ported vacuum switch causes rough idle with choke open?

[BagelsAndDatsuns]

Hey Guys,

 

My 84 720 z24 with orig carb is idling poorly. It starts okay and idles fine with the choke closed but once it heats up and the choke opens it idles very poorly. I've already changed the PCV valve and checked the EGR and AB Valves. I've ruled out most things non-vacuum as well. I noticed that the little brownish red ported Vacuum switch that has a line going out to under the air cleaner box is not giving me any suction both with the choke closed at initial heat up and with the choke open during the poor idle. I assume it should be open sometime, but when? I'm thinking that it is stuck shut.

 

could this be the reason for the poor idle?? I figured I'd post about it cause its $50 and thats alot to spend on a hunch! I'm off this weekend and look forward to getting under the hood tomorrow.

 

All help is always greatly appreciated!

 

-Dave

 

[datzenmike]

There are so many emissions components...

 

Is this the thermal vacuum valve (T V V) with the three hoses to it??? The top one goes to the air filter?

 

Or post a picture...

[BagelsAndDatsuns]

Here is a photo. Its the 3 port thing that has "Vac line C" comming out of the top port which goes to the bottom of the air cleaner box.

 

 

[BagelsAndDatsuns]

 

[BagelsAndDatsuns]

Hi, I can't get a photo to upload. In another thread you told a guy that it is a "temp sensistive vacuum bleed" and referred to it as a TVV later in the caption.

[Lockleaf]

Have you tried the good old fashioned starter fluid trick to find a vacuum leak? Good chance it's intake manifold or carb base gasket leak

[datzenmike]

This is an bleed that closes when warmed up. Vacuum advance and EGR ported vacuum signals are connected to this valve. When cold the bleed is open and this destroys the vacuum signal so there can be no vacuum advance nor EGR when the engine is cold. As the engine warms up these bleeds are closed off and vacuum can then be applied to either the vacuum advance and/or the EGR. I don't know which one comes on first or at what temperatures.

 

Either way I don't think the T V V operation affects idle.

[BagelsAndDatsuns]

Thanks guys!

 

I'll have to keep looking for the problem. Hall Monitor, I haven't tried the starter fluid test yet; I was confused as to where to start with it but I am familiar with the teqnnique and you gave me a good starting spot-The intake and carb gaskets. I'll go pick up a fire extinquisher before I try this out...

 

Mike, Thanks for pointing me away from the TVV, i'll clean the current one and put it back in without the high hopes of it fixing my problem.

 

As for the EGR; what is the best way to clean the ports? carb or brake cleaner would work?

 

Thanks,

 

Dave

[datzenmike]

EGR.... just wire brush the valve clean.  If the valve has exhaust deposits it may leak inert exhaust in at idle, a big no no. Inert exhaust just takes up space and will weaken the idle or not allow an idle. It's more important that it close rather than open.

 

The EGR receives a ported vacuum signal from the carb. The port is just above the throttle plate so it reads atmospheric at idle when the throttle is closed. As you step on the gas the throttle plate rises to and above the open port and intake vacuum is applied. Vacuum advance for the distributor works the same way.

[BagelsAndDatsuns]

Hey all,

 

So I fgured I'd give an update. I found a vacuum leak in the carb base gasket as well as the EGR gasket. A mechanic friend of mine has been trying to sell me a weber he had for a while and I figured as long as I'm doing the gasket why not buy the carb and get it all set up in one motion. SO I DID.  I must admit that the Weber 32 36 does make my 720 a bit faster however the truck is still idling poorly and since I've combined troubleshooting the idling problem with putting a diffrent carb on I don't know if its the carb or if there is another vaccum issue or if it is just something else.....

 

The gaskets I changed definetly altered thhe iidle. Before it would barely stay running, now it does, but it is very sloppy. I've deleted a bunch of the vaccum lines and juut kept the neccesary ones t keep the EGR hooked up as well as the Vaccum advance and the charcoal casisiter stuff (The 3 metal tube rails that incllude the vacuume advance). I think my  carb is installed correctly and I suspect I still have a vaccum leak. I will keep looking this weekend. 

 

A question about my new carb though:

 

I am using an import direct inline fuel pump from Oreily that I've had on for a while now, Is it possible that it is flooding the weber? Should I be using a pressure regulater??? I can smell gas in the cab when I turn over the engine and I hear some surging in the rough idling. Also I have'nt driven it a lot but it seems like it's using more gas than usual.

 

If ya'll think a pressure regulater might have a positive outcome I can pick one up right away and put it it, otherwise any advice is appreciated.

 

Thanks in advance,

 

Dave

[datzenmike]

The weber may need proper tuning and adjustment. What engine is it from? I don't care for someone else's old carb. You never know what's been through it.

 

Fuel pressure should be about 3 PSI. But I wouldn't go out and by a regulator until everything else has been checked out. Maybe float is badly adjusted.

 

http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm

 

http://www.webercarbsdirect.com/v/vspfiles/images/Weber%20Trouble%20Shooting%20Guide.pdf

 

http://www.classicinlines.com/WeberTune.asp

[BagelsAndDatsuns]

Here's an update!

 

First off: the vaccum leak was at the bottom of the intake manifold-fixed that. Second off:  I will never buy a used carb again! Mike was very right about "not caring for someone's old carb." so it took me a while now to get it all dialed up but the weber redline website instructions were very helpful and it is running well. The choke was not responding correctly and it is currently left permenantly in the disengaged position until I further try to adjust it and/or take off the coil to see what shape it's it. That being said, it needs 2 or 3 minutes of rough idle before it smooths out and runs well. The only problem I am having now is when I give it full throttle it stutters and hesitates before it catches up with itself and accelerates. When driving conservatively you would not even notice this problem but when ever I punch the gas pedal it lags for 1-3 seconds then speeds up (pretty fast, faster than with the stock carb). At first I thought that it was Vaccum advance related but I found a thread in which the ratsun elders seem to debunk that a poor vaccum sigal from the distributer could be causing high RPM hesitation. the EGR is currently on the car(meaning i didnt take it off and block the port) however I do not think I have the vaccum lines set up correctly, I just have everything capped for now. If anyone has a picture of thier 84 z24 (non calif) with a Weber and The EGR on and running that shows me how to get my Vac lines as minimalistically hooked up while still running the EGR that would be great and really helpful! right now I just have the advance to the distrbuter from the port on th carb and everything else is capped.

 

all thay said; problems are hesitation at full throttle and I need some directions on the proper vac line set up to run my EGR.

 

 

Thank you everyone! 

 

-Dave

[datzenmike]

The stock carb is a vacuum secondary. It's designed to pull open only when the engine is revved up and needing it. If you floor it it does not open... unless needed.

 

The weber is a progressive secondary. This means when you stomp it ... it opens, even if not needed. Opening too soon can drop the air speed through it and cause a flat spot or 'bog'. Carbs need good fast air flow so that they will suck fuel in. Try flooring half or 3/4s and then slowly all the way. Gives the engine a chance to catch up.

 

Having said this there is one other cause of an acceleration flat spot... The accelerator pump is not squirting in enough gas to fill in the flat spot

[BagelsAndDatsuns]

cool, i'll inspect the acceleration pump and consdier a new one, they have themm at pegasus racing for 13 bucks. You are totally right when I give the throttle a nice slow transistion in rarely bogs.

[datzenmike]

The jetting may also be off. Webers are a one size fits all carb but an A14 is much different than a Z22 so some 'tuning' is needed.