Thread: Lean Condition?
04-25-2008, 02:29 PM #1
This is the top of the Mag piston in my buddies SL 750...the hole in the top says lean condition/detonation to me, but the amount of carbon and the color of the top makes it look like it was running rich. Opinions? I say this because on my 96 SLX 780 with 150 hours, I can read the numbers on the tops of my pistons when I look in there with a flashlight.
Last edited by FlSpearhunter; 04-25-2008 at 02:35 PM. Reason: Forgot to post pics
04-25-2008, 03:00 PM #2
Looks very lean with no piston wash...needs to be about the size of a thumbnail.
04-25-2008, 03:18 PM #3
- Join Date
- Oct 2006
- Cleveland OH
Lean on the MAG cyl usually indicates a bad stock fuel pump. Has your buddy installed a triple outlet fuel pump? Has he removed the autocock?, Replaced fuel lines? Cleaned filters and carbs lately? If not, he probably should.
Solid black piston crown is lean. You should have a few clean spots on the crown about the size of a finger nail as indicated above.^^^^^
04-25-2008, 03:29 PM #4
I would also go ahead an remove the oil pump an switch to pre-mix, while you already have the engine out. Thats just my 2 cents.
04-25-2008, 08:36 PM #5
- Join Date
- Sep 2006
Ditto on all of the above. Mikuni fuel pump, go pre-mix. Lot of info on this subject and SBT sites
04-25-2008, 10:13 PM #6
Guess I had it figured wrong...my thinking was the dirtier the piston top, the richer the mix. Thanks for the insight!
We are restoring this machine completely. The carbs will be rebuilt. A new fuel pump will be installed as well as the fuel valve, pickup, and all the lines...if you look close at the condition of the studs and nuts on the cylinders in the pic, you will get a good idea of what the rest of the engine compartment looks like.
We snapped all four bolts fastening the exhaust pipe to the manifold, causing us to have to remove the manifold from the engine inside the hull. We also snapped all but two of the bolts holding down the cooling rail...corrosion was so bad, I don't think the PO EVER did any maintenance.
Oh yeah...just for the heck of it, I pulled the water bypass fitting out to look at the screen...packed solid with corrosion!
I'm thinking we'll be hanging around on Ebay a lot on this one...
04-26-2008, 04:12 AM #7
I'd like to say welcome to the forums!!!
Here is (in my opinion only) one of the best threads on this very subject to grace the net.... and it's right here on the Greenhulk!!! Check it out. It's worth the read!!!
04-26-2008, 05:26 AM #8
- Join Date
- Jul 2007
- Cedar Rapids,Iowa
Welcome too! Pull up a chair and enjoy the school.You've found the best place on earth to learn from the Experts. (I'm still in class,Flunked a few courses). Thanks Crazy A for bring that link back up. That should be a STICKY.(AL,BEERDART, Crazy.... ?) Enjoy the stay,we're all here too help and enjoy in the party.,
04-26-2008, 08:32 AM #9
- Join Date
- Sep 2006
04-26-2008, 01:55 PM #10
Thanks for all the warm welcomes...I've been reading through these pages for a few weeks now and it didn't take very long to realize that ya'll know your s**t! The service manual PDF file was one of the first things I stumbled across and man I think it's awesome that someone would make an effort like that for everyone else's benefit!!! Beerdart, I think it was...that's class!
Crazy, thanks for the link...great thread...even bookmarked it for later reference...
I'll keep ya'll updated on our rebuild...for now I gotta yank the pump off my wife's SLT...I think the stator bearings are burned up. We were out this morning and she couldn't get it over about 5000 R's and it was making a racket from the back. When I got it home, I went thru everything enginewise before I realized when I pulled the sparkplugs and turned the driveshaft by hand, I could here the impeller grinding into the stator housing. When you look up in there w/a flashlight, there is day light between the impeller and housing on top, and none on the bottom. It had to wait until we had a perfect day to ride too!
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