Stalls while braking right before coming to a stop

[Kurt751990]

Alright so my 82 Ram 50 is giving me a slight problem. While driving along let's say in 4th gear at around 50 mph when I let off the throttle and shove my shifter into neutral then hit the brakes to slow down at say a stop sign just as i'm about to come to a stop my engine starts stumbling and then stalls on me. All other times my truck runs perfect. It idles fantastic. Moves nice and fast. Is a great truck but this stopping issue and the kicker is even when I just let it slow on it's own no brake at all it does this.

I have tried a few things. I have disconnected the brake booster vacuum hose and plugged it and it still happens. I have fiddled with the idle mixture screw and idle speed screw till I am blue in the face only for it to help a little and then sometimes my truck still stalls after doing adjustments. I'm out of ideas but know that when it starts to stall if I tap the gas it revs right back up. If I slow down with the hand brake it doesnt do this. I've sprayed all over for vacuum leaks and found none. I installed a vac canister and still the stall happens.

I notice my vac advance likes to pop noticeably loud and tick as it works. I'm not noticing any mentionable movement in my distributor. I do notice that when shining my timing light at the crank pulled the notch likes to move back and fourth not majorly but is definitely moving between 2 and 4 degrees as the truck runs when I work the throttle under the hood.

I'd like to get this stall issue under control as it's literally the only issue my truck has.

[geezer101]

There is a fuel cut solenoid on the carb. Normally if this decides it has died it will just kill the engine by starving it of fuel (and it will do it randomly like hitting a bump or a hard launch) The fact that is only doing it under braking means there is some sort of event that is triggered by the mass of the engine decelerating. Could be the fuel float (?) or the fuel cut solenoid, or something that is causing an electrical fault that is disabling the ignition circuit. Any other symptoms like engine detonation/pre-ignition? You will find there is always some timing flutter with aiming a timing light at the crank pulley. Try spraying the innards of the distributor with WD40 as the advance plate can get gummed up with crap and prevent smooth advance. If it was a continuous fault like a vacuum leak theoretically it would do it all of the time. Just an opinion

[Kurt751990]

Do you know exactly where this solenoid is? I have the 32/36 weber and I dont see any wires plugged into it at all.

[SubGothius]

If your Weber is mounted with the fuel float bowl towards the rear, the tendency to stall on abrupt deceleration seems to be a side-effect of that carb orientation. Momentum allows fuel from the bowl and fuel galleries to surge forward into the barrels, causing a rich condition that can lead to stalling. Going downhill can also run slightly rich due to gravity and the fuel level tilting towards the front, though usually this isn't bad enough to stall. Optimal bowl orientation is to have it in front, so it runs slightly lean on deceleration and downhill, and slightly rich on acceleration and uphill.

I'm not sure there's any easy way to mitigate this aside from braking gently and well in advance whenever possible; I usually also shift to Neutral to brake with the engine at idle, which seems to help. Turning the carb around to put the bowl in front should solve it, but then you've got to improvise throttle cable routing/orientation somehow. For this reason, the Weber DFEV is preferred over the mirror-image DGEV for intakes on the left-hand side with the cable coming from the right as our trucks have them.

[geezer101]

That's the missing piece. I thought you were still running the stock carb... Orientation of the Weber is crucial for proper operation. A hard deceleration would be more than enough to starve the fuel flow.

[Kurt751990]

You guys both raise an interesting point and I appreciate another factor to consider however before I sink a few hundred more dollars into my truck I need to exhaust all other options and potential causes first. I dont believe it's a fuel issue. I do not believe the fuel bowl is emptying as I can let off the brake and hit the throttle and the truck revs up and moves like normal. This is the point i've arrived at in trying to isolate the issue. I have found that the truck only does this under load i.e. when the truck is moving and I hit the brakes the truck starts stumbling and stalls. I had the idle set at 700 when the stalling would occur. I tweeked that number and idled my truck up to 1000-1100 rpms idle the truck no longer stalls but still loses a ton of rpms and as long as the brake is on drops to 600 rpms. This is what is pointing towards some kind of other issue being that the brakes applying are creating load so much so that it overcomes the power the engine is turning out and thus stalls the engine. This similar phenomenon occurs on my old tractor when dragging my plow too deep. The load simply becomes too great for the engine and the engine stops spinning. This is further shown when I idled up the truck to 1000-1100 rpms idle speed when the engine is now spinning/generating enough power to withstand the load and continue running. I will also add this in I have tried stopping the truck and holding the clutch down at the same time and the truck still loses all that power and if I have it idled down to 700 it still stalls. I dont have to tell you guys why that bit of info is important and creates yet another question. The clutch being pressed at the same time should disconnect the engine from the transmission/drivetrain and prevent the stalling altogether as then engine is then spinning independently of the drivetrain.

So before I drop a few hundred dollars on my truck a few questions must be answered. Why when I push the clutch in and hit the brakes does the stalling and rpm drop still occur? And also why are the brakes creating such a load that so much power from the engine is lost by simply applying the brakes? If it were a loss of fuel from the bowl in the carb I was experiencing why am I able to hold the throttle ever so slightly while braking and not experience this issue? And lastly if the bowl was emptying of fuel at such a rate or the fuel was not accessing the carb at such a rate why when I idle the carb up does the stalling not happen, if the fuel being inaccessible to the carb is the issue here no amount of increased idle would fix that?

[SubGothius]

It's not "emptying" the fuel bowl or "starving" the engine of fuel, which would be a lean condition.

Rather, it's a rich condition as fuel sloshes forward from the bowl, into the carb's fuel galleries and from there into the intake barrels, effectively flooding the engine with excess fuel that causes the stall.

Raising the idle or feathering the gas pedal helps mitigate this, as it allows the engine to burn off that rich intake charge more rapidly before it can snuff out combustion.

[Kurt751990]

Alright so with the air filter off if I push the truck forwards I will see the gas sloshing forward into the carb is that right?

[Kurt751990]

Yesterday afternoon I jacked my truck up from the back and cranked it up. Why did this not create a rich condition?

[geezer101]

Ok it is a rich condition from fuel surge as SubG has pointed out. The float is still going to want to shut off fuel supply when the bowl is full and the engine isn't experiencing it (the flooding) all the time, only from a long constant deceleration? It's probably the reason why you can't replicate the conditions while your truck is stationary.

[Kurt751990]

Alright well I need a way to test this definitively. There must be a way to recreate this phenomenon in a way I can visually see the fuel flooding into the engine. If anyone can tell me of a way to do this i'll do it.

[Kurt751990]

Another thing of note is by using engine braking staying in 4th gear as I press the brake pedal I can come to a stop without any issue what so ever.

[SubGothius]

You won't be able to see or replicate it when stationary or just pushing it around. The issue is momentum; when you brake the truck at speed, the fuel in the bowl keeps moving as fast as it was, so it rushes forward into the intake. Maybe not enough to even see if you, say, had a camera trained on the carb barrels, but enough to richen the mixture so much that combustion gets snuffed.

Like, you know how if you have a sack of groceries sitting on the passenger seat, and you brake abruptly, the sack can tip over and dump its contents on the floor, right? Now imagine that, instead of groceries, you've got an open pan full of liquid sitting on the seat -- it'd slosh forward and dump that liquid onto the seat and floor, right? Similar thing going on in your float bowl.

Most folks who've done the Weber swap used the cheaper and more readily-available DGEV, and just learn to deal with the brake-stalling issue one way or another -- e.g., braking gently and well in advance whenever possible, raising the idle, feathering the gas, etc.

[geezer101]

Another thing of note is by using engine braking staying in 4th gear as I press the brake pedal I can come to a stop without any issue what so ever.

The transmission and drivetrain is forcing the engine to maintain rpms, preventing the stall out. It will run hell rich, but as you reach the end of the 'deceleration curve' the surging fuel phenomenon is no longer being exaggerated (well, that's my theory...) I would be tempted to try modifying the ignition tune - smaller plug gap/more advance to improve air-fuel charge burn. The Weber is more sensitive to tuning than the factory Mikuni carb.

[Kurt751990]

I appreciate all the help. I work at an Aamco and the builder said if I bring my truck up here we can take the bottom plate off and take a look into the transmission. If we find anything and tinker with it ill report back what happens. I know both of you know about these webers a great deal and I am not discounting your wisdom but if the issue is momentum throwing the fuel into the intake by jacking the back of the truck up the fuel should be doing this while stationary as that's the position the vehicle is in when all this fuel throwing is happening.

[SubGothius]

Jacking up the back of the truck would only reproduce a downhill grade, not the momentum issue that the fuel briefly keeps moving at speed when you brake. Same reason we wear seatbelts -- if you crash, the truck stops but you'd keep moving without a belt strapping you to the seat.