Fuel Pump/Pressure Problem?
Mountain Pass
Joined: Aug 2007
Posts: 167
Likes: 31
I’m no carb expert. To me, a carb is a calibrated leak sitting on the intake manifold.
The engine seemed to accelerate okay, but then it hit a brick wall and would rev no higher. Could that be a power valve? Does the 2150 2bbl even have one? Is there a way to test it if so equipped?
The engine seemed to accelerate okay, but then it hit a brick wall and would rev no higher. Could that be a power valve? Does the 2150 2bbl even have one? Is there a way to test it if so equipped?
Laughing Gas
Joined: Aug 2010
Posts: 983
Likes: 49
From: Northern Kentucky
2150 carb definitely has a power valve. Seems like that could be the issue but I am no expert.
ETA: with the truck loaded as it was, it seems feasible that you were into the power valve more than usual. If it was weak, that could cause some form of failure. However, that doesn't explain the return to normal after the "washboard run.
ETA: with the truck loaded as it was, it seems feasible that you were into the power valve more than usual. If it was weak, that could cause some form of failure. However, that doesn't explain the return to normal after the "washboard run.
More Turbo
Joined: Oct 2020
Posts: 529
Likes: 54
From: Houston
You said the washboard road seemed to fix it at least temporarily. Could it be the float is sticking? I'm thinking sudden heavy load may let the bowl empty at bit, and rather than the float dropping and letting free flow of fuel, it stays at the happy, high, low load position. The bowl drains some, and it behaves like the float is mis-set. Low bowl level means less fuel intake. Testing is easy: next time it happens, pull over and give the bowl a few solid raps. That usually will loosen it up. If that fixes it for a while, you'll have found the problem.
Laughing Gas
Joined: Apr 2013
Posts: 1,049
Likes: 65
I could see a bad power valve or maybe a clogged main jet, but my fuel delivery problems have generally felt like running out of gas. Sputtering and cutting out. Feather the throttle for a minute to let the fuel bowl fill back up, and power is restored until the bowl is drained and it’s sputtering again. Try to push harder on the throttle when it’s sputtering and it’ll die.
Could the choke be closing?
Do you have a tach? What’s it doing when you’re losing power, Is it steady or bouncing around?
Otherwise FWIW:
Do you have an EGR? Maybe there’s a malfunction there that’s diluting your mixture with exhaust gasses at the wrong time.
Popping out the exhaust? Retarded ignition timing can cause it to run hot and lose power. Maybe the vacuum advance arm got disconnected from the pickup plate and the timing is off?
Dragging brakes on the truck or tow vehicle?
You already changed the coil. The Duraspark box could be acting up and changing it to a known good unit is about the only test. And it’s easier to try than changing out the pickup inside the dizzy.
Could the choke be closing?
Do you have a tach? What’s it doing when you’re losing power, Is it steady or bouncing around?
Otherwise FWIW:
Do you have an EGR? Maybe there’s a malfunction there that’s diluting your mixture with exhaust gasses at the wrong time.
Popping out the exhaust? Retarded ignition timing can cause it to run hot and lose power. Maybe the vacuum advance arm got disconnected from the pickup plate and the timing is off?
Dragging brakes on the truck or tow vehicle?
You already changed the coil. The Duraspark box could be acting up and changing it to a known good unit is about the only test. And it’s easier to try than changing out the pickup inside the dizzy.
Moderator
Joined: Jan 2001
Posts: 56,997
Likes: 2,742
From: Virginia
When the power valve fails, the engine will run noticeably rich. Failure it the diaphragm tearing. The only other failure which would be very rare would be a clogged passage to the power valve.
You could very well have some dirt in the bottom of the carb, and it can partially clog one or both main jets. You just have to pull the top of the carb off and have a look.
You could very well have some dirt in the bottom of the carb, and it can partially clog one or both main jets. You just have to pull the top of the carb off and have a look.
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Lead Driver
Joined: Nov 2013
Posts: 7,178
Likes: 1,174
Doh! Another little clue that escaped my mind:
When engine power was reduced, and I had to downshift, I was getting a light popping sound from the exhaust when I stepped on the clutch and let off the gas. Never had that before.
Also noticed the same light popping when compression braking down a hill. Never had that, either.
Sorry I forgot to mention these clues. Kinda had a lot on my mind, trying to nurse the truck home while switching to Plan B to salvage a little residual fun on this trip. The mechanic in me finds it hard to relax when I just want to fix it. At the same time, I know better than to tear apart the carb under less than ideal circumstances, especially since the engine seems quite capable of getting us safely home.
I have read up a bit on the power valve. Not super easy to diagnose, but most of the symptoms sound similar. It’s one of the first things I’ll check when I get home. Finding fuel on the dry side of the diaphragm would mean I’m on the right trail. I’ve got one on the way just in case.
When engine power was reduced, and I had to downshift, I was getting a light popping sound from the exhaust when I stepped on the clutch and let off the gas. Never had that before.
Also noticed the same light popping when compression braking down a hill. Never had that, either.
Sorry I forgot to mention these clues. Kinda had a lot on my mind, trying to nurse the truck home while switching to Plan B to salvage a little residual fun on this trip. The mechanic in me finds it hard to relax when I just want to fix it. At the same time, I know better than to tear apart the carb under less than ideal circumstances, especially since the engine seems quite capable of getting us safely home.
I have read up a bit on the power valve. Not super easy to diagnose, but most of the symptoms sound similar. It’s one of the first things I’ll check when I get home. Finding fuel on the dry side of the diaphragm would mean I’m on the right trail. I’ve got one on the way just in case.
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Lead Driver
Joined: Nov 2013
Posts: 7,178
Likes: 1,174
No EGR, blocked off with a plate when I closed off the exhaust crossover passage in the intake manifold.
Tach was steady during all this.
Thought about dragging brakes, but hadn’t noticed anything such as when coasting. I’ve had brakes drag on other occasions, and it was quite noticeable.
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Lead Driver
Joined: Nov 2013
Posts: 7,178
Likes: 1,174
Covered about 120 miles today. Did just fine cruising around 70, but still had a sluggish band from approximately 50-60. Above or below that you’d never know there was a problem. Still scratching my head over this one.
One additional clue, if it means anything. When in that sluggish band, I noticed a loud resonant droning, apparently from the exhaust. Once I got above 60, things quieted down dramatically. Throttle position had virtually no effect. The droning did stop with my foot off the gas, but otherwise the noise was consistent from 1/8 to full throttle. It wasn’t like the noise increased the wider you opened the throttle. The noise was either off or on. Jog anybody’s memory?
One additional clue, if it means anything. When in that sluggish band, I noticed a loud resonant droning, apparently from the exhaust. Once I got above 60, things quieted down dramatically. Throttle position had virtually no effect. The droning did stop with my foot off the gas, but otherwise the noise was consistent from 1/8 to full throttle. It wasn’t like the noise increased the wider you opened the throttle. The noise was either off or on. Jog anybody’s memory?
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FTE Legend
Joined: Nov 2015
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From: Angier, NC
You have a cat on the truck but I think not because of the GVWR?
How old is the muffler?
I have seen them plug up either from a cat that falls apart and gets trapped in the muffler.
The other is a baffle in the muffler that broke and is now blocking flow.
Sometimes you can bang on the muffler and if it rattles the baffle may be broken.
Dave ----
How old is the muffler?
I have seen them plug up either from a cat that falls apart and gets trapped in the muffler.
The other is a baffle in the muffler that broke and is now blocking flow.
Sometimes you can bang on the muffler and if it rattles the baffle may be broken.
Dave ----
Lead Driver
Joined: Jun 2013
Posts: 5,669
Likes: 1,160
From: Tolland, CT
You have a cat on the truck but I think not because of the GVWR?
How old is the muffler?
I have seen them plug up either from a cat that falls apart and gets trapped in the muffler.
The other is a baffle in the muffler that broke and is now blocking flow.
Sometimes you can bang on the muffler and if it rattles the baffle may be broken.
Dave ----
How old is the muffler?
I have seen them plug up either from a cat that falls apart and gets trapped in the muffler.
The other is a baffle in the muffler that broke and is now blocking flow.
Sometimes you can bang on the muffler and if it rattles the baffle may be broken.
Dave ----
That's where my thoughts are leaning, too.
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Lead Driver
Joined: Nov 2013
Posts: 7,178
Likes: 1,174
The exhaust system seems new in my mind, but when I checked my records that was seven years ago. I will try the tap test as suggested and will figure out how to check backpressure, too.
That resonant drone sure has me confused. That, and the sluggish band. Probably more than one issue going on, who knows.
Lead Driver
Joined: Apr 2002
Posts: 5,339
Likes: 1,248
Because you can hit 70 with a camper on flat ground I'm leaning away from clogged exhaust. If it is the problem then it's only a partial block. The drone could be a leak or a plug.
Have you tried clearing the jets by turning in the fuel air mixture screws? Count the turns in and open the same after clearing the orifice.
Also on the grades were you encountering head winds? With a camper that can be a significant factor.
Have you tried clearing the jets by turning in the fuel air mixture screws? Count the turns in and open the same after clearing the orifice.
Also on the grades were you encountering head winds? With a camper that can be a significant factor.