Jets for Pods and header

[Steven LaPlume]

I have a carb rebuild kit coming from Mikes XS. My carbs work fine now. However I am changing to Pods. The pipe I have is actually from an XS-650 but it seems to work fin on the XS-400. The muffler is I guess what's called a tapper tip style.

I had read that the jets are different sizes for each carb because of how the air box is configured?????

So with pods and this exhaust I have no clue what size. This is going to be a cafe racer when I get done. And yes I am building it in my living room over the winter. Because I am single and can do that Thanks for any help you can give me.

I am an ex Superbike racer so I have no issue removing carbs and replacing jets and adjusting needles But a starting point will be quite helpful.

This is the first XS I have worked on. I had an XS 650 but before I did anything with it my buddy bought it off me so I kept the bulk of the parts for the 650 until I can figure out what I can use or graft on to the 400.

 

[amc49]

Are you SURE that header pipe fits tight all the way around at the head? The fitup there looks loose but the head stud and pipe coming out look out of parallel and I for one find 650 fitting 400 somewhat odd. And looks like 2 into 2 which is NOT a header.

But I've been wrong before.

 

[Steven LaPlume]

Are you SURE that header pipe fits tight all the way around at the head? The fitup there looks loose but the head stud and pipe coming out look out of parallel and I for one find 650 fitting 400 somewhat odd. And looks like 2 into 2 which is NOT a header.

But I've been wrong before.

It's just sitting there loose with no gaskets in just to show what the pipe was. I have to do some welding so did not want to fit it on permanent.
I don't know what its called technically, nor do I care. That's why I provided the pic so you can see what I have and offer a suggestion to my question.
So do you have a solution/answer or do you just want to bust my balls for your own edification?

 

[spectra]

Remember you are also working with a DOHC bike...........they are a different animal.........

I upped my mains I think one size on my SOHC when running UNIS I would not run Pods if I was you......I am doing a DOHC bike now and had the carbs rebuilt and he swapped out the jets but not sure whats in there........been a few years and the project was put of the shelf........just picking it back up now....

Start a build thread on your bike. Interested to see what way you go with it.........

Good luck!

 

[amc49]

The solution is the pipe may not work. Need to go there to verify it before any ideas of jetting.

Before you start in you should know I have built hundreds of engines both car and bike 2 and 4 stroke, I have jetted just as many. Lots of racing stuff up to 700 inch+ 1500+ hp. pro stock big block Chevrolet running 7's at over 200 mph.

 

[Steven LaPlume]

The solution is the pipe may not work. Need to go there to verify it before any ideas of jetting.

Before you start in you should know I have built hundreds of engines both car and bike 2 and 4 stroke, I have jetted just as many. Lots of racing stuff up to 700 inch+ 1500+ hp. pro stock big block Chevrolet running 7's at over 200 mph.

OK but if the pipe is the exact same diameter as the stock one I do not see the issue. It literally bolts right up once I get the gasket in there and tighten everything down. The only issue I see is the header part (Which is what Mikes XS was calling it) is needing to be cut back a few inches as the can/muffler part sticks out the back a bit more than I would like.

I realize everything works together and has an effect on each other. I'm honestly not going to do things like jetting until the spring. once I put on pods and with the new exhaust I figure I'm looking at a few full days and a lot of logging things in and testing before I get the jetting where it needs to be. I might not even get where I need to be with these carbs. Maybe I will need to put on some other ones but I would rather try with these and invest in a lot of jets than buy 400 bucks worth of high performance carbs, which I can't afford at this time.

Yes I have built quite a few Superbikes but this old bikes a bit new to me. I would think the same principles apply to some extent. I guess I'll see. If all else fails I will get a good after market exhaust made specifically for the XS400 and try again.

 

[Steven LaPlume]

Remember you are also working with a DOHC bike...........they are a different animal.........

I upped my mains I think one size on my SOHC when running UNIS I would not run Pods if I was you......I am doing a DOHC bike now and had the carbs rebuilt and he swapped out the jets but not sure whats in there........been a few years and the project was put of the shelf........just picking it back up now....

Start a build thread on your bike. Interested to see what way you go with it.........

Good luck!

Unis really? Why them as apposed to the traditional air pod type filters? Does it have an air flow difference that makes it run better? I just like the look of the pods is why I was going with them but I can change it up. Not afraid to chose function over form.

 

[amc49]

I use foam as well, the K&N type will work but they pass more dirt. Hold a run in one up to sunlight and see all the pinholes where dirt can pass through without even touching the filter media at all, Uni types foam do not do that, the route is more circuituous and the twists and turns pass less dirt.

The front tube IS called a header but differentiate that from true header, which is a pipeSET with a number of pipes matching the cylinder count that all dump into a common collector to mass scavenge individual cylinders.

Jetting? Go a couple sizes and leave needle alone and call it a day, nothing sophisticated about a non-tuned setup like that one will be. CVs tend to not like pods as it lowers resistance enough to lower the slide action, it depends on a somewhat rarified environment to lift slides faster and the other carbs if all are under a slight vacuum tend to aid each other to work slide faster too. The problem being one of if slide opens a bit slower it's rich while making the actual move but may be not rich once moved and how does one tell the difference when it comes to jetting?; it drives people batty.

 

[Steven LaPlume]

I use foam as well, the K&N type will work but they pass more dirt. Hold a run in one up to sunlight and see all the pinholes where dirt can pass through without even touching the filter media at all, Uni types foam do not do that, the route is more circuituous and the twists and turns pass less dirt.

The front tube IS called a header but differentiate that from true header, which is a pipeSET with a number of pipes matching the cylinder count that all dump into a common collector to mass scavenge individual cylinders.

Jetting? Go a couple sizes and leave needle alone and call it a day, nothing sophisticated about a non-tuned setup like that one will be. CVs tend to not like pods as it lowers resistance enough to lower the slide action, it depends on a somewhat rarified environment to lift slides faster and the other carbs if all are under a slight vacuum tend to aid each other to work slide faster too. The problem being one of if slide opens a bit slower it's rich while making the actual move but may be not rich once moved and how does one tell the difference when it comes to jetting?; it drives people batty.

Appreciate the insight.

 

[Bear Hands]

I put pod filters onto a GPZ500 (EX500 in the US?) a long time ago and it ran like crap (GPZ also used CV carbs). My local bike spares place told me to go 10% bigger on the mains, which I did (145 in place of 130 I believe) and it ran adequately well for my purposes. I plan to follow the same logic with my XS when I get to the carbs.
This is by no means a recipe for you, but it might be a good starting place to ensure you dont start off super lean.

 

[amc49]

You use the 10% number on direct lift carbs not CV, and the two kinds of CV are even different. The kind closer to direct lift is the rubber diaphragm type. The no rubber labyrinth type like Honda sometimes uses are not as slide active as the rubber ones are. Jetting those you use less than 10%. The other engine mods will affect that. Especially a really good tuned header.

CVs by virtue of what they are somewhat self jet by adjusting for the difference in airflow unlike direct which doesn't. Pretty hard to actually run them real lean and they like it to begin with, the slide will open faster when they are slightly lean and always an issue with CVs. When you go richer than lean best power the slide action drops off and the slide will often not open up fully in high gear at WFO speeds. Even more on smaller engines.

CV engines run like crap when pods are used because the airbox usually is set up to share suction impulses and pods get rid of them, the CVs used those to open slides faster and more time taken to slower opening then goes rich automatically because slower they are lower than they would normally be and that allows the smaller opening for same jetting to pull harder to richen. But it may only last until the slide DOES open but at a slower rate, meaning you were rich on the accel then it drops back to leaner and a mixed jetting demand issue (go lean or rich?) and one reason why jetting CVs gives so much trouble. They also take longer for a set jetting issue to settle in for the same reason, so you are jetted to 'run great' that day until running the same package a month later begins to result in problems with too rich but you are slow to realize that was from what you did 2-3 weeks ago. It can drive you nuts.

GPZ here was a 550 cc. four, the EX500 was a twin.

 

[Bear Hands]

Ok, the EX500 carbs are the style of CV with the rubber diaphragm, which I believe is the same style as the XS?
Real world experience for me; I put pod filters on CV carbs, it ran like crap. I put 10% larger jets in them, it ran a lot better. BUT it definitely didn't run as well as with a proper airbox, and I'm sure a wizard with a dyno would have got it closer than me (no way did I have the money for a dyno tune!).
I now have exactly the same issue with my Katana 600 engine (also running pods on CVs), it is pretty much unrideable at the moment. Lets see what 10% does to that.

I entirely agree that CVs work better with an airbox, but to many it doesnt fit with the look, and in the case of my Kat engine, its in a different frame so there is no airbox that will fit!

In short, I believe that putting pod filters on the XS, even with the "self adjusting" nature of CVs that AMC49 described, will make it run lean. As a good starting point I would recommend 10% larger, and thats the starting point I will be using with mine.

 

[amc49]

Missing part of the point. CV slides simply settle down a little further when too lean to go richer and WHY does a CV engine make more power with a restricted intake box? That's the opposite of normal reaction. Many assume the bad running is too lean when it may be too rich.

The 10% extra fuel only applies when you can control the FULLY opening carb yourself, with CVs you can't do that. It may be half open when you have the butterfly fully open. That throws the 10% idea in the trash.

Give some thought as to the exact physics of why you have to jet up with more air flow, to begin with the airflow increase must actually BE there. With CVs it may not be at all. CV air quality will never be the density amount you get with direct carbs.

I did lots of early first gen Honda DOHC and we ran bigger carbs from 900 (32s) and 1100 (33s) on 750s (OEM 30s) with zero jet changes at all, they ran perfect and the plugs color perfect too.

The OEMs use them for emissions reasons, and the fact that on modern hyperbikes they detune a chunk of power that would otherwise kill many people who do not fully recognize how fast you can get into trouble on one.

You can't make blanket assumptions with CV type carbs, they break too many normal assumed carb 'rules' and why so many get into trouble with them.

 

[amc49]

BTW, not arguing, just throwing more wrenches in the works.