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Old 11-30-2012, 08:01 AM   #6324
Crazy Diamond
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Joined: Aug 2011
Location: Out and about.
Oddometer: 726

Originally Posted by elsalvadorklr View Post
ON THAT NOTE..........................

wtf is going on now

so I went to test ride my oem carb...

first WOT run with plug already in the bike top speed 84mph. The plug came out looking perfect though nice and light tan

during ride down to the flats where I test my bike at sea level I notice my idle has a tendency to hang so Im thinking still lean and I take not of this

after first wot run I decide to adjust idle too...out a half turn so Im at 2 turns restarts nicely twice this way

second WOT run I decide to put the new dpr8 plug in for a real plug chop this with the 152 main. and HOLY SHIT IS IT WHITE! top speed 90mph only ran wot for a mile.

I could not pull top speed or 5th to its max potential, I noticed this before too on the old plug so great.felt like I was yanking on the throttle and it struggled.

I have my pack of jets ready to go, plop in a 155ab jet aka precision engineering jet and wham another pass for a mile or so and my top speed is now 93mph

ok we are getting somewhere...

then I restart the bike and all is good..the bike restarts nicely and no kickback and there is no lean cough and die issue either so I finally decide to do ONE last WOT plug chop

for almost 45 seconds...nice and long at full speed

my top speed is no 98mph same as the mikuni

I look at the plug and is has some chocolate colour to it....just on the strap...finally some color so I say well this is good enough and start the ride back up the hill to my house

I detour on some dirt and ride with great fun about 30 minutes...

I notice at this time that the bike responds and feels great really good acceleration no flats spots and really revvy...

so I come back home all happy and cheerful and check the oil

in order to do this I let the bike idle down for a minute or so and let it sit upright while it idles...

oil is at full so great....check that off the list



I take out the plug for a final looksy just to confirm my seat of the pants jetting and plug chopping and what do I find

A BLACK FUCKIN sooty mess of a new plug...........

now what peeps?

did the minute long idle do this and why would half a turn out do this


is my midrange way fat(where I rode most of the 30minute hill ride up the mountain at) obviously not WOT

to take notice is that my needle is in the second to leanest clip

so one more to go and Im all lean

that just cant be right can it?

please save me folks!

Calm down....

Here are some random thoughts that I'll try to make understandable...

It's all about Suck- Squeeze - Bag - Blow and how the engines brain(camshaft) is effecting it.

From my experences a larger cam makes jetting interesting.

At idle the increase in duration and overlap tends to reduce A/F charge velocity. This decreases the vacuum signal at the carbs venturi at idle. The increased overlap seems to cause the engine prefer a slighty richer A/F charge to run real smooth at idle. The decreased vacuum signal requires a larger pilot jet to be used to offset it. Both are reasons why larger primary jets appear to be needed with the larger cams. The longer intake/exhaust duration shortens the power stroke and compression stroke duration. Basically your engine no longer idles as efficiently, it runs better slighty richer and needs a larger jet to offset the lower vacuum signal/air speed. That's why the idle is slightly rougher. The increased overlap can also allow some A/F mixture to excape at idle making plug readings fun...

At WOT the larger camshaft flows more air at higher rpms increasing the vacuum signal/air speed which will require a smaller main jet to offset the increased suction at the carb venturi. This is because the larger camshaft increases the engine efficiency as the rpm's increase. At least WOT plug chops aren't harder to read.

If you saw a WOT air fuel ratio chart on your bike it would probably start at about 13.5 at low rpm and drop to 12.5 or so after it comes on the cam sweet spot with the right jet.

Don't concentrate on plug chops, Your a$$-o meter is an important tool too.

The needle jet has the hardest job of all. It has to deal with everything in the middle... It is a hard to get a needle spot on. The bigger the cam the harder it is. It runs rich at some rpm/load combos and lean at others. I try to tune it slightly rich when it's "on the cam". I found it to helps keep the A/F mixture from going too lean at lower rpm/high load conditions. The profile of the needle makes the difference.

I say lower that needle any go take an a$$-o-meter reading...

When you start your pig do you kick it fully to the bottom and hold it there until it starts or stops spinning before raising your leg??? Thats how I avoid kickback. I had issues with kickback until I started to do that.

Thats all for now... I hate typing, it hurts...

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