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  #1  
Old 09-11-2013, 08:31 AM
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vacaisle vacaisle is offline
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Accelerator pump question

I'm wondering if I put the wrong accelerator pump in. My kit came with two. One has a slightly longer shaft. Would the longer shaft yield a bigger shot of fuel?
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  #2  
Old 09-11-2013, 11:41 AM
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Quote:
Originally Posted by vacaisle
I'm wondering if I put the wrong accelerator pump in. My kit came with two. One has a slightly longer shaft. Would the longer shaft yield a bigger shot of fuel?

You mean the height of the button on the diaphragm? You should use the one that looks like the one that came out of there.

The pump shot is already adjustable, by choice of which holes you put the rod into. That is specific to your engine too.
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  #3  
Old 09-11-2013, 12:20 PM
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I think they mean the push rod on the diaphragm itself.

The carb rebuild kits often come with two pump diaphragms: one with a little button on it, and another with a long shaft. Somewhere else in the kit should be a small rod that if placed on the button diaphragm, should bring it to the same height as the shafted one.

Differences in length here will have an effect on the accelerator pump shot. The accelerator pump diaphragm should be not quite all the way out with the throttles completely closed, and the diaphragm should be all the way in when the lever on the throttle shaft hits the throat body. That way, the full volume of the pump can be used.
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Old 09-11-2013, 12:24 PM
JeepWrencher JeepWrencher is offline
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From what I remember when I rebuilt mine one of the shafts is for a manual and one is for an automatic.

It functions by pushing a bubble of fuel into the throat of the carb when you stab the peddal down. This is to make for better throttle response and acceleration.

I agree with the statement that when you rebuilt it you should have replaced it with the one that came out of it. I needed the longer shaft for my 83 J10.
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  #5  
Old 09-11-2013, 12:40 PM
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Yes. The push rod is what I'm referring to. I have the longer one in now. I bought a longer one and a shorter one, then months later bought a rebuild kit which came with the longer one. It had the longer one in it.
The issue I'm having is when I first start up in the morning I get a nearly un-noticable lag in acceleration. After about 2 times accelerating it goes away. It could also be choke related or maybe cold operation related. I'm just nit-picking because I just finished getting the carb dialed in perfect.
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Old 09-11-2013, 05:23 PM
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I vote for warm-up related issues.
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  #7  
Old 09-11-2013, 06:15 PM
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Yeah I'm not going to sweat it. It's pretty minor.
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Old 09-11-2013, 07:09 PM
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Quote:
Originally Posted by vacaisle
...The issue I'm having is when I first start up in the morning I get a nearly un-noticable lag in acceleration. After about 2 times accelerating it goes away. It could also be choke related or maybe cold operation related. I'm just nit-picking because I just finished getting the carb dialed in perfect.

That would most likely be because the choke pull off is a tad bit too lean for the initial cold condition. You could fuss with it... BUT if it starts up acceptably, I'd leave it alone and count your blessings. However, if the lag thing gets worse with colder weather then time to get out your 1/4" driver for more pull-off adjustments.
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  #9  
Old 09-11-2013, 07:41 PM
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yup

choke adjustment
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  #10  
Old 09-11-2013, 08:49 PM
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Quote:
Originally Posted by Rich88
That would most likely be because the choke pull off is a tad bit too lean for the initial cold condition. You could fuss with it... BUT if it starts up acceptably, I'd leave it alone and count your blessings. However, if the lag thing gets worse with colder weather then time to get out your 1/4" driver for more pull-off adjustments.

Why would you want a richer mixture for cold weather?
Wouldn't the pull off adjustment only affect the initial start up, then once you blip the throttle and take off the choke unloads based on the weakening spring tension in the housing?
Isn't this what rotating the choke cover is for?

Seems to me you'd want a leaner mixture so the choke unloads faster in cold weather.

Edit: I just read an older post of mine where you pretty much answered my question.
http://ifsja.org/forums/vb/showthread.php?t=166763
Quote:
Originally Posted by Rich88
The choke plate adjustment (turning the round choke thermostat housing) determines how long the choke stays on. The Haynes method is how I do it too. The tighter the spring, the longer it takes to unwind as it heats up.

The choke pull-off determines how much the choke plate opens upon initial start-up. This is critical to the choke mixture, which determines how well it stays running....

I'm still curious though; why would you want a richer mixture in colder weather?
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Last edited by vacaisle : 09-11-2013 at 11:03 PM.
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  #11  
Old 09-12-2013, 07:17 AM
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Quote:
Originally Posted by vacaisle
...

I'm still curious though; why would you want a richer mixture in colder weather?

The rich mixture overcomes the gasoline's tendency to condense out on the inside of the manifold passages when the engine is cold. Liquid fuel won't fire. The colder the ambient temp is, the harder it is to get fuel/air mix to the cylinders. Rich mixture - condensing fuel = normal mixture, more-or-less.
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  #12  
Old 09-12-2013, 10:17 AM
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Some of the bog is just the nature of a carburetor when the choke is engaged, and is to be expected, but you can minimize it.

As said, the accelerator pump needs to be adjusted just right, and as I mentioned, I set them to their richest position. Of course, I don't have to pass emissions...In the days before emissions, it was customary to over-fuel the pump, anyway.

There are a couple of things to check on the choke. One is the thermostat setting, or the round black cover. It adjusts how the enrichment reacts to increased airflow through the carb. If this adjustment is too lean, the engine will bog on tip-in and falter out at higher RPM when cold. Too rich, and tip-in will be messy and load up at higher RPM. The thermostat should be set to the index mark, and never moved more than 1/4 inch from it if necessary. It shouldn't need to be messed with if everything else is working properly.

The pulloff adjustment mainly affects the idle mixture, but also has an effect on tip-in. It is hard to get adjusted because an engine will idle on a very lean mixture, but will bog like crazy when loaded or accelerated. Set it to factory and go from there. When you set it to the factory setting, use a drill bit on the choke plate and use a finger to push the plate towards the closed position to take out slack in the linkage.
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  #13  
Old 09-12-2013, 12:07 PM
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I readjusted the choke today after discovering that the mark on the cover was slightly off center. The old cover I had which cracked and broke didn't have a mark on it and was positioned so that the electric connection was pointing straight down when it was on the truck. So that's how I put the new one on since I didn't see the mark and don't have any experience with 2150 choke settings. The Haynes manual says to set it 1.5 to 2.5 notches rich. 2 notches rich according to the mark and index notches was the point at which the choke plates fully closed when rotating the housing with the cam on the highest step so that's where I made the adjustments. I started it up and drove around a bit and didn't have the issue so hopefully this was the problem. I think I would describe the issue I was having as a messy acceleration and not a bog according to your descriptions of too rich vs too lean.

This is what it looks like. Does this seem about right?


The Haynes manual is really confusing because the diagram has slightly different instructions than the printed instructions. The diagram says to rotate 90* rich while the print says to rotate until the plates close. This is true for both the pull off adjustment and the fast idle cam adjustment. So this time I went with the printed instructions. Also on ristows rebuild post he doesn't mention rotating the housing.
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Old 09-12-2013, 12:46 PM
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Looks like the hot air connection is capped off. The choke is thermoelectric and won't work right without both electric and hot air connections.
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  #15  
Old 09-12-2013, 12:57 PM
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Yes I know. It just takes a little longer to unwind.
Does that orientation of the housing look about right though?
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Old 09-12-2013, 01:34 PM
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The electrical heater in the choke housing will not begin to warm up until it reaches 100 degrees from hot air supplied by the manifold heat tube. Without that tube, the engine will start and run well for a few minutes, but the choke will stay on longer than it should and the engine will run excessively rich until it warms up enough for the electric heater to kick on.

That's probably why you're loading up on acceleration.

Plus, it looks like some genius capped off the heat connection with a rubber vacuum cap, and since the choke housing is connected to manifold vacuum, the engine will draw a vacuum on the choke housing, which is not particularly good.
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Old 09-12-2013, 01:52 PM
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Ha! I'm the genius that capped it off. Wouldn't it be a vacuum leak if the hot air line isn't there? Planning on getting one soon before it gets cold.

But, is that roughly the orientation the housing should be in? I have no reference because when I got the truck the PO had done/broken all kinds of stuff.
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Old 09-12-2013, 02:10 PM
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It's normally connected to the air horn via the choke stove. There is an orifice in the choke body that limits the amount of air it can draw. So it's not very much more open with the cap off, than when connected to the choke stove.

Of course, with the cap off and not connected to the choke stove, the air that goes into the choke cover will not be filtered.
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Browless and proud: '82 J20 360/T18/NP208/3.73, Destination ATs, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
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Old 09-12-2013, 02:18 PM
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So is it a vacuum leak that is "supposed" to be open?
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Old 09-12-2013, 03:42 PM
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Quote:
Originally Posted by vacaisle
So is it a vacuum leak that is "supposed" to be open?
Yes. It is a controlled vacuum leak much like PCV and is compensated for in the calibration of the carburetor. It is there to pull hot air from the intake manifold stove through the choke housing to heat the coil. Filtered air from the air cleaner is supplied to one end of the heat stove and is pulled through the choke housing by manifold vacuum. Simply pulling off the vacuum cap will let unfiltered air into the carburetor.

There are lots of controlled vacuum leaks. As long as they are distributed to all cylinders equally and the carburetor is jetted just a tad richer to make up for it, the engine doesn't know the difference. A carburetor itself can be thought of as a controlled vacuum leak with lots of fuel added.
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Last edited by FSJunkie : 09-12-2013 at 03:46 PM.
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