'07 XR 650L Timing


16 replies to this topic
  • gabriel

Posted July 16, 2007 - 07:28 AM

#1

I recently changed out the piston in my '07 XRL for a 10.5:1 piston from JE pistions but now i am getting pinging (or what I think is pinging) at about mid range full throttle. Does anyone have any experience with this and how to remedy it? I was thinking of advancing the timing but can this be done and if yes, how? I i am also running 91 super unleaded. Why would my motorcycle ping with a 10.5:1 when other motorcycles are running higher compression and they have no problem?

  • XR650L_Dave

Posted July 16, 2007 - 07:38 AM

#2

If you left the stock cam in, that could do it.

Its a very conservative cam, which would lead to more effective compression.

Dave

  • martinfan30

Posted July 16, 2007 - 09:26 AM

#3

try race fuel. what about an octane booster? so what has happened with the stock cam being closed(the valves) longer, has bumped eff. compression to maybe 11:1??

  • gabriel

Posted July 16, 2007 - 09:30 AM

#4

try race fuel. what about an octane booster? so what has happened with the stock cam being closed(the valves) longer, has bumped eff. compression to maybe 11:1??


i've tried octane booster but it doesn't do anything, im going to the local airport today to pick up some 108 octane to see if it makes a difference. I called the guy over at xr's only today and he said i shouldn't be having any problems with that piston.

  • Denn10

Posted July 16, 2007 - 10:17 AM

#5

GABE where you live? octane booster is crap anyway if your gonna try race fuel try mixin it 50/50 maybe first ive seen some others that used the 10.5 piston with stock cam and dont remember them saying they had a problem. i was asking them cuz im interested in doing it to mine.

  • gabriel

Posted July 16, 2007 - 10:29 AM

#6

GABE where you live? octane booster is crap anyway if your gonna try race fuel try mixin it 50/50 maybe first ive seen some others that used the 10.5 piston with stock cam and dont remember them saying they had a problem. i was asking them cuz im interested in doing it to mine.


I live in the Inland Empire and I get AVgas from the corona airport, its good stuff (same as race fuel if you ask me but cheaper) but it contains lead. Im starting to think that i may just need my valves adjusted (which I don't know how to do)

  • Rockjockey

Posted July 16, 2007 - 10:45 AM

#7

Has the jetting been changed? Is the mixture correct? Does it ping when cold, or after it warms up? Mixture could have an effect on the heat build up (too lean), too much heat could lead to detonation. You might check your operating temperature and take a plug reading. Detonation (Pinging) occours on acceleration. Loose valve adjustment (Clattering) occours constantly.

  • gabriel

Posted July 19, 2007 - 06:42 AM

#8

Ok, put Avation gas in it (108 octane) and I have absolutly no problem...it actually runs awsome and I can actually feel the power from the new piston! Since I don't have access to AVgas 100% of the time, my next step will be to increase my main jet from 160 to 168...maybe that will enrichen things. In the meantime, im having fun with leaded fuel! :ride:

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • martinfan30

Posted July 19, 2007 - 06:44 AM

#9

Ok, put Avation gas in it (108 octane) and I have absolutly no problem...it actually runs awsome and I can actually feel the power from the new piston! Since I can't run AVgas 100% of the time, my next step will be to increase my main jet from 160 to 168...maybe that will enrichen things. In the meantime, im having fun with leaded fuel! :ride:


how much a gallon?

  • gabriel

Posted July 19, 2007 - 06:52 AM

#10

how much a gallon?


Honestly, Im not sure becuase a family friend works there and the gas was on him. If i had to guess, i would say that it's close to 4 dollars, which is still cheaper than racing fuel (?) and the same thing IMO. Back in the day when I bought it for my two stroke it was exactly two bucks.


NOTE* avation gasoline does have lead in it and don't confuse it with jet fuel (JP), which is closer to kerosene and diesel.

  • Denn10

Posted July 19, 2007 - 07:56 AM

#11

I only asked you this cuz i worked as an engine mech with General Atomics, they build the UAV drones for the military, and we had Rotax engines in our first smaller planes and when i did engine rebuilds the buildup from the AV fuel was alot! We had forged pistons and used walnut shell in our media blaster and i would clean piston tops and ring groves with that and in only 300 hours of run time the buildup was alot more due to the av fuel. Just some FTI info i know i will never use AV after seeing how it burns thats the only reason i threw out the 50/50 race/pump combo.

Im up in the desert from ya in Apple Valley your valves are pretty easy to adjust you just have to get the tank off to get to them and open the covers and check with a feeler gauge.

  • crmc33

Posted July 19, 2007 - 08:11 AM

#12

I run a Wiseco 102.4mm piston with small dome XBR500 hi comp head and HRC cam. It doesnt ping with 98 or 99 RON.
Not tried with 95 yet.

Octane booster should sort it.

  • gabriel

Posted July 19, 2007 - 08:21 AM

#13

honestly, im starting to think that my while pinging problem with pump gas is becuase im runnin' too lean. im going to change my jet from 160 to 165 and see what happens. I do love the way the AVgas runs though.

  • Rockjockey

Posted July 19, 2007 - 11:22 AM

#14

I'm using a 170 main at 600ft in the XRL. I use Avgas 101LL mixed 50/50 with superunleaded 93 in my 440 for enduro work and have never seen any deposits on the piston or valves.

  • kellismechanic

Posted July 19, 2007 - 02:41 PM

#15

Gabe,
I have a 96 600R with a 650L cyl and JE piston, with a hotcam, I do have more engine noise that resembles a ping, you might have a leak in the head gasket, mine did, if you have the fiber or paper gasket, change it to the all metal one, the fiber ones are wrong, and I would retorque the head to 30 to 32 ft/pounds, instead of the 25 in the book, that sealed mine up great and no more noise, oh, make sure the valves are adjusted correctly, stock cam should be .004 on intake, .006 on exhaust, it's simple to do, but follow the book if you have the auto decom still installed.
Good luck bro:thumbsup: :prof:
Oh yea, you can't change the timing, that is done in the CDI box, can't do it without changing the box

  • HawkGT

Posted July 19, 2007 - 10:20 PM

#16

...I was thinking of advancing the timing but can this be done and if yes, how?....


I'd say an ignition timing change is probably not the best solution. However, you'd actually want to retard the timing to alleviate a knock problem. Perhaps you could do it by making you're own woodruff key for the flywheel. I know on the XR400 there are woodruff keys that are machined in such a way they advance the timing. It's probably possible to do the opposite. If you twist the flywheel one way or the other on the crank you can advance/retard the ignition timing.

As XR650L_Dave hinted at, you might look into a cam swap to lower the dynamic compression. Your static compression (10.5:1) won't change. But static compression isn't what really matters. It's the dynamic compression that matters and the timing of the intake valves' closing plays a key role in that. HotCams makes a reasonably priced drop-in. I don't know the stock cam specs so I couldn't guess at the dynamic compression drop--but it's a fair bet the HotCams cam is quite a bit more aggressive. That will lower the dynamic comp.

You could also try doubling up on your base gasket (or find a thicker one--ask Cometic what they've got to offer). I wouldn't call that an ideal solution (especially doubling a gasket), but it will lower the compression. It doesn't seem like gasket thickness would make a substantial difference in compression--but it can.

FWIW, it doesn't surprise me all that much that a 10.5:1 static comp piston in an XR650L might knock on pump gas (especially 91). It's air cooled, has a large bore, sees a lot of high-load pavement use (generally), and we're in the high intake temperature time of the year. I had a 87mm bore RFVC Honda engine with a 10.8:1 piston and a fairly aggressive cam that knocked unacceptably on Phoenix area 91 pump.

Bear in mind that the octane rating we see on the pumps is an imperfect gauge of knock resistance. Different 91's from around the country are going to perform slightly differently despite having the same rating. We don't ever really know the MON rating of our pump fuels and that's really a better measure. The particulars of the (perhaps) several dozen fuel blends around the country will make some more sensitive to intake temperatures than others. That variable isn't captured especially well in the octane ratings we use. And there's other stuff along those lines too....

With luck the issue can be reduced to a manageable level with correct jetting. Let us know what happens. :ride:

BTW, 100LL is 99.5 MON (that's the minimum spec--101 or 102 MON might be typical). 100LL is not normally tested for RON, but the one instance of 100LL RON testing I'm aware of had it at about 107. That would put 100LL at or just under 105 when put into the terms used for pump gas (MON+RON/2). Not sure where you're getting 108 from [shrug]. Info only. :thumbsup:

  • gabriel

Posted July 20, 2007 - 08:01 AM

#17

[quote name='HawkGT']I'd say an ignition timing change is probably not the best solution. However, you'd actually want to retard the timing to...QUOTE]

Hey thanks for the info Hawk, i appreciate that...i think you are right, i believe that i can get the pinging to an acceptable level or eliminate it through proper jetting, from what im getting, i think im still runnin' a little too lean. I'll keep the thread updated. Thanks again. :applause:





Related Content

 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.