I got the engine started! No boost and it will not stay running. I have taken the pull starter off and I'm using a drill with a 1/2" drive socket chucked in it. This feels good, finally! It's been 2 years of off and on work, TONS of money on fittings and mistakes, and untold amounts of time.
By turning the air screw I can get the engine to stay running until it gets hot than it will not start again. 1200Rpm with no throttle up to about 3000 (no load or boost) with full throttle.
The current set up is: a 12.5 pilot and a 130 main with the needle set all the way to the top (it's richest setting) and my AFR is reading 19.something.... parts of air at it's richest. Compression is good, spark is good. Plug is dry, and the engine gets hot fast!
I have ordered:
134-2XXX Jet, Mikuni, Main, Round Slide (Small Body) [Mikuni Jet Size:140] 1 $4.00 $4.00 134-2XXX Jet, Mikuni, Main, Round Slide (Small Body) [Mikuni Jet Size:145] 1 $4.00 $4.00 134-2XXX Jet, Mikuni, Main, Round Slide (Small Body) [Mikuni Jet Size:200] 1 $4.00 $4.00 134-2XXX Jet, Mikuni, Main, Round Slide (Small Body) [Mikuni Jet Size:135] 1 $4.00 $4.00 134-00XX Jet, Pilot, Round Slide Mikuni [Mikuni Jet Size:15] 1 $4.20 $4.20 134-00XX Jet, Pilot, Round Slide Mikuni [Mikuni Jet Size:17.5] 1 $4.20 $4.20 134-00XX Jet, Pilot, Round Slide Mikuni [Mikuni Jet Size:20] 2 $4.20 $8.40
Had to bend actuator on float because it would not fill bowl.
Had to bend float a little back because it was pissing fuel out of the overflows when I turned the fuel pump on.
Changed jets to a 135 main and a 17.5 primary started but too rich if you gave it any throttle.
Tried a bunch of positions on the needle, to no avail.
Went to a 15 primary, still rich on throttle.
Going back to the original 130 main.
Went to 130 main (with 15 primary) too, lean with any throttle.
As a side note, every time I change a jet I seem to need to adjust the float.
I'm going to play with the needle position, then change approach.
Breakthrough! I fixed my "float problem", too much fuel pressure. I have now set it to around 1-2psi over atmosphere. The pressure was simply pushing the float valve down and forcing more fuel in.
Next is Needle positions, back to 12.5 primary with a 135 main.
The 135 and 12.5 runs a little but then leans out and dies with any throttle. The needle is adjusted all the way up (most possible fuel). I also have cleaned the residual bowl seal glue out, as the gasket, that looks to be in good shape, has started to leak.
Went to 145 main, bent on the float to get it back to original geometry. Now i get no fuel in the bowl. Even when I max the fuel pressure (trying to push the float). I get nothing.
With the help of Sandy Andrews an aircraft mechanic and Buell enthusiast, we found that Adjusting the needle makes a big difference. We found that the 15 Pilot, and 130 Main with the needle at it's richest gets it running it's best on the low end.
I did have to play with the float and fuel pressure (about 1 psi) again to get it flowing. It runs rich on the low speed (low throttle) it seems like when the engine switches to boost, it goes lean. Engine still dies at around 3200 RPM no load.
The problem is, I really don't know if it goes too rich or too lean when the engine dies, the 3200 RPM limit is probably telling me that it needs more fuel, but the AFR gage will always show max air (22.5) when the engine stops running. This is because, rich or lean, if the engine stops firing, the O2 content will be at it's greatest. So I can tune at low speed, but it's not really telling me much when the engine dies at half to full throttle.
I think my next set up will reflect that on boost is going too rich however.
Next Setup: 17.5 Pilot 130 Main (or smaller if I can find one) with the needle set to the leanest (lowest) setting.
Starts Without choke with the 17.5 Pilot, 130 main, lowest needle setting and runs around 10:1 AFR! (Carb is leaking around the gasket) Goes lean when I give it any throttle.
Tried the needle in the middle position and turned the air-screw a half turn out. This let me give it a little more throttle before it leaned out.
Tried the needle set to it's highest position. Engine seemed to do worse! I don't understand that one.
Tried a 140 Main with needle set back to it's lowest, mid, and highest setting. I could not even get it to start unless I covered the intake with my hand. Seems like I would have gotten more fuel not less.
Next Im going to try a 135 main, and all needle positions and if that doesn't tell me anything, I'm going to try a really big pilot with the air-screw all the way out, the needle all the way down and a small main. Feeeewwww, this is not super fun.
The 135 main would not start, I pulled the plug and it was uber-wet. Gonna try the 135 with the air-screw way out and the needle as lean as I can get it.
Great, batteries died, relay fails to ignition ground. Time to recharge.
Tried and engine wouldn't start, plug is now dry though, tried one full turn of the air-screw in.
Looks like no fuel was getting to the bowl. I turned the drain acrew (flowing into the turbo pressure sign) and did not get fuel until I boosted fuel pressure. Starting tune over now.. Hey it starts, running rich.. Needle is fully lean. Choke is off.
O.K. I went back to a 130 Main with a 15 Pilot, with the needle in its richest setting. It starts! It Idles (high)! 12:1 AFR!
Goes way rich beyond 2400RPM and dies. I only know this by pulling the plug and seeing that it's wet, the wide-band will always read 22.5 (it's max) when the engine dies because it is pumping unburned air a few cycles before it stops. That's partly why it's been so hard to tune (and I don't know what I'm doing doesn't help).
So here's the deal, The farther down the needle is, the more you rely on the pilot jet. As the needle is brought away from the pilot, the less "sign" it has to operate (even though the needle will allow more fuel to flow from it). When the engine switches over from vacuum to boost, the jets (Pilot and Main) that would meter fuel in a normally aspirated engine, become way too big, I suppose because the air becomes more dense. I am now going to scour the internet for a WAY smaller Main jet.
SUCCESS!!! At least a little bit. Density is the key. When the engine goes into boost, BAM way too rich. I put a 115 Main and kept the larger pilot. The larger Pilot-Jet keeps the engine going providing enough fuel with the added vacuum out of boost (by that I mean, when the turbo is not producing boost, it is a much greater vacuum going through the carb than if the carburetor was normally aspirated.), the super small Main-jet (which is still too rich) gives me LESS fuel when the density increases under boost. The Turbo-Kart now gets around 5 pounds of boost, under no real load, at about 4000 rpm. I'm getting close!
SUCCESS-ER!!! Here's a video, I know I'm not a camera-man..
It is still WAY rich at the top end, but I stays running now with full throttle! This means I'm getting really close. The next Main will be a 90. (I say in the video that it is "dying rich" But it is in fact not dying, but reaching a "wall")
Tried the 90 Main, and I cannot get the engine to start. I presume too lean. Going to try to keep the 90 Main and go to a fatter 17.5 pilot
I went back to the previous setting. What I need is a Main larger than 90 and smaller than 115. I'm not going to put ANY more cash into this. Maybe some day, but I just broke the brake master cylinder and sprung a turbo oil leak from the pump. Not a big deal, but it all adds up. I set out to make boost and I have. I had visions though of going way too fast in a clone-powered kart. This is just not feasible at this time. I would call the mission a small success, as I DID learn how much is required to slap a turbo on something from scratch! I would have liked to have taken a video of driving it while it was being tuned, but I won't loose any sleep over it, Maybe next time!
Turbo Predator Table of Contents
Click to go to BrainLubeOnline.com