[JoeS]

The sound is pretty obviously from the vacuum advance kicking in but yea Ive never heard one klunk either.. seems like theres a spring missing or something holding the diaphram back.

I just dont know what else it could be. But would that explain the high idle speed?

[batman09]

I would recommend you private message docvette...this guy is super smart and really knows motors.tell him everything that is going on.I'm sure he can help you with your motor.(he helped me quite a few times)I'm stumped.You must be going crazy.I didn't sleep for days until I got my motor dialed in.(i was in the garage at 4:30 am cussing and throwing wrenches)All is good now.What kind of car are we talking about?Good luck.bm

[mcgrsr]

I know this is an old post but thought you could help . I'm running in the same problem that you were having.what did you finally do to resolve it . i would love to get it right just not sure what to do

[Rick WI]

Originally posted by JoeS
So when I plug in the vacuum line to the distributor I can hear a distinctive clunk. Could it be that the vacuum advance canister is kaput ?

Well let's eliminate what it is not, based on your post. It appears your timing marks are set properly relative to TDC and the distributor is phased properly because your findings when advancing and retarding timing all make sense. The Vac advance seems to be working based on some of your reading so the can appears to be operating as designed. So I'll assume those issues are non issues.

Now what it could be. The most basic is simply octane intolerance. You simply may need a higher octane. You did not indicate what you are burning. I suspect 93 octane would be the minimum I would want to burn.

If I recall the ZZ motor has the fast burn heads. So timing should work out to 10 initial and 35 total by 3000. Thats where I would tune to for base timing and for total that should be within 1 degree plus or minus.

If your mixture is dead lean on the bottom end that could also cause problems. Under low speed steady state cruise if you sense the motor is surging then that would be a symptom of a lean condition. You may want to try and richen the idle mixture 1/4 of a turn and see if that helps.

Operating temps also can make a motor sensitive to detonation. A 180 degree thermostat seems to work best for overall operation on the street.

Although BG has said they work hard to avoid defects out of the box we always tear down Demons prior to bolting them on the dyno. We inspect and clean/blow out all pasages. We also take time to set floats correctly. Demons can be a bit more touchy setting floats it seems versus a typical Holley.

Plugs that are too hot can also cause detonation. Make sure you have the correct plug installed. Going one step colder drops tip temps about 100c (212 degrees) and sometimes will cure a minor detonation problems. Extended tip plugs are more prone to detonation than standard tip plugs.

Proper fuel pressure is very important as well and low pressure can give you a lean condition.

The benefit to manifold vacuum is you can tune in a much smoother idle. Combustion is slower at idle and the additional advance makes a drastic difference in EGT temps by keepign the combustion heat in the chamber and not blown out the exhaust. Once the throttle is cracked both manifld and ported operate the same.

[skeeveman]

Your hose isnt getting pinched and holding a vacuum is it?

Just a thought.

[mcgrsr]

another question i have is how do you set the timing if thers no timing tab on the timing cover. It's a zz 383 from gm this is what it states in the manual that came with the motor.

set the timing at 32degrees before top dead center at 4000 rpm with the vacuum advanceline to the distributor disconnected and plugged. This setting will produce32 degrees of total advance at (wide open throttle). the HEI vacuum advance canister should remain disconnected.

help please

[Rick WI]

Simple, you buy an adjustable bolt on timing tab from Tavia, roll the motor to TDC #1 using a piston stop, set tab to zero on the balancer and tighten down tab pointer.

[ZZ4fan]

I am having same problems as JoeS with my lowmile ZZ4. It has brand new Barry Grant / Crate demon carb ,made for ZZ4 and brand new pertronix flame thrower billet distributor. New wires and new set of Ac Delco MR43LTS plugs.


I have set the timing to 10 btdc and distirbutor gives total advance of 35 degress. Timing is set without vacuum advance. Starts fine and electic choke works like a dream. But i cant get idle speed down and it diesels heavily when i stop it. I could not not believe in vacuum leak. I do have moroso sandwich style gasgets under the carb for heat protection.

[Frisco]

Originally Posted by ZZ4fan

I have set the timing to 10 btdc and distirbutor gives total advance of 35 degress. Timing is set without vacuum advance. Starts fine and electic choke works like a dream.

Timing is in the ballpark. Connect the vacuum advance to a full manifold source after checking/setting the timing.

Originally Posted by ZZ4fan

But i cant get idle speed down and it diesels heavily when i stop it.

Throttle plates are open too far. This will cause the high idle and the dieseling. The air/idle screws are also not adjusted correctly. They are probably screwed out too far. Adjust them to yield the highest vacuum readings. Then close the idle stop screw some to reduce the idle RPM's.

FYI:

The original post is six years old. Posting your question as a new post is a better alternative.

[SDLuck]

Some barry grant carbs have a idle speed system located below the air cleaner mounting screw .
http://www.barrygrant.com/fromBarryG...e-Addendum.pdf

[eric32]

I don't know if this will help out or not but it sound like you have a stock type vacuum advance canister on your engine and from what I read they vary and on most stock type engines they where about 20 degrees of advance and you can't change that on them type.

Get an accell adjustable vacuum advance canister and you can dial it in to only give you around 12 degrees of vacuum advance and I bet that will help you out a lot. My brothers engine had a similar problem like yours and after adjusting his vacuum advance to give only 12 degrees it took care of the problem.

Check your spark plugs for extreme leanness from the carburetor. Is your zz4 motor the 355 hp crate motor with the l98 aluminum heads and the zz4 roller cam with 208/221@ 50 with 474/510 lift by chance? If it is what octane rating gas are you running as well? I believe GM rates it at about 10:1 which you will have to run 93 octane even with aluminum heads. Take care

Eric

[ZZ4fan]

THANK YOU GUYS FOR ALL REPLYS!!!

Originally Posted by Frisco

Timing is in the ballpark. Connect the vacuum advance to a full manifold source after checking/setting the timing..

This is confusing..Why there are so many different opinions on this. I did set the timing off course vacuum hose plugged.And once set then connected it to the ported vacuum. Once i have solved the high idle mystery then i can test it on the full vacuum side too.

Originally Posted by Frisco

Throttle plates are open too far. This will cause the high idle and the dieseling. The air/idle screws are also not adjusted correctly. They are probably screwed out too far. Adjust them to yield the highest vacuum readings. Then close the idle stop screw some to reduce the idle RPM'

Yes exactly! By the demon instruction manual the throtlle blades should set allmost closed position at trasfer slot i barely seen under the carburator. And there is my problem. I have backed the idle stop screw totally up and it wont even touch the throtlle blade shaft. And still there is at least 3 times too much transfer slot seen under the carburator by the demon manual.

So what can i do to get the butterlies more down? I have checked many times and nothing binds or keeps the butterflies open.


As SDluck wrote: Some barry grant carbs have a idle speed system located below the air cleaner mounting screw .http://www.barrygrant.com/fromBarry...ze-Addendum.pdf


Yes there is and its not mentioned in the manual. But still even with the EZ-IDLE i should get the transfer slot smaller since my engine should idle way below 1000 rpm . I just came from the garage and saw SDLuck reply and have not yet to try to adjust it. I will but i still liked to get the blades more down.

Originally Posted by Frisco

FYI:

The original post is six years old. Posting your question as a new post is a better alternative.

Yes sorry for this. I found this topic with google and did not realize it was so old. I can start a new if you guys think its good idea.

With best regards Johnny

[SDLuck]

Sometimes the butterflies are hitting in a tiny spot,Loose the screws that hold the butterflies open and close the throttle shafts then retighten.Some screws have loctite.

[ZZ4fan]

Originally Posted by SDLuck

Sometimes the butterflies are hitting in a tiny spot,Loose the screws that hold the butterflies open and close the throttle shafts then retighten.Some screws have loctite.

I try that too!

Thanks SDLuck!!

[Frisco]

Originally Posted by ZZ4fan

This is confusing..Why there are so many different opinions on this. I did set the timing off course vacuum hose plugged.And once set then connected it to the ported vacuum. Once i have solved the high idle mystery then i can test it on the full vacuum side too.

Connecting to the ported source was used for emissions and the timing was then set very low (0-4 degrees BTDC sometimes even a negative BTDC). For best overall results for street performance you will find that setting the initial timing up higher (12-18 degrees BTDC) and hooking the vacuum advance to a FULL manifold source will work best. Try both and see.

If you have emmisions testing where you live, you may have to use a lower timing and ported vacuum to pass. You will also see higher coolant temps and lower overall performance. That's the trade off.

I have found that a hesitation when going from a stop to WOT will result from one or two sources most often. The first is not enough pump shot and the second is being connected to a ported source.

When setting the timing with the vacuum advance hose dis-connected and plugged, remember that when you re-connect the vacuum advance hose to a FULL manifold source the idle will increase. You then lower the idle with the throttle stop screw so that the idle is around 650-750 RPM when the trans (if automatic) is in DRIVE. It will be around 900 RPM in PARK. If you opt to connect the vacuum advance hose to a ported source the idle will not change.

Originally Posted by ZZ4fan

Yes exactly! By the demon instruction manual the throtlle blades should set allmost closed position at trasfer slot i barely seen under the carburator. And there is my problem. I have backed the idle stop screw totally up and it wont even touch the throtlle blade shaft. And still there is at least 3 times too much transfer slot seen under the carburator by the demon manual.

So what can i do to get the butterlies more down? I have checked many times and nothing binds or keeps the butterflies open.

The throttle linkage is probably sitting on a higher ledge of the 'high idle' cam. This is the position the throttle will self adjust to when the choke is engaged on a cold engine when the throttle pedal is initially pressed before starting the engine.

To adjust/check the throttle blade position when the carb has been removed, just slip the linkage off the 'high idle' cam position to enable the throttle blades to drop to their lowest point. While the carb is still off, and looking from the bottom of the carb, adjust the throttle stop screw to adjust the throttle blades so that the idle slot looks like a small square. This is the position you want. After re-installing the carb, when you first attempt to start the engine you would press on the throttle pedal fully to set the choke and squirt a stream of fuel into the throat of the carb. At that point, the choke will be closed and the throttle linkage will be on the 'high idle' section of the throttle cam. After the engine has started and the choke has fully opened, 'blip' the throttle and the throttle stop should fall off the high idle cam plate and return to the lowest position that you pre-set when the carb was off.

The idle should fall fairly close to what you want. If not, slight adjustment of the throttle stop screw should get the idle RPM in the range you want. If you make any adjustments to the air/idle screws, the idle stop screw will usually also have to be re-adjusted.