Blue printed carbs "dyno tuned"

Hi Guys,

Being a noob to karting, can you guys explain to me what it means to blue print a carb.

I’m seeing prices of +200 for a blue printed, dyno tuned carb…
What does that mean exactly, and how can you dyno tune a carb if you buy it without the engine it was dyno tuned against?

1 Like

Blueprinting makes sense, in other words optimizing the carb while staying within the rules. I’ve never heard the term “dyno tuned” in relation to the carb.

So It’s definitely worth while getting a blue printed carb…

As for the “dyno tuned”… that was on a very well known site that I will not mention here.

1 Like

Sometimes we “dyno tune” carbs in the sense that we test different carbs with different engines, because sometimes a certain carb and engine might match up better for whatever reason. I know I’ve had some carbs that work well on engine #1 but are more problematic on engine #2 for no good reason.

But that’s not really “tuning” a carb, it’s more just picking the right carb for your engine.

Unless they mean they run through different carb settings on the dyno so they know where you should have it set at in different conditions?

I interpreted “dyno tuned” as figuring out what the ideal settings are for the carb, at least within the dyno room, so that you’d be within the ballpark when you get to the track.

Why not? You’re asking a fair question and they’ve already published that they offer the service.

I don’t want to say something that I don’t know too much about the subject matter.

Link:

It states that it’s dyno tuned!!

1 Like

They could just be saying they put every carb on an engine and run it on the dyno to make sure it flow properly, not necessarily that they are “tuning” them.

2 Likes

What I would assume here is they’re putting it on a control engine, on the dyno and tweaking the needles for optimal settings for that particular carb and then scribing the needles and body so that you know where the baseline settings should be for that carb in optimal air. You could argue that test is better done on your particular engine but lets ignore that variable for now.

Is it necessary? no, does it help as a quick reference, yes!

Many of the builders will do this on their fully blueprinted packages, some won’t because they feel like the carb tuning is a continual evolution and those baseline settings could change over time based upon developments they find in testing. I have 2 engines and one is scribed and the other is not. I feel like the scribes allow me a quick check of where things are at with a glance without needing to dig out tools to verify down to the minute / degree where the settings should be.

Does anyone think Comet or anyone claiming to “blueprint” a carb has somehow permanently modified the carb from stock? My understanding is the carb body can’t be enlarged but could fuel openings in the venturi be changed? Could something inside the carb be changed?

They typically would be setting lever arm height and pop off to their preferred and tested specs. I’m not sure of the rules for x30 but I don’t think you can bore most new carbs. If you can do something within the rule set they’re most likely doing it.

What you are buying from Comet is their knowledge. Like all major engine builders they have run these motors in hundreds of different configurations on the dyno looking for what they believe is the ideal setup. You’re buying the result of that work by getting a carb that is setup the same way they’d do on any blueprinted motor they sell. You also get the benefit of knowing they put it on the dyno to verify it’s working as intended and you’re not buying a dud.

So as soon as you service the carb yourself (full service kit) and you change the lever height slightly, you lose the “blue printed” advantage? If that’s the case, the 200 dollars extra is not worth it IMO.

1 Like

so you’re not measuring where the lever height and pop-off is when you take it apart and adjusting the new parts to be at the same spec? you’re just throwing new parts at it and hoping it works?

That’s not what I mean… Let’s say a builder sets the pop of to 10.3 psi…

When I do the rebuild, I adjust the lever and measure pop off to 9.9 psi.

Then pull the spring and stretch it a little bit until you get back to 10.3

It’s a little time consuming and tedious but it’s not hard to copy your builders work to keep it in spec with how it came from them.

I’d say in your case if you don’t want to make the most of your purchase, then save $200 and don’t always worry about having the top level equipment.

This is new and helpful information to me.
Thanks

Little more info here…

When I refresh a carb it’s almost always just pumper gasket (the kevlar / mesh one) and diaphragm, it’s quick, easy insurance that it’s going to run well and like $8 worth of parts. I call this a “minor” refresh.

While It’s apart I will inspect the fulcrum arm to make sure there’s no visible signs for wear and I’ll check the needle from time to time to make sure where it contacts the seat doesn’t look too worn.

It’s only about 1-2 times per year that I actually replace the needle, seat, fulcrum arm and or spring in the carb kit.

The fulcrum arm height is literally adjusted by bending the thing (gently), generally with a screw driver, to get the top of the arm to sit where you want it to in relation to the body of the carb.

The pop-off pressure is determined by the spring under the fulcrum arm. To adjust pop-off pressure you either compress the spring or stretch it out a little bit to get where you want it. Maybe in an extreme case you might need to cut a coil out of the spring.

If you measure all these variables when you get a carb that’s been “blueprinted” you should be able to duplicate that original work time after time when you rebuild it on your own from there and even then it’s only on what I’d call a “Major” rebuild vs. just the minor ones that I do most of the time.

1 Like