Simmy's Naked Turbo Project

Except a sleeper delivers more than advertised, LOL.
This advertises more cc's than actual, seriously no one is ever going to see it anyway.

I'm planning to set up a wide-band O2 sensor and controller so I'm currently trying to buy specific #1&2 Turbo head pipes on eBay.
I'll weld the bungs in place to mount the sensor so I can determine what my fuel air ratio is at any given RPM.
Yamaha provide test ports right at the bottom of the pipes but the sensor mfr specifically warns not to mount them there.
Any condensation or raw fuel on the sensor will screw the readings.
I don't expect this to be pretty, that's why I'm looking for sacrificial pipes just for testing purposes.

The Turbo has 127.5 main jets on 1&4 and 132.5 on 2&3 so that's why I'm testing both pairs.
Planning to get baseline data as a 650 turbo before installing the big bore kit.
There is debate whether this will make the carbs/engine run richer or leaner, my bike shop guy insists it will be richer.
The XJ750 has richer jetting than the XJ650 which defies his experience.
I have not found anything on the net to reference turbocharged blow-through carbs and installing a big bore.
I'm not aware of any other factory turbo with blow-through carbs, maybe there were WW2 fighter planes I don't know.
I'm learning lots.

 

Lotus Esprit turbo (Dellorto carbs), MG Metro turbo, MG Montego turbo (single SU), Renalt 5 turbo , Renault 18 (Solex). Loads more...
With your original carbs, bigger engine shifts more air - thing to watch out for is the slides don't hit stops too soon, this would be disastrous, but its so difficult to measure (I've spent hours trying to do it). Denser air creates more lift, so in theory as boost rises the slides will rise, reducing the (relative) vacuum at the jet, weakening the mix.
In truth I've no idea....

 

Wow thanks @Minimutly you guys on the other side of the pond saw a lot of cars we didn't.

can you explain more on this?
What I thought was a can of worms is starting to become an oil drum full of snakes.

 

If the spring is too weedy, the slide tops out and further engine demand is only pulling the fuel the needle and jet can provide with the available area of the annular around the needle as it sits in the jet, no more. This means that more air can't get the right amount of fuel and a weak mixture results.
Weak mixture, high speed, holey pistons.
In my messing around with the SU on the GS, I've had this at the back of my mind for years and it's something I try to avoid, in my farting around.
I've had an AFR gauge on the collector for a few years, and can't be certain of its veracity - it might be what you refer to above, the positioning isn't optimal, so I tend to err on the side of caution.
What I found in the past with another engine, that just before the piston holed the engine was going like a fecking rocket.

 

Whats the general consensus on shimming the needles up to get into the enrichment earlier? I'm not turbocharged (XJ750) but running into a lean out condition running #122 mains and #42 pilots. The issue is above 3/4 throttle it goes flat, drop it back and it pulls again. Floats are at spec and I balanced the carbs along with checking the valves which are on the tighter side of book spec.
Sorry to jump in like this but I saw the carburetor talk and wanted to ask.
Thanks Guys

 

With the slide topped out there shouldn't be further engine demand?
Unless the turbocharger continues ramming increasingly more air in?
My maximum boost 9psi is already achieved early, wastegate cracks probably 8,000 rpm and holds 9 psi to redline.
The fuel regulator will always hold fuel pressure 2.8 psi higher than boost.

What brand do you have? Is it just a gauge? I'm not sure what I really need yet.
The Innovate Motorsports LC-2 was recommended to me.
https://www.innovatemotorsports.com/wp/content/uploads/2022/05/LC-2_Manual.pdf
they sell add-ons you can data log AFR compared to RPM, gets expensive though

how do you know it is lean?

As @Dave in Ireland related, going slightly lean should not behave as you described.
When you say "drop it back it pulls again" are you talking about dropping the needles back or dropping the throttle back?

 

Sounds and feels lean over 3/4 throttle and on the edge of breakup until I drop the throttle back then it picks up and the exhaust is more even toned.

 

Well, yes, the engine will carry on running on a lean mix, to the point where it stops entirely.
My AFR is from Canada...one of these (since superceded) plus gauge.
https://www.14point7.com/products/spartan-lambda-controller-2

 

The slide is lifted by the vacuum under the bottom of the flat bit being fed to the top of it - yes I know, with the turbo there is no vacuum, but everything is relative, and the pressure diff across the diaphragm is this vacuum from the underneath compared to the turbo boost pressure seen at the inlet. The whole thing gives the needle a constant vacuum - CV, what you lot call constant velocity.
But, denser air gives more lift, so does this lift the slide higher? I don't know. If the slide goes all the way up the constant vacuum at the needle is lost, once this happens I suspect the mix will go rich, since the vacuum will increase at the jet, but all control is lost.

 

My AFR sensor and gauge showed up.
There is a blemish you can see on the gauge, I'm hoping this is just oil or something between the lens.
I bought extra bungs and plugs so I can move it between cylinders 1 and 2.
I have extra header pipes for #1&2 and need to install the bungs.
I plan to make another bracket to screw into the LH mirror mount to hold the boost and AFR gauges.
Maybe I'll look into a Go-Pro to film the tach and these 2 gauges in the same screen.
I want all this information while it's still a 650 Turbo.

 

I added some green to the forest.
I’ve been enjoying the bike as is, haven’t installed the O2 sensor yet.
The headlight quit working, the OEM fuse box finally gave out, when I tried bending the tab to clamp the fuse tighter it broke, so new fuse box next.

 

Damn that is one sharp lookin' machine! Love that color scheme.

 

Today I fixed the broken fuse box.
Below is how I restored the old Yamaha one.
I salvaged an old box from a Seca Turbo wiring harness I had hanging in my shed


I found these 4 way fuse blocks at an electronics discount store several years ago.


I cut the bottom out of the OEM fuse box and made a loose fit with the new block



make sure there is a gap all the way around for the epoxy to fill
screw it onto a board with wax paper in between



apply epoxy along the 4 seams and push the new block in place.
Smear some epoxy on the salvaged sticker identifying the 4 circuits and stick it back in place


when it dries, it will pull right off the wax paper and leaves a nice smooth surface on the bottom


Sydney says good job



re-soldered all the connections,
I like using old-school glass fuses but now I can use SAE standard size instead of the weird Japanese standard Yamaha used


keeping the standard appearance was important to me. There is nothing elsewhere on this entire wiring harness which does not look factory Yamaha

 

On the fuse box, since doing 2 fuse boxes like this I’ve since learned Chacal sells the OEM fuse clips that crimp onto the wires.
This is the best way to go, a crimp is more secure on a vibrating machine and it returns things to 100% original.
If I do another fuse box that’s what I will do

 

THATS A NICE UPGRADE. I prefer original, too.
Perfect

 

Question for you (and maybe @chacal) on head gaskets. The 750 I have has a head gasket that looks like it's from a 650 - it overhangs the 750 boore. The 750 pistons have a relief around the top that looks like its designed to avoid this overhanging gasket, so did Yamaha take a bit of a bodge and not change the gasket? Or has someone fitted a 650 gasket to my 750 engine? I suspect I know the answer but would like confirmation please? Can someone measure the 900 gasket for me please also?
I have a bunch of 650, turbo, 750 and even an 850 engine, so am in the mood for some modifying for better performance....

 

Gasket 68.5mm

 

XJ650 all:: 64.10mm ID for both the Turbo and normally-aspirated engines, but the design (and thus the gaskets) differ between NA non-yics, NA yics, and turbo models.

XJ700 air-cooled: 66.20mm ID
XJ750 air-cooled: 66.20mm ID
NOTE: XJ700-air and XJ750-air gaskets will interchange, but the 700's use a slightly thinner gasket

XJ900 RK/RL (853cc): 67.70mm ID
XJ900 F/N/FN (891cc): 68.25mm ID

 

My 750 gasket (used), measures 63.75mm, which looks awfully like a 650 gasket - (once crushed the "hole" diameter shrinks I guess. So someone fitted a 650 gasket to the 750...
At least the correct 750 gasket does not overhang the bore.
Much thanks.

 

You know what they say about "previous owners"...................