73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Dirka on July 29, 2012, 03:18:18 pm
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I did some readin through the archives and found a similar problem talked about, the only difference in the two were that my 77 stalls out once put into any gear. Idles good but once gear it wants to stall out unless I feather the accelerator. My fist step is going to do this:
My first suggestion would be to check the incoming fuel filter. My second guess would be something got into the jets on the carb. Sounds like a fuel flow problem only because you said it worked great before and after changing out the intake and carb. and at idle it is fine and at w.o.t. it moves slow.
Does the engine sound like it is starving for fuel when you are trying to drive it ?
I didn't know if anyone else might have a different idea? They guy I bought the truck from says it needs the valves to be reseated and this issue the truck is having bc of a vacuum issue, which also at low rpms inhibits the brakes working properly. Any truth to what he said? Before I take apart the topend, I like to see if there is any easier fix to this.
Thank you
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Put a vacuum gauge on it (full manifold) and see what it reads. I assume you have a TH350 or 400, both have a vacuum modulator that could be bad causing a severe vacuum leak.
If the vales were not sealing it wouldn't idle very well either. Maybe he meant readjusting the valves?
What carburetor do you have?
Stock 350 motor?
Big camshaft? if so, may be you need a higher stall torque converter.
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TH350 yes.
He mentioned one or more of the valves were loose when he redid the bottom of the engine.
The carb is a Edelbrock 600cfm, model number unknown. see attached picture.
it's a 305 motor, for the most part I believe it's stock besides carburetor and he said it has a mild cam but no idea specs on it for duration and lift etc.
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What's your idle RPM?
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Idle rpm im not for sure I don't Have any of the necessary tools to do any of those checks, it does idle pretty rough though. Im a total newbie to this
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There are a lot of things to check before you take the top end off.
I would adjust the valves and see if that helps smooth out the idle. Also use a vacuum gauge to see how much vacuum you have and if the needle is bouncing all over the place.
You may have a large vacuum leak somewhere. You can plug everything vacuum operated and see if that helps and then reintroduce one at a time until you find the problem.
When I say plug, use rubber plugs to cap off all ports on the carb and intake manifold.
Also check your timing.
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AutoZone has vacuum diagrams online, and this is a link for the 77 350, so the 305 should be the same.
(http://i227.photobucket.com/albums/dd22/Dnstclr/77VacDiagram.gif)
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Thank for you the diagram!
I will check on those vacuum lines tonight. I got ahold of a family friend who has the vacuum gauge and a timing light so hopefully between those we can get this figured out later this week.
Greatly appreciate the info!
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Another quick question,my truck is a 77 custom deluxe came with AC and a 400ci motor from factory, but it currrently has a 305 with a edelbrock 600cfm carburetor and new distributor (we think it's a PerTronix Flame Thrower)
When looking for the vacuum line diagram from autozone, should I looking at the 400 diagrams?
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The emission controls will be similar for both engines but follow the 305 diagram.
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I adjusted the valves to specs I read on here on and now the truck won't start at all. We did try advancing the timing of the distributor and got it to run once, but the distributor was bottomed out counter clockwise against the firewall. Adjust the distributor a tooth or two over so it would sit straight on, and nothing again. Changed HEI units and still no start up. wondering if maybe the harmonic balancer/ timing might off when the previous owner installed a new, what I'm assuming is an RV cam. But then again why would it run before (with stalling issues talked about earlier) and now not after adjusting the valves?
Side not the one time we got it running, it sounded smooth and running like it should to, according the mechanic helping me.
Ideas??
Also the vacuum lines I have, are the PCV, one to the distributor and then to brakes. I don't have any of the EGR lines.
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The 305 balancer has the timing mark at the 12 O'clock position, and if your timing pointer on the timing cover is at the 2 O'clock position you will never see the timing mark on the balancer with your timing light. You will either have to change the balancer or the timing pointer.
Bottomed out against the firewall counter clockwise on the distributor is retarded timing not advanced.
If you can determine you have the correct balancer and timing mark, I would start over with the distributor. Remove the cylinder number one (front drivers side) spark plug and turn the motor over (I like to do it by hand with a breaker bar) until you are TDC on the compression stroke (air will escape around your finger if you stick it in the spark plug hole). Then turn the motor over a little more until you are 10 degrees advanced on the balancer. Then stab the distributor so your rotor is pointed exactly at your number one terminal. The motor should start and then you can set your timing with a light.
Did you set your valves zero lash and then 1/4 to 1/2 turn? Does it have roller rockers or original stamped? You may have the valves too tight.
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I did set the valves at zero lash and then a 1/2 turn. I have original rockers.
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Try just a1/4 turn. You're valves may still be open. Also sounds like you need to pull the dizzy again and rotate the crank till cylinder #1 intake then exhaust rockers go up and down, then line the slot on the balancer up with the 0 on the timing mark. Find #1 on the dizzy and there you go. Easy ask cake :D
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Have you set valves before? Zero lash is using your forefinger and thumb only, twisting the pushrod until you feel enough resistance (from tightening the rocker arm nut) to stop the pushrod from twisting. Its a fairly light touch. Then 1/4 to 1/2 turn more. I also like 1/4 turn myself.
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I have not set valves before, though this is the 3rd time I've tried on this truck, first two times I did it wrong. I adjusted exhaust valve with intake open instead of closed. I did the zero lash at the first sign of slight resistance between forefinger and thumb. It's very possible that I'm just getting them to zero lash like one is suppose to.
454man, in regards of finding #1 on the dizzy after all that, if it's not pointing at the "true" number firing position should I just put the number one plug where it's pointing and then follow the firing order from there? Currently the dizzy is at the "true" #1 firing spot with the balancer at 0 mark. I haven't been able to try to 10* advance on the balancer like fairlane suggests, I'll be trying all these things tomorrow on my day off.
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Going to go slightly off topic here, if everything is done right and it still doesn't run good because maybe the valves are bad, need redone. I found a complete SBC 400 that ran good before they took it out of their 77 4x4 (same year as mine) for $425. For that price would it be a good buy instead of getting the 305 heads redone? Local machine shop charges start at $250 and could be as high as $400 depending on what is needed. Probably a no brainer by most people. This truck is my winter driver, eventual workhorse for towing and other things you need a truck for, it will never see the drag strip.
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Ok, sounds like you may have the valves adjusted properly. Now lets concentrate on the distributor.
Remove cylinder number one spark plug. Place your finger in the park plug hole and turn the motor over until you feel compressed air escaping around your finger. You should also be watching the balancer and see the timing mark coming up to the timing pointer on the front timing chain cover. Stop turning the motor over when the mark on the balancer lines up with the 10 degree mark (advanced) on the timing pointer.
Now check the distributor rotor and see where it is pointing. This is where you want the rotor pointing directly at the number terminal in the distributor cap. You can use a sharpie to place a mark on the distributor body to indicate where your number one terminal is. This way when you remove the cap you know where the number one terminal is located.
It if does not line up, remove the distributor and re-stab it until it does. Sometimes the distributor will not go all the way down, in this case rotate the motor until it drops down fully seated. You can then rotate the motor until you come back the the compression stroke on number one cylinder and check your rotor alignment. Hopefully is will be lined up 10 degrees advanced and pointing directly at number terminal on the distributor cap.
If the distributor does not drop down when you first re-satb it, its because the oil pump shaft and the distributor shaft and not clocked right, but all you have to do is rotate the motor like I stated and it will drop into place.
10 degrees advanced should give you a good start up and then you can time it where you like, I think 12 advanced is nice. If you have 20 degrees advance in your distributor (mechanical) that would give you a total of 32, which should be safe.
The other critical factor is whether or not you have a 305 balancer or a 350. The 305 mark is at 12 O'clock and the 350 is at 2 O'clock. If you timing pointer on the timing cover is at 2 O'clock position and you have a 305 balancer the whole process I described above will be off and the motor will probably not run (maybe but it will be way retarded in timing)
I had a 305 balancer on my Goodwrench 350 and I couldn't find the timing mark while using my timing light because the timing pointer was a 2 O'clock. I then replaced the balancer with a 350 and all was good. There is a way to remark the 305 balancer but I don't' know how.
My 305 balancer was very thick looking compared to my new 350 balancer.
One other thing.......when you adjusted the valves, it should be when the exhaust valve BEGINS to open you can adjust the intake on the same cylinder, and then when the intake BEGINS to close you can adjust the exhaust. So when you see the beginning of the closing or opening is when you adjust.
Ok, one more thing :) 10 degrees advanced on the timing pointer is to the left of 0, each mark is 2 degrees.....of course if its a stock pointer.
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One other thing.......when you adjusted the valves, it should be when the exhaust valve BEGINS to open you can adjust the intake on the same cylinder, and then when the intake BEGINS to close you can adjust the exhaust. So when you see the beginning of the closing or opening is when you adjust.
I did the intake valve the way you described, but the print out I followed had me adjust the exhaust valve just before the intake is fully closed.
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So going back to the beginning of this post a bit and talking about vacuums lines. I was on edelbrock.com watching troubleshooting videos on the carb that I have. I have an automatic trans and noticed that where they say to plug the vacuum line for an automatic transmission, is not where the previous owner has it going. Mine attaches to a line from the manifold which splits off, one goes to brakes, the other goes behind engine to where I can't see (guessing it goes to the transmission) Would that be a potential reason as to why the engine wanted to stall out once put into gear?
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The manifold vacuum is good so thats not the problem.
Sometimes when putting the transmission in gear and it stalls, it is because you have a large cam and you need a higher stall torque convertor. I don't think this is your problem.Another could be you have the idle set too low.
It may still be you have vacuum leak somewhere, causing poor idle and then killing the motor once in gear. I would plug all vacuum ports for now and try to get the motor to run. Then add each vacuum line one at a time until you find a problem.
Using a vacuum gauge connected to a full manifold vacuum source can help.