Pods, Carbs and Jet's... Oh My: The 7th Layer of Hell

Hi,

I'm working on getting my 81 XJ650 up and running. I'm going to use pod air filters on it with the stock exhaust. I've been reading a bunch on pod's and jet sizes. From what I've read I'm a little confused. According to the math in this artical
http://xjbikes.com/Forums/viewtopic/t=1 ... +pods.html

I need

+4 main fuel jet sizes for individual pod filters (no airbox)
- Add up all the main fuel jet size increases and subtract 2 sizes.
so -2

- Decrease main fuel jet size by 2 sizes per every 2000' above sea level.
so -2 because Las Vegas is 2,300 feet

- Under a mis-match condition, such as when using pod filters with a 100% stock exhaust, or 4-into-1 header with stock filter and air box, then subtract 2 main fuel jet sizes.
so -2 again because I'm using stock exhaust.

The grand total is -2 sizes for the main jet?? So I should get #108 for the main jets?
and
No change for the pilot jet?

Is that right? It seems that I should go up on the main jet since I'm increasing the air flow.

Anyone ever done a setup like this?

Thanks,

Perry

 

I think you may be fine with stock jetting but may need to tweak the idle mixture slightly, or maybe not even that. If you end up with a negative value from the jet calculation you are probably fine at stock jetting. However the jet calculation is simply a guideline to get you in the ballpark, only plug chops will truly tell you what you need to do with the jets.

You aren't exactly increasing air flow because you have stock exhaust which limits the exhaust flow thereby also limiting the intake. Adding pods from my understanding/experience simply increases the volume of air available (by un-restricting the intake), you just aren't really making use of it until you change the exhaust system.

Have you picked up the filters yet? I would recommend the K&Ns, for a couple reasons. You can clean/re-oil them when they get dirty. The ebay filters (emgo?) will get dirty and then you have to throw them out and buy new ones, exposed to the open outside air, they can get dirty quick! Second, I think the emgo filters, unless modified, tend to partially obstruct the air jets thereby potentially limiting the airflow to the fuel jets. I'm no expert but I think that could cause a lean condition.

Cheers,

Trev

 

Thanks for the input. I got probably the cheepest air filters from e-bay. $20something for 4, i'm not expecting to much from them. I'm going for uber-budget build at the moment. When I get closer to being able to walk/ride again I'll change some stuff, but for now it's just to get it going and ideling/reving fine. I think the filters come in today, i'll post what I find after installing them.

 

Damn, I have some pretty new k+n pod filters I'd have given to you if you took care of shipping. Went with pods for a couple of months and hated it but still have the filters at the garage.

 

I'll take the K&N ones. could you send me a pic? PM me with your info.

 

By the way, why did you hate the pods?

 

The pods are going to give you hell in tuning. You'll never get the bike running right with pods and cv carbs. i know that isn't what anybody wants to hear but this is good advice. I wasted over $1400 in carb mods and it was all a waste of time. The bike with the airbox out performs the bike with pods on almost every level. So i was lucky enough to squeeze the airbox back in and rejetted back to almost stock (but 2 !/2 sizes higher due to the 4 into 1) If you click on my project link under my signiture you'll see pics with the pods installed. They have been discolored (which is what happens to pods) and a little mishapen due to the squeeze between the frame rails and the carb bodies. But they are fully functional. i can get a couple of pics on here later if need be... will pm them to you. But other than looks, pods are a huge headache. CV carbs are NOT made to be operated with unrestricted air-flow. You'll have a huge amount of slow moving air when youneed a restricted amount of fast moving air. The cv carbs RELY on that principal. It was what came after direct slide valve carbs.

 

There is NO Formula!
If there was a Formula we would have it and it would be a Sticky.
We'd have had is Printed on a Vinyl Card and mass mailed-out to all the Members.

If we all chipped-in and shipped you ALL the Jets in the World; plus a machine that would produce Jets in Custom sizes, ... you aren't going to find the combination to deliver you what you need.

The Battle Cry for those who install Air Pods is:
"You have to re-jet."
Re-jetting: Suppling more or less Fuel. Is not the problem.

The first problem is controlling the Volume of Intake AIR.
The secondary problem is supplying enough MAIN AIR to surround the Nozzle to enrich the Mixture.

 

Has ANYONE gotten the pods to work as hoped or just half a$$?

 

My bike ran fine with pods once it warmed up. when it was cold it stubled at low RPM. but give it a couple minutes to get warm and it had no problems. And that was with unsynced carbs. I bench synced them but never went further then that so that could have contributed to that also.

 

sorry to derail the thread, but can you elaborate on your jetting? i also have a 4 into 1 on an '81 750 Seca. currently have 124 mains and 41 pilots with 2 small washers shimming up each needle.

it's no longer so lean i'm worried about burning it up, but it's still on the lean side of dialed in. it's a little flat between 5k and 6k RPMS and i'm trying to decide if i should up the pilot to a 42 or swap out for a thinner needle (or both). and lately, i've been thinking about seeing a therapist, cuz i've been toying with the notion of changing my air jets, too.

anyhow - i was just curious if you found something that works or did anything different than i did with "educational" results.

 

Oh hey, skeeter. The original jet size for the 550 maxim is 112.5. Mac says you don't have to re-jet for the 4 into 1 I got but I ended up getting the wrong size jets anyway so I put them in. They are 115 so for now that is the only mod to an otherwise stock set up. And by the way, Primus is awesome.

As far as I have been told and have gathered here, the 550 is the least finicky about exhaust changes.

 

ah, nuts, i should've read your sig line.

and, i believe you meant to say, "PRIMUS SUCKS!"

 

Interestingly enough, ... Increasing the AIR Jet Size is essential to get the Mixture from being too Lean.

The MAIN AIR Passage feeds the AIR surrounding the Emulsion Tube.
AIR that is NEEDED to be drawn-through the Emulsion Tube and ASSIST Pulling Main FUEL JET Supply up and out of the Emulsion Tube into the INTAKE STREAM.

But, the Main AIR Passage can only handle what is able to drawn through its drilled passage.
The AIR Jet provides restriction of flow.
A LARGER Jet would be beneficial, ... exactly.
The "Right" AIR Jet ... is --> LARGER <-- than the existing Passages.

You cant get enough MAIN AIR through the Passages to meet the NEED of the INTAKE Air Stream.

This problem was addressed by the people who brought you the famous: "Dial-A-Jet"
They recognized that there would never be enough Main AIR Flo through ANY Emulsion Tube ... So, they invented a method to provide that FUEL through an Auxiliary Orifice which had the means of External Adjustment.

 

if i read that right (and i ain't too sure about that) - it sound's like you'd be better off removing the main air jet completely . . .