Okay here's some info about the car. I've got an 87 IROC that I bought a 350 from JASPER for....it's the 300HP 350. Anyway I put my RPM Air Gap intake manifold and a Edelbrock Performer 600 CFM carb. The thing RIPS, but only after it sputters and stumbles for a couples seconds. Once it even died on me when I floored it. I know everything else on the motor is fine, EXCEPT I think the carb needs to be tuned better. It takes forever and a day to start the car ( it just cranks and cranks til finally it catches) and like I said before, has some serious hesitation problems. I'm not too familiar with carbs, especially Edelbrock as my car was TPI before the motor swap. Any help on how to tune the carb would be greatly appreciated. Thanks!

 

im not a carb expert,but ive heard about this problem before and it was the cat. was clogged. do u know if urs is? i know u cant really just look in it easily but it could help out. just tryin to help

 

May be the carb but make sure your valves are adjusted correctly too.

 

I know the cat's not clogged and the vavles are adjusted properly...like I said I KNOW it's the carb, I haven't tuned it since I have no experience with carburators before now. I just need someone to tell me how I can adjust it to improve the hesitation and starting issues.

 

If an engine stumbles when you hit the gas, first thing to check is the accelerator pump shot. With the engine off, look down the primaries of the carb and work the throttle. You should see two squirts of gas, one into each primary throttle. If you don't see them, could be a blocked passage or a bad accelerator pump. Not familiar with Edelbrocks (nee Carters), so I can't give you any specifics, just generalizations. Would also explain your hard starting, no gas shot available to get it going.

Another possibility: has your car been parked or a while? Possible gas is a little old? That would also explain hard starting. Gas for carbs is more critical. Formulation is changed by refineries in accordance with the temperature, easier to evaporate in the winter, harder in the summer. Winter gas evaporates too easy in warm weather and will vapor lock the carb. Summer gas will give the kind of problems you describe if used in the winter. So will old gas, since it is harder for the carb to atomize until there is enough rpm to pull it strongly.

Carbs have their quirks. In the old days, it wasn't unusual for refineries to cause problems by switching formulations, then having weather do something unexpected. That would lead to vapor locks or hard starts depending on the time of the year.

Injection made that history, except for those who still run a carb.

 

Well I'll check tomorrow about the two squirts of gas. The car didn't sit for too long and it's been behaving like this since the swap, about 20 gas tanks ago until now so it wouldn't be old gas. Anyone else know much about how to tune this carb?

 

i have this same problem, you hit the gas, it stumbles then goes. I still havent found a solution...
Please help guys!

 

Are you still using the ECM controlled distributor? If you are, the TPS from the TPI thottle body needs to be used to get the ECM to kick in the WOT timing curve. I had the same problem and made a bracket and linkage that would work the TPS when the carb butterflies open. The ECM changes to a WOT timing curve when it sees 50% or more TPS signal. Without it you won't have enough timing advance to burn the extra fuel your pouring in with the carb.

If you're using a different distributor, you have to tune the timing curve with the mechanical advance weights and springs. Try starting at 12 degrees intial timing (idling) and 36 degrees total timing, all in by 3000 rpm. Most 350 ci Chevy engines like 34 to 38 degrees total timing. Initial timing will vary according to how big the carb and intake is. For example, my 355 uses an 800 cfm carb and Victor Jr. intake. I have to run 20 degrees intitial timing to keep it from hesitating with the big carb and single plane intake, but still have 36 degrees total at 3000.

If the timing is right and the carb is definately the culprit, just call Edelbrock and ask for help. A friend of mine used a 600 Edelbrock carb on a 350 in his pickup. It stumbled and ran lean. One phone call and they told him exactly what springs and metering rods to use in the carb. Did what they said and it ran perfect.

 

ok, i might as well throw in my question here too since its similar i think (hope i dont steal your thread too bad!)

so i just got my firebird, and when you get on the gas real hard the car makes a loud popping sound and then will start accelerating. the guy i bought it from said the timing needed to be adjusted, so ive been playing with it. if i turn it down lower it doesnt really knock, but it will want to die a lot. right now i think its around 7 or 8 degrees, its on the notch farthest to the passenger side on the harmonic balancer. also, when it starts the first time every day, it will die when i put it in gear, then when i start it again its pretty much fine. i just found hte sticker under the hood that says timing should be at 4 degrees. if i set it at that, will it run ok you think? or could that popping be due to something else? thanks a lot guys

oh, and also it seems like it starts a lot easier when its warmed up. the first time i start it each day i gotta pump the gas a lot, any other time it seems like it starts almost instantly. whats that all about?

 

Big_Z,

If your Firebird came originally equipped with a carb, it sounds like you may have a bad accelerator pump. Rebuild the carb. A new accelerator pump will be in the rebuild kit. Check angel71rs post about looking for pump shot.

 

ok, some more info on my situation:

it gets a lot better as far as dieing after it is drivin a little. am i just too used to fuel injection, do i gotta let it warm up a couple minutes? it also seems a lot worse when it doesnt have a lot of gas, it had about a quarter tank and it ran terrible and died several times, then i filled it up and it ran pretty badly for a few minutes (i got on the gas pretty hard one time and the engine barely revved at all) but then after that it seemed to be running pretty well. ill check the accellerator pump tomorrow, right now its at a friends house because a tie rod end busted out yesterday oops. and if i do need to get a carb rebuild kit, where can i get one from? thanks again!

 

Should be able to get a rebuild kit from any auto parts store.