idle sucks

ok just dropped the 351 reverse rotation in the 79, set the timing 8 degrees advance. went to the lake oh yeah I have a four blade prop from acme. the boat responds well, I ran it full throttle we toped at around 38. we noticed the idle was rough as in it shook the boat alot more than it should. So we loaded the boat up went to the shop changed out the elctronic ignition with a different one still the same I checked the firing order timing over and over, Ive got good gas new hoses plugs wires I even swaped the distributer from anotther identical engine still this rough idle. does anyone have any ideas Im going to work on it all day and would rather be drinkin beer with my lady friends all day cruisin.

Hi Corey
You have changed the timing, so you should adjust the carb to suit.
You need to adjust you primary mixture screws, and probably your static idle
What type of Carbie do you have.

Below are some instructions for a tuning a Holley Carb. You can Download technical information from the holley web site on tuning carbs.

IDLE MIXTURE NEEDLES:
Idle mixture needles control the air/fuel mixture at idle. These have been preset at the factory and SHOULD NOT need any adjustments.

However, if you feel that adjustment is necessary, you can use the following procedure to do so. When tuning the idle mixture, you’re actually tuning for the best manifold vacuum. Idle mixture needles are found on the primary metering blocks. If you change one idle mixture needle, you must change the other idle mixture needle by the same amount.

Here are the proper steps for setting the idle mixture needles.
1. Attach the vacuum gauge to a manifold vacuum port on the throttle body (Figure 3).
2. Adjust each idle mixture screw (Figures 10 & 11) 1/8 turn at a time, alternating between each screw. Turn them equally, until you achieve the highest possible vacuum reading without adjusting the curb idle speed screw. Turn screws in to lean the mixture. Turn them out to richen the mixture.
Figure 9
3. Now that the idle mixture is set, it may be necessary to go back and reset the idle speed using the curb idle speed screw, as shown in Figure 9.
4. If a vacuum gauge is not available, use a tachometer to obtain the highest RPM.
Figure 10 Figure 11
ROUGH IDLE AND VACUUM LEAKS: If a rough idle persists after the engine has been started and the mixture screws adjusted, check for manifold vacuum leaks. These could result from unplugged vacuum fittings or a carburetor flange gasket that was torn during installation. Recheck for proper attachment of all vacuum lines and check the lines for cracks.
If the manifold was changed, a manifold vacuum leak could occur at the cylinder head/manifold surface due to damaged gaskets or improper torquing. Frequently, manifold vacuum leaks occur from the valley side of the manifold. These are very difficult to detect, unless a discernible whistle can be heard.
NOTE: In most cases, when rough idle occurs after a carburetor/manifold change, they result from manifold vacuum leaks similar to those described above. Assuring a proper manifold installation rather than assuming the carburetor is not functioning properly will ultimately save time.
10

check this out mad my heart sink, we did a compression test this morning first cylinder 120 next cylinder 10 holy sh*t. next step pulled the heads cracked valves on cylinders 2 and 7. So I did what any man would do bought a set of GT40 heads thinking I could get some gaskets today but nope had to order some. So once again my motor is sitting on a stand. I needed to switch trannies anyway I noticed the prop spinning while in nuetral figured I would use my spare and get the other rebuilt. Im hoping the rings are ok and there are no other problems. I am positive the carb is set correcctly and almost positive the lower end of the engine is good. Im only going to run it until november than rebuild so hopefully the bottom end will hold up. The heads that went bad are bone stock and probably went bad from not using a lead additive. what you guys think?

It had a slight miss when I picked it up from you actualy it was the same miss I just was hopiing it was timing and carb not the heads but I still saved alot of money either way. Ill send pics next week of a finished product, I thinkalmost everything in the boat is knew.

Gotaski I agree with you never knew you could adjust the idle mixture screw on a FI motor. It's got to be pretty hard to do since there are none to adjust. Now a carb has them but I have never seen one on throttle body or multiport fuel injected motor, then again I don't believe corey is injected either. and in that case the procedure would work but they are not preset and should not be adjusted. If you want you engine to run right they have to be adjust anually if not by monthly depending on use.

40 hp should be about right coming from stock 351w heads- the GT40's were the primary difference between the 240 horse base motor and the 285 proboss.

There are other choices out there, but GT40p's are really the only other iron head that I know of that will give you better performance than the GT40's- and the difference shouldnt be huge. If you got a good deal on these low hr heads, I dont see how you can go wrong. My dad made the switch on his '92 and saw a nice improvement.

Hi GottaSki

If you are going to sl*g me off on this forum, at least have the decency to say what is wrong with the information that I posted.

If you read my post:
I asked what type of Carbie Corey was using.

The information that I posted about tunning was information supplied from the Holley web site for a Holley 4010, purely as a guide.

There is nothing wrong with the tuning information.

The only information that I did not agree with is the sentence about adjustments being factory preset and not needing to be adjusted.

GottaSki
You want me to grow some skin,
May be I could borrow some of the foreskin that you wear on your forehead

What information have you actually provided?

I love it,you are such a expert. You dispute the info on tunning a Holley carb distributed by Holley

If Corey does not have a Holley carb then so what he can ignore the info.