pto plug darker than others???

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srxserge

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Feb 3, 2012
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Quebec, Canada
I have a 2000 srx 700 ohlins and have just about overhauled pretty much everything on it. Is it normal that the number 1 cylinder (pto) plug is darker and wet compared to the 2 others. I know that this cylinder is jetted higher than the others but I adjusted the fuel screw the same (2 turns) and my oil pump is at 19 mm. Do I need to bring back the fuel screw on that cylinder to lean the plug or is there something else. My main jets are 148.8, 147.5, 147.5. I don't know the other jets size as I didn't see a marking on them when I cleaned my carbs. It seems to ride nice like this but it hasn't been out for a long ride since my last test drive. Thanks for your inputs.
 
I just changed this piston and cylinder (pto) and only the piston on the center cylinder after a burn down on my first run. I put used oem yamaha parts that were fairly fresh. I cleaned the carbs out and changed the gas. If I remember from last year, it was a heavy smoker (rich) on all tree as the p.o. had it set up to run that way. I have gone with my own adjustments after the rebuild since my first run I noticed that I was running quite lean at around 100:1, the pto plug was darker than the others even at this setting. The oil pump was at 23mm and I had the fuel screw all at 1 3/4 turn. Hope it's not the rings.
 
I wouldn't go tweaking carb settings at this point. You mention you couldn't read the other jets, my first thought would be maybe it has fatter pilots than needed, that with fatter main your running a little on the rich side. I would try to verify pilot size (should be stamped on side) or replace the plug caps (cheap) that cylinder may have a little more resistance causing weaker spark = not 100% burn. Do the pipes seem evenly hot? Warming up evenly? Being as you had motor apart I assumeing the reeds are in good shape? Only other thing I can think of is maybe that pipe has a little more back pressure (mouse nest?) or that power valve not opening all the way. Have you done plug checks threw out rpm range? Whats the piston wash look like? Lots of little factors can add up
 
No mice nest in pipe since I had them off and painted them, PV are new as are cables from last year (had them out for rebuild), has a brmp can on stock pipes. Plug cap is something to look at as I haven't replaced any yet. My eyes must be going out on me because I didn't see any marking on pilot jets, but at 45 this is normal (no glasses yet). I haven't removed the reed valves but inspected them by peeping through the holes, can't say. As for piston wash, I've read it on this site often but how do you see them? I've looked through the plug hole with a flashlight but that's not convincing. Do I have to take the heads off every time? I haven't done a plug check threw out the rpm range. Motor was only rebuild from base up with new top end gaskets. I did not open base, just cleaned it.
 
Some times any of the jets can be a PITA to read (no glasses yet either LOL) Some times tipping them just right towards/away from light you can read it. There is a write up by Mr.Viper in the tech section on reading plugs and piston wash. As far as piston wash you can get a little flash light (with a bendy head on it) and stick it down threw the plug hole. Moving the flash light around looking past it you can see the top of the piston WAY better than just shining light into plug hole.
 
I've read that write up was very informative. What I really want to know is, since the #1 cylinder is jetted higher than the others doesn't it make sense that it would burn richer or is there something else to understand. I'm going to swap the plug cap with #3 and see if there is a difference. Compression is around 140 on all three.
 
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I was wondering if a slightly out of adjustment float on this cylinder might also be the cause of a foul plug on the #1 cylinder? Also how do you know if a reed is going bad? Thanks
 
[QUOTE What I really want to know is, since the #1 cylinder is jetted higher than the others doesn't it make sense that it would burn richer or is there something else to understand.[/QUOTE]

"jetted higher".....Higher number is bigger jet, bigger jet = more fuel = richer burn. Could be a float adjustment or a leaky needle and seat. Essentially trying to flood that cylinder. As far as reeds they usually chip or crack or even break altogether.
 
the pto cylinder is either, A: jetted richer or B: has lower compression. this is on all yamaha sleds because the pto also has to deal with heat from the clutch. thats why your plugs are darker
 
Thanks for all your comments and help, just got back from riding hard for 5+ hours and it felt great. Since it's Sunday, I couldn't get new plug caps so I taped the old pto with electric tape and also noticed when I activated the choke that it would bind and not go back on the carb for this cylinder. So I lubricated it real good and after warm up verified that it was completely closed. I also put new spark plugs, bought at the dealer for a wooping $42 bucks (for 3 plugs br9ecs). I will be buying them elsewhere from now on. And lastly, I brought the oil pump back at 21 mm. I checked the offending plug back home and it was nice and brown. The piston wash was also perfect so now I'm a happy camper, thanks again.
 
srxserge said:
Thanks for all your comments and help, just got back from riding hard for 5+ hours and it felt great. Since it's Sunday, I couldn't get new plug caps so I taped the old pto with electric tape and also noticed when I activated the choke that it would bind and not go back on the carb for this cylinder. So I lubricated it real good and after warm up verified that it was completely closed. I also put new spark plugs, bought at the dealer for a wooping $42 bucks (for 3 plugs br9ecs). I will be buying them elsewhere from now on. And lastly, I brought the oil pump back at 21 mm. I checked the offending plug back home and it was nice and brown. The piston wash was also perfect so now I'm a happy camper, thanks again.
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Probably that choke plunger more than anything else. The best price I have ever found on the BR9ECS is at Advanced Auto (chain here in the states) Don't know if they have any over there. They do have a website, unsure what you would be looking at with shipping.
 
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