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New owner '74 620 pick up.


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Received in trade for labor 1974 620 pickup. A farm truck with original sales slip from Nebraska dealership. Having some trouble with carburetor (at least I think it's carburation) starts and will idle all day long but stalls and dies when I rev it up unless I go very slowly. Once reved up stalls under load. I can move it around by revving it up and riding the the clutch but not able to drive reliably. Bought an ebay carb but it looks like one for L16 engine. Being a '74 it has an L18 engine. Pics of L18 carb don't quite look like mine. Looks more like a z24 carb.  Any help is appreciated.

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Some pics of the parts you are working with would be helpful. 

I would start with the fuel filter.  First get a new one and then dump the old one out to see what is in it. 

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New filter, fresh gas,filter still looks clean. I have been reading other posts on this topic and will be testing things out and keep posting as I go along.  Had this truck for 4 years now but just getting around to reviving it since retirement. Looking forward to being on this forum.

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Check the fuel level when running. There's a glass with a line or a dot on the window. But as it idles it's probably ok.  There are three circuits on this carb all separate. Idle, primary (low and mid range) and secondary (high speed and power). There is a slight overlap between idle and primary so you can rev it a bit but if the primary jet is blocked or partly blocked it will not get enough gas for the air rushing in. 

 

The primary jet us under the window on the front of the carburetor but a pain to get at. Probably better to spend half an hour and carefully remove the carburetor and do it right.

On the left side, below, are to hex shaped cover plugs that look like bolts. The primary is the bottom one, or the one that would be closest to the valve cover. Take the cap off and use an appropriate screw driver to reach up inside and remove the brass jet. I find that when you have a screw driver with the proper width on the end it won't fit the hole, so I ground it down. 

101_0099.jpg

 

The jet looks like this...

122-xx.jpg

 

 

Likely there is a blockage of the hole in the center. Poke it out with something soft like a toothpick. 

 

At this time it might be a good idea to remove the front window on the carburetor and clean out the fuel bowl of any sediment that may be there. Have a care... there are several small parts that can fall out.

 

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You may have traded one problem for another...

A worn out, oem carb, for a chinesey pos carb.

Or some other restriction to fuel flow.

These older trucks have accumulated a lot of crap in the tanks over the years, and the pick up tube may be sitting in a pile of rust flakes & mud.

My 521 was like that, and ended up having to replace the tank, because it had set for 12 years before I picked it up due to moisture in the mud rusting the steel bad enough that I pushed a hole through it with a stick when trying to see how much fuel was in it.

Your fuel line may be rusting closed also.

Once on the 521, when trying to chase down the fuel starvation problem, I ran a external tank in the bed , and a hose from the bed to the carb. Allowed me to get the engine tuned, before finding a fix for the rotten tank.

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make sure the gas is being squirted in when you cycle the linkage. This will be the accell pump in the carb.

 

also a bad condensore or points might cuase some of this or a worn out distributor bushing. But look like carb at first.

 

replace the fuel filter is good  But lets start with the basics before you swap out too much and introduce a proplem. These are very simple motors that Bushman in Africa can keep running.

a out of time distributor can cause this also.If you got the truck pretty much FREE was it bad when you got it. Maybe they did a timming chain and installed the distributor spindal off or something.

I always ck the motor timming and cam timming when I ck a unknown motor.

Edited by banzai510(hainz)
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I appreciate all the advice. I was told by previous owner that the distributor was replaced, new rebuilt alt, new starter, new battery, plugs and wires. Many other people have had their fingers in this truck, a lot of make do parts due to being a farm truck, so I am having to begin at square one. Quite possible that timing is off a tooth. Carb has been messed with as some of the screw head slots are distorted.  I have the carb off and will be doing a thorough cleaning.  Need to pick up a timing light and dwell meter to check timing. A work in progress! I normally hate working on vehicles because it was out of necessity (needed to be running to get to work kinda thing) but this is going to be a fun project. Still working on getting pics posted. Thanks!

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I also replaced the accelerator pump but did a monkey see monkey do so if previous owners messed with it, linkage may be in wrong. I do see it squirt fuel but don't know if it was too much or not enough. I will be downloading manual I saw posted so I will have a better idea of what to do to fix.

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I would maybe pop the valve cover to see if the rockerarms are ok and maybe adjust them. or a lash pad fell out unde a rocker arm. while there put the motor at TDC and ck the distributor orientation(Look under cap) and the cam timming.

 

I seen on stock carbs that the 2ndry side should have a spring to keep it closed.if weak it will prematurely open up causing a loss of vaccum

 

 

keep us posted

 

Edited by banzai510(hainz)
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Your problem is also the exact symptom of a bad condenser in the distributor.  New ones can and do fail.  Stock engine timing can do the same thing, so think about resetting your engine timing up a little higher like 10 degrees BTDC at idle, vacuum line disconnected.  

 

DO NOT assume that any of the "rebuilt" components were more than cleaned and reinstalled.  The distributor is one of the trickier ones to get right so pay close attention to your engine timing.  Rev the engine and watch the timing marks with a light.  Make sure it always goes back to the same steady mark at idle or you'll never get the carb adjusted right chasing moving timing.  

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