Quote:
I'm thinking the intake manifold has a vacuum leak or maybe timing chain has jump a tooth.
Your vacuum gauge should answer this shouldn't it?
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| How to diagnose a intake manifold leak? https://www.slantsix.org/forum/viewtopic.php?t=55519 |
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| Author: | Sean Mallory [ Wed Jun 04, 2014 7:39 am ] |
| Post subject: | How to diagnose a intake manifold leak? |
I'm nearing wit's end with my 1980 truck. Missing/stumbling at idle bad. I've tried multiple carbs and everything I know. I'm thinking the intake manifold has a vacuum leak or maybe timing chain has jump a tooth. Recently I bought a NOS Holley reman, which is definitely the right 1945 for my truck. When I adjust the curb idle speed on the carb, there is a spot where the motor starts running way worse. The adjustment is not smooth. Is there anyone on this forum that builds /6s? I am at a point where I am likely going to find a local shop to build a complete motor for me. Basically I have given up and the /6 appeal is waning. After work, I'm spending each evening in the garage getting nowhere. |
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| Author: | Danarchy [ Wed Jun 04, 2014 8:47 am ] |
| Post subject: | |
Do you have a vacuum gauge and timing light? this article is a simple and helpful start. http://classicinlines.com/vacuum.asp |
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| Author: | rlklaus [ Wed Jun 04, 2014 8:57 am ] |
| Post subject: | |
I'm a little hesitant to post this, but: Have a fire bottle handy, put a small amount of fuel in a spray bottle. Idle the engine and spray a bit of fuel on the gasket area. You will hear a change in the idle if you hit a leak. This is an old school test, and does have it's hazards. I fact I would be extra careful on a slant six, as you will be spraying fuel onto the exhaust manifold as well. |
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| Author: | wjajr [ Wed Jun 04, 2014 9:23 am ] |
| Post subject: | |
Quote: I'm a little hesitant to post this, but: Have a fire bottle handy, put a small amount of fuel in a spray bottle. Idle the engine and spray a bit of fuel on the gasket area. You will hear a change in the idle if you hit a leak.
Yiakes! More like old phool... LOLThis is an old school test, and does have it's hazards. I fact I would be extra careful on a slant six, as you will be spraying fuel onto the exhaust manifold as well. Just spray carburetor cleaner around gaskets of intake system. No back flash if it catches a flame, and tis stream is easily controlled and directed. A warped carburetor base may be hard to find by spray alone as it is too large a leak; remove carb, and put a straight edge on its base in several directions looking for gaps. If power brake equipped check booster for vacuum leak. |
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| Author: | Sean Mallory [ Wed Jun 04, 2014 9:31 am ] |
| Post subject: | |
hey thanks for the replies gents I got a reman brake booster on order. Yes I have vacuum gauge, timing light, even an old Sears engine analyzer. I've spent many hours playing with the idle and mixture screws and the timing. I called a highly reputable shop today and I am going to drop her off next week and let those guys keep her as long as they need. I might try the spray bottle check. I hold myself responsible for any advice I may heed. Edit I have some carb cleaner on the shelf. |
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| Author: | DadTruck [ Wed Jun 04, 2014 12:29 pm ] |
| Post subject: | |
what do you mean by Quote: NOS Holley reman
is it NOS?or remanufactured? carbs rebuilt by the mass-remanufacturers can be troublesome and have you set the idle air fuel mix, adjust for max manifold vacuum,, but remember to bring down the idle speed between changes. http://forums.holley.com/entry.php?429- ... lley-Carbs |
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| Author: | Danarchy [ Wed Jun 04, 2014 12:44 pm ] |
| Post subject: | |
Quote: I'm thinking the intake manifold has a vacuum leak or maybe timing chain has jump a tooth. Your vacuum gauge should answer this shouldn't it?
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| Author: | Sean Mallory [ Wed Jun 04, 2014 12:56 pm ] |
| Post subject: | |
Reman by Holley I said NOS because the PN is discontinued I am getting 17 on the vacuum gauge but it jumps all around because of the missing. Basically this problem is out of my league methinks. |
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| Author: | wjajr [ Thu Jun 05, 2014 5:28 am ] |
| Post subject: | |
Quote: I am getting 17 on the vacuum gauge but it jumps all around because of the missing.
May be missing because of stuck valve, or incorrect valve lash adjustment.
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| Author: | Sean Mallory [ Thu Jun 05, 2014 6:59 am ] |
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I adjusted the valves live. Took two days to do it. But I have never done that before. Every vehicle of mine before this was done statically. Maybe I screwed them up. Anyway, I'll report back in awhile when I get her from the shop. |
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