last summer i swapped my throttle linkage because my factory linkage was not opening my secondaries all the way. so now, when i put the pedal to floor i get a true WOT at the carb. now, since the carb hadn't been opening up all the way prior to this new throttle cable setup, i wasn't sure how the carb would react because it had been on for a few (3) years and never opened the secondaries. well, i have taken her for a few rides so far this year, and notice one flaw, which i am going to troubleshoot this weekend and would like your thoughts.

from a dead stop, if i floor it to WOT, i get some tire spin with a strong first gear through powerband (no misfires), chirps second with a strong second gear through powerband (no misfires), then as soon as it shifts into 3rd it bogs down and seems to misfire until i back off the throttle a bit then it fires as normal again. so my thinking is A) spark/timing issue or B) fuel supply issue.

so, i ordered a new fuel tank sending unit cuz they are cheap enough and i have never replaced mine, so i will for good measure. also, i have a new Edelbrock steel fuel line & filter that attaches to the carb which i will install this weekend...this will replace the old fuel filter and line which are about 2 years old (maybe they are clogged??) i assume my fuel pump is fine as the engine is getting fuel and runs great under partial throttle. this also leads me to believe the timing is correct.

i have brand new MSD plug wires & HEI distributor i put in last year so i rule those out, but the plugs themselves have about 3 years on them. so, i am going to pull the plugs and diagnose their condition. if they are good i am going to regap them for good measure and if i feel the need, i may just buy a whole new set of plugs, we'll see how they look.

my thinking is, if i do all this and the problem still occurs, it's either my carb needs a rebuild/cleaning OR my timing advance curve could be off. if there's anything i'm missing that is worth a check, please let me know. any other suggestions will be considered, thanks!!

 

Set your timing for full mechanical advance at 3500 RPM to 34-36* btdc with vacuum disconnected. Then note where you initial winds up.

 

Could be fuel starvation, new sock and fuel filter may help.

 

i do feel like it's fuel starvation, that was my first comment to my buddy who went for a ride with me. i said to him "it seems like it's not getting enough fuel when i floor it."

i would think if it was a timing issue i would notice misfires at other times as well, but maybe not, i am not an expert on this stuff. it's always those things you havn't addressed in a while that sneak up on you. the fuel filter and plugs have a couple years on them untouched, and god only knows how old the sending unit is, that filter could be full of crap for sure.

 

could u elaborate on that a bit?? i'm not sure how i would go about doing that. also, not clear on what u mean by "note where you initial winds up"

 

Also make sure your accelerator pump gives 2 solid streams of fuel when you open the throttle. Setting your timing that way will rule it out, as most V8's like it around that setting and you can't use the stock initial setting with an HEI.

 

my buddy has a timing light that i can use if needed, but not sure if it's a setback or not, if there's a difference.

 

Do you have a setback timing light? It allows you to set your timing at high rpm's by dialing in what you want on the light and setting your timing to "0" on the indicator. If you set your timing this way let us know where your initial winds up.

Sorry about this being out of sequence, I was editing.

 

Third gear is cruising gear.
Downshift to second for acceleration.
Other than that I'm guessing it's a quadrajet..if so,upgrade to a new Holley.

 

okay, so there is a difference between a timing light and a setback timing light, i presume. i have never used one of the setback timing lights, but if i understand correctly, it works the same as a regular timing light except you can identify where your advance curve puts you at higher RPMs. so your asking me to perform this check at 3500rpm and see where it reads?? and your saying it should be at 0??

 

i don't think your understanding my problem....if i was running a quarter mile my foot would be to the floor and the car should not bog when i hit third, right?? and my sig clearly says i have a 600cfm edelbrock performer, i'm done with Holley's. thanks for your suggestion, however.

 

What rpm range?
I believe HEI is rated to 5500 rpm,but some claim 7k is obtainable.
If your satisfied with performance everywhere except at high rpm,you might want to invest in a High performance coil before changing all your timing settings.

http://www.circletrack.com/techartic...m/viewall.html

 

well, 2nd gear with rev up to about 5000-5200 before it shifts into 3rd, which starts at right about 3200rpm. but, when it shifts from 1st to 2nd it is right in that same RPM range and it's fine. it's almost like when it shifts to 3rd the tranny ratio is closer which puts more demand on the motor, which in turn demands more fuel. this is why i think it's a fuel problem.

 

I was going to suggest trap-door adjustment if it was a Q-jet, but now, being a Carter, check your fuel filter - it's happened to me, exactly your symptoms!
ETA - unless your fuel line has a restriction!

 

i will check all the "EASY" possibilities this weekend, i'm hoping the spark plug check and fuel supply check with fix the problem. i feel like if it was timing i would have other problems as well. the car is running strong otherwise. and if i go 3/4 throttle it runs smoothly and strongly all the way into & through third gear.

 

subscribing to this thread. I have a very similar problem, I too have an Edelbrock 600cmf carb on a stock 350 motor, with HEI. Very interested in what you find.

I've recently changed the inline fuel filter, adjusted timing to 16* approx initial and 35 all in, have done a tune up in the past 700 miles, and tried 93 gas. No real difference at all. It doesn't appear the edelbog carb has a fuel filter inside it, and I've taken it apart to change out the accelerator pump.

Ironically, the new accelerator pump was worse than the old. Keep us updated.

Also, I think I can rule out the carb not being big enough, my uncle has a 70 impala with a slightly done up chevy 350 and only a 500cfm carb, and in the high range, from say 80mph to WOT he'll pull on me pretty good, unfortunately.

 

i just spoke to a friend who is a mechanic and he says first thing i should do is change the fuel filter. he also said if i havn't replaced the sending unit i should do so as the sock is probably full of crud, so i was on track with those to possibilities. but, he also said that because the secondaries are now actually opening with the new throttle cable setup, that my air/fuel ration may be off. he thinks it could be running lean. and i guess that makes sense since 2 barrels would require less fuel/air as opposed to 4 barrels. in other words, my air/fuel ratio could be set for the old "WOT" which in actuality wasn't REALLY WOT. now that the carb is hitting true WOT, my air/fuel ratio could need to be richened up. maybe with 3rd gear being a 1:1 ratio, the engine has a higher load so in turn the fuel demand is increased?? i would think the air/fuel ratio being off would affect the first 2 gears as well, but not sure.

 

It may also be your fuel pump. If it is not working to full efficiency, your carb may be running out of fuel under WOT............

 

but only in 3rd gear??? the "only in third gear" part is what is throwing me off. my fuel pump is an old school holley mechanical, about 10 years old, but i just thought the mechanical fuel pumps either work or they don't. that would also be a pretty cheap fix as well though. i won't rule it out...

but let me ask this....if it is fuel, why would it only be a problem when i hit 3rd gear?

....if it is plug issue, why would it only be a problem when i hit 3rd gear?

....if it is a timing issue, why would it only be a problem when i hit 3rd gear?



keep in mind, the pedal is to the floor (WOT) the whole time from a dead stop, it runs perfectly through 1st and 2nd.

 

This a distinct possibility, or it could be your float adjustment.

Getting back to the setback timing light, something along these lines:

http://www.summitracing.com/parts/SUM-G1059/

 

I would try raising the float level,sounds like there is not enough fuel available quickly at the rpm /gear change.
If fuel is available at 3/4 throttle but not abruptly at the gear change,fuel could be sloshing around the float bowl.
After the slight hesitation,the fuel returns to the correct level.

 

that makes sense as well, i will add that to the list of check points....again, not sure why this would only be a problem in 3rd gear?? what is it about 3rd gear that exposes this "problem" ??

 

Well on prolonged run if the fuel level is not high enough, and the pump is not keeping up, it will run out of fuel at some point and stumble. When you release the throttle enough fuel gets back in the carb and presto your back in business.

I would not think it's a jetting problem as your not sputtering at high rpm's in first and second. Your rear gear ratio is problematic but it will not cause the engine to fall on its face at higher speeds.

Btw, what is your initial timing set to?

 

well the timing was set at 7.5 degrees BTDC when the HEI distributor was installed 2 years ago, the timing has not been checked or re-adjusted since then. however, i have never checked the timing at high RPM's with a dial back timing light as mentioned above, so i'm not sure what my full advance timing is at the moment.

 

With an HEI I can tell you for sure 7.5 is not what your engine wants. There is a very different advance curve in an HEI vs std points. Bump your timing up 14-16 and I bet most of your issues will go away. Also I'm assuming your using 8mm plug wires, and your plugs are gaped @.045.

 

Even with a stock distributor,all vacuum should be in by 3000 RPM.
Adjustable Vacuum advance just lets you bring it in earlier.
Sure sounds like a fuel related problem since its at the same rpm/gear position.
I hate playing with timing when the car runs so good otherwise.

 

so the more i read about similar problems people have had, the more i feel it is fuel related. so here's my plan to get to the bottom of the problem, and i will update this thread as i troubleshoot:

1) replace fuel tank sending unit
replace fuel filter
check plug condition & gaps (possibly replace them all with new plugs)

if that doesn't fix the problem, then:

2) adjust air fuel ratio on carb
adjust float level on carb

if that doesn't fix the problem, then:

3) check/adjust timing (i'll give the 14-16 a try as suggested, i just don't want to mess with it before i attempt the other possible solutions)



i was wondering, would it be worth installing a fuel pressure regulator?? i was thinking about putting a regulator (low pressure 4.5-9psi) between the fuel pump and the carb. i can run one line to the carb and another to a pressure gauge. this way i can monitor my fuel system pressure remotely while driving the car...your thoughts??

 

i'm using MSD 8.5mm wires, and i did gap the plugs (2 years ago) at .045

 

Adjusting the air/fuel ratio? Do you mean the two screws on the front? That only adjusts your idle fuel ratio. Jetting is what controls your off idle fuel ratio.

I don't think you have a fuel delivery problem from the tank.

The edelbrock carb likes no more than 6 lbs fuel pressure.

At WOT vacuum plays no part.

I would try the timing. It takes 2 mins to set.

 

Tee in a temporary 0-15lb fuel gauge with 1/8" line at the carb fuel inlet and tape it to the windshield so its easy to see. Go do your WOT through 1,2, and 3rd gears and see what happens. If pressure drops way down you know what's going on then go back through your fuel supply to see where the problem is.

 

^^^^^^^^^ What he said! Been there.. done that.. had an Edelbrick 600 on a healthy 351W a few years back. Every time I'd get on it it would fall on it's face half way through 4th gear. I took the 'brick off and put a 650 Holley mechanical on it and the problem was solved! I tossed the Edelbrock in the back seat for times when i had to park on hills to put behind the tire... only good use I've ever found for one

 

I've had quite a few Q jets that ran good...but I won't spend money on purchasing/rebuilding one.
The Holley's are so nice to tune.
Most carbs either work or they don't,as any minor malfunction usually results in poor performance.
Although lots of folks blame the carb,when there are other problems present.

 

Ill throw it out as a fuel delivery issue, either floats or volume.

I think the 3rd gear thing is because after the first 2 gears at WOT the carb is running out of fuel because of low float height or not enough gas getting to the carb. when it hits third its out of gas and recovers quickly when you lift your foot off the gas.

try a sustained high rpm 2nd gear run then shift to third probably does the same thing. i would guess nailing it at ~60mph in 3rd it doesnt show up

alos OC is right about the HEI timing 35° or so at 3k rpms w no set back light at a minimum set the intial at 15° (if no pinging or hot start issues) it will wake up your cars low end.

I run an HEI w Ebrock on a 350 w no issues intial at 15° (could go a little more)

 

well guys, this problem has actually molded into a good thin because i was able to re-establish a relationship with an old acquaintence that i spoke to when i was 14 years old about my car when i first got it from my grandfather!!! come to find out, this guy lives next town over from me and does automotive repairs and machine work right in his own shop at his house. he has been an olds enthusiast for over 25 years, with drag racing & engine building experience....all with oldsmobiles. i remember when i went to his old shop years ago, he had a 69 cutlass w/ 455ci pushing over 600HP. the cowl induction hood read "All Throttle, No Bottle!!"....this thing had dual demon carbs, dual ram air intake, ported & polished heads, re-located daul oil filters, MSD ignition, big *** rear end housing with slicks and wheelie bar, & drag suspension. i was too young at the time to really know what i was looking at, but those are things i remember seeing specifically.

but anyway, i got his number through a friend who is actually a cousin of his. spoke to him on the phone last night (his current toy is a 69 442 convertible w/ 468ci, beautiful car) and his diagnosis without seeing the car first hand is a fuel delivery problem as well (which correlates what most have been suggesting here). he said i may have the delivery pressure, but not the delivery volume, which means somewhere the fuel is being restricted. whether it's the sending unit, the line itself, or the filter. he said if the fuel pump wasn't working, the car wouldn't run. if the timing was off, i'd have problems way before i hit 3rd gear, especially at WOT.

so i'm going to take it over to him this weekend so we can go for a ride and he can see what happens first hand. he said he'll check the timing, which (also, as mentioned) should be in the 15 range at idle and about 35-36 all in. we may T off at the fuel pump, send one line to the carb, the other into a bucket so we can see what kind of volume is in the bucket after running the motor for a certain amount of time. he also said i could take it for a spin, go through the gears, and as soon as it bogs down in third i can pull over, pull any plug and look at it's condition to determine if it's running lean or rich. if it's running out of fuel, they should indicate lean conditions. all in all, he doesn't think it sounds like a huge problem. the fact that it runs strong up to 3/4 throttle but stumbles when you apply MORE GAS means it's probably not getting MORE GAS like it wants. sounds pretty simple when you really think about it i guess.

in addition to this, i started talking to him about what my next step would be for more power out of my 330. we started talking about heads and cam, which mine are basically factory specs. he advised me not to even think about aluminum heads, waste of money compared to what he can do with a set of cast iron olds factory heads. he said after he's done with them, my heads would flow better and make more power than most aluminum heads available, and for less money. he'd do new valves, springs, rockers, port & polish. he could even mill them down if needed to make sure they are true. he mentioned something about heads i never thought of...the fact that aluminum heads on a cast iron block means heating and cooling time differences between the 2 materials which can be a major stress on the block and gaskets, another reason to stay away from aluminum heads. he also said he could thrown in a cam along with the head work and get my 330 at over 400hp. this is all with the factory crank and pistons, he says they can handle it, just wouldn't recommend reving over 5800rpm.

so needless to say i'm excited about that, and glad i could get back in touch with this guy, as we all know local Olds gurus are hard to come by. come fall when the leaves start to fall, i think may car may end up in this guys shop for a few weeks and let him have at it:-)

 

Let us know what you find!

 

I would be willing to bet it will end up to be the fuel pump is just not keeping up with the demand from the carb. I had exactly the same thing happen to me years ago. I had a 79 Malibu back then with a chevy 286 & a Qjet. Ran great, strong motor. But when she was on the quarter mile track, hit 3rd, bog, let off, back she would come. I to messed around with timing, fuel mixture, jetting, etc. Then I went from a standard mechanical fuel pump to a high volume pump. That fixed it. What a difference. IMO qjets work great if they are adjusted properly & are given enough fuel to keep the bowl full.

 

what type of pump did you go with?? was it a mechanical type or electric?? the only high flow mechanical fuel pumps i see are the $30 chrome ones that are no name brands, is there a better option??

 

Back then i had an electric. I have heard of a couple of mechanicals around though. Holley makes high output mechanicals, not sure which is for Olds engines. Also I've heard of Robbmc is another high output pump, http://www.robbmcperformance.com/.

 

never heard of robbmcperformance...looks like some quality parts!! thanks for that link. i like the billet thermostat housings alot too. well, i already bought a repop 3/8" stainless sending unit because in the 14 years i've owned the car i've never touched the one that's in it, so it needs to be done anyway. after we check the volume of fuel the pump is putting out, i'll know if i need to step it up to a high volume pump. if i do, i'll be grabbing one of the RobbMC pumps for sure. it also says they recommend a fuel pressure regulator for use with their pumps, so i guess i'd need one of those as well. i swear i have a holley hi-flow pump in it now, but it may not be, i can't remember what i bought years ago.

 

I was just reading about vapor lock, sounds like that could be my problem right there. Which is still basically lack of fuel delivery (due to gas pockets in the line) to the carb causing the bowl to drain under high throttle conditions. although it says usually vapor lock happens at idle and low speeds, so maybe not.

but still, relates back to a fuel delivery problem. i found an article on car craft's website about building a fuel system to your engine's needs. they have a formula to help figure out what GPH your carb needs.

2 x ( flywheel HP x .5 / 6) = required GPH

my application -> 2 x ( 320HP x .5 / 6) = 53.33 GPH @ 6psi


it also noted that most fuel pumps advertise their GPH capabilities at 0 psi. so a pump that advertises 80gph will actually pump less as the fuel pressure increases. as pressure increases, flow decreases....so we need to figure out what the pump needs to deliver at the psi your system will run at. mechanical pumps will usually increase pressure at RPM's increase. since i have an eddy performer, my fuel system should deliver at 6psi. so i need a pump which will deliver at least 53.33 GPH @ 6psi. now....if i do the heads and cam this winter and get up to let's say 400HP at the flywheel i'll need at least 66.66GPH. so i'm thinking my fuel system is about to get a complete reconstruction for higher volume delivery.