Jetting issues after head rebuild

[vorhese]

Ok it's been a few weeks. I got the (non epa?) mixture screws from scabber, thanks!

Again bike is a 1980.

I think a big problem was a loose connection at the ignition switch. I tightened that and no more sputtering.

BUT

I went through the carbs again before that. I got a M6 X .5 tap to clean the mixture screw hole threads out with. I replaced the rubber o-rings on the float valve seats. Plastic floats are set to 22mm. Pilot jet is one size bigger than stock, 45. And mains are 2 sizes bigger than stock, 137.5. The new Mixture screw is currently at 1 turn out, doesn't seem lean at all yet. I went from an NGK B8ES to a BP7ES plug, gapped at .7mm.

My left side is still running rich and not showing a good burn. The right plug looks a tad dark, and the left plug looks wet with no real carbon indication. A little bit of smoke comes out at idle, and a bit more after a throttle blip.

I've swapped plugs.
Swapped coils.
Swapped the intake manifold barb covers.

Other than float height being incorrect... what else could it be?

I have that extra pair of '78 carbs I'm cleaning up I could try soon, I just need a larger pilot jet.

 

[vorhese]

Ok I decided to pull the carbs off yet again and be very anal with the float level. I pulled the gasket off instead of estimating it being .5mm, and did it off the carb surface. I favored 23mm. It seems to have fixed my initial smokiness.

So I think I'm jetted rich. I did a test ride with mixture screw 1 turn out, and had sputtering at 1/2 throttle. Did another test ride with 2 turns out, and sputtering again at 1/2 throttle, killed the engine, really black plugs.
I'm running pods and BUB exhaust (baffles).
Should I go back to stock 43 pilot and only 1 size higher main, a 135?? The mx screw, as well as the BUB pipes, seemingly really changed my jetting.

 

[5twins]

Try it. All these bikes respond differently to mods. You may even want to start stock. That new mix screw is the red herring here. There's not much info on it or its settings. The old style screws it mimics were usually run 1 to 1.5 turns out but who knows what it needs on a BS34 that originally had an E.P.A. screw. The BP7ES plug is what's speced. An 8 is one step colder and the plain "B" type isn't a projected tip like the "BP" style.

 

[kopcicle]

Are these adjustments being done with the airfilter in place ?

~kop

 

[vorhese]

It's running pods.

Unfortunately I dont have either stock jet so another week for an order to come in.

 

[vorhese]

It's running pods, but yes, they are on.

Unfortunately I dont have either stock jet so another week for an order to come in. It runs great except for heavy acceleration or mid throttle. i probably could just zip around town like it is. I'm assuming the non epa mixture screw is letting in a lot more that stock.

I'm going to try one more test ride with the mix screw all the way in.

 

[vorhese]

Yeh, with screw all the way in, it still putters midrange. I feel it is a bit better, but still sputters. Guess I'll get some jets, maybe try the 78 carbs.

 

[kopcicle]

That's got CV's? Take a #2 phillips screwdriver, heat the tip with a torch until cherry red and plunge it into your eye. It will hurt less. Really. Do a search using my username (elr658) and read the HUNDREDS of posts I've made advising against pods and removing the airbox. Look at my facebook. Bikes with CVs have airboxes. Bikes with slide needle carbs have pods. Even Mark Dobeck, former owner of Dynajet, cops to a loss of midrange using his kits.

Anything that makes a machine more difficult to service GOES!

And for the other eye heat a 3/4" drill bit chucked up in an air drill ...

I can get BS34's to almost work on the 998-1100 with one serious caveat . They will pull hard with the throttle arbitrarily pinned OR they will mix fuel cleanly at part throttle cruise . Pick one I don't know how to give you both . Mark Dobeck and I went back and forth for most of a summer getting several of my customers bikes and my 998 urban terror two wheeler running right . The customers are probably still pissed even though I neither recommended nor supplied this serious impediment to performance . In the end I knew neither was right (thanx for the flash runs Ron !) But the one that was the best and closest to right got me the most grief . That guy thinks I'm an idiot and in ten years hasn't wasted an opportunity to say so . Funny that the last two guys to touch it asked how I was able to get it so close . The one that isn't so good , that guy thinks I'm magic .

just a partial list

various attempts at
springs
needles
needle jets with and without discharge shields
pilots
mains
main air bleed
air horns within the air filters
closer to or further away from the head
adjustable cam sprockets
different headers ....

All because in one case the owner wanted to look like all the other cool kids
and the other thought it was a pain to get the carbs in and out with the stock aribox

coincidently both of these mental midgets went from 35-36 mpg to 30-31mpg and might have gained a couple of hp on top at the expense of having me spend untold hours filling a huge hole around 4k .

So I was asked recently if I would jet another 998 for "pods" ( is it that hard to say individual air filters ? really?) good thing I kept my notes .

127.5 main , 37.5 pilot , possibly even less for the 650
anything more than 140 and you really need to investigate main air bleed modifications or different needle/needle jet .Careful opening of the main air bleed may help in some circumstances. If you don't konw how to find it look in the intake bell of the carb and blow smoke or carb cleaner into the just and it will be obvious . Carefully opening the holes in the bottom of the slide and experimenting with lighter slice springs may also help .
Even with header the liter bikes usually don't use more than a 42 something pilot .
The BS34 was NOT designed to work with individual air filters . If you must use individual filters make them big and even try to fit a velocity stack inside the filter if one isn't molded into the filter .


~kop

 

[vorhese]

There's a lot of shit talk in that post, isn't there.

Anyway I rode with these same pods and carbs for 8 years with no problem. I bought it with them. No midrange issues. Quick take offs, high speeds, great curvy road acceleration. I'm just now having issues.

 

[kopcicle]

I'm admitting to my shortcomings as well . I eventually gave up once I was close at all .
Shit ? You want shit ? Oh I have plenty of shit if you want it but I stayed as close to factual experience as possible while adding a bit of humor .

It's simple really . CV carburettors in general need a still air volume at their intake or curious things happen . More power to ya and I did supply general jetting .

Just a reminder that with the press in needle valve seats sometimes the fuel will leak past the o-ring making all your adjustments useless .

~kop

 

[vorhese]

I'm all for shit talk! Well KOP I'm giving in to the pods/cv shortcomings.

I rebuilt the 78 carbs I was given and managed to get them on. Started right up. I swear it sounds a hell of a lot stronger, but it still suffers from the midrange stutter. It's running the stock 27.5 pilot and 2 sizes up main 140. I guess I'll live with this until I can save up for some roundslides.

Thanks for all the help!!!

 

[5twins]

The '78-'79 carbs will suffer upper midrange break-up with larger mains unless you lean the needles. Yamaha jumped the mains from a rather small 122.5 in the previous carb set ('76-'77) to a 135 in your '78 set. That's a very big jump. In order to do so, they needed to lean the midrange. They did that by reducing the needle jet from a Z-8 to a Z-2. Still, the midrange is right on the verge of being too rich from the factory in the '78-'79 carb set. It doesn't take much to push it over the edge and a main jet size increase will do that.

When you lean the needle, that will also effect the upper part of the idle circuit and may create an off-idle flat spot. A larger pilot may be needed.

 

[vorhese]

Great info, that's an easy enough thing, it's nice to have adjustable needles again. New pilots and move the needle down all the way. Maybe get some Uni filters too.

 

[5twins]

No, not all the way, just one step down. Stock position is in the middle or #3 clip slot. Move it to #2 .....

And yes, if you are going to run pods, get the UNIs. I won't argue the fact that a stock airbox is probably best for CV carbs but these twins can usually be tuned to run well with pods, the proper type of pod that is. What kop is referring to are the problems encountered when trying to use pods on a CV equipped 4 cylinder. After 25 or 30 years, their owners have finally realized this and those in the know don't support pod use on a 4 anymore.

 

[retiredgentleman]

Love my air boxes

 

[vorhese]

I ordered 30 pilots, and in the meantime lowered the needle one clip (raised the clip to next to highest position). Wow, what a difference that made. The bike is completely unrideable now. Very bad stutter on take off. The stutter made me think it was somehow richer, but that can't be right. Guess I'll wait for the pilots to get here to see what happens.

 

[5twins]

Make sure your mix screws are open enough. Stock setting for that carb set is 2.25 turns out but many times they like a bit more, like 2 1/2 to 2 3/4. You can also shim the needles with a thin washer to achieve half step settings. If you can eliminate the upper midrange stutter by only leaning the needle a half step, that's better. As you've seen, the needle setting also effects the upper idle and idle to midrange transition area. Leaning your needles the least amount possible is best.

 

[vorhese]

So I don't quite understand what's going on. Dropping the needle I expected to make a lean condition, but everything I see it seems to be richer. I've adjusted the mix screw from 2-1/4 to 2-1/2 and 2-3/4 and that made it worse, and down to 1-1/2, that was bad too. My plugs look wet to me. Me putting on a 30 pilot when it comes in could only possibly make it worse, right?

Perhaps the midrange issues are POD related? I don't have UNIs to test this.

 

[5twins]

Yes, if you've got the cheapo pods, they can cause all sorts of problems. Some block the air jets and that means mostly fuel and no air - and that means rich running. Take the pods right off and try it.

 

[vorhese]

HOLY SHIT!
I took the filters off and the midrange stutter is gone gone GONE!
It runs like a demon now!

I definitely will be spending some cash for some UNIs and I'll pop the 30 pilot in this saturday when it comes.

Thanks for all the help fellas!