Idle mixture and idle speed screw un responsive (1 Viewer)

[fjc-man]

Do you have a vacuum gauge? What’s your vacuum at idle?

 

[yomumsbum]

Do you have a vacuum gauge? What’s your vacuum at idle?

nah mate no vac gauge unfortunately

 

[Mark W]

Sometimes the shafts that the butterflies are attached to get sticky. Use your hand on the carb linkage to make sure it is closed all the way. If this makes a difference, and if it tries to stick without closing all the way after you have reopened it, try installing a heavier throttle return spring. This is not an uncommon problem. it make not be *your* problem, but check and eliminate this possibility before going any further.

Mark...

 

[73FJ40]

nah mate no vac gauge unfortunately

Make your own with clear tubing and a ruler. One mm hg = 13.6 mm water. You hang the tubing in a vertical "U" shape, partially fill it with water, attach one end to manifold vacuum, the other end open to atmosphere.

20 mm of Hg = 27.2 cm of water (10.7 inches of water for the imperial folks). You could attach it to a board an mark it with your own graduations. Keep it vertical.

 

[yomumsbum]

Sometimes the shafts that the butterflies are attached to get sticky. Use your hand on the carb linkage to make sure it is closed all the way. If this makes a difference, and if it tries to stick without closing all the way after you have reopened it, try installing a heavier throttle return spring. This is not an uncommon problem. it make not be *your* problem, but check and eliminate this possibility before going any further.

Mark...

great suggestion, thanks

 

[yomumsbum]

Hey heres a bit of an update for you all. I had a spare carby laying around so i put that bad boy in. the good news is i can get the revs down to 600 rpm.
looking down the barrel of the carb there is no fuel squirting when idling and cutting power to fuel solenoid kills engine. so i think those are good signs. However the idle mixture screw is still having extremely little if any effect on rpm, so i cant do this lean drop still. Timing looks good its just above the standard timing mark (not the bb). Took it for a drive it feels quite underpowered and got the odd missfire/ sputter so i really want to get this mixture right

 

[charliemeyer007]

What is your dry and wet compression? How old is the gas - add some gas dryer anyway. Put on a new fuel filter. How loose is the rotor bug shaft in the distributor? I'm talking rocking perpendicular to the rotation axis.

 

[yomumsbum]

What is your dry and wet compression? How old is the gas - add some gas dryer anyway. Put on a new fuel filter. How loose is the rotor bug shaft in the distributor? I'm talking rocking perpendicular to the rotation axis.

Thanks for your reply, i havent done any compression tests. As for the fuel, i just fueled up the other day, i will get a new filter tomorrow the other one is a couple months old. And there is a small bit of play in the rotor but it still feels tight.

 

[charliemeyer007]

Early spring and late fall I can have hot days and cold nights. If the gas tank isn't full, then the air exchange condenses tons of water out of the air into the gas tank - big fan of gas drier - other wise the truck runs like crap. Some gas station have bad gas - never get any if they are filling their tanks from the truck - dumping it in mixes up all the crap they have in the bottom of their tank. Every once in a while I top mine off with mid or high grade - different detergent/additive package can help clean your system.

 

[Mark W]

Look for vacuum leaks.

Mark...

 

[pb4ugo]

If your timing is set "just above the standard timing mark(not the bb)", it's gonna run sluggish and like crap.

 

[trainbufftony]

The order of operations says Compression check first.
If your engine has no compression or low compression, nothing that you do externally will ever make it run right.
If you check it and get 150psi or better on all holes, then you can be confident that you've got a good healthy engine and begin working on external stuff, valve clearance, timing, vacuum leak elimination, then (and only then) should you start diddling your carburetor.

 

[Pighead]

If your timing is set "just above the standard timing mark(not the bb)", it's gonna run sluggish and like crap.

This^. The BB in the center of the window is the 7* BTDC the book calls for. It's fine for getting it running, most of our engines like a little (or more) advanced timing to drive. A lot of people like 17* advance, that's where the BB is just disappearing out of the window.

 

[yomumsbum]

hopefEarly spring and late fall I can have hot days and cold nights. If the gas tank isn't full, then the air exchange condenses tons of water out of the air into the gas tank - big fan of gas drier - other wise the truck runs like crap. Some gas station have bad gas - never get any if they are filling their tanks from the truck - dumping it in mixes up all the crap they have in the bottom of their tank. Every once in a while I top mine off with mid or high grade - different detergent/additive package can help clean your system.

I did notice my old carby was pretty filthly (only 4 months old) with a lot of big particles in the main barrel. I have got a bottle of Fuel additive, hopefully it keeps this new carb clean for longer.