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Engine still will not run more than 4 or 5 seconds
https://www.slantsix.org/forum/viewtopic.php?t=66443		 Page 2 of 2
Author:  matv91 [ Sun Feb 13, 2022 5:34 pm ]
Post subject:  Re: Engine still will not run more than 4 or 5 seconds
https://www.autozone.com/emission-contr ... 435518_0_0 for bottom steel gasket might work
Author:  k7seh [ Tue Feb 15, 2022 12:00 pm ]
Post subject:  Re: Engine still will not run more than 4 or 5 seconds
I got things put back together yesterday and finished the details this morning. The engine will start but has some backfire, and after warming up a bit the vacuum was pretty steady at about 5 Inches if the throttle was not moved. Number 3 exhaust port still has a gap of about 0.015" between the gasket and the manifold flange. There is no gap between the manifolds now, and the exhaust is going through the header pipe which is cut off of the tailpipe for now to allow me to remove the header when I could not remove it from the manifolds. My vacuum interpretation charts are telling me there is a vacuum leak in either the carburetor or the intake system. There are only 3 things that can leak. The carburetor, which has gaskets on either side of the riser. The manifold gasket, which I am fairly certain is not leaking, and the power brake booster, which I think I checked leaks a few months ago, but I will check it again. I have another cleaned and ready carburetor to try if I need it. I don't want to use it because it is a manual choke model unless I can transfer the automatic choke components over to it. I don't have a machine shop near me, so I might try adding a piece of one of the old gaskets on the leaking exhaust port. At least now I can keep it kind of running once I build a little heat in the engine, so I guess that is progress.
Author:  k7seh [ Tue Feb 15, 2022 1:38 pm ]
Post subject:  Re: Engine still will not run more than 4 or 5 seconds
I assembled most of the manifolds and finished other details this morning. There is still a 0.015" gap between the manifold gasket and the number 3 exhaust port. All other port surfaces are tight now. There is no gap between the manifolds so that connection is sealed. The exhaust is going down the header pipe which is cut off of the tail pipe to allow me to remove it with the manifolds before I freed up the bolts that hold it on. Now I can start the engine and it will continue to run with a lot of coaxing during warm up. The engine randomly backfires. Once a little heat is built up in the engine the vacuum gauge shows me about 5 inHg when the throttle is steady but still backfires at times. From what my vacuum reading information says this is likely a vacuum leak somewhere in the intake system. I think the manifolds are now sealed, so that leaves the carburetor and the power brake amplifier. There are no other vacuum accessories on the truck and the caps on the vacuum tower are all capped with new caps. I remember testing the power brake amplifier a while back and it passed then. I will check it again. As a last resort I can put the original carburetor back on the engine. It is a manual choke, and I don't want to use it, but it is all rebuilt and ready to go. The carb now on the engine has an automatic choke and has been cleaned up and the idles passages cleared, but the gasket between the upper halves were not changed. I think it is in good condition, but I don't know what it would do if there is a leak there. The PCV valve is free and has been cleaned, but not replaced. Could this be a cause of my problem?

Unfortunately, there is not a machine shop in my area, so I am going to cut a small piece from an old exhaust gasket and try to fill the gap without causing a leak on the adjacent intake port for now. Another 0.015" to fill is asking a lot without having the manifolds machined to guarantee they are all flat and will fit tight against the head. In spite of trying every way I can look by comparing valve positions and using a camera looking at #1 piston compared to the crankshaft position, I am still wondering if the chain has slipped one tooth on the gears, and how hard that is to detect without opening up the timing chain cover.
Author:  Rick Covalt [ Tue Feb 15, 2022 2:27 pm ]
Post subject:  Re: Engine still will not run more than 4 or 5 seconds
I don't mean to be a downer, but you really just need to bite the bullet and fix the known leak you have. It will continue to leak and only get worse. Get the manifolds all flat and tight and then you are set to figure out if it really is something else. You can disconnect and plug the PCV and Brake boosters altogether and see if that changes how it runs.
Good luck.
Author:  volaredon [ Tue Feb 15, 2022 3:44 pm ]
Post subject:  Re: Engine still will not run more than 4 or 5 seconds
Like Rick said.
Since you know already that you have warped gasket surfaces, I'd have taken the manifold set that you intend to run "as a set" to a machine shop and have it resurfaced already,/ so I could totally ELIMINATE that possibility from causing a problem again/ (unless you like redo's and chasing your tail that is) There are places that are "OK" to "try it and see" and there are places NOT ok to do so' You have an admittedly known issue with your setup. fix it right, THEN reassemble, and see what you get.
you could get another intake and/or exhaust manifold/ but especially if you have to have it shipped, you could have the problem corrected on the parts you already have for less money and less hassle and probably sooner. and know it won't be an issue again, with those parts? We're dealing with 40+ year old castings that have been heated and cooled who knows how many times?
with only 5" on the vacuum gauge, you have a serious vacuum leak. Could be a warped intake manifold yet, as well. even if you can't get a feeler gauge between manifold and gasket. (which isn't the right way to check for warp, anyhow) and who's to say that any replacement parts you may get your hands on, aren't warped, too?

If there's any way you can beg or borrow a precision "machined flat" straight edge, Id set that against the (bare) head and try my feeler gauge in there, too when you have it all back apart again..... if there is warp on the head, you may have to yank the head and have that surface machined flat, as well. AND THEN reassemble and use the Remflex gasket to assemble as has been suggested. You're just creating so much more work (and expense in rebuying gaskets each time) by trying to piece meal everything.

I have $150 in machine shop services just on my exhaust manifold, on my motor. But I already had lots of my own time and expense for my air compressor running/ plus various carbide burrs, in porting and deburring that manifold. I had to have all 5 bolts (3 hold manifolds together, 2 hold exhaust pipe flange to manifold outlet) lasered out, because they all busted. It was either that or throw it away, get another manifold, and start all over again. I wanted to preserve all of my time I had invested already, at that point/
Author:  k7seh [ Mon Jul 18, 2022 12:07 pm ]
Post subject:  Re: Engine still will not run more than 4 or 5 seconds
It has been a while since I posted an update. I replaced the timing chain and gears, after which I needed to move the distributor one tooth and now I hear the points snap at the center of the adjustment rotation. The truck still would not run well at all. Like it was not getting enough fuel, which the new plugs also indicated. Because the fuel in the tanik is over a year old I put an electric pump in and fed fuel from the 5 gallon fuel tank for my lawn mower. When I turned the pump on I saw a 1/8" stream of gas coming from the bottom of the carburetor fuel bowl. After removing the carb and inspecting it there is a plug shown in the picture that is leaking fuel out of the fuel bowl. I have the original rebuilt manual choke carb for the truck, so I swapped the choke components over and now the original carb has an automatic choke. The carb pictured on the left is the original carburetor. The carb on the right according to the Carter carb manual and its internals is a true Super 6 carburetor. Too bad the bowl leaks. The battery is dead (my fault) so I have to wait to see what happens. I forgot I needed a return spring for the original carb. Not being able to find the bracket I made a new spring anchor bracket. While fitting it I saw a drip from the original carb. Is there a problem with this plug, and if there is, is there a fix?

Attachments:
File comment: The carb on the left is the original carb. On the right is a later Super 6 carb with the leaking fuel bowl.
both_carbs.jpg
both_carbs.jpg [ 67.77 KiB | Viewed 1210 times ]
File comment: This is the plug that was leaking from the fuel bowl.
leaking_plug.jpg
leaking_plug.jpg [ 50.89 KiB | Viewed 1210 times ]
Author:  Jase [ Tue Jul 19, 2022 8:45 am ]
Post subject:  Re: Engine still will not run more than 4 or 5 seconds
Random thoughts:

1) Are you still using the electric fuel pump? If so it may be delivering excessive pressure to the carb, causing leaks. 5 to 7 PSI is the max fuel pressure commonly used in a carb. Some only tolerate 2 or 3 PSI.. I believe your BBD's will do ok with 5-7. That needs to be addressed first. I would go back to the last known combination that did not leak in terms of fuel pump and carb setup. Then start searching for the vacuum issue.

2) Does the engine run better when the choke is closed or partially closed?

3) 5" of vacuum is a pretty large vacuum leak... unless you have a modest vacuum leak, and retarded timing. Plug off all the vacuum lines, and manifold ports. Use some carb cleaner with the straw to carefully explore where the excess air is getting into the system with the engine running. When you find the spot, idle speed will increase. Avoid hosing down large areas as then the engine will ingest the carb cleaner through the air filter/air horn and give you a false positive.
Author:  Rick Covalt [ Tue Jul 19, 2022 8:59 am ]
Post subject:  Re: Engine still will not run more than 4 or 5 seconds
Quote:
I replaced the timing chain and gears
Did you degree the cam?
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