Hello,
This is a continuation of a continuing project that I have been working on. I had changed my dads heads on his truck and we are just getting it back together and it sounds strong but it won't idle. I checked the vacuum lines and some are clogged so I will be changing them. I checked the EGR and its was clogged and I cleaned it out and it still won't idle. I was wondering if you can help me? Am I forgetting to check anything here?
Thanks.
Do you have access to a vacum gauge and can you read vacum at a idle? (what it is and how it acts before it dies)
I can't get it to idle. It simple dies. It won't even get close to idle before it dies. I can have it run at high speeds though. I checked the timing and it was very advanced but that could be because its running so fast. Do you know how it runs when the vacuum line in the front of the carb is disconnected? Or if the EGR is open and it just dies instead of idling that's how its running. I checked the vacuum lines up front and plugged the EGR and it still is doing it.
I don't have a vacuum gauge either.
Valves adjusted ok. Any backfiring thru the carb.
Some but it could be the timing issue because it clears up when I adjust it out.
Might be worth it to get a hold of a compression tester and find out if each cylinder is capable of creating vacuum.
I would aquire a vacum gauge too because it could be VERY helpful here.
I agree......It may the wrong base gasket under the carb causing a major vacuum leak
I thought that I followed the installation procedure when I installed the intake. I even waited for the PCV to dry in the corners before I put the intake back on. I didn't remove the carb but I will check all those spots to see how they are sealed.
I was wondering what the compression should be on the cylinders though? I did come across a compression tester.
I am not getting all the post in my news reader. I don't know why either.
Since you did remove the heads it's best to start at the beginning where vacuum is created and go from there. Compression could be as high as
150psi. So let's use 100psi as minimum acceptable. Disconnect the coil wire to be sure the engine won't start and set the carb to stay wide open. Hook up the gauge and turn the engine 4 compression strokes. Watch the gauge on each stroke...a low reading on the first stroke which does not build up on the following strokes indicates leaking valves, blown head gasket, or even a cracked head. If you have two adjacent cylinders with similar low compression it's most likely the head gasket not sealing.After you replaced the heads, what method did you use to adjust the valves.
I started at TDC on the #1 piston set the rocker arm by twisting the push rod until it had a little drag then I rotated the crank 90 degrees to the next cylinder in the firing order and did the same for all of them. I got back the #1 plug and set the other rocker by setting the lash with a little drag. I had a friend help that might not have moved the correct 90 degrees because he didn't understand why I wasn't setting the lash while the engine was running so I might have over set the lash on a few. I did notice some backfiring when I started the car and put a load on it.
I think I have to start over setting the lash. And then check the timing again. If it idles I could check for a vacuum leak in the intake manifold.
I was going to change the carb because the one on there sucks. But I still am not sure where I should be focusing on. The carb I was looking at is a edelbrock 650. But I don't know if it will be to much.
When starting on #1 TDC lift the distributor cap to see if the rotor is pointing at the #1 terminal. At this point the lifters for both intake and exhaust should be off the cam lobes (valves closed). Check the rotor to terminal position as you go down the firing order. You more than likely have hydraulic lifters but the set up you describe would be more correct for solids. Once you know you are on the #1 compression stroke go ahead and adjust both intake and exhaust in the same method as you did earlier before moving on to #8. Turn 90 then set both for #8. Turn 90 then on to 4, 3, 6,
5, 7, 2. If in fact these are hydraulic lifters...once you have the free spin out of the push rod, give the ratchet an extra 1/2 to 3/4 turn. Once you have these base settings and are reusing the original cam and lifters it may be necessary to do as your friend suggests and make a final adjustment with the engine running. You mention the carb...this could also be the cause of poor or no idle. If it's a quadrajet...personally I would clean and rebuilt it as opposed to the edelbrock. But first things first, set the valves and check the compression.
A vacum leak is not going to show up in a compression check! He need to buy or borrow a vacum gauge as it will tell you EXACTLY what is wrong (if it is a leak and how bad it is. That year engine should idle at around 16 to 20 inches or vacum and hold that range as reved up under no load once RPM?s stabilizes. If you are seeing a lot less vacum then you have a leak. If the vacum gage fluxs badly it could point to valve problems or improper lifter adjustment.
When you set the "lash" on that year engine, the correct why is to make sure you are on the correct spot for that cylinder and then tighten rocker stud bolt to zero clearance then add 3/4 of a turn more for proper preload and posititioning of plunger in lifter bore.
Not looking for vacuum leak at this point. He had the heads off. Engine won't idle. Backfiring thru carb. He said he's not convinced that the valves are set correctly. His method of adjustment indicates that they probably are not. I'm suggesting a compression check to see what he has or reset in a different manner.
I understand what you are saying but a misadjusted lifter may or may not show up in a compression test becuase it has not pumped up yet. Also a bad vacum leak will cause very lean mixtures in some cylinders and can cause severe back firing too. In the mid to late 70?s, new cars backfired a LOT through carbs, especailly when cold because of very lean cold mixtures for emissions purposes. A overly lean engine mixture can backfire through carb a lot but granted is not the only cause of it but one of the most common causes.
Ok I just got a chance to work on it again. I pulled the valve covers and set the #1 to TDC and checked the rotor and it was pointing at the #1 plug wire. I figure this was on the compression stroke so I tightened the valves closed again. (There were few that were loose too) I went on the next one setting the lash again for each one. Some needed it some didn't. I started finished and we started it up. My dad pushed on all the valves and he didn't tighten any down. So I guess it passed his inspection. While it was stated and with the valve covers off we put it in gear. There wasn't any backfiring thru the carb this time. I was happy to see that. But we couldn't advance the timing anymore either. And when it got down to what seemed like a good idle. And was checking the timing the mark was very advanced. Like 1-2 inches past the last mark on the timing mark thingy. We tried to retard it a little and it was coming back too. But then it started ticking. So we advanced it and the ticking stopped. But it is back to where we started. The carb that is on it now came off my brothers truck and is a manual chock. I don't really know if its a POS. But we bought a Holly II remained Quadra or Rochester that we are looking to put back on it. The old carb that we pulled off had an electric choke and this one has a vacuum choke. I don't know if this matters though?
We will put it on in the morning and see what if any difference it makes. But I think that I should add that I had to set the idle high on the old one just to get it to run and when its turned off there is a cloud of smoke that comes from the carb and it lingers there like fog. I know its gas but I don't know for sure if its the idle of the fuel pump that is adding so much gas that it flows like that. My dads truck vapor locks during hot weather so he put a electric fuel pump in there. And the truck fires right up. It could mean that his old fuel pump is bad because its not delivering the gas in hot weather. Or that the electric inline fuel pump is to strong.
When let me know what I can do and if I am missing something?
D.L. Man
Egads, Stop the torture. Tow the dang thing to a Mechanic! Charles
Sounds like you are making some progress. Did you reset ALL the valves whether they were loose or not and did you give the ratchet an extra 3/4 turn. Just to rule some things out...did you remove the distributor or timing chain at any time. Check the vacuum advance on the distributor. Take the vacuum line and suck the air out and look to see if the rod on the advance is moving. If it does not move or cannot hold the vacuum it will need to be replaced.
I did turn the valves another turn before we put the valve covers back on. I didn't mess with the timing chain. I did have to remove the distributor though.
I will check the vacuum advance also.
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