Vaughn Posted April 13, 2013 Share Posted April 13, 2013 My son Liam has a 71SS Monte. This winter he took the engine out and in for a rebuild. Basically a stock rebuild, 30 over with 10:1 compression. The shop does not have a dyno so we got it fresh. Dropped it in the car, fired up nicely, did the 2000rpm break in for 20 minutes. The problem is that we can't get the idle down below 1200 with out it stalling. It runs best with timing at 30 BTDC. Rebuilt the qjet carb as well. Called the engine shop and they say we need to get the dist recurved. Does this sound right, almost appears as if the timing chain is out one cog. As we are not engine experts, any insite would be appreciated. Thanks in advance. Quote Link to comment Share on other sites More sharing options...
footballubet Posted April 13, 2013 Share Posted April 13, 2013 Distributor out a tooth? Quote Link to comment Share on other sites More sharing options...
Vaughn Posted April 13, 2013 Author Share Posted April 13, 2013 Thats what I thought Scott, but pulled and dropped a tooth either way and makes it worse. Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted April 13, 2013 Share Posted April 13, 2013 Can you run a compression test? Quote Link to comment Share on other sites More sharing options...
Rooster Posted April 13, 2013 Share Posted April 13, 2013 get the dist recurved? this dosent sound right to me and if the timing chain is off a tooth I wouldn't think the engine would sound right even at 2000 rpm's. Be careful because if the cam timing is off you could risk some major damage. Does the car seem under powered when you drive it and does it sound ok above 2000 rpms? Could be carb needs to be tuned in. It's really hard to say without hearing the motor run. When you set the timing its at an idle and the advance curve should have nothing to do with it at that point. Even if the ignition starts to advance too early when your setting your timing at 30 deg, its 30 deg. Just my thoughts, hope it helps... Quote Link to comment Share on other sites More sharing options...
overdrive Posted April 13, 2013 Share Posted April 13, 2013 Check for a vaccuum leak. Is the power brake booster connection tight at the carb? Check for any leaks at the carb and intake manifold. Dan Quote Link to comment Share on other sites More sharing options...
Vaughn Posted April 13, 2013 Author Share Posted April 13, 2013 Thanks for the help. I did not think recurving the dist had much to do with getting the car to idle, but as stated before I am no expert. The motor sounds "right" when running, just cant get it to idle down. Have not driven the car so I can't say if its under powered or not. I will check for vacuum leaks then I think I will drop another carb on it and see what that does. Quote Link to comment Share on other sites More sharing options...
Mo's70MCs Posted April 13, 2013 Share Posted April 13, 2013 From the description it sounds like vacuum leak to me as well, I'd make sure to have a steady and within the range of 17 – 22 inches of mercury. A stock motor should read within those readings. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 13, 2013 Share Posted April 13, 2013 I was thinking carb or vacuum leak also Quote Link to comment Share on other sites More sharing options...
Leghome Posted April 13, 2013 Share Posted April 13, 2013 My 72 used to have a Holley and the idle was a little fast. Whenever you punched it while driving it would choke and almost die. My son in-law and I were working on that problem when we discovered that the base of the carb was bent, it was sucking air badly. There was a 3/32nd" gap causing the problem. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 13, 2013 Share Posted April 13, 2013 while you have it running...manually close the choke flap and see if it picks up RPM, if it does you have a vacuum leak carb problem Quote Link to comment Share on other sites More sharing options...
wallaby Posted April 13, 2013 Share Posted April 13, 2013 I agree with the above: it sounds like a fuel mixture problem, and it takes a bunch of timing to overcome the issue. It could be a vacuum leak, or idle mixture screws wrongly adjusted...any number of things including valve adjustment. Double check the obvious stuff first. Make sure you have the firing order right, and points set right (if you have 'em). Dial the engine speed down as low as it will go and still run, then try cupping your hand over the carb opening to choke off some air. Does it like that? If it does it could be a clue to having the mixture screws too far in, or a vacuum leak. Qjets have a problem where the throttle shafts get sloppy in the carb base and cause vacuum leaks, but it's not normally as bad as you describe. Check the teperature of the exhaust coming out the tailpipe, does it feel dry and blazing hot? Right now at 1200rpm the carb is running in a transition period where both the idle mixture and main circuit are in use. Your goal is to slow it down so only the idle circuit is being used. It's impossible to tune when the rpms are so high. Slow the engine down as best you can, then make adjustments. If it likes what you do it will speed up, and you can turn it back down and adjust again. Changing the carb for one that's known to be good isn't a bad idea. Sometimes the battle is easier when you know what the problem ISN'T. Unless you are running a points-type distributor, I'd expect that to be one of the last places you'd find a problem. Quote Link to comment Share on other sites More sharing options...
CrazyDavey Posted April 13, 2013 Share Posted April 13, 2013 Vaughn the guys have hit it pretty good....re-curve the disto?? it has nothing to do with idle once the initial is set...look at the carb/vacuum...especially the carb since you had it worked on.... Quote Link to comment Share on other sites More sharing options...
Vaughn Posted April 13, 2013 Author Share Posted April 13, 2013 Thank you for all the help, I really appreciate it. I am on the road working but should be able to tackle the car next weekend, will let you know what we find. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 13, 2013 Share Posted April 13, 2013 call me if you need too!!!!! always willing to lend a hand to you Vaughn!!!! Quote Link to comment Share on other sites More sharing options...
Vaughn Posted April 15, 2013 Author Share Posted April 15, 2013 Oh I will Sam!! I did not even think of a vacuum leak. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 15, 2013 Share Posted April 15, 2013 Vaughn...how many turns out do you have the idle jets? Quadrajets like to be out 3-4 turns and that could cause your issue if you are only out 1-2 turns Quote Link to comment Share on other sites More sharing options...
Vaughn Posted April 15, 2013 Author Share Posted April 15, 2013 I honestly dont know Sam. I was just trying different settings trying to get it to idle down enough. I will be sure to check the idle jet settings. Quote Link to comment Share on other sites More sharing options...
overdrive Posted May 6, 2013 Share Posted May 6, 2013 Did you locate the problem? Dan Quote Link to comment Share on other sites More sharing options...
Vaughn Posted May 25, 2013 Author Share Posted May 25, 2013 First of all thanks again for all the replies, it helped immensely and we seem to have figured out the problem, well problems, LOL. The first thing that I did was remove all the vacuum lines on the carb and plugged the outlets off on the carb. Then checked the idle mixture screws and found they where out only one turn so I backed them off to 4 turns. Started the car and found a noticeable improvement right away. Got the idle down to 900rpm and a smother running engine. Only had 6 pds of vacuum though and could get the idle no lower. So on went a rebuilt qjet with same base gasket, and it ran a little better but not much. So replaced the base gasket with a new thicker one. Big difference and got the idle down to 600 with 10 pounds of vacuum and a nice idle, with timing at 16. So off with that carb and put the original qjet back on with the thick base gasket. We had rebuilt the original during the rebuild. Played around with dist timing and idle mixture screws. In the end we have the car idling at 700 rpm (seems to like that) 10 pounds of vacuum and running the timing at 9 degrees. Hooked all the secondary vacuum lines back up and noticed that the idle and timing floating around and not staying constant. Found a leak in one of the lines and repaired. Starts right up and shut off nicely. Took the car for a 30 mile trip and it seems to run nice, kicks down good (no pinging). Took it easy, as it is a new rebuild. One thing that I did notice is that it burned over ¼ tank of gas though. Is this normal because it is a new break in???????? Or do I need to replace the jets? The engine has a very mild cam, not lumpy but 10.0/1 compression. From what I can tell so far it will have very nice street manners, which was our goal. It has been raining ever since we did the work but plan on putting a few more miles on it soon to get her “broke in” Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted May 25, 2013 Share Posted May 25, 2013 you should have more vacuum than that with a mild cam, I have 9 with a muthr-thumper cam at 850 rpm in gear with my foot on the brakes, you sure it doesn't want some more base timing? you should have at least 12 or more inches of vacuum at idle,,,IN GEAR! Quote Link to comment Share on other sites More sharing options...
wallaby Posted May 25, 2013 Share Posted May 25, 2013 Your problem probably isn't the Q-jet. If the float levels are correct, then the rest is usually ok. The Q-jet is a pretty clever assembly...even if it has the factory rods/jets, it should be pretty good on any engine you bolt it to. You may have room for improvement on your timing. With an aftermarket cam you can pretty much throw out the factory timing numbers and dial in what the engine wants. Because the cam overlap of hiperf cams bleeds off cylinder pressures at lower speeds, they idle poorly, and tend to like more ignition timing to make up for that. Maybe it's just me, but i tend to do my ignition timing bacwards: I rev the engine up to about 3000 rpm, hold the throttle constant, and then rotate the distributor back & forth to find the spot the engine likes best. (I use the distributor as if it were a high-speed mixture screw). Often times I can eliminate a choppy sound from the tailpipe this way and it runs like glass on the highway. Once the engine slows down you "have what you have" for initial timing and carb adjustmant can usually iron out any idle issues. Quote Link to comment Share on other sites More sharing options...
LostnFound Posted May 27, 2013 Share Posted May 27, 2013 A new or freshly rebuilt engine always uses more fuel. You will notice a difference once it is broken in. Cheers, Larry Quote Link to comment Share on other sites More sharing options...
Vaughn Posted May 27, 2013 Author Share Posted May 27, 2013 Thanks again Mark and Sam. Well we went back out today and tried some of your suggestions. First thing we did is what Mark suggested and ran the motor up to 2500 rpm and tried timing it that way. When it idled down we were at 900 rpm and 12 inches of vacuum, timing at 15 degrees. turned the idle down from there and played with the idle adjustment screws. We are now at 16 degrees timing, 12 inches of vacuum and 800 rpm at idle. Once in gear the idle remains close to 800 which I think is a step in the right direction. Took the car for a ride and it seems to run smoother. It is now running about 10 degrees cooler, and waaaaaayyyy better on fuel, not that fuel mileage is the goal here. Just seemed super excessive last trip out. Does not ping or have run on after it is shut off, but still does not have the power that I think it should have, seems something is still missing, just not sure what it is. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted May 27, 2013 Share Posted May 27, 2013 that's great news Vaughn! how does it's performance compare to your '71SS ? is the mechanical/vacuum advance in the distributor working? I'll give you a call later, I know it's only 7:30am there right now Quote Link to comment Share on other sites More sharing options...
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