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LazerCow

WR450F Carb on a '98 WR400F. A trail of Breadcrumbs for the next person.

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Hi All! I wanted to share a noob-perspective tale of carberuation and old Wr400f modernization.  This post is about putting a much more modern aftermarket Chinese wr450F knockoff carb on a '98 wr400F.

I recently bought a '98 wr400F secondhand. It has clearly seen many years of hard use. After replacing tires, fluids, stripped bolts, chain, sprockets, oil, etc, and doing a road-legal dualsport conversion on it, I started to get an aggressive bog/dead spot above 1/2 throttle. Long story short, this progressed to not even starting. The carb was messed up.

After some reading about the nasty failure modes and general difficulty of the stock wr400F carbs, I decided to drop a little more coin to upgrade to the modern wr450F carb.

Because i'm poor-ish, and not about to drop $1000 on a carb for a $1700 bike, I went the chinese knockoff aftermarket route. Bought a brand new "OEMSTD" chinese knockoff carb from "wincycles" through Ebay ($190). Great! I thought. It said it was already set up for this bike. Drop it in and go, right? 

Ha.

Here is my tale of learning:

When you pull the old carb, there is a vacuum port on the motor side that needs to be blocked. I did this at first by bending the tube over, crimping with pliers, and using a Zip tie.

If you do this conversion, you need new throttle cables, the ones for a wr450F. The ones for the 400 will not fit the new carb. Learned that the hard way.
The jetting _DOES NOT COME CORRECT RIGHT OUT OF THE BOX_. Couldn't get it to fire at first. Changed the spark plug out of frustration (which was on my to-do list anyway). That didnt help.  Guess it's time to actually learn something about how a carb works. Damn.

There is a fuel/air screw right next to the bowl that is key to the functioning of a carb. After immense frustration, and futzing with the fuel screw, new carb on, I could get it to run (poorly) with the choke on. It died the second you turned the choke off.

The absolute best $11 you can spend is on an aftermarket adjustable fuel screw. Got one of those. After some reading, everyone seems to agree that on the WR450 carbs, the JDJetting kit is the cats meow. Plenty of (not terribly helpful) shit talking in the forums about chinese jets.

So, I order an adjustable fuel screw, JD jet kit, WR450 throttle cables, a billet hot start thingy to eliminate a potential fail point, and a hot start cable and lever (which wasnt a thing on the wr400Fs but apparently is on the 450s.)  BAM!  THAT should so it! Right?

Wrong.

Pull the carb, put on all the farkles. Follow the JD Jetting instructions to the letter for my temp and altitude. Reassemble the bike. Kick, kick, and kick again.... nothing. With choke.... without choke...  every combination of fuel screw position....    Nothing.


I am Jack's frustrated rage.

I literally kicked a hole through the soft sole of a pair of cheap Sketchers I was wearing in the garage.

It (sort of) ran with the Chinesium pilot jet on, so it's definitely the jetting.

 

The cheap Chinesium OEMSTD Wincycles carb is so cheap that it did not even have the size stamped on the pilot jet that it came with. So I have no idea what size the pilot or main were that came with the carb. There was zero documentation or stamping that came with the kit. "Here's a carb! Good luck!"

Shit. Time to buy a whole range of jets and start guessing. The 48 that the JD kit came with is very clearly wrong. But in what direction?

Back to Ebay, order a whole range of pilot jet sizes. While i'm at it, I might as well block that vacuum port properly. If you dont want to buy a grab-bag of 80 assorted vacuum caps that you will probably never ever use again like I just did, you need one 7/32" cap.

Thank the Lord, swapping pilot jets is easy and doesnt require removing the carb. IF you have the right tools. I bought a small inspection mirror on a stick, and a small Craftsman thumb size screwdriver that took adaptable bits, and a longer flathead screw bit to fit in it (that pilot jet lives pretty deep down in there in a skinny hole). $15 well-spent.

The bowl drain screw on the Wincycle OEMSTD carb was cheap and possibly overtorqued. Despite great care, it wanted to strip rather than open, so I had to just straight-up open the bowl while still full, which made it a messy job. (17 MM socket BTW)

I guessed, and threw in a 42 jet.

 

Bingo! Fired right up no choke to a high idle 4th or 5th kick with the fuel screw starting at 1 3/4th turns. Backed the fuel screw down to about a 0.5 turn, where it seems to now be sitting at a nice friendly happy idle. (it dies if you take it fully closed)    64 degrees outside at about 850 feet if anyone cares.

I now need to ride it, and see what sort of additional carb-related hilarity ensues.

 

SO! For anyone else thinking of doing this, here are the things I have learned (so far):

In addition to the Chinese knockoff carb, you will need an adjustable fuel screw, WR450 throttle cables, one 7/32" vacuum cap, and a 42 pilot jet at a minimum. If the pilot is wrong, then the main is also suspect. May as well just buy a kit with a range of jets. The stock carb jetting is all wrong, and the JD Jet kit _WILL NOT WORK ON ITS OWN_ on a converted wr400f (the 48 pilot is too large). 

I will reply to this thread with any additional learning that I incur as I take this out for a ride with my buddies tomorrow. I anticipate my main jet will be not quite 100%, but wont know till I ride it.

I hope this saves somebody multiple days of grief and aggravation in the future, and perhaps assists someone similarly totally new to carbs who wants to modernize their wonderful Yamaha wr400f, eliminating that potential failure mode with the stock carb that sends metal slide bits into the whirley parts of the motor.

If any carb geniuses want to weigh in with thoughts RE the main/needle, your input would be appreciated. Per the JD instructions, i'm currently on a 168 main jet, red needle in 4th clip position.

 

Oh, and OEMSTD/Wincycles, if you read this, would it really be so hard to include a few instructions/documentation, and go to the not-even-negligable expense of stamping the sizes on your jets? And also, fix/dont overtorque your bowl drain screws.

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Um yeah I am not a fan of Chinese knock off carbs for the reasons you are having. I have jetted many many carbs but I wouldn’t work on the China stuff. I just don’t like stuff that can even vary from carb to carb and isn’t built to great standards. So no offense in your buying it but your seeing the hassles. 

I have seen and had friends buy Chinese carbs and none of the jets from my perfectly jetted Japanese carbs worked in their carbs. Even the more expensive OKO carb that is suppose to be a good copy of a 28mm PWK Keihin is not and ends up using different jets. The part that really hurts is you can have someone perfectly jet a carb list the jets on the web then buy a Chinese carb and nothing works. There are some Chinese carbs that are really bad by the way and it could be very difficult to make them run decent. 

The only advise I can give you is to get many jets if the bike doesn’t run right. Determine where in the throttle it isn’t working right and change it. You can put a mark with tape on the throttle gripe to determine if it’s 1/4 1/2 3/4 and so on throttle. Sometimes putting in a jet three sizes big or small tells you what happens or what that circuit in the carb does. But be sure you are working on that part of the circuit so you don’t get lost. I always start with getting the pilot jet right first.

Good luck, remember if all else fails you might be able to buy a good used factory carb. Then use jetting that others have known to work. 

 

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Thanks. I tooled around the neighborhood a bit after the initial post. 0.5 on the fuel screw was too low. Setting at 1.75 turns seems to be just right. No more popping on decel and it's purring like a kitten (mountain lion kitten).

Just took it for a short highway-then-dirt-then-singletrack test ride up Nestor peak, and it's running better than it ever did on the old carb. It might have a very VERY minor hesitation when cruising at high speed on the highway doing 60 at 1/2 to 2/3rd throttle?  Or it might just be wind and PTSD in my head from the problem I was having before with the stock 400 carb. Its smooth through the whole powerband, and it's totally happy at WOT, though I do see myself doing the throttle stop mod in the future.

Seems like the 168 main is working just fine.

I couldn't find anything online about jetting from those that have done this conversion before, especially w the Chinese carb. Hopefully this will help give someone else a good starting point. Seems to be working brilliantly now. Big offroad ride tomorrow with some buddies. I will post if I discover anything wonky.

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On 10/19/2018 at 7:12 PM, LazerCow said:

Thanks. I tooled around the neighborhood a bit after the initial post. 0.5 on the fuel screw was too low. Setting at 1.75 turns seems to be just right. No more popping on decel and it's purring like a kitten (mountain lion kitten).

Just took it for a short highway-then-dirt-then-singletrack test ride up Nestor peak, and it's running better than it ever did on the old carb. It might have a very VERY minor hesitation when cruising at high speed on the highway doing 60 at 1/2 to 2/3rd throttle?  Or it might just be wind and PTSD in my head from the problem I was having before with the stock 400 carb. Its smooth through the whole powerband, and it's totally happy at WOT, though I do see myself doing the throttle stop mod in the future.

Seems like the 168 main is working just fine.

I couldn't find anything online about jetting from those that have done this conversion before, especially w the Chinese carb. Hopefully this will help give someone else a good starting point. Seems to be working brilliantly now. Big offroad ride tomorrow with some buddies. I will post if I discover anything wonky.

Ya Chinese are to big a hit or miss. For that price u can pick up a used honda crf450 carb. Preferably 06 and newer. Its 1mm larger in size. Helps immensely especially if your not stock intake or exhaust. Minor modifications to make it happen is just the throttle cable. I went down to just one cable on my WR and it worked great for racing. Was a rocket after that. 

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Another clue emerges for folks putting this OEMSTD Chinese wr450 carb on their wr400f. I was noticing some significant hesitation at partial throttle, roughly 1/4th to 1/2, while cruising on the highway. It seemed to get acutely worse at higher altitude and colder temperatures.

I also had the bike overheat on me pretty significantly during a long partial throttle somewhat technical singletrack hillclimb. Both symptoms of a lean needle. 

I had to pull the tank anyway to replace a leaky fuel petcock, so I figured while I am at it, I might as well adjust the needle. Went down one clip position from 4 to 3 on the JD red needle.  It TOTALLY CURED the hesitation and no further signs of overheating. So for anyone else doing this swap, I would recommend a richer needle configuration than is recommended in the JD jetting instructions. Go with a #3 clip position vs a #4.

Riding between 400 and 3000 ft in 50-60 degree weather.

 

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Oh, and I went ahead and removed the hot start lever and cable entirely. Have no problems at all starting the bike while its hot, so it was just taking up space.

On an 80 mile extremely varied ride yesterday it was running perfectly and very smooth at all speeds and throttle positions. It does seem to be down slightly on peak power compared to the original wr400f carb. That is likely fixable with the throttle stop mod that folks have talked about at length here? I'm not in a hurry to do that as it's already putting out more than enough power for my dual-sport playtime needs.

Edited by LazerCow

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More learnings to pass along. As the cold pacific NW weather hit, the bike got more and more troublesome to start, until it just wouldn't. I begrudgingly rejetted today, pulled out the 42 pilot and swapped in a 45 pilot, and it fired right up first kick. 46 degrees outside.

Also, my overheating issues on long partial throttle climbs seem to have persisted. Symptomatic of a lean condition.  I swapped in the JD Blue needle, which should richen the whole lower end of the throttle band, and at risk of running super rich, stuck it at a #2 clip position. Only did a minor shakedown ride so far, but seems to be dramatically improved, and may have even found a few of those ponies that it felt like I lost when I swapped away from the stock 400 carb. Tellingly, when it was totally cold and right after I kicked it, I tried cracking the throttle a little before it had warmed up. Previously this would tend to kill it before it got warm. Now it seems like a nice smooth linear response from cold idle into low partial throttle without the tendency to die out it had before.

More clues for those rocking the chinesium carb.

Cheers!

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I wonder how much of your troubles is just from the fact that youre using a carb set up for a 450, on your 400 😯

Also,  most carbs requires a little tinkering, and not everyone ends up with the same settings.

Keep up the good work, and I hope you'll sum op the final settings, for others to use in the future 😃

Edited by Jens Eskildsen

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