i'll try to list off the useful details of my motor, let me know if theres anything i can tell you.

I have a "330hp H.O." gm crate motor, with my mods i figure it should be running at least 330-350hp

-weiand dual plane intake manifold
-edelbrock 1406 jetted 2 stages rich on primaries (metering rod change) and secondaries (jet change)(car had a bad lean bog)
- 12 degrees of timing advance (93 oct fuel)
- Sanderson headers, xpipe, 2.25" true duals, Magnaflow straight-through mufflers
- 2" air filter on a drop down plate w/ no carb spacer (Hood clearance problems)
-2.88 rear end


Took the car to the track (1/8th mile) last night and ran everywhere from 10.8 to a 9.2@78 mph.
the car leans out and bogs if the coolant temp is over 170 deg.
even when the car does not bog it still feels sluggish

judging by the "1/8th mile hp calculators" i'm running 250-275 hp at the crank. I was not getting any wheel spin to throw things off. I know these are not the most accurate ways of finding hp however, it certainly feels that slow...

I know i need a carb spacer and possibly a larger intake but can those 2 things really be robing me of 50-75 hp??


Thanks in advance buys, I really appreciate the help

 

I'm relatively new to this carb thing, but I can tell you that the 2.88's aren't helping you. What is your total timing?

 

I couldn't tell you what my total timing is, all I know is I'm running 12 degrees advance at idle

 

How is your distributor curved, and what are the symptoms of your "lean bog"?

 

The add for a 1406 states it is tunned 2% leaner then a 1405
have you tried to richen up the mixture adjustments
are you running a stock distributor do you know if the vacuum advance is working you may need to purchase a weight & spring kit to dial your advance
i'm sure your cam has a higher rpm band

 

Doesn't explain why he thinks it's bogging lean.

Idle mixture screws have no effect at WOT.

Vacuum advance has no effect at WOT.

It's a peanut... .435/.460, 212/222 @ .050" flat tappet.

 

Um... What is a peanut?
I'm running a standard hei distributor from auto zone. I have not changed out any springs or weights and i'm not really sure what the specs or the stock ones are.

When the car gets warm and I take off at full throttle, it will sometimes loose power and make a loud intake noise as if it were running out of fuel. If I let off the gas for a second and allow fuel to fill back up and the car will take off again. Sometimes if I launch the car against the stall converter it will bog slightly then take off.

The problem lessened when I richened up the carb. It only bogs when the car sits for a while. For ex: sitting at a light or,waiting in line at the track.

 

Is this a new carb, or used?

 

It's new, the whole setup has about 8 thousand miles on it

 

It sounds like your carb is not tunned proper
OR you do have a FUEL problem did you buy a new pump and or check your fuel pressure at idle and WOT and it's very lean thats why when you reach temp you hear the engine pop


AND Apeiron your right the curve and idle adjustment don,t help at all
@ wot BUT he did mention bog at the holeshot And they will most certainly help then till 2000

 

Did you follow all the instructions in the Edelbrock manual about setting the float levels and the entire process for tuning the carb?

 

wow! I totally skipped over that part about the floats. i'll have to check those out tomorrow. I did however, make an adjustment to me accelerator pump, which seems to have helped my holeshot problem quite a bit. still boggs at the top end when warm though...

I'm not sure what my fuel pressure is, I'm not currently running a gauge. Anyone know of where i could get a really cheap one, off the top of your head??

Thanks a lot for all the help guys

 

You want to buy a cheap REMOTE fuel pressure gague setup from Summit or wherever. I have a setup that I duck tape to the outside of the windshield (temporarily!) when I make a run. SOMEWHERE YOU CAN ACTUALLY SEE IT WHILE YOU MAKE A RUN. If you're outrunning your fuel system it will be obvious- fuel pressure will nose-dive in the upper RPMs of 1st and maybe 2nd gear.

Accelerator pump..... if you made a change and it helped, that's good. My experience with Eddy carbs is that you put it in the hole closest to the fulcrum point and leave it there. Haven't found the Edelbrock carb yet that didn't run best with as much pump shot as you can throw at it. This can sometimes be a "night and day" difference coming out of the hole.

And map out that ignition curve!! 12* at idle is good, but don't just assume you're getting up to the 32* that engine calls for higher up in the RPMs. Get a dial-back timing light and map out everything from idle to 3500-4000. It SHOULD kick up from 12* at idle to 32* by no later than about 3000 RPMs (vacuum advance disconnected and plugged) and then stay at that timing from there to redline. Most stock/stock replacement/mild performance HEIs deliver about 20* of maximum centrifugal advance (the difference between 12* initial and 32* maxed out), but not all of them do. I've run into cheap parts store HEIs that give as little as 14* maximum centrifugal advance! That can absolutely kill power in the upper RPMs if you're 6* shy of maximum power-producing ignition advance. Vortec heads only need about 32* advance to make best power, but it doesn't mean they run very well if you're only giving them 25-26*.

What would really knock your socks off is if you find that the centrifugal advance is totally stuck (no centrifugal advance at all)! I've run into it rarely. It's a bummer to find out you got a bad distributor, but once you fix the problem it's quickly fogotten becuase the power difference is HUGE. About the time you've laid down 100 yards of smoky rubber on the road you forget all about the original problem and just enjoy having it fixed.

 

First thing I'd do is get that gear out of there. First thing I did with my 88, to a 3;23 ratio it was a whole different car.

 

Just ordered a cheap gauge off ebay, Should be here by thursday. I'll run out to the track thursday night and see what It'll do with a carb spacer and a 3" filter.

I set the timing a few weeks ago and did notice that the dizzy advances when I apply throttle however, I did not take the time to look at what RPM and degrees it maxed out at.

The soonest i'll be able to get a hold of that timing light is friday. I'll have to check the timing then. Could different weights allow the dizzy to give out a little more advance if need be?

The gears gave got to stay, I put about 250 miles a week on the car (highway). It averages around 24 mpg and runs 2k rpm at 80. As fast as I would like the car to go, It is a highway car first, and a race car second.

Plus I know it's something in my motor holding me back right now. My dad has an 06 r/t charger which pulls WAY harder than my car, weighs at least 400lbs more, Has "later" shift points than I do (45mph,75ish,120-130,etc.) / my 700r4 shifts at (35-40,70ish,130), AND hypothetically, I should be making similar horsepower.

I've AT LEAST gotta beat that Mopar.

Thanks for all the suggestions guys, keep em coming! hopefully I'll have this figured out by the weekend!

 

I agree with looking at a fuel gauge during your track pass. Make sure that you put it close to the carb.

What I think the problem might be is vapor lock. I had a problem with mine running out of gas at the end of the track and then when I would let off it would fill back up and start going again.

Does your fuel pump or regulator have a return line that goes back to the gas tank? The stock setup uses a return line to avoid the vapor lock program. When the fuel lines get hot it turns to vapor and then the pump can't pump it.

 

if you're not running a return line, you can drill a pin hole in the gas cap to prevent vapor lock.

 

The car was once fuel injected and does have a fuel return line however, I didn't have anywhere to run it so,I just capped it off. I am running a mechanical fuel pump and it only has one input and one output for fuel. Is there anywhere on the carb I can run the fuel return line to?

 

i think there are pressure regulators with provisions for return lines built in, or you could run a tee?

 

I see... Wouldn't a tee just pump good fuel back into the tank tho...? thereby lowering my fuel psi? I think I might have an old regulator laying around the garage somewhere... I'll have to take a look when I get back in town. I don't remember it having a return line on it though.

 

I bet you 5 buck that's your problem. If I were you, I would get a stock fuel pump, I think it's only 15 dollars, and put that on to test it. Drive it like you were with the return line hooked up and see if the problem goes away.

Get a stock fuel pump for a 1986 camaro with a 4bbl carburetor. It will have 1 in and 2 outs, the little one goes to the return line I believe. There are aftermarket pumps like this too. I'm pretty sure five7kid found a nice carter fuel pump with a return line for like $30 or 40 bucks. Search around and you will find the part number.

You could also get a return style regulator. Holley makes a good one for a decent price ($70), make sure it has a return line though. I took one of those apart and it's a pretty good design I think. This is the more expensive route though, I would just deal with the source of the problem though instead of band aid it.

The whole point of a return line is to keep the fuel flowing through the lines when the neadle and seat close on the carb. Otherwise fuel just sits in there and if they get hot enough, the fuel turns to vapor and the pump cant pump it and then the fuel bowl in the carb goes empty and the motor runs out of fuel.

I learned about vapor lock first hand when I had a single in/out pump. A member on this board saw it and when I told him what the car was doing (dying at the end of the track), he told me to put the stock pump on it. Sure enough it solved the problem.

 

sweeeet. I've been researching more and more about vapor lock and fuel return lines and it's really starting to sound like my problem. Hard starts when warm, bogging after sitting at a light for a while (fuel gets warm in the lines and vaporizes), etc. I also think i've found that the fuel filter from a 68-69 vette has a return line built in. That should work fine right? (as long as it's run after the fuel pump)

Thanks, Cody

 

I dunno. Anything you put between the mechanical pump and the carb is going to reduce fuel pressure to the carb. I would put a stock pump on there. They're supposed to be good for 400hp.

 

If the car was originally fuel injected, and the stock in-tank electric fuel pump is not operating and has not been removed, you're making it impossible for the mechanical pump to pull enough fuel through the non-operating electric pump. This will make a vapor-lock prone car even worse about vapor lock, to say nothing about being able to deliver enough fuel to the engine under power.

Either get the in-tank electric running and use a return-style regulator like the Mallory 4309 (might be able to use a stock return-style mechanical pump as the regulator - theoretically it should work, not sure I could say someone has tried it), or drop the tank and remove the in-tank electric pump.

 

I actually have removed the stock elec. pump. As far as I know, there shouldn't be any restrictions in between my tank and my pump (aside from my fuel filter).

 

Filters on the pump inlet should be low restriction screens. If you put a screen on the pick-up, that is adequate.

The filter itself should be on the pump outlet line. A fuel pump is able to push fuel through a filter easier than it can suck fuel through a filter.

 

Phew... I've got quite the list here for when I get home...

Move my filter after the pump.

Check for vac leaks

Check timing

Adjust floats

Check fuel pressure

Run fuel return line... That's all I can think of right now...

I'll keep you guys posted.

Thanks,
Cody

 

UPDATE!

found a cheap fuel filter w/ a return line output on it. Figured I might as well get a new filter anyways. It is currently hooked up right before my carb.

The less restrictive 3/8" end is running to a t fitting (runs to fuel press gauge and carb) the other (more restrictive 5/16" line) is running straight to my fuel return.

When blowing through the inputs/outputs of the fuel filter, the smaller (return) line is noticeably more restrictive than the larger 3/8" line (just an observation)

The car used to bog lean after sitting at a light or waiting in line at the track, this (vapor lock, I'm assuming) is now completely gone. Here is a video of me going WOT after letting the car sit at idle for about 5 minutes. http://www.youtube.com/watch?v=oS3GOV5LN1E

the needle on the psi gauge bounces back and forth violently from 0-5/6ish psi until i apply throttle. at a light cruise it reads about 3 psi. then... at wot it fluctuates between 0-0.5 psi.

should be concerned that I am getting such a low reading? or is my fuel return line to blame? if I kink off the return line the needle starts bouncing from 0-8psi at idle (I have not tried to run the car w/ the fuel return line kinked) Even though I am getting funky readings, the car has never ran this good when warm.

ALSO, I am currently running 2 fuel filters until tomorrow morning. AZ was out of 3/8" male to male fittings to replace my pre-pump filter with so, I'm temporarily running 2.

I also fixed a small vac leak which seemed to get rid of a 2-3k rpm flat spot I had.

Although the car is not bogging I have not noticed any real "seat of the pants difference". Tomorrow I am going to make some runs with a dyno app on my friends iphone (you laugh, but, it's actually pretty accurate!).hopefully that will offer more realistic changes as opposed to the "seat of the pants" factor.

lemme know what you guys think,

thanks,
Cody

 

Been watching this post for a bit and was waiting for an answer that would help me.

Now I'd like to give my 2 cents as you may benefit.

In no way am I saying I'm an expert.

I installed a GMPP ZZ4 and GM stated that a 600CFM would be good. My parts guy sold me a Holley Street Avenger w/670CFM.
I took it to a performance guy and he could not down-jet/rod it enough to compensate for the lack of airflow this carb had. I went back to my shop, installed the factory Q-jet I had and drove back to the dude with HUGE smiles on. I couldn't keep my tires on the pavement even before I let him tune it. Apparently my Q-Jet is either a 750 or 795 CFM. I haven't measured the Venturies to clarify what this carb is, but this motor WANTS air.

I also had tried an Edelbrock #1407 ( 750 CFM ) after the Q-jet install. I was able to Jet and Rod it enough but I hated the carb.
I still run my Q-Jet now, passing emmisions, and beating many cars with my heavy truck on the street.

600CFM from factory is BS

 

Burgurboy, glad you found the problem. I'm interested to hear what that iphone says.

 

Nowhere near enough fuel pressure. A properly functioning fuel system will hold near-constant fuel pressure at all RPMs and throttle positions. If it's dipping anywhere below even 4 PSI at WOT, you're getting into the danger zone. Plug the return line and check again.

Factory return lines/return-style fuel mechanical pumps many use a 5/16" return line but there is a restriction built into the pump itself that's only about .060". Most aftermarket pumps don't use a return line.

 

well. shoot... Plugging my return line will pretty much return the setup back to normal. I think i'm going to go ahead and pick up that fuel pump... I found one for $20 at AZ down the street.

greg zz4: I'm starting to think i have the same problem as you. Even though the car is currently running great (no hesitation / bogging) it's still not running at my full potential. When you had the 600 on your zz4: did it bog and run like trash... or, was it just slow?

I might start looking for a used holley 750 for kicks and giggles. I just dont want to over-carb it or, buy a new carb if the problem is something I can fix.

Thanks, cody

 

I don't see above where you had the FP gague hooked up before trying the cobbled-together return line. There's a variable that hasn't been checked yet.

Plug the return line and try again. I'm going to take a guess and say that you see ~6 PSI at idle and light throttle but it nose-dives at WOT in the upper RPMs. That's classic "inadquate fuel supply" symptoms.

I HIGHLY doubt you have vapor lock. That's mostly a hot weather phenomenon. Comes from the fuel literally boiling in the fuel lines (running close to the exhaust, etc.) when fuel demand is low- idle, light throttle. It flashes to vapor and the pump can't move it- it's designed to pump liquid fuel, not fuel vapor. Once you get some serious fuel moving through the lines (WOT) the chances of boiling it on it's journey from the tank are very low.

A restriction in the system is much more common at WOT/high RPMs and that's when you'll see fuel pressure drop way off, especially in the upper RPMs.

In any case, you can NOT tune around fluctuating fuel pressure. It needs to be near-constant under all conditions or your efforts will end in frustration.

Make sure the fuel pressure is steady under all conditions, THEN tune. It's the only way to do it or you'll always be making trade-offs, never getting tot the root cause.

 

MORE UPDATES

Went out and bought that 86 camaro fuel pump and installed it this afternoon. I ran my return line from the pump and I am now running about 5 psi @ wot. the car seems to accelerate smoother however, not a whole lot faster.

Regardless, the bog is still non existent so, I suppose for the most part, my main problem (the lean bog) is fixed. HOWEVER... throughout this process the car has not seemed to pick up any noticeable gains in H.P.

I'll jet the carb down to it's original setup tomorrow at the track. I had only jetted it richer in attempt to get rid of the bog in the first place. so... I might be running a little rich

I'm still thinking about looking into something like a holley 750 though. For a 350 with vortec heads and a mild cam it's not too crazy. What do you guys think?

 

why not get a Q jet for a 350 - 454

 

I've gotta be honest... I don't know anything about the q jet. can they be had for pretty cheap? will they line up on my existing intake? I also have terrible hood clearance problems... are q jets tall?

I just found an edelbrock 750 w/ electric choke for $100. sound like a deal? or should I look further into a q jet?

 

if you're familar with setting up and tuning holleys, why not get a 650 double pumper? it can handle the flow of the 350 easily, and i guarantee you'll get the "seat of the pants" improvement you're looking for.they are real easy to rebuild, and are infinitely tuneable. part # 4777's ROCK!

 

I've never touched a holley. I'de rather keep it as simple as possible and its also my daily driver in town / hwy so, MPG is a big concern. From what i've been researching, the Q-jet 750 looks like the way to go


Updates!!!

finally got the car to the track tonight... not good.

the car only bogged if I launched off the TQ converter otherwise, if i just floored it from idle, it ran just fine.

--------here is how the car ran with the given setups---------

I ran the car twice on each setup

Richer metering rods / no mufflers(for kicks): 9.6 and 9.4

Richer metering rods / w/ mufflers: 9.3-9.4

stock metering rods/ w/ exhaust: 9.4-9.4

the track closed before I got the chance to start fiddling with my secondary jets.

basically... no big changes, just better consistency. 9.4 E.T average. Ran the iphone app on the car and got (as I had suspected) 272hp (w/ a calculated 20% drivetrain loss (700R4) and 3800 lbs.)


so... do you guys think i'm just under carbed? I've always been told that a 750 on a mild 350 is too much. the car now runs smoothly (thanks to the fuel pump setup) and consistently, it's just running AT LEAST 50 hp under it's rated HP numbers, and tuning the carb seems to make no significant changes.

Sorry if I'm starting to sound like a broken record. It's just aggravating to know that my motor has so much potential tucked away somewhere and I can't find it!

Thanks again guys,

Cody

 

Cody, read my post above about my Carb.

 

I really think you should borrow a Q jet in the 750 CFM range from 79 - 85 truck
GM put this on the 350 Vette.. not Holley!!!>>> seems to be a carb that takes infinite times to tune.. correct.. you can find Q jets for $40.00 there are a few good tricks like cut a 1/8 off the pump rod lighten the spring tension on the 2ndaries they do not have the blowby valve problem like Holley to fall off and go where straight down the intake OPPSIE
yes there a lil tricky ?? to take apart.. but do not have 50 pieces like Holley
take a forum pole most people hate there HOLLEY

 

You're not under-carbed at all. What was your trap speed with the fuel-delivery problem fixed?

 

trap speed was 77-79mph with a 60ft time of about 2.1 sec

the car is quick out of the hole with it's short 1st gear. but, once I get going down the track, the car is slow pulling through second/third.

The car gets spanked by just about everyone from a roll.

I have a friend that runs a junkyard. I'll head out there next week and see if I can bum any any Q-jets off of any 350ci+ trucks.


Thanks,
Cody

 

You can't run a Qjet if your manifold is squarebore. Besides, you'd just be changing one un-tuned carb for another one. The Edelbrock isn't a great carb, but at least there are rods and jets readily available for it.

Did you ever check the distributor curve? What were the trap speeds on each run when you changed the mixture? Don't worry about the ET when you're tuning, trap speed is what's important.

 

yes we know you cant put a Q jet on a Square bore but with a lil 1 inch spacer
you can

 

And that little spacer is going to shroud the secondaries something fierce and eat up another inch of hood clearance.

 

I don't hate my holley!

 

sweet your about <<<<1 out of a 100.. you can port match if that is a concern
burgurboy can try one for free. will put GM's selection to the test
but the spacer will be like a gift.. and give a few more CFM's and RPM's
the Q jet will win !!!!!! and save lots of money trying a HOLLEY

 

we need to know trap speeds. that is the main tattle tail on the carb tuning.

 

57kid and one92rs are also quite pleased with there holley setups.

So that makes at least 3/100. JEESE

 

CRAP... I'm definitely running a Square bore manifold... well, that kills plan A.

I also didn't get the chance to check my timing this weekend. I'll have to do it this thursday...

My trap speeds varied between 77-79 on any given run. There was no linear changes between the different metering rod setups. still running in between 4-5 Fuel psi.

I'll put the stock secondaries back in thurs. Runnin low on cash SO i'll probably be sticking to the "dynolicious" app for tuning and HP improvements.

so... Do we pretty much have it narrowed down to timing or Carb tuning?


on a side note. You guys might find this interesting. Swapped a manifold, 750cfm carb, and a slightly better cam on and got 377hp and 400+lb/ft. IIRC the cam only got them 7 extra HP and I've already got a weiand dual plane and headers on mine...

http://www.carcraft.com/projectbuild...all/index.html

SO. I think my motor would take the bigger carb BUT. that still does not explain why i'm down so much hp.