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  1. #1

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    66v - mid range bog & one cylinder seems to run cooler when idling

    I recently rebuilt a 2001 XLT1200. I don't know original cause of failure, bought as a project. New OEM crank. #3 got got a renicked cylinder (U.S. Chrome) and new OEM piston. New OEM rings on all three pistons. Reeds looked good, no gaps. Rebuilt carbs with Mikuni kits. Compression even on all three cylinders. D-Plate. Premix 32:1. Stock jetting, Stock F/A, no air box, breaking it in a little rich, 1.75 turns on highs, 1.25 on lows. Installed primer kit and removed choke plates. Strong ~20mm spark gap on all cylinders. Still have stockl accel pump. Runs 58mph on dream-o-meter.

    I have noticed a couple issues:
    #1: Seems to bog around 25-30 mph, very "throaty" sound coming from exhaust, comes an goes as I pass up thru or down thru that particular speed range. Seems to get worse after engine runs a while. Power seems to surge when passing up thru it right after "throaty" sound quits. Any ideas?

    #2: Noticed when idling for a very short period <20 seconds on dry land, no hose hookup, the #3 cylinder doens't warm up like #1&#2. U3 doesn't warm up at all. Thought it might not be firing at low rpms, obviously it is at high rpms or I'd never hit 58 mph. So I started trying to diagnose the problem. Engine starts and with #3 plug wire disconnected. Also runs with #1 disconnected (#3 reconnected), runs same as when only #3 was disconnected. Engine won't keep running with 2 spark plug wires disconnected but sounds same when any one is disconnected. Sounds to me like #3 is firing but can't understand why the cylinder is not warming up like #1&#2. I blow the water out everytime I take it out of the water. Any ideas? Maybe I'm worrying too much.

    Thanks for any help. Please let me also know if you see any issues with my setup.


  2. #2
    Diznasty's Avatar
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    I'm in the middle of upgrading some carbs myself and from what I have read you need to rejet the carbs if you are running F/A's, removed choke plates and the accelerator pump should be removed. I could be wrong but I think the modifications you have listed requires different jet sizes, different N&S, along with new springs. You might what to double check what you did and make sure its correct because you could damage your engine.

    Have you checked your powervalves to make sure they are opening or arent stuck open?

  3. #3

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    He said stock F/A. You may want to look at the carb for #3 again, maybe you bumped the adjustment for the low screw, or it is clogged up. I had a similar issue on a fresh rebuild that ended up being a weak fuel pump check valve, and not enough fuel to that carb. If you do the restrictor mod, that allows the other pumps to make up for any weak pump in the system. If you removed the chokes you may want to increase the high speed screw to compensate for the less restriction/signal at higher speeds.

  4. #4

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    I based all my carb thoughts on this thread: http://www.greenhulk.net/forums/showthread.php?t=70129

    I'll take a look at the #3 carb again and check out the restrictor mod. Typically my plugs are pretty wet after idling but this is probably because the lows are at 1.25 instead of the standard 1.0. My thought if when idling and shut off and the #3 plug is wet, then it shouldn't be lean. Sorry I forgot to include that earlier. I already have the highs at 1.75, do you think I should open them up more because I removed the chokes? I was wondering if I should put back on the stock air box though.

    Have you got a link to the restrictor mod?

  5. #5
    A child of five would understand this. Go get one. pierowman's Avatar
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    Go to the how to section and the restrictor mod is at the top by Osbill.

    Having the stock air box off is going to allow more air in. This will make the carb settings run leaner not richer. I might consider putting that back in so your settings more closely match. Sure at idle your rich but higher up the curve you may in fact be lean.

    Also make sure you dont have any air leaks on the carbs. Did you check the pop-off when you rebuilt the carbs? These are must do's for proper performance.

  6. #6
    Diznasty's Avatar
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    He said stock F/A with no airbox with no choke plates.....so wouldnt that let more air in and you'd possibly need to re-jet?

    Quote Originally Posted by LT1GMC View Post
    He said stock F/A. You may want to look at the carb for #3 again, maybe you bumped the adjustment for the low screw, or it is clogged up. I had a similar issue on a fresh rebuild that ended up being a weak fuel pump check valve, and not enough fuel to that carb. If you do the restrictor mod, that allows the other pumps to make up for any weak pump in the system. If you removed the chokes you may want to increase the high speed screw to compensate for the less restriction/signal at higher speeds.

  7. #7

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    I've run several without the air box at the front on stock jetting without a problem. Although that is a bit risky if anything else is not perfect, but these PV motors are risky lean anyway on stock jetting. The F/A mods and rejets are a safer bet, and they do run much better. The chokes are a different story for top end. You need to either crank the high screws open farther, or rejet the main jet up.
    Quote Originally Posted by Diznasty View Post
    He said stock F/A with no airbox with no choke plates.....so wouldnt that let more air in and you'd possibly need to re-jet?

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