New to broncos need help!!
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New to broncos need help!!
i just bought a 1984 bronco xlt off some guy on craigslist, he told me the only problem was it needed a new rear main seal, ends up the rear main seal was new, i got everything back in it, and it has an eratic idle and it gets stuck at a very high idle, plus it likes to stall if it is not at this very high idle. it does not have an egr of any type and it has an oversized holley 750 cfm double pumper carb on it. this is my first vehicle and was supposed to be a daily driver. need vacuum diagrams and pictures to help with making sure everything is hooked up right. motor was rebuilt not too long ago by previous owner and only has 20,000 miles on it.
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From: Boise, Idaho
If you're able to, when it gets stuck in high idle, stop and get out and check the linkage to the carb and make sure it's not a physical bind. Although it was on an I6 (quite a different setup), it was continually getting stuck in high idle and it turned out to be the linkage itself that was sticking, not some vacuum problem. (Don't rule out a vacuum problem though, this is just something to check.)
Other than that, it does sound like you're having vacuum leaks somewhere. Scour the engine bay for any vacuum lines that may be disconnected, or cracked. Then, if nothing, check for base gaskets under neath the carb that may be sucking air.
Lastly, rebuild the carb. Although, unless you're good with carbs, double pumpers are generally for racing applications, and not the best (or easiest to tune) for daily driving. Not sure why he put one on there.
Other than that, it does sound like you're having vacuum leaks somewhere. Scour the engine bay for any vacuum lines that may be disconnected, or cracked. Then, if nothing, check for base gaskets under neath the carb that may be sucking air.
Lastly, rebuild the carb. Although, unless you're good with carbs, double pumpers are generally for racing applications, and not the best (or easiest to tune) for daily driving. Not sure why he put one on there.
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im sure the linkage isnt sticking i got out and checked last time i was messin with it, im not too good with carbs and there are a few lines/hoses laying around that arent hooked up, but i need a diagram or a picture to find out where or if they go anywhere. also i just found out that the carb spacer has melted away and the over excessive amount of fuel is very apparent, little blue flames are shooting out the side.
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From: Broken Arrow
a 750 is way to big for a 302/351 if you have the money I would get an edlebrock 600cfm and a linkage kit. its a great carb I never had to do any work on mine. as far as the vacuum diagram there should be one under the hood next to the hood lever
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From: Boise, Idaho
The hoses and lines that aren't hooked up are definitely going to cause problems too. As for a diagram, there should be one under the hood, but they get pretty complex. Also, I agree that you should pull that carb off, sell it, and get yourself around a 600 - 650 or so. A 750 double pumper for a daily driver just seems like way too much trouble.
Cargo Master
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Rebuild kit would explain which holes go to which vacuum lines, and would help with the excessive fuel present.
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carb wise when i get the money im going for a 450/500 cfm just for the mileage, and the diagram under the hood doesn't help much its pretty confusing and the truck seems to be missing a lot stuff under the hood. ( a lot of stuff that is on the diagram and has vacuum lines leading to them on the diagram. )
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From: Boise, Idaho
If that's the case, I imagine that a previous owner stripped the emissions equipment off the engine. Until you can get it sorted out, at least cap off everything so nothing's sucking air.
I'm thinking a 450 - 500 may actually be too small for a V8. A carb with secondaries is designed to flow a lot of fuel when the secondaries are open, and if your engine is too big for it, the secondaries will be open all the time.
A good mathematical formula for carb CFM = (CI * Peak RPM) / 3456
If it's a 351, I think they peak out at around 5500, so:
(351 * 5500) / 3456 = 558
So a 600 would do you rather well. The only way you'd want to go with a smaller carb is if you went for a 2bbl.
I'm thinking a 450 - 500 may actually be too small for a V8. A carb with secondaries is designed to flow a lot of fuel when the secondaries are open, and if your engine is too big for it, the secondaries will be open all the time.
A good mathematical formula for carb CFM = (CI * Peak RPM) / 3456
If it's a 351, I think they peak out at around 5500, so:
(351 * 5500) / 3456 = 558
So a 600 would do you rather well. The only way you'd want to go with a smaller carb is if you went for a 2bbl.
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From: Boise, Idaho
The secondaries are designed to regulate the amount of fuel your engine is getting. Under normal cruising, two of the barrels are completely closed, so that your engine is only using the other two. This improves your gas mileage.
When you step on the gas, the two extra barrels will open up, delivering a boost of fuel to the engine, allowing it to build more power.
If the engine is too big for the carburetor, you'll be pulling those two extra barrels open all the time, sometimes even if you're just cruising down the interstate and not needing them. That'll waste a lot of gas.
As far as the vacuum lines go, vacuum is used to regulate things, like your timing, fuel metering, etc. It's closely metered by different systems since some will only need 4 vacuum, some need 8, some 20, etc to operate. If there's an open line anywhere, the suction will pull ALL the air from that source, throwing all of that metering out the window and screwing it all up.
If you cap off the ones that are open to the air, at least you have a closed vacuum system, and the important features like the distributor and carburetor have the necessary vacuum they need to operate correctly.
When you step on the gas, the two extra barrels will open up, delivering a boost of fuel to the engine, allowing it to build more power.
If the engine is too big for the carburetor, you'll be pulling those two extra barrels open all the time, sometimes even if you're just cruising down the interstate and not needing them. That'll waste a lot of gas.
As far as the vacuum lines go, vacuum is used to regulate things, like your timing, fuel metering, etc. It's closely metered by different systems since some will only need 4 vacuum, some need 8, some 20, etc to operate. If there's an open line anywhere, the suction will pull ALL the air from that source, throwing all of that metering out the window and screwing it all up.
If you cap off the ones that are open to the air, at least you have a closed vacuum system, and the important features like the distributor and carburetor have the necessary vacuum they need to operate correctly.
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oh ok, thanks i'll look through and cap off the lines i find.. im putting the new spacer in now, is the carb supposed to shoot smoke out of a hose in the front or is that supposed to be hooked up to something?
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From: Boise, Idaho
Do you have a picture of the hose? Some do have vent tubes that just vent to the air, but most of the 4bbls I've seen have the vent tubes going back up into the air filter and not out the front. Either way, it shouldn't be smoke.
Postmaster
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From: Harrisburg, NE
welcome to the forums! i got my 84 bronco when i was 16 (for $75! i had to put an engine into it), traded it off when i was 17, then snatched it back not too long ago.
imho i would forget the holley and get a 600 edelbrock, much more user friendly, especially if your new to carbs. i did so on my capri and never looked back.
and if your getting flames at the intake, i would check the timing as well.
imho i would forget the holley and get a 600 edelbrock, much more user friendly, especially if your new to carbs. i did so on my capri and never looked back.
and if your getting flames at the intake, i would check the timing as well.
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