help car car falters at the track

[AusRs]

HELP
I have had this issue since i put the car on the road
normal driving NO issues occasionally when stabbing the accelerator peddle i get a slight hesitation ,nothing to worry about ,driving along the road at 50 mph and stab the peddle hard and there is NO hesitation whatsoever which brings me to my problem
went to the track again yesterday (not so worried about timeslips as the track temp was 127 F and ambient temp was 44 c

here is what happens
stage roll through the water for burnout all is good everything does what it is supposed to do and the car runs well ,
roll through to the tree and stage hold revs until its time to go racing all is great ,take off no hesitation whatsoever runs through 1st and 2nd gear at wide open throttle just as the car hits top gear at wot it falters ,does not matter whether you keep your foot into it or feather the accelerator it stays bogged ,out of 4 runs yesterday it almost ran clean on 1 pass and time slip was 15.3 (again ) every other time i have this issue
stock electric fuel pump (new)
since getting the car on the road i have
changed the fuel filter
relocated fuel lines in the engine bay and insulated the lines where they run across any hot areas
taken car back to carby re builder and had it re tuned ,without load on the engine i cannot duplicate this condition
carby is a quadrajet
when i fitted the engine to the car i did replace the HEi with an aftermarket (chinese ) one from a reputable seller
as far as the car goes it is a great daily driver with NO issues whatsoever ,this issue really only surfaces when i go to the track !


anyone have any ideas what /where i should go from here ?

[marco_1978_spyder]

Hi Aus, here's what I'd do...


I'd begin reading the plugs...the carb tuner can only give you a decent baseline with the carb off the car.

Maybe next time bring a few plugs with you to the tuners shop, so it will be known if you need to go a few steps richer or leaner.

Here's some other items...You could hook up a vac gauge thats visible and see if the reading tells you anything when the car bogs.

Same thing with a A/F meter if its not to expensive.

Do you have your brakes vacuum line (if power) tee'd into your PCV line? if so get them separated.

As far as timing (I'm sure you probably got it right).... But just to double check, run your engine up to 3000 rpm and check to see that your advance is showing about 36 degree's
I do this without a dialback light, with 3 penciled in marks 10 degree's apart.

When the 3rd mark gets to the 6 on the timing tab I know I'm there.

[AusRs]

Marco
carb was tuned on the car
i do not have an A/f gauge ,,,maybe i should get one
brake vacuum is plumbed in on its own
I only have a very basic timing light

[marco_1978_spyder]

Marco
carb was tuned on the car
i do not have an A/f gauge ,,,maybe i should get one
brake vacuum is plumbed in on its own
I only have a very basic timing light

Thats all I have too...All you need is a pencil and it will do just fine.

I moved the timing mark up to 10 and scribed a visible line 0. Then move that line up to ten and repeat. Then repeat one more time. Theres your 30* mark. Works with any basic timing light.

I know A/F meters are a little pricey and once you get everything down pat, you don't really need it anymore, so I know for me, its hard to justify buying one. But it would be great to have at tuning time. Reading the plugs should get you set up to run without a bog. I know I could use an A/F meter - I suspect my carb run's massively rich at all times.

I'd guess the bog is carb related unless the timing is way retarded. Maybe a Q jet guru will chime in here.

[72 SS PNL]

since it a high gear issue id look at fuel , kinda sounds like the pump cant keep up

[cosvega76]

I agree, sounds like you're running out of fuel. Barry Grant says that a 12-second car's fuel system should be able to fill a gallon gas can in 35 seconds:

http://www.barrygrant.com/bgfuel/defaul ... 81#FUELCAN

Also, check to make sure your fuel tank vent system is working properly.

Chuck

[AusRs]

I agree, sounds like you're running out of fuel. Barry Grant says that a 12-second car's fuel system should be able to fill a gallon gas can in 35 seconds:

http://www.barrygrant.com/bgfuel/defaul ... 81#FUELCAN

Also, check to make sure your fuel tank vent system is working properly.

Chuck

Chuck
fuel vent system .....when i take the gas cap off i get a rush of air going in to the tank ,from memory only 2 lines come from the monza tank ,1 for the carby and 1 fro the charcoal cannister

[HI WINDING MONZA]

1) Qjets have a small fuel bowl that empties pretty fast doing a burnout and running the 1/4. Look for a better pump. ( mechanical or switch to electric)

2) Could be vapor lock also, clip a wooden spring clothspin on the fuel line between the carb and the pump , see if that helps ( old timer trick )

3) Some fuel filters ( that go inside the carb) have a check valve in the inlet that sticks sometimes. remove it to see if it helps. ( Fram filters are famous for it)

4) Look under the car for a pinched fuel line or hose near the fuel tank.

Doug in Az

[AusRs]

Thanks Guys
I am now back to being confident that it IS a fuel delivery issue
the fuel filter is an inline one and there is no filter in t he front of the carby

here is what i am going to do
re manufacture the fuel line from the the fuel tank to the firewall out of 3/8 aluminum
take the charcoal canister line and make it into a simple breather by making several coils in the line

then find a nice straight stretch of road and try it out

As an aside to the problem i am having with this car
I now have some $ put aside so i can start to get a new bigger and better engine for the car
I spoke to engine man today and costing is not bad ,he even suggested at similar price to 350 rebuild ,making the engine a 383 .which brings me to my next question ...............what rods are the better choice for clearance issues with the Monza sump ?????I beam or H beam ?

[72 SS PNL]

rod , which ever uses a smaller crank end , which would be up to the manufacture

3/8" fuel line will help , a higher volume pump will be the best choice , i dont think your fuel evap is part of your cause , so depending on your emissions standards in AU , id probably leave it

also reason you notice this from a dead stop and not out on the road , is you use more gas getting it moving and coming up through the gears , then you would a 2-3 run from road speed

depending how much hp you want , you might wanna think about 1/2" diameter fuel line

[AusRs]

OK
today's exercise
removed old charcoal canister lines and fuel lines
charcoal canister line was blocked suppose that would cause the rush of air when i opened the cap up ! just fitted a coiled breather line with a rollover valve inline so it should at least vent the tank
Old fuel lines had many divots in it most hidden by the coiled spring ! couple were deeper than others I am going to run the 3/8 line as at the moment i still have the 350 and will do for a few months (line was $30 au) I am thinking of running the fuel line up where the charcoal canister was run as it puts it on the correct side of the engine bay for the carby intake and does not have to run across the firewall and along the manifold in all the heat ,will just need to insulate about 4 inches where it runs across the exhaust system
Hopefully will have that all finished by Thursday and take the car for a run to see if i have done any good

good thing about my car and aus emission standards .................they have NO idea what a Monza is let alone have any idea what it is supposed to have

[Len]

I think you found your problem With the plugged canister line try it with it with a new line and not connected to the canister how ever you want to do that but with no poss of restriction in it . And a dumb question how much fuel is in the tank when running the track? Could be that the launch and next gear are causing the pump to run dry momentarily . But really having a vacuum or low pressure above the fuel is not a good thing while trying to pump it. I do believe that is why fuel injected motors run more pressure than needed at any given time with a regulator, not only to accommodate the pressure drops across the injectors but also allow for for any other anomilities in fuel pressure like a restricted filter ect.
Len

[AusRs]

my tank now has about 2 feet of coiled aluminum line coiled up and attached to the canister line at the tank with a speedflow fitting on it that will vent to the atmosphere at 3psi
I am going to use the right side (passenger ) to run the new fuel line to avoid that crossover of the firewall and just insulate the small area that goes past the exhaust

[HI WINDING MONZA]

I dont have any fuel problems running sometimes at 115* air temp. All I added was a Red Holley pump and a Fram see-thru filter just before the pump. ( a glass inline filter replaces the carb filter)

I still use the stock fuel lines ( untill it comes to the engine compartment ) then it goes across the top of the firewall , along the top of the passenger fender, then to the carb.( away from heat sources)

Never runs out of fuel, even with a 1/16 of a tank, but again 1st and 2nd gear burnout and shift points never exceed 4600 RPM.

One thing I allways do on Qjets is bend or break the tang on the base plate that prevents the secondaries from not opening. Makes it more a mechanical carb but if you hit it too fast, it gets too much air and can stall out. ( I removed the choke and linkages on my current carb)

Check and make sure the secondaries are opening , the choke may be holding up a little , not letting them open. ( you can tie the choke linkages wide open to make sure thats not the problem)

Doug in AZ

[80 MONZTA]

( a glass inline filter replaces the carb filter)

I just have to say, if you have a glass filter, get rid of it now BEFORE it cracks and dumps fuel everywhere, just don't want to see anyone's car burn't up. Several years ago I wanted one of those neat looking glass filters, until I saw online pic's of a nicely restored car that had one of them crack and started a horrible fire.