Stumble after hard braking or deceleration down hill

orange150

orange150

Well-Known Member
Joined
Mar 20, 2005
Location
Fairfax City, VA
I’m having an issue with my Jeep where it stumbles after I brake firmly or if I’m decelerating (engine braking) down hill.

I just finished going through the carb (mc2150) to make sure it was nothing internal; I replaced the power valve, accelerator pump diaphragm, and needle and seat. I also set the float at 29/64, dry.
I have not yet had a chance to check it wet.

I’ve confirmed it has nothing to do with the brake booster, if I mash the brakes it doesn’t bog or anything, but if I roll forward and hit the brakes hard enough to slosh my drink it starts to stumble again.

I have not yet tried rolling backwards to see if that makes a difference.

Any ideas what could be the cause of this stumble?
Like I said, I need to still check the wet fuel level, but outside of that I’m stumped.
 
a_kelley said:
Bad wiring/ignition wires shorting?
Click to expand...
That’s actually one of the reasons I just swapped to HEI. The wiring and computer was so old that I just wanted to swap it.

I’ve not ruled out the fuel pump, but it is only a few years old. Can’t remember the brand but I’m 99% sure it came from NAPA.
 
I bet fuel is sloshing out of carb bowl into venturis. Raise your bowl vent up with rubber hose kind of just jam it in there on both sides to raise them up temporary and see if changes anything. If it does drill them and tap them and raise them up or run a crossover tube between them with small holes drilled across the top.
 
Infamous1 said:
I bet fuel is sloshing out of carb bowl into venturis. Raise your bowl vent up with rubber hose kind of just jam it in there on both sides to raise them up temporary and see if changes anything. If it does drill them and tap them and raise them up or run a crossover tube between them with small holes drilled across the top.
Click to expand...
I’ve had that thought! Similar to those “off road” carbs Holley sold. I will definitely try that.
 
Ok, I've not yet tried the bowl vent trick yet. Will probably run by the parts store tomorrow to pick up some hose to fit the vent.

What I did do was confirm proper float level with a wet measurement. I set the dry measurement to 29/64 per the internet, what I found with the wet measurement was the fuel level was below what it should have measured, .875". So I corrected that and it's still doing it.
I will still try the vent trick just to be sure. I still think I might swap the fuel pump too.
 
Getting close. I replaced the fuel pump and extended the vents all the way to just below the air filter lid (about 1/4" - 3/8" from the top) using some 5/8 hose around the vent horns. Now the only time I can get it to stumble is under firm braking on an downward incline whereas before it would do it even if I braked hard on flat ground. It doesn't stumble nearly as bad as it did before either.

I guess I'll mess with my float level a bit to see if I can't get the rest of the stumble out? There's a guy selling a kit that blocks off one of the vents completely and reduces the size of the other, I may try to DIY that.

I wouldn't be so concerned about it if I wasn't planning to actually use the dang Jeep. I would actually like to wheel with some of y'all at some point!
 
Looking at the fuel bowl itself I don’t quite understand how it’s still happening, especially with the vents raised so much.

Front of the vehicle is to the left.
F9FB8539-6C83-496B-A06A-19C759B5E012.png

This is a screen shot from a video, top of the float is wet from me messing with it.
 
I had to back the float level down on my old 2100 farther than the interwebs recommended.
At "spec" level, it would flood taking a hard turn off an exit or slamming the brakes.
Just kept lowering it until that stopped and it would stay running everywhere else.

Another thought, does the gasket you're using cover the bowl entirely?
 
I'll keep fiddling with the float. Before I was worried it was too low and uncovering the jets.

I'm using this style gasket. You can see the drivers side vent is a near direct shot to the bowl. I believe that's why that one is typically capped.

IMG_7066.JPG
 
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