Jetting woes of the turbo seca carbs

So, its been running pretty good but I'm having some jetting issues.

1st weird thing is that my needle clip height appears to control my air fuel ratio during cruise... as in, at 100-120kmh, using a sliver of throttle, my air fuel mixture is directly related to the needle jet height. I would have thought it would have been running on the pilot jet at this point and the needle jet shouldnt take effect until at least half throttle?

The other issue is that whenever I punch it, say at 3000 rpm, my air fuel ratio gauge goes so rich... to 10.0 AFR, which is basically the richest the gauge will read. The problem here is that when i punch it and it goes to 10.0 AFR, the turbo is not spooled yet and sometimes what happens is that it is so rich it will just sit at 3000-4000rpm and just chug and chug and not even rev up. It would be nice to lean it out here so i can rev up faster and elimiate the bog/chug.

I tried to lower the needle clip to fix this, but then my cruise AFR is much too lean (16.0-17 AFR), and the needle didnt even effect the AFR during spool up.

It seems as tho punching it causes the vaccum slides to open right up dumping too much fuel. Some would say decrease the main jet size, well the problem with that is i need to go to a bigger main jet as over 12psi, it starts leaning out.

So any advice? what are my options here, other than going to EFI and ditching the carbs. (which will probably happen this winter)...

Carbs float levels have been wet set. Pilot screws are turned in quite a bit i think only 2 turns or so... turning it in leans it out on the mikuni turbo carbs right?


THanks

 

interesting problem . no one have any ideas?

 

I just trust the Factory setup to do it's job, I don't know how many others have ventured as far as you have. It is interesting though.

Two turns in does sound too lean, maybe you've leaned the pilot circuit too far (and out of the equation). Then you wouldn't get idle where you should relative to the throttle position. If you fix this by adjusting the idle screw to bring the idle back up, you'll enrichen the mixture, but not by involving the pilot circuit.

 

sounds like its overfueling to reduce det, common on car turbos. Also make sure that you have enough air going to the turbo, might be worth checking the boost pressure too.

 

At only 2.0 Turns Out, ... I don't think you are Rich enough to prevent a Starvation Hesitation issue.

You need the Bike to IDLE with the Throttles closed.
I'd start with Bench Syncing the Throttles using 3X5 Card Strips.
Colortune the IDLE >> Blue.

Tweak PAST the Blue to add Supplemental Richness.
You add Richness to Fuel the Transition from IDLE to OFF IDLE.

The Turbo Bike needs this Low-end to be right so that the Plant makes power to get-moving and generate Exhaust Pressure to spin the Turbine.

 

rick. wideband is showing 10.0 AFR.... and actually richer than that as 10.0 is the rich limit... thats SUPER DUPER rich.
I dont know whats making it dump in so much fuel...

The wideband doesnt lie. It is rich.

 

What rick and I are saying is that your Idle Mixture adjustment is off. You leaned out the pilot circuit too much. The pilot circuit alone meters fuels for idle when properly tuned, because the other fuel circuits are closed off by the throttle butterfly.

After leaning the pilot circuit out too much, you likely adjusted your idle screw to get the engine to idle correct? You might still get a good idle, but your butterflies are open past their idle position, which is most of that "Supplemental Richness" comes from for off idle performance. It's actually another set of holes just behind the throttle butterfly when idling.

So now you aren't going to get anything close to the proper off-idle performance, because you've leaned the pilot circuit too far out. You're trying to compensate for that off idle performance with the later fuel circuits, but as expected, it isn't working, but it's affecting the later circuits.

Think of the circuits in order idle (pilot)--->off idle-->mid range (needle)->top end (main jet). By leaning out the pilot, you've ended up shifting the whole curve to the left, and carbs just don't like to work like that.

If you follow Rick's advice and re-bench sync your carbs, you'll likely find that it won't idle because the pilot circuit is too lean. You should enrich the pilot circuit until get it to idle and get a good AFR. Then tweak the idle screw, sync, and fine tune from there.

Oh, and you'll start to lean out over 12psi if your fuel pump is original. The carbs require 2psi differential between fuel and boost pressure, and the pump is rated at 14psi. You'll need a higher pressure pump if you want to increase boost pressure past 12psi, and that's likely why it's the limit for the yamaha power up kit.

 

While you sort-out Carb-related issues, pay attention to your Plugs.
Running Lean can lead to serious problems for Pistons, Valves, Head Gasket and Turbine
Assure that BOTH Air-Jet Passages are clean.

Air-Jets on Mic's are in the Intake Horn.

While engaged in the process of Fine-tuning the Turbo Plant you have to become a "Tweaker".
You need to put-on your precision hat.
When you arrive at Tuning the Pilot Mixture Screws remember that the Pilot Screw is primarily an Air Valve. The AIR you control siphons Fuel supplied by the Pilot Fuel Jet.

I Bottom Tapped all 4 Air Screw Tunnels.
Wrapped all 4 Screw Barrels with Teflon
Coated the Holes with Anti-Seize.
After Adjusting was done, I plugged the Air Screw Holes with Brand New Erasers from Number-2 Pencils.

You're "Tweaking" ... when the Adjustments you are making are miniscule.
Barely moving the Pilot Screws within the width of a Nickel.

Make yourself a Tweaking Screwdriver.
Cut a Pocket-clip type Screwdriver to let you make adjustments without removing the Fuel Tank.
Cut the Plastic Handle off half-way or less.
Shorten the Shank. Grind, Dremel or File a new tip that fits the Slot of a Air Screw perfectly.
Notch the Handle. Burn a narrow notch, parallel to the tip, on the handle with a red-hot Bobby-pin.
Fill the burn-notch with White Nail Polish.

And, ... make sure you are prepped for Fine-tuning with good compression and Valves within Spec.