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

[TobyB]

Quote

 

And thats determined by the size of the chokes.

AND how fast the engine is turning AND how far the throttle's open AND how well the mixture's burning AND how good a match the spark timing is for the aforementioned

AND compression ratio AND exhaust AND intake AND baromtric pressure AND temperature AND camshaft overlap AND phaseofthemoon...

 

phew.

 

Chokes, schmokes.  Yes, if it's falling on its face at 7200, you might need bigger ones.

When it transitions onto the mains poorly NO MATTER THE JET then maybe it's too big.

But at 4500, ANYTHING smaller than a 42 can be made to run pretty well.

And a 32 is a fine place to START.

 

Then you adjust the phase of the moon...

 

 

Now, about that Lynx...

 

heh

 

BTW, if you're going to duals, I'd REALLY STRONGLY no matter the phase of the moon MEASURE THE ONE YOU HAVE VERY CAREFULLY!

I had problems with the main jet well drilling- it sat several MM too low (Tell Steve- he'll be able to tell by looking at it)

 

only because that bit me before, once, and I spent half a season chasing my ass only to find out I had 3 barrels and a piece of Sonotube...

 

t

 

[pkchopp]

Steve over at Top End Performance in So. Cal. Is the authorized Lynx dealer in the USA . I had this setup on my 74' "WOW" what a torque monster! It will get sorted out... Call him for the choke & jet sizes to start. 

[Carlc939]

I have the lynx setup.
I had trouble getting it right.
I tried different jets, with basically no effect.
I found a weber expert, yes, the Ferrari dealer uses him to get carbed ones running well.
He found that my new mechanical advance distributor was curved wrong, he recurved it, made some very minor jet changes and it works ok, definitely all the carb I need.
I have a 292, tii 9.5 pistons and shorty Ireland header


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[abrokenframe]

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

Edited June 28, 2017 by abrokenframe

[Chris_B]

You don't need to add progression holes. You are already getting too much fuel in every range except for the "dreaded" lean spot. At what RPMs does the motor idle? Have you checked your fuel level?

[abrokenframe]

38 minutes ago, Chris_B said:

You don't need to add progression holes. You are already getting too much fuel in every range except for the "dreaded" lean spot. At what RPMs does the motor idle? Have you checked your fuel level?

 

I have tried setting idle at a few different speeds, but it seems the happiest at around 1,000RPM. Haven’t checked my float or fuel pressure yet, but it’s on the “to do” list.

 

 I know I’m running rich at idle, but thought around 12.5afr was acceptable for cruising speeds, no? It’s only in the 11’s when I’m going over 75mph.

 

One of the problems I’m having at all speeds is if I lift off of throttle, then open again, I get a stumble and it goes lean. The only way I have been able to combat this with my current jetting is by overcompensating with a rich idle. If I set the idle to around 13-14 AFR, the stumbling when opening the throttle gets a lot worse. In this scenario, wouldn’t putting a fourth progression hole directly above the butterflies allow me to run a leaner idle since it would be dumping more fuel in at partial throttle?

 

-Ryan

Edited June 28, 2017 by abrokenframe

[Chris_B]

12.5AFR is fat for everywhere except WOT. If you want reasonable fuel mileage, you should be aspiring to high 13s/low 14s above 2K RPMs at every steady speed (not under a load, like up an incline). above idle.

 

On the idle/flat spot issue, have you lined up  your throttle plates with the first progression hole yet?

 

 

[Chris_B]

You really need to check/set your fuel level before you try anything else. Should be ~25MM from the top deck of the carb. The current method is to use a piece of paper (like printer paper) torn into strips of the right length and width.

[1mike]

Was this the Mintgrun 75 out of Simi Valley?

[inquisitive]

3 hours ago, 1mike said:

Was this the Mintgrun 75 out of Simi Valley?

 

Yup. 

[abrokenframe]

8 hours ago, Chris_B said:

12.5AFR is fat for everywhere except WOT. If you want reasonable fuel mileage, you should be aspiring to high 13s/low 14s above 2K RPMs at every steady speed (not under a load, like up an incline). above idle.

 

On the idle/flat spot issue, have you lined up  your throttle plates with the first progression hole yet?

 

Thanks for the help. I am admittedly a novice when it comes to tuning, so this is helpful (only tuned my 912 Webers and old '02 Solex).

 

Lining up the the throttle plate with the first progression hole opens the throttle and lets way too much air by the plates, so the car idles at 2K+. Weber tuning guides say to have the throttle completely closed and above the first progression hole, so there's definitely a disconnect there.

 

From what I've read, this is the main reason for adding an additional progression hole directly above the throttle plate and probably the reason why Weber started manufacturing the 45 152G (adds a fourth hole). Currently, I think the stumble occurs between throttle initially opening and passing the first hole which is .5mm away from closed throttle. I could be way off, but it makes sense to me!

 

-Ryan

[Chris_B]

You are right about the lean stumble. That is why the throttle plate needs to be lined up with the first progression hole. Does your carb have air bypass screws?

[bitbckt]

Off topic, but close to my heart: stop putting Webers on your 912s!

 

Back to your regularly scheduled program.

[abrokenframe]

10 hours ago, Chris_B said:

You are right about the lean stumble. That is why the throttle plate needs to be lined up with the first progression hole. Does your carb have air bypass screws?

 

Yes, it has air bypass screws. 

 

10 hours ago, bitbckt said:

Off topic, but close to my heart: stop putting Webers on your 912s!

 

Back to your regularly scheduled program.

 

Don't look at me! The PO put them on about 35 years ago. I'd love to have a pair of p40ll's on there. Just haven't spent the time to find a decent pair of carbs, air filters, throttle linkage, and 912 fuel lines. It's the '02's fault! 

[bitbckt]

2 hours ago, abrokenframe said:

Don't look at me! The PO put them on about 35 years ago. I'd love to have a pair of p40ll's on there. Just haven't spent the time to find a decent pair of carbs, air filters, throttle linkage, and 912 fuel lines. It's the '02's fault! 

 

I'll let it slide... just this once.  I totally understand the "distraction" of the '02. I have the same problem!