortyx250
08-29-2011, 03:53 PM
OK is that the Carb and Riser gasket your talking about.

Cooter
08-29-2011, 04:12 PM
The runners are the long tubey lookin things that attach to the heads. They are below the carb/riser and are horizontal.

shortyx250
08-29-2011, 04:24 PM
I dont see a runner/tubey. Do you pull the intake manifold to get to this or are o utalking about the intake manifold gasket?

Cooter
08-29-2011, 04:41 PM
Sorry for the lame answer. Yes, the intake manifold gasket. A vacuum gauge will tell you if theres an intake leak. "NEW" 351? I'd call the place you got it from and see what type of warranty they have. I'd also put a torque wrench to the intake manifold bolts and re-torque them. The builder might have missed the front ones.

thatsmrmastercraft
08-29-2011, 04:52 PM
Before torquing anything, I would use a can of carb cleaner to check for vacuum leaks around the intake manifold gaskets.

shortyx250
08-29-2011, 04:57 PM
Well its 2 years old and I put the motor in after buying a long block. The original motor was cracked when I got the boat. So that makes me the installer of the intake mainifold. So its under warranty for labor just have to buy parts. :) Yeah I will get some carb cleaner and check for a leak. Thanks.

Hollywood
08-29-2011, 06:15 PM
Considering the boat is a 1980 model and most likely has an engine tilted at ~15 degrees this is just how it is.

pkskier
08-29-2011, 06:21 PM
Hollywood is right, it is the slant of the engine in the boat. Not much can be done about it.

CantRepeat
08-29-2011, 07:33 PM
Considering the boat is a 1980 model and most likely has an engine tilted at ~15 degrees this is just how it is.

I wouldn't think the suction from 1,2,5,6 cylinders would not be able to over come 15 degrees.

Cooter
08-29-2011, 07:33 PM
Hollywood is right, it is the slant of the engine in the boat. Not much can be done about it.

You can install 1 size larger jets in the front bowl of the carburetor (assuming its a Holley).

CantRepeat
08-29-2011, 07:35 PM
You can install 1 size larger jets in the front bowl of the carburetor (assuming its a Holley).

The carb doesn't work that way. The front, primary, feeds all the cylinders, while the back, secondarys adds more full for WOT but still feeds all cylinders as well.

Rejetting the carb will affect all cylinders.

thatsmrmastercraft
08-29-2011, 07:38 PM
I have had no problems with fuel distribution in my '77

shortyx250
08-29-2011, 09:28 PM
I checked for vacuum leaks and thats not the problem. The boat runs good I was just checking the plugs and noticed them to seem a little lean. Whats the stock setting for the idle mixture screw? I am at 1 turn out on both. In is rich and out is lean right? I thought 3 out was the stock setting. I have a 1/2 mile of idleing/no wake before I get to my dock.

shortyx250
08-29-2011, 09:34 PM
If the engine is bored 30 over do I need fatter jets?

CantRepeat
08-29-2011, 09:39 PM
I checked for vacuum leaks and thats not the problem. The boat runs good I was just checking the plugs and noticed them to seem a little lean. Whats the stock setting for the idle mixture screw? I am at 1 turn out on both. In is rich and out is lean right? I thought 3 out was the stock setting. I have a 1/2 mile of idleing/no wake before I get to my dock.

Idle air screws are adjusted based off of vacuum readings. I have a how to post on here for idle mixture, I'll have to see if I can find it. Your block being 30 over shouldn't change jetting. If you had changed cams/rocker ratio, gone with more compression, changed exhaust or heads then you might need it.

thatsmrmastercraft
08-29-2011, 10:05 PM
1 1/2 turns out is the place to start with the idle mixture screws. Out is richer, in is leaner. Ideally you would set this with a vacuum gauge for highest vacuum at idle speed. You can also do this with RPM. I keep my idle speed at 625 RPM in gear (on the water , of course). The makes for about 800 RPM in neutral. Turn each screw 1/4 turn each to get close to highest RPM adjusting the idle speed screw as needed to get the proper speed. When close, adjust the screws 1/8 turn each to fine tune.

JimN
08-29-2011, 10:40 PM
I wouldn't think the suction from 1,2,5,6 cylinders would not be able to over come 15 degrees.

Not just the angle, the effects of gravity and acceleration have a bit of effect, too. It doesn't take much difference in the amount of fuel delivered to create a lean situation. As long as the spark plugs, valves and pistons aren't melting, it may not be a big deal.

JimN
08-29-2011, 10:41 PM
I checked my sparkplugs and the front ones are leaner than the rear. Its a 1980 S&S with a new 351W. Any ideas? Maybe a leaking intake?

What color are the plugs? If they're tan, it should be OK. If they're white, it's definitely too lean.

CantRepeat
08-29-2011, 10:48 PM
1 1/2 turns out is the place to start with the idle mixture screws. Out is richer, in is leaner. Ideally you would set this with a vacuum gauge for highest vacuum at idle speed. You can also do this with RPM. I keep my idle speed at 625 RPM in gear (on the water , of course). The makes for about 800 RPM in neutral. Turn each screw 1/4 turn each to get close to highest RPM adjusting the idle speed screw as needed to get the proper speed. When close, adjust the screws 1/8 turn each to fine tune.

Like Peter said.

Get the engine up to operating temp, make sure the choke is completely off. I would go with turning the screws all the way in and backing them out 1 full turn. What you are trying to get is the highest vacuum reading. Hook your vacccum gauge up to a non ported vacuum. Turn each screw out 1/8 of a turn, doing one side then the other until you reach the highest vacuum reading. IE 1/8 on the left, then do the right, check the reading then left and right... if the vacuum drops then 1/8 in.... make sure left and right are the same number of turns out.

You might need to raise or lower the idle with the idle screw, do not be confused between the idle screw and the idle mixture screws.

CantRepeat
08-29-2011, 10:52 PM
One other thing you might want to check is the float level... while it shouldn't make a differnce to the cylinder readings from front to rear a low float level can affect a lot of stuff.

shortyx250
08-29-2011, 11:32 PM
The plugs are white. I think I have my idle mixture screws to far in. They were a half a turn out. Not sure how that happened. To many beers maybe. I am going to back them out to where they should be, and go from there.

thatsmrmastercraft
08-30-2011, 12:24 AM
While you are at it, remove each mixture screw and spray some carb cleaner (using the straw attachment) to clean out any junk. When replacing the screws, lightly seat the screw then back out the 1 1/2 turns.

CantRepeat
08-30-2011, 12:38 AM
While you are at it, remove each mixture screw and spray some carb cleaner (using the straw attachment) to clean out any junk. When replacing the screws, lightly seat the screw then back out the 1 1/2 turns.

1/4 beer for each turn would work best. :D