carb questions

[nachoman]

When you look down the bore of a carburetor, should you see liquid gas coming out of the venturi? I know you see some from the accellerator pump when the throttle is opened, but what about from the veturi itself? I am thinking this is not supposed to happen...

a little background - I replaced my old holley 1940 carb on my 200 with a NOS 1940 carb. The new one says it is for a 250 and the throttle plate is lager than the old one. Other than that, they appear to be exactly the same. It ran great for 2 days, and now bucks and surges at almost all speeds except WOT and idle. When I look down the carb and open the throttle - I can see liquid gas coming out of the venturi in additon to the throttle pump squirt. I took the carb apart, the float level and needle seem okay. I tried reducing the jet size, and all it did was make it idle worse.

So, CAN I get this carb to work on my 200?

thanks,
kevin

 

[mustang6]

No, you should not see fuel coming out of the main fuel circuit like that. I've seen this before in carburetors that are causing the same poor running conditions that you are experiencing, so I'm pretty sure you have identified your problem.

Flooding due to a sticking float or leaking needle valve are good first things to check. Also you could have a plugged air bleed passageway in the carb. I've also seen this when the idle is just set too high, sometimes seeming necessary because of a vacuum leak and the idle screw(s) have to be adjusted to rich & too far open to cover the extra air from the vacuum leak. Where is your idle mixture screw? It should be somewhere around 1-1/4 turns out. How about your curb idle speed screw? It should only barely be cracking the butterfly open in the carb.

 

[fordconvert]

What is your fuel pressure/pump? New old stock so that should rule out a bunch of stuff... How did the car run before the carb swap? Any other recent changes?

 

[nachoman]

I thought it could be a fuel pump problem and i replaced it. no change. The problem started about a week ago, about 2 days after I put on the NOS carb. The old carb was a SCV carb, and I was swapping for a non SCV carb. The old one ran okay, but probably needed a rebuild. I havent put the old one back on yet to see if it works. Other recent changes included cleaning and gapping spark plugs and retarding the timing a little (2 degrees) to get rid of a high speed knock.

 

[fordconvert]

Is it possible that the carb is old enough that there are some gasket issues due to age? How about due to its age something in the modern fuels ate some gasket or seal? Did the needle have the rubber/plastic tip? Maybe it was supposed to?

 

[MustangSix]

It ran great for 2 days, and now bucks and surges at almost all speeds..............

If it ran great for two days and then started running badly, it's not because the jet size suddenly was wrong. Go back and replace that.

What you have is either a gasket that has failed or a piece of dirt or debris that has clogged something. My guess is that the extra fuel is coming in thru the gasket between the base and the body. Maybe the screws are loose; maybe the gasket is bad.

 

[cfmustang]

As a side note, please be carefull when looking down into a carb while the engine is running. A backfire through the carb at the wrong time...