I'm in need of an engine genius! I've got a V8 that just won't idle. Here's the skinny. First, background on the engine: it's a '71 302, with not more than 5-8k miles on it. I had it torn down and completely rebuilt from the ground up, in other words, all parts (ALL parts) are either new or refurb'd. The origin of my problems lie in a broken rocker arm stud about six months back, which led me to having to pull the heads to have them repaired. Status post re-assembly, she won't stay running. I had her running once, and took her for a drive, but now my engine problems seem to have morphed from the general tuning of timing/carb/rockers, and changed into something else. The symptom feels fuel related to me, but I've done everything I can think of with the fuel, and the symptom hasn't changed. So here's the rub; it fires up pretty easily. I hit the throttle, lean on the starter and it jumps to life. After starting, it revs high for a second, then the rpms taper down and it just dies. If I give it a little gas, keep the rpms up around 1200-2000, it seems to be able to run indefinitely. I've got an Edlebrock 650 sitting on top, which was also recently rebuilt. Another piece of information is that she was running too fat, so I swapped out the jets and rods, and dropped it two stages leaner. That shouldn't affect the idle though, correct? It just feels like a simple problem with a simple solution, but not having been around engines for a lot of time I feel like I'm missing something. What I've done so far is: - Checked and rechecked timing. I have it at about 8 BTDC, as best I can tell. Close enough that it shouldn't be causing this problem. - The gas is fresh. I gave her a full tank and added a bottle of Sea Foam. - I replaced the gasket between carb and manifold, as it was looking a little ratty. No change noticed. - Checked fuel pressure in case it was flooding. I'm running between 5-6psi. - Re-adjusted float bowls. They were a little too high, so I bent the tabs a little down, in case the valves weren't sealing and she was flooding. No change noticed. - While I was adjusing the float bowls, I thoroughly cleaned all ports and parts in the carb with carb cleaner and compressed air. I also replaced both the inline fuel filters in case I was letting junk through and the jets were gettting clogged. No change. - I adjusted the front idle mixture screws per the Edlebrock tech support. I have them at an appropriate setting, close enough so that it should at least be idling (4 1/2 turns out). I adjusted them the time she was running, and used the method that Edelbrock recommends. - I don't think it's a vacuum leak. I replaced all vacuum tubing and rubber end caps. I also had her on a vacuum tester, and noted that she was pulling between 11-13mmhg. - I've adjusted the rockers on the drivers side three times, and on the pass side twice. The really weird thing is, for a few days she wouldn't start at all, not even a hiccup. So I got all frustrated and left her alone for a week. Then one day I have a chicka out in my garage, and I'm all "Yeah she won't even start." Then I turn it over to show her, and the engine fired right up! No hesitation, just BOOM rumple rumple... So I came back a few hours later and adjusted the valves again. Then I waited a few days, came back, tried to start her and she had nothing. Just rrrr-rrrr-rrrr. And just to clarify, I tinkered and researched and tinkered, and since the above mentioned day that she wouldn't start, I now have her at starting but no idle. Which is where I'm currently at. I dunno where to go next. I guess I'll do electrical, pull the plugs, make sure they're firing and all. Maybe I should check compression in each cylinder, but I'm sure it's fine since it's a brand new rebuild. Is it possible my coil's going bad? If that were the case it shouldn't even start, right? Anyone have a helpful hint as to where I should head to next? ANY info'd be GREATLY appreciated! Thanks in advance!
What cam do you have? When it won't start is there any voltage at th positive post on the coil? The idle screws sound like they are pretty far out. Usually they are around 1.5 to 2.5 turns off there seats. The high idle problem sounds like a different problem than the no starting problem. The no start could be the coil, distrubtor, wiring, or ignition switch. The high idle sounds like a vaccum problem or idle circut problem. The intake gasket may be leakin.
i think you might have the valves to tight ,sounds like they beeld down after sitting and pump up when started ,when you adj them the 1st time did you pump them up in oil , or at least run the starter with the rockers alittle loose till you get good oil pressure ,then adj them on one side then crank motor again till oil pressure and do other side ,when i adj hyd . cams i take the pushrod down to zero clearence ,it will turn easy but not move up or down any,then i go a 1/4 turn more it should be tight to turn ....when done
Hmmm interesting. It's possible the valves are too tight. I adjusted them via the Chevy method (shhhhh), I have an old valve cover that I cut the top out of, and I adjust the valves while the engine is running. I didn't do "run the starter with the rockers a little loose till you get good oil pressure,then adj them on one side," so maybe I'll try adjusting the valves again using this method. When I adjusted them last, I did 1/4 turn, plus a 1/8 turn. That is to say, I loosend the rocker nut until I hear knocking, tighten slowly until the knocking stops, then I tighten 1/4 turn, stop, then I tighten 1/8 turn. I've got sure-lok rocker arm nuts so they're easy to keep precise. I'll add this to my list of things to check out.
Currently (I'm sorry, the timeline was a little confusing), she will start. She just dies a few seconds later after a high idle. I also added a carb spacer, so I'll a) replace the gasket between spacer and manifold (which I haven't done; I only replaced the gasket between carb and spacer), and if that doesn't do it I'll try running with out the spacer at all. I'll delve into the idle circuit as well. Maybe I've still got dirt in it, or maybe I need to do more work on the carb. Is it possible that this is still a carburetor problem? I've been over that carb about five times now. I guess that's why they invented fuel injection I guess...
i know alot of people do that and i use to also,but then i started working a a engine shop that built super stock motors ,im now retired ,we found that it seemed to make them more const. at the track to do it this way ,so ive done it that way for 25 yrs now ....hope it helps you ....jay
Im not sure which ignition system your using, but malloy unilites tend to have this type of problem when going bad where one day they start the next day they dont. As already mentioned it could be a coil too. But personally sounds more like its running lean. By the way going off memory with Edlebrock carbs, I believe there is a big brake booster vacuum port in the back which if left open will cause this. Try opening the idle screws about 5 or 6 turns out and see if you get it to idle better, if so, then you have vacuum leak somewhere.
Never re-use a paper gasket...Period.Replace the gaskets (both) between the carb and spacer and intake and spacer.Turn your mixture screws in till they stop(dont crank em down) back em out 2 turns...Betcha it starts and idles after this.You have a gross vacuum leak and too much on the mixture screws. Then play with your valve adustment.If the valvetrain is all stock,its a positive stop designe.Turn the rocker nuts till they stop then give em a quarter turn or 15 to 20 ft lbs with a torque wrench and your done.
Two things: One is the timing is retarded too much. 8*BTDC isn't enough. Second is the Edelbrock carb
I know, right??? Is the general consensus that Holleys and Speed Demons are better to deal with that Edelbrocks? Thanks for the timing tip. What is the most appropriate to run it at? I know each engine is different, but should I be shooting for 12, 14?
I start with 12 as a minimum setting. Give it as much initial timing as the fuel will allow (without pinging) I was just joshing about the Edelbog carb. I'm a Holley guy. The Edelbrock/Carter carbs are just too Fugly for me to bolt one on. And it further pushes me away from em with all the BS you hear on the net about Holley's being "hard to tune" and "hard to keep tuned" From what I've read about the E/C carbs, they're actually more complicated than a Holley. Tune a Holley to the engine, run it with a good electronic ignition system, feed it nothing but clean, quality fuel, and it'll run for years without having to adjust anything.
