@*&^#^ Jetting

[Wobbly]

Ok, so went for a bit of a leasurely roll around on the drz today ... bike runs great down on the flat, but up the top of reefton it was farting carrying on like nobody's business. Partial throttle at higher rpm was often netting some on-off-on-off action, and I had a few stumbles at high rpm WFO (but not many).

When I did the rebuild I went from a 165 main to a 175, due to the extra capacity, more aggressive cam profiles and cut up airbox (which should net a weaker signal to the carb, needing larger jetting to compensate). In this config it has been running fine down here on the flat.

Recently I raised the needle by a clip position to stop the bike from the surging it had been showing at partial throttle at low/mid rpm. It still does it a bit, but not nearly as much, in fact I was thinking of going yet another clip pos richer again. However, my higher altitude problem seems to have either been from either an ordinary batch of fuel, or from the bike running too rich?

So now I'm wondering if I should go back to the 165 main in preperation for bright, given the altitude difference there... :-k

Thoughts?

[Muzzard]

Go back to the 165, and adjust the pilot air screw in front/underneath the bowl for surging correction.
Try that and see how you go and with the clip in the original position pre rebuild too.

[Flash]

You could always put it on a dyno for 100 bucks and get it right straight up!

[Muzzard]

Dyno's are not going to have hills and dickheads in front doing the stop start deal... :roll:

[Wobbly]

I wouldnt mind doing a run on the dyno with a gas analyser just to get my main jet baselined, but needle and slow jet/air screw will still need manual fiddling. Wish I had got that extended fuel screw after all :roll:

[Flash]

Agreed you can't simulate it exactly, but if you get a good (experienced) guy on it he will get it very close. Better than most.

[Wobbly]

The other thing is that since the rebuild I have done a run up through the spurs, but only the one when I was *cough* running in the new bore ... it seemed to go allright then, although it was a bit cooler from memory. Maybe I'm just on the cusp of bad jetting? :-k

[Cal]

I have the extended fuel screw in mine. As we spoke about, neil, i feel your jetting pain. You only want to pull the carb out of a DRZ as few times as possible, seeings as the hardest dirt bike in the world to work on ;) My jetting pain means i'll have mine out again this week. Hopefully I won't lose any of that arm tearing bottom end that I picked up when I go back to the main that was in it.

[discobob]

When I uped the CRF450 to a 480 the jetting stayed the same, this is due to the extra air being sucked in , also sucking more fuel at the same time - I think ?
The jetting remained the same

[Flash]

2 words for you Neil..... Krooz tune!!! You would have change out $100 bucks

[Muzzard]

I'm with Ben on this one Neil,
Go back to what you had before and see what does/doesn't happen mate.
I am confident it is all there just like Ben said, more airflow..

[rookie517]

mr mighty burned once said

with bigger bore cc bike
When I did the rebuild I went from a 165 main to a 175, due to the extra capacity

u actually lower ya jet size...

i don't quite get it, but i remember it!!

go back to stock size and maybe smaller, it may helps

:D

[Wobbly]

Yeah, the increase in capacity alone probably doesn't warrant the jetting increase, but I thought the greater duration in the cams would ... but then again maybe it doesn't, because there's more time for it to draw the charge due to the greater duration itself :shrug:

Anyway, I'll try her out back to the 165 main and with a 1/4 turn more on the air screw :up:

[Cal]

Got mine sorted tonight. Tears my arms off now.

[Wobbly]

The old main jet and new pilot works a treat then? :up:

[Cal]

Yeah, it rips now. 3rd gear wheelies off the throttle with stock gearing are too easy now and the top end still has plenty. I was more concerned about keeping that bottom end as in the bush i'm always riding it off idle to climb hills and stuff.

[jakestein]

Yeah, it rips now. 3rd gear wheelies off the throttle with stock gearing are too easy now and the top end still has plenty. I was more concerned about keeping that bottom end as in the bush i'm always riding it off idle to climb hills and stuff.

What state of tune is this bike in?
I ask coz if its stockish Neil should be pulling it up on onewheel in 5th :P

[Wobbly]

Except I've got the highest gearing you can get without custom making sprockets ;)

[jakestein]

I am in the same boat as you with the gearing but my bike will come up in 4th with a hefty tug on the bars, seeing me into the 120-130ish shit-myself wheelie :shock:

[rookie517]

how is the stock jetting does?

is it better??

[Wobbly]

I've gone back to a 165 main and gone down on pilot to 2 turns (instead of 2 1/4) which seems to have crispened up the bottom end. Left the needle where it is for the time being. Hopefully should stop my occasional stall problems in warmer weather too. Top end seems much the same, but hopefully it'll behave itself a bit more at altitude.

The big man at TT recommending actually going smaller on the main, down to a 160 or even a 155. Have to pull the carb apart again and order jets and stuff, so won't do it quite yet...

[Sibbo]

Have you done any WOT plug reads?

[rookie517]

bigbore thumper only add more torque instead of more top end power.

hmm, correct me if i'm wrong.

[Cal]

What state of tune is this bike in?
I ask coz if its stockish Neil should be pulling it up on onewheel in 5th :P

That part was a mystery. It has a Staintune muffler. I bought it 2nd hand and it had been jetted by the previous owner. The reason I figured it was out was because I rode Kimo's DRZ and it had more power than mine, especially off the bottom and he has stock jetting and full Pro Circuit system. Mine has an extended fuel screw and also a non standard main. Instead of the usual Keihin hex main, it has a riser adaptor with what looks like a Mikuni round main in it with 140 stamped on it. I'd say it also has either an after market needle or the clip height has been changed. I decided to put a 48 pilot (from 45) and go to a stock (165) main. I had great bottom end punch, but it was way rich up top, stuttering and carrying on. Then I read some more stuff. Fuel screw mostly effects idle and just above. Needle height will effect 1/4-1/2 throttle and main jet will effect 1/2-full (which is where I had the problem). Changed the main back to the bastardized thing that in there and now it's got everything, stomping bottom end, good mid and good high, with no hesitation anywhere in the range.

So the final setup is:

03 DRZ with Staintune muffler
Airbox lid removed and 1 x 63mm hole in RHS as high as possible to avoid water probs through creeks etc..
Twin Air filter
48 pilot jet
Unknown needle and main combo
Fuel screw 2 1/2 turns out

[Wobbly]

You've definately got something interesting going on there cal, as I just had to lean out my bottom end by going for the standard 45 slow jet and running only 2 turns of fuel screw, and its definately more snappy of the bottom now. I'm guessing a different needle is the most likely thing here, or something to do with the exhaust, or maybe the different cam setup on mine :shrug: Too many variables to make any sort of real worthwhile observation no doubt :)

Rook - while you're right about the big bore not adding a lot of top end (since the valves are now essentially under sized for the cylinder volume), the hotcams exhaust cam definately opened up a whole world of top end. And the main culprit for the need to lean the jetting out as it works out, as the extra duration of the cam results in a greater amount of time area for the motor to pull its inlet shot...

[rookie517]

cool, thanks for clarification.