Runaway idle but sooty plugs???!

harmsworthj wrote: I've run it without the filter on and it runs just as rough.

That's no surprise, with stock air box you have some restriction and smooth air flow, do you also run aftermarket exhaust?

kevski wrote:

harmsworthj wrote: I've run it without the filter on and it runs just as rough.

That's no surprise, with stock air box you have some restriction and smooth air flow, do you also run aftermarket exhaust?

Take a closer look at his intake. Airbox discussions are sort of moot in this case. But barring other issues, it shouldn't be too hard to tune it. It's a simple carb and others have been able to run this successfully.

However, I know there is a range of carb sizes that will fit, but some are too big to run on that motor. I don't recall which vm is the preferred size.

Setting ignition points on "T" mark is to much to late = unburned fuel
Re-jetting to 140 and do a test drive and spark plug coloring.

harmsworthj wrote: not sure. potentially 40yrs? its not burning oil while running or on startup tho. would;t i see blue smoke?

Not necessarily. If they aren't sealing, a small amount of oil will get past them causing a rich mixture. You can lean it out but eventually they will start fouling plugs and smoke. Mine barely smoked at startup but I'd get fouled plugs in 2-400 miles. When I changed them I had to rejet all over again.:pinch:
Steve

Ok here's the update: Took it on a little 5min drive around the neighborhood (long enough?) with the #135 main and #25 pilot jets in.
Plugs are looking better I think!
But since going to the smaller main, I no longer have the snappy acceleration I had before, it now bogs between like 1/4 and 1/2 throttle, and I can hear the carb sucking hard before something catches up
Also, my pilot screw and idle adjuster now seem to actually be registering when I make adjustments, which they weren't before.

Still has hanging idle though, can be brought back down with a quick blip but then is super low and uneven.

I think on these carbs I can actually change an air jet on the inlet right? Would I ever need to do that?

It seems you are trying to jet the midrange using the top end adjustment. Perhaps changing the main wasn't the course of action to take. Is there no way to adjust the needle? That's what needs the adjustment based on your description, then your top end power will probably return. A shim will usually adjust the needle by .5mm. That's a good starting point, but if it's too much look for shim washers that are in the .3mm to .4mm range.

I would avoid changing air jets. Stick with the simple stuff first: Main jet, pilot jet, needle adjustment, and air screw for idle mixture.

I do have a clip on my needle! It came stock in the middle of the 5 notches. I will move it down one (so needle opens sooner right?) and try

Since you say the idle adjuster seemed to make no difference prior to this last change, there are still probably other issues.

Besides the possible vacuum leaks, make sure the throttle cable has slack and allows the carb's slide to close all the way down. If the cable has no slack, any change in handle bar position can affect the throttle.

I drove it around with the needle clip 1 lower and its better!! Not completely, but idle didn't hang near as often and that transition between idle and throttle was slightly better think. Still every once in a while the idle would hang when I pulled the clutch to shift gears and once the idle just tanked to chunky uneven. But before the idle would have hung every gear change, so I think its much better. I tried playing around with the throttle cable while it was running and once when I was moving the cable around, the idle suddenly dropped, so maybe there's something going on there, I will check it out.
But do you think I should maybe actually go up with the main jet, since I seemed to have better throttle transition back when it was 200?

I can't really say about whether you should go up to 200 or not. The best way is to try it. Jetting takes a long time, and that is why... many many trials (unless you go to a wideband o2 system).

But jetting will take much much longer, maybe forever, if there are other problems getting in the way and fooling you into thinking the jetting is wrong when it's actually timing or a vacuum leak or a sticking cable, etc.

Have you read the dynojet instructions I posted? It has a step by step procedure, but more importantly it will get you to know how a mixture is affected by RPM, throttle position, and throttle movement. When you go through the steps and see how the bike responds, it will all start to make sense.

For instance, if the bike is lean, it will run like a bat out of hell if you get really ham fisted with the throttle. At first you might think the jetting is great, but then as soon as you start using light throttle movements it will start to cough and sputter etc. That is the classic symptom of being too lean on the needle and main. Mechanical slide carbs, like yours, are much more sensitive to how fast you open the throttle, than on a CV carb.

Have the valves been adjusted?
Steve

yup, did the valves!