OzVMX Forum
Marque Remarks => Honda => Topic started by: Tahitian_Red on June 15, 2014, 04:41:30 am
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I'm going to upgrade the carburetion on my '83 CR480. I have two carbs I am going to try, the first is an class legal Mikuni TM 38mm and the second is a more modern style Keihin PWK 39mm. I will be running a V-Force reed and an aftermarket pipe. Does any one have a baseline jetting setup I could use for either of these carbs?
Anyone running the PWK on their CR500?
Thanks!
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Well I now have all the parts. I will jet the PWK like a stock CR500 PJ Keihin, as a baseline. Anyone running a PWK on a "modern" CR500? Does the pilot jet need to be smaller in the PWK?
I'm not sure about using the 250 reeds in a 500, but will test them out and try reeds from a CR500 V-force if needed. Anyone have experience with this?
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Well I now have all the parts. I will jet the PWK like a stock CR500 PJ Keihin, as a baseline. Anyone running a PWK on a "modern" CR500? Does the pilot jet need to be smaller in the PWK?
I just tossed the stock PJ from my 1997 CR500, and installed a 38mm Quad-vent PWK airstriker from a 97 KX250. The bike starts so much better now! Main jet will be close to what the PJ used. You are right in thinking the PWK will like a leaner pilot jet than the PJ did. I'd start with 2 sizes smaller pilot in the PWK than what you were running in the PJ. You may still have to go smaller on the pilot, but 2 sizes smaller than the PJ is a good starting point.
I live at 5000' above sea level in the US. I was running a #50 pilot in the PJ. I initially tried a #45 in the PWK, but it still started hard and was way too rich when the bike was warm. I ended up going to a #42, then a #40, and I've finally settled at a #38 pilot. The bike now starts with 2-3 kicks cold, and will idle within about 60 seconds of starting if the temperature is above 60 degrees F. When warm, the bike still idles great and has smooth, responsive low-rpm power.
Hope this info helps! ;)
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T-Red have you checked out http://www.cr500riders.com/ lots of info on there for you.
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Hoony,
I did a Google search on CR500 PWK jetting and found a few threads on that site. I am just going with the stock CR500 PJ jetting with a few steps leaner pilot. Hopefully that will be close.
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I am going to install everything tonight and hopefully get to test it soon. :)
(http://i1101.photobucket.com/albums/g438/Tahtitian_Red/IMG_2491_zps7fd9b98c.jpg)
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Wish I was there to test ride it ;-)
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I'm fixing the forks next, so she will be waiting for you when you come back. ;)
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Started the bike up for the first time yesterday and it does start easier! ;D ;D
It may be a little rich on the pilot though, but it was also 104 degrees F here. I am looking forward to the first test/jetting session when it cools down a bit. LOL
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Here is what it looks like mounted. I need to loosen the clamps and wiggle it a bit to make it fit perfect in the air boot and add a fuel filter, but it was a pretty easy install.
;D
(http://i1101.photobucket.com/albums/g438/Tahtitian_Red/PWK_V-Force3_zps70fdb31c.jpg)
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was the ohlins shock hard to find ? and is that a standard kick lever or some other? but back to the topic anyway!
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Bought one of the last ones the East Coast (USA) Ohlins guy had, but you may be able to get one from VMX Racing (they were the last place I saw selling them.)
Kicker is from a 90's Honda TRX Quad. I think they are still available form Honda dealers, but I wouldn't use one without the compression release setup on the head.
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ok. good info!
Are you running a flywheel weight as well?
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How did you go with the setup on forks ?
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Sean, Derrick Redding has one of those quad kickstarters on his 480 and an Ohlins shock. You'll see it at conondale.
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ok. good info!
Are you running a flywheel weight as well?
Yes 16 oz.
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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
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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. ;D
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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
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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
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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.
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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.
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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 ;-)
(http://i1093.photobucket.com/albums/i423/JohnnyRacer89/CR480RDGlenHelenholeshot_zps5c1fac74.jpg) (http://s1093.photobucket.com/user/JohnnyRacer89/media/CR480RDGlenHelenholeshot_zps5c1fac74.jpg.html)
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so is the new carb a big improvement on the original PE keihin?
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How's that upgrade worked out?
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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 ;)
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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.
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your going to hell Bill for Blasphemy ;) oh hang on you were going already for collecting Suzuki and Kwaka's.
Meet you there :D
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(http://i155.photobucket.com/albums/s297/Lozza85_2007/006-2.jpg) (http://s155.photobucket.com/user/Lozza85_2007/media/006-2.jpg.html)
Did this 480 yonks ago, the carburation was never an issue. Is there a vmx bike that doesn't need the head sorted :D
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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.
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The motor completely overwhelms the brakes and suspension, which I assume was in a reasonable balance beforehand. Owner was/is mad as a cut snake and too much was never enough, it has a "lot more" than the standard 480, power was smooth and predictable, got many holeshots but would all go pear shaped at the hairpin turn on the second lap(front brake was only good for 1 application). Last I heard from the owner he had sourced a disc for the front, but I think that moved him into another class.
I haven't seen the pipe you mentioned but that pipe is about the correct tuned length for the rpm ceiling
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How's that upgrade worked out?
I was not running the stock PE before the switch. The bike had a 38mm Mikuni round slide with a UFO slide kit.
The carb conversion worked great! The starting and idle to off idle performance is improved (but I did the carb and the V-force at the same time). I started the bike 8 days in a row, using my same routine and it fired on the first full kick each of those times. I am dealing with a PVL issue now and that is why I have not posted recently.
This carb would not be legal for most racing associations where I live, but for the one event I will race it at it should work fine.
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(https://lh5.googleusercontent.com/-HdUzxS7p1tU/VGCjtQIL_SI/AAAAAAAABAk/umVt0RlkRWw/s144/IMG_20141110_180656_561.jpg)
(https://lh5.googleusercontent.com/-MBO8mbgU4AE/VGCjtQY3ZAI/AAAAAAAABAk/udnj1A4sBb4/s144/IMG_20141110_180555_209.jpg)
Here is a pic of the standard and PFR pipe.. pretty different.. I have just blown the dents out and acid cleaned the standard pipe, still to be painted then tried.
the bike is a tractor with the PFR pipe, but not a ball tearer .. but hard to see how the PFR would improve performance, it is 110 dia in the belly as opposed to 100 mm for the standard pipe.
sorry bit of a hijack as you were quiet:
So I have the PE carb. it seems ok. Its easy to start with the decomp, but wasn't nice before I did that.
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The decompression valve and squish band head mods are the single best thing I did for the bike.
The PFR pipe mellowed the hit and the PVL helped to lengthen the powerband. I changed to the PWK carb to improve starting and idle circuit even more. With an Ohlins shock, Simons Link and Cartridge Emulators already installed all I have left is to do is fine tune the front brake.
;)
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can you detail the squish band mod?
the bike I bought has the ohlins. I would like to look at combining the later CRs uppers into the lower legs.
Would like to source the Simons link ( where , how?), but the forks are more of an issue than the back in choppy stuff. All works well on smoother tracks.
The front brake is terrific on mine and the rear brake is pretty dam good too.
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http://forum.ozvmx.com/index.php?topic=35638.0
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I wouldn't be doing that to the squish,that runs against everything a squish band is meant to do.
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Lozza,
Are there other methods to modify the squish on 2 stroke big bores? I have only seen the Eric Gorr method and this RK Tech method:
(http://i1101.photobucket.com/albums/g438/Tahtitian_Red/CR480RKtech_zpsaa784ecb.jpg)
What would be the downside(s) to making these modifications? My bike seems to run fine, but I was planning to pull the head soon and check things out.
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Yes, interesting. What does the Eric gorr method look like?
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Kelsey's(RK tek) head is a different way of doing the same thing. That is create turbulence. When you have a very short time to get an effective burn turbulence is what allows that. Faster the burn time less deto more power. If you want to know what happens at the highest levels of 2 stroke tuning. Works on any engine. full stop.
http://www.pit-lane.biz/t117-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked
You will have to join to see the pics, up to pg 16 it's in French (pics are in English though)
Eric Gorr method is a dual taper squish.
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got me curious enough over the morning coffee to pull out bells 2 stroke book and read his take on 2 stroke heads..
a basic summary with out all the formulas though a 0.9 -1.2mm squish for a 500, and a wider squish band better for torque, narrower for revs, but compensating and checking compression ratios. too many pages for me to sift through now to find pics on that link you have suggested lozza, will look at it later .
I will be checking out my squish dimensions though..
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That RK Tek head just looks like what I did to my 500RE head :-)
Loz, even though the pics are English, they will have a strong accent I feel ;-)
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got me curious enough over the morning coffee to pull out bells 2 stroke book and read his take on 2 stroke heads..
a basic summary with out all the formulas though a 0.9 -1.2mm squish for a 500, and a wider squish band better for torque, narrower for revs, but compensating and checking compression ratios. too many pages for me to sift through now to find pics on that link you have suggested lozza, will look at it later .
I will be checking out my squish dimensions though..
I suggest you put Bell's book under the leg of that wonky table and put the time into reading the link. You will find Frits' Formula to be ideal squish gap is 1% of stroke. The most powerful engines have a "shadow" of the squish band on the piston.That is from the piston almost touching the head in over rev and over run when cylinder pressures are not so high.
Spot the mistake here, granted a 500 isn't about extracting the maximum
(http://i1101.photobucket.com/albums/g438/Tahtitian_Red/Head_Mod_zps85abe594.jpg)
(http://i1093.photobucket.com/albums/i423/JohnnyRacer89/CR500cylhead2_zps2c16fb47.jpg) (http://s1093.photobucket.com/user/JohnnyRacer89/media/CR500cylhead2_zps2c16fb47.jpg.html)
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Lozza,
I am not trying for max power, just trying to eliminate most detonation. ;)
Are there any detrimental effects you know of using the Eric Gorr cut, besides less than max power?
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I know that Jay and Gorr modification will do nothing to lessen the chance of detonation, any effects it does have is from slightly less compression.
Take the time to read the link I posted it will explain it all
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I tried the standard pipe- wow ! seems a lot more snappy than the PFR. No wonder they were putting a flywheel weight on them back in the day. Just a work boot rap in the paddock though... too hot and dry to ride..
Will have to do a trackside compare sometime with both
Tahitian Red - where did you source your simons link + washers?
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sa63 where you based?
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Spot the mistake here, granted a 500 isn't about extracting the maximum
One mistake, if you have an 84, is the suggestion to use a plug mandrell as the turning fixture.
The finnies have an angled plug.
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Spot the mistake here, granted a 500 isn't about extracting the maximum
One mistake, if you have an 84, is the suggestion to use a plug mandrell as the turning fixture.
The finnies have an angled plug.
That's correct now you reminded me of it. Been a fair while but IIRC used the base gasket to close the squish up.
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Spot the mistake here, granted a 500 isn't about extracting the maximum
One mistake, if you have an 84, is the suggestion to use a plug mandrell as the turning fixture.
The finnies have an angled plug.
Yes the 480's and '84 500 are bit harder to do than most heads.
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sa63 where you based?
SEQ