What is stock jet size for a 2100 on a 302?

[Nothing Special]

Does anyone know what the stock jet size is for an Autolite 2100 2 bbl carb on a 302 V8 in a '71 Bronco?

I got my carb from a junk yard and have just been running it with the 48 jets that were in it when I got it. Generally it's worked well, but this year I'm definitely noticing that it will misfire if I don't pull out the (manual) choke just a bit.

I think it's doing this worse than it has before, but I think it's generally been running a bit to the lean side. So I was wondering if the 48s seemed reasonable or not.

Thanks

 

[Rightpace]

From what I remember the stock size jets were 49-51 for small block V8. 51-55 for big block

 

[Rightpace]

The misfire condition and pulling the choke indicates a lean condition. Check out the power valve condition and float level when you get a chance. If there is trash/varnish in your bowl you need to clean the carb out

 

[Nothing Special]

Yep, I get that it's lean. That's why I'm thinking I might need slightly bigger jets.

Everything's very clean. I've been going at that for a while now.

The power valve is new from a rebuild kit I got this winter (a project over the winter was to put bushings in for the throttle shaft to reduce the huge vacuum leak I was getting from the worn out bearings). I'm not saying I know it's the right power valve, but it is new.

I did set the float level dry. I haven't checked it wet yet (running the engine with an open float bowl doesn't excite me).


It does sound like I might be a little small on the jets though. Does anyone know where to get Motorcraft jets (5/16" OD threads)? All I'm finding is Holley jets (1/4" threads).

 

[1970 Palmer]

Check with Mike's Carburetors.

They have a very good site information, and small parts selection. I liked their carb kits also. Fast service.

John

 

[Nothing Special]

Thanks. I did find some on-line and placed an order for a pair of 49s and a pair of 50s this evening.

 

[jckkys]

Actually most the 2100/2150s for 289/302 engines had 47s. These were carbs that had 1.08" venturis. Ford used a range of jet sizes in any carb. The exact size was determined by flowing them. So even tho your 2100 has a size larger it may be correct for that 2100. Your fuel level in the float bowl may be a little low explaining the lean mixture. The correct fuel level is about 0.90". This is the important set up spec. The float level is just the preliminary setting, to get the engine running. Then you have to take the top cover off and set the fuel level.

 

[DirtDonk]

The fact that it's changing too, could mean you have tuning issues on top of it being borderline lean (if it is) that are making it worse.
A weakening ignition, increasing vacuum leaks, a PCV valve that's sticking partly open, and probably other things too.
Not saying that going up a jet size or two won't help. Just that it sounds like you might have other stuff going on as well.

Paul

 

[Nothing Special]

.... Your fuel level in the float bowl may be a little low explaining the lean mixture. The correct fuel level is about 0.90". This is the important set up spec. The float level is just the preliminary setting, to get the engine running. Then you have to take the top cover off and set the fuel level.

I did run it before setting the dry float level. It ran about the same as it does now. When i checked the dry level the float was a little high. So I dropped the float a bit, which didn't seem to have much impact. So it could be low now, but I did run it a bit higher earlier which didn't help. Still, I suppose I should check it wet.

The fact that it's changing too, could mean you have tuning issues on top of it being borderline lean (if it is) that are making it worse.
A weakening ignition, increasing vacuum leaks, a PCV valve that's sticking partly open, and probably other things too.
Not saying that going up a jet size or two won't help. Just that it sounds like you might have other stuff going on as well.

Paul

I don't doubt there are other things going on, but I'm running out of things to check, so just richening the mixture is sounding better and better.

I'm running a DUI HEI ignition. I suppose it's possible that it's weakening, but it doesn't seem like a likely candidate.

I should have fewer vacuum leaks than I had last year since I bushed the throttle shaft over the winter. I've sprayed carb cleaner around the carb with the engine idling. I get a slight drop in rpm when I hit the throttle shaft (but no where near as much as last year) and no change anywhere else. The only vacuum lines I have are to the PCV and the distributor and they are solid. I guess I haven't checked around the intake manifold. I probably should, but it doesn't seem that likely.

I disconnected the PCV and capped the port without any effect, so that doesn't seem likely either.

So like I said, I'm running out of things to check. So I guess I'll throw the slightly larger jets in when they come and cross my fingers.

 

[armynavy17]

I should have fewer vacuum leaks than I had last year since I bushed the throttle shaft over the winter. I've sprayed carb cleaner around the carb with the engine idling. I get a slight drop in rpm when I hit the throttle shaft (but no where near as much as last year) and no change anywhere else. The only vacuum lines I have are to the PCV and the distributor and they are solid. I guess I haven't checked around the intake manifold. I probably should, but it doesn't seem that likely.

Have you checked your vacuum advance diaphragm? They do fail from time to time which affects both timing at some engine conditions and creates a vacuum leak. Should be able to pop off the distributor cap, put a vacuum on the line, and see the linkage move.

 

[Rustytruck]

are the heat risers tubes for the choke from the exhaust manifold hooked up and operating properly. has the fuel pump been flow and pressure checked. does you needle screw adjustments seem to work properly when you adjust the screws they are not set at extremely closed or way out to get it to idle. Make sure the choke works properly or there can be an induced vacuum leak at the wrong time.

https://www.therangerstation.com/tech_library/pdf_documents/motorcraft_2150_carb.pdf

 

[Nothing Special]

Have you checked your vacuum advance diaphragm? They do fail from time to time which affects both timing at some engine conditions and creates a vacuum leak. Should be able to pop off the distributor cap, put a vacuum on the line, and see the linkage move.

That's a good point. I'll check that when I get a chance.

are the heat risers tubes for the choke from the exhaust manifold hooked up and operating properly.... Make sure the choke works properly or there can be an induced vacuum leak at the wrong time.

No. There are no heat riser tubes, but it's a manual choke, so it's not clear to me how this might be a problem

.... has the fuel pump been flow and pressure checked....

The fuel pressure is a steady 4.25 psi pretty much no matter what (it will drop a little lower at a low rpm idle)

.... does you needle screw adjustments seem to work properly when you adjust the screws they are not set at extremely closed or way out to get it to idle....

The idle needle screws don't seem to be very sensitive. I'm running them about 1.5 turns out. Going in much will drop the idle speed, but going out to about 2.5 turns doesn't really seem to affect it significantly. Going much past that will drop the idle. So does that seem normal? I guess, but I would've expected it to be a little more sensitive in the 1.5 - 2.5 turn range.

 

[DirtDonk]

I don't have any other clues to add, but was wondering about something. After re-reading your initial post I'm wondering just how/when the misfire occurs, and what form it takes?
Does it bog on acceleration?
Does it buck and misfire at higher rpm only? Acceleration only? Any other specific range, or just generally?
Is it only noticeable upon initial acceleration?
Just a general roughness when it happens, occasional heavy miss, or does it fall on it's face completely unless you close the choke a bit?

Enquiring minds want to know!
But basically I was just going back to the power-valve that Rightpace mentioned, or even an accelerator pump squirt that's not happening.
Or even some lightly fouled spark plugs perhaps.

Paul

 

[Nothing Special]

It's mostly during steady-state cruise. It doesn't happen so much when I mash the throttle, so I think the accelerator pump is fine.

It doesn't completely fall on it's face or buck or anything. It's more a general roughness that anyone who typically rides with me probably would never noticed. And it smooths out with just a touch of choke.

I notice it mostly around 2000 rpm, but that might be more due to that being the engine speed I'm mostly at in steady-state cruise.

 

[Nothing Special]

A little more data. I checked the wet float level, .81". I don't know what the actual spec is, but in a bulletin board thread I found 7/8". If that's accurate my float is a little high. But since my issues could possibly be caused by a LOW float, I think I'm going to call the .81" good.

And I pulled the passenger's side spark plugs. They were all very white, indicating a lean condition. With those 4 plugs agreeing I decided not to bother pulling the (much harder to get at) driver's side plugs.

But with the symptoms of running lean and the plugs saying I'm running lean, I'm thinking I'm just running lean. Hopefully the jets I ordered will be here soon (I did get an e-mail that they shipped). And hopefully I went big enough! I have 48s and I ordered 49s and 50s. So we should see in a few days if that takes care of it,

 

[1970 Palmer]

I think I would have pulled all of the plugs for a look see, and run a compression check while they are out. You might be chasing a very simple to fix problem. It could be as simple as a cracked plug, or maybe a bad plug wire. Looking at all the plugs (and the compression numbers) could be a start to determine which cylinder is giving you the problems.

Changing only one or two jet number sizes is a really subtle change, and it's a change at mid, to full throttle. Since the jets are flowed, your larger number size replacements might not flow as much fuel. I doubt it's either the cause, or the cure for your drive-ability symptoms. You want to read the porcelain down into the plugs, not just the tips. If the symptom does improve with the larger jets, I think your just masking another problem running a richer mixture. What altitude is this vehicle at when your having the miss? What kind of RPM, and throttle load/open position? You mentioned it has a manual choke, is the engine fully warmed up. You can easily test the rich/lean problem while your driving. If it's lean, it should be cured by just pulling out the choke while your driving at the exact load condition that causes the miss. If it does not fix the miss, you have another issue.

While you have the carb top off rechecking your float fuel level, pull the venturi booster, (do not move the accelerator while the booster hold down screw is removed, you will drop the check valve ball into the intake). You want to check the emulsion tubes. The very small holes have to be very clean, you need to make sure they are not partially blocked, or maybe the booster was dropped at some point and the tube bottom is dented/restricted. Make sure they are not cracked. A lean idle circuit can cause your symptoms. By the early 1970's the idle circuits were very lean from the factory in order to meet federal emission numbers.

Sorry for your problems. At this point, I think you need to step back, go to the basics, and recheck everything. Check the plug wires with your ohm meter, check the distributor cap for cracks, etc. What year is your carb? Is this problem one that "just started", or has it been a problem for a longer period?

Remember, the fix is almost always simple, correctly diagnosing the problem is the time consuming part.

John

 

[jckkys]

I have a Motor Auto Repair Manual that covering '66-'72 that has the fuel levels for 2100 carbs in cars. The car type 2100s in '70/'71 all had 13/16" or 0.812" fuel level. It would seem a safe bet truck carbs are the same. I run mine a little lower like the '66/'67s because it's a 4X4. But you already seem a little lean. Vacuum leaks would effect idle circuit more than cruise and 1 1/2 turns is about right. So it may be a good idea to try 50s. These;https://www.ebay.com/itm/Ford-Autol...662?hash=item2157b5fa56:g:T08AAOSwp7RbjJS3are the least expensive I can find.

 

[Nothing Special]

.... You can easily test the rich/lean problem while your driving. If it's lean, it should be cured by just pulling out the choke while your driving at the exact load condition that causes the miss. If it does not fix the miss, you have another issue....

As I've said in almost every post, pulling the choke out a bit does cure the miss.

Yes, there could be several causes for running lean (vacuum leak, blocked carb...) but since I've ruled most of them out as much as possible, simply having the mixture too lean seems like a reasonable cause, and richening the mixture by going to bigger jets seems like a reasonable cure.

If I've missed anything in the rest of your post, I apologize, and I'd appreciate it if you could point me to what you think I've missed. But since this one paragraph says that if pulling the choke out fixes the problem (which it does) I probably am running lean, I'm not going to think too much about the rest of your post which seems to be saying that I'm probably NOT running lean.

 

[Nothing Special]

I have a Motor Auto Repair Manual that covering '66-'72 that has the fuel levels for 2100 carbs in cars. The car type 2100s in '70/'71 all had 13/16" or 0.812" fuel level. It would seem a safe bet truck carbs are the same. I run mine a little lower like the '66/'67s because it's a 4X4. But you already seem a little lean. Vacuum leaks would effect idle circuit more than cruise and 1 1/2 turns is about right. So it may be a good idea to try 50s. These;https://www.ebay.com/itm/Ford-Autol...662?hash=item2157b5fa56:g:T08AAOSwp7RbjJS3are the least expensive I can find.

Thanks, that gives me more confidence staying at the .81" that I'm at now.

The jets I ordered were a little under $5 each, so a little cheaper than the $11.50/pair your link has. But I also had to pay shipping, so your link is probably cheaper overall. If I need to go bigger yet I'll keep that in mind.

 

[jckkys]

Maybe you could share your source. I usually go to Walker where jets are 3 bucks ea. but they're out of stock.