No vacuum on Carbtune

[rcbailey56]

Well, I got my '92 Royale running. I thought it felt a little rough, not bad, after warming up. So, I got out my CarbTune and there is no vacuum showing on any of the cylinders. If I blip the throttle, I get a little spike but none of them are even. I set the idle mixture at 2 1/2 turns out on all carbs, still nothing.

 

This seems crazy to me. It idles with choke off. The throttle response is good. I just can't synchronize.

 

Anybody ever have a problem like this?

 

Thanks in advance for any ideas,

[billmac]

you have the hoses on in the right direction. this will happen if you have them on backwards.

[cimmer]

Make sure the restrictor is on the carb end of the hose and not the carbtune end. You might want to make sure you can blow or suck thru the hose to test of air flow. Another test would be to put your finger over the vacuum port on carb and see if you feel a vacuum there with the engine running.

Good Luck.

Rick F.

[lonestarmedic]

Exact same problem here. Hoses clean and restrictors are correct. Carbtune 2 about 7 years old. Have cleaned and polished rods. Cleaned the brass bushings also. I used 4/0 steel wool very lightly and some WD40. No change. Rods at the bottom of the unit and sometimes barely move. Hooked to a Mightyvac and can make them move. Made a manifold and joined the hoses. Hooked to the Vac-seal unit in the kitchen. Rods go up but not equal. Can tap the unit and make them change. I noticed with the mightyvac I needed a very constant strong vacuum to keep the rod up on the scale. Honestly I am ready to blame the carbtune.

 

Carbs are rebuilt. New Coasting enrichment diaphragms. All new O-rings etc. Checked airbox and carb boots. All good. Removed runners to head and inspected. Look to be good. New O-rings installed. Checked the little vacuum ports and made sure tight. Re-shimmed valvetrain. Made a way to shoot propane around the intake. hose and straw connected to a bernzomatic torch. Sprayed around all intake. Used the straw to concentrate it around the throttle shafts checking the end seals. All steady and no RPM rise.

 

I synced the throttles using a piece of 30 gauge wire between the throttle plate and wall. Old bench method. Good but not perfect. Idle is at 1050 or so. Pulls strong in all ranges. Fuel mileage has been 33-35mog 2 up and highway speeds. So over 425lbs of people.

 

Will be watching this thread with interest. Gotta be a correlation.

[frankd]

Compare the Carb-TUne to the gauge on the Mighty-Vac. Normally 1st Gen Ventures idle at about 9.75" of vacuum. Pump the Mighty-Vac up to about 9.75" and see if the Carb-Tune reads normally. That'll tell you where you really stand.

[lonestarmedic]

Frankd-

Tried that and it does not hold steady enough. You pull up with the Mightyvac and have to keep pumping it to hold the rod up. Almost needs a variable vacuum source that is continuous. Maybe get them lined up so I can see both in same field of vision.

[lonestarmedic]

Thinking of extra cruise control pump I have and a bleeder valve. Adjust it using a vacuum gauge.

[Great White]

This is why I still use an old set of mercury filled carb stix.

 

Too bad they've gone the way of the DODO bird....

[frankd]

Frankd-une

Tried that and it does not hold steady enough. You pull up with the Mightyvac and have to keep pumping it to hold the rod up. Almost needs a variable vacuum source that is continuous. Maybe get them lined up so I can see both in same field of vision.

 

It would hold steady if the Carbtune wasn't leaking. Check the seals around the movable piece and see if you can renew or repair them. They have to be leak free to indicate vacuum accurately.

 

Frank

[lonestarmedic]

Frankd- no seals on my Carbtune. Just brass bushing at the bottom of the tubes. Checked hoses and they are good. Top rubber piece on carbtune seems good. Only way to tell is pull the rod, plug bottom of tube, and apply vacuum.

 

If there are seals between the brass and the moveable rod, they are gone!!

[rcbailey56]

Hey,

 

This is all good stuff. I didn't consider it might be the Carbtune that was the problem. I'll be checking that as soon as I can get back to it.

 

Thanks to all,

 

Richard

[van avery]

I'm having the same problem on an 88 royale. Just got the carbtune and I have the restrictors in the correct end. I connected the hoses to the old set of vacuum gauges and was only getting 1 " vac at 1000 RPM and 2" at 4000 RPM.

I have not done a compression check yet.

Did you ever figure out what the cause was?

[Marcarl]

Simple check would be to pull the boot off the vacuum port while the engine is running. If the engine reacts then the port is open and you have vacuum and the carbtune should work. If the engine doesn't react then you either have a plugged port or your hooked to the wrong place.

If an engine runs, it will have vacuum, dirty carbs or not. There may not be the right amount of vacuum, but there will be enough to measure.

Could be, that if you screwed with the settings, that the sync is out so bad that vacuum will not show really anywhere, although 1 cylinder should always show some.

Vacuum is created by a close butterfly, so if the butterfly is open too far, and the engine is running too slow, say at idle, then you may loose all vacuum on 3 of the cylinders very easy. These engines have an amazing way of running, even if one cylinder is dead, or the sync is way out. Once you get it right, then you'll notice how smooth they can be.

[djh3]

Try your gauge on something know to be good. Like your car or truck. See where your gauge is functioning. Sucks to be trying to troubleshoot something with a faulty diagnosis equipment.

[van avery]

As I posted earlier I had the same problem on an 88 royale I'm working on. Used my old vacuum gauges and was only pulling around 1 to 1 1/2 inches vacuum. Too little for the carbtune to really show. This afternoon did a compression check and #2 cylinder was running 20 PSI and the other three were running 140PSI. Put in a little oil and it raised the pressure to 30 PSI so looks like the valve need to be adjusted.

You might want to do a compression check.