Smartcarb revival

[axel]

Thought I'd write something dirt bike related in this dirt bike forum

So a couple months ago I took loan of a 38mm Smartcarb (cast model). Thought I'd try it in my '08 300EXC and see what the 1/4 - 1/2 throttle performance was like with it. Was actually looking for a PWK38 to try but no one I knew had one to play with.
Was also interested to see if any of the other claims come to fruition - fuel economy, no fuel loss tip-over (good for HE), altitude compensation and so on.

When I received it in a box it was so choked with evap fuel it was stuffed.
Pulled it down completely and ultrasonic cleaned the whole thing in a jar of unleaded.

Emailed Smartcarb USA for the default metering rod position (clicks). They know all about the carb's history from the SN. The purchaser and the original bike it was purchased for (2002 300EXC).
Started first kick.
Left the fuel tap on and the crankcase hydro locked. Advice for anyone wanting to drain the crankcase of fuel - bike on it's side easiest with rag over the plug hole. Make sure kill switch is off and a water hose is within reach to put the fire out (just in case).

Replaced fuel seat and float needle (Mikuni TM38) $50 delivered.

First ride ran very fat. Smokey. 1/4 burble was bad. Road riding particularly showed hunting from 1/4 - 1/3 throttle really bad. Float bowl o-ring looked to be leaking as the dust was decorating the outside nicely. I got about 70km from 9L. Yikes.

Made a float bowl o-ring from a spare head o-ring. See how that goes. Not being a scab or anything but the rebuild parts from USA is US$40 postage. It would all fit in an envelope...

Dialed the metering rod leaner 3 clicks whilst riding around the streets (lockdown) seems to have cleaned up the hunting.

2nd test ride this weekend.

Image

[Motoxfox]

Axel you might consider 'setting up' a test sheet with all the critical test points.
Sounds like there's many. Easier to navigate your way thru.
A few new plugs and go out and run it at the particular throttle / rev setting / light load / heavy load etc.
Run only at each set check point with new plug. Check plug. Make change. repeat.
Once you've got it in the ball park you wont need to replace plug.

Just reading thru my post.....Oh dear.
never mind your prob already about to do this...
Good luck with it. OK, Resume normal transmission.

[axel]

G'day MFox, yes indeed I'll be taking a look at plug readings to confirm the jetting once all the other factors are sorted.
How I didn't foul a plug on the 1st run amazes me.

There are a few un-scientific factors to take care of first:
1) Lean the metering rod until the hunting stops (achieved but tbc)
2) Lean (again) so we maintain idle (achieved but tbc)
2) Make sure there isn't excessive hanging idle, tang-tang pipe bang, bog on big throttle openings. Too lean.
3) Fuel Economy to at least where the old carb was ~100km per tank or better.

Single jet. Adjustable on the track.

After that I'll check with a new plug when I'm reasonably happy. Checking the plug readings on my bike fkn annoying - seat and tank off.

[Motoxfox]

Axel ...I'll see you ala the piss fight to get the plug out of your 300 2T,
And dble it further.
Try getting the plug out on the 250/350 4T Kato!
Even getting the plug cap off required wd40 on the cap so it has a co-efficient of slip on the frame rail above.
And it can only slip the cap off to the right side....wont come up the left side of the frame.
Hoe vey! friggin mattinghoffen engineers had a big pissup lunch that friday arvo when the signed off on the design! hey.

Note I have yet to get the socket ( a special tool comes with bike) onto said spark plug yet.

[axel]

Yes mate I've heard all about it from a mate with a 350. It's like KTM denying that anyone needs to get to the plug for any reason. We have stuff we sell at work like this. Not made to service easily - the manufacturer must be in complete denial that it would ever stop working or have any issues...

Engine dpt discussed offsetting the plug to one side. "Nein, let the frame/chassis dpt deal with that issue"

[axel]

Back to the Smartcarb.
- Bowl no longer leaking, nice.
- Still has a burble off the bottom. Clicked it leaner again mid ride but still not clean. Fuel economy appears to be much better but have to measure it out to know for sure. If it's not getting 10km/L it's not right.
- Making metering rod adjustments on the track is fraught with danger. It's not that easy to feel/hear the click as well as yanking the throttle full on to engage leads to flooding which happened and embarrassment among the riding buddies. Hopefully I get the hang of it, or better still, get it right and have to not touch it again.
- I've clicked it one more leaner and will assess this weekend. Worried about being too lean mid to top end. If I can clean up the bottom I'll check the midrange with a plug check. Top end I'm not fussed - I don't go there much.
- Actually was just thinking I should swap in the green spring to make sure that PV stays shut for longer so it doesn't mess with my changes.

Last weekend before regional opens up 11 Aug!

[axel]

8hrs of riding on the weekend.
Went yet another 2 clicks leaner during the weekend.
Awful burble better but still pronounced as always. I rode a 2015 250EXC and it has the burble too, but hardly noticeable. I'm starting to look at blaming the hardparts FMF pipe and shorty muffler on it now. Will try the standard pipe on it next. Then the standard muffler...
Iridium plug fouled. In it's defense, we did a heap of super slow bush bashing in 1st gear.
Also had 3 instances of what appears to be flooding. Had to WOT kick to start it up.
Idle isn't consistent. Sometimes good, sometimes low leading to stalling if in gear clutch in when coming to a stop.
Annoyed but I'm persistent.

[axel]

Rode near Mudgee up and down some altitude with yet another 2 clicks leaner. Seems quite good now. Idle has come up from the leaner jetting and it won't stall in gear on down hills. I fitted the original long muffler. Burble seems better, probably due to leaning out. Going to put the yellow spring in to hold the PV shut for longer as an experiment.
50km of new plug:
IMG_20211106_141046.jpg

[axel]

Update so far. I've gone some clicks leaner again and things are still looking fine. Very little spooge on the muffler ring and I noticed in the mountains for a 2 day ride (HE Bronze) the coolant temps were high which I think is related to the leaner jetting. Might check the plug and stop there as the cooler months will likely require some richer clicks.
Saturday was 65km and I used about 6l of fuel...

As for the burble, I don't have a green spring so it's yellow for now. Might consider going red again to cover over the burble but it means we will be in band quicker.
I've gone to the original pipe and muffler which has reduced the burble. I'm now to the point where it's there and it's part of the design of the engine. After riding a Beta 250 some months ago I was annoyed that it had no burble at all. It's just a sh!t in tight going that's all. Buy a new bike lol.