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10/29/17 2:13pm - Original Message: 'rebuilt carb, whistling sound and idling high and small pops/backfires'
Target30
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1973 350 T-tops

Joined: 10/16/2017
Posts: 31
starting a new thread for my carb issue.  the other was in electrical as i thought somewhow they were related.   just coincidence...

short short version of back story.

bad fuel line.  repaired it
bad fuel pump, replaced it.  bad out of box new fuel pump.  replaced it again.
carb gunked, rebuilt it.  
no gas through carb, found accelerator pump tight, took apart and reseated everything.  
car now starts after a couple of years of sitting. 

i am mechanically inclined, rebuilding the carb was not bad at all, but tuning it, for my old car, is not going well.
I got it to idle at 1000rpm.  some small pops occasionally.  i know it should idle lower, like it did before, but cant get it down.  there is a vacuum leak, but tried spraying carb cleaner and no luck finding it.  

after it idling at 1000 for a few minutes(and enjoying my success that it was running again!) i gave it a couple of revs.  idle went up and stayed up.  looks like one of the secondary nozzles is dripping into the bowl.  (probably have to pull apart again?)

I have never really worked on a carb before, and have watched way too many videos and read too many posts to the point where im on information overload.  

anything jump off the page of something stupid i have done or missed?
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10/30/17 8:53am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
C3RACER
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Lexington, NC - USA

Vette(s):
1974 Stingray. Street Scoop. Lots of new parts and working on getting it painted.

Joined: 9/27/2017
Posts: 17
I had this issue once it was the Carb Bolts not torqued to spec. It was sucking air around the base at the gasket. Another time it was a (NEW) bad Power Valve. Just a couple of thoughts.
Good Luck


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10/30/17 1:47pm - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
Target30
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1973 350 T-tops

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cool, i'll take a look.  i know, now, that the person who originally installed this holley carb, put in a few spacers to raise it up give or take a half inch.  im guessing there is no point in trying to tune it until i figure out the whistle/air leak.

edit:  found the noise, ill try to upload a pic, screw hole right by throttle lever.  i put a small screw in and the noise stopped.  need to figure out why there is flow through it now and not before.  got the car idling around 900rpm.  did well for a while, but when i gun it per say, when it comes down it will die out.  starts up pretty good, but i need to keep on the gas a bit to get it to "warm up" and stay running.  even after it was already warm.  im sure i need to tune it alot better, but i've never done it before and the videos make it look easy!  haha!  


|UPDATED|10/30/2017 11:47:09 AM (AZT)|/UPDATED|
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10/31/17 7:56am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
C3RACER
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Lexington, NC - USA

Vette(s):
1974 Stingray. Street Scoop. Lots of new parts and working on getting it painted.

Joined: 9/27/2017
Posts: 17
If it has stopped popping. You may want to look at jetting. I moved from Colorado to North Carolina had a hard time with cold idle. Re-jetted 67 fronts and 73 rears (both are what Holley says is best at sea level) also adjusted the timing and was able to get mine to idle at 750 even after WOT (Wide Open Throttle).  I am not an expert but I have learned from about from trail and error as well as Holley Customer Support.

By the way, you would benefit from cutting down on the number of inserts under the carburetor. You can find different size spacers if you need them. I have need really like the thin insets. If you have room under the hood just use a slightly higher spacer and new gaskets. 

Hope all goes well. 


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10/31/17 12:14pm - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

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Make SURE the gaskets used under the carb, and for the "spacers" are correct, and are not leaving even the tiniest of spots un-sealed. You'd be surprised at how small a leak can be and cause all sorts of idle problems. 

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11/1/17 9:30am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
Target30
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1973 350 T-tops

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when i can get it running on its own(without giving it gas to stay running) there is some small pops occasionally(like every 15-20 seconds).  it starts up fine, the choke works as it should, but it takes a minute or 2 of giving it gas when the rpm's drop or it will die out.  it will eventually stay running, and i see the flap open as it warms up.  the plugs and wires, though they are 6 years old, have only about 20 miles or so on them, and maybe 2 hours of run time.  just starting it up throughout the winter a few years ago.  they may have gotten fouled through the fuel pump issue and cranking without fuel.  i'll probably just change them out since they are cheap. 

i just really dont know what to listen for to diagnose any issues that may be causing it not to run well.  i am looking for someone to come and check it out.  they can probably see it and listen to it and tell me what the problem is fairly quick.  i did find the whistling and plugged the hole it is coming out of base of the carb.  it was the left of the 2 holes directly behind the accelerator cable.  the original gasket must have covered it before.  
i do get an air sound that sounds like it is in the carb, not a whistle, more like a hiss, that is stronger when you hit the accelerator.  
,
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11/1/17 10:47am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
C3RACER
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Lexington, NC - USA

Vette(s):
1974 Stingray. Street Scoop. Lots of new parts and working on getting it painted.

Joined: 9/27/2017
Posts: 17
This is a helpful guide. /member_uploads/50801_50900/50867/D32FB_carb_troubleshooting_guide.pdf

try this too.

1) check your carb base gasket, unbolt the carb and retorque to around 10-12 foot pounds, if you over tighten a carb you can cause the base to bow slightly and cause a vac leak.

2) reset your idle mixture screws to 1.5 turns. if you rebuilt the carb you changed the little cork 
gaskets around the needle screws.

Adjust throttle screw to keep engine running so you can work on it

3)get an assistant, and a bunch of rags: put the rags around the 
carb base open the primary fuel bowl sight screw if fuel comes pouring out you need to lower the fuel bowls, drop the level with the adjustment nut and tighten them up, start the motor and have your assistant watch the sight hole if fuel is still pouring out, cut the engine and readjust, repeat as necessary. and do the same for the rear bowl.

secondary’s open under engine load, you won't see it engage revving the engine in neutral or park. 

if you rebuilt the internals correctly, changed all the 
gaskets and replaced the power valve, your problem should just be adjustments, of the carb.

you can fine tune the idle screws with a vacuum gauge
your aiming for max vacuum at your desired idle speed. or you can close down each idle screw until you hear the 
engine rpm drop by 200 then back off 1/4 turn

you can confirm your idle mixture screws are not leaking by closing them all the way the engine should stall. if not, you could have a stuck butterfly or another leak in the idle circuit

finish up by re adjusting the idle as needed.


Help something helps. I know what it is like to chase something. Do you know an old an school car guy that a six pack of beer may get them over to take a listen. Sounds like you are close. 

Good luck, If I can help let me know.



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11/2/17 3:38pm - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
Target30
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1973 350 T-tops

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thank you for that!  that actually helped.  ive read all of it before in different places, and tried to follow it, but i did it again, and got it to idle pretty good at 800rpm.  any lower and the engine is shaky.  

i found the new air leak, directly under the bolt that i used to plug the other leak.  i wonder if i used too long a screw and ripped the gasket.  going to pull the carb off again to check it all out.  but i used a piece of gasket and kinda plugged the new leak, and got the car to idle pretty good.  

this is a pic of the riser plates/gaskets.  not sure if they are one piece or multiple.  i'll know soon!
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11/3/17 8:34am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
C3RACER
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Lexington, NC - USA

Vette(s):
1974 Stingray. Street Scoop. Lots of new parts and working on getting it painted.

Joined: 9/27/2017
Posts: 17
It help you a lot to get rid of off those thin spacers. Check out the Holley website for what you need.

looks like a 1/2" one would work but you should measure for yourself.

The holes you are plugging up are they vacuum ports?





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11/3/17 9:06am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
Target30
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1973 350 T-tops

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cool, thanks.  i'm going to delve into it today.  i have to check to see if they were sucking in, i think they were.  i know the last leak is a gasket issue of some sort, it is under the hole i plugged with the bolt.  i looked back at pictures from before and there was nothing attached to the holes originally.  so when i rebuilt the carb, the gasket must not have covered it.  
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11/4/17 7:59am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
Target30
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1973 350 T-tops

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so some updates.  when i put te carb back on after rebuild, i used the gasket.  apparently the spacers have a rubber gasket, and the regular gasket i put on messed with things.  i pulled it off, cleaned it, and put it back on without the paper gasket.  no more air issues!  
She started right up again, couple of quick revs and got it to stay steady.  once it warmed up, i played with tuning.  seems i cant get it to idle under 1100-1200rpm no matter what i do.  it runs smooth and no more popping, but i turned the idle screw all the way out, and played with the idle mixture screws.  they are at 2.5 turns out, and almost seem like they will fall out.  it seems to idle faster with them all the way in.  i'll play some more, but i would think it should slow the idle when i turn them in.  otherwise, it seems to running great, at 1100-1200rpm.  so i've made some progress!
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11/4/17 11:32pm - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
F4Gary Gold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
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On my Holley 4150, there is a small set screw that holds the secondary butterflies slightly open at idle.  If it is holding them open to far, then it is hard to get it to idle down.  It is underneath on the pax side.









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11/6/17 9:35am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
Target30
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1973 350 T-tops

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oh no!  i have to take the carb off again!  haha!  i'll take a peek and see what i have on mine.   thanks for the info
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11/6/17 11:34am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
F4Gary Gold Member
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Grapevine, TX - USA

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1972 LT-1 convertible with factory air.

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I have one of these and can do it without removing carb.




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11/6/17 3:47pm - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
Target30
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1973 350 T-tops

Joined: 10/16/2017
Posts: 31
yeah, that would have been helpful!  haha!  so you are the winner!  i backed that off a bit, and then played with the idle screws, they are now at 1.5 out.  oddly, it seems like when i turn them in, the idle gets faster... i did read about a smog version(or something like that) that would follow this.  either way, its idling at 8-900rpm and fairly smooth.  it never was the smoothest thing, plus i was a kid when i drove it before and never really thought much more than "is it running?  yes, then drive!"
if i drop it to 600-650rpm, it really feels like it is going to die.  i've read that where it should be, but under 800 and i'll be on the gas pedal to keep it running.
getting tires this week, going to get it on the road!
Thank you to everyone for your help!  every little piece of information helped and now i can say i have rebuilt a carb, and the car actually ran afterwards!  haha!
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11/8/17 11:59am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
Target30
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1973 350 T-tops

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so i got new tires, and took her for a spin last night, in the dark because no plates yet!  i live next to a small school, so i just pulled out of the driveway, in to the school parking lot, went around once or twice, then back home.  i need some more carb work!  did well out of the driveway, a little sputtering up the small hill to the school.  literally 50 yards to the parking lot.  ok in the parking lot, but when i pulled back into my driveway, the idle went down and i stalled.  started right back up, but the idle was obviously lower, down to 500.  had to do a 50 point turn to get her back into the garage past my other cars, stalled every time i stopped. idle is way lower now.  i did let it warm up before i drove it.  

it was nice to at least get her on the road after so many years.  though i was worried the whole time and it was only 50 yards!
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11/8/17 2:17pm - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
C3RACER
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Lexington, NC - USA

Vette(s):
1974 Stingray. Street Scoop. Lots of new parts and working on getting it painted.

Joined: 9/27/2017
Posts: 17
Have you set your timing? Sounds like it may be retarded a bit. 

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11/9/17 7:59am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
Target30
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1973 350 T-tops

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Posts: 31
forgive me, for this may be a really stupid question/comment...would i need to set it after rebuilding a carb?  it was running fine before all this crap went down(fuel line rotten, then pump went bad, then rebuilt carb).  i did take the distributor cap off once to check the position of the points, but it wen back on at the exact same place.
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11/9/17 9:00am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
C3RACER
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Lexington, NC - USA

Vette(s):
1974 Stingray. Street Scoop. Lots of new parts and working on getting it painted.

Joined: 9/27/2017
Posts: 17
Few different things. 
1. You always want to verify the three things that make a motor run: Fire,Fuel & Air
2. Timing can need to be readjusted after a carb rebuild, it mat have been set to over or under compensate for a carbs poor performance.
3. If the car ran good before what was the need to rebuild the carb? 
4. If very well could be the carb not set up properly. Do you have anyone that is in your neck of the woods that knows anything about old school motors if so it may be a huge benefit for you to ask.
5. Recheck everything on the rebuild. I have had new power valves in the carb be bad.
 Here is a PDF that might help you,

I will help you all I can from here.

Good Luck


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1974 Stingray
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11/9/17 10:29am - Reply: 'Re: rebuilt carb, whistling sound and idling high and small pops/backf'
F4Gary Gold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
Posts: 869
You may have plugged a vacuum leak with that screw you put on the carb.  If that is the case, then you will need to recheck your timing.
On a side note, you may be using ported vacuum instead of manifold vacuum.  I've switched to manifold vacuum and have my LT-1 timed at 16* BTDC.


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