I'm having a very difficult time getting my car to idle smoothly around 650 rpms. I'm not even sure if it's suppose to run at 650 rpms either. If the rpms drop lower than 750 it begins to run very rough and almost dies. Sometimes when I start it up cold or hot it will run at a different idle speed somewhere between 600 and 900 rpms and it's pretty rough. When I start the engine I tap the throttle to raise the rpms about 200 but but it seems the throttle doesn't come back down all the way. How could I fix a sticking throttle (if that's one of the problems). It also jumps from park to drive or reverse real hard feels like something is going to break and my idle speed screw is completely out. Sometimes I get pretty bad pre ignition too but only sometimes. The timing is at about 9btdc (not sure if that's right either) and the idle mixture screws are both set about a 1.5 turns out from their fully seated position. I've also checked and found no vacuum leaks and spark plugs and cables are both fine. Does it matter if I set ignition timing before setting idle speed?
I am far from being a "tune up" expert - but I can tell you that adjusting the timing to the correct location is the place to start.
Adjust the idle speed after that.
A couple of questions:
Year and engine size? Is it the factory motor? Is the engine still "factory stock" (stock carb, cam...)
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
Sounds like a carb issue to me. The idle screww has to be backed out to let the throttle plates close before it will idle good. I'd bet your timing is off and that's why you have to have it cranked way out to keep it running. Does the idle fluctuate too? Another sign the plates aren't closed and gas will continue to drip.
650 RPM seems a bit low but you never said what your engine and cam are. Your Timming at 9 deg also seems low to me. Should aim for around 12 but it also effect your total timing so it would be go to know how much mechanical advance you have. When you increase your timming you also increase your idle RPM so you may need to turn down your idle screw. Also 1.5 turns out is just a good starting point you should adjust both sides 1/4 turn at a time to reach the highest RPM then turn them both in just slightly until you see the first hint of idle drop that way your just a tad on the lean side. Hopfully your doing this check with the car warmed up and your vacuum can disconnected and pluged. If your car has a cam with low vacuum at idle your idle circuit may need modified.
Like Rohrt said, we don't even know what he's working with, how long it's been like this or did it just start, what kind of carb are we dealing with etc, etc...
any diagnoses at this point is just a "best guess" until we get more info...Ah I remember those customers, "just needs a tune up", come to find the MIL lamp is on and he's failed smog twice already and between him and his brother-in-law they've dumped a grand into it...couldn't hit water if they fell out of a boat...dam, starting to sound like Amervo????
I have a 1968 with a stock 400 engine and carb. I have rebuilt the carb once about 5 months ago. This all started about a year ago when my throttle cable broke once I replaced it I was hard to start rough idle, not getting full throttle and no more passing gear. Unfortunately I don't have a vacuum gauge yet I have just been adjusting the mixture screws with a tach. I have chilton's repair and tune up guide book and it says timing should be 9B and idle 650/500. I tried these settings and everything around them with no luck. How do I know what is a good timing and idle setting for my car. My biggest concern is the pre ignition this started about a week ago all of a sudden. Once I put the timing at about 16b it seems to be better but still present but then the car idles at like 1000 rpms and my idle screw is already all the way out and even then it's still rough like one of the points is missing but I have put electronic ignition in it about four years ago.
Only in your dreams because you will never match him in any way shape or form. (What I cannot understand is why anyone would want to pretend to have automotive repair skills. A doctor, lawyer, rocket scientist, yes, I can see why. But pretend to be a grease monkey? And I thought that I didn't have a life.)
You cannot sound like him because you lack basic internal logic. Notice that he didn't add to this thread because it would be pissing in the wind, based on the information provided.
While we're at it:
<I am far from being a "tune up" expert>
No chit! Timing has little if any affect on engine idle other than rpm. What is so fascinating about pretending to be a grease monkey? I wish I had never been one.
By the way dr d: The choke also has zero affect on engine idle other than rpm.
Ouch! lol Reason i havent responded. To many varibles. Vacuum gauge, good tach, and timing light a must have.
Different rpm's on start up's sounds like throttle shaft and/or linkage binding and/or sticking. Have good return spring tension? No vacuum leaks? Qjet carb/stock engine? Lightly seat idle screws and turn out 1-1/2 to 2 turns. Back off fast idle screw and turn in 1.5 turns when shaft starts to move. Dont worry to much about where rpm is yet. Try to get a decent steady idle 1st. Have to experiment with all 3 screws ALITTLE at a time. Check timing with and without vacuum to distributor. Let us know what happens.
Yeah we're just a bunch of no nothing clowns huh? It's a wonder we've been able to keep on breathing on our own this long I guess. We should all just bow to the master mechanics and stop trying to lend a hand to someone that is asking for help or advice. I don't pretend to be a mechanic. Never wanted to be. But somehow I've been able to keep all my cars in good running condition for the better part of 35 years(everybody gets lucky sometimes I guess). So whatever dude. I'm sure everyone appreciates all the expert help you offer. Keep up the good work.
No chit! Timing has little if any affect on engine idle other than rpm. What is so fascinating about pretending to be a grease monkey? I wish I had never been one.
And thank you for backing up my point exactly.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
One more thing: This kind of chit is the reason I act the way to do--all these idiots offering advice in a subjet of which they have no clue.
I was talking to a car friend just the other day about this site and telling him that (in the 8 months or so that I've been around), I have yet to read a post from an arrogant, know-it-all, blowhard.
8 months was a pretty good streak, I must say.
1969 Firebird, 350/350, Goldenrod Yellow, Gold, numbers *NOT* matching. Plan is to make a 400 "tribute" car but many detais TBD. Resto-mod-on-a-budget project.
What is funny is I went to a tech. college for auto engine repair. Worked as a mechanic in a buddies garage for 5 years part-time. Rebuilt app. 8 engines of different cubes. But I am by no means an expert. Without actually seeing it first hand No master mechanic can give you "what is wrong with it" without all the variables. Guessing is all anyone can do hear with the situation this gentleman is having. Sounds carb related to me. But could be numerous things.... Carb could be gas flooding the cylinders or starving the cylinders at idle. Like I said guessing is all it is without seeing.... Oh by the way I stopped working on engines about 10years ago. I gave up working on them because it was so hard to get the grime from under the finger nails... But here today I am working on them again. I love getting greasy now. Wierd huh???
When I set my car's curb idle at 900 rpm and shift gears from park to drive or reverse it jumps into gear real hard and pulls the whole car forward or backwards going into reverse. I have to keep a real strong foot on the brake when changing gears. I'm not sure if that is normal. To eliminate this I have to keep the idle lower than or around 700 rpms.
400 4bbl (stock Q-jet) automatic transmission is 600rpm in park 500rpm in drive.
I just has mine rebuilt and reinstalled two weeks ago.
All I did was bottom out the mixture screws then come back 1 1/2 turns and tweak it from there. I'm about 1 1/4 turns and 650rpm in park.
All new vacuum lines, PCV valve and grommet.
I don't know if this has been mentioned. Try spraying some carb cleaner at the carb/intake gasket and the gasket that separates the upper and lower parts of the carb. See if you have a vacuum leak there.
I didn't check with a vacuum gauge, but it starts, idles and runs good.
I'm no expert, but it sounds like you have a vacuum leak somewhere.
BTW...just checked the manual: Correct idle speed for a '68 Firebird 400 4 holer with auto tranny is 650 RPM...500 in gear. (section 6D-1)...Manual Tranny is 850 or 1000(400/RamAir)
I'm a hobbyist. Not a professional. Don't be hatin'!
So I borrowed a 1971 Pontiac carburetor from a friend and installed it. It pretty much solved all of my problems except not getting full throttle. So now I'm wondering if I need a new carburetor or another rebuild. Is it possible that my carburetor is in such bad condition that a rebuild cannot fix it? Are all rebuilds the same? I got a quote from a place that will rebuild it for 320 bucks is that worth it? And if I have to buy a new one how do I go about buying a new one that is compatible. This 1971 Pontiac carburetor that my friend let me borrow has a little extra piece on the front which prevents the air filter from fitting on top of it so I can't really use it.
There's as many different grades of rebuilds as there are rebuilders. For $320 it better come with a lifetime guarantee. Carbs can become so warped that they are not easily repaired. Sometimes it takes more than just a kit to put things right. That's when it takes a real expert and they are few and very hard to come by. That kind of money can buy a brand new carb that can be bolted on right out of the box and will need nothing.
Worn Q-jets are notorious for throttle plate shaft leakage.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
Kinda jumping in in the middle of this, but recently I had a few issues relating to a Qjet as well. Turns out a good friend of mine does a bang up job rebuilding these. He rebuilt mine and also added an electric choke. I was amazed at how many different variations of the quadrajet there are out there after some long discussions with him. My car now runs great. He does them more as a hobby and to get soem extra cash on the side.
He also knows a lot about converting Firebirds and Camaro's to tilt steering, he has a lot of different options he works with, including adding cruise control. If anyone is interested I can get you his contact info. Again this is not what he does for a living, he works on projects for the military
When he was done with my carb it was actually a gold in color for the main body and looked and ran as if it were a new carb.
86 Pontiac 2+2 69 Firebird Coupe(Under Construction) 69 Firebird 4 speed Vert Driveable but Under Construction 64 1/2 Mustang (Under Construction) 86 Z28 Convertible Weekend driver
I had a Carter AFB and a Q-jet done by these guys over the years. The Q-jet recently was $110 rebuilt. They've been around 30+ years and just do carbs. You could probably ship it to them. Give them a call.
what is the numbers on this carb to start off with???? If it is a good carb then try to get rebuilt. If there are worn out parts but the body is good it can be rebuilt. If it is a later carb buy one already done to save on time waiting for rebuild. If you need the correct carb good luck!!!!
The number on the carb is 7028262 0144. I don't know what but something is wrong with the carb. The body looks fine I guess, there is no visible physical damage to the body of the carb. I've heard that if the carb is really worn that it can't be rebuilt. I don't know if that's true or if my carb is one of those that can't be rebuilt.