carb jetting issue

greenbarn · July 14, 2013, 18:35:17 PM

Quote from: mumbles on July 13, 2013, 23:45:44 PM
If you're going to Grampsize or install a less restrictive air box then yes, the oem pipes need to be debaffled.
For best results install an aftermarket performance exhaust.

Yes, what mumbles said.... You won't get much improvement in air flow, I wouldn't think, from the airbox mod unless you increase the flow through the muffler too.

mumbles · July 13, 2013, 23:45:44 PM

Quote from: Darth Wraith on July 13, 2013, 03:02:05 AM
OK, i'll grampsize the old lady - should I debaffle my pipes, also? I like the sound of the OEM pipes, eventually I could manufacture some black pipe like the old Chiefs from the fifties to preserve the originals for some uncertain future...

If you're going to Grampsize or install a less restrictive air box then yes, the oem pipes need to be debaffled.
For best results install an aftermarket performance exhaust.

Darth Wraith · July 13, 2013, 03:02:05 AM

OK, i'll grampsize the old lady - should I debaffle my pipes, also? I like the sound of the OEM pipes, eventually I could manufacture some black pipe like the old Chiefs from the fifties to preserve the originals for some uncertain future...

CDNRatMan · July 12, 2013, 20:47:19 PM

ok got you now....thanks.

greenbarn · July 12, 2013, 19:57:49 PM

No, I'm agreeing with you. I understood Darth to ask if it was OK to use the same jets I used, if he's only changing out the filter.

That would be way too rich. The stock jetting is pretty lean so maybe a slight increase would be OK, but I wouldn't even think that would be needed

CDNRatMan · July 12, 2013, 19:51:51 PM

I asked at the shop today GB about if I just switched to a K&N air filter if I needed to do anything to the jets, the mechanic said it should be just fine as long as the air box and the rest was not changed. Are you saying different?

greenbarn · July 12, 2013, 18:01:50 PM

I think it would be way too rich with only changing the filter. The air mods I did seemed to be HUGE, with the amount of air restriction I removed from the picture.

Darth Wraith · July 12, 2013, 08:09:53 AM

Is it ok to rejet like this only with a K&N air filter? ( stock airbox&pipes)

greenbarn · June 25, 2013, 17:14:17 PM

Thanks guys for the input on this.

Troll - you're correct that rolling on the throttle keeps it from doing it - it does it so infrequently it's hard to say "exactly" what does it, but it seems to be a quick close and open that makes it pop.

Mumbles - thanks, I'm relatively sure the boot is tight, but I'll double-check that when I get a minute.

Thanks for the help.

mumbles · June 25, 2013, 00:14:27 AM

It's called a carb fart.
Make sure the carb is seated properly in the intake boot. Also do not over thighten it.

If no air leaks at the carb/intake boot then adjust the a/f screw out 1/4 turn.

Troll · June 24, 2013, 18:28:37 PM

Harleys, even injected ones, do this all the time. The official H-D explanation is called EGR crosstalk. Seems they claim that small amounts of exhaust gas are reverted into the intake tract, and this causes the pop back in the intake. S&S claims you can minimize it with a stronger accelerator pump shot and "rolling" on the throttle instead of snapping it open. When I put the Keihin blockhead CV carb on my '80 shovelhead, a little tweak to the accelerator pump linkage all but eliminated it. I had a Super E on my '98 inch Glide, and that would only do it when the engine was cold, of if I tried to pull hard from under 1500 rpm...it's a V-2 thing......Sooooo, it's maybe just a little on the lean side...but the main jet isn't the cure....the pilot is just a little small.....and the pump shot is a little thin.

greenbarn · June 24, 2013, 17:27:59 PM

Over the winter one of my projects was to do a moderate/major modification of the intake system, and to rejet the carb. I followed the "grampsizing" mod on russwolf's website, including the exact jet sizes.

http://www.angelfire.com/ak5/russwolf/documents/grampsize.PDF (I used the OEM needle, with a 170 Main/52 pilot --OEM sizes are 135/48) I know that's a lot bigger, but that's what the mod that seems to be tried-and-true suggested as a starting point, so that's where I started.

Results: everything seems great, the bike runs fine, with one small exception:

Sometimes, infrequently, if I close the throttle suddenly, and then open it again quickly, it will give a single "pop", I believe back through the carb., and usually (but not always) it will die. Most of the time this happens when rolling up to a quick stop-and-go- this will usually result in a stall, but it's happened at least once while moving down the road (but of course then it doesn't stall).

So my question, is this typical for "too lean" or "too rich", and which circuit are we talking about?

It also does smell rich at idle speeds. I probably at the very least need to adjust the fuel mixture screw: it's set at the suggested starting point from russwolf, and it ran so good there (with exception of these two little issues) that I haven't messed with it yet. Not to mention, I'm getting significantly better fuel mileage since the mods...

Suggestions? I hate to have to take off the carb, because the problems seem so non-eventful.