Rochester Quadrajet #17080291.2849.CYJ

I'm going to order a another new base plate gasket and try this again.

Any thoughts....comments on the pictured, I believe the carb gasket was the right one.

 

Aflac
man i hope that it isnt the boss thats cracked back there...
Man I hope so toooooo.
Avette4me
might be something to check, take the carb off and put a straight edge along the base.
Good suggestion, I will and get back to you since the carb is off at the moment.
nitronick
It would be nice if you could give me the carb number. I would also like to see a pic of the carb off of the manifold, a pic of the carb mounting area of the manifold and maybe even a pic of the mounting gasket(carb side).
Done, see previous post.
Who built this carb
The carb was built by my son's auto class teacher who worked as a license mechanic in a GM dealership for appoximatly 22 years.
The previous carb was rebuilt by a license mechanic that had done several carbs ( so he says ).
it might be of help to know the kit number used, if that is the case.
I took the carb apart and soaked it in a degreaser and provided him with a new " Hygrade carb kit # 1517 it's a blue box.
Don't worry bud, we'll get you going!
PLEASE LET THE NIGHTMARES STOP!
I can only hope, and that's what keeps me going Nick..
Thanks

Frank

 

Here is the new base plate gasket, I've left it in the package because if I open it they won't let me return it. Do you think this one will match up?

 

Don't open that new gasket. From your pics the old one looks fine.
That carb is from a 1980 Chevy truck, probably a Suburban, 350L engine, standard transmission.
I was really hoping to find something blantly wrong, but so far I don't see anything. But I am still looking.....

 

nitronick
Don't open that new gasket. From your pics the old one looks fine
I don't mind using the new one if it's gonna solve the problem. I can see a difference in the opening, but then again I didn't see any gaps in the gasket that just came off.

Frank

 

Yeah, I don't see any problem with the old one either. Just save the new one and get your money back.

 

I agree - you should see 19 - 21" manifold vacuum (at the source for the brake booster) at 800 rpm if you have a stock or mild cam. At 1200 rpm the vacuum should be higher - like 20 -22". You haven't said if the motor has been rebuilt and what cam it has.
A partially plugged exhaust will give poor vacuum and it will get worse if you increase the idle speed a bit. Check that out.
Why might you get variable idle with a plugged exhaust? Myaybe something is moving around giving variable restriction.

The other thing I thought of is something most people miss when they rebuild a Q-jet. There is a rubber gasket where the choke shaft passes thru the wall of the carb. Since a rebuild doesn't seem to require removing the choke housing, the gasket doesn't get changed. When it breaks, it can cause varible binding of the choke shaft which causes variable idle via the fast idle circuit. But that doesn't explain your poor vacuum (unless you have a hot cam).
Don't give up!! Maybe one of the members near you can loan you a known good carb.

 

nitronick
Yeah, I don't see any problem with the old one either. Just save the new one and get your money back.
Sorry nick, I jumped the gun and installed the new one, 3 things
1. it will idle now at around 850 rpm, and surges 1/2 as much as it did before and occasionally doesn't surge at all.
2. I noticed I had forgotten to install the spring where the fuel filter goes and now it's installed. When it does stall now it's more gradual. Eg. it slowly revs lower till it finally stalls rather than a quick stall as before.
3. When I apply ether to the same spot as before, ( which was just below where the connection to the brake booster is at the rear of the carb ) it revs only about 350 rpm higher and the same effect when I place my hand over the top of the carb.

Rich's'78
You haven't said if the motor has been rebuilt and what cam it has.
It has been rebuilt with 10:1 pistons from 8:5 stock and a 350 hp. cam
A partially plugged exhaust will give poor vacuum and it will get worse if you increase the idle speed a bit
I placed my hand at the rear of both exhaust tips and there seems to be alot of pressure.
There is a rubber gasket where the choke shaft passes thru the wall of the carb. Since a rebuild doesn't seem to require removing the choke housing, the gasket doesn't get changed.
That's something I'll have to look into.
Thanks



Frank

 

I played with the fuel air mixture for quite a while and ended up at around 2 3/4 turns out on both.
The idle is at 850 rpm in park and it surges approximately 100 rpm. It was idling for about 1/2 hour and didn't stall.
When I apply ether around the rear and passenger side of the carb it still idles higher.
The timing is presently at 24 deg. BTDC with vacuum advance plugged.
With these settings I get the best idle, unfortunately when I put it in drive it eventually stalls.

Guys, I think it may be isolated to the carb and/ or gaskets. What are the chances of having 2 bad rebuilt carbs? Go figure!

Frank

 

That all depends on who built them!

I have certified mechanics with decades of automotive experience that bring their carbs to my shop to get rebuilt. Why?
They're general automotive mechanics, while I have spent the last 25+ years specializing in the remanufacture of carburetors. As I said before, there is a big difference between a remanufactured carb and one that has had a kit put in it. Most people assume it is the same.

 

Well I'm at a stand still right now, I've overdosed on my car for now, I need to take a day's break, then I need to figure out this timing situation.

Lars is coming to town this weekend, if he has the time maybe, well just maybe he can look at the carb or carbs for that matter.

Wish me luck!

 

this is a great thread. thanks to maymyvetteliveforever and everyone who is contributing to a very printable thread.

This is my first time seeing the ether, propane, and leak down troubleshooting moves for diagnosing leaks around a carb.

Thanks again to everyone

 

Update ?

 

Update:

Lars took a look at both Q-Jets I brought with me to the Toronto Larsfest
1. He removed 75Rags Q-Jet off of his car (Same year as mine) and installed the carb I was presently using on mine since his car was in good running order. The car wouldn't idle, ( same as mine ). Therefore it was safe to say that the problem was with the carb.
2. Upon disassembly of the Q-Jet he noted it was missing pieces, set up to run lean, and at first, identified that it came off of a truck. Float was not set right and it should have had a nitro fill float instead of a brass, (due to the weight difference), the choke pull off was weak, at this point in time I couldn't keep track of the remaining problems so I decided to scrap that carb.
3. The second Q-Jet was off of a Camaro, which was a good match, but the top section of the carb was warped and again the carb was not set up to proper spec. The list went on and on. Again I couldn't keep track since it was a loooooong day, therefore I made the decision to scrap that one also. Just image how devastating that was.


In conclusion, the problem was with the carbs all along. Moral to this story, Just because a carb has been put together with a kit as nitronick stated doesn't mean it's been remanufactured. Although I now have to check my funds and am on a mission to find a replacement carb. I'm finally at ease that my 6 month " Massive Vacuum Leak " ordeal is at an end.

Many thanks to all that gave me great suggestions and didn't give up on me. And special thanks to Lars for putting this to rest in less than 1/2 hour .....Oh, I forgot....... and to 75Rag for letting us use your his vette as a guinea pig.

 

Glad you finally got it figured out. Nothing like being there to troubleshoot a problem.

 

Here's your regular update guys. I managed to get a Q-jet from another member and installed it as is. I still think I need to set it up properly but YAHOO....it finally idles, no ifs, ands, or buts. I was unlucky enough to have two bum carbs...go figure. Thanks again for sticking with me through this nightmare.