hi everyone i have 91 chevy tbi engine that i switched to carb and its in a 91 silverado. I had the motor rebuilt a few years ago it was bored .060 over due the rod bearing overlaping, the cam has .488 lift, it also has electric water pump and fans, edelbrock shorty headers, edelbrock torker intake, edelbrock 1407 750 with spacer, and a holley regulator set at about 5-5.5 psi. also an accel coil in cap hei with msd wires. once i first got it running it wouldnt rev past 2500-3000 rpms got that fixed by changing module in dist. i took down the road and to town a few times and by normal driving i guess you could say light throttle it would be hesitate or bog down not sure but if you stomp on it wouldnt be as bad and it will also rev fine in park well i fixed most of the problem by relizing the choke wasnt all the way open "about half way" lol new to carb. also when i had the revving up problem i thought the carb was to big and was getting to much gas so i took out the .113 prim and .107 secs and put in .101 and .95 and that was all i changed and i still have them in there, but im still having the hesitation or bog cant really tell and it does it the most right when im creeping up around 2000 rpms. it smells like it could be running rich and theres also a little wetness around the pump at the top of the carb. one other thing my wife was behind me one day when i got on it and she said it had llke this burnt smell but no smoke came out. any help would be greatly appreciated.
03-18-2012 04:28 AM
If you put those pieces into a stock engine with stock heads the combo is severely mis matched.
03-18-2012 07:29 AM
had the same problem years ago in my 55 Chevy. I did'nt have the same configuration that you have but my problem was not enough fuel when i stomped on it. I went from an 750 to an 850 duel feed and that did it. was turning high 12's in the 1/4 mile.
03-18-2012 09:08 AM
Are you trying to use a efi pump with a dead head fuel pressure regulator?
If so, that is a bad idea. You need to use a return style fuel pressure regulator with the stock efi pump.
what are the cam specs? Bigger cam require more timing at idle.
bogs at low rpm tend to be low timing and/or not enough accel pump.
03-18-2012 04:35 PM
im not sure on cam specs just know the lift which .488 but im not usins a stall. also im playing with fire lol b/c i still have the tbi heads on the engine and they're stock just havent the money yet to buy some im thinking about aluminum heads. i'm not sure what you meant by dead end fuel reg. its a holley with 1 inlet and 2 outlets with one of them plugged and im using my stock intank pump. what would cause the wetness around the accel pump at top of carb, also i turned the psi up on the regulator and all it did was flood it out after i shut it off and tried to restart. do you think changing the jets back to the bigger ones would help but like i said it smells like its running rich. and how would i set the timing to advance. thanks everyone
03-18-2012 04:36 PM
to 454c10 i meant dead head
03-19-2012 06:34 AM
Nothing wrong with using the stock efi pump. But you need to get a fuel pressure regulator that returns the fuel back to the tank. This is called a return style fuel pressure regulator. A dead head regulator doesn't return the extra fuel back to the tank (it just stops there).
Not only that, the pressure behind the regulator is very high with a dead head regulator with a efi pump. This will kill the efi pump.
03-19-2012 08:05 AM
Change the position of the rod that pushs the pump to the last hole on the lever.That will make it squirt more fuel.Its going to run rich at idle with that size of carb.Problem is air flow is slow thru carb.You need a smaller carb. like a 600.I had this same problem,I could never make my 750 Eddy not run rich at idle.I barrowed a 600 eddy and most of the rich idle went away.You might try using your smaller pri. Jet and a fatter rod and if your vacuum is more than 14 in. use the strong spring, I think its the purple one.Air flow thru a 600 is faster.Your going to be like me I have a 750 Eddy that is almost new that I cant use.Also your efi pump is putting out around 60 or 80 psi when you only need 5 or 6 psi for your carb.The return will send that excess pressure back to the gas tank.
03-19-2012 09:14 AM
alright i try a different hole for the carb pump and ill look into a different regulator but want be able to get one right away. I also read somewhere that the torker intake could be some of the problem if not most. Is there a way to tell if its getting to much gas or not enough without any smoke coming out the exhaust? I think also i will change the jets back to the bigger ones that came with it which are .113 and .107 b/c i had .101 and .95 in the carb and i looked at chart earlier for the 1407 and didnt see an option for .95 or .101. and i never changed the rods when i done the jets could that be it. also a recap before i do any of this the engine bogs or hesitates from take off light throttle and once i apply more pedal it tends to lighten up. thanks everyone for the help :)
03-19-2012 09:43 AM
quick question since my truck had tbi before there was a hose that went from the evap tank to the front of the tbi and when i installed the carb i reinstalled the hose to the driver side port. im pretty sure thats what it is called the other end of the canister goes to the fuel tank. not sure if thats causing any problems
03-20-2012 07:32 AM
The two ports are for the vac. advance on the distributor,pass.side is unported,driver side is ported.I think you need to connect the evap. some where elas,or not use it.Not sure on intake manifold,but you need a duel plane manifold single planes are all out HP.
03-20-2012 03:21 PM
ok well i havent changed the jets b/c i decided to take a couple spark plugs out to look at them (1 n 7) both were pretty wet and black so im guessing the bog was from too much gas so i moved the linkage to bottom hole on the pump , furthest away from the carb and i also tried to adjust the idle screws to see if it would help with the richness at idle and still not sure if there set right bc the engine sounds diff at idle doesnt lope as much at idle but at the same time i think some of the richness went away. after doing all that i took it down the road and most of the bog was gone so i was wondering if the linkage was the problem so i moved it back to the middle and immediately i could feel the bog or cut back around 2000 mark so i moved the linkage back to bottom and it mostly went away. does any one know how to correctly adjust the idle mixture screws, ive watched an edelbrock video about doing but dont know how much to tighten down to drop the idle. also ive dropped the psi to 5.5 it was set at 6 psi. are the spark plugs suppose to have some wetness or are they suppose to be completely dry if so should i take them out to dry them or will it burn the excess gas. i may switch the intake when i get some diff heads but the single plane intakes looks so good lol. also i think my pump only has 13 to 14 psi the vortec engines has 50 to 60 psi for tbi not sure though. one other thing i have open spacer not a 4 hole between carb and intake should i keep it on or take it off. thanks for all the help
03-20-2012 07:58 PM
91chevyss- "also i think my pump only has 13 to 14 psi the vortec engines has 50 to 60 psi for tbi not sure though. one other thing i have open spacer not a 4 hole between carb and intake should i keep it on or take it off. thanks for all the help"
You are right about your in tank pumps only running 13 to 14 psi. Most people you talk to will tell you they should be running upwards of 50 or 60psi but on those really early 90's models and on the late 80's throttle body models they run a much lower psi than people think. I have a 1991 454 with a throttle body and it is suppose to run right around 14 psi. Now i took apart the throttle body and opened the regulator a bit and fit an in line 23psi pump on it for a little more power but the stock in tank ones are supposed to run 14. I ran into a lot of grief when i was trying to get a 21-25psi pump cause everyone was telling me it was not enough and trust me my truck is running like a champ.
03-20-2012 08:06 PM
Using a single plain manifold and a 750CFM carb is not very good. You loose low end torque response. You be better off using a dual plain high rise manifold. It makes the motor think you installed a smaller carb. Or install a smaller 600CFM carb.
03-20-2012 10:11 PM
i thought that was right about the psi for fuel pump do you think thats too much to run with a dead head regulator at 5.5psi or should i look into a returm style. I also have a mechanical fuel pump to use if i need to just wasnt sure how to get the fuel from the tank. but before i get done with it ill be putting a fuel cell in the bed b/c the old one will scrub once i get the airbags on it. I dont have the money for the dual plane intake right now so ill have to make do with what i got but for now do you think ill be better off with or without the spacer. also the low end doesnt bother as much b/c of the 3:73. thanks again.