318 carb issues

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BigBlockMopar28

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318 in the ram was bone stock with all smog, removed the smog stuff and took the a/c off, installed a 340 alum intake and 600 holley street warrior vacuum, timing is good for sure. Long story short, had to tie off the choke because it would want to idle high when the truck was perfectly warm, and did not want to idle down for anything except on a few random occasions. It doesnt like to idle on cold starts without alittle pedal assistance for a min, i guess thats normal for one without a choke? Idles pretty low in gear (truck shakes some), but any higher and it wants to slam into gear. Has a bad flat spot around half throttle, especially when coldish. If i push past the flat spot around 3/4 throttle it will pull just fine, just has that flat spot that has me stumped. If i pedal it some in that spot it helps it for just a sec, leading me to believe its starving for fuel, but any adjustment on air/fuel makes it worse, its very sensitive. Fuel filter had some resistance, put a new one in and it barely changed anything. Carb is brand new, back bowl wanted to leak just a tad but i tightened it up and it seems to be ok now. I'll add that around that flat spot it really wants to hesistate, almost stalls out with to much pedal when cold. Idles and revs just fine, only acts up under load. Any ideas? New to this stuff so any help is appreciated. Thanks FABO!
 
Type of choke on this carb? Mechanical/electric?
Engine cold,choke goes closed,vacuum applied to choke break and it should pull plate about 3/16”. Fast idle should be set on second highest step.
It likely came kind of dialed in from stock but choke needs to be adjusted full open at operating temp.
Accelerator pump may play a part in this too.
 
Type of choke on this carb? Mechanical/electric?
Engine cold,choke goes closed,vacuum applied to choke break and it should pull plate about 3/16”. Fast idle should be set on second highest step.
It likely came kind of dialed in from stock but choke needs to be adjusted full open at operating temp.
Accelerator pump may play a part in this too.
Electric, ill have to take a look at adjusting that.
 
Ill add that currently the air/fuel is rich to the point where it shoulf probably be flooding, just so that it gets enough fuel. Tried to call holley to see what they would say, turns out they are still closed for holidays
 
This just dawned on me... could this be a fuel pump issue? Only acts up in that one spot, but i guess it could kind of make sense. Lol
 
"Timing good for sure" "It should be" when asked about the vacuum working.

Exactly where is the initial timing set? Have you actually checked the vacuum advance for operation? Although it will not necessarily cause your issue, it could be a contributing factor if the diaphragm is ruptured and it has a vacuum leak there.

Word to the wise:

Never say "this is good" or "that is good"when asking for help. Because more than likely that's where the problem lies. Unless you're willing to be open to those possibilities, then we may as well stop right here and now.
 
Old thread but the problem is still here after a new timing chain (old one slipped shortly after this), and new fuel pump. Air/fuel screws are set at 1 1/2 turns out, that seems to be where it likes. Same issue, no issues in neutral, but big flat spot under load around 1/2 throttle. Different ignition as well, lean burn was swapped in favor of a non digital msd 6al
 
Sounds more like a jetting issue to me. Is the intake a single plane or dual? If single plane it needs a lot more of a pump shot or bigger squirters. Check the jets also.
If it wants to idle high look for a vacuum leak. I’ve been in the same boat when converting mine from TBI to carb

59E25BAD-4A61-4B34-B6E1-8542E4AC4373.jpeg
 
Sounds more like a jetting issue to me. Is the intake a single plane or dual? If single plane it needs a lot more of a pump shot or bigger squirters. Check the jets also.
If it wants to idle high look for a vacuum leak. I’ve been in the same boat when converting mine from TBI to carb

View attachment 1715159866
Dual plane. But good idea on vacuum leak, that may just be the issue
 
IIRC the 87 318 ram was equipped with vac controlled emission and electronic spark control. (lean burn) I would bet that the distributor advance (mech and vac) is calibrated for those controls. I would ck your distributor to see if you are getting the advance that you need.
 
Msd 6al with old style vacuum advance currently, but it is a former lean burn truck. And will do scott
 
With or without vacuum advance makes no difference, timing adjustments made no difference, and no vacuum leaks on any hose/line I could find. What is a good baseline setup for the accelerator pump? That's the only thing I haven't touched on this one and i'm not too familiar with them.
 
It just occurred to me that the pump nozzle size could be off... From what i've read my carb currently has a #31 nozzle, would it be best to try a bigger nozzle or smaller at first? Kind of torn because holley says smaller nozzles are best for heavy vehicles and/or vehicles with tall gears, and that bigger nozzles are best for vehicles with good power to weight. The truck isn't light compared to an A-body (its almost 5,000lbs), but it does have 3.55's and a 727. Stock 318 w/ dual plane 340 intake and 600 holley vacuum. Choke is no longer a factor as it has been tied off. TIA
 
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