Off-idle bog theory

[SSonnentag]

How are you measuring the air/fuel ratio? Is there an instrument of some sort to take this measurement?

[jdavidr]

How are you measuring the air/fuel ratio? Is there an instrument of some sort to take this measurement?

I'm not, (seat-of-pants dyno only), but mx_rob is... check out his thread here.

[jdavidr]

In response to a PM question about part #'s and a source for jets, I thought I'd post the info here in this thread.

Pilot jets part #: MIKUNI PILOT JET N151.067 available here.

Pilot air jets part #: MIKUNI AIR JET BS30/97 available here.

They're probably available other places as well.

[gazinga]

I have the same bog issue with my BST on a '92 DR650. One thing I have found is that the end of the butterfly rod that sticks out the other side of the carb body and is held on with a circlip has an o-ring sitting under the clip. When idling, I found that if I sprayed carb cleaner in that area, the carb would start to bog. Upon inspection, I found that the o-ring is made of what appears to be FELT or some sort of porous cloth. I was wondering if swapping that for an actual rubber o-ring would help by getting rid of an unwanted air leak. The fact that the throttle is a push/pull cable set up makes me believe that I shouldn't have any issues with friction. Any thoughts?

[IdahoJim]

What elevation are you at, what exhaust mods, what air filter?

I've got a cut-open airbox top, stock air filter, supertrapp quiet with 10 disks, DJ 150 main, needle clip in 3rd notch from the top. I'm at about 5300 feet ASL.

I started with the DJ 160, the clip in the 4th notch and the off-idle problem was a killer. It would stall off-idle unless I was VERY careful with the throttle. Changing the pilot screw didn't do much of anything. I dropped the needle one notch and it improved slightly, but not much. IdahoJim recommened going smaller with the main because of my elevation and so I dropped down to a DJ 150 (only slightly larger than stock) and the problem is almost gone. I need to mess with the pilot screw to see if I can get rid of the off-idle bog altogether, but I've grown tired of burning my hands trying to adjust it and I'm waiting for the extended screw from Jesse.

The other problem is that with the 160 I felt a pretty large increase in power. Now with the 150 the power gain, if any, is pretty minimal and it seems like all I've bought myself for all the mods is the off-idle problem! ARRGGHHH!

Thanks for starting this thread jdavidr. Hopefully once I get the pilot screw I can contribute more information about my own off-idle problem and attempts to solve it.

Hey Gary...thanks for the "kudos"...LOL. Something I did later to mine was increase the pilot air jet to a 1.1. That's going the opposite of JDavidR's idea, but I thought it made the off idle throttle response noticeably quicker. I thought, because of my elevation, that the fixed portion idle circuit might be a little rich. I'm at 4,500', and am running the stock exhaust and air cleaner, with the DJ150 main, of course. header weld ground, and airbox modded as per Jesse.

Jim

[NordieBoy]

Just ordered a 45 pilot and 1.2 pilot air jet to put on the bike when the GSXR pipe goes on tomorrow

[NordieBoy]

Final set-up (DR Mod#4): Jesse-cut top-open airbox, K&N filter, bug screen removed, drilled slide, slide spring with 3 turns cut off, DJ needle clipped at 4th notch down, DJ160 main, #1.2 pilot air jet, #45 pilot jet, Idle adjust nearly all the way screwed out, pilot screw 3 turns out, stock piston, all valves and float height in spec, unground stock exhaust header, Supertrapp Quiet with all 12 disks, sea-level to 3000 ft. elevation.

I used your settings as a start point for my re-jetting.

Open airbox top.

TwinAir Filter.

No bug screen.

Drilled slide.

3.5 turns off the slide spring.

DJ needle 4th down.

DJ 160 main.

145 pilot.

1.2 pilot air.

Float parallel.

Idle just on.

Header weld grind.

GSXR/Hindle combo.

Idled sweetly.

Bogged like a dog. A big fat dog that drools everywhere.

Originally I was running a DJ 152.5 + needle 2nd down + 42.5 pilot + 1.0 pilot air with the (almost) stock exhaust and it ran sweetly except for some bogging off idle and when I put the pipe/exhaust combo on I just turned the mixture screw out a turn.

Going back a step to the 155 main to see what happens there.

[NordieBoy]

160 main, needle 4th from top, 45 pilot, 1.2 pilot air. Big time bogging.

155 main, needle 4th from top, 45 pilot, 1.2 pilot air. Big time bogging.

155 main, needle 4th from top, 42.5 pilot, 1.2 pilot air. Big time bogging.

155 main, needle 2nd from top, 42.5 pilot, 1.2 pilot air. Minimal(ish) bogging - pronounced popping on the overrun.

70-100kph in 4th gear was about 3 secs which is the equal of anything I got out of the dynotuned SuperTrapp setup.

45 pilot going back in when it cools down to check the difference on the overrun...

[NordieBoy]

45 pilot back in and much less volume on the over run popping.

So it looks like that for my bike it's mainly the needle height that affects the off-idle bog.