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  1. #1

    2001 GP1200R - Power Valve Missing?? - With Pics

    I bought a GP1200R a few months ago, owner had tried rebuilding the carbs unsuccessfully. When I dug in I found a bent throttle plate on the center carb and an overall dirty system but nothing crazy. So I did a full cleanup and rebuild and in the process "synced fuel pumps", deleted the accelerator pump, removed chokes, installed primer pump and an overall re-jetted 110/125/1.5 for Riva Filters per the instructions here. Converted her to premix too. Cranked her up and after a few 15-20 second warmup off hose the MAG and Center cylinders were warm but the PTO cylinder was cold. Checked for spark, it was good. Seemed wet inside the cylinder so I think I'm getting fuel.

    I started investigating everything and when I opened up the power valve covers I found that it has the newer style (SBT?) pin retainers on the Power Valves. Great! But... the PTO PV was missing the M4x8mm hex bolt holding it to the shaft. Not great. Further investigation (pulled the head) showed that the lower half of the power valve was just gone. Broken off and MIA completely.

    Miraculously, the piston and cylinder look almost new. There is a tiny 0.5mmx2mm nick in the edge of the piston near the rear of the exhaust hole. And a "scratch?" in the sidewall of the piston near the same area (see pic #2 and #3).

    My question is...

    #1 What should be my concerns here? Just throw a new Power Valve in and go? Pull the rest of the exhaust (stinger is already off)? I don't think any PV pieces could make it into the lower end of the block could they?
    #2 How does that "scratch" look to you??
    #3 Would this whole problem cause a cylinder to not fire (to be cold after a quick run-up off hose)? Just wondering if I need to look at the PTO carb (99% I rebuilt it perfectly) or whether this is likely what my problem was?

    As a quick note, reeds were good, and compression was 120/120/120 when I checked them during the carb rebuild process.
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  2. #2
    butterbean_29512's Avatar
    Join Date
    Sep 2013
    Bennettsville, SC
    You are very fortunate indeed! Lots of times they will crack at the stem, usually caused by heat fatigue. Be sure and check your wash. I would install a new PV and run it.

  3. #3
    jeffg426690's Avatar
    Join Date
    Jul 2015
    Sarasota, FL
    Agree w Jack. I had a pv break and vanish although mine broke at bottom of the stem.
    You may have an sbt motor, won't know for sure until the time ever comes to pull the jugs - sbt rods have sbt embossed on them.

  4. #4
    butterbean_29512's Avatar
    Join Date
    Sep 2013
    Bennettsville, SC
    I missed is a sleeved motor. Nothing wrong with sleeves though, especially since I finally found a guy local to bore them for me!

  5. #5

    Join Date
    Aug 2006
    Missing power valve will not cause it to not fire though, you have a separate issue for that. Might not have as much fuel as you think in that cyl, could be a carb problem.

  6. #6
    Myself's Avatar
    Join Date
    May 2007
    North Central Arkansas
    Agreed. I rebuilt an 800 this summer that was missing both powervalves and had the pv motor unhooked. Owner said it had low hours when they bought it and have never had any issues until this point. After break in they told me how it never had the get up and go that it has now but top end is about the same. I have to assume it had been running with no power valves the whole time they have owned it!!

  7. #7
    I’d guess that the last owner rebuilt it because the power valve dropped and wrecked the unit. He maybe didn’t realise it was the power valve that caused it, hence the reason it’s still missing. No way the power valve has dropped and the unit is still as good as your pictures. It usually totally wrecks the unit when it happens. You will need a new one or it will not perform as it should.

  8. #8
    I am curious if the previous owner has ever gotten punched in the gut. With 120 compression across the board it's sounds like a fuel or spark problem, get it idling again and spray brake cleaner in the suspect cylinder carburetor to see if it fires. The mark on the piston looks okay, what ever made the mark has hopefully been ejected or stuck to the bottom of the crankcase.

  9. #9
    I think brake cleaner will wash every ounce of oil away and dry out in a bad way. Maybe it what some recommend by the looks, but I wouldn’t be doing that. Each to their own.

  10. +1 by:

  11. #10
    Quote Originally Posted by QBhoy View Post
    I think brake cleaner will wash every ounce of oil away and dry out in a bad way. Maybe it what some recommend by the looks, but I wouldn’t be doing that. Each to their own.
    It's a bad habit, you are right to be concerned about this. As an acid test it is quick and convenient cause everybody has brake or carb cleaner around.

    Ironically I thought to myself a couple days ago, "imagine if there was a 2-stroke specific starting fluid that includes lubrication". From the looks of googling, you have to mix your own 2T starting fluid.

    Maybe something like this could be used to store your diy 2T starting fluid:

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