1970 Bronco Wheeler

[DirtDonk]

What can it hurt to try bumping the timing? Pretty much nothing, as long as you know what you're doing and are careful to note how it drives afterwards.
What is your initial timing set to currently? I think you said 12-13 or so? I say go for it.
Set it to 15-17 and see what that nets you in driving. Does it ping under load with that much advance? If not, then run it for awhile including with the vacuum advance connected and see what it drives like.

Which carb is this again? Rebuilt, reman, new? If it's been worked on by anyone but you, you don't now how the throttle blades were zeroed unless you check. If they're not perfectly centered in the bore they might be hanging up the linkage.
By the same token, your choke linkage can hang things up to the point that the idle-speed screw no longer does anything beyond a certain low point. So check that too. Make sure that the high-idle screw attached to the choke linkage is not too far extended and hanging up on the choke's high-idle cam.
Either one of those can get the carb wonked up to the point you can't close off the transfer port for the advance.

So verify that nothing is restricting the closing of the throttle blades. Then get the higher idle however you can initially (600-650 is a good point, but frankly 500-550 is not completely out of line) through timing and verifying the idle speed screw is doing it's job, then see what happens.

Seems to me that you should be able to stall the engine by turning the idle speed screw out to the point it's no longer touching the throttle lever.
I'm sure there are legitimate scenarios where you can't fully stall the engine, but I can't think of anything other than something wrong with the carb.

You don't have a throttle control solenoid, do you? Sometimes known as "emmissions soleniod" or "anti-dieseling solenoid" or maybe another name or two, but it's also used for setting idle parameters. So if you have one, make sure it's not creating trouble for you as well.

Paul

 

[pocketlock]

What can it hurt to try bumping the timing? Pretty much nothing, as long as you know what you're doing and are careful to note how it drives afterwards.
What is your initial timing set to currently? I think you said 12-13 or so? I say go for it.
Set it to 15-17 and see what that nets you in driving. Does it ping under load with that much advance? If not, then run it for awhile including with the vacuum advance connected and see what it drives like.

Which carb is this again? Rebuilt, reman, new? If it's been worked on by anyone but you, you don't now how the throttle blades were zeroed unless you check. If they're not perfectly centered in the bore they might be hanging up the linkage.
By the same token, your choke linkage can hang things up to the point that the idle-speed screw no longer does anything beyond a certain low point. So check that too. Make sure that the high-idle screw attached to the choke linkage is not too far extended and hanging up on the choke's high-idle cam.
Either one of those can get the carb wonked up to the point you can't close off the transfer port for the advance.

So verify that nothing is restricting the closing of the throttle blades. Then get the higher idle however you can initially (600-650 is a good point, but frankly 500-550 is not completely out of line) through timing and verifying the idle speed screw is doing it's job, then see what happens.

Seems to me that you should be able to stall the engine by turning the idle speed screw out to the point it's no longer touching the throttle lever.
I'm sure there are legitimate scenarios where you can't fully stall the engine, but I can't think of anything other than something wrong with the carb.

You don't have a throttle control solenoid, do you? Sometimes known as "emmissions soleniod" or "anti-dieseling solenoid" or maybe another name or two, but it's also used for setting idle parameters. So if you have one, make sure it's not creating trouble for you as well.

Paul

Thanks for the response. I currently am using a new aftermarket MC2100/2150 carb I got off Amazon. (I know, I know, but it was cheap and I was on a budget.) I am running 12-13 BTDC advance right now, I was thinking about bringing it up to 15-17 to see how it likes that so I can bring the air/fuel mixture down a bit from where I had to put it to bring the idle up. Nothing seems to be hanging it up. I can watch on the vacuum gauge when the choke full snaps closed and I go from 20 inches to 0 in a snap. I'm certain there can be some adjustments made on the choke as to how fast it's getting off manifold vacuum, but I don't believe it's hanging me up once warmed. I've never heard of stalling the engine with the idle speed screw not touching the lever, I've always just used it as an assist in getting idle up when everything else is where it needs to be and idle is still low. I was going off the 600-650 idle from recommendations I've seen in here, but if 500-550 is an acceptable range than I have no problem getting it there as well. Just trying to do right by this engine to keep an LS out of the truck haha. There's no throttle control solenoid that I am aware of. I do have a vacuum pot behind the choke that came on this carb but I have an electric choke. I've never seen the vacuum pot before on other MC2150 that i've worked on but decided to leave it alone if it came with the carb.

 

[DirtDonk]

Got a pic of the choke side of the carb? I see in your previous video that the choke plate is still moving with the throttle. Meaning that at least for that one, the choke was not open all the way.
The vacuum pot might be a choke pull-off. Is it behind the carb on the choke side? Or is it on the side of the carb?

Yes, it's absolutely normal for an engine to stall out when the carb is fully closed. Because it's just that, fully closed. So no air can get past the throttle blades, therefore no air to run the engine. Stall...
Same thing (almost) as putting your hand over the carb throat and killing the engine. We had a discussion recently about not being able to kill the idling engine by choking off the carb. Don't remember how the air was getting by, but it was.

If the choke is not all the way open, then the fast-idle cam might still be engaged and holding the throttle linkage open slightly.
Of course, that does not explain the idle being so low at even such a high setting as the vacuum appears as soon as you push the throttle, but we're getting down to the nitty gritty now.
Speaking of which, just exactly how far do you have to row the throttle lever before you see vacuum on your gauge? If it's just a teensy-weensy bit, it's coming on too fast. If it's just a little bit, then that's pretty normal.
Maybe 1/4" of movement or so at the tip of the throttle lever? I never took a measurement and have not used a carb much for a long time now. So I might be off on my "somewhere between teensy-weensy and little bit" part.

Paul

 

[pocketlock]

Got a pic of the choke side of the carb? I see in your previous video that the choke plate is still moving with the throttle. Meaning that at least for that one, the choke was not open all the way.
The vacuum pot might be a choke pull-off. Is it behind the carb on the choke side? Or is it on the side of the carb?

Yes, it's absolutely normal for an engine to stall out when the carb is fully closed. Because it's just that, fully closed. So no air can get past the throttle blades, therefore no air to run the engine. Stall...
Same thing (almost) as putting your hand over the carb throat and killing the engine. We had a discussion recently about not being able to kill the idling engine by choking off the carb. Don't remember how the air was getting by, but it was.

If the choke is not all the way open, then the fast-idle cam might still be engaged and holding the throttle linkage open slightly.
Of course, that does not explain the idle being so low at even such a high setting as the vacuum appears as soon as you push the throttle, but we're getting down to the nitty gritty now.
Speaking of which, just exactly how far do you have to row the throttle lever before you see vacuum on your gauge? If it's just a teensy-weensy bit, it's coming on too fast. If it's just a little bit, then that's pretty normal.
Maybe 1/4" of movement or so at the tip of the throttle lever? I never took a measurement and have not used a carb much for a long time now. So I might be off on my "somewhere between teensy-weensy and little bit" part.

Paul

Here is a screenshot of the carb I ordered. I’m not 100% sure how much throttle movement it takes. I’ve only noticed it when I’m on the idle screw, so not sure how it translates. If I were to back the screw off I would say I would probably have 1/8”-1/4” at the top of the throttle before it dropped but I would have to check it again tomorrow to be certain. I took the video today after idling for about 10 minutes or so which was when I saw the ported vacuum drop to 0. The choke was not 100% vertical though and I could push it back with my hand with no change to idle. But I can’t remember if that’s normal or not honestly.

 

[DirtDonk]

Yes, it’s somewhat normal for it to act like that. But if you push it all the way open and hold it there and then flip the throttle a time or two that’s when the choke mechanism is supposed to back all the way out.
And sometimes, as I mentioned, it will stick on the lowest high idle cam and not let the carb shut all the way down.

You can also adjust the choke for correct cold (almost closed) and warm (open) operation.
Check for any video instructions or links to discussions here.
Good to double check how they set it at the manufacturer.
Often they are just slapped together.

 

[pocketlock]

Yes, it’s somewhat normal for it to act like that. But if you push it all the way open and hold it there and then flip the throttle a time or two that’s when the choke mechanism is supposed to back all the way out.
And sometimes, as I mentioned, it will stick on the lowest high idle cam and not let the carb shut all the way down.

You can also adjust the choke for correct cold (almost closed) and warm (open) operation.
Check for any video instructions or links to discussions here.
Good to double check how they set it at the manufacturer.
Often they are just slapped together.

I'll get it warmed up again tomorrow and check some more things. Thank you again for the suggestions! It's bee about 8 years since i've messed with getting idle and vacuum right on one of these so I can't remember all the fine details, and that was on a 258 so a bit different. I'll look into it tomorrow and see what I come up with. Thank you!

 

[pocketlock]

Tweaked some stuff today. Bumped timing up to 17 BTDC. Reset idle air screws to 2-3/4 turn out. Fiddled with the throttle idle screw to get the idle around 550. Now the vacuum rolls in like I would think it should. Feels like it idles fine on manifold vacuum around 20 with a slight flutter. Still has a slight pop on slow acceleration, but that might be because its open headers.

 

[Oldtimer]

So now you can adjust mixture screws for leanest smooth idle, then adjust idle speed screw, and repeat.

 

[DirtDonk]

Or just forget ALL of that until you finish the engine. By installing a legit exhaust system!
Open headers are not going to get you fully tunable. You need to get that done and not worry too much about the idle.

Paul

 

[pocketlock]

Or just forget ALL of that until you finish the engine. By installing a legit exhaust system!
Open headers are not going to get you fully tunable. You need to get that done and not worry too much about the idle.

Paul

Definitely! Just happy it’s smooth and stable, not cutting out or needing to bump the throttle until it warms up.

 

[micked]

Here is a screenshot of the carb I ordered. I’m not 100% sure how much throttle movement it takes. I’ve only noticed it when I’m on the idle screw, so not sure how it translates. If I were to back the screw off I would say I would probably have 1/8”-1/4” at the top of the throttle before it dropped but I would have to check it again tomorrow to be certain. I took the video today after idling for about 10 minutes or so which was when I saw the ported vacuum drop to 0. The choke was not 100% vertical though and I could push it back with my hand with no change to idle. But I can’t remember if that’s normal or not honestly.

Is this carb a replacement for the stock one? Mine is leaking like a siv and this seems like a reasonable deal


Sent from my iPhone using Tapatalk

 

[pocketlock]

Is this carb a replacement for the stock one? Mine is leaking like a siv and this seems like a reasonable deal


Sent from my iPhone using Tapatalk

It was a bolt on replacement for my mc2150. Seems like it had a few extra vacuum ports and some slight differences but nothing that stood out as crazy. Has exhaust choke port as well. For the price I couldn’t beat it.

 

[micked]

Cool I’ll order one up
Thanks!


Sent from my iPhone using Tapatalk

 

[pocketlock]

Been tinkering this weekend. Got my bumper/winch mount started so I will at least have recovery on the trails. Started working on a center console to cover the shifters so I can put stuff down, have a drink, etc. tried to flex the suspension as much as I could with my jack. Still plenty of travel obviously but it was nice to see nothing binding yet. Got the holes for the cab body mounts drilled, just need a second set of hands to torque it all down. Getting there slowly. Still need to pull my fuel line and replace a fitting that’s got a slow leak and might need to replace the thermostat housing due to a small leak.

 

[sprdv1]

Definitely! Just happy it’s smooth and stable, not cutting out or needing to bump the throttle until it warms up.

amen to that

 

[sprdv1]

Been tinkering this weekend. Got my bumper/winch mount started so I will at least have recovery on the trails. Started working on a center console to cover the shifters so I can put stuff down, have a drink, etc. tried to flex the suspension as much as I could with my jack. Still plenty of travel obviously but it was nice to see nothing binding yet. Got the holes for the cab body mounts drilled, just need a second set of hands to torque it all down. Getting there slowly. Still need to pull my fuel line and replace a fitting that’s got a slow leak and might need to replace the thermostat housing due to a small leak.

Keep after it, every little bit gets you closer

 

[pocketlock]

Few updates! Got driveshafts and brakes installed, was able to go and flex the bronco out in my ditch beside the shop. Been buttoning up small stuff in the meantime, seatbelts, cupholders, grommets for wiring, tying up wiring and fuel lines, installing breather tubes, etc. Been working on the short drive from my house to the corner to see how everything feels. In second gear I have all the power and acceleration I could want, carrying it all the way to 20-25 mph, hit 3rd and feels like I can’t give it any gas or it bogs down. It will accelerate under light throttle but any more and it bogs. Carried that up to 35-40 and went to 4th, same thing was able to get up to 50 before my house so acceleration feels good other than the fact that I can’t get into it at all. Any tips? I’ve tuned the idle air in as far as I can with smooth vacuum. Idle is around 575 with ported vacuum staying closed. Timing is at 12-13 btdc. I mean it’s drivable but frustrating. Leaning towards a possible jetting issue based on other reviews of the carb (MC2150 clone) but not sure yet, looking for some ideas when I go to mess with it when I wake up today. Clutch and shifting are starting to feel better though after feeling a bit odd the first few trips. Wondering if this could be an issue with gearing, being 3.55 on 35s, but not having any issues at all in second gear has me doubting that slightly. Any tips? Going to try a short trip in 2:1 low range and see if it still does it in 3/4 but not sure what this will tell me to be honest, but was recommended by another person.

 

[pocketlock]

SOLVED(?): seems to be a gearing issue. If I hold second a little longer (3k rpm) and do the same in third the bog is mostly gone. If anything 4th gear wants more throttle at that point and the bog is on the low end. Acceleration feels good at this point the truck is just loud haha. I strapped my timing light to my center console to use as a tach while I was testing. Used a gps speedometer and found that if I was going around 25-30 (just a little more than what I was doing yesterday the bog in third was gone and if I shifted around 45-50 into 4th the bog was mostly gone.

 

[DirtDonk]

Which transmission again? If a 435 the gears are pretty widely spaced. Same for just about any wide-ratio 4spd trans for that matter.
Which sounds like what you were dealing with, what with big rpm drops between shifts.
This is fine if you're properly geared in the differentials for the tire size, but in you're case they're not well matched right off the bat. Using 35's with 3.50-ish gears is a well known recipe for bogging.
Your timing might not be helping, but also an accelerator pump squirter that is not putting out enough maybe? How far up is it adjusted? And have you verified it's working at all?

Paul

 

[pocketlock]

Which transmission again? If a 435 the gears are pretty widely spaced. Same for just about any wide-ratio 4spd trans for that matter.
Which sounds like what you were dealing with, what with big rpm drops between shifts.
This is fine if you're properly geared in the differentials for the tire size, but in you're case they're not well matched right off the bat. Using 35's with 3.50-ish gears is a well known recipe for bogging.
Your timing might not be helping, but also an accelerator pump squirter that is not putting out enough maybe? How far up is it adjusted? And have you verified it's working at all?

Paul

I believe it’s gearing as well, yes np435. I have some adjustment on the linkage for the accel pump. How do I verify its working?