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Kadron syncing and idle mixture woes
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chrisd1891
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PostPosted: Thu Nov 15, 2012 9:21 pm    Post subject: Kadron syncing and idle mixture woes Reply with quote

Hey guys,

Got my synchrometer today. Got things roughly synched, and went to adjust the idle. So I am listening for it to start missing, and I can pretty much turn the right carb mixture screw all the way in without any difference being made. If I lean it out all the way, the RPMs don't decrease, or even change very much. So my question is, why does changing the mixture on the right carb have no effect on the RPM, whereas the left carb's mixture entirely dictates things?

Secondly: after I did all this and went for a long drive, it became much harder to start when warm than it ever has. Any ideas?

Also, a happy idle speed was pulling in a little over 10kg/h of air per carb, where I read it should be around 6? Engine is a 1800cc, freshly rebuilt, with kadrons and an electric fuel pump. Doesn't really matter much to me, it just seems odd.
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noneed
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PostPosted: Thu Nov 15, 2012 9:32 pm    Post subject: Reply with quote

What is your fuel pressure ?
Kadrons like 2 PSI or slightly less...and most electric pumps put out 3 -3.5
That can and will drive you nuts if it's too high.

Have the T bodies on your Kadrons been re-bushed ?
If not, they could be sucking air creating a false air condition...even if they are new they can leak there.
One carb not responding to mixture adjustments is usually a sign of a vacuum leak somewhere... Check all of your gasket areas. Leaks can be really sneaky !

Try pinching off the crossover tube. If it tries to die when you do that, the motor is attempting to run off of one carb, and that's another usual indicator of a vac leak.... not always, other things can cause that... but more often then not it's a vac leak.

Idle on Kadrons usually winds up being somewhere between 4-7 with a snail IMOPE.
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Last edited by noneed on Thu Nov 15, 2012 9:44 pm; edited 1 time in total
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chrisd1891
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PostPosted: Thu Nov 15, 2012 9:43 pm    Post subject: Reply with quote

noneed wrote:
What is your fuel pressure ?
Kadrons like 2 PSI or slightly less...and most electric pumps put out 3 -3.5
that can and will drive you nuts if it's too high.

Have the T bodys on yours been re-bushed ?
If not, they could be sucking air creating a false air condition...even if they are new they can leak there.
One carb not responding to mixture adjustments is usually a sign of a vacuum leak somewhere... Check all of your gasket areas. Leaks can be really sneaky !

Try pinching off the crossover tube. If it tries to die when you do that, the motor is attempting to run off of one carb, and that's another usuall indicator of a vac leak.... not always, but usually.

Idle on Kadrons usually winds up being somewhere between 4-7 with a snail IMOPE.


I have a regulator, but have yet to install it. I'll get the correct fittings this weekend and install it.

The throttle bodies have not been re-bushed to my knowledge, but I did check the play on them it's minimal on both.

I haven't tried pinching off the tube. It's only for the brake booster though. There are no other vacuum tubes, so unless air is getting in under the manifold, I'm not sure how a vac leak would be possible. I'll give that a shot as well.

Thanks for the tips!
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noneed
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PostPosted: Thu Nov 15, 2012 10:05 pm    Post subject: Reply with quote

Sure.

Pinch that tube off and then put the snail on it...
I'll bet your readings will be a lot different between both carbs.
The tube is there to compensate for any differences between both carbs.
If there is a problem with one, like a leak somewhere, the tube will try to make up for that or any adjustments you do make to one carb to correct the problem.
Try pinching it and making small adjustments to each carb. You should notice a difference turning your mixture on either one if you are on the idle circuit. It does take a few seconds to change... it's usually not immediate.
Get them to match and then release your clamps, and adjust your idle...
That should get you closer. Just remember that NO set of dual carbs work perfectly right out of the box...they all take some time, patience, and finesse, but are worth the effort once they are dialed in.

Get that regulator on and dialed down to 1.75-2 PSI though.
Just make sure to check it for leaks periodically...some of those cheaper ones love to spring leaks.

Make sure your final dial in is with the motor at full temp too.
You want your carb and linkage settings to be dead on with the motor at operating temp, not cold or while warming up.
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PostPosted: Fri Nov 16, 2012 5:30 am    Post subject: Reply with quote

X2 and 3 - If a mixture screw doesnt do anything, your synch is way off and making sure that you understand that they are talking about the crossover tube from one manifold to the other - you need to isolate the carbs to synch,
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chrisd1891
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PostPosted: Fri Nov 16, 2012 11:41 am    Post subject: Reply with quote

andk5591 wrote:
X2 and 3 - If a mixture screw doesnt do anything, your synch is way off and making sure that you understand that they are talking about the crossover tube from one manifold to the other - you need to isolate the carbs to synch,


Ok, I was reading on lowbugget that it's not a good idea to pinch the balance tube off, because you don't drive with it pinched, so his rational was why would you sync it like that.

I'll give it a go though. Thanks.
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PostPosted: Fri Nov 16, 2012 1:36 pm    Post subject: Reply with quote

Mark Harney's carb clinic site says TO PINCH TUBE OFF when doing single barrel duals. 35 Pdsits work the same as Kads. I set them by pinching the tube, then going back and readjusting once it is free again.

Check John's tech articles at aircooled.net. He says how to tune most carbs.
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PostPosted: Fri Nov 16, 2012 3:19 pm    Post subject: Reply with quote

AJ also states that the car runs better without the balance tube - I dont run it on amy of mine, but I also am synched really well. Also I strongly suggest setting the idle speed a little higher - like 1000-1100 RPMS. There is a charge robbing effect with single barrels and you will find at idle one cylinder on each side is much cooler at normal idle speeds. Bumping up the idle a little and properly setting up the carbs corrects this issue.
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PostPosted: Fri Nov 16, 2012 3:47 pm    Post subject: Reply with quote

andk5591 wrote:
AJ also states that the car runs better without the balance tube - I dont run it on amy of mine, but I also am synched really well. Also I strongly suggest setting the idle speed a little higher - like 1000-1100 RPMS. There is a charge robbing effect with single barrels and you will find at idle one cylinder on each side is much cooler at normal idle speeds. Bumping up the idle a little and properly setting up the carbs corrects this issue.


Where would the vacuum line for the brakes go in that case? Confused
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PostPosted: Fri Nov 16, 2012 5:26 pm    Post subject: Reply with quote

Well - seeing as all I have are type 1s, have no idea....
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PostPosted: Fri Nov 16, 2012 5:44 pm    Post subject: Reply with quote

Make sure you start with the idle as low as possible.
It is important to have the throttle plates almost completely closed in order to keep the carb from running on the transition ports.
They only have to move just the slightest bit to uncover the next set of ports in the carb wall.
If you aren't getting a response from the idle screws it means you are getting fuel from somewhere else and that could be the transition ports.
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PostPosted: Fri Nov 16, 2012 5:45 pm    Post subject: Reply with quote

That is a long tube running up to the booster, make sure there is no leak in the hose. Isnt there a check valve or something too?
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PostPosted: Sat Nov 17, 2012 9:09 am    Post subject: Reply with quote

For crying out loud... first if you close the throttle plates all you get are dead cylinders. How in hell is the engine supposed to get air?? When the engine is idling, you ARE on those ports. Hence it is called IDLE circuits. When you move the throttle plate, it will pass the rest of those ports for smoother transition.

Do NOT sync the carbs w/ the linkage installed. Unhook the linkage, then sync. Mixture screws get 1 1/2 - 2 full turns - that is it!

The idle speed is dictated by the throttle plate screws. All you are doing is opening the throttle plates more when you turn in the screws. With throttle plates from fully closed, turn in screws 2 full turns => this will open the plates and you are able to run the engine. With linkage unhooked, run engine. The idle will be high so what? Just back out on the throttle plate screws (idle screws) to get the idle down. Check your timing... start at 7 degrees w/ reasonable idle speed.. 850 - 1000RPM.
check full timing later after carbs get sync'ed.
Sync the carbs by reading flow...flows should be the same no matter what it is reading. Turn throttle plate screws in/out to get the flows even...same time watching idle speed and timing. When you get those good to go, set the linkage end-to-end length. The flow should NOT change on LEFT carb (driver side) w/ linkage on. If it does, it is too short. Adjust balljoints.


Last edited by nsracing on Sat Nov 17, 2012 9:14 am; edited 1 time in total
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PostPosted: Sat Nov 17, 2012 9:11 am    Post subject: Reply with quote

..and don't pinch the tube between the carbs.

There should be a sticky on how to properly tune a set of Kadrons. WE go through this everytime.

Enjoy.
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PostPosted: Sat Nov 17, 2012 3:23 pm    Post subject: Reply with quote

There are different ways to skin a cat........I use the linkage to synch - not the stops - I use one side to set the idle and have the other side back out. Seeing as you dont drive at idle, and as soon as you touch the pedal, you are off the stops and relying on the linkage, why would you want to do it otherwise......
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PostPosted: Sat Nov 17, 2012 10:11 pm    Post subject: Reply with quote

nsracing wrote:
..and don't pinch the tube between the carbs.

There should be a sticky on how to properly tune a set of Kadrons. WE go through this everytime.

Enjoy.


Been doing it with the tube pinched off since my first set in 1987.
What works for you and what works for someone else can be two different things.
You have to isolate the carbs from each other in the case of determining a vac leak, bushing leak, or a problem with one carb. You simply CAN NOT expect to accomplish anything with a tube running between both manifolds....
Simple physics.
The motor will try to run off the other ( non problem ) carb.
That's why the tube is there in the first place....to compensate between the two carbs if there is a difference.

In a perfect world, with two perfectly pre-set carbs, with no issues whatsoever on either, or they're installation, yea, you can set them with the tube WFO since they are already real close but honestly, unless they were hand delivered by someone that re-bushed them and pre-set them perfectly for that application that's really not realistic is it ?
Chances are one is off from the other...and a snail will only be accurate if there is no link between the manifolds.

First get your fuel pressure right.
Get both dead on with the tube pinched off, then release the clamp, and re-adjust your idle, recheck again, and THEN set and hook up the linkage so they both open at exactly the same time.
Your idle settings should be right around where the idle speed screw hits or slightly more. Too much and you are off the idle circuits and into the progression circuits. If you are pulling a 10 on your snail at idle this may be part of your problem... just a guess... you may have the idle speed screws turned in a little too much, and your mixture adjustments won't do much if that's the case.

You should T your brake booster line into the balance tube on your Bus.
Don't run it off of one carb. run it off of both.
There should be a check valve on the hose up to the booster. You need that. T into the balance / crossover tube after it.

Kads do have better "snappiness" without the tube and if you have them dead on you can certainly run without one if you don't have power brakes, but I've always run the tube myself.

Another thing to ask... were these Kads set up for an 1800cc motor or are they set up for a 1600 and just have T4 manifolds ?
Where did you get them ?

Mark Harney's carb clinic site was a fantastic resource but is it still up ?
I thought it was down...
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PostPosted: Sun Nov 18, 2012 10:46 am    Post subject: Reply with quote

How in hell do you figure the engine will run from one carb and not the other? Do you think there is enough pressure differential in the tubing to pass air/fuel mixtures and cross over to the other side?? If you have the linkage off and only one carb is opening, you are still NOT going to feed both banks from that one carb. Even if you managed to sqeak some form of mixture in through the other side, probably not enough to support a combustion.

With both throttle plates open at the same time and same flows, how do you get preferential use from only 1 carb for both banks??

We measure FLOWS w/ a snail (if this is what is used) above the throttle plates...not vacuum. Manifold Vacuum is below the throttle plates. They are not the same.
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