XJ650 carb tuning with the dreaded "pods"

They come in all different sizes, and I checked and they carry something like 30mm all the way up to 60mm

 

Do you know off hand what the size of the intake boots are? Pretty sure they're 50mm...

 

So this is the email I got back from them...decisions decisions....

Hi,
For your 4-cylinder engine, the key is the throttle body.
We don't have the suitable throttle body for 4-cylinder.
There are two methods to convert it,
1)You find the suitable throttle body for 4 cylinders on the aftermarket or eBay, we provide the rest.
2)We provide one big throttle body and 4x fuel injectors, you need to make the manifold, 1 inlet and 4 outlets, and install the fuel injectors on the manifold for each cylinder.
ECU controls fuel only, you use the stock ignition system.
The price is more than $1299.
What do you think?
Are there four carburetors? what's the size of each carburetor?
And please tell us the ignition type and max rpm on the engine.

Thanks

 

You'd really have to want EFI to throw down that much money! You might as well buy a bike with it already at that point, would be my thought. If you are doing it just for giggles though, and have the scratch just laying around, have a blast!

 

Hah I know right? I just thought it would be a cool idea. It would be a cool if they already had all this stuff pre made, but the fact that I'd have to make my own intake manifold, I dunno. I mean it would be fun and all, but for 1300$+, I dunno if it's worth the headache.

 

I think the project would only be viable if you were to cobble things together as SQLGuy did:

Although I understand carbs can be a hassle, the time/effort that it would take to do all this would be more than it would take to do a few carb cleanings, church and all, I think. Sounds like it could be fun if you had an extra bike just laying around that you wanted to fool around with.

 

This is a thing that I have long wondered.

Why do all the FI setups on bikes use separate throttle bodies, where cars use the manifold with one TB and multiple injectors? Seems like the single TB would be a lot easier.

 

I think it would definitely be a challenge but not impossible. I would just try and adapt a different intake manifold off of a different bike rather than using a car.

 

I like your thinking, I would probably go with a single throttle body as well. I should ask them to sponsor me lol.

 

$1200 will almost buy you a brand-new set of Khein carbs with intakes, jetted and ready to go.

 

There are performance advantages to using individual throttle bodies/ carbs. Have a look at any Ferrari engine. Not a single-carb/TB setup to be found.
There are cost advantages to using a single throttle body/ carb. Have a look at almost every Harley Davidson, and your car (assuming that it doesn't have a prancing horse on the hood).

 

What's so great about these carbs vs efi?

 

More time riding, less time spent with initial tuning. You can get cable operated ones as well. Then you can run pods without having a flat spot.

 

I live near mountains. So I thought that might be an issue with carbs...

 

Not really. It depends on the carb, how they are set up, and what the altitude difference is. It's a bigger issue for motorcycles with narrow powerbands (like 2-strokes).
CV carbs tend to do a better job of compensating for altitude changes than cable-operated slide carbs.

 

Interesting! So the lower air pressures slows the flow of air through the carb, preventing the mixture from getting too lean?

 

Sort of, except it keeps things from getting too rich. Lower air pressure (more importantly less oxygen per cc of air) effectively increases the amount of fuel in the mix.

CV carbs have their limits, just like any other carb, it's just that those limits are bit more broad (this is part of why there were (to my knowledge) no high-altitude jet kits provided for the XJ series.

The CV carbs fitted to aircraft have an altitude compensator that broadens the range of air pressures where it can deliver a good fuel/air mix.

 

On a side note guys, what type of ignition system do these bikes use? What is the max RPM, and how many pulses per revolution?

 

redlines at 9500k, ( which can be exceeded)
it is a wasted spark ignition plug fires every time the cylinder comes up
1000 rpm 1000 fires per cylinder


tci ignition Transistor control ignition

not cdi ignition

edit red line value for correctness

 

Redline is 9,500 RPM for all models, not just the 550.