XJ650 carb tuning with the dreaded "pods"

They're asking me "what's the piston phase of twin cylinders?" What the hell is that supposed to mean? Firing order?

 

I'm pretty sure that piston phase is the location relative to another on the crank shaft.. So it would either be both pistons move together, or move opposite of each other. I could be dead wrong, but that's how I've always understood it.

 

1 and 4 move together, 2 and 3 move 180º out of phase with 1 and 4. When 1 is at TDC on the compression stroke, 4 is at TCD on the exhaust stroke.

 

Sooo...question fellas, the guys at ecotrons have a throttle body up to 65mm. Currently I'm looking at the 50mm TB. If I'm going to be running 2 inch intake piping for each cylinder, would there be any benefit if I go larger than 50mm(2in) up to 65mm(2.5in) in terms of being able to suck more air in? Or is it just going to be a waste of money and space?

 

anybody?

 

You really don't want to go too much bigger than stock or you'll never get the fueling right (While a larger throttle body can increase intake volume, it is limited by the size of the intake port, and going too big will reduce intake velocity to a point where fuel will puddle). I bet if you give them the intake port diameter and cylinder volume (per cylinder) they can suggest which throttle body would be a good match.

 

Yeah, thats what I was afraid of. How big is too big? Do you happen to know off hand what the cylinder volume is?

 

On a side note, I'm thinking about the intake manifold...and I'll have to make one from scratch. I was thinking of a couple options, and since you're smart guy I value your opinion. The first option would be to use the existing tubing that connect from the head to carbs, and attach them to intake tubes, and so on. That would be the easiest option in my opinion. However....the main thing I'm worried about is the injectors not being pointed in the correct direction, and spraying on the intake hose, instead of directly into the cylinder. It'll be a real pain in the butt to get those bungs welded on at the correct angle and see how much sag the intake hose has. I realize I will have to make some kind of support bracket for the intake manifold so that it doesn't pinch the intake tubes.

My second option is a lot more labour intensive, and I'm not even sure if it's physically possible, but it's an idea. I was thinking of bringing the head back to the machinist I deal with, and have him drill two holes into the head above and below each intake hole so that I can just bolt on the intake manifold, vs it just being hung and held up with a bracket. All I would need to drill is 1/4" into the head, and tap it with a fine threaded tap. I know this is far fetched, but do you think theres enough "meat" to drill into it? Next thing I'm worried about is the head cracking at those holes. Do you think its a possibility?

Maybe I should start an EFI thread lol.

 

There are already holes in the head for bolting on intake manifolds. That's what the rubber boots are. They are held on with machine screws. Be careful removing them (looong soak with penetrating oil) as they tend to want to snap off.

Yes, do start a an EFI thread.

You might also want to have a look at the old threads about the subject.
https://www.google.com/search?clien...-8&oe=UTF-8#q=fuel+injection+site:xjbikes.com

 

Sweet! I'll attempt to take em out, but I may just drill them out larger. Looks like this EFI project is getting closer to becoming a reality....So what do you think I should do? Bolt on the intake manifold?

 

size of bike divided by 4
thats if its a true size unlike the 550 which is a 528cc

xj 650 =653 cc

 

Yes, bolt on the intake manifolds, whichever ones that you use (even the stock ones).

 

Well I haven't heard back from them yet about how they can time the system properly. K that's it, starting an EFI thread!