Misfire when hot

[UKSquarebody]

Morning all,

I have had a ton of work done on my truck since I bought it 18 months ago - yet barely done 100 miles in it.
Apart from the body and paint being sorted (I run a Classic car paint shop), I have had a third party rebuild the 700r4, and swap out the fully programmable MSD ignition and Holley 750 race carb - and replace with an Edelbrock 1406 and standard HEI.
The engine ran mint with the first setup - but was doing about 6mpg!
The motor is just a 327 with a ‘slightly warm cam’ according to previous owner, who was wanting a more ‘racey’ truck.
I just want a road truck for work!

Anyway point is, my mechanic has the truck running great. Idles well, drives well. ……..until up to full temp where it misfires.
All new plugs and leads. He has done several smoke tests - no air leaks anywhere.
He is suggesting it is the HEi - the coil essentially braking down.
He says he has no way of testing this.
I am no mechanic - and currently bed bound following an operation.
The HEI is a generic eBay buy (sorry!). A new MSD basic HEI is just £280 - but I am tired of throwing money at the truck, and still having issues.

Given the above info - is this a likely cause/fix?

Any help much appreciated
Keith

 

[dsteelejr]

Always start with the basics, the easiest things you can check before tearing everything apart. You said you’re running a Holley 750 race carb, does it have a choke? Is the choke fully open at operating temperature and staying open?

If that’s not it then try changing the ignition module and coil. The HEI module is cheap and easy to swap without replacing the entire distributor. Try an AC Delco D1906 or MSD 83647 module. Upgrade to a name brand in cap coil.

 

[Sad Sack]

 

[UKSquarebody]

Always start with the basics, the easiest things you can check before tearing everything apart. You said you’re running a Holley 750 race carb, does it have a choke? Is the choke fully open at operating temperature and staying open?

If that’s not it then try changing the ignition module and coil. The HEI module is cheap and easy to swap without replacing the entire distributor. Try an AC Delco D1906 or MSD 83647 module. Upgrade to a name brand in cap coil.

Thank you.
It WAS running a Holley 750, now on a new Edelbrock 650 with auto choke.
Will check the choke, and swap out the module

 

[UKSquarebody]

Thank you

 

[Ricko1966]

1406s are very sensitive to fuel pressure. Check your fuel pressure if it's over 5 psi,post back we can discuss some ways to lower it.

 

[UKSquarebody]

1406s are very sensitive to fuel pressure. Check your fuel pressure if it's over 5 psi,post back we can discuss some ways to lower it.

It’s running at 5psi through a regulator and filter on the bulkhead before the carb.