Im running a holley 1940 ontop of a 200ci. Whats strange is the fuel mixture screw doesnt do much at all. If you go almost all the way in it misses a little but then you can turn it all the way out and it runs normal. Also, my idle speed screw wont go any lower. It idles at 700 rpm now and the only way i can lower it is to retard the timing. any ideas as to what could be wrong?
whats wrong with my carb?
- Thread starter rmoe88
- Start date
pedal2themetal45
Famous Member
Disconect the pedal linkage at the carb just to be sure its letting it return all the way... I have seen that happen on many ocation.
If you can screw the mixture screw all the way in and the motor doesn't die then there may be a vacuum leak OR if it is idleing to fast it can be past the idle circut.. and the mixture screw does'nt realy do anything then.
Also there is two (2) idle screws are you adjusting the right one?? one is for the Fast idle.. it well rest against a notiched cam attached to the choke linkage. the other well be aginst the linkage where the pedal linkage hooks up..
As Far as the idle mixture screw adjustment goes.
1) turn it in untill the motor starts to miss or the ilde drops
2) turn it out to the best/smothest idle
3) lean drop it by turning it in just enough to hear a small drop in idle.
This adjustments are fine tunning the carb and a little goes a long way 1/8 to 1/4 of a turn at a time.
Good luck
Tim
If you can screw the mixture screw all the way in and the motor doesn't die then there may be a vacuum leak OR if it is idleing to fast it can be past the idle circut.. and the mixture screw does'nt realy do anything then.
Also there is two (2) idle screws are you adjusting the right one?? one is for the Fast idle.. it well rest against a notiched cam attached to the choke linkage. the other well be aginst the linkage where the pedal linkage hooks up..
As Far as the idle mixture screw adjustment goes.
1) turn it in untill the motor starts to miss or the ilde drops
2) turn it out to the best/smothest idle
3) lean drop it by turning it in just enough to hear a small drop in idle.
This adjustments are fine tunning the carb and a little goes a long way 1/8 to 1/4 of a turn at a time.
Good luck
Tim
thank you tim, i still have some more questions for you 
I just checked the pedal linkage, it seems fine and lets the carb return completely to idle.
The idle screw wont let the engine go any lower than 700rpm but what do you mean by "OR if it is idleing to fast it can be past the idle circut.. and the mixture screw does'nt realy do anything then."
Im adjusting the idle speed screw, the one that pushes on the pedal linkage, the second one you mention.
idle mixture screw adjustment - does the mixture lean out or richen when you turn it clockwise?
i did #1 and #2, what does "lean drop" in #3 mean? is that suppost to be after i have found the best idle in #2? other than when the mixture screw is most of the way in (it misses then) turning it doesnt realy do much at all. you say 1/8 to 1/4 turns but i cant see, hear, or feel anything unless i i turn it 3-4 full revolutions either way. my rpm guage doesnt read a difference either.
I just checked the pedal linkage, it seems fine and lets the carb return completely to idle.
The idle screw wont let the engine go any lower than 700rpm but what do you mean by "OR if it is idleing to fast it can be past the idle circut.. and the mixture screw does'nt realy do anything then."
Im adjusting the idle speed screw, the one that pushes on the pedal linkage, the second one you mention.
idle mixture screw adjustment - does the mixture lean out or richen when you turn it clockwise?
i did #1 and #2, what does "lean drop" in #3 mean? is that suppost to be after i have found the best idle in #2? other than when the mixture screw is most of the way in (it misses then) turning it doesnt realy do much at all. you say 1/8 to 1/4 turns but i cant see, hear, or feel anything unless i i turn it 3-4 full revolutions either way. my rpm guage doesnt read a difference either.
Mercury Mike
Famous Member
There's a screw on the valve cover side of the carburetor. That's the fast idle screw, and it doesn't only control the idle speed when the car first starts up. Turn that one as far out as it will let you without the car dying, and then adjust the idle mixture screw. Once you have the mixture where you want it, use a tachometer and turn the fast idle screw in until you get the desired RPM. Then go back and forth adjusting them until it's right where you want it.
Mercury Mike
Famous Member
Turn the fast idle screw all the way out, and then the mixture screw all the way in. The car should die. If not, your timing is too advanced, or you have a bad vaccuum leak. Recheck for top dead center, with the distributor out, make sure that the rotor is pointing towards #1 plug node, and fire it up with the distributor slightly tightened. Then advance the timing, with the vaccuum to the carburetor plugged, and set the timing to like 12*. Tighten it down, reconnect the vaccuum. Adjust the idle now.
well i went over to my dads to have him help me. Before we started to do what 65stang200 suggested he did something that suprised me. With the car running he cuped his hands and put them over the carb and it didnt die or loose any rpm! he even took a rag and did the same thing and nothing. so we started looking for leaks. When i took off the little breather over the hole where you pour oil into the valve cover i noticed a MASSIVE rush of air INTO the hole. the air was trying to go through the pvc valve into the engine. i took the breather off and ducktaped the hole shut (just temperary) and the car lost like 200rpm, and now the idle mixture screw seems to react more, but still not like pedal2themetal45 discribed. But even then you can put your hands over the carb and it wont die. so i took the pvc valve off and pluged the intake log end (for now) just to shorted my list of places a leak can come from. We cleaned the carb recently and tightened everything well so i dont think the leak is coming from the carb. Can anyone think of other places to look for a leak, or show me if my logic is wrong.
thanks.
thanks.
Mercury Mike
Famous Member
Check the timing still.
Is it an auto? If so, are you setting the idle speed in D with a decent load on the alternator and vacuum advance plugged (if not a Load-O-Matic)?
The idle mixture adjustment screw could have a damaged tip or seat, also. It should be controlling the fuel metering, regardless of whether air gets past the butterfly or via the PCV.
You could possibly try a PCV with stiffer spring, but generally they work within their nominated parameters quite happily. Try matching the PCV to the carb setup. Early ones with a flow-through oil cap need the correct cap, washed with solvent and lightly oiled. This will present a slight airflow restriction. Later units that feed from inside the air cleaner housing, to the rocker cover and then back through again (2 grommet cover), probably use a different PCV.
As to timing - I'm a big fan of confirming TDC first. Keeps the guessing under control.
Cheers, Adam.
The idle mixture adjustment screw could have a damaged tip or seat, also. It should be controlling the fuel metering, regardless of whether air gets past the butterfly or via the PCV.
You could possibly try a PCV with stiffer spring, but generally they work within their nominated parameters quite happily. Try matching the PCV to the carb setup. Early ones with a flow-through oil cap need the correct cap, washed with solvent and lightly oiled. This will present a slight airflow restriction. Later units that feed from inside the air cleaner housing, to the rocker cover and then back through again (2 grommet cover), probably use a different PCV.
As to timing - I'm a big fan of confirming TDC first. Keeps the guessing under control.
Cheers, Adam.
65Stang200 -- yea ill do all the things you mentioned a little later tonight. Ill check tdc before i time it too. Which way does the balancer slip? like if i was to set it to 10* on a slipped balancer whould it actualy be more advanced or retarded?
addo -- no its a stick shift /wo load-o-matic. it has the vaccume + weights advance. Ill check the condition of the idle screw tonight too. My oil cap was just a small air filter. the huge suction of the intake log pulled air through the pvc valve through that little air filter, skipping the carb altogether. I think im going to set up my pvc like the Later units you were talking about. Run the Pvc line into the side of my air filter housing and plug the hole on the intake log. Would that work?
addo -- no its a stick shift /wo load-o-matic. it has the vaccume + weights advance. Ill check the condition of the idle screw tonight too. My oil cap was just a small air filter. the huge suction of the intake log pulled air through the pvc valve through that little air filter, skipping the carb altogether. I think im going to set up my pvc like the Later units you were talking about. Run the Pvc line into the side of my air filter housing and plug the hole on the intake log. Would that work?
Mercury Mike
Famous Member
Don't use the mark on the balancer. Set TDC with a pencil, eraser down, in the #1 plug hole. After that, you will know where TDC is. If the mark lines up, then you'll know it hasn't slipped, but it's nice to have the timing where you know it is correct.
MercuryMarc
Well-known member
If turning the idle mixture screw does not really change the idle speed, then it seems to me that you may have fuel entering the carb bypassing the idle circuit. I wonder if your throttle plate is really closing all the way- if it is stuck semi-open it might cause the RPM to stay above a ceratin level as you may be running through the main circuit, even if you turn the idle speed screw all the way out. Could the throttle plate be stuck by hitting a gasket or something else? Another possibility is fuel leaking around the idle mixture screw- basically just dumping/drippng fuel into the carb regardless of the screw setting.
Just my 2 cents.
I have 3 1940's but am currently running a bored out HW5200 2V on my 250
Good luck!
Just my 2 cents.
I have 3 1940's but am currently running a bored out HW5200 2V on my 250
Good luck!
I have never looked close at the 1940 but how about worn throttle shaft not letting it close correctly? Is the idle passage it near the throttle shafts? Maybe a vac leak from the throttle shaft is pulling fuel from some other port like accel or decel (if it has one)? If the gaskets are like the 1100 and you get a few extras in the kits make sure they are all right and on the right way. Get a good picture to make sure, dont count on the last guy getting it together right.
And for what its worth: (mine could blow up tomorrow)
The 'hand test' on mine (1100) makes it change but wont stall it, the easy way to stall it is a good shot of carb cleaner at the base of the carb on the linkage side. I can barely feel the play in the throttle shafts but I put a blob of hi temp grease on the shaft and did the same spray test (before it melted) and no problems. My mixture screws do respond normal and it never stalls so Im going to live with it for a while and work on other stuff.
The PCV on mine will suck your finger up to the valve if you pull it out hard enough that you have to yank it off but with it in the valve cover thare is only a breeze at the oil filler pipe.
And for what its worth: (mine could blow up tomorrow)
The 'hand test' on mine (1100) makes it change but wont stall it, the easy way to stall it is a good shot of carb cleaner at the base of the carb on the linkage side. I can barely feel the play in the throttle shafts but I put a blob of hi temp grease on the shaft and did the same spray test (before it melted) and no problems. My mixture screws do respond normal and it never stalls so Im going to live with it for a while and work on other stuff.
The PCV on mine will suck your finger up to the valve if you pull it out hard enough that you have to yank it off but with it in the valve cover thare is only a breeze at the oil filler pipe.
pedal2themetal45
Famous Member
Moe$":nr3fn1zd said:
1) hose from pcv valve goes to intake log.
2) then eather have a air filter oil cap. or a oil filler cap with an attachment for a hose that goes the the air filter.
3) The flow of air for the PCV is throu the oil breather fill cap, throu the PCV , to the intake log. It only goes to the air filter if you don't have a breather oil fill cap. then like I said above the fill cap would need to have a nipple for a hose that goes to the air filter..
tim
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