single 45 DCOE on a Lynx mani, about to throw in the towel!

[Harv]

Ha! Me too!

 

john

[Chris_B]

Have you checked to make sure the air bypass screws are closed? You may want to try lining up the throttle plates and leaning out the idle mixture to drop the idle speed. 11.5-12 is pretty fat.

[abrokenframe]

37 minutes ago, Harv said:

Ha! Me too!

 

john

 

Funny! you know what my third car is? A '91 e30 325i coupe. Love that car!

 

31 minutes ago, Chris_B said:

Have you checked to make sure the air bypass screws are closed? You may want to try lining up the throttle plates and leaning out the idle mixture to drop the idle speed. 11.5-12 is pretty fat.

 

I only barely open the bypass screw on one barrel to sync the air flow @ idle. Moving the throttle plates to cover the first progression hole lets way too much air by hence the 2k+ idle to get a decent AFR. I'll give it another shot though!

 

-Ryan 

 

 

[burndog]

On 6/28/2017 at 8:24 AM, abrokenframe said:

I know you are going dual webers, but I’m sure someone will stumble upon this thread when trying to find info on the lynx setup, so I thought I’d chime in. First off, here’s some specs on my carb:

 

-Weber DCOE 45 152

-Main Venturi:  36

-Aux Venturi: 4.5

-Main Jet: 145

-Em Tube: F16

-Air corrector: 155

-Idle jet: 60F8

-Pump Jet: 45

-Pump Exh: 40

-Needle V: 2.00

 

Except for the larger idle jet that the PO put in, this carb is setup how it comes out of the box. Here’s some of the problems that I’m trying to sort out:

 

-Shaky/high idle

-Stumbling on partial throttle

-Poor fuel economy of 12-15mpg

-Car stalls on deceleration from high speeds and randomly at idle

 

I picked up a AEM AFR Uego gauge and installed it last night to help understand what’s going on with the carb. Here’s what I’m seeing so far:

 

-Idle: 11.5-12

-Light throttle shoots up to 15/17 for half a second then drops

-WOT up to 4Krpm: 11-12.5

-Cruising at all speeds: 11.5-13.5

 

I’m still in my engine’s first 500 miles, so I’m not revving it up past 4k for the time being, so no readings there. So what solutions am I considering?

 

First off, I called Metric Mechanic since they built my engine to get their opinion. They didn’t have much experience with the single Lynx setup, pointed to a couple of issues that they think come along with the Lynx and basically recommended trying out the 38/38 I have sitting on my shelf. This is something I am heavily considering given the mountain of time/money I am about to put into this carb. THEN I called Top End Performance since they sold the Lynx to the PO. I told them my jetting and they said that was pretty close to where they would start and make small adjustments on a car to car basis. They said stick with 36MM venturis. So do I fix the DCOE or move over to the 38?

 

When considering the DCOE. My first thought is jetting to fix the progression circuit. But after doing some research, my car seems to be suffering from the same problems that a number of others have had with 152’s and I think the main culprit is the progression holes. This Alfa thread has a good write-up and mirrors my symptoms: http://www.alfabb.com/bb/forums/carburetors-fuel-injection-air-intake/32856-weber-dcoe45-152-45dcoe-progression-circuit-modification.html

 

If I stick with the DCOE, It makes sense for me to investigate this before jetting since it will affect my jetting anyway. If I do need a 4^th progression hole, this requires removing the carb and bringing to the local machine shop to drill the holes. I might as well rebuild the whole damn carb if I do that since it’s already coming of the car. THEN put it back on and potentially tackle the jetting, which could get pricey in its own right.

 

I’m heavily considering the 38/38. I bought the carb off of a local racer’s ’02, so I’m sure it’s in good working order. Not as sexy, but seems so much more reliable and easy at this point.

 

-Ryan

 

I understand that 13.3 AFR is the ideal for Wide Open throttle under load. Additionally, I am sure you are not running enough compression to be anywhere near 12.5 let alone getting even lower numbers. LEAN that baby out! across the board!!!

[Chris_B]

Having the barrels balanced at idle is not that important- besides you can a slight imbalance in airflow with your idle mixture screws. I suggest closing the bypass and adjusting your throttle plates so you can just see the front (toward motor) edge under the progression hole.

[Chris_B]

I would argue that 12.5AFR is ideal for WOT in the higher RPM ranges (say, >5500).

[Stevenc22]

How many turns on the idle mixture screw for Weber 40 DCOE (later model 151). Based on my reading it should be 2 1/4 to 3 turns. Sounds about right?

Edited June 30, 2017 by Stevenc22

[TobyB]

whatever makes it idle well...

 

Chris, just so we're clear, here, you want the throttle plate to COVER the entireity of the first progression hole, right?  So it's not flowing fuel?

 

I'd add to that- at least.

 

The progression holes are in different places on different carbs, and it's OK to use the idle

circuit (the ONLY one completely tuned by the idle SCREW) to let the plates close a bit

BEYOND the first progression hole, if that's what needs to happen.

Unless the car bogs transitioning off idle, it works fine.  If it bogs, then you have to use other means

to get the progressions open sooner.

And the idle air bypasses CAN be used to get the plates closed farther if the car won't idle with the progressions covered.

 

12.5 is safe at full load.  14 is safe at cruise.  As lean as 18 works at 'gentle loafing along'.

 

I always do my best to get even flow at idle and up onto the throttle linkage. 

It's hard.  It helps idle. It helps transition. Then I tune for best idle with the mix screws.  One at a time...  then I rebalance...

 

t

 

[Chris_B]

Toby, I agree about the idle mixture setting. There is no magic formula WRT turns of the screw, and different idle jet sizes will affect how many turns it takes.

 

Re. the first progression hole, yes- ideally the entirety of the progression hole should be covered. However, he seems to be having a problem with a really high idle when the throttle plates are set there, so I suggested backing off a bit to see what happens with the idle speed (and leaning out the idle mixture).

 

So his problem is the opposite- he needs to open the throttle setting to move the plates toward the 1st transition hole. If he opens the air bypass screws, that will cause the idle speed to increase, right? Or, am I thinking backwards after my second beer....?

[TobyB]

Ah- I read it the other way, that his plates needed to be even more closed than covering 1st progression to reduce idle.

And adding fuel with the idles is ok in that case.

 

But I'm on g&t here, so...errr...

 

>hic<

 

t

[abrokenframe]

I tried opening up the throttle to where I can see the beginning of the plate when looking through the first progression hole and leaned out my idle. Bleeders closed. I can get it around 1100rpm. This made light throttle even more lean with lots of popping and stumbling. The car was barely drivable. Confusing to me and goes against my logic.

 

The best overall setting from the numerous I've tried seems to be throttle almost closed (not covering the progression hole at all), bleeders slightly open, and a verrry rich idle (11.5-12). Light throttle is then bearable. Still have to rev it up more than I should when engaging the clutch to compensate for it leaning out. This setting is still far from ideal and hasn't solved any of my problems. I'll check my float level when my gasket set comes in.

 

My hood hinges have definitely been getting a workout the last two weeks! I'll shoot a little video of my AFR gauge to give some visual backup. 

 

Thanks for the input everyone. 

 

-Ryan

[zinz]

What is your igintion timing at 1000 rpm and 1500 rpm?

[Chris_B]

Ryan, you should measure your fuel level from the top of the carb in the main jet well. Trying to get the right level (~25MM from the top deck) is very difficult to achieve by adjusting floats. What size idle jets are you running? Sounds like you are drowning the idle circuit.

[abrokenframe]

4 hours ago, zinz said:

What is your igintion timing at 1000 rpm and 1500 rpm?

 

With my IE distributor:

 

1,000- 14

1,500- 16

2,000- 22

3,000- 32

 

 

2 hours ago, Chris_B said:

Ryan, you should measure your fuel level from the top of the carb in the main jet well. Trying to get the right level (~25MM from the top deck) is very difficult to achieve by adjusting floats. What size idle jets are you running? Sounds like you are drowning the idle circuit.

 

Fuel level is at 25mm. Didn't realize it was that easy! Very difficult to set idle above 12.4 AFR. 

 

-Ryan

[Chris_B]

Ryan, which idle jets are you using?