Weber jets??All who live for their triples please read this

[steve260z]

Asking if the differences are significant enough for concern. Really, just concerned about throttle number 1. Thanks for the numbers!

[Leon]

I set mine more-or-less equal. Seems like your carbs have seen better days and maybe have a seal going out or a bent throttle shaft. It'll make the engine a bit more finicky at idle and low-load, depends on how concerned you are with performance under those conditions.

 

I take it these are older DCOEs without the air bypass screws?

[steve260z]

Yea, no bypass screws. These are dcoe 40-18s. It shouldn't make much difference at 1/3 throttle and up correct?

[Leon]

Yea, no bypass screws. These are dcoe 40-18s. It shouldn't make much difference at 1/3 throttle and up correct?

 

Probably but if it's street driven, you'll spend a lot of time below 1/3 throttle. If it drives fine, don't worry about it.

[steve260z]

Yea, I'm not too worried about it. To fix that one particular carb I need to take out the throttle shaft. Not too fired up about that. Idle is a bit up and down but I can live with it.

[steve260z]

New issue,

I set the idle at around 1100, which is where it idles well..Not too high or low. Engine is happy and sound good.

But, coming to a stop or letting it sit and idle it will drop down to around 800 and nose dive and die. Not every time but about 50%.

If I set the idle higher then its too high and will pull around corners other low speed situations too fast. Any idea what could cause this? Well, its either not enough air or not enough fuel...

 

One guess is my chokes are too big for low speed operation. Running 36s on my dcoe 40s. Maybe its just borderline to big. At low air speeds the chokes are too big and not enough vacuum. But that really shouldn't effect the idle? Think that's a bad guess....

 

Why can the car idle fine for 10 minutes at 1100 rpms then die after that?

Any help is greatly welcome...

 

Thanks

steve 

Edited August 14, 2016 by steve260z

[zredbaron]

For me, this kind of issue was always due to carb linkage either sticking or slipping on the common throttle bar, that is, a link from one of the carbs is not travelling wide open or won't fully shut with the other two.

 

Sometimes it slips hitting WOT, sometimes it slips when closed shut. How smooth or hard on your pedal you are also is a factor: loose linkage vs. tight but not tight enough. My instances were more typically pronounced, but not always.

 

Regardless if where/how/why... my instinct is carb sync / linkage friction / spring tension. You might be able to find some play, limited travel or some sticking while the engine is off.

 

Are your synchrometer numbers still the same? If so, try doubling the return spring tension on the carb linkage, to ensure a fully closed throttle across all 3 carbs. (Or try letting the return spring close them and them close them further with your hand while the engine idles. It shouldn't change.) This may stall your engine, which would identify your issue.

Edited August 16, 2016 by zredbaron

[steve260z]

Yea, I doubled the spring. Wow...strong pedal now. While messing around I sprayed carb cleaner around the throttle shafts and got rpm reductions on 4 or the 6 areas. So, that could be my problem. Fixing that then see what happens.

[Leon]

If you need it perfect, reseal the carbs, that's your issue. Nice job finding it. 

 

Your gut feeling is correct, venturi size doesn't affect the idle circuit.

[swa240z]

Ok, I guess it's time for me to join this excellent discussion to see if I can get some help with the issue I'm having with the Weber Type 2 triples on my L24.  First some history on the engine and the original carb setup.  The engine was originally rebuilt about 2 years ago and was mostly stock.  With the setup below, the engine ran pretty well.  No real noticeable issues.

 

125 mains

F16 e-tubes

150 air correctors

50f9 idle

135 pump jets

50 pump exhaust

30mm chokes

4.5 aux venturis

Idle screws at about 3/4 turns

about 3.5 psi fuel pressure

Pertronix ignition

Ignition timing at 12* with 24* mech advance

No vacuum advance

2.5" 6-2-1 header/exhaust

ZX 5-speed with Subi 3.90 LS rear end

 

After a couple hundred miles, I started hearing some odd disconcerting noises in the 2000 to the 2500 RPM range.  Late last winter I tore the engine down and took it to a different (and more respectable) machine shop for inspection and rework.  Come to find out that the last guy over honed the cylinders by about .011 using standard pistons.  I guess I was hearing some piston slap.  Anyway, the engine was rebuilt .5mm over.  In the process, I added an L480 Isky cam, had the head ported and polished and the valves unshrouded.  In addition, the head was milled about .035 to achieve a 10:1 compression ratio using a 1mm metal head gasket.  I have also added a Kameari adjustable cam gear to assist with cam timing due to milling the head and the thinner head gasket.

 

With the engine rebuilt and the carbs reinstalled, I noticed a fairly bad stumble when accelerating moderately hard off idle or low RPM.  Since then I have been fiddling with various jets and e-tubes but the bog is still there BUT the engine now runs much stronger in general than it did before.  The new engine has about 200 miles on it now.  Here is the current setup:

 

125 mains

F11 e-tubes

170 air correctors

50f9 idle

140 pump jets

50 pump exhaust

30mm chokes

4.5 aux venturis

Idle screws at about 1/2 turn

about 3.5 psi fuel pressure

Fuel levels adjusted to 25mm (I think) based on Keith Franck's recommendations.

Throttle shaft seals replaced

ZX dizzy with ignition timing at about 20* with 17* mech advance

No vacuum advance

Kameari cam gear set at the 2* advanced mark (I assume that is 2* cam and 4* at the crank but not sure)

2.5" 6-2-1 header/exhaust

ZX 5-speed with Subi 3.90 LS rear end

 

The engine seems to run smoother with the F11 vs. the F16 e-tubes.  Definitely more kick with the 140 pump jet upgrade.  The higher initial ignition timing with the ZX dizzy seemed to help with overall performance as well BUT the bog is still there.

 

I plan to purchase some sort of fuel level sight tool to confirm the fuel level in the bowl is correct.  I have been using a strip of index card that was marked at 25mm and dipping it into the fuel well until it made contact with the fuel.

 

AFRs are in the upper 11s to low 12s at idle.  I have tried to get that a little leaner, but the engine idles worse if i lean it out any more. I have tried dropping the idle jets to 45f9s but the engine ran way too lean below 2500 RPM so I put the 50s back in.  Cruising AFR's are in the 13 range.  WOT AFR is in the 13s to about 14.  When the engine bogs after hitting the throttle hard off idle or at low RPMs, the AFR's lean out in the 16s but once I get past the bog which lasts about 1 second or less, the car pulls hard and the AFRs get back to the 13s.

 

I have contemplated some larger idle jets since the engine seems to be lacking fuel during the bog, but I'm not sure how that will play out given I'm only running about a 1/2 turn out on the idle mix screws with the 50f9s.

 

I have not messed with the cam timing at this point, but it is currently set on the 2* advanced mark.

 

If I can get this car to launch without issue, I'll be a very happy camper!  Let me know if you have any ideas or if I need to provide any more info.  Like I said earlier, I plan to buy a tool to better measure the fuel levels in the bowl just in case my current measurement method is giving me false readings. 

 

Any help would be greatly appreciated!

 

Steve

 

[Chickenman]

WOT AFR's of 13 to 14 are too lean. Should be around 12.5 to 12.8. I'd bump up your mains to 130's and see what that does. I think you're lean on the low speed to mains transition. You may even want to go with 135 mains. Ideally your AFR curve at WOT should remain dead flat between 3,000 RPM to redline.

 

If it starts to go lean on the top end at WOT install a slightly smaller Main Air corrector. If the AFR curve starts to go rich on the top end, then install a slightly larger Main Air corrector.

 

Main jets affect enter fuel curve. Main jet effect is primarily from 2,800 RPM upwards.

 

Air jets are used for trimming upper RPM fuel curve. Air jets primarily affect mid to high RPM range.

 

Low speed jets ( Idle jets ) affect from idle to approx, 2,800 RPM

 

Idle screws affect idle primarily.

 

All circuits overlap somewhat.

 

An IC engine is nothing but an air pump. Modifications such as a bigger Cam, Port and Polish, Higher CR, high flow exhaust ) all increases the Volume metric Efficiency of the engine. To make more HP you need to feed it more fuel. So bump up the main jets.

 

Your idle jets are also a bit small. This causes your low speed an tip in Flat Spot. With the engine modifications, and particularly the extra Cam overlap of the Isky 280 cam, you should up the idle jets to a 55F8 or 55F9.( F9's have a smaller air bleed and are a bit richer than F8 Idle tubes )

 

Your 30 mm Venturi's were fine with a stock engine. With the improvements you've made thye are a bit on the small side. If you are running 40 DCOE Webers switch up to 32 to 34 mm Venturi's. That will unleash a lot more HP on the big end. Be prepared to make corresponding jetting changes. Both Fuel and Air corrector.

 

Note; Don't go too big on the Venturi's. Venturi size should be a maximum of about 80 percent of Carb bore size as noted in Weber Technical manuals.. Anything larger than 80% absolutely kills Booster signal. A strong Booster signal is the  key element  to efficient Carburation and drive-abilty. And it is one of the most over looked items in tuning any Carburator. 

 

Using the recommendations by Weber. A 40 DCOE can be equipped with up to 32mm Venturi's and still maintain good drive-abilty. 34mm Venturi's may make more power on the top end with a modified engine, but at the loss of some low end drive-abilty

 

The following links have some VERY good info on setting up Webers. Note that when 36mm or larger Venturi's are used you should go up to a 45mm Bore carb. Otherwise Booster signal becomes too erratic and weak.

 

http://www.s262612653.websitehome.co.uk/DVAndrews/webers.htm

 

http://www.teglerizer.com/dcoe/inglese/inglesetuning.htm

Edited September 20, 2016 by Chickenman

[Leon]

Ok, I guess it's time for me to join this excellent discussion to see if I can get some help with the issue I'm having with the Weber Type 2 triples on my L24.  First some history on the engine and the original carb setup.  The engine was originally rebuilt about 2 years ago and was mostly stock.  With the setup below, the engine ran pretty well.  No real noticeable issues.

 

125 mains

F16 e-tubes

150 air correctors

50f9 idle

135 pump jets

50 pump exhaust

30mm chokes

4.5 aux venturis

Idle screws at about 3/4 turns

about 3.5 psi fuel pressure

Pertronix ignition

Ignition timing at 12* with 24* mech advance

No vacuum advance

2.5" 6-2-1 header/exhaust

ZX 5-speed with Subi 3.90 LS rear end

 

After a couple hundred miles, I started hearing some odd disconcerting noises in the 2000 to the 2500 RPM range.  Late last winter I tore the engine down and took it to a different (and more respectable) machine shop for inspection and rework.  Come to find out that the last guy over honed the cylinders by about .011 using standard pistons.  I guess I was hearing some piston slap.  Anyway, the engine was rebuilt .5mm over.  In the process, I added an L480 Isky cam, had the head ported and polished and the valves unshrouded.  In addition, the head was milled about .035 to achieve a 10:1 compression ratio using a 1mm metal head gasket.  I have also added a Kameari adjustable cam gear to assist with cam timing due to milling the head and the thinner head gasket.

 

With the engine rebuilt and the carbs reinstalled, I noticed a fairly bad stumble when accelerating moderately hard off idle or low RPM.  Since then I have been fiddling with various jets and e-tubes but the bog is still there BUT the engine now runs much stronger in general than it did before.  The new engine has about 200 miles on it now.  Here is the current setup:

 

125 mains

F11 e-tubes

170 air correctors

50f9 idle

140 pump jets

50 pump exhaust

30mm chokes

4.5 aux venturis

Idle screws at about 1/2 turn

about 3.5 psi fuel pressure

Fuel levels adjusted to 25mm (I think) based on Keith Franck's recommendations.

Throttle shaft seals replaced

ZX dizzy with ignition timing at about 20* with 17* mech advance

No vacuum advance

Kameari cam gear set at the 2* advanced mark (I assume that is 2* cam and 4* at the crank but not sure)

2.5" 6-2-1 header/exhaust

ZX 5-speed with Subi 3.90 LS rear end

 

The engine seems to run smoother with the F11 vs. the F16 e-tubes.  Definitely more kick with the 140 pump jet upgrade.  The higher initial ignition timing with the ZX dizzy seemed to help with overall performance as well BUT the bog is still there.

 

I plan to purchase some sort of fuel level sight tool to confirm the fuel level in the bowl is correct.  I have been using a strip of index card that was marked at 25mm and dipping it into the fuel well until it made contact with the fuel.

 

AFRs are in the upper 11s to low 12s at idle.  I have tried to get that a little leaner, but the engine idles worse if i lean it out any more. I have tried dropping the idle jets to 45f9s but the engine ran way too lean below 2500 RPM so I put the 50s back in.  Cruising AFR's are in the 13 range.  WOT AFR is in the 13s to about 14.  When the engine bogs after hitting the throttle hard off idle or at low RPMs, the AFR's lean out in the 16s but once I get past the bog which lasts about 1 second or less, the car pulls hard and the AFRs get back to the 13s.

 

I have contemplated some larger idle jets since the engine seems to be lacking fuel during the bog, but I'm not sure how that will play out given I'm only running about a 1/2 turn out on the idle mix screws with the 50f9s.

 

I have not messed with the cam timing at this point, but it is currently set on the 2* advanced mark.

 

If I can get this car to launch without issue, I'll be a very happy camper!  Let me know if you have any ideas or if I need to provide any more info.  Like I said earlier, I plan to buy a tool to better measure the fuel levels in the bowl just in case my current measurement method is giving me false readings. 

 

Any help would be greatly appreciated!

 

Steve

 

Hi Steve. If you're familiar with Keith's work you're already ahead of 99% of Weber "tuners" out there...

 

Make sure float levels are even at 25-26mm, carbs are sync'd, valves adjusted, and the ignition system is in tip-top shape before dipping into carb tuning. Once that's all set, you can try F7 e-tubes and 130 air jets for better tip-in (if you want to stay with Weber jetting).

[steve260z]

Yes, boy all that sounds way too familiar. First regarding the head shaving. I can't remember the amount shaved off the head to use cam tower shims but do you need those? Does the new sprocket actually adjust for the geometry change? Check that out.

 

Ok, carbs. You need to look at each carb individually. Take the linkage off each carb once it's running and warm. Rev each carb by hand to see if u get the bog with the car just sitting there. Since the engine has no load this is an easier test for the carbs to pass. Hopefully u still get this bog during this test cause it's very useful. I think you need to get the throttle plates in a different position at idle. It all starts there. Assuming u get the bog in this test make adjustments on the throttle plates and idle jets until the bog is gone. Now, I don't treat the standard setting suggestions as absolutes, by any means, but it's noted in many set ups that the idle jets should be turned out near 1 1/2 times. U are way less than that which would indicate they are too big. But, I have the same amount of turn out on my idle jets as well so go figure. I've set mine to achieve AFR.

 

What happens when you have over run on the engine? (Let off throttle at 4K plus? Does the exhaust pop and or what is AFR at that point?)

 

Spray starter fuild all around the intake and throttle shafts , anything happen? If you have vacuum leaks the engine speed will drop.

 

Steve

Edited September 20, 2016 by steve260z

[swa240z]

 

Your idle jets are also a bit small. This causes your low speed an tip in Flat Spot. With the engine modifications, and particularly the extra Cam overlap of the Isky 280 cam, you should up the idle jets to a 55F8 or 55F9.( F9's have a smaller air bleed and are a bit richer than F8 Idle tubes )

 

 

Chickenman - I too was thinking that the idles might be too small causing things to go lean before the transition.  I keep reading about where idle screws "should" be, but given mine are only 1/2 turn out with 50f9s, I'm guessing that they will be something less than a half turn out with 55s.  Is that really a problem - assuming everything seems to run fine?  The carbs are all sync'd and flowing the same at idle.  To get idle RPMs around 1000 or a little less, the throttle plate is covering about 75% of the first progression hole.  I don't know if that is good or bad, but that is what it takes to get the idle where it needs to be.

 

Also, I was thinking about your recommendation of going with 130 or 135 mains to richen things up at higher RPMS.  Will increasing both the idles and mains at the same time maintain the same basic lean shortfall at the time of transition?  In other words, to close the gap, should the idles go up a couple sizes with maybe just one size jump in mains to help close the gap?

 

Leon - I have just recently subscribed to Sidedraft Central to get more insight into what Keith Franck is doing in regards to the Weber DCOEs.  He has a tremendous amount of knowledge.  I'm just learning about how the webers work in regards to using the weber jetting.  I'm also trying to learn more about his proprietary jetting and e-tubes and determine what combination might work well with my setup.  My problem is that even though I am now a member of the group and receiving the daily email updates, I can't seem to get logged into the group to actually read what is already posted on the site. I hate the way Yahoo Groups works.

[swa240z]

Yes, boy all that sounds way too familiar. First regarding the head shaving. I can't remember the amount shaved off the head to use cam tower shims but do you need those? Does the new sprocket actually adjust for the geometry change? Check that out.

 

Ok, carbs. You need to look at each carb individually. Take the linkage off each carb once it's running and warm. Rev each carb by hand to see if u get the bog with the car just sitting there. Since the engine has no load this is an easier test for the carbs to pass. Hopefully u still get this bog during this test cause it's very useful. I think you need to get the throttle plates in a different position at idle. It all starts there. Assuming u get the bog in this test make adjustments on the throttle plates and idle jets until the bog is gone. Now, I don't treat the standard setting suggestions as absolutes, by any means, but it's noted in many set ups that the idle jets should be turned out near 1 1/2 times. U are way less than that which would indicate they are too big. But, I have the same amount of turn out on my idle jets as well so go figure. I've set mine to achieve AFR.

 

What happens when you have over run on the engine? (Let off throttle at 4K plus? Does the exhaust pop and or what is AFR at that point?)

 

Spray starter fuild all around the intake and throttle shafts , anything happen? If you have vacuum leaks the engine speed will drop.

 

Steve

 

Hey Steve - I was writing my last post while you posted yours.  Regarding shimming the cam towers, I talked with Ron Iskenderian about this.  He isn't a huge fan of shimming cam towers because it throws off the geometry of everything under the cam cover.  With a new timing chain, tensioner and guides, he said there was enough room to take up the slack created by shaving the head.  He was the one that suggested an adjustable cam gear to make up for the retarding of the cam due to the head shave.  I bumped it to about the 2* advance mark on the cam gear to compensate.  At one point, I had seen where someone posted in one of the z forums a formula for calculating the cam timing effect of shaving the head by a certain amount but I can't find it anywhere.

 

Regarding the carbs, the flat spot is evident when revving all carbs with the car just sitting there, but not as evident as when under load on the road.  I never thought about running this test with each carb but I can give it a try and report back.

 

Regarding the idle screws, see my comments in the previous post.  I agree that the "norm" is about 1.5 turns out but my engine runs terrible if I do that.  I'm a little concerned about going with bigger idles but I think the engine needs it to help alleviate the lean spot that seems to be causing the flat spot.  The idle screws are all relatively new and purchased from Pierce Manifolds a couple of years ago.  Maybe they are ground at different angles than the seats?  

 

I replaced the throttle shaft seals this past weekend since I was suspecting some air leak around them.  Five of the seals were in ok shape, but there was no grease left behind them.  One of the seals was shot and I'm sure leaking air.  That was the one cylinder that I was having trouble syncing.  All cylinders are now sync'd and the engine idles much smoother, but not perfect.  I still suspect a small air leak somewhere but I can't find it.

 

Steve

Edited September 20, 2016 by swa240z

[steve260z]

I replaced all my leather seals and the carbs acted totally different. As in different but not much easier to tune!!!

You have to spray around and get rid of the air leak. Maybe you have one maybe you don't.

Another thing since everything matters with these carbs. I assume the flat spot occurs when the pump jet is put into action. In that you are not slightly feathering the throttle.......Do this, yes take the carbs off AGAIN...Keep the the gas in the carbs, activate the throttle plates so gas shoots our the pump jets. Yes, it will come spraying out. Make sure they are actually spraying out and working. I happen to have 1 pump jet that just dribbles out. Haven't decided if that's a problem yet but at least make sure they are working.....

 

I was able to tune the carbs and get rid of 90% of the flat spot by working each carb by itself in the manner I described above. You can move the throttle plates from the idle position, then to transition holes then to pump jet and main jet. This allows you to see where the problem is occurring and allows to see how each carb transitions and see which ones are good and which ones are bad. It also allows you to exclude the linkage as a problem issue since its not connected. If I had to do it all over again I would have bought new carbs verses used ones but that's a totally in the past thing.

[swa240z]

Hey Steve - I'm confident the leather seals aren't leaking since I replaced them this past weekend and have a nice layer of grease between them and the bearings. The old seals were questionable, but one was in very bad shape.  If I have a leak, it is probably around one of those damn soft mount gaskets with the o-rings and plastic spacers - but I can't find it using carb cleaner.  As far as the pump jets go, they were all definitely shooting out a good stream of fuel.  I checked them before dumping the fuel out of the carbs.  

 

I think I'm going to order some bigger idle jets to see what effect they have.  From a dead stop, the flat spot is very noticeable as soon as I hit the pedal.  The flat spot becomes less noticeable the higher the RPMs are when I hit the gas (I don't know if that is indicative of anything though). Once I'm past the transition point, I don't really notice the flat spot.  I wish I knew someone with a pile of extra jets so I could experiment.  That would save a lot of time and a lot of money!

 

Steve

[Chickenman]

The idle mixture adjustment screws should not be significantly  affected by changing the the Idle jets...if at all. Idle jets are more correctly called low speed jets as they mainly affect off idle fuel mixture up until the mains start coming in. There will be some overlap, but minimal.

 

Having the throttle blade uncovering too much of the progression hole is the #1 problem of having too rich of an idle. Independent runner carbs, particularly with larger Camshafts, need a LOT of static ignition timing. 15 - 17 degrees BTDC minimum set on the dizzy at idle.

 

Better yet. Hook up the Vacuum advance to manifold Vacuum and add another 10 degrees of Vacuum advance at idle. Yes that is a total of 25 degrees advance at idle. If you can hook up a balance pipe system to run manifold vacuum to the Vacuum advance it makes an amazing difference to the idle quality. That allows the throttle blades to be closed more at idle and makes the isle screws much more responsive.

 

A lot of sites advocate disconnecting the Vacuum advance when running IR crabs. That works fine on Race cars that are run on a race track. However, it is a bad idea on a hot rodded Daily Driver. It adversely affects fuel mileage, idle quality and low speed drive-abilty. David Vizard has an excellent  book called " Performance with Economy ", where he explains the importance of running a Vacuum advance on modified street car. It's well worth ordering this book.

 

Cam overlap greatly reduces VE and also provides a natural EGR at idle. Because of the closed throttle blades ,VE is very low and that creates a low density mixture in the cylinder. Dynamic compression ratio is reduced. Commonly by 30% or more. So a calculated 10 to 1 CR actually is more like 7 to 1 or less. ( That's why when taking a Compression Test the instructions always recommend jamming the Throttle Blades wide open ). This low density mixture takes longer to burn. Thus you need more advance to light things off sooner. Overlap on larger cams needs more ignition advance. Then there is the EGR affect of larger overlap cams.

 

Factory stock EGR is normally turned off at idle, because it dilutes the mixture too much. But you can't turn of EGR generated by the extra valve overlap of a larger Camshaft. So you have further reduction in density of the Air/Fuel mixture  and pollution of the AF mix by exhaust gases. And that requires even MORE ignition timing at idle. A hot rodded engine wants 25 to 30 degrees of Total advance at idle in an ideal situation. An adjustable vacuum pot is one way to get this. Fortunately the Nissan Matchbox dizzy's do have an adjustable Vacuum pot. Both in stroke and spring tension.

 

Set static ignition timing to 15 degrees BTDC ( vacuum hose disconnected ) Then hook the Vacuum advance up to manifold vacuum. Biggest problem with IR carbs is that you need a balance pipe system to draw vacuum from all four ( or six ) manifold legs. You can't just pull the Vacuum off of one manifold leg. Cylinder pulses are to strong and pulsating on the IR design. Another reason why most guys don't run a Vacuum advance with duals or triples. But it's a mistake ( for drive-abilty ) on a DD.

 

Adjust the Vacuum pot stroke so that you have about 10 degrees of additional advance. Loosen the spring tension so that the rod pulls all the way in at a lower setting than stock. I use a mighty vac for this. I usually set a cammed engine so that the rod pulls in all the way with only 10 hg of Vacuum. Check out Jason Greys article on tuning Datsun dizzy's and Vacuum pots. .

 

http://newprotest.org/projects/510/jasonGrayDistributor.pl

 

Here's a very good thread on Weber Tuning on " The510realm". Some very good info there. Including a few suggestions from your's truly.

 

http://the510realm.com/viewtopic.php?f=30&t=28635 

 

Hope this helps.

[steve260z]

The 510 article above addresses the throttle position I was mentioning. Good find.

[Chickenman]

The 510 article above addresses the throttle position I was mentioning. Good find.

Yes, as you mentioned, the positioning of the throttle plates in regards to the progression holes is very important to getting a smooth idle and it also affects tip in as you also mentioned. The pictures tell a thousand words.