Building A L28 (Na)

[TheCrazySwede]

14 hours ago, Chickenman said:

34 Chokes are pretty big on a 40 DCOE. On the street 32's should make it crisper and get rid of the idle to low speed stumble. If you can't get the drive-ability you want on the 34's, consider going down a bit in Choke size.

34's are OK on 45 DCOE's for the street ( On a STRONG engine )  , but reduce the booster signal too much on 40 DCOE IMHO. There is a ratio of throttle bore size to venturi size that has to be maintained. 34 Chokes on a 45 DCOE will create a stronger booster signal than 34's on a 40 DCOE because of the larger variance in size between throttle bore and venturi size on the 45's

This of course all depends on usage and engine specs. But on the street it's always best to be a bit conservative on choke size rather than a bit too big.

 

Thanks for the advice Chickenman!

I went for 34's due to the specs of the engine and because I'm trying out 145 mains. After playing around with the idle and the timing, the car runs much smoother, but bogs when anything over 30-40% throttle is applied. The float height is the only thing I haven't checked because I haven't had the time. I've removed the emulsion tubes and I noticed that the fuel line is a bit above where most people recommend, so I figured the floats need to be adjusted.

Once I've got the floats settled and the carbs tuned steady again, I'll see how the 34's run. I live about 30min away from a Weber Carb shop, so I can always go down and pickup different sized chokes if needed.

Thanks again for the input everyone! Tuning these carbs have proven to be far more fun than I originally presumed - or maybe it's because I haven't pulled all the hair out of my skull yet  

[Chickenman]

Once you get Weber's dialed in properly, they should drive like a Fuel injected car. The good point about Weber's is that everything is adjustable. The bad point about Weber's is that everything is adjustable.....

Big chokes will make Power at the Top end.. but at expense of drive-ability and low end Torque on the street. Unfortunately, a lot of Weber choke size information pertains to Racing engines, which seldom run below 5,000 to 5,500 RPM's. On the street ( and Autocross and Hillclimbs) I'll take 10 ft/lbs Torque with a nice fat and  flat Torque curve over 10 HP at Peak RPM any day. Actually, on most Road Courses, I'd take that trade-off as well..

 

 

Edited February 20, 2016 by Chickenman
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[Travel'n Man]

I have added a Colortune gizmo to my dial in process - that way you can see each independent spark-plug firing color...........FWIW.

 

[madkaw]

Your dealing with one of the hardest aspects of dialing triples-transition! 

Buckle down for some endurance tuning, and then the weather changes. I fought and still fight the battles with my Mikunis. My recipe is a large pilot jet that might be a bit rich at idle- it's a compromise. But these carbs were made more for hard driving than anything else. 

These engines like the fuel! 

[TheCrazySwede]

Just now, madkaw said:

Buckle down for some endurance tuning

We might be a rare breed, but this is a challenge I accept with open arms. Tuning the Webers has been the most fun part of this entire engine build so far. 

There's a short video written by previous BBC Top Gear host, Jeremy Clarkson, about being petrolheads (gearheads) and how we are a dying breed. It was made as a PR video for a racing sim, but it's amazing and it still gives me chills. Explains perfectly why we all go through hell to get our beautiful machines to run.

Here it is, if anyone is interested:

 

[madkaw]

Is the transition issue during moderate acceleration or hard ?

[TheCrazySwede]

2 hours ago, madkaw said:

Is the transition issue during moderate acceleration or hard ?

I actually got past the transition issue by messing around with the timing and idle mixture. But I do have an issue where the carbs don't like anything above 40% throttle.

If I'm smooth with it, it'll rev nice, but if I cave my foot into it a little, it starts to sputter.

[madkaw]

being smooth probably gets you past the pilot circuits , so maybe you do have a transition issue . Depends on your definition of smooth. Loading has an effect also. Climbing a small grade will show up a transition issue easier. 

Accel pumps on these carbs?

[TheCrazySwede]

On 2/21/2016 at 2:12 PM, madkaw said:

being smooth probably gets you past the pilot circuits , so maybe you do have a transition issue . Depends on your definition of smooth. Loading has an effect also. Climbing a small grade will show up a transition issue easier. 

Accel pumps on these carbs?

Spent some more Juan-On-Juan time with the Carbs, with the help of a local carb shop. Turns out 5/6 of the Accelerator pumps were in bad condition. Yikes!

I had measured the float height and adjusted them accordingly. Car actually runs much, much nicer now, but doesn't like anything past smooth throttle. Now I know why.

These carbs aren't mine. I'm just the temporary custodian of them. A friend of mine owns them, hence their wonderful condition. I wanted to buy my own carbs, but I'm really interested in the OER/SK Japanese ones. My engine's builder, Eiji Hosomi, spent a good 15-20min with me over the phone explaining some of the reasons why he absolutely dislikes Weber Carbs - and he made some great points. 

The Japanese carbs don't seem to work much differently, and when they do it's for the better. No emulsion tubes to deal with, the mixture of the accelerator is adjustable externally and so are the floats. Sounds a lot more practical to me...

Anyone have any experience with these? I'm seriously considering picking up a set to keep the engine "Japanese" entirely. 

[TheCrazySwede]

On an unrelated note, here's the new Abarth Exhaust! Had the inlet modified to pack some more beef.

[rossiz]

On 2/21/2016 at 5:31 AM, Travel'n Man said:

I have added a Colortune gizmo to my dial in process

what model colortune works for the L6 - i see a host of different sizes/models...

how well does it work? 

[grannyknot]

44 minutes ago, TheCrazySwede said:

Spent some more Juan-On-Juan time with the Carbs, with the help of a local carb shop. Turns out 5/6 of the Accelerator pumps were in bad condition. Yikes!

I had measured the float height and adjusted them accordingly. Car actually runs much, much nicer now, but doesn't like anything past smooth throttle. Now I know why.

These carbs aren't mine. I'm just the temporary custodian of them. A friend of mine owns them, hence their wonderful condition. I wanted to buy my own carbs, but I'm really interested in the OER/SK Japanese ones. My engine's builder, Eiji Hosomi, spent a good 15-20min with me over the phone explaining some of the reasons why he absolutely dislikes Weber Carbs - and he made some great points. 

The Japanese carbs don't seem to work much differently, and when they do it's for the better. No emulsion tubes to deal with, the mixture of the accelerator is adjustable externally and so are the floats. Sounds a lot more practical to me...

Anyone have any experience with these? I'm seriously considering picking up a set to keep the engine "Japanese" entirely. 

I had a set of SK/OER 40's for a few years, I really liked them. The externally adjustable float level and accelerator pump are a nice feature while you are setting them up and for tweaking. Much better then pulling everything off and removing the top cover like Webers, but they most certainly do have emulsion tubes, in fact they accept Weber e tubes and jets. Maybe you just mis heard what he said. They are a good set up and if you are starting fresh then SK's or Mikunis would be the way to go.

Chris