250 inline 6 Stalling issue, new to me truck!

South90 · Mar 10, 2026

Just picked up an 84 c10 with the 250ci inline 6 yesterday (automatic)! As far as I can tell everything is completely stock! Looks to have the varajet 2se in it. (Previous owner told me about this issue before I purchased, not a big deal just looking for guidance as I’m not too familiar with carbs!)

Truck starts right up, drives great! Really loves old country back roads 45-55 cruising!

Issue is….

If you put it in reverse and not giving it enough throttle, she stalls. Doesn’t matter if the truck is cold or fully warmed up.

Also as your slowing down to a stop light or stopped traffic, most of the time as soon as you come to a stop it’ll stall out. Only once on the way home it stalled as I was coming to a stop.

Previous owner had the truck since 2019, and he told me as he coming to a stop he would just pop it in neutral and feather the throttle to keep it from stalling, or just keep it in drive and do the ol 2 foot action of holding the break and feathering the throttle to keep it from stalling!

All of my research has proven to show me it could be as simple as carb adjustment, vacuum leak, to rebuilding the carb, etc. I noticed there is like 100 vacuum lines (exaggeration) but it’s like a spaghetti of them and drives my ocd crazy! Would like to simplify and clean the engine bay up if possible to! Just looking for some advice and pointers or if someone has had this same issue!!

Thanks everyone!

Sad Sack · Mar 10, 2026

But first:

https://www.amazon.com/dp/B08P4P97H2/

Use manifold port.

Bextreme04 · Mar 10, 2026

South90 said:
Just picked up an 84 c10 with the 250ci inline 6 yesterday (automatic)! As far as I can tell everything is completely stock! Looks to have the varajet 2se in it. (Previous owner told me about this issue before I purchased, not a big deal just looking for guidance as I’m not too familiar with carbs!)

Truck starts right up, drives great! Really loves old country back roads 45-55 cruising!

Issue is….

If you put it in reverse and not giving it enough throttle, she stalls. Doesn’t matter if the truck is cold or fully warmed up.

Also as your slowing down to a stop light or stopped traffic, most of the time as soon as you come to a stop it’ll stall out. Only once on the way home it stalled as I was coming to a stop.

Previous owner had the truck since 2019, and he told me as he coming to a stop he would just pop it in neutral and feather the throttle to keep it from stalling, or just keep it in drive and do the ol 2 foot action of holding the break and feathering the throttle to keep it from stalling!

All of my research has proven to show me it could be as simple as carb adjustment, vacuum leak, to rebuilding the carb, etc. I noticed there is like 100 vacuum lines (exaggeration) but it’s like a spaghetti of them and drives my ocd crazy! Would like to simplify and clean the engine bay up if possible to! Just looking for some advice and pointers or if someone has had this same issue!!

Thanks everyone!

Personally, I would start simple. Adjust the idle screw in so that the RPM isn't dropping low enough for it to stall.

You likely need to go through the entire tuning process if the previous owner did not know what they were doing(sounds like they did not).

First, make sure you have NO vacuum leaks and the choke is operating properly. If the choke is engaged all the time or not engaged when cold, you will have a really hard time tuning it.

Then you need to let it get fully warmed up and run through ignition setup/tuning to make sure you have timing correct, then disconnect the vacuum advance and plug at the carb.

Now go through the steps in this video to set idle mixture, hot idle RPM, choke, and cold idle properly.

xc_hide_links_from_guests_guests_error_hide_media

If you do it right and there isn't anything wrong with the carb itself, you should have a great starting and running engine after that.

DoubleDingo · Mar 10, 2026

South90 said:
Just picked up an 84 c10 with the 250ci inline 6 yesterday (automatic)! As far as I can tell everything is completely stock! Looks to have the varajet 2se in it. (Previous owner told me about this issue before I purchased, not a big deal just looking for guidance as I’m not too familiar with carbs!)

Truck starts right up, drives great! Really loves old country back roads 45-55 cruising!

Issue is….

If you put it in reverse and not giving it enough throttle, she stalls. Doesn’t matter if the truck is cold or fully warmed up.

Also as your slowing down to a stop light or stopped traffic, most of the time as soon as you come to a stop it’ll stall out. Only once on the way home it stalled as I was coming to a stop.

Previous owner had the truck since 2019, and he told me as he coming to a stop he would just pop it in neutral and feather the throttle to keep it from stalling, or just keep it in drive and do the ol 2 foot action of holding the break and feathering the throttle to keep it from stalling!

All of my research has proven to show me it could be as simple as carb adjustment, vacuum leak, to rebuilding the carb, etc. I noticed there is like 100 vacuum lines (exaggeration) but it’s like a spaghetti of them and drives my ocd crazy! Would like to simplify and clean the engine bay up if possible to! Just looking for some advice and pointers or if someone has had this same issue!!

Thanks everyone!

I would suggest replacing all of the vacuum lines, one by one, so you don't mess up the order or routing of them. You'd be surprised the problems a vacuum leak or leaks will cause. Don't rule out the carburetor base gasket either. Get a replacement while swapping the vacuum lines. PCV, replace that if it's not free-flowing.

Then, with no vacuum leaks, you can tackle the timing and air mixture on the carburetor. Using a timing light and vacuum gauge, get the engine running at maximum vacuum while idling and at operating temperature.

Once it's running good, add some quality fuel additive and run a couple tank-fulls of some cleaner additive fuel through it.

Adjust the valves, not required, but probably due for it.

Basically, give it a good tune-up, and get it cleaned out.

DoubleDingo · Mar 10, 2026

Bextreme04 said:
Personally, I would start simple. Adjust the idle screw in so that the RPM isn't dropping low enough for it to stall.

You likely need to go through the entire tuning process if the previous owner did not know what they were doing(sounds like they did not).

First, make sure you have NO vacuum leaks and the choke is operating properly. If the choke is engaged all the time or not engaged when cold, you will have a really hard time tuning it.

Then you need to let it get fully warmed up and run through ignition setup/tuning to make sure you have timing correct, then disconnect the vacuum advance and plug at the carb.

Now go through the steps in this video to set idle mixture, hot idle RPM, choke, and cold idle properly.
xc_hide_links_from_guests_guests_error_hide_media

If you do it right and there isn't anything wrong with the carb itself, you should have a great starting and running engine after that.

The only thing I would say to this, is, if you have the factory air cleaner housing, follow the tune-up adjustment directions on it, sometimes you have to leave everything hooked up, including the air cleaner housing screwed down to the carburetor when adjusting the timing. My 81 is like that. I have to have everything installed, and the engine at operating temperature, disconnect and plug the vacuum line at the distributor, adjust the timing, hook up the vacuum again, leaving everything installed still, and then make the other adjustments, six steps total. After re-reading that on my label, I need to go back in and readjust everything. It runs great, but maybe it can be even better.

Edit: The video doesn't show a varajet. The mixture screw adjustment is pretty much the same on carburetors, but there may some other adjustments needed on a varajet. I personally have never worked on a varajet, but a video showing the varajet should help you get yours working properly.

South90 · Mar 10, 2026

Bextreme04 said:
Personally, I would start simple. Adjust the idle screw in so that the RPM isn't dropping low enough for it to stall.

You likely need to go through the entire tuning process if the previous owner did not know what they were doing(sounds like they did not).

First, make sure you have NO vacuum leaks and the choke is operating properly. If the choke is engaged all the time or not engaged when cold, you will have a really hard time tuning it.

Then you need to let it get fully warmed up and run through ignition setup/tuning to make sure you have timing correct, then disconnect the vacuum advance and plug at the carb.

Now go through the steps in this video to set idle mixture, hot idle RPM, choke, and cold idle properly.
xc_hide_links_from_guests_guests_error_hide_media

If you do it right and there isn't anything wrong with the carb itself, you should have a great starting and running engine after that.

Thank you! Yea previous owner knew nothing about vehicles, this was just a “cheap” truck to him. Found some vacuum diagrams on this site to help me run through them when I get home today! That was my first initial thought as I saw two that I know of just hanging out and didn’t look like they were supposed to be! That’s what’s got me baffled is it starts right up and idles fine, then will stall at stops, but once stop and put it in park It idles fine.

South90 · Mar 10, 2026

DoubleDingo said:
I would suggest replacing all of the vacuum lines, one by one, so you don't mess up the order or routing of them. You'd be surprised the problems a vacuum leak or leaks will cause. Don't rule out the carburetor base gasket either. Get a replacement while swapping the vacuum lines. PCV, replace that if it's not free-flowing.

Then, with no vacuum leaks, you can tackle the timing and air mixture on the carburetor. Using a timing light and vacuum gauge, get the engine running at maximum vacuum while idling and at operating temperature.

Once it's running good, add some quality fuel additive and run a couple tank-fulls of some cleaner additive fuel through it.

Adjust the valves, not required, but probably due for it.

Basically, give it a good tune-up, and get it cleaned out.

Thank you! I will definitely do that! Checking and replacing vacuum lines is my first step!

South90 · Mar 10, 2026

DoubleDingo said:
The only thing I would say to this, is, if you have the factory air cleaner housing, follow the tune-up adjustment directions on it, sometimes you have to leave everything hooked up, including the air cleaner housing screwed down to the carburetor when adjusting the timing. My 81 is like that. If I disconnect the vacuum line like I have always done, the timing is off when I hooked it back up, the timing on my engine has to adjusted with everything hooked up, and the air cleaner housing screwed on to the carburetor, and the engine at operating temperature.

Edit: The video doesn't show a varajet. The mixture screw adjustment is pretty much the same on carburetors, but there may some other adjustments needed on a varajet. I personally have never worked on a varajet, but a video showing the varajet should help you get yours working properly.

Oh that’s very good to know! I was thinking of doing it with the air cleaner off to make life easier to access the adjustment screws! But that makes total sense! Thank you for that! Yea I have found a couple schematics on the varajet 2se to help with adjustments!

DoubleDingo · Mar 10, 2026

South90 said:
Thank you! I will definitely do that! Checking and replacing vacuum lines is my first step!

That should fix a lot, but will definitely allow troubleshooting to go smoother without having vacuum leaks.

DoubleDingo · Mar 10, 2026

South90 said:
Oh that’s very good to know! I was thinking of doing it with the air cleaner off to make life easier to access the adjustment screws! But that makes total sense! Thank you for that! Yea I have found a couple schematics on the varajet 2se to help with adjustments!

I was curious, so I found a photo of my label, and wouldn't you know, I misread it/misunderstood it years ago when I read it. Either way I was wrong, I AM supposed to disconnect the vacuum on my engine at the distributor. I have to admit, though, when I have disconnected the vacuum to adjust the timing, the timing wasn't quite right after hooking the vacuum line back up. But, admittedly, I am going back in my memory banks here, I didn't readjust the timing when I changed all of my vacuum lines. I did have vacuum leaks galore and chased issues for a very long time, but I did not go back and check or adjust timing. Now that I am running the truck more and have fresh fuel in it, I need to do that, and do it per the label on the air cleaner. FYI: I did edit my post that you quoted, that way if someone comes in and reads it, that info will be correct as well. Glad I went and looked again at my label.

I hope you can get your truck running good. Keep us posted on anything you encounter or if it all works out and your issues get resolved.

DoubleDingo · Mar 10, 2026

Valve adjustment per the 2-Roll-Method...

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Ricko1966 · Mar 10, 2026

South90 said:
Thank you! Yea previous owner knew nothing about vehicles, this was just a “cheap” truck to him. Found some vacuum diagrams on this site to help me run through them when I get home today! That was my first initial thought as I saw two that I know of just hanging out and didn’t look like they were supposed to be! That’s what’s got me baffled is it starts right up and idles fine, then will stall at stops, but once stop and put it in park It idles fine.

Do not run the throttle stop screw in any more than you have to,and remember to get things set right in the near future,so you can get the throttle stop screw back in its correct position. A throttle stop screwed in just a little too far robs fuel from the transition circuit to idle. Then when you step on the pedal you've already used your transition,so you get a lean stumble when you step on the gas.

South90 · Mar 11, 2026

UPDATE: yesterday when I got home from work, since the time has changed and it’s sunnier longer now, I decided to start tackling the vacuum issue! Once I figured out what I was looking at and looking for it clicked! I ended up finding about 8 hoses that were not routed like the diagram(s)! Rerouted everything how it was supposed to be, along with checking all the lines for holes one at a time, she fired right up, and the idle even sounded a lot better! I wasn’t able to drive it around besides just my little drive way since I don’t have tags yet. When you put it in drive or reverse the rpms still drop a good bit! But on the plus side, It never once stalled out! Only time it did was turning the wheel to full lock! All in all a big difference from what I could tell!

My next step I would assume would be to get the vacuum guage and timing light from my father in law. Do the normal tune up. Check timing, vacuum, and make sure the carb is right!

S/n- (I’ll attach a picture) didn’t get into messing with the carb as I lost daylight but I took a picture with my phone and according to the layout, my fast idle screw isn’t touching anything? Shouldn’t it be?

DoubleDingo · Mar 11, 2026

South90 said:
UPDATE: yesterday when I got home from work, since the time has changed and it’s sunnier longer now, I decided to start tackling the vacuum issue! Once I figured out what I was looking at and looking for it clicked! I ended up finding about 8 hoses that were not routed like the diagram(s)! Rerouted everything how it was supposed to be, along with checking all the lines for holes one at a time, she fired right up, and the idle even sounded a lot better! I wasn’t able to drive it around besides just my little drive way since I don’t have tags yet. When you put it in drive or reverse the rpms still drop a good bit! But on the plus side, It never once stalled out! Only time it did was turning the wheel to full lock! All in all a big difference from what I could tell!

My next step I would assume would be to get the vacuum guage and timing light from my father in law. Do the normal tune up. Check timing, vacuum, and make sure the carb is right!

S/n- (I’ll attach a picture) didn’t get into messing with the carb as I lost daylight but I took a picture with my phone and according to the layout, my fast idle screw isn’t touching anything? Shouldn’t it be?

That's good news. RPMs will drop in gear, just the nature of the beast. If the engine was warm and the choke was open, the fast idle screw should not be touching anything.

South90 · Mar 11, 2026

DoubleDingo said:
That's good news. RPMs will drop in gear, just the nature of the beast. If the engine was warm and the choke was open, the fast idle screw should not be touching anything.

Ok sweet! I just wanted to make sure! Yea I knew they would drop, it just seems like it’s a bit too much still. Just gotta figure out how to adjust that

250 inline 6 Stalling issue, new to me truck!

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