1986F150Six Posted October 27, 2020 Share Posted October 27, 2020 Wow! Thanks! That is an incredibly generous offer. Let me take a look at everything when I get home. If it seems like I may need a MAP Ill let you know! I could even return it after I do my intake and carb etc. And now I have some good reading to do as well! Thanks David! A high idle is often caused by a vacuum leak. Look on the intake manifold in the area under the carburetor. There is a vacuum "tree" which has 6 or 7 ports, to which are attached several vacuum hoses. Not all ports are used as it depends on options. This area is covered with numerous vacuum lines [hoses and plastic] as well as wiring. One of the ports is angled toward the cab and is nearest the engine block and exhaust manifold [high heat]. This port is difficult to see and when spraying with carb cleaner, looking for vacuum leaks, is easy to miss. The rubber cap gets hard and brittle with age and cracks, creating what can be a large vacuum leak. I found this condition on two trucks, both with what appeared to be original caps [1984 and 1986 with 4.9L engines]. Link to comment Share on other sites More sharing options...
StraightSix Posted October 27, 2020 Author Share Posted October 27, 2020 A high idle is often caused by a vacuum leak. Look on the intake manifold in the area under the carburetor. There is a vacuum "tree" which has 6 or 7 ports, to which are attached several vacuum hoses. Not all ports are used as it depends on options. This area is covered with numerous vacuum lines [hoses and plastic] as well as wiring. One of the ports is angled toward the cab and is nearest the engine block and exhaust manifold [high heat]. This port is difficult to see and when spraying with carb cleaner, looking for vacuum leaks, is easy to miss. The rubber cap gets hard and brittle with age and cracks, creating what can be a large vacuum leak. I found this condition on two trucks, both with what appeared to be original caps [1984 and 1986 with 4.9L engines]. Ok- I found two problems I believe. One was a vac hose coming off of the carb right at the throttle plate on the passenger side. It wasnt hoing anywhere, but I found a bent metal tube that goes from under the carb town to below the exhaust manifold that was the right distance so I hooked it up. My surge is gone but Im not convinced that hose is what fixed it. I also found an open port on the vacuum distribution tree you all told be about. It was indeed drawing a lot of air. The engine sounds different after plugging it but still idles at 1100. So Im headed to the gas station to do something I never thought I would do- buy a swisher sweet. Link to comment Share on other sites More sharing options...
StraightSix Posted October 27, 2020 Author Share Posted October 27, 2020 Ok- I found two problems I believe. One was a vac hose coming off of the carb right at the throttle plate on the passenger side. It wasnt hoing anywhere, but I found a bent metal tube that goes from under the carb town to below the exhaust manifold that was the right distance so I hooked it up. My surge is gone but Im not convinced that hose is what fixed it. I also found an open port on the vacuum distribution tree you all told be about. It was indeed drawing a lot of air. The engine sounds different after plugging it but still idles at 1100. So Im headed to the gas station to do something I never thought I would do- buy a swisher sweet. The "smoke test" showed me a leak around the bowl of my carberator on the front side between the main housing and the "lid". There was also a minor fuel leak there. I tightened down the few bolts there (they were barely finger tight), and my idle dropped from 1100ish to 1000ish. But I just saw a fuel drop drip from that spot. I guess that the fuel drip means that spot isnt sealed up. Maybe it got a little better when I tightened the screws. Is it likely that the vac loss through that spot would cause my high idle? Now I need to figure out what to do. I really dont want to spend a lot of time on this carb since its all coming out in about 35 days anyways for that upgrade but I dont think its wise to drive around with a fuel leak right over the exhaust manifold. Drats. Im sure you can buy the carter 1bbl rebuild gasket kits at any decent parts store. With nothing else showing up on the "smoke test" Im sorta at a hault. As always, thanks for any advice. Btw, I did get those free exh manifolds! The fellow was in a big hurry and didnt have time to talk about the rest but I srill think it was a really good deal. Link to comment Share on other sites More sharing options...
Gary Lewis Posted October 27, 2020 Share Posted October 27, 2020 The "smoke test" showed me a leak around the bowl of my carberator on the front side between the main housing and the "lid". There was also a minor fuel leak there. I tightened down the few bolts there (they were barely finger tight), and my idle dropped from 1100ish to 1000ish. But I just saw a fuel drop drip from that spot. I guess that the fuel drip means that spot isnt sealed up. Maybe it got a little better when I tightened the screws. Is it likely that the vac loss through that spot would cause my high idle? Now I need to figure out what to do. I really dont want to spend a lot of time on this carb since its all coming out in about 35 days anyways for that upgrade but I dont think its wise to drive around with a fuel leak right over the exhaust manifold. Drats. Im sure you can buy the carter 1bbl rebuild gasket kits at any decent parts store. With nothing else showing up on the "smoke test" Im sorta at a hault. As always, thanks for any advice. Btw, I did get those free exh manifolds! The fellow was in a big hurry and didnt have time to talk about the rest but I srill think it was a really good deal. If you have a drip from the carb between the body and the top then the float level is way too high. WAY too high. It really shouldn't leak there, but the fuel level should never be that high. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted October 28, 2020 Share Posted October 28, 2020 If you have a drip from the carb between the body and the top then the float level is way too high. WAY too high. It really shouldn't leak there, but the fuel level should never be that high. Ill add that vacuum leak above the throttle butterfly can not increase idle speed. It would have to be at the base of the carb or somewhere on the intake manifold. Link to comment Share on other sites More sharing options...
StraightSix Posted October 28, 2020 Author Share Posted October 28, 2020 Ill add that vacuum leak above the throttle butterfly can not increase idle speed. It would have to be at the base of the carb or somewhere on the intake manifold. Thanks guys. I already talked myself into the rebuild kit for the carb and Ive picked ut up and just got back home. Sounds like I srill have a vac leak after that though. Â Link to comment Share on other sites More sharing options...
StraightSix Posted October 28, 2020 Author Share Posted October 28, 2020 Thanks guys. I already talked myself into the rebuild kit for the carb and Ive picked ut up and just got back home. Sounds like I srill have a vac leak after that though. Well, Ive got the "top" off of the carb and everything seems ok. The float/needle assembly looks fine, the old gasket was showing signs of a good seal all around and the fuel level in the bowl is about 3cm below the rim. Its seems pretty clean too. Im at a bit of a loss for where the air and fuel were coming from. Perhaps the air was leaking through the loose "lid" and the fuel was actually coming from the fuel filter that threads in right there? Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted October 28, 2020 Share Posted October 28, 2020 Well, Ive got the "top" off of the carb and everything seems ok. The float/needle assembly looks fine, the old gasket was showing signs of a good seal all around and the fuel level in the bowl is about 3cm below the rim. Its seems pretty clean too. Im at a bit of a loss for where the air and fuel were coming from. Perhaps the air was leaking through the loose "lid" and the fuel was actually coming from the fuel filter that threads in right there? One thing that's not at all uncommon with these carburetors is that the body comes loose from the base because vibration causes the screws to back out. It's recommended to apply blue Loctite on the screws before putting it back together. Link to comment Share on other sites More sharing options...
StraightSix Posted October 28, 2020 Author Share Posted October 28, 2020 Well, Ive got the "top" off of the carb and everything seems ok. The float/needle assembly looks fine, the old gasket was showing signs of a good seal all around and the fuel level in the bowl is about 3cm below the rim. Its seems pretty clean too. Im at a bit of a loss for where the air and fuel were coming from. Perhaps the air was leaking through the loose "lid" and the fuel was actually coming from the fuel filter that threads in right there? The fuel leak culprit! The fuel has been leaking through the crimp on this two piece fuel filter. I can only assume that some air may have been escaping from the fuel bowl and that tightening the screws did solve it. Either way, everything but the fuel filter is put back together now and seems to be holding. Still idling around 1000rpm. Presumably I still have a vac leak somewhere. Link to comment Share on other sites More sharing options...
Gary Lewis Posted October 28, 2020 Share Posted October 28, 2020 The fuel leak culprit! The fuel has been leaking through the crimp on this two piece fuel filter. I can only assume that some air may have been escaping from the fuel bowl and that tightening the screws did solve it. Either way, everything but the fuel filter is put back together now and seems to be holding. Still idling around 1000rpm. Presumably I still have a vac leak somewhere. I frequently liken these truck to onions. We peel the problems, layer by layer, and cry. But eventually we have enough onion rings for a Blooming Onion! So, one problem down and more to go. Yep, you probably have a vacuum leak causing the fast idle. Link to comment Share on other sites More sharing options...
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