strega

Hi guys,

I have a problem with my newly rebuilt 454 alpha and wondered if you had any advice.

Firstly the engine.

It has got an edelbrock performer rpm intake, mildly uprated valve springs, oval port heads and a new marine q-jet carb. Other than that I believe it to be standard.

My problem is I just can’t seem to get the tuning right. I can get it to idle no problem but it bogs on acceleration and backfires through the carb at about 1500-2000 rpm. The timing was set to base 8 degrees and have played with moving to 10 but do not want to damage the engine as tuning these things is new to me.

I am from the UK where we have no support for these sort of problems, so your help would be greatly appreciated.

sprink58

Double check your spark plug wires. Make sure the firing order is correct...1-8-4-3-6-5-7-2. Port side is 1-3-5-7 from front to rear, starboard is 2-4-6-8 front to rear. The back firing through the carburetor is a symptom of one or more of the spark wires being crossed..

Good luck with this.

dereknkathy

if firing order is right, next culprit will be the new carb. just cause it is new, don't mean it is perfect...

88Spyder

If you want to make sure it is not a cylinder misfire you can ground each cylinder one at a time and put the engine under load, if the back fire goes away it is in that cylinder, also a vacum gauge is a very good timing tool. This would be after checking the firing order to be sure it is correct. Who adjusted the valves after the springs were replaced?

strega

I adjusted the valves several times as wanted to make 100% sure I had done it right! Not that I am saying I didn't screw up!!

I will check the ignition leads next time I am down at the marina.

What do you guys think the timing advance should be? Am I correct to start at 8 with a mildly tweaked engine?

strega

What can I do to check the carb? I bought new to save any hassle!

dereknkathy

put the old one on if it ran ok.

strega

The old carb was utter junk along with the rest of the boat.
I have just completed a 2 year restoration on the entire boat and engine and am so close to getting it sorted.

sprink58

With understanding that the carburetor is new...I would consider problems with it to be near the bottom of the list.

Regarding timing...don't get a fixed point of initial timing at idle at the top of your list of concerns. Moreover, concentrate on a total timing advance of 32 degrees at 3000 RPM. You must have a timing light with a variable timing adjustment in order to check total advance.

It is possible that you have a vacuum leak. Double check for open ports in the intake manifold, carburetor, etc. Also check for any cracked or split vacuum hoses....as well as obvious leaks around the intake manifold.

I can't over emphasize the spark plug wire problem potential. That issue is so easily created and overlooked that based on the symptoms you describe....must go to the top of my list.

As the old mechanic once said..." A gasoline engine requires fuel, air and ignition...if all three arrive at the same time...it will run well."

keith2500hd

if plugwires correct put wire spacers, to keep the wires off each other. get number off side of carb and make sure it is proper application, sounds like off-idle, transition circuits are lean. we use ultrasonic cleaner for carbs, but still run copper wire thru emulsion vents to clear gunk. these are the small holes in forward part of primaries. check manifold vacuum with gage and make sure no leaks.