I am having a problem with the combo in my signature. accellerating hard the car will begin to break up around 3500 rpm but only in the lower gears. Accellerating from say 45 MPH in 3rd gear it doesn't seem to happen. In fact the car will storm through 100 mph in 4th with amazing accelleration. I have run the car to 5500 in 4th shifted fifth and it keeps accellerating. It seems to happen most often from a standstill but not always. Any ideas?

 

just at first guess i'd say a lean condition. have you checked plug color?

 

what kind of fuel pressure are you getting....fuel pump might be on the way out....just another guess..

 

Everything is new, the fuel pump is a GM performance stock replacement pump. The plugs look normal, i'm running The CCC qjet so they don't really get too white or black. I was thinking fuel starvation. I have heard of problems in third gens under heavy accelleration, but i cant understand how so many fast GM factory cars ran this same setup without a problem?

 

do you have the means of checking your fuel pressure at Idle and under load?

 

yeah, i guess its just lazyness that has stopped my. my friend has a repair shop with all the pressure gauge stuff i should need. I just need to find time to get down there and get some one to ride along with me.

 

What ignition are you guys running? How high have you reved

 

In the sig.

6300 on several occasions without a hiccup.

 

It's not uncommon to have fuel deoivery problems in the lower gears. It's not the VOLUME of fuel the pump can deliver, it's the long DRAW from the tank. Under load it's like the pump has to pull it uphill against the force of acceleration. A fuel pressure gague duck taped to the windshield (temporarily!) where you can read it while making a WOT run will tell you real quick if this is your problem- fuel pressure will nose-dive just before the engine starts to stumble.

The fix is relatively simple- an ADDITIONAL low pressure electric fuel pump back by the tank to give the fuel the slight boost it needs to get up to the mechanical pump does WONDERS for solving these kinds of problems. Carter makes a low-amp 5PSI electric (that I have used several times) and HOlley makes a 7 PSI electric that I have also use a couple of times. Both work great.

 

or you could do the v-6 to v8 swap...then you have plenty of fuel pressure you can regulate with a Malory 3-port..
P.S. not real economical...I'd try as mentioned above..

 

I have heard about the fuel pump problem before i started my buildup. I didn't really give it much additional thought because i figured that all the old fast chevy's used essentially the same setup. I amwondering if maybe the tank venting system or fuel slosh adds to the problem. I am planning to upgrade to a fuel injection in tank pump like in the zz4 conversion, but i need to get the intank assembly that mounts the pump with the electrical connections. Does anybody have a part number for this? also who can reccomend a pump? I want stone reliability with plenty of flow. I also plan on going to fuel injection sometime in the future so installing this pump will save me the trouble later.

 

have you simply tried to richen it up?

 

yes

 

what was the result, better, worse, and what did you change to richen it up?

 

not much of a difference, i tried richer secondary rods, i adjusted the rich and lean stops, i even tried to go very rich at idle to see if it would help. the problem only happens in lower gears during hard acceleration, its fine in higher gears. It will pull up to 5500 in fourth ( i suppose it could go higher but thats pretty fast for a public road). In fact its a real beast on the highway, i havent been out run yet. Its just from a standing start, it will get through first fine then it loses power. Once i shift it seems to go soft then run rough then it will pick up but not for a second or two.

 

I have the same problem with my stock setup... but only from stand still... if i punch it to wot the engine will rev to 4000 then bog to 2000 and start pulling very slowly... at half thortle it'll pull harder when it revs up slowly to 3000 then shifts in D.... its faster for me to give it only half throtle untill 3rd then punch it... i think my pump gone... not sure though.

 

i was thinking about making some kind of a plug to close the gas tank with an air valve. this way i can put say 3-5 psi of pressure on the tank and see if the situation goes away. It sounds a little crazy but if you limit yourself to a few psi ( say normal fuel pressure ) it might be an easy way to check.

 

No, you don't want to do that.

The more I think about this, I'm thinking you have a hot fuel problem. The fuel that's been sitting in the bowl gets warm, meaning it is less dense, and therefore doesn't have as many molecules to mix with the gas. As demand empties the fuel bowl and fresh fuel comes in, it is cool, more dense, and therefore delivers the right mixture ratio.

I'm assuming the stock replacement fuel pump is the type with the return fitting. If not, there you go - get one with the return functioning.

If it does have the return, then a "pusher" electric pump back by (or in) the fuel tank like Damon suggested, along with a 3-port regulator as close to the carb as possible, will help keep cool fuel circulating and feed the carb cool fuel as soon as possible.

 

well HITHERE had the right Idea ayway!!!

 

??? Hackers?

 

HITHEREHITHEREHITHEREHITHEREHITHERE HITHEREHITHEREHITHEREHITHEREHITHERE. LOL

Anyway. Its sounds like HITHERE fuel starvation problem maybe from vapor lock. HITHERE'm having the exact same problem and it only happens when the car gets warmed up. My fuel lines (stock as of yet) lay on the exhaust in many places. HITHERE'm putting HITHERE fuel pump in the tank and running 1/2 inch fuel line.

 

4/1...

 

well it appears that i found a little known engine performance secret, when you really powerful new motor exibits a loss of power attributed to fuel starvation, consistently, all you need to do is hook up a fuel pressure gauge to make run better than ever!!!

Thats what happened today, i finally got around to setting up the fuel pressure gauge, it never dropped below 4 psi, usually 5-6. MY car ran better than it ever has! I was really impressed with how hard it pulled, all the way to 6000 rpm, not somuchg as a hiccup.

I'm going to look into electrical problems, sombody please shoot me!!

 

are you talking fuel pressure regulator???

 

glad it all worked out for ya....

 

no i have a carb with a mech pump no reg. I put a gauge on it today and beat the hell out of it to see if the fuel pressure was high enough on the top end.

 

First time I think I have heard of installing a gauge to correct a fuel delivery problem....but if you say sooo.....

 

yeah, i'm surprised more people don't know this "Performance" trick. I was wondering if my car would go faster with a boost gauge!! i know i don't have a supercharger or turbo but what the H it may be worth the 40 bucks for a 50% HP gain. I wonder what other gauges i can install, hey maybe some vinyl graphics would help too?

 

i would check what No4Njunk said about the vapor lock....i was burdened with the same problem. but instead if installing a new elecrtic pump in the tank (which i already took out thinking it was the problem, it was dead and i figured it was there from the time when it was fuel inj. and the mech pump couldnt pull the fuel throught it) ..i put some hot pipe isulation surrounded by a home made sheet metal cover where it gets close to the headers. worked pretty well...looks ugly as sin....now that i think about it....i could have just wrapped the headers AND the fuel lines in exhaust wrap...would have been neater...damn...

 

LOL. I did the same thing and then decided to buy all new aluminum fuel line. Its definitely a problem alot of these cars have.

Actually I have a Vac/boost guage. I use the vacuum side to tune my carb and set timing and it also allows my to see whats going on while driving. Best tool I've got and I got it for free. Just had to get a gauge pod for it.

 

Rotflmao!!!!!

 

thinking of putting two in my truck, the extra is in case i run up on a faster car.:hail:

 

I put this Boost Gauge in my car. It actually runs much quicker now. Only thing is, when I rev to 6K, it never goes past 0.
Maybe the gauge is stuck or broken.