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| Carburetor idle problems https://slantsix.org/forum/viewtopic.php?t=33693 |
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| Author: | SlantSixDan [ Wed Feb 18, 2009 10:00 am ] |
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I fixed your link — the only problem was that you put a period at the end of it. You can't do that with any punctuation at the end of any URL. You have to put a space after the last character of the link, before any punctuation. I misread/misunderstood what you had originally stated — the machined washer ears on the exhaust manifold are usually slightly thinner than those on the intake, to allow the exhaust manifold runners to shift and drift with thermal cycling. I may have run into this what you show (exhaust ears thicker than intake) before, but if so, I don't recall it! |
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| Author: | sam03v [ Mon Feb 23, 2009 6:03 am ] |
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Yeah, I'm wondering if the intake I bought off ebay was modified by someone else. I used the truck this weekend and it seems okay. The idle is still high. I set the timing to ~8-10 BTDC and also turned the idle set screws in a bit to slow it down. Now its at 850-900 once warmed up. According to the literature I'm supposed to turn the idle screws in until the engine stumbles then back them out until max rpm is achieved but no further. If I do this the idle will be 1100 rpm. So I turned them in until it stumbled and backed them out ...but not until max rpm. Is there anything wrong with doing this? |
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| Author: | SlantSixDan [ Mon Feb 23, 2009 6:59 am ] |
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You do realise the idle mixture screw(s) is/are different from the idle speed screws...right? There are two idle speed screws — one for cold idle when the choke is on, the other for hot "curb" idle. Then there are one or two idle mixture screws, to control the fuel/air mix at hot (curb) idle. I've added adjustment info to this post. |
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| Author: | sam03v [ Mon Feb 23, 2009 10:00 am ] |
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Quote: You do realise the idle mixture screw(s) is/are different from the idle speed screws...right? There are two idle speed screws — one for cold idle when the choke is on, the other for hot "curb" idle. Then there are one or two idle mixture screws, to control the fuel/air mix at hot (curb) idle.
Yes, I understand the difference. When I said "idle set screws" I should have said "idle mixture screws" .Separate problem/question: The charcoal canister is not hooked up yet(the previous owner disconnected it). Should I leave the vent from the carb open to atmosphere or blank it off? I have left it open so far.. |
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| Author: | SlantSixDan [ Mon Feb 23, 2009 10:21 am ] |
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Definitely leave the bowl vent open if it's not hooked to the charcoal can. Make sure the other ports (purge, etc.) are blocked off to avoid creating vacuum leaks. Does this carburetor have a small hole in each throttle plate? |
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| Author: | sam03v [ Mon Feb 23, 2009 11:37 am ] |
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No, it doesn't have the holes in the throttle plates. I checked them for the holes the last time I had the carb off. |
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| Author: | sam03v [ Tue Feb 24, 2009 5:31 am ] |
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Is it possible that the throttle plates are slightly open when they should be closed? Is there an adjustment to make sure the plates are all the way closed besides the idle speed screws? |
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| Author: | SlantSixDan [ Tue Feb 24, 2009 6:55 am ] |
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It's certainly possible the throttle plates are not closing all the way, if they were removed from the throttle shaft for some reason and not reinstalled correctly. It's also possible you've got air leaking past the throttle shaft/throttle body junction. If you squirt carburetor cleaner at either end of the throttle shaft, does it get sucked in and does the idle change? |
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| Author: | sam03v [ Tue Feb 24, 2009 7:42 am ] |
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Quote: If you squirt carburetor cleaner at either end of the throttle shaft, does it get sucked in and does the idle change?
Nope. Tried that last night. Sprayed "Seafoam" at each end of the throttle shaft and no idle change. (The seafoam worked for finding the intake manifold leak.)It looks like the gasket between the upper housing of the carb and the lower housing might be leaking. It looks wet all the time, but it is not dripping fuel. I sprayed seafoam all around the gasket but didnt' hear any changes. I'm half tempted to buy a rebuild kit, but my gut says it'll be a waste of money at this point. |
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| Author: | sam03v [ Thu Feb 26, 2009 5:39 am ] |
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I think I'll get the dummy award here,but it seems I've found the problem. I took the PCV valve out of the valve cover and removed the hose from the carburetor. Then I plugged the PCV port on the carb and left the valve cover PCV valve port open. Started the truck and the idle was about 500 rpm and the engine was stumbling a bit. I was able to get the idle at 750, and the distributor advance seems to be doing something now. Before when I had the high idle and plugged the distributor advance hose to adjust the timing there was no difference in the idle.. now there is. Took the truck for a ride and it definitely runs better and has more power above 50 mph. So does this mean I just had a bad/plugged PCV valve or hose? I previously had taken the PCV valve out and shook it and also sucked on the hose (tasted good ) and I thought it was okay. I think I understand what happens with a plugged PCV valve, but could someone explain it to me? I've got a real shop manual now and have read how the ventilation system works, but there isn't any specifics on what happens when the valve is plugged. Thanks in advance, |
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| Author: | SlantSixDan [ Thu Feb 26, 2009 6:13 am ] |
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If the PCV valve (or hose, or carb port) is plugged, you'll get less idle air than intended, which will slow the idle down substantially. If the PCV valve is faulty, though, and the shuttle is stuck or broken (or the hose is cracked), then you'll get much more idle air than intended, which will speed the idle up considerably. Perhaps that was your problem - what happens with a new PCV valve, grommet, and hose? |
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| Author: | sam03v [ Fri Feb 27, 2009 2:03 pm ] |
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I put a new valve and hose in last night. The grommet was still good. Drove the truck to work this morning. Ran okay, but the idle was about 850 and it dieseled a bit when I shut it off so I'm gonna bump up the timing. Hopefully this weekend i'll get it all straightened out... |
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| Author: | sam03v [ Mon Mar 02, 2009 7:56 am ] |
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Still idling at about 850-900 and there is also a whistling coming from the carb air horn. If I cover half of the air horn with my hand it goes away. The whistle is definitely coming from inside the carb. I assume this is a leak that is not helping the idle. Anybody else come across this? |
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| Author: | Rug_Trucker [ Tue Mar 03, 2009 5:35 am ] |
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whistling is a lean condition. While it is running jiggle the throttle shaft and see if the sound changes. AFA the fuel leak, the tops warp. I have rebuilt 2 BBD's in the last couple of weeks. They spend some time on the statioary belt sander to flatten them. The last one I did was a pain because the hole where the metering rod piston dropped through the top it was raised and I didn't want to grind that off.. One of those carbs was really warped really bad. I also flip the main body over on the sander. |
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| Author: | SlantSixDan [ Tue Mar 03, 2009 6:40 am ] |
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Quote: whistling is a lean condition.
H'mm. I've never seen or heard of this diagnostic. Whistling as an air leak, yes, but as a direct indicator of a lean condition…? Interesting.
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