main jets after pod filters

bkmarsha · Posted: October 23, 2008, 9:06 am Post subject: main jets after pod filters

i just recently installed pod air filters on my bike and it is running horible

the consensus seems to be that i need to go up one size on the main jet and maybe up a size on the pilot jet also

just wondering how i can check what size my main jet is and then how does the numbering system work (increasing numbers or decreasing numbers)

bkmarsha · Posted: October 23, 2008, 9:07 am Post subject: Re: main jets after pod filters

here is info on my bike thought it would be in signature but geuss not

78 650 special
emgo air filters
no other mods.....yet

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

The Emgo air filters are probably part of, if not most of your problem. They have a large inner rubber lip that blocks the air passages around the lip of the carb intake bell. This causes bad break-up and stumbling at about 4500 RPM. Guys have gotten them to work by cutting the rubber lip out or moving the filters back on pipe sleeve extensions but, honestly, your best bet is just to replace them with a better filter - they're crap.

Jets have numbers stamped on them. The larger the number, the bigger the jet and the more fuel it flows. Check what's in your carbs now before you start buying new jets. Many of these bikes have had their jetting fooled with by P.O.s and it's not stock anymore.

One size up on the mains will probably be good for you with just filters added. Stock on your bike was a #135 so you'd want a #137.5. You shouldn't need a larger pilot unless you lower your needle to compensate for the larger main. You won't know if you need to do that until you do some road testing at full throttle through the midrange. If you get stumbling between 4 and 5K, you'll need to lean your needle setting. That may also cause a stumble just off idle, in which case you'll need the larger pilot. Stock pilot on your bike was a #27.5 so you'll want a #30.

Here's a chart I drew up with stock jetting specs. As I said, insure your carbs have the correct sizes to begin with and then take it from there .....

bkmarsha · Posted: October 23, 2008, 10:58 am Post subject: Re: main jets after pod filters

hopefully i will be able to get it to run just by modifying the filters and maybe with new mains

i will make another post once i do more work to keep you updated

what air filters would you recomend if i decide to go that route

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

I prefer real K&Ns but many find it hard to pay the price. I justify it because it's a one time purchase for the life of the bike - and they work correctly. If you wanna cut corners and save some money, do it elsewhere. Air filters are very important.

UNIs are also good and cheaper. The new filters offered by MikesXS are supposed to be OK but I've not tried them. Of course, he used to sell those Emgos and no mention was made of their problems in his ad copy.

Tomterrific · Posted: October 23, 2008, 11:41 am Post subject: Re: main jets after pod filters

The EMGOs are your problem. You may also have other problems but you will need to ditch the EMGO filters before proceeding. The new XS Performance filters from mikesxs.com are probably okay. I bought his original filters and went through all the nonsense getting them to run right. Now I have true K&N filters with stock jetting and my stock 77D runs fine. I did raise the needle by dropping the clip one notch but I'm not sure I needed to do this.

Pull your EMGO filters off and see if your bike runs okay. That's a good test to see if they are the problem (which we know they are).

Tom Graham

tweedy64 · Posted: October 23, 2008, 4:52 pm Post subject: Re: main jets after pod filters

xs performance filters are fine got em on mine work just great cheaper than k&n's. cheers tweedy

bkmarsha · Posted: November 2, 2008, 6:19 pm Post subject: Re: main jets after pod filters

got her running it has taking some time and some embarasing dies at stop lights but i think i have the idle and the mixture set to where it runs well

now i have a new problem that i think may be related somehow

ever now and then when i am starting the bike it will backfire through the carb and blow the right carb out of the seat

not sure why it backfires (asume it is a pressure buildup and release) also dont know why the carb always comes disconected

woud a new seal solve the problem

any recomendations or advice would be great

jayel · Posted: November 2, 2008, 8:05 pm Post subject: Re: main jets after pod filters

if your timing is set correctly, a tight intake valve will do that, these carbs are heavy and if you don't have them supported at the back (as in running pod filters) they will blow off, what kind of clamp do you have on the intake? the stock band clamp or a screw/crawler type radiator clamp?

bkmarsha · Posted: November 2, 2008, 9:07 pm Post subject: Re: main jets after pod filters

yes i do just have the stock clamps on the carbs

is there anything i use that might give me a tighter fit

i hadnt even thought about the fact that the back is no longer supported by the air box, that probably plays a large role in the problem

jayel · Posted: November 2, 2008, 10:10 pm Post subject: Re: main jets after pod filters

the crawler type raditator clamp will go down tighter but if it blows off it's harder to put back on without a screwdriver, does the 78 have that bar or plate that connects the two carbs together? could you run a brace from it to a rear mounting point? hold the carbs in

bkmarsha · Posted: November 3, 2008, 2:16 am Post subject: Re: main jets after pod filters

well my pocket knife has a screwdriver on it and i have that with me 95% of the time so i will probably try crawler clamp

the 78 does not have a connecting plate just the connection for the choke

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

I had that problem with mine for a while. You need to tighten the clamp screws fully until the 2 clamp halves touch. If you have the original Phillips screws in the clamps and the heads are rounded out some, you may not be able to do this. I replaced mine with Allens. Although shorter than the originals, an M5 x 16 works fine.

weekendrider · Posted: November 3, 2008, 10:23 pm Post subject: Re: main jets after pod filters

bkmarsha if the lower plate is gone (dam! PO's) you will want to replace it.
It is 7/8's angle, 1/8 thick, 6 1/2" long. That plate was used on the C through the F models.

jayel · Posted: November 3, 2008, 11:16 pm Post subject: Re: main jets after pod filters

here's what the mounting plates look like, if your carbs have a flat area with the mounting holes behind the float bowls adding the brace will help to keep them in place

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

jayel -- 3M at 650 Central sells special manifolds with his VM34 kits. Will those work in this situation?

jayel · Posted: November 4, 2008, 9:20 am Post subject: Re: main jets after pod filters

looks ok don't know how much heavier they are but they do use the radiator type screw clamps that would tighten down better, I still think if he checks his valve settings/timing and gets rid of the backfire it would be better than just throwing money at the problem

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

jayel wrote:

looks ok don't know how much heavier they are but they do use the radiator type screw clamps that would tighten down better, I still think if he checks his valve settings/timing and gets rid of the backfire it would be better than just throwing money at the problem

Of course it's best not to throw money at a problem until you find out that the solution requires money. I only just wondered -- those 3M manifolds are engineered to provide additional support to hold the VM34s in place WITHOUT an airbox. I just wondered if the 3M manifolds would work with stock carbs if lack of support proved to be the problem here. I don't know if the stock carb and the VM34 have the same diameter at the manifold end.

Mikesxs · Full Member Joined: Feb 06, 2007 Posts: 134 Location: FL

Just For everyones info Mikes XS does Not and has NEVER sold Any EMGO brand products (Pod Filters, Mufflers Etc.) as stated by frequent commentators on this site.

Mike Lalonde Mikes XS

Jake68 · 650Rider Supporter Joined: Mar 23, 2007 Posts: 841

I think I may have been supplied some by an agent of yours Mike in Germany. He's a top guy and I get on really well with him..so I wont complain too much Smile

ine are oval and crome and my bike is doing exactly what people describe..its hard to break past 70mph and the machine bangs and pops and hold back breaking the 4500rpm barrier..

What Happened to 650rider.com?

Yamaha xs650