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  1. #1

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    Cylinder #1 running lean

    What can cause cylinder 1 to run leaner than the rest of the bunch, besides a wrong jet? Cylinders 2 and 3 look beautiful (look like they're a touch rich, which is how I want them) but cylinder 1 looks lean (black all the way across the piston top, swirl marks are very tiny and I had to search to find them.

    That's the problem for those that are in a hurry, those of you that don't mind lengthy, detailed posts, please continue reading for more details.

    I just recently got going again with a new (to me) used 1300 motor in my GP1200R. Motor is "stock" inside except these cylinders: http://greenhulk.net/forums/showthre...ight=cylinders

    Exhaust is stock 1200 stuff, carbs were rebuilt and rejetted, pressure tested, all that jazz. Got flame arrestors and converted to pre-mix. So stock 1300 motor, decked cylinders with the ports "cleaned up", 150ish psi, 115 pilots, 135 mains. pop-off matches across the board (don't remember # off the top of my head), leak test passed. Stock impeller, stock ride plate, stock exhaust with homemade "free flow" mod, 1200 riva/R&D intake grate, waveeater clips and couplers, pump tunnel reinforcement, tiny tach, and flame arrestors.

    I got it broken in a bit, have about 5 hours on it now. I've still been trying to vary the throttle a lot and avoid leaving it pinned. I've been trying to get everything tuned in right, so i've been doing a lot of playing around and a lot of removing of spark plugs.

    Lows are set at 1 turn out. That may be a bit rich, it loads up a bit when it's been idling for more than about 30 seconds. If it only idles for a second, it jumps out of the hole cleanly and runs great.

    At top end, I tuned them for top RPM and backed them out another quarter turn, then I gave the rear one an extra quarter turn out to keep it from overheating (correct me if i'm wrong, but I've read that the rear cylinder doesn't cool as well and should be run a little richer to compensate). This resulted in (front to back) 1.25, 1.25, 1.50 turns on the highs.

    Seems to run well, except I'm only getting about 61 mph top end. I've also been pulling the plugs and looking in the cylinders between runs, and I've found that the front cylinder looks like it's just too lean. The middle and rear cylinders look beautiful, they're definitely rich enough but don't look too rich. Based on looking at the patterns on the top of the piston, they're right where I want them. The clean areas are good sized, bigger than they should be for optimum power but not so big as to indicate an overly rich condition washing down the cylinder walls or anything. Front cylinder is brown all the way across, with little tiny clean marks that are small enough that they may just be the reflection of the bridges across the ports in the cylinder wall.

    I plan to pull the carbs back out and take a closer look at #1 to make sure I didn't do something stupid like put a stock jet back in it, and to verify that everything went together right. I will inspect the reeds and check all the gaskets at that time. Is there anything else that could be causing these problems?

    Only other potential issues that I can think of are 1 - head gasket is suspect. It looks fine and I don't see any evidence of leaking but it's been on and off a couple of times. 2 - carb gasket, the spongy one that seals all 3 carbs has been reused a couple of times. I've used a liberal amount of gasket dressing on it each time. I have a new head gasket to put on, but I wasn't going to do it right away. I want to get everything dialed in if I can and get a few hours on it, then pull the head to inspect everything and check for wear. I was hoping to get 10-20 hours on the new motor before doing that.

    Also - why am I going so slow? 61 mph with nearly full fuel, my fat ass (225 lbs) and most of a six pack on board. Prop is stock but revs are only getting into the 7000-7100 range. Prop appears to be in good condition, no excess clearance between prop and tunnel, pump shoe is sealed, pump tunnel reinforced, ride plate is not sitting proud of shoe, shoe is not sitting proud of intake, and all the joints are caulked nicely. I went this fast with the 1200 motor, I was expecting at least 65 with the 1300.

    Thread from when I blowed it up and fixed it:

    http://greenhulk.net/forums/showthread.php?t=97901


  2. #2
    Its better to burn out than fade away christian79's Avatar
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    When you remove them let us know what the pop off is set to. I believe bill said that if it is too high then the carb will starve. Also did you drill out the restrictors and put in a 90 main jet to balance the returns?

    Lean Condition will arise from;

    Leaking Crank Case (Tested and Passed)
    Clogged Carbs (Cleaned and Rebuilt)
    Incorrect Pop Off (?????)
    Incorrect Jetting (Check Bills and Ferchos posts. But I think that is right)
    Not Enough Turns on the High Speed

    Let hope that others chime in also.

    Keep Us Posted and check the compression to see if you have done any damage.

  3. #3
    All hail the Chief! fullboogie's Avatar
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    Do you know your fuel pressure? The carbs are fed from #3 up to #1, so a fuel pressure/starvation problem could manifest itself in #1 (the last one to receive fuel from the feed line).

    Don't ever reuse the crappy spongy carb gaskets. They are bad to begin with, so get some new ones. Check air leaks as already mentioned, and go through the carbs.

  4. #4

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    I'll order some new gaskets. Problem is nobody local stocks this stuff so when i'm wrenching and I want to ride "today" I end up reusing stuff.

    I didn't do the return jet thing to balance the fuel pressure. Do I really need to?

    I have no idea what fuel pressure is. The fuel pressure gauge I have is not suitable for measuring it on a PWC. Low fuel pressure is a possibility, but the "fuel pump" should be good since I just rebuilt it (part of the carb). I suppose there could be a restriction in the intake line somewhere. Any good ideas on how to check that?

    I got 80 gram springs and 1.5 needles and seats so that should be 38 psi popoff. When I tested it I was close to that but not dead on, I can't recall what it was exactly. All 3 were close to each other, within 1-2 psi. That was a messy, pain in the ass test, so i'd like to avoid repeating it if I can.

    Jetting and needle settings seem good on #2 and #3 though, so that means air leak at the carb, wrong jet (maybe I put a stock one back in or something stupid like that), low fuel flow, or pop off on that carb went terribly wrong on it's own. I should be able to see evidence of an air leak when I tear into it. I'll check the jets, and i'll probably break down and test pop off too. And I'll probably take a good look at hte fuel pump side of the carb as well.

    Damn it. Why can't anything just be easy?

  5. #5
    All hail the Chief! fullboogie's Avatar
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    I feel your pain, bro. I just lost a brand new engine because of a pin hole in the #3 pulse line. At least you have the opportunity to fix the problem before it implodes.

  6. #6
    YudLuz2's Avatar
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    Everything sounds ok on your setup as far as jetting, I figure if anything
    your rich on your carb settings. If its a good stock prop you should be able to turn it over 7300 rpms. Which would at least get you close to 65 mph. Is your bottom end used? if so I would have a close inspect of your crankshaft, you could have lower end problems. Are you using GPS?

  7. #7

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    I'm going to look really closely at the pulse lines, and probably just replace them anyway. That's one thing that could definitely cause a lean condition up top on just 1 cylinder.

    Other folks were saying these settings should be a bit rich, so I bought 130 jets at the same time figuring I could swap if necessary. But the 135's seem right. I don't want to have too many turns on the high speed screws as that can cause a lean siezure just off WOT, according to what i've read. I'd rather have the jets a little rich and not use much (if any) high speed screw. Based on what some other forum members said, I was almost expecting to be at less than 1 turn out.

    Whole motor is used, bottom end doesn't have too many hours on it though. I didn't tear into the bottom end at all before install, but it does turn freely, there doesn't seem to be any play in the rod bearings or anything that I can check from outside the motor. I got the whole thing from treemoney on here. He said the bottom end only has 30 or 40 hours on it, the top end had 10 hours or so and one of the cylinders (#2) had zero hours. Add another 5 or so since i've had it together.

  8. #8

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    Everything in the carb looks good. Pulse lines look fine. Pump side looks good, jets are right, nothing amiss. No evidence of an air leak. I used some gasket dressing when I put it back together and i'm pretty confident that it was still sealed up good when I took it apart. That goes for the big gasket and the little gasket. No apparent problems with the reed valves either.

    I ordered new pulse lines and gaskets from boats.net. I think the one gasket will get here tomorrow so i'll use that. the rest of it's on back order so I'm SOL. I'll put it together with the gasket I have and use automotive line to replace at least that one pulse line just to be on the safe side.

    Only other thing I can think of is mediocre fuel availability from the tank. Any ideas how to chase that down?

    I really want to have it together this weekend. I have a 4 day weekend and if I can get a day when I don't have people clamoring to go boating (preferably females) I want to blast around on my ski.

  9. #9

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    Fuel filter had crap in it. Not sure if it was clogged or how much it was restricted, but when I turned it over chunks came out so i'm going to try to replace it today. Hopefully the local place has it in stock, they open in 10 minutes. If not i'll be calling around. I want to ride that fucker today. 4 day weekend and i'm sure i'm going to have passengers clamoring for a ride on the real boat the rest of the weekend, so i need to get my riding in today!

  10. #10

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    I put about 40 minutes run time on it yesterday, and it #1 is a little richer. How long does it take for the piston wash to really start to show? The carbon is cleaning off a bit, but it still doesn't look as rich as it should. Should I give it some time to catch up to the other 2, or give it another quarter turn richer on the high speed? It's already a quarter turn richer than #2.

    Also found a little bit of scuffing on #3 cylinder wall. Not pleased, but hopefully it isn't bad. All I can do at this point is run it like I stole it. No time left in the season to worry about that. Hopefully the marks in the cylinder wall just look worse because of the angle i'm looking at them through the bore scope. Piston doesn't show any damage and I can't see the ring. Maybe the grooves will just help keep the ring from spinning.

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