new fuel pump

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1981 Vette

You say it runs on starter fluid?  I presume you are spraying it in the venturi s?

If it were my Edelbrock carb, I'd reset the initial carb settings and see if it would start, then adjust.

If not, maybe you have junk in your carb.




|UPDATED|12/30/2013 6:05:43 PM (AZT)|/UPDATED|

i have the orig Quadra Jet carb, ran good then all of a sudden just cranks no start

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1981 Vette

Still run on starting fluid?

this site sells Quadrajet rebuild kits but also has identifying information, parts and troubleshooting tips.  Some more guys will chime in soon who know more than me.

Jim

yes i tried key on and i do not see fuel spray i am thinking the carb float is stuck?

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1981 Vette

It really sounds like a fuel delivery problem.  An engine only needs fuel, air, compression, and spark to fire and if it's running on starter fluid you've got air, spark, and compression.  If you've got fuel in the bowl of the carb, it's just not getting to the engine.  Stuck float, or clogged jets perhaps?  I would check the float, and then go straight to a carb rebuild.  But then again I'm a "ready, shoot, aim" guy.  Someone may have a more simple solution.  

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"Let them that don't want none have memories of not gettin' any."
- Brother Dave Gardner

is it better to rebuild or just buy a rebuilt carb? i am looking to keep it orig and stock

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1981 Vette

I'm sure that everyone has an opinion, but I'd swap it for an Edelbrock.  You can keep the Rochester to rebuild if you ever want to go back stock again.  But the Edelbrock will probably improve the car's performance and fuel mileage.  However, it's $300 to $400 for a new carb and $20 for a rebuild kit.

I'd definitely get a second opinion before dropping the money, though.



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"Let them that don't want none have memories of not gettin' any."
- Brother Dave Gardner

If you cannot see a fuel spray in the venturi when pumping the accelerator, try tapping on the carb with a small mallet, right at the front of the carb. If the float is stuck, that usually will knock it loose. If that does the trick, you need a new float, at the very least. Quad floats are made from a foam-like material, with an epoxy coating.Over time, they tend to absorb fuel. This usually makes them heavier, and they flood out, but sometimes, especially on cars that sit, they can swell up, and hang. If it happens to hang in the full UP position, it will not allow fuel into the car bowl.
Try the small hammer deal, and see what happens. I like to tap on the very front, center screw of the carb top, since that will normally beak the float loose, whether it is hanging down, or up.
Alternatively, you can also run a small screwdriver(or awl) down thru the vent tube to push the float down.
If it works, you will still need to rebuild the carb with the new float, and gasket kit.



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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Process of elimination. 1st, Q jets are very easy to rebuild. They have just a few parts that need servicing. 2nd, they are well made effective carbs. The new Edelbroks are nothing more than prettier Q jets.
Now, since the engine runs with fuel (starting fluid) then you have no fuel entering the engine. If it just "stopped" after running well this suggest a clogged circuit.

1st question: are you seeing fuel spray into the primary venturi (front barrels) when you pump the throttle? This is your accelerator pump shot. It pulls its fuel from the main well. If no spray then your not getting any fuel into the carb itself. This would be the stuck closed (up) float or something in the needle jet the float operates. If the tapping does not free up pull the top of the car off to inspect. If yes you have spray from the accelerator pump move on.

2nd step: since you have fuel in the main well your float/needle are working then your idle circuits are clogged. On start up fuel is pull from the main well through some idle feed tubes that are very small in diam. If you had old fuel sitting int the carb these often clog up. You can try shooting some Berrymans B12 in your idle mixture screw ports (after removing screws...turn in, count flats, then remove). This may or may not help as there are air bleeds that may get all the cleaner instead but its worth a shot. If Berrymans b12 won't unclog then no other spray cleaner will. Your main jets are not part of the start up equation and really will not become plugged since the needle jets run up and down within them keeping them clear.

If the carb still does not supply fuel (and your sure your fuel pump is doing its job) then its time to pull the carb top. Be sure to pull the choke rod off the top butterfly and then push the accelerator pump lever pin inwards towards the carb body with a small nail or similar. Tap slowly and drive it just enough to release the lever. This will leave a small amount of space between it and the carb body allowing you to get a flat head screw driver blade behind it...which is how you push it back in when done. The rest of the carb top removal is just screws. The dangly things are your jet needles. you will need to remove the gasket to see down into the main well. It will come up around your power valve (the little spring loaded plastic thing with stiff wires in the middle of the carb body) with a little care. The gasket has cuts in it for just this purpose. Now clean that sucker out!

Dave


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My Christmas present to ME! Bought Sat 11-30-2013. 72, 350 4 spd, Silver with blue interior...Can't you just hear Pablo Cruz playing in the background?

You know I'm being a little dumb here and missed some obvious stuff.

Check your fuel filter...hopefully its a kinda see through deal

Can't see through the filter...might as well move on to your fuel pump. Take the out port hose from your fuel pump (pull from carb or where ever you can access a few inches of flexible hose) and point it into a catch container. Have a helper crank the engine and see if your getting good fuel flow.

Quick carb check: put a length of fuel hose onto the in port of your carb. Blow into the other end. If the float is up (carb thinks its full of fuel and the needle jet is then closed, float up condition) you will not be able to blow at ALL into the hose. If you can blow into the hose then the float is down some and the needle jet/float is not the issue.

Main well full, float up, fuel flow cutoff
Main well low, float at mid range, fuel flows

Dave


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My Christmas present to ME! Bought Sat 11-30-2013. 72, 350 4 spd, Silver with blue interior...Can't you just hear Pablo Cruz playing in the background?

I'd stick with the Q-jet.  They have a bad rap in many circles, but they're actually a pretty good design and the beauty of them is they can remain somewhat economical (normal sized primaries) but still be able to handle a decent amount of HP (giant secondaries).  They are not impossible to rebuild for folks with decent mechanical (and organizational) skills and with decent tools.  And a little patience.  I'm proof - no special training or experience with carbs and my car runs pretty darn good with a q-jet that I built.  Not much tuning or messing with it either.  I have two main tricks: 1) use a good book and 2) use a high quality rebuild kit.  For the books there are two that I can recommend: 

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My personal opinion on quadrajets.  Once they are set up properly, you can run them over with a tank and they stay set.  Holly, I've had problems with them having to be reset after a few hundred miles of abuse.  I have am edelbrock 1406 on my crate engine now and have had them on a couple others as well and like it.  If you're trying to stay original the quadrajet is a good carb.

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Dave C..........My mantra: I can not be bought!!      Long and short term leases available.

I'm assuming your '81 is all stock. So if it is, that carburetor is one of the first "electronic" carbs GM put on its cars aside from the '80 California 305 vettes. There should be some wires going to the carb. The one on top by the choke horn controls the metering solenoid and plug in one on the side reads the TPS signal. 

|UPDATED|12/31/2013 1:46:17 PM (AZT)|/UPDATED|


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GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.

I agree Sarge81 i see the electronics and i am going with a defective TPS, carb was clean,the only thing i saw was a worn needle that was all, float floats,good fuel pressure, no vac leaks,

|UPDATED|12/31/2013 2:22:55 PM (AZT)|/UPDATED|


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1981 Vette

Here is a good article pertaining to the electronic Q-jets. 

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GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.

Thanks for the info, i have decided to rebuild the carb and replace the TPS and the Metering solenoid  all at once for being a orig and un rebuilt carb. it was real clean inside for sitting for 15 years...

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1981 Vette

SO...can we assume you have the carb off now? Sarge is correct...the mixture control solenoid should click rapidly with the key on. A problem with either the mixture control solenoid OR the TPS would not keep the car from having fuel to start, tho. Might not run perfectly, but it would still fire off and run. The TPS on these turds was a problem even when new....the failure rate was unbelievable. The mixture control solenoids were much more durable.
Since you saw no fuel squirting, and you said the float floats, seems like the accelerator pump, or check ball might be the problem, as far as not getting a fuel stream when pumping the pedal.
Definitely time for a carb rejuvenation. Just make sure when you remove the primary metering rods that you count the number of turns it takes to get the adjusting screw loose....it needs to go back as close as possible to the original setting, unless you are changing the metering rods.


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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Be sure there is no slop in the throttle shafts while your at it. Very common issue with these carbs. The bushing kit will tighten them right up eliminating that small vacuum leak point. 

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GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.

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My Christmas present to ME! Bought Sat 11-30-2013. 72, 350 4 spd, Silver with blue interior...Can't you just hear Pablo Cruz playing in the background?

|UPDATED|1/1/2014 3:47:34 PM (AZT)|/UPDATED|


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GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.

Sarge, there are 3 or 4 different versions of the E-brock Q-jets.  You can put whichever metering rods you want in them, and jets.  Just a quick swap out.  I have one of the versions that could probably be considered a "truck carb" but I just changed out primary metering rods and jets for those recommended by Cliff's High Performance (or you can go by the papers written by the guru, Lars) and it runs great.  Secondary rods were fine.  I 100% agree, though, that it's very common for the throttle shaft, especially primary side, to be loose and cause a minor, but possibly significant, vacuum leak.  There are kits on E-bay and the previously mentioned q-jet dealers that provide bronze bushings and installation tools to install them.  Highly recommended to take that extra step.  

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