This carb has been on my car for 18 years. Its been a pretty good carb for the most part. Lately its been acting weird. After driving for 30 minutes it starts to miss at idle, for example at a stop light. I recently installed a Holley retrofit intank fuel pump thinking the mechaincal pump might be the issue.
Im thinking the carb probably needs to be rebuilt or maybe I should up grade to a better carb. I was thinking efi but decided to stay carburated. You guys have any suggestions on carb upgrades or rebuild and see if that solves the flutter issue?
Well, I think for a mild build 351, I’d rather have a 650 or 750, depending on rear gear and driving habits. But, before you spend the coin on a new carb, double check your ignition. You said the engine had been modified, do you know for a fact the condition of the timing gear set? What kind of distributor are you using? Points, or a modern electronic replacement? Vacuum advance working smoothly?
I’m using a Holley 3259-1, 725 CFM on my built 351. T5 trans, 3.89 rear gear with a Detroit locker diff. Lots of fun to drive.
BLOCK:
351W, 1970 block
Bored 4.03 over
5.5cc flat top pistons
CAM:
Lunati Voodoo flat tappet
.483 IN, .499 EX lift at valve
112 lobe separation
213 IN, 219 EX
Duration @ .050 tappet lift
Advertised duration is 256 IN, 262 EX
Inake closes 34.5 ABDC
108 Deg cntr line of IN lobe, 4 deg adv
HEADS:
Trickflow Twisted wedge
61cc combustion chamber vol
170cc IN port vol
2.02 IN valve dia
66cc EX vol
1.60 EX valve dia
Calculated compression ratio 9.8:1
IGNITION:
Stock distributor
Patronix electronic Ignitor
MSD Blaster II coil
Ford 3G 130 amp alt
The 4 barrel Autolite carbs that were stock on a 4V version were pretty tiny and lame carbs anyway with all their leaks. The 2V carbs were reliable but again tiny. I would use a 600 CFM Holley 4V vacuum secondary Model 0-1850. There is a reason it has been Holley’s best selling product for decades. They sell a version with automatic electric choke or a version with manual choke. Both are beyond reproach.
I have been using an Edelbrock carb on my 1969 351W for many years. No issues, It worked great out of the box. I nel.eded to fabricate the fuel feed line and adapt the throttle linkage to the configuration of the carb, Not a big deal.
I used a Holley previously but got tired of dealing with leaks and stuck floats.
I ran a Holley for 15 years and 400,000 miles with no issues. I have purchased Edelbrock carbs both 600 CFM and 750 CFM versions. In my opinion they are not as good as Holley carbs but they are an alternative that provides less performance and less mileage.
I recently had a miss at intermittent RPM… it was my coil wire , it had a connection block leaking electrons down onto the block/china rail/manifold.
Whenever I floored it the coil wire would swing onto the block and short giving me an acceleration miss that felt like a carb stumble. Happened when hot (I can’t explain that bit)
Unlikely to be your problem, but easy to check and discount. Wire vibrating on block at idle?
Ha - I had that exact same problem back in the day. Mine was also temp dependent. Found out the reason was that the plastic wire insulation got more flexible at warm temps allowing it to flex into places it wouldn’t normally have gone.