Low rpm bog!

[WoWman]

Hey all!

My 89 has a bad bog when whiped open (3/4 to WOT) at lower RPMs. Not real low in the power band either, anywhere from idle to 4 or 5k. Sometimes it will chug out of the bog after a second, but that usually doesn't happen.

I have to either close the throttle and open it a bit until high rpms or grab the clutch. Both a PITA!

To try and get rid of this I cleaned the whole carb REALLY good, made a decent difference but only helped down low power. Didn't do too much for the bog.

So then I messed with the air screw, and found that 2.25 - 2.5 turns out gives the least bog....but the bogs still there.

Heres what I'm running:
Stock needle at 3rd clip position (i think, can't remember exactly)
Stock silencer with a few holes drilled in baffles
PC pipe-all banged up though
158 main
48 pilot
And all testing done at sea level

I am thinking the main could be too fat, or the needle needs to go down (clip up). My plug always has a bit of spooge on the threads, but none on the electrode-it is a dark brown color.

Any suggestions as to what's causing this?

Alittle off topic but whats a good aftermarket needle to run? I really don't know a whole bunch on the PWK.

Thanks to all...again!!! :worship:

 

[David Trustrum]

I assume you have checked if the power valves are working? Use [search] key above for how.

Check Simple stuff first, like replace airfilter if a bit old. Spark plug & plug cap (perhaps if at low revs spark a bit feeble).

Check there are no airleaks & the reeds are worth a look to see they’re not damaged.

& the ugly bit is the carb slide is probably worn a groove in it making jetting a bit hit & miss. Replacing mine helped a lot but they are not cheap.

 

[WoWman]

Uh....all of the above? :)

Well lets see...I just changed the air filter, new plug, spark is good, reeds checked out good, the slide DOES have a grove on it and the power valves probably DO need to be cleaned. But when I take off that cover on the left side (says KIPS) the inside does have fresh "carbon stuff" on it, soo....I dunno.

I checked the carb boots no air leaks I could see of.

How much would a new slide soak me?

I didn't think that the kips being clogged up would make it bog so hard though. It is really bad! I have to be VERY gentil on the throttle when the bike is just getting warmed up or it will stall. Sounds like a deep muffled tone when it bogs.

 

[JasonWho]

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[David Trustrum]

Well probably about $90 of your capitalist greenbacks.

Yeah I know.

While you are rooting around perhaps you have a look under the LHS cover & look for oil, the crank seal may be sucking air.

I would at least measure that plugcap, a good spark in the open air means little under load. Perhaps your stator may be a little weak? Just throwing suggestions out there.

 

[WoWman]

90 BUCKS!!!! Geebus that's expensive!

Well I'll inspect a bit more tommorra and maybe try a smaller main (155 sounds to my likings).

Thanks alot David and Jason! Any other suggestions are welcome. :confused:

 

[IrishEKU]

WOWman, try your clutch, it'll slip at low rpm and cause the bog your talking about. Even a simple adjustment up at the perch will liven up your beast. My old zinger would bog at take off and I fiddled with the carb thinking it was a fuel problem. I then read a post on here about free play in the cluth lever and noticed mine was a little too loose, 3 turns on the perch and :eek: "Sorry didn't mean to Roost Ya!" :)

 

[John Harris]

Drop the needle way down is the fastest and easy thing to try. Next to top or top ring on needle. Sounds like jetting is way too rich.

 

[canyncarvr]

If you're in the market for a slide, talk to ron @ RB designs:

[email protected]

His website: http://www.rb-designs.com/

I ordered one from my local parts place $75...got two of 'em...both the wrong size. Ron sent me one in a couple days for $40. AND it was the right one!

The bog you are describing is exactly what you get with a mis-jetted bike. Yeah...could be a spark problem, and air filter problem..a number of other things.

Which needle? A 'C' (1.5º taper) series is a good wakeup for the kdx...a CEJ or so 3-4 clip.

 

[fishhead]

A lot of good advice!

A bog usually indicates a lean condition.

I would check to make sure the main is clean and if so try one size larger main based on your description of where the bog is occuring

 

[WoWman]

OK....I dropped the needle to 1st clip, it was on the 3rd. Fresh air filter cleaned, fresh gas, 70* or so (farenhiet) and dry out.

Didn't bog nearly as much in the mid rpms, but I had to be gentil with the throttle down low.

But starting it is a complete bitch now! Even before I dropped the needle it was starting to get finicky on starting, but seems a bit worse now.

Have to put the choke on and hold throttle open for a sec, then start kicking. 10 kicks later she usually starts up, but have to keep the revs up and the choke on or she will die. Once all is warmed up (3-5 minutes) I shut the choke off and start out, keeping the revs up.

It takes about 10 minutes of RIDING before I can drop down to the low revs without having to worry about killing it/bogging easily.

But a half hour into the ride it was running really good, didn't bog much. Only when low rpms (idle-2.5k) and snapped open would it bog. Other than that instant throttle response. I may have to try a new slide (ouch) and see what happens from there.

Thanks for all the advise guys! :thumb:

 

[canyncarvr]

As fishhead said, a bog-when-quick-wicked off idle is usually a lean condition. Certainly, dropping the needle made things much leaner on the bottom which is why you're starting sequence is hose-eh-vooed.

Some basic things need to be addressed. The main needs to be 'set' first. WOT plug chop will tell you that. A 'wrong' main can give you starting trouble AND throttle response issues. Looking at plug 'color' in a general sense (say, after a days ride) won't tell you much at all cuz too many circuits have been in play. That's the point of the plug chop test..it tests one circuit (the main) under fairly controlled conditions.

From setting the main, a lot of jetting/tuning will come from the seat of your pants. Don't forget the AS in this equation. It has a BIG effect in the off-idle response area..AND in choke-cold starting. Sounds like you know that part already.

The fact that your bike runs much better hot than cold, that indicates a lean condition, too. Shouldn't have to have the choke on at ALL after starting.

Still...other things could be the cause of the way your bike is running...but all the other things can be just fine, and JETTING can do the SAME thing!

Set the main.
Verify your pilot. What's stock in an '89? In the 2 1/2 out area, you're on the edge of a 'too rich' pilot.

Every circuit affects other circuits. It's easy to be chasing the wrong one.

 

[swingarm]

your low speed jet is too fat. Go down one size at a time until the bog goes away. After word you may have to make the main jet fayyer or move the needle clip down. By leaning aout the low speed jet you are taking fuel away from the rest of the rpm range

 

[Matt90GT]

You have to first mark the throttle to find out where the problem lies.

Read this for TONS of help on jetting:

http://www.motocross.com/motoprof/moto/mcycle/carb101/carb101.html

 

[David Trustrum]

Man everyone is throwing their 2 cents in, “It’s rich on the submarine jet” “It’s lean-on-the-post jet”

I’m telling you with the groove on the slide you will have problems. It is sucking air through a part of the carb that isn’t effectively drawing more gas through a jet. Same as an airleak, you can’t properly correct for it with jetting.

Take the bitter pill, I know I had to. Still, -looks like a nice little piece when it arrives in the mail you can look at it for a couple of days.

 

[kc]

WoW - did you ever get it fixed? - i'm workin' on an 89-200 that has EXACTLY the same symptoms.... jettings been perfect for 15 years. Tell me how the story ends...
thanks
kc

 

[cyclebradd88]

I'm surprised nobody has mentioned compression. Low compression should always be suspect with lack of low end power and hard cold starting.
Also, I wonder if there are any temp/quick fixes for that grooved slide. Maybe some epoxy to fill the groove...then at least you can see if that fixes the prob.

 

[Rhodester]

KC, If it's been good for 15 years I would suggest that you have developed an air leak (like a worn out grooved slide). Clean your carb and do a leakdown test (6 lbs for 1 minute). Jetting over an air leak is just a waste of time and $$. What WoWman described is a lean condition induced by an air leak.

 

[David Trustrum]

Epoxy in that groove would be chattered out by the same vibration at idle that originally caused the groove & the epoxy would be ingested through the engine.

Of more concern it may cause the throttle to stick -which is an easy was to have a bad day.