Bad gas?

So how's your compression after the shimming?

14 inches is kinda low and 120 is too with the 40P heads unless your gauge(s) are off.

You've probably read about different causes which is probably why you're buying shims.

You're probably referring to the link I posted the other day with Shep 72's method, it can't hurt to check. It works good.

I'd guess you won't need the shims and that the valves are OK, but you'll know soon.

This is just idle on the trailer. I might be mistaking but I’m pretty sure I gave it some gas and vac actually increased to 20. I ordered some shims and Holley rebuild kit. Going go back thru valve adjustment one more time. Read great post yesterday on here gave me better idea. Think I’m also going drain tank and start fresh with rec 90. I’m about wore out working on it. Seems I’m stuck and going over things multiple times.

I'm not a carb guru but if your throttle plates don't close far enough it causes the idle circuit problems.
If you can close the throttle more the idle circuit may start functioning better.
When they are not closed properly the carb will pull fuel ignoring the idle circuit.
If memory serves me correctly the screws on the side of the Holley adjust fuel flow. Screwing them in is supposed to reduce fuel.
Look down the primary / front barrels a slot should be exposed with the throttle closed.
Open the throttle all the way and look with a flashlight to see the full slot.
Do a little reading and you will get dialed in how to set up your throttle plate setting.

Thanks Tim.   I know Chevy's, My Nautique has the Ford. Still learning.

I did a little forum searching and it is stated that the GT40P Heads have the fast burn chambers so max total timing recommended with a good fuel mix is 32.   The GM 1996 and newer Vortec heads are similar in needing less timing than the older head designs for max performance. As hard as boat engines work you might want to start with 30 total timing and tune from there to avoid any detonation issues. Sorry to mislead stating 35 or 36 should be safe.   With the old heads that would have been safe but not with the GT40P heads. I run a 1995 GT40 with P heads but it is computer controlled so I have not needed to check timing but thanks to your engine now I know.

I had to put a timing tape on my harmonic balancer and Mark new lines last time I set timing. Marks are gone now I need to remark it. I didn’t hear any pinging running. Going to check it after work today.

MrMcD wrote: It will have more horsepower and torque with your new heads. A good move on your part. Glad you got it back running again. Since you now have more compression you will want to verify how much timing you have at 3,000 to 4,000 RPM.   You need to know the amount at this RPM so you know the engine is safe to run hard. Each head design has unique known timing constraints, some can only accept 28 degrees while others need 40 degrees for max performance. The 351W heads I believe are happy at 35-36 degrees but I will let others with more Ford knowledge advise you. A set back or dial back timing light helps to determine how much centrifugal advance your distributor has and if it advances smoothly without sticking.   Once you know your advance you can set your timing at idle to allow the right amount at 3,000. Most want your centrifugal advance fully in by 3,000 for best performance. If you find your distributor allows 24 degrees of advance and you want 36 total timing at 3,000 you would set idle to 12 and your good to go.   It is just math. If the distributor does not advance properly this is the right time to fix it. Proper timing makes a huge difference in performance and economy. Hope this helps.

How are you determining when detonation occurs? Are you going by ear? Dangerous territory! Are you using 87 octane as your base fuel?

It will have more horsepower and torque with your new heads. A good move on your part.
Glad you got it back running again. Since you now have more compression you will want to verify how much timing you have at 3,000 to 4,000 RPM.   You need to know the amount at this RPM so you know the engine is safe to run hard.
Each head design has unique known timing constraints, some can only accept 28 degrees while others need 40 degrees for max performance. The 351W heads I believe are happy at 35-36 degrees but I will let others with more Ford knowledge advise you.
A set back or dial back timing light helps to determine how much centrifugal advance your distributor has and if it advances smoothly without sticking.   Once you know your advance you can set your timing at idle to allow the right amount at 3,000.
Most want your centrifugal advance fully in by 3,000 for best performance.
If you find your distributor allows 24 degrees of advance and you want 36 total timing at 3,000 you would set idle to 12 and your good to go.   It is just math.
If the distributor does not advance properly this is the right time to fix it.
Proper timing makes a huge difference in performance and economy. Hope this helps.

Gary S wrote: KENO wrote: Also there is talk about what spark plugs to use in the thread. Now Ken,depending on what oil I use,what make filter I choose,how often I change my impeller or what type of rag I remove wax with- whats the best brand plug to use?

Your favorite brand of course

Gary S wrote: KENO wrote: Also there is talk about what spark plugs to use in the thread. Now Ken,depending on what oil I use,what make filter I choose,how often I change my impeller or what type of rag I remove wax with- whats the best brand plug to use?

Deep cycle or starting battery???

I ordered from Clearwater had them put brass freeze plugs and told them to drill them out. I have a new set of autolites I guess I can’t use now if someone wants them.

A set of gt40p’s are on the way. Hopefully they just bolt right on without getting into anything else like the pushrods and rockers lol. I’m prob already getting in over my head. Some of the best fishing and weather is coming up at the end of the month trying not to miss it lol.

Lots of options when you do a search on ebay for "GT40P heads"

Ya at the time I looked think it was about $1200. Think maybe skidim had them. Havnt seen one lately though.