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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: rockable on September 11, 2012, 06:33:31 pm
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My 86 C10 w/ 305 has bugged me since I bought it. It is stock with the exception of the air pump being removed. I put a rebuilt factory correct Q jet on it and fixed all the vacuum leaks after I got it. The timing is 4 degrees BTDC at 550 rpm idle speed. I just adjusted the idle mixture again and put new plugs on it.
From idle, when you just ease down on the throttle it hesitates or bogs momentarily before finally accelerating. When you look at the timing, the advance is working but it is controlled by the esc. It doesn't advance until the engine gets to maybe 1200-1500 rpm. So, when you crack the throttle, it bogs, doesn't advance and then revs and advances.
I'm convinced that timing is the main culprit here but don't know how to fix it. Has anyone else encountered this and come up with a fix?
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I would get rid of the ESC, get a straight HEI distributor and set your initial timing at 10-12 degrees advance.
I have an 84 with a Goodwrench 350, I removed the ESC distributor and put in a Summit regular HEI with an adjustable vacuum advance. I turned the adjusting screw all the way clockwise and then 8 turns back CCW. I set my initial timing (with vacuum disconnected and plugged) at 12 degrees and then then used a full manifold vacuum source on my Qjet for an additional 10 degrees advance (with vacuum advance) at idle. Its runs great with no hesitation.
550 rpm seems a little low for an automatic ( I assume), especially with A/C
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i had the exact same problem with my 86 that had the ESC on it and i just bought a hei distributor and put it in and set the timing around 12* and that solved the problem. it rilly had me confuesed.
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I thought about buying another distributor but I figured why not see what everyone is talking about with the 375 center plates and 41 weights from a 80s suburban. I spliced the black and green wires going to the esc controller, then later found the center plate and weights that give 20° of mechanical timing and limited my vac advance to 10°. I also used the medium springs from the moroso kit which bring my timing all in@3200 rpm. This truck is a total different beast. It feels like I picked up a ton more tq and hp through out the entire rpm range. It idles smooth all the way down to 350 rpm with a lope like I have a bigger cam. Truck doesn't shake a bit. Ill try to get a video clip going if anyone its interested. Even if I do get another hei I would still use the same center plate and weights.
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rebuilt factory correct by who?
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If you put a straight HEI unit in, does that mess up the ECM in any way? I know it will also take the knock sensor out of the loop. I still have all the multitude of vacuum lines connected to my EGR and I don't want that to malfunction in any way.
550 RPM is spec with the AC off. It's at 650 with the AC on.
Mountain Man Fuel Systems - Ted, rebuilt the carburetor. He does nice work.
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Ok, after some research I realize that what I called the ECM only controls the distributor and timing for the most part. I am putting a straight HEI in it as soon as possible and will let you know if that fixed it.
After that, I may remove the EGR and all those giggered vacuum lines, now that I understand how the TCC is signaled.
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Put a standard HEI distributor on and it improved the acceleration and throttle response. I still have a slight hesitation but it is better. Overall, the engine runs much better with a stock HEI distributor. Wish I had done it long ago.
Recently replaced the stock catalytic perverter, too. The new one made a big improvement in performance and sound.
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What is your initial timing?
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8 degrees. 12 was too much. 8 seems ok. Connect the vacuum to the timed port, not the full vacuum port.
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Why was 12 too much? Did you try the vacuum advance on full manifold vacuum?
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Pre ignition and knocking like heck under load. Same deal with full manifold vacuum. Idle timing at 34 degrees BTDC is too much. That's what I had with full vacuum.
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Ok, sounds right. You might try using a vacuum gauge on full manifold vacuum to tune the idle mixture screws on the quadrajet. You want the highest reading on the gauge.
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34° should be initial+ mechanical and not initial, mechanical, and vac. How many regress do you have in mechanical? the reason you can only go with 8°btdc is because there is too much mechanical advance built in. if you lower the mechanical your initial can be raised.
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I set it with the vacuum disconnected to 36-37 degrees. That was too much. Backed it down 4 degrees and was all good.
How do you change the mechanical? Change weight and springs? Forget it. Its running so much better than it was, I'm good.
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375/ 41center plate and weights. Google them.
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Grrrr. I have my truck running great except for when it is cold. When it is cold and the choke opens and you blip the throttle to take it off fast idle, it dies. Once the coolant warms up, it idles fine. This indicates to me that I have done something wrong with the vacuum lines maybe.
I have disconnected and plugged the two bottom lines on the TVS that used to go to the ESC distributor. I put a tee in the timed vacuum port and fed the new branch directly to the standard HEI distributor. The only thing the TVS does now is close the heat riser valve when it is cold and open it when the coolant warms up.
What did I do wrong?
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Is the heat riser tube in place from the exhaust manifold to the air cleaner housing? This will allow hot air and should cure the lean condition you describe.
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No. Right now, the air cleaner is off of the carb. The heat riser on the. Air cleaner has not been functional for a long time. I never had this problem before changing distributors and removing the two vacuum lines.
After thinking about it, it seems that I must have a vacuum leak AFTER the coolant warms up, which means it is switched by one of the TVS valves. I know the one controlling the EFE is normally open and closes once operating temp is reached. Got any ideas where I should focus my search?
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Used one of those hand vacuum testers and could find no leaks. Therefore, I used the vacuum gauge and adjusted my idle mixture. It turned out quite a bit richer than I had it set but now it idles when cold or hot. The hesitation is almost gone. I'm pretty good with it now. It's so much better than it was.
One question. What should the manifold vacuum at idle be?
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Depending on your cam, anywhere from 15-19 inches is about normal, the smaller the cam the larger the vacuum amount should be.
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16" max. It's running pretty well but the accelerator pump has to be a little worn. I may replace it with a different carb.
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If it wasn't for bad luck......
Yesterday, I towed a uhaul trailer about 200 miles round trip on the interstate to help my son move. On the way over, loaded, I towed in drive. Since it was a small trailer and empty, I put it OD on the way back. About thirty miles into the trip the engine started to miss. Since there was nothing I could really do, I drove it home on 7 cylinders.
Today, I pulled the plugs and all of them looked really nice except number 8. It had a chunk of metal or carbon welded to it. After putting in a good plug, it still didn't run right. I notice what seemed to be too much blowby comin from the crankcase, so I checked the compression. There is almost none on number 8. I may have holed a piston. I don't know. All I know is now I have to either rebuild the 305 or buy another engine. What is my best option?
Will all my accessories fit a 350 crate engine? I know I will have to change the intake and I want to change the carb. Anything else? Any other suggestions?
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Sorry to read of your trouble. You probably have too much timing, causing detonation - you need to assess/correct that. Limit your total advance (initial+mechanical+vacuum) to ~32° and make sure it doesn't come in too quickly.
You'll need to tear the engine down to know for sure, but it will likely be cheaper to reslug #8 than replace the motor (if that's all you have to do), unless you find a complete, low-mileage, running engine for cheap that you can swap in. All accessories on your 305 will bolt onto a crate 350.
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This engine has 90k miles on it, so I wouldn't repair one hole. I would either rebuild the engine or put a new one in it. It was using a little oil because I could see it smoke on startup occasionally. If that hole was getting more oil, that could have caused it to have pre ignition in that hole only. The other 7 plugs looked fine and I was at 33-34 total advance. Sometimes stuff just happens.
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I am going with a basic crate 350. It's the easy way out and gives me more torque and hp than the 305. I just can't see throwing good money and time back into an engine I never loved.
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I will throw in my two Pennies... Search around for the hei 375/41 center plate and weights. This makes the perfect mechanical that a close to stock small block needs.you will see a big diff in the engine sound, tq, and HP all around it will run the best it ever has. Trust google them and them google other methods of getting 32° or 34° of mechanical. Nothing else is correct... When trying to achieve the correct admit of timing. If you need help finding them let me know ill look around here.
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I have looked but have had no success finding the 375/41 plate you refer to. If you find it, please post a part number. Thanks.
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No where to by them except the yards with suburbans.no one has mass produced them.read the thread provided pay attention to ignitionman then google him you'll find he is very knowledgeable on this subject. If you can't find them near by ill look around here on my time off.
http://www.chevytalk.org/threads/showflat.php?Cat=0&Number=1448054&page=0&fpart=1&vc=1
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What year Suburban or truck?
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Found mine on an 84 burban with a 350, but 80s burbans seem to be where they can be found with ease.
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Well, then. Does my stock ESC controlled 86 305 distributor have that plate? I haven't looked and don't remember if they even have centrifugal advance.
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Yes. If the distributor you find with the plates is in good condition. You can just swap the whole thing mine were in an esc distributor. They look just like the ones that come in the after market kits, but they are the right weight and have the correct curvature needed
The #s are stamped in the top of the center plate and weights. All you have to do is look under the rotor to find them
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Cool. I'll check it out. I've still got my ESC distributor. Thanks!
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Yep no problem. All you will have to do is add a couple medium springs from an aftermarket kit and limit the vac advance to 8° and your good to go. Oh and of course set your initial to 10 or 12°. I'm still using my esc dist, just bypassed the controller.
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My RSC distributor had 444/60 combo in it. :(
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Awe its ok. :-) I would say test them out with msd timing tape on the balancer and a timing gun when you get your new engine. Just to see how much mechanical timing they provide. Any how. Keep an eye out for the ones we spoke about. Its a direct swap