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I've discussed this on another thread, and had thought it was taken care of. My '84 F-150 is idling REALLY high, like 3500 RPM. I just replaced some vacuum hoses, so I thought maybe there was a vacuum leak. I'm including a picture below, of this 'Bowl Vent Tube' on my carb. This nozzle has come loose before, and I can pull it out and put it back in. It feels like it gets wedged in there pretty tight. But, I started spraying around with brake clean to see if I could find a leak, and the idle dies down if I spray right around where the nozzle comes out. I put a hose clamp on the hose that connects to this nozzle to make sure the hose isn't the problem, and it didn't help. So it seems like I have a leak in this small gap between the nozzle and the carb housing. Maybe there is a slight bend in the nozzle, creating space? What can I do to plug this up? Is the nozzle supposed to just wedge in like that? Can I just glue it in with some kind of silicone?
That's just a bowl vent and cannot cause you any problems besides a gas smell when the truck is sitting. If you take your spray and spray directly down the throat, it should slow down like it did when you sprayed around that hose connection.
Looks like you have a 300 six with the computer system. 1st thing I would do is take all that stuff off and put a regular distributor on it. Your problems will go away.
Dave, is that correct? I thought it needed to be atmosphere pressure inside. Obviously needs to not have positive pressure, but idk that you want manifold vacuum either.
That's just a bowl vent and cannot cause you any problems besides a gas smell when the truck is sitting. If you take your spray and spray directly down the throat, it should slow down like it did when you sprayed around that hose connection.
Looks like you have a 300 six with the computer system. 1st thing I would do is take all that stuff off and put a regular distributor on it. Your problems will go away.
Okay, so it doesn't need to be sealed around that vent?
Maybe it is time to get rid of this ECM. Can I decouple the carb from the ECM simply by swapping out the distributer? What kind of distributer should I look for?
I should add, that when I push the choke plate closed, the idle dies down. I thought maybe that indicated a vacuum leak.
Yes it does and if it is at "3500 RPM" and comes down then it has to be a pretty big leak.
BTW I don't think it is 3500 RPM maybe 1500 to 2000 and even then think that is high.
With the bowl vent hose removed and motor running put your finger over that nipple did it change? It should not.
Put your finger over the hose end that you removed from the carb bowl vent did it change? It should not.
Does the carb cleaner have a little plastic straw? If not get one as that is the only way to use it to check for vacuum leaks.
Motor running spray around the base of the carb, along the intake manifold & head.
Power brakes? Pinch off the hose did it change?
Being you were near the carb grab it at the top and try and shake it, they like to come loose at times.
Dave ----
Okay, so it doesn't need to be sealed around that vent?
Maybe it is time to get rid of this ECM. Can I decouple the carb from the ECM simply by swapping out the distributer? What kind of distributer should I look for?
I don't know about the decoupling question. Not sure what happens to the carb when you take the distributor out of the equation. Not familiar with the Feedback System.
That said, the Duraspark 2 is a pretty typical route to take. You will need an ignition module, for one thing. AutoZone sells them for $30 with a lifetime warranty, part number F102. I use Summit for a lot of things, and they have the Motorcraft brand for $62.99. If you're a name-brand guy, that's an option. I gave my spare junkyard one away ages ago to a classmate trying to get a Bronco running that promised to give it back when he got a new one. It never happened.
You will also need a distributor. There again, you have options. Have the parts store of your choosing look up the distributor for a 1983 F-100 with the 300. I bought this Duralast Gold one with lifetime warranty for $76 for my new engine. My old one worked fine, I just wanted the new and shiny.
You may or may not need a coil. I don't know what coil those came with. The 1985 engine I put in my truck had a TFI style coil on a bracket in front of the fuel pump, so I assume yours might be the same? I think that one was feedback carb. There's a difference in resistance, I believe, the old one may work, but the preference would be to swap it out. I put this coil from Summit on my new engine because I liked the color lol, but any of them would work.
I know there's one more plug that goes to the factory harness, but you may just want to wire that one directly. EDIT: Never mind, if you want to keep the warranty on the module, might just want to get the plug...I don't have a part number for it, but it appears maybe an SMP S629 may work? With the third prong not being used? I am not sure on that one....
For the time it would take to build, I would personally buy the more, erm, painless option, but that has more to do with laziness than fiscal responsibility.
There's more in-depth wiring diagrams out there, but that should give you the general idea.
Adding to what he said, rockauto.com has the motorcraft icms for $50 and clipsandfasteners.com have the plugs to make your own harness in the $5 range last I checked.
I don't know about the decoupling question. Not sure what happens to the carb when you take the distributor out of the equation. Not familiar with the Feedback System.
That said, the Duraspark 2 is a pretty typical route to take. You will need an ignition module, for one thing. AutoZone sells them for $30 with a lifetime warranty, part number F102. I use Summit for a lot of things, and they have the Motorcraft brand for $62.99. If you're a name-brand guy, that's an option. I gave my spare junkyard one away ages ago to a classmate trying to get a Bronco running that promised to give it back when he got a new one. It never happened.
You will also need a distributor. There again, you have options. Have the parts store of your choosing look up the distributor for a 1983 F-100 with the 300. I bought this Duralast Gold one with lifetime warranty for $76 for my new engine. My old one worked fine, I just wanted the new and shiny.
You may or may not need a coil. I don't know what coil those came with. The 1985 engine I put in my truck had a TFI style coil on a bracket in front of the fuel pump, so I assume yours might be the same? I think that one was feedback carb. There's a difference in resistance, I believe, the old one may work, but the preference would be to swap it out. I put this coil from Summit on my new engine because I liked the color lol, but any of them would work.
I know there's one more plug that goes to the factory harness, but you may just want to wire that one directly. EDIT: Never mind, if you want to keep the warranty on the module, might just want to get the plug...I don't have a part number for it, but it appears maybe an SMP S629 may work? With the third prong not being used? I am not sure on that one....
For the time it would take to build, I would personally buy the more, erm, painless option, but that has more to do with laziness than fiscal responsibility.
There's more in-depth wiring diagrams out there, but that should give you the general idea.
Great, thanks. I'll probably come back with questions on the conversion. But I think I have a vacuum leak here, and I need to get that fixed first.
Adding to what he said, rockauto.com has the motorcraft icms for $50 and clipsandfasteners.com have the plugs to make your own harness in the $5 range last I checked.
Nice! Even better. I use RockAuto for some stuff, but Amazon gets it to me in 2 days with no shipping charge. And usually if I order from Summit it's over $100 so I get them free shipping and have it two days later. Only problem with RockAuto is having to pay shipping, if they aren't from the same warehouse, you pay more, yada yada. I do love their prices, though.
There's some really good threads on the DS2 conversion on this forum, too.
Yes it does and if it is at "3500 RPM" and comes down then it has to be a pretty big leak.
BTW I don't think it is 3500 RPM maybe 1500 to 2000 and even then think that is high.
With the bowl vent hose removed and motor running put your finger over that nipple did it change? It should not.
Put your finger over the hose end that you removed from the carb bowl vent did it change? It should not.
Does the carb cleaner have a little plastic straw? If not get one as that is the only way to use it to check for vacuum leaks.
Motor running spray around the base of the carb, along the intake manifold & head.
Power brakes? Pinch off the hose did it change?
Being you were near the carb grab it at the top and try and shake it, they like to come loose at times.
Dave ----
Okay, I'll try all this later tonight. But, is there any reason I shouldn't seal up that nozzle, and remove that as a possible culprit? I've got some weatherproof silicone sealant type stuff.
Great, thanks. I'll probably come back with questions on the conversion. But I think I have a vacuum leak here, and I need to get that fixed first.
Vacuum leak, maybe, maybe not. You would think if you were pulling in a lot of air, the engine would run fast, but run rough because of being lean. You would think spraying a fuel into the carb or holding the choke a little bit closed would make it richer and run even faster. It's hard to say. While all engines seem to be a little different, my feedback system would run fine during start up, but after it warmed up it would suddenly idle very fast and had a miss-fire. I traced it down to the timing was suddenly being advanced for whatever reason. Guess what controls the timing on the feedback system? The computer. I pulled the codes and had so many error codes, would have took hundreds of dollars, countless hours and hunting for obscure parts that I possibly would not have been able to find.
I then decided to convert. Like I said, all engines are different. In my case all I did was change the distributor and ignition module. I am still running the original computer controlled carb, the wires are just not hooked up. It runs so much better than it did before.
If you get a duraspark II distributor and ignition module and get the harness inbetween the dist and the module, the rest will plug right in to your original factory harness you have now, it's already wired for it. They had many different engine setups that used the same harness, some had the duraspark II system with this harness from the factory, your truck has it too.
Or you can buy a aftermarket HEI distributor and stab it in place and wire it in.
If you think you are having carb problems, you can get them new also online.(the regular type with no wires).
Yes it does and if it is at "3500 RPM" and comes down then it has to be a pretty big leak.
BTW I don't think it is 3500 RPM maybe 1500 to 2000 and even then think that is high.
With the bowl vent hose removed and motor running put your finger over that nipple did it change? It should not.
Put your finger over the hose end that you removed from the carb bowl vent did it change? It should not.
Does the carb cleaner have a little plastic straw? If not get one as that is the only way to use it to check for vacuum leaks.
Motor running spray around the base of the carb, along the intake manifold & head.
Power brakes? Pinch off the hose did it change?
Being you were near the carb grab it at the top and try and shake it, they like to come loose at times.
Dave ----
I tried most of this. The carb is bolted down tight. I removed the vent hose, plugged the nozzle and the hose with my finger, didn't notice a change.
The idle dies down with I spray on the back of the carb. I can't get back there very well, so I'm not sure what I'm spraying that's causing the idle to slow. I just rebuilt the carb a few months ago, so the gaskets should be good, but I'll take the carb off tomorrow and inspect the back there and the gaskets.
I did notice, that sometimes when i start the engine, I think when it's cold, the idle seems fine, until I start to give it throttle. Once i start gassing it, the idle really speeds up.
Vacuum leak, maybe, maybe not. You would think if you were pulling in a lot of air, the engine would run fast, but run rough because of being lean. You would think spraying a fuel into the carb or holding the choke a little bit closed would make it richer and run even faster. It's hard to say. While all engines seem to be a little different, my feedback system would run fine during start up, but after it warmed up it would suddenly idle very fast and had a miss-fire. I traced it down to the timing was suddenly being advanced for whatever reason. Guess what controls the timing on the feedback system? The computer. I pulled the codes and had so many error codes, would have took hundreds of dollars, countless hours and hunting for obscure parts that I possibly would not have been able to find.
I then decided to convert. Like I said, all engines are different. In my case all I did was change the distributor and ignition module. I am still running the original computer controlled carb, the wires are just not hooked up. It runs so much better than it did before.
If you get a duraspark II distributor and ignition module and get the harness inbetween the dist and the module, the rest will plug right in to your original factory harness you have now, it's already wired for it. They had many different engine setups that used the same harness, some had the duraspark II system with this harness from the factory, your truck has it too.
Or you can buy a aftermarket HEI distributor and stab it in place and wire it in.
If you think you are having carb problems, you can get them new also online.(the regular type with no wires).
Okay, I'd like to eliminate a vacuum leak as the problem before I go and replace the distributor and such. I did notice, that when I start the engine cold, the idle seems fine, until I start giving it throttle. When I give it gas, the rpms just sort of stay up where they got to with the throttle. Wonder if that could be similar to the timing issue you had.
so I get them free shipping and have it two days later. Only problem with RockAuto is having to pay shipping, if they aren't from the same warehouse, you pay more, yada yada. I do love their prices, though.