I have a 351M in my 66. It was running rich and I took off and verified the previous owner put in a kit just before I bought it (Holley 1460). It has the good Blue gaskets and everything looked new. I adjusted the rear float after putting it back on, (which was my problem to start with). It runs good, no flooding etc. but my throttle sticks when running. When the truck is off I have no binding or anything, great free movement. When I start the truck I feel pressure on the throttle when operated by hand. When I let off the throttle it will idle around 400 RPM above normal unless I pull the throttle closed. (I don't have a tach) I have both idle jets turned all the way in and I know my power valve is good, but it is still running.
When the truck is not running there is no binding. Can the vacum be pulling on something?
Engine not running, I open the secondarys which are vacum, they spring back shut. At idle if I open them the same way, they stay open until I pull the closed or kill the engine.

I think I have a vacum problem, but what?

What am I missing??????



Michael

 

If the engine will not stall with the idle mixture screws turned all the way in, there is a problem in proper metering at idle.
Are the secondary throttle plates closed? or is there a gap around them in the bore? There is a secondary throttle stop screw that must be properly adjusted or it will not idle correctly.

The vacuum can for the secondaries draws its vacuum signal from the primary and secondary venturi's, at idle there should not be any signal to the vacuum can. Did you verify that the check ball is installed in the vacuum housing??

 

What is the list number on the front of the choke horn? Some Holleys have a reverse idle circuit that works backwards.
If you have a mechanical throttle linkage, you may need to adjust it a little. The torque of the engine when running, could be binding and holding the throttle open. Try starting it with the linkage unhooked and see if the problem goes away.

 

# on horn list-1850-3
0449

Try starting it with the linkage unhooked

Yes it still binds, but it does not if the engine is not running.

There is a secondary throttle stop screw that must be properly adjusted or it will not idle correctly.

?? I will look for this

The vacuum can for the secondaries draws its vacuum signal from the primary and secondary venturi's, at idle there should not be any signal to the vacuum can. Did you verify that the check ball is installed in the vacuum housing??

will have to figgure this one out also.

 

OK, the 1850-3 does not have the reverse idle circuit. It is a universal 600 cfm carb.
You are getting fuel somewhere if the carb still idles with both screws truned in, then it either has the wrong gasket for the metering block or a bad power valve. The vacuum for the secondaries is drawn from the small hole in the passengerside primary barrel near the top. As enough air rushes by the hole, it creates a vacuum that pulls the secondaries open.
There is a secondary throttle stop on the bottom of the carb. It should be adjusted out until the plates bottom out, then turn it back in until it just starts to open the blades. This should be close enough.

 

The engine will idle too fast if the secondaries are open too much at idle. The secondaries DO contribute fuel and air at idle, and the engine will run on this if they are open too far. They designed it this way so if grandma is the only one that drives the vehicle, and the secondaries never get used, the fuel will not sit in the rear of the carb and get stale. Plus the rear float will jostle around over bumps and sometimes let a little bit of fuel in. If this happens over a period of time, the fuel level can get too high in the rear. So they let a little bit of it out at idle.

If someone has messed with the secondary idle stop, it's a pain in the rear to set. You have to take the carb off, and turn the screw from underneath.

A couple of times I have rebuilt these carbs, the linkage rod to the secondary diaphram gets in a bind or something. In each case, while the engine was running, I loosened the phillips head screw on the passenger side, and then re-tightened it, and the idle settled down.

You also may be able to fudge this situation a little bit with the timing. If you have your vacuum advance on the dist hooked up to manifold vacuum, this will make the idle speed high, which will force you to turn the idle screw way back. If you hook your dist to ported vacuum(no vacuum at idle), this will lower the idle speed, which will let you turn the idle screw back in a little bit.

What's happening is you are forcing the front butterflies against the walls of the carb, and they are sticking against the throttle plate. You also may get a weird stumble when you hit the gas if you leave it way down like this.

 

vacuum advance on the dist is hooked to the front part of the carb where it says in the holley manual to hook it.

"What's happening is you are forcing the front butterflies against the walls of the carb, and they are sticking against the throttle plate. You also may get a weird stumble when you hit the gas if you leave it way down like this."

It is having this problem I have the idel screw not even touching the linkage and the butterflys are sticking at times. But don't need the idel higher.
I am going to get a Holley book, another kit and redo the whole rebuild next week.

Michael

 

Sounds like the rear blades are open too far. They aren't catching on the gasket or intake are they?
The vacuum advance goes on the port in the metering block on the passenger side in front of the choke assembly.

 

You need to check idle timing and make sure it is reasonable, it should be in the 8 to 12* BTDC range. If you have the vacuum advance hooked to manifold vacuum, it will cause a high idle, try unhooking the vacuum advance and see if the high idle is still present. If it still will not idle down, then you definitely need to adjust the secondary throttle stop.

The idle stop screw is usually about 1-2 turns in from initial contact with the linkage.

 

OK , I have not mentened this but If I pump the linkage a couple of time with the engine not running Gas comes out of the linkage. I suspect my throttle rod is worn out. Woud this be correct?

Michael

 

Move the throttle half-way open with your hand and then wiggle it back and forth. There should be no slop in the shaft coming out of the side of the carb. A lot of slop would certainly make the butterflies slide around inside the carb, and possibly affect how much air is going around them. You still can probably compensate by shutting the secondaries a little bit, but if it's real sloppy you will end up with a low idle one time, and possibly a higher idle the next, if the butterflies are really moving around in there.

 

the secondaries have been checked and are just barley open. I did as stated above " There is a secondary throttle stop on the bottom of the carb. It should be adjusted out until the plates bottom out, then turn it back in until it just starts to open the blades. This should be close enough."

there is some movement when I wiggle the throttle back and forth. I am going to check the timing Wednesday again. I think I have it at 10 deg.

Other than running with the idle screws in and not being able to get the idle screw to set the idle it runs good, but very poor fuel economy.

Michael

 

If you look down the throttle bore with the engine idleing, can you see gas dribbling into the bottom of the throat, just above the plates(primary or secondary)?? I am beginning to suspect a wrong metering block gasket. There is definitely something wrong with the fuel metering here!!!

 

No fuel dripping into carb.

Ok I had time this morning to really get into this thing. I noticed after setting my timing at 10 deg BTD I still had the high idle and still unable to use the idle screw. I grabbed just the secondary throttle rod pushed it toward shut it moved ever so slightly and wa la, the engine went to normal idle. So they were open HA. I got to looking and the linkage from the main throttle to the secondary which looks like it pushes them back closed was lacking an 1/16 or so of an inch. Just ever so slightly. So I took the trusty old pliers and bent it so that when I let off the throttle it forces the secondary’s shut. I now have it set and running good. If I screw in the idle screws it dies Yea Baby! And my idle screw is how I adjust the idle now Oh yea.

Question, if I had the secondary’s closed all the way and started the truck they would pull open, so as I am driving now does this mean they are cracking open now and why? And how do I fix this?

Only thing now is that it wants to Run on after I kill it. I have adjusted most of theis out but still small problem.

Thanks for all the help.



Michael

 

Try opening the primary by hand (engine OFF) and push up on the secondary link(pass. side of carb) to the vacuum secondary diaphragm. Does it spring back slowly to closed?