good idle, no acceleration
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good idle, no acceleration
I have a recently acquired 86 with 302 NON EFI (2 bbl carb) setup. It just started bogging on acceleration to the point of shutting down unless I feather the throttle or push the pedal to the floor, where it eventually catches up. It will run good at speed, if it ever gets there.
The only two changes since the last time it ran fine:
1. I found that the bimetallic spring in the electric choke was not connected and the choke plate would never open up. Now that it is connected, the choke plate acts normal as the engine warms up.
2. I put gas in it. (same place I fuel up with my other vehicles)
I just replaced the fuel filter, since the problem started, but it made no difference. In park, and revving the engine manually, I can see two strong streams of fuel from the jets...so its getting fuel (under those conditions).
Would the position of the choke housing affect the 'warm' running condition? or acceleration? I reinstalled it in the same basic position that it was in before fixing the spring issue but of course it wasn't working then.
I don't want to overthink this and start chasing ghosts since I feel this is probably related to either #1 or #2...
The only two changes since the last time it ran fine:
1. I found that the bimetallic spring in the electric choke was not connected and the choke plate would never open up. Now that it is connected, the choke plate acts normal as the engine warms up.
2. I put gas in it. (same place I fuel up with my other vehicles)
I just replaced the fuel filter, since the problem started, but it made no difference. In park, and revving the engine manually, I can see two strong streams of fuel from the jets...so its getting fuel (under those conditions).
Would the position of the choke housing affect the 'warm' running condition? or acceleration? I reinstalled it in the same basic position that it was in before fixing the spring issue but of course it wasn't working then.
I don't want to overthink this and start chasing ghosts since I feel this is probably related to either #1 or #2...
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From: Northeast, OK
Ok, let me check my understanding. The truck ran well until you "fixed" the choke? And, after that it idles fine but doesn't want to pull unless you give it full throttle?
If that's the situation, then I think the "fix" isn't right. The position of the choke can easily impact the warm running and the acceleration. And my guess is that for some reason the choke is on rather than off.
If that's the situation, then I think the "fix" isn't right. The position of the choke can easily impact the warm running and the acceleration. And my guess is that for some reason the choke is on rather than off.
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another thought...
Since the choke is working now, at least in terms of opening/closing the choke plate, wouldn't the carb need to be adjusted to compensate? In other words, before (when the bimetallic spring was disconnected, the choke plate stayed almost closed...like it would in a cold start position. Now, the plate fully opens after a brief warm up and allows much more air into the mixture...correct? Do I need to richen the mixture to compensate for the larger air input?
Maybe I'm over exercising my idiot's knowledge of carburetors...
Since the choke is working now, at least in terms of opening/closing the choke plate, wouldn't the carb need to be adjusted to compensate? In other words, before (when the bimetallic spring was disconnected, the choke plate stayed almost closed...like it would in a cold start position. Now, the plate fully opens after a brief warm up and allows much more air into the mixture...correct? Do I need to richen the mixture to compensate for the larger air input?
Maybe I'm over exercising my idiot's knowledge of carburetors...
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Ok, let me check my understanding. The truck ran well until you "fixed" the choke? And, after that it idles fine but doesn't want to pull unless you give it full throttle?
If that's the situation, then I think the "fix" isn't right. The position of the choke can easily impact the warm running and the acceleration. And my guess is that for some reason the choke is on rather than off.
If that's the situation, then I think the "fix" isn't right. The position of the choke can easily impact the warm running and the acceleration. And my guess is that for some reason the choke is on rather than off.
Maybe I should go back in and disconnect the spring.
Gary, I'm also the one with the hack job DSII conversion that needs to be re-wired (although seemingly functional). I can't rule out something there too I guess, although the timing of my current condition seems coincidental around my recent "tweeks"
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From: Northeast, OK
Yes, the timing makes the choke suspect. As for adjusting the carb, about all you can adjust on a 2150 is the idle air/fuel mix. Yes, you should adjust that with the engine warm and the choke off. Adjust it for max RPM or vacuum - same difference.
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So, rotating the choke housing seems to modify the amount the choke plate closes at rest, when cold. Does moving it alter anything other than that?
Assuming the above answer is 'no'...I should warm up the engine and set the air/fuel screws equally to provide the max rpm possible at idle? I've turned them all of the way in, then equally out 2.5 turns. Engine ran a little rough, so I backed them out another .5 turn (3 turns total) until it idled smoother. Any further out than 3 turns didn't seem to have any further effect.
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From: Northeast, OK
Rotating the choke housing changes how much the choke comes on at any given temp, and the time it takes to come fully off.
Your approach on adjusting the idle mix is good, but I'm concerned that opening them up more that 3 turns had no further effect. You continue to add fuel to the mix the further you turn the screws out, so at first blush you'd think that you could eventually make the mix too rich and bog the engine. However, two things may be coming into play. First, you may have vacuum leaks that are admitting air into the system so the amount of gas through the idle ports may not be enough to go seriously rich. And, there are restrictions placed in the idle passages to limit the amount of fuel, so those may be preventing the mix from going seriously rich.
So, I think you need to look things over very closely for leaks. Check all of the vacuum lines from end to end looking for cracks. Pull each line off and plug the port where it goes with your finger and see if the engine changes RPM significantly, which could indicate that the hose or whatever is hooked to it is leaking. And, check the gasket where the carb bolts to the manifold.
Your approach on adjusting the idle mix is good, but I'm concerned that opening them up more that 3 turns had no further effect. You continue to add fuel to the mix the further you turn the screws out, so at first blush you'd think that you could eventually make the mix too rich and bog the engine. However, two things may be coming into play. First, you may have vacuum leaks that are admitting air into the system so the amount of gas through the idle ports may not be enough to go seriously rich. And, there are restrictions placed in the idle passages to limit the amount of fuel, so those may be preventing the mix from going seriously rich.
So, I think you need to look things over very closely for leaks. Check all of the vacuum lines from end to end looking for cracks. Pull each line off and plug the port where it goes with your finger and see if the engine changes RPM significantly, which could indicate that the hose or whatever is hooked to it is leaking. And, check the gasket where the carb bolts to the manifold.
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I looked everything over this afternoon and replaced a couple of plugs on vac lines that were cracked...didn't notice any change when removing the cracked plug and plugging with my finger though. Sprayed carb cleaner around the gaskets and vacuum port areas with no noticeable change to rpm.
As it sat, I had ~21cm vacuum pressure running warmed up. I reset the air/fuel mix to 1.5 turns out and the vac dropped to ~15. Turning them in 1/2 turn increments, I was able to max the vac pressure out at 21cm @ 3.25 turns out. Turning the mixture screws out any more had no change in vac pressure. I reset the idle speed along the way to keep the idle "normal".
Took it for a quick spin and had the same results...runs fine at idle to light throttle but quickly dies when taking off from a stop or quickly accelerating.
Is it possible that I have junk in the carb, causing fuel restriction when under load...but not at idle/revving? I'm thinking my next step is to remove and clean the carb...?
As it sat, I had ~21cm vacuum pressure running warmed up. I reset the air/fuel mix to 1.5 turns out and the vac dropped to ~15. Turning them in 1/2 turn increments, I was able to max the vac pressure out at 21cm @ 3.25 turns out. Turning the mixture screws out any more had no change in vac pressure. I reset the idle speed along the way to keep the idle "normal".
Took it for a quick spin and had the same results...runs fine at idle to light throttle but quickly dies when taking off from a stop or quickly accelerating.
Is it possible that I have junk in the carb, causing fuel restriction when under load...but not at idle/revving? I'm thinking my next step is to remove and clean the carb...?
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From: Northeast, OK
I think you did a good job setting the idle air/fuel ratio. So, let's move on.
It is very possible you have junk in the carb. That carb is easy to work on - even w/o pulling the carb you can pull the top off and look into the bowl.
It is very possible you have junk in the carb. That carb is easy to work on - even w/o pulling the carb you can pull the top off and look into the bowl.
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Have you tried that yet? Right now you're getting good advice about checking for junk in the carb, etc., so I'm very hesitant to steer you in another direction. However, since that was the only mechanical change you made before the sudden onset of the problem, it seems likely to be a factor. It would only take a couple of minutes, right? Normal troubleshooting flow would have you try it, maybe if only to humor me before getting deeper into other possible causes.
Could be the previous owner found the choke plate somehow closing when it shouldn't. His "fix" may have been to disconnect the spring, and it sorta worked. I'd suggest disconnecting the spring again for giggles and try it that way. Try one pass that way and see what happens. Maybe even try a second pass with the choke linkage wired fully open. Triple check that doing so won't affect the throttle linkage, just to be safe. Once you've ruled out the choke, you can proceed again with the previously suggested carb troubleshooting.
I just had another thought while typing. What if reconnecting the choke spring fixed that issue, but changed the vacuum level as sensed by other systems? Perhaps the EGR valve (or something else) is not fully closing and a change in the vacuum signal is partially responsible. I'm just thinking out loud here, so don't rush out to mess with that.
Could be the previous owner found the choke plate somehow closing when it shouldn't. His "fix" may have been to disconnect the spring, and it sorta worked. I'd suggest disconnecting the spring again for giggles and try it that way. Try one pass that way and see what happens. Maybe even try a second pass with the choke linkage wired fully open. Triple check that doing so won't affect the throttle linkage, just to be safe. Once you've ruled out the choke, you can proceed again with the previously suggested carb troubleshooting.
I just had another thought while typing. What if reconnecting the choke spring fixed that issue, but changed the vacuum level as sensed by other systems? Perhaps the EGR valve (or something else) is not fully closing and a change in the vacuum signal is partially responsible. I'm just thinking out loud here, so don't rush out to mess with that.
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ok. I took the top off of the carb(with it still mounted) and cleaned the bowl out. There was a little fine junk at the bottom but it was very minimal. Did a fuel pressure check, measured @ 8psi...which I believe is normal, I read somewhere that it should be 5-7. Put it all back together and got the same result. Dies on takeoff.
Tested the fuel output...got 12oz @ 20 sec and 18oz @ 30 sec. Shop manual I have says 1 pint over 20 seconds...so, I'm quite a bit lower than that. Not sure if that's enough to make a markable difference...? Fuel pump looks like it's rated for 5.5-9psi / 30gph.
Disconnected the choke spring as suggested. No change. Still dies on acceleration.
I notice that what I would consider "normal" throttle for takeoff is where it fails...just normal takeoff, not trying to burn the tires off. However, if I give it substantially more gas (jackrabbit takeoff) it will get up and accelerate somewhat normally...most of the time. A couple times once I got it up to ~35mph it felt pretty surgey, almost like a fuel restriction.
Any ideas on what I should check next? Still starting and idling ok...
Tested the fuel output...got 12oz @ 20 sec and 18oz @ 30 sec. Shop manual I have says 1 pint over 20 seconds...so, I'm quite a bit lower than that. Not sure if that's enough to make a markable difference...? Fuel pump looks like it's rated for 5.5-9psi / 30gph.
Disconnected the choke spring as suggested. No change. Still dies on acceleration.
I notice that what I would consider "normal" throttle for takeoff is where it fails...just normal takeoff, not trying to burn the tires off. However, if I give it substantially more gas (jackrabbit takeoff) it will get up and accelerate somewhat normally...most of the time. A couple times once I got it up to ~35mph it felt pretty surgey, almost like a fuel restriction.
Any ideas on what I should check next? Still starting and idling ok...
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Am I dreaming or did you say you have two strong streams of gas shooting into the carb when you hit the accelerator? If so, then it isn't the accelerator pump, although it sounds like it is. If not, then I suggest that's the problem.
But, if you do have two strong streams then I'm at a loss. Another frequent problem is the power valve, but your symptoms are the reverse of that being bad.
But, if you do have two strong streams then I'm at a loss. Another frequent problem is the power valve, but your symptoms are the reverse of that being bad.