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Big cubes can throw everything you know out the window on tuning, sometimes you just got to give them what they want instead of what equipment is saying they need.
Explanation: those big cubes can pull large amounts of air in reversion back through the bigger exhaust in decel and goes lean, the engine is still trying to recover out of a lean condition at idle but takes a few seconds and can die before recovering or pop out the carb when trying to throttle.
Experience: tried setting my idle at 13.8-14.1 afr(normal) and didn't have a fighting chance when slowing down to a stop with dying or coughing when quickly trying to take off, afr gauge would head towards 15.5-16.0 although my low speed jet was giving me a 12.8 afr running low speeds. Just starting turning the air screw in small increments until the cough went away when slowing down to idle on a small throttle blip, cough and dying disappeared with the final result the afr was 12.8 at idle. May not need this much idle fuel with your engine but this method of tuning for the decel/idle has been rock solid for 5 years, after putting the apes on i bumped the air screw putting the throttle cable back in place and had to set it again because the same symptoms started back up.
Try and give it what it wants with the air screw to offset reversion the big cylinders are pulling air back, on EFI you can load the 0% throttle area on the map @1000-2500 rpm's with fuel to take care of the problem, on a carb we need to carry fuel over on the way down so chalk up a win for EFI on efficiency but still love a carb with cubes.
Last edited by 1997bagger; Jun 28, 2019 at 06:45 PM.
I tried something over the past couple of day. Here are the results.
I retarded the timing. It made the bike sluggish and did not help on the stalling issue.
Today when I rode to work, I advanced the timing a little. It did not stall on me. My revs did hang up a little when letting off the gas but that's probably because I didn't change the idle mixture to a happy place and had it rich. I adjusted it when I got to work. We shall see on the ride home.
I'd replace that advance unit with one with bearings and the thick washer under the spring, if you can see rust at the pivot pin which I do they are bouncing on you, fought that battle many times with shovels.
Secondly at an idle with brake clean and the little tube give it a quick shot or two to the insulator between the carb and manifold and the butterfly shaft ends where they come out of the carb, the shaft does wear and sucks air just enough to screw with it during decel and low speed transition to the intermediate jet.
May bump the intermediate jet up to .033" and maybe drop the main to 76.
Spark plugs, I'd run NGK's or Denso platinum or iridium gapped between .028 to .035, bigger engines like a tighter plug gap. Play with plug gaps till you find what your engines happy with.
With the advanced timing (by about two degrees) it has not stalled on me at all. However, it is breaking up just off of idle or at low rpms. Like it's missing. The acceleration is not as strong as the recommended timing. But it is waaaaaaay easier to start!
So with a bit more timing she doesn't stall but is not as smooth off of idle. Any new suggestions with this new found info. Still think larger intermediate jet? I just realized that I never told you guys what exhaust I was running. It's a kerker supermeg 2-1
I'm thinking like twisted.. I don't like the look of the one spring on your advance unit... I have one in the shop that I'll take a look at later and match to yours..
Your post said you were stalling on decel and idle, you are on the idle circuit which is the screw, why don't you just turn the screw out some to see if it helps instead of circling the wagon, if it doesn't then turn it back and proceed in replacing parts
Your post said you were stalling on decel and idle, you are on the idle circuit which is the screw, why don't you just turn the screw out some to see if it helps instead of circling the wagon, if it doesn't then turn it back and proceed in replacing parts
The last time I had problems such as you describe the problem turned out to be that black rubber accordion looking boot that covers the accelerator pump rod.
It had dry rotted and was letting in air to the accelerator pump system.
Bett its this ^^^^^^^^^^^^^^^^^^
That lil boot can have a small slice in it and cause a problem.
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