Truck sputters and dies but idles good

[kudu]

I have a weber 32/36 on my l20b with an iske cam in it for some reference. For some context I was driving my truck for a few months with no issues but started to see some binding in the carb so i let it sit for a few weeks while getting the part and swapped out the bent arm. After putting the carb back on it starts up and idles great, but when you put it in gear and start to move it pops and dies. It floats around mid 13s at idle on my afr and has 10 in hg of vacuum(seems low to me). This is with my mix screw almost all the way in, with it further out it’s in the 12s and vacuum basically stays at 10. all of the wheels spin and nothing seems to be locked up. I’be talked to a few people but it’s net nothing in return. Anyone have any ideas what could be going on?

[Stoffregen Motorsports]

Did you remove the accellerator pump for any reason?

[banzai510(hainz)]

On 8/2/2022 at 5:42 PM, kudu said:

some binding in the carb

what does this actually mean?

620 use a cable so I dont see how it would bind unless a half ass cable run with a sharp bend

 

most times to me idle then loads up is a distributor timing off/Instralled wrong.

 

As for the mension accel pump one should see gas being pumped when gas cycled. If yes then thats good. after that its vacuum going thru a main jet.

 

Is the choke ELECTRICAL CHOKE  still ON and cutting it out? where you forgot to hook up the 12volt choke wire?  mess with choke adjustment on the heatercoil.

 

 

was anything else done you didnt tell us.

 

 

[banzai510(hainz)]

could be a clogged fuel filter but this happens at a higher rpm as the float bowl should have enough to drive a few hundered yard before it empties out.

since you got elelctrical ignition its not a point igntition bounce issue

[kudu]

On 8/4/2022 at 9:20 AM, banzai510(hainz) said:

what does this actually mean?

620 use a cable so I dont see how it would bind unless a half ass cable run with a sharp bend

 

most times to me idle then loads up is a distributor timing off/Instralled wrong.

 

As for the mension accel pump one should see gas being pumped when gas cycled. If yes then thats good. after that its vacuum going thru a main jet.

 

Is the choke ELECTRICAL CHOKE  still ON and cutting it out? where you forgot to hook up the 12volt choke wire?  mess with choke adjustment on the heatercoil.

 

 

was anything else done you didnt tell us.

 

 

one of the rods on the carb bent that moves the upper butterflies and it was causing them to bind open sometimes and make a scrapping noise. it does have the electric choke but it isn’t wired up. that’s how i got the truck so i assumed it was fine that way. the fuel filter is new. the accelerator pump squirts fuel on the pull of the bellcrank i can watch it do that.

[kudu]

i did just do a compression test on the motor and it threw 75 65 65 70 which makes me believe that that could be the cause of my issue. am i off on this? It does have an iske cam in it that the previous owner put in so i was going to ensure timing was right but let me know what you think

[Ooph!]

Compression test done with full open throttle?

[datzenmike]

AFRs mid 13s so slightly rich, but ok. 12s is totally wrong. 14.7 would be great and much cleaner burning if you idle a lot and don't want the plugs to foul.

 

Vacuum should be more like 18 but you say cam, so high overlap will kill the vacuum. Still 10 seems way way too low. I would check that all your valves are at the proper lash. Adjust the carburetor using a vacuum gauge to get the highest reading at idle.

[Stoffregen Motorsports]

15 hours ago, kudu said:

one of the rods on the carb bent that moves the upper butterflies and it was causing them to bind open sometimes and make a scrapping noise. it does have the electric choke but it isn’t wired up. that’s how i got the truck so i assumed it was fine that way. the fuel filter is new. the accelerator pump squirts fuel on the pull of the bellcrank i can watch it do that.

The "upper" butterflies are the choke plates and should be open during normal operation, so I doubt that's your problem. They do tend to make noise when opening and closing.

 

Compression tests are great for diagnosing a tired motor, or a blown head gasket, but I doubt if it has much to do with what you have going on.

[kudu]

21 hours ago, datzenmike said:

AFRs mid 13s so slightly rich, but ok. 12s is totally wrong. 14.7 would be great and much cleaner burning if you idle a lot and don't want the plugs to foul.

 

Vacuum should be more like 18 but you say cam, so high overlap will kill the vacuum. Still 10 seems way way too low. I would check that all your valves are at the proper lash. Adjust the carburetor using a vacuum gauge to get the highest reading at idle.

i went to adjust the valves and i got the notch lined up on the crank pulley but the cam “1” is slightly off to the left of straight up and down. Yet on the cam gear there are three “V” notches that I can see through the four holes on the gear yet there isn’t one that’s behind the hole closest to the 1 on the gear. I’m not sure where to go from here since I don’t know if the cam is off since i have nothing to go off of to line up with the sprocket notch. any ideas?

[kudu]

also with the mix screw on the carb basically all the way in is the mid 13s i was getting for the AFR. unscrewing it would drop it down below 13 into the 12s and still with 10 on vac

[kudu]

7 hours ago, Stoffregen Motorsports said:

The "upper" butterflies are the choke plates and should be open during normal operation, so I doubt that's your problem. They do tend to make noise when opening and closing.

 

Compression tests are great for diagnosing a tired motor, or a blown head gasket, but I doubt if it has much to do with what you have going on.

when it was idling they were open, no all the way but they were open

[datzenmike]

Set to exactly TDC on the number one cylinder's compression stroke* by turning up to the timing mark in a clockwise direction. If you overshoot, back up well before the mark and try again. Must be clockwise direction and stop at precisely TDC. This assures that the timing chain on the tension side had no slop and gives an accurate reading.

 

* If you have the valve cover off the first two cam lobes should be roughly 2 o'clock (exhaust) and 10 o'clock (intake) as viewed from the front. This only yells you you are on the compression stroke.

 

Look through the top hole on the cam sprocket and down behind it. There will be a V notch and just above it on the cam thrust plate is a small horizontal etch mark. To be properly timed the V should be below and slightly to the right of the etch mark as viewed from the front.

 

 

This is an L16/18 that is perfectly timed. They are set on the #1 hole at the factory. L20Bs are set on the #2 sprocket hole. See what you have but DO NOT try to remove sprocket and change anything until you know how to block the chain tensioner. This is important!!!