CR480 Carb Upgrades

[Tahitian_Red]

ok. good info!
Are you running a flywheel weight as well?

Yes 16 oz.

[Brett_41]

Some jetting specs I have from an old article in Dirt Bike for the 38mm TM on a 1984 CR500. I'll be testing this soon on a 84 500.
Probably a reasonable start for a 480

Pilot             50
Main             350
Needle jet     R-0   Possibly Q-8 R-2 depending on altitude and temp
Slide             2.5
Needle          6FM46
Float Needle  3.5

[Tahitian_Red]

Thanks Brett,

What DB issue is that in?

As a footnote: I have gone out to the garage the last five evenings, gone through my start-up routine and she started right up every time. 

[Brett_41]

DB Feburary 1984 vol 14 no.2. to quote "with the carb switch, the Honda got a new personality. Gone was the raspy power delivery and the hard starting. Detonation and pinging were greatly reduced." I've got one on order as I feel it will be as good as anything for a class legal carburettor.

Brett

[Brett_41]

Also found this in my notes. Again for a 1984 CR500. Not sure where I got it from but it looks ballpark

PWK 38 or 39.5
Main            175
Pilot            48
Needle         1368 for 38, 1370 for 39.5
Clip              3
Cutaway       6
Idle              2

I've got a 38mm PWK quad vent air striker on a 2014 300 EXC. It is easy to tune and pretty much faultless using triple taper Suzuki needles (NECJ). The over rev with the 38 is impressive with no loss off the bottom. Great carby if only I could use one on the 84 500.

Brett

[Tahitian_Red]

That is what I am running except I have a 50 pilot and I am switching to the 48 now (may go down to a 45 but no lower).  I have the air screw turned out 2 1/2 turns and still it feels slightly fat.

[Tahitian_Red]

48 pilot is a little crisper, but this is in the cool of the morning.  I will wait till it heats up and then play with the air screw, but I am probably heading towards the 45 pilot.  Hopefully I will not have to play with the needle too much, although the pilot is the toughest thing to change.

[John Orchard]

Looks like it went ok with the old set-up Jay, as Aussie rider gets holeshot in allpowers 2-stroke (including water-pumpers!) race at Glen Helen  ;-)

[sa63]

so is the new carb a big improvement on the original PE keihin?

[sa63]

How's that upgrade worked out?

[William Doe]

Surely the best carb upgrade for a CR 480 would be to
 
Step 1 Remove the carb from the CR 480 and place carefully on the bench .

Step 2 wheel the CR 480 out to the scrap bin

Step 3 Wheel in a KX 500

Step 4 Fit CR 480 carb to KX 500

Step 5 go out and win races

Even with the inferior CR carb the KX will still be streets ahead of that Fugly CR 

[John Orchard]

Ha ha Bill  ;-)

I read much on the internet about the bad PE38 carb on the 480's & 500's, I have done a few mods to my 500 and the PE38 is working perfectly!

All it took was a re-machined head with a narrower squishband and the mating surface machined .7mm to close the squish clearance to 1.2mm. I also went to multi-taper needle, DGL I think it is? 

I also modified the reed cage to increase flow area by 10% but I don't think this is related to its better running.

[Hoony]

your going to hell Bill for Blasphemy    oh hang on you were going already for collecting Suzuki and Kwaka's. 

Meet you there 

[Lozza]

Did this 480 yonks ago, the carburation was never an issue. Is there a vmx bike that doesn't need the head sorted 

[sa63]

that's  one hell of a pipe! How did it go?I see its a dirt tracker.It looks very different to the ones PFR is making for the 480s -which has  very short  header and quite a short baffle cone when compared to the stock pipe although it is fatter in the mid section.