Help with very rough idle...
Thread Starter
Safety Car
Joined: Oct 2006
Posts: 3,993
Likes: 9
From: Gig Harbor WA
Help with very rough idle...
OK...'72 350/200, auto, no air....car has sat for around 18 yrs, I'm told. Starts right up but VERY ROUGH IDLE!!!!!
So...in the last few days...
-new fuel tank
-rebuilt Rochester (for now, until I can rebuild the original carb)
-blew out all the fuel lines.
-new plugs, cap, points, rotor
-new wires
-new exhaust system
Havent gone thru the vacuum system yet, but neither the wiper system nor headlites will move, though I believe the wiper dash switch is powered.
Car will not idle when in gear (without my foot on the accelerator).
I plan to go thru the entire car, in time. It needs a full resto. I know the rough idle can be caused by alot of things, like vacuum, cam, carb, etc. Just was hoping for any ideas on easy things that I may have missed. The engine is quite smooth at a fast idle, say around 1500 rpms.
Just looking for any quick ideas from all the corporate knowledge that you guys have!! Havent pulled the valve covers, done a compression check, or checked the timing...yet. I'm tired and time to call it a day!!!
Thanks,
Rob the Noobie!!
So...in the last few days...
-new fuel tank
-rebuilt Rochester (for now, until I can rebuild the original carb)
-blew out all the fuel lines.
-new plugs, cap, points, rotor
-new wires
-new exhaust system
Havent gone thru the vacuum system yet, but neither the wiper system nor headlites will move, though I believe the wiper dash switch is powered.
Car will not idle when in gear (without my foot on the accelerator).
I plan to go thru the entire car, in time. It needs a full resto. I know the rough idle can be caused by alot of things, like vacuum, cam, carb, etc. Just was hoping for any ideas on easy things that I may have missed. The engine is quite smooth at a fast idle, say around 1500 rpms.
Just looking for any quick ideas from all the corporate knowledge that you guys have!! Havent pulled the valve covers, done a compression check, or checked the timing...yet. I'm tired and time to call it a day!!!
Thanks,
Rob the Noobie!!
Burning Brakes
Joined: Feb 2005
Posts: 1,235
Likes: 0
From: Mesa AZ
probably a vacuum leak. disconnect all the ports on the intake and carb and plug them with vacuum caps. that will eliminate any leaks in the hoses. get some carb cleaner and spray it around the intake gaskets to see if there is a leak there. idle will increase if there is a leak because it will suck the carb cleaner in.
i'd do a comp. check too . if it sat for 18 years it could be sticking valves, collapsed lifters, etc...
i'd do a comp. check too . if it sat for 18 years it could be sticking valves, collapsed lifters, etc...
Thread Starter
Safety Car
Joined: Oct 2006
Posts: 3,993
Likes: 9
From: Gig Harbor WA
Well I did a search of the archives (shoulda done it first I guess...bad me) I think vacuum is the first place to look, since the wipers and headlites are TU. I'll pinch off some lines and see what happens...Guess I need to order a vacuum resto kit!
Thanks..
Thanks..
Thread Starter
Safety Car
Joined: Oct 2006
Posts: 3,993
Likes: 9
From: Gig Harbor WA
WOO-HOO!! Windshield washers work after 18 yrs!!! Well at least the wipers work if I manually raise the door!!! Check off another one!!!!! I'm checking for vacuum leaks tonite...
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
If you have to raise the wiper door to get them to work, vacuum is probably the main thing to work on. As mentioned before, disconnect all the vacuum "drains" (don't forget the power steering, if you have it). Plug off all the supply lines and go to work on dialing the engine in. Once that's done, you can diagnose the various vacuum systems....one at a time. An inexpensive vacuum gage will be a big help to you; the other necessary item is a clear vacuum schematic that identifies all of the parts in the system. Good luck! [We've all been there--at least once.] 
Thread Starter
Safety Car
Joined: Oct 2006
Posts: 3,993
Likes: 9
From: Gig Harbor WA
Originally Posted by kdf1986
7T1 Vette,
Where is the vac. hose for the power steering?
I am working on a similar problem, and am interested in
reading what Makoshark72 finds out.
kdf
Where is the vac. hose for the power steering?
I am working on a similar problem, and am interested in
reading what Makoshark72 finds out.
kdf
Thanks for all the help!
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The large line off the back of the carb goes to the vacuum booster diaphragm. It is manifold vacuum, too. The hose can get cracked or the connections can get loose. My point was to eliminate ALL possible leaks in order to dial in the engine. After that, you will have a max. vacuum level (vacuum gage reading) with the "dialed-in" engine as a reference point. Then you add back one system at a time....making sure each system works correctly and doesn't contribute any significant leakage. Continue on and you will eventually find all of the vacuum leaks and fix all of the problems. Don't forget the check-valve and the filter can that are connected into the vacuum lines behind the carb; they can cause the problems if they are not working correctly.
Thread Starter
Safety Car
Joined: Oct 2006
Posts: 3,993
Likes: 9
From: Gig Harbor WA
Originally Posted by 7T1vette
Don't forget the check-valve and the filter can that are connected into the vacuum lines behind the carb; they can cause the problems if they are not working correctly.
Thanks
Last edited by MakoShark72; Nov 8, 2006 at 11:22 PM. Reason: signature
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The filter media [inside of the in-line vacuum filter] is pretty flimsy and usually disintegrates when left unused. It won't perform its function of keeping the intake manifold (valves, etc.) clear of contaminants. For a few bucks, why take a chance? Replace them both...they're OLD!
To test the check valve, get a piece of clean tubing. Remove the check valve; put the hose on one of the outlet tubes (the side with two tubes) and suck to see if you get flow(you should). Then blow gently to see if the check valve works (you shouldn't be able to blow into it). If one side works, try the other tube. If they both work, it is still servicible. But...again....why take a chance for a few bucks?
To test the check valve, get a piece of clean tubing. Remove the check valve; put the hose on one of the outlet tubes (the side with two tubes) and suck to see if you get flow(you should). Then blow gently to see if the check valve works (you shouldn't be able to blow into it). If one side works, try the other tube. If they both work, it is still servicible. But...again....why take a chance for a few bucks?
Thread Starter
Safety Car
Joined: Oct 2006
Posts: 3,993
Likes: 9
From: Gig Harbor WA
Originally Posted by 7T1vette
For a few bucks, why take a chance? Replace them both...they're OLD!
Thanks!!
Rob
Last edited by MakoShark72; Nov 8, 2006 at 11:54 PM.
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
If you use forceps and pinch off the main manifold Vacuum line (Just behind the carb) and disconnect and plug the power brake booster on the Q-Jet I believe you will have only engine vacuum to anylize as all other circuits are now blocked off
Make sure you set your timing to factory specs (hopefully theres still a sticker on the firewall near the brake booster) 12* is a guess
As far as the rebuilt carb goes... if all vacuum ports are blocked and it still idles rough.............theres a very good chance thats the source of the idle problem
Good luck and congrats! 
Make sure you set your timing to factory specs (hopefully theres still a sticker on the firewall near the brake booster) 12* is a guess
As far as the rebuilt carb goes... if all vacuum ports are blocked and it still idles rough.............theres a very good chance thats the source of the idle problem
Good luck and congrats!
Thread Starter
Safety Car
Joined: Oct 2006
Posts: 3,993
Likes: 9
From: Gig Harbor WA
Originally Posted by Bob Onit
As far as the rebuilt carb goes... if all vacuum ports are blocked and it still idles rough.............theres a very good chance thats the source of the idle problem
Good luck and congrats!
Good luck and congrats!
Thanks for chiming in,
Rob
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Originally Posted by MakoShark72
I was remembering that when I picked the car up, we (me and the seller) did get it started, even with old, grungy gas....BUT..it did idle fine.
Its on the linkage side towards the rear stamped vertically
Should start with 7042 or at least 70
If the replacement a commercially rebuilt Q-Jet I would return it ASAP if possible...
If it's a Champion rebuilt then let me know and Ill tell you how I got them to take mine back as they usually wont take it back once it's been mounted.
I cant stress enough about finding a GOOD local rebuilder to rebuild your original if it still runs lousy
Dont forget to replace the fuel filter in the original QJ
Good luck
Last edited by Bob Onit; Nov 9, 2006 at 09:57 AM.
Thread Starter
Safety Car
Joined: Oct 2006
Posts: 3,993
Likes: 9
From: Gig Harbor WA
carb # 7042202
I did a search about this, but....if it is the rebuilt carb, whats a good alternative for a replacement carb if ultimately I want a little more power....something to build on. I checked a while ago on rebuilding the orig, and its pretty darn pricey around here, like $4-500. Does this sound reasonable? Never had it done before.
Rob
I did a search about this, but....if it is the rebuilt carb, whats a good alternative for a replacement carb if ultimately I want a little more power....something to build on. I checked a while ago on rebuilding the orig, and its pretty darn pricey around here, like $4-500. Does this sound reasonable? Never had it done before.
Rob
Last edited by MakoShark72; Nov 9, 2006 at 10:03 AM.
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Originally Posted by MakoShark72
$4-500. Does this sound reasonable? Never had it done before.
Rob
Rob
I have a local guy here that will rebuild it for about $160-$180
I bought a rebuilt which he even supplied the core for $160 and its a great carb.
I do get a little better deal from him as I do throw him newer cores when I find them (which are useless to me) but he has customers that need them for newer vehicles