Fang333333

-Rough engine sometimes on startup used to get better when warm now seems to get worse warm. Rich fuel mix. Vapor ping pops carb exhaust. Loss power. Fuel in exhaust. Hesitation.-

I had posted a thread about the fuel cansiter that seem to just drop off the face of the planet. Im giving this one more shot, with little faith, honestly. After hooking up canister it flooded, caused engine to ping, lose power backfire/ misfire. Now after disconnecting canister this a permenant feature of the car. I did new tune up EVERYTHING to spec, plugs wires etc. the 1978 vette now loses power (or hiccups) than comtinues to accelerate.
It has, loss of power, runs rich no matter what settings on carb. If the choke plate closes the car dies. It is a Rochester carb. Fuel comes from exhaust. Paricullary left exhaust driverside exhaust (exhaust is short header system came with car) Constant yet random non metallic (vapor) pings and pops from both carb and exhaust (not gun fire loud but still crappy).
On a acceleration, vrrrrooom stop VRRROOOOM. It has a vapor smell but no amount of adjusting seemsto stop the richness. Spark plugs appear to be more dirty than expected. I had similiar accel issue when bought car and mechanic fixed it by "bypassing the headlight somehow on off switch?" Then car stolen and this is how I got it back. Plugging vac house before check valve does not make difference so headlight hose leak does not seem to be the issue anyway. I question the choke functionality however if choke closes ENGINE DIES NEVER STARTS. After tune up it ran amazing and occasionally it still does for 5 10 minutes.
I have stumbled in dark for over a month, no suggestions, no help nomatter where I go. My once beloved car is dieing on me, on top of hardcore medicle issues I am having with my back. It would mean everything in the world to have it run but this is getting impossible.
Yes pops com from both carb and other times exhaust. Bad gas=no. Bad fuel pump?=maybe? Fuel filter=brand new. Spark plug ignition test, with tester = good. Hose leaks (besides vacuum system which for xmas bought myself entire new system,actautors, hoses, valves, relays everything only to have engine crap on me) anyway hoses no apperant leaks just headlight system (once again pluging hose before check valve does nothing anyway.) EGR very clean and cleaned 2x. Pushing plunger up on egr causes engine to stumble so egr has flow. I have not messed with timing however i STRONGLY doubt it timing for many reasons and because engine ran great for years and even up until recent. And still runs smooth on occasion 5-10 minutes. Rochester carb gaskets look great on outside yet carb problem I could see that? Carb rebuilt by holley 6 years ago.

There is everything. Absolutely everything. Its an L48 small block 78. Black red interior. Theres that too. This is last hail Mary

Big2Bird

My best guess, listing your symptoms, regardless of Holley rebuilding it 6 years ago, is the float is stuck open. If it is a quadrajet, I would pack it up, and send it to Lars Grimsrud.

Haggisbash

Hi, do you have a timing light and know how to use it? I would be eliminating the ignition as a cause before I looked at the carb based on you mentioning that no matter what setting you have on the carb it runs rich, I assume by that you mean the idle mixture adjustment? The idle mixture adjustment doesn't have much effect on things once you have your foot in it but if you have already fouled the plugs the engine is going to miss and hesitate.
Unfortunately I know nothing about Quadrajet carbs but I believe you can take the top off them and look in the fuel bowl, that would be my next move to see if there was any dirt in there possibly causing it to flood.

Fang333333

Thank you for response. I do not have a timing light and I would however you heard and saw engine I think you would agree it is a fuel issue. I am not ruling it out however, I just believe more fuel troubleshooting is needed.

Fang333333

Thank you for response. I have just recently become suspicious of carb. I have very little money ( I'm a student living off small loans who just spent well 2 grand with tires and other parts/repairs. Either way Who is lars and how is there any other troubleshooting for carb? What percentage would you say it is in favor of being carb issue. Not holding you to anything, just want to see how likely you think it is. Also, what anout doing it myself? Curious.
Joe

Les

I'm no Q-jet expert but it sounds like you have a messed up needle and seat, which would set you up for an over rich condition.

CanadaGrant

Since you say it will sometimes run normally for 5-10 mins sometimes then seems to flood I would look at the needle and seat for dirt and also the float level but before you take the carb apart, if you have a spare HEI distributor cap, give it a try just to rule out the ignition module which might work normally for a few mins. until it gets a bit of heat in it.
At first I figured vacuum but you said you blocked it at the check valve and there was no change but you might pull the line off the power brake booster and put your finger over it and see if the idle improves.

Fang333333

Thanks for response. How would I get in touch with lars? Any DYI tips.

Ryan Menzies

A couple things come to mind:
1- Possibly some dirt in the float bowl/worn-dirty needle and seat. Possibly from changing the fuel filter in the inlet of the carb.
2-MAYBE a seizing weight issue in the distributor but unlikely given the severity of your symptoms.

Can you post a video of it running poorly ?
Also, hook a vacuum gauge up to it on manifold vacuum (Below throttle plate) so we can see what it is doing.
If it is only giving you issues when accelerating you may to load it up in drive to duplicate the "test drive" for the video.

There a few things to verify/confirm though regarding testing. Haggis was right by checking timing. Also it would be beneficial to see what the timing is doing up through the RPM's.

Cheers,

Ryan

Fang333333

Again thanks for reading post. I do not have a different cap. However I did replace cap rotors in tuneup and engine had popping noise with old cap. I bought an excellent tuneup kit from eckelers...I did not replace the actual top top part with the coil in it I hope this is not what you mean...however do believe coil in good condition. After a few pumps from peddle (and with choke open) car seems to fire up quite well I say. Even in the cold. ALSO I do have brake line leak although it very minor. Just off memory isnt brake line metal?

Big2Bird

V8Fastcars@msn.com

Ryan Menzies

This goes back 25 years ago but if I recall correctly-
Take the top of the carb off by removing the Phillips screw on the passenger side that holds the choke butterfly rod on.
Take a small punch and tap the roll pin (Driver's front of carb) through the accelerator pump rod (Light Green). Only tap the rod through just enough to get the linkage off of the pump shaft - You still have to have room on the other side to get a flat blade in on the roll pin when installing the linkage back on the pump.
A series of Phillips and possibly torx screws to unbolt the top of the carb. Seems to me there wee two flat blade screws as well toward the middle of the carb.
From there you can see the Black float in the body of the carb. The float lifts out with the needle we are talking about. BE CAREFUL- the needle is hold on by a very small wire clip that just hangs off of the float (If I recall)

Fang333333

Here are 2 videos of it when its running a little better. I am going outside to make a video of when it REALLY ACTS UP

Ryan Menzies

What is that noise ? Flex plate rubbing on inspection cover ? Also, there seems to be a hesitation on your throttle blip. Accelerator pump ? Vacuum advance working ?

Les

This will give you a very basic idea of what's involved but it's not all inclusive by any means. If you only have limited mechanical experience, I wouldn't recommend fiddling with a Q-jet. They are somewhat complex and finicky. Lars would definitely be your best bet.

Fang333333

The only noise would be the generator. The wire on the alternator needs a new end. If its not in right the gen will run and misbehave. That is actually a simple problem I plan to fix with a new end and then a new engine harness down the road. I just didnt have it plugged in for vid.Here is a video of the engine "sucking out" on acceleration. All the metal rattles are coming from interior which I am rescrewing in things after being stolen. There is NO engine metallic noises from engine(cam knocking etc.)Only vapor. Ironically alot of people tell me how great the engine sounds when its not misbehaving. (Even today) siigh... And it does sound good when working...not not on this video
Of course,

Fang333333

Thank you. I do have limited mechanical experience however it seems I am learning fast. I was feeling ready to do valve seals just yesterday...however I believe this is gas from engine as the exhaust stains disappear. Even still how does one contact Lars?

Fang333333

Also I do not know if its accel pump or vaccum. The engine reads about 13.25 at check valve higher off manifold I believe. Harbor freight vacum tester lol) According to other posts and a few other peoples opinions this should be about right as engine was rebuilt. Some kind of performance cam I assume. I bought car with rebuilt and asided from the slightest misfire in the past the car engine has ALWAYS gotten high praises from mechanics. Many mechanics from various citys through the years. This is worse the car has ever been and it breaks my heart.

SH-60B

Big2bird gave you a link to lars.
Thats not gasoline coming from your exhaust, it's water vapor, normal.
I would not go one step further until I checked the ignition system thoroghly, including the timing and timing curve. Static, mechanical, and vacuum advance need to be verified, something could be way out of spec, then you are left chasing ghosts in the carburator.

Big2Bird

If you stated where you lived, a member might be able to look at it with you.