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420 rebuild running hot

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ok... so as some of you know i rebuilt my 400 this summer and pot the wiseco 87mm, 416 kit.... stock carb (first start was with 60 pilot, 2 turns out, and 160 main, 3000') and went from a xrs only header and exhaust back to stockers with gordon mods 4 holes b/c xrs only header was cracked.  snorkel removed, uni filter, i put in the same old stock cam, new crf chain, tusk heavy duty clutch, kw valves and springs, and an iridium plug, maxima 20-50

 

the thing purrs... runs nice and smooth... starts easily (almost too easily.... thought i didn't have any compression today, but it started right up)...

 

i let it warm up and cool twice one day before taking it for a 10-15 mile low-mid rpm cruise the next day...

 

another day rode it about 30 miles, mid+ rpms... all seemed good... thought temp was "normal" or didn't notice anything... usually runs 200+/-...

checked valves... possibly set them slightly tighter than normal... but could still drag the feeler guage out.... changed the oil to Napa 20-50...

 

next day i went out and worked it up into higher rpms, WOT a few times, road turned kinda sandy still fifth gear... looked at temp about 20 miles in to the day  and it was on 250, teetering over.... mellowed out and went home, pulled plug and it was bright white... lean, right?

 

seems to be 60 is the fattest pilot for the stocker and i ordered all the higher mains... a 162, and 165...

 

put the 162 in this evening and temp reached 240-245 after 5 or 10 miles of 5th gear riding, mid+ rpm... no stumble WOT... get home... white plug...

 

put the 165 in and similar temps... settles in around 240... can barely feel a stumble WOT... plug still bright white, might barely see some gray, not brown though...

 

going to try the maxima oil again... what about the iridium plug? what about no fatter jets and still a white plug?  what happens when you are too lean on the break in?

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Try a normal NGK plug.  For your long desert runs you should try the cooler recommended plug.  Also it's hard to read plugs with modern gas but bright white doesn't sound good.

 

What you want to do is drag race through the gears to top speed, pull in the clutch and shut 'er down, coast to a stop.  Then read the plug.  That's your main jet reading.  The main is more forgiving than the pilot.  You can run a size or two over optimum power to run cooler which I think you are close to.  If you're too lean, it's melted aluminum. 

 

240F doesn't sound bad for an air-cooled engine.  How are you measuring it?  What was it before.

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Everything BR said.

NGK DPR9Z plug.

60 pilot is not the smallest available. You should be able to find a 62 and 65.

My XR is a 440. With running the cooler plug, Two2Cool oil additive, a good quality full synth oil and proper jetting, 220*-230* is typical, with 240* being as high as I ever see with the XRs Only Oil dipstick.

Edited by Trailryder42

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measuring with XRs Only Dipstick....

 

when i was running the straight 397cc with xrs only exhaust and both the pumper and later the stock carb i was always running about 200... 250 was when it would get HOT...

 

i've been drag racing down my driveway holding 3rd or 4th WOT, then doing the plug chop thing, coasting into my shop and then burning the F out of my hand getting the spark plug out....

 

going to try the cooler plug and different oil... guess i'll do the plug first and see if it works, not both at once...

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You write you WOT a few times, and mid+ RPMs, so raising the needle might have more effect then changing the main.

 

I run my 426 with fullsynt, and pumper set intentionally a bit rich, no 240+ temps even in tight hot summer trails.

 

What Maxima oil are you using?

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Did you bore the stock sleeve to 87mm? I'm curious how much sleeve material is left at that point, as you get thin heat transfer is not as efficient. Perhaps this is adding to your elevated temps more than jetting/oil are. I agree on the plug, ditch the iridium plug and go to the cooler NGK.

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Yeah that california needle can definitely make you run lean, if you buy the outlaw racing carb rebuild kit it comes with a needle that is comparable to the 49 state and cheaper than the honda needle.

 

Big bore usually doesn't affect the main jet that much, some guys even go down in size due to pulling more vacuum, but with the CA needle the bike had stock, I hit 270 exterior head temperature!!! The PO ran it like that for 7 years!

 

Although if you want to move over to the dark side the BSR42 is an awesome carb.

Edited by mudguy

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Are you sure about that? If yes, XRs are really indestructible!

Yes through the trail tech. Mind you I am running head temp just in front of the plug. Not the oil temp.

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ok... so i first changed the plug.... no change...

 

double checked the clip... i thought it was in the bottom, it was one above, so i moved it down to bottom... still no change...

 

came back and changed the oil and filter back to a motorcycle one... maxima premium 20-50... still no change... eventually running 240ish at low throttle and pushing 250 at higher rpm....

 

i think i have a stock cali needle... it says A2EA on it....

 

still no stumble at WOT or anywhere making me think its still lean somehow... would like to try different needle and fatter pilot (although i have the fattest rocky mountain offers) first... then send the mikuni out to be rebuilt b/c the slide keeps binding open on me (only when bike is running, 20%-50% of throttle releases)

 

 

i was running the mikuni pumper and xrs only header/exhaust previously, but they both failed and haven't sent them out for repair yet... stocker was reliable and easy for me... i feel like its back where it was when i got it the first time, except for the handlebar controls and a lot more flat spots on the wheels... i get to rebuild it all over again!  i'd like to service the rear shock and find a new wheelset next instead of the power mods i did as a rookie...

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 i feel like its back where it was when i got it the first time, except for the handlebar controls and a lot more flat spots on the wheels... i get to rebuild it all over again!  i'd like to service the rear shock and find a new wheelset next instead of the power mods i did as a rookie...

 

i rode on a rear wheel that was cracked and dented as sh1t... sure was nice to build that new silver excel... i can actually ride it as a DS now without getting bounced down the road...

 

good luck with the heat issue..

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didn't realize they were the same on all bikes... mains are not... the OEM page list a bunch but not those big ones...

 

anyway, might be able to get that local tomorrow and not have to order it...

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didn't realize they were the same on all bikes... mains are not... the OEM page list a bunch but not those big ones...

 

anyway, might be able to get that local tomorrow and not have to order it...

Pilot and mains jets are the same for most Keihin carburetors, Honda just has a bunch of different part numbers for the same part. You can use pilot or main from any fullsize XR, any 4 stroke with an FCR carb (so CRF, KX-F, YZF, RMZ, all KTMs) or most full size 2 strokes that come with a Keihin.

 

Trash the CA needle and then see how its running with the 49 state needle. If its running hot on the trail I'd bet money its from the needle. You aren't going to be on the main all that much. Making the pilot richer is just going to make it hard to start when hot. You haven't done anything to need a richer pilot. Like mudguy mentioned, the bigger piston is pulling more vacuum. The relationship between vacuum and fuel flow isn't linear, if vacuum is increased, fuel mixture will get richer. 

 

Also plug reads are pretty much worthless with pump fuel these days. If its running bad pull the airbox door off and try again. If it gets worse, you're too lean. If it gets better, you're too rich.

Edited by XR250rdr

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I know this is elementary, but have you confirmed your pilot circuit:

 

http://www.thumpertalk.com/topic/271735-how-to-confirm-your-pilot-circuit-setting/

 

On my 250 it's a toss-up between running a 40 @ 3 turns or running a 42 @ 1.5 turns.  The 40 @ 3 seemed to start more often on the first kick.  Like fifteen times in a row sometimes.

 

 

 

240F is only 20-25 degrees warmer than modern water cooled vehicles.  

 

Is the dipstick a new addition that's freaking you out or did it run cooler before the rebuild?

Edited by Baja Rambler

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dipstick is not new... had it for years... always read 200....

 

in my opinion, my xr400 always ran COOLER than modern watercooled 4strokes... only once did i have an "overheating" issue... gas tank started boiling! other than that it always ran cooooooool.....

 

my guess is that its got to be the pilot circuit at this point, can't believe it changed so much...

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i was running the mikuni pumper and xrs only header/exhaust previously, but they both failed and haven't sent them out for repair yet... stocker was reliable and easy for me... i feel like its back where it was when i got it the first time, except for the handlebar controls and a lot more flat spots on the wheels... i get to rebuild it all over again!  i'd like to service the rear shock and find a new wheelset next instead of the power mods i did as a rookie...

If you let the stock carb sit for any length of time, I guarantee you that the pilot is clogged. Even if you can see light through it, it probably has gunk buildup making the hole smaller.

Spray carb cleaner through it and use a small piece of wire to knock out any debris.

I used 60/160 jetting with the 49 state needle, the pilot was a bit rich but kept things cool.

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just put the 62 pilot in... had trouble starting it while 2.5 turns out...

 

went in a turn and it fired up w/half choke....

 

took it for a spin... slower to rise in temp... thought it was settling in at 230ish which was a little cooler, but still got it up to 250 on way home....

 

 

 

currently... with the bike idling at Normal operating temp, 62 pilot,  i can both close the fuel/air mix all the way in and bike still runs.... i can also turns it 5 turns out and the bike still runs... not a whole lot of change in RPMs...

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