Lazy man's rejet?

[Jlovvorn]

I continue to run lean. Plug is not white on the tip, but certainly light brown.

I have ordered new jets, and assuming I can get the mangled old ones out (why would someone strip them down so tight?), I am going to go up to 150s.

My airscrews are only open 1/4 turn from closed.

Question - In the meantime, can I run with some choke in order to get things a little richer?

Should I close down the airscrews entirely?

I have read all kinds of seizure horror posts, and I don't know how worried I should be about my lean condition.

Thanks!

PS I am sure I am lean because of the pod filters I put on. But they seem like a huge running improvement over the old airboxes.

[mike in idaho]

Lean running is a valid concern these days, with ethanol being blended into today's gas. 10 percent more main jet area is a good place to start. You might try raising the needles in the slides one notch, in the meantime, that will richen the mid-range a bit and will affect (slightly)full throttle also.

[Jlovvorn]

I bought 150 mains to solve this, but they didnt fit (they were late, not early).

So I drilled out the 135s to match the diameter of the 150s, and it seems to be better.

I am just barely there, would like to be a little richer.

My problem is and continues to be refusal to idle under 1800-2000, and hesitation after warm up. (see other thread).

[Buck]

Sounds like you have an air leak somewhere.

[teazer]

Running with choke partly on is not a fix. It works as a get you home trick but if you have a problem it needs to be fixed.

Air screw 1/4 turn out suggests it's lean at the bottom end. Main jet won't help there, but it suggests that there may be an air leak or partial fuel restriction.

You mention a light tan color - under what conditions? riding around, flat out, idling in the drive with new plugs? It makes a huge difference. For example new plugs on a motor that's idling or running light take forever to develop any color because the tip is not hot enough to burn the deposits onto it. New plugs on the dyno often show no color. They got hot enough at the top but not for long enough.

I like to see plug tips white and just a 2mm smoke ring where the insulator meets the steel shell. But that's a flat out plug chop for the main jet. But unleaded fuel tends to leave more carbon black on the tip and some motors need a hotter plug to stay clean.

In other words, we don't have enough information.

Does the bike run better at the top if you roll off the throttle slightly? Does it have stock filters and exhausts? Do you have air leaks? Are the jets spotlessly clean and did you clean out all the fuel and air drillings?

Did you take off the carbs and clean them and did you check that the mounting flanges are flat? the flanges tend to bend if they are to tight. Is the tufnol insulator flat? Are the
O rings still good.

Start with the basics and get it to idle at 3/4 to 1 1/4 turns out on the air screw. Then see if you need to re-jet.

10% ethanol (E10) can make a minor difference to your jetting compared to straight old school gas. Ethanol needs a slightly richer mixture, so 10% of ethanol needs about a 3-5% increase in jet size if the original jetting was perfect. That would be a 140 or 145 assuming that the bike needs it.

I'd recommend getting your carbs ultrasonically cleaned and checked and set up correctly, make sure everything else is good and stock and then see if it needs to be re-jetted.

[mike in idaho]

Pull the low speed jets out and clean them with a wire, varnish build-up in the holes won't come out with just blowing through them with carb cleaner. Use a little care, you need to clean out the holes without oversizing them.

[Jlovvorn]

Thanks. Slow jets have been replaced with new, and carb was removed and cleaned well. I didn't run a wire, and probably need to. May do ultrasonic as well.

Lean condition seems to be managed, so we can close down this thread.

My continued problems recounted in another thread.

I think I either have fuel restriction or air leak or both.