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Stock main jets for 2150 carb on 76 Bronco

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Stock main jets for 2150 carb on 76 Bronco

 
  #1  
Old 02-06-2019, 05:36 PM
ofbg76
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Stock main jets for 2150 carb on 76 Bronco

Hi, new guy to the forum here, but not new to early Broncos. I presently have a 76 wagon with 302, manual transmission,
which I am working on resurrecting. Carb was missing so I bought a rebuilt motorcraft 2150. It came with no. 58 main jets.
I need to verify if these jets are the correct stock jets. Then, I need to rejet for 6000 foot elevation.
Can anyone help?

thanks
ofbg76
 
  #2  
Old 02-11-2019, 01:20 AM
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Originally Posted by ofbg76 View Post
Hi, new guy to the forum here, but not new to early Broncos. I presently have a 76 wagon with 302, manual transmission,
which I am working on resurrecting. Carb was missing so I bought a rebuilt motorcraft 2150. It came with no. 58 main jets.
I need to verify if these jets are the correct stock jets. Then, I need to rejet for 6000 foot elevation.
Can anyone help?

thanks
ofbg76
Is the triangular shaped carb ID tag still in place on the air horn? If so, type the code from it.
 
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Old 02-11-2019, 07:19 AM
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Who did you buy the carb from? The odds of a remanufactured carb still having the tag on it are slim. I'd at least try it with those jets. A good carb rebuilder will have flowed it on the bench so they should at least be in the ballpark. Keep in mind too the power valve # (economizer) is based on local altitude. Most rebuilds probably have a 6.5", that's what the kits have in them. That may be too high. At minimum you'll want a mechanic's vacuum gauge for setup and tuning. Maybe you know this already. Welcome to FTE btw.
 
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Old 02-11-2019, 02:00 PM
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Stock main jets for 2150 carb on 76 Bronco

Thank you NumberDummy and Tedster9 for your responses.
Tedster9 is correct, there was no tag on the rebuilt carb.
I have ordered a "official" Ford truck manual CD that I am hoping will contain the detailed carb specs.
I did not know that the power valve had an influence on elevation so will look into that also.
Am also looking at the different venturi sizes available on the 2150 carb (I currently have a 1.08) to see if a
larger one might be more advantageous.

Thanks
ofbg76
 
  #5  
Old 02-11-2019, 04:29 PM
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As a general rule, probably the most common error with carburetors is to install too large of a carburetor. Most of the information out there for carb selection, power valve, jetting and tuning is geared for racing, which is not what people need or want for driving around on the street.

The power valve opening point is based on manifold vacuum. This is what holds it closed. A stock engine tends to have a high average idle vacuum of 18" to 20" at sea level. At 6,000' it may be a fair bit lower. Maybe 15", something like that. But the principle is the same. If a mild or performance camshaft is installed the manifold vacuum will be lower yet. In some ways the power valve is more critical than jetting for altitude.

This is one reason why I mentioned a mechanic's vacuum gauge. Don't guess, measure. If the power valve opens too early it will make carb run way, way too rich and waste LOTS of gas. This tends to be already a bit of a problem at higher elevations, and also would make initial selection of the correct jet size pretty much impossible. Maybe you live at 6000', but if I had to bet, you drive to 10,000' too, or plan on it. So you have to make some allowances for that as well.

Make certain that the power valve is closed at level ground steady cruise, before ever looking at plugs say, for jetting indications. Consider getting a wideband O2 sensor if you're serious about dialing a carburetor in, it takes a lot of the mystery out. They aren't giving them away but the price has come down a lot. The fuel savings alone should pay for itself pretty quick.
 
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Old 02-11-2019, 07:50 PM
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Tedster9,
I understand and appreciate all your comments. Your comment about too large of carburetor made me chuckle. I bought the Bronco in late 76 with 5,000 miles on it. Sold it to a couple of my nephews after having driven quite a number of years, then got it back from them. (Lived in lower elevation at that time). When I got the Bronco back, they had installed a 4 into 2 manifold adapter with a large 4 bbl holley on it. Kind of like trying to drive 4 cows through a barn door wide enough for only two. I found a couple of references on sizing a carb with respect to engine size and max operating RPM and replaced the 4 cow carb with the 2150.

I rebuilt the engine with a cam for a modest increase in mid range power.

I do have a cheap vacuum gauge and will try to determine the power valve operational vacuum values. Sounds
like, because of the elevation and different cam, I'll probably need to change the power valve.

I do like the 02 sensor idea and may just do that as a fine tuning exercise. Could also be useful for dialing in my old Brit Bike carbs.

Thanks again
Randy
 
 


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