Rejetting help.

[ECHO5]

1981 Heritage Special, EMGO pod filters and EMGO shorty mufflers. According to parts fiche, the bike had 135 and 40 jets. Someone said on a thread here that they went to 140 and 45 jets for pods and shorties, so I ordered some. The bike was running decently with the old jets, but with the new jets it seems to run on one cylinder and barely stays running. Give it any throttle and it dies. I'm guessing I'm running too rich now, but I haven't synced carbs. I just wanted to see if anyone has any experience or suggestions to offer. Should I be able to tune the carbs appropriately with the jets that I have or is there a chance I'll have to get different ones? I'm working on getting a manometer to sync the carbs. I've got a colortune too but it's a 12mm, and I'm not sure if they make an adapter for 12mm to 14mm for the colortune.

 

[bcware]

My best suggestion is to ditch the emgo pod filters; they block the pilot air jet on the carb mouth due to a thick lip they have on the inside of the silicone/rubber collar where they clamp on.

I tried them and could not get my bike to run right. I switched to mikesxs K&N filter clones and have had good results.

 

[BBS360]

Many people have trouble tuning their carbs with pods filters installed. In addition to the jet blockage described by bcware the pleated filters introduce turbulence into the carbs, destroying the venturi effect that the carbs need to run properly.

If you can mount the pods on the stock h-pipe you should be able to avoid most of the issues bcware mentioned. The extra distance between the filter and the carb body helps even out the turbulence.

I have basically no experience with jetting though. I know some diagnostic information can be gleaned from spark plug condition after a good ride, assuming the bike runs well enough for a good ride.
Also depends on the pilot screw settings but I believe that mostly affects idle speed, jetting for higher RPMs requires arcane knowledge that I do not have.

 

[ECHO5]

Thanks for the advice. I might consider ditching the pod filters, but the stock H-pipe was toast and it was a cleaner/neater look anyway. I wonder if anyone makes a foam prefilter for the pods. That should smooth things out. But I'd love for someone to point me to some sources for the pod filters creating turbulence. I can't find any solid source that confirms it, and more sources that suggest otherwise, such as:

where did this myth come from about airbox airflow being smooth and pods having turbulence?

not for the xj but on my suzuki i made a "wind tunnel" type of thing where i cut 3 different intakes in half including the filters and mated them to a piece of glass. i used a fine tip on a bee hive smoker and watched the air stream coming through the filter and down the tract. the airbox, similar in design to that of an xj, was the worst, the intake air eddies around after the sharp cornered exit from the box, with no bell to smooth things out.

as for the clamp on filters, they were smooth as a babies behind.

Apparently the idea they make turbulence isn't limited to the XS, and I realize he is talking about a different bike, but his experiment with the pod filter is still valid, thats of course if his testing methods were good. I'm just making sure this isn't misinformation being passed along, or if it's really true.

I still have the stock airbox as well and I can probably seal up that H-Pipe well enough for a test to see if it changes anything. We are trying to put this bike together on a very small budget, so I may have to engineer a solution to this problem.

 

[BBS360]

I don't think he says whether the pods were used with the stock intake, with or without any kind of straight pipe before or after the filter, or with nothing attached.

For anyone else's curiosity the quote is from here: http://xjbikes.com/forums/threads/pod-filters.28832/page-2.

They might suggest in that thread that pods do not create turbulence, maybe it's the wrong word, but they do find that pod filters are garbage.
They come up with some wacky mods to compensate for the pods but the easiest method is still to put the stock h-pipe between the carbs and pods. It keeps them from obstructing the various intakes on the carbs and smooths out airflow, acting similar to velocity stacks on race bikes.


These filters are probably the coolest I've seen, combining velocity stacks with a common filtered plenum: http://forums.sohc4.net/index.php/topic,79491.575.html
Their member TinTop had each component custom manufactured for CB550's and CB750's.

 

[ECHO5]

These filters are probably the coolest I've seen, combining velocity stacks with a common filtered plenum: http://forums.sohc4.net/index.php/topic,79491.575.html
Their member TinTop had each component custom manufactured for CB550's and CB750's.

Those are sick. Too bad they are for CB's, although I've owned several of those bikes myself. Thanks for the replies. I will probably just buy another H-Pipe and use it with the pods, or go back to the stock airbox. Probably not before I fiddle with it a little more though, haha. Anybody have opinions on the jet sizes?

 

[bcware]

Pretty much any setup only needs one size larger on the pilot.

I have a mac 2-1 exhaust and k&n knock-off pods directly on the carbs and I run 2 sizes larger on the mains. Standard needle position.

 

[ECHO5]

Pretty much any setup only needs one size larger on the pilot.

I have a mac 2-1 exhaust and k&n knock-off pods directly on the carbs and I run 2 sizes larger on the mains. Standard needle position.

Thanks. I'll order some 42.5's.

 

[bcware]

If you start bumping the mains or shimming the needles just be conservative. If these bikes are lean at all, in my experience, it tends to be at idle or very low rpms. I bought every main jet size available and tried them all with a fresh set of plugs every time (I have piles of them left over). The bike just started to bog down at high rpms with the larger jets and I felt no benefit.

For me messing with the needle height didn't do much, so I just left it alone. If anything raising it led to poor performance when combined with a +3 or larger main jet.

I am strongly considering going back to the stock h-pipe plastic piece with pods as I am not really happy with the performance after a few seasons with pods directly on the carbs.

 

[oli36]

Where are yous guys ordering new jets ?

 

[bcware]

Brand name jets: http://www.pjmotorsports.com/mikuni-jets.html
Knock off jets: www.mikesxs.net
Probably knock off jets: http://www.dimecitycycles.com/motor...amaha-xs400-caferacer-carburetors-intake.html