I have a 50hp mercury blue band outboard, that I installed on my boat myself.
I have had a problem where it's not getting much power at full throttle, I have tried adjusting the cables but to no avail, and when I'm at full throttle and move the carb by hand it throws a lot more power out.
see if the throttle lever on carb is adjustable as my 70 HP carb. (Upper) the screw may be lose and thus taking all the cable when trying to adjust it. There is quite a bit of movement on mine and if it where lose then i would think that would be a cause Butterflies are not opening fully. look into the carb throat and give it full throttle to see if this may be the problem. JMO
If you have the controls moved fully forward and there is still more movement that can advance the throttle body then it has to be either the kNurl at the cable end connecting at the motor or at the other end within the controls. They both screw in and out. Th other possibility is the stop screw on the power head that limits the advance.
What year is your motor....this will help to figure this out. Do you have a manual?
disconnect all cabling. Try to figure out how much more cable movement is needed to open the butterflys on the carbs. Then try to figure out why the cable won't move the required distance. Adjust whatever part you must to eliminate the distance that the cable must move to open the butterflys. Hook it back up and try again. What year, serial number is the motor?
i found this post interesting and helpfull.by Clams Canino.
Manual specs are different for each but this is close enough to get them all REAL close. This assumes nothing is broken or "wrong" with it. This also assumes that the timing pointer is properly adjusted (if adjustable) to accurately read TDC of the #1 piston.This basic procedure will work for all the 2/3/4/6 cylinder inlines from 1960 to 1988. It's not for the newer 3 and 4 cylinder loopers.Engine offDisconnect throttle cablePull throttle arm to full throttle and verify carbs open fully. Adjust main throttle stop so that the carbs are JUST hitting thier own little throttle stops. The idea here is that you want the screw stop and NOT the carbs acting as the "final stop" for your throttle lever.Return the throttle to idle, carbs should be closed. Set all idle screws to 1 3/4 turns out from lightly seated.Remove all plugs except #1, hook a timing light to #1. Then follow the narritive.When the throttle is in the idle position the carbs should be fully closed and the ignition retarded. It is the amount of retardation that determines your idle speed and is set later with the idle stop screw. Timing Event One - throttle pickup.As the throttle is advanced, the spark timing advances toward TDC and then to before TDC. As the timing is just passing TDC the 1st (minor)throttle pickup should hit and start to open the carbs. Use the timing light. Adjust the tang or trigger screw to make this a reality. All of them are speced different, but if the 1st pickup hits at 3-4 degrees BTDC advance - you win. Use the timing light with a friend cranking it to complete this setting.Timing Event Two - max advance.As you continue to advance the throttle the timing will advance while the carbs slowly open a bit more. The next adjustment is max advance, this is the point where the distibutor (or trigger) can advance no more. Set the max-advance stop to 21 degrees for "direct charge" crossflow inlines and 34 degrees for the older plain vanilla crossflows. Use the light, - err to the side of caution.Right after max advance, further throttle motion should cause the second throttle pickup to hit and open the carbs to full. You already set that -now verify it.Leave the throttle cable disconnected and go to the water. Leave the boat strapped to the trailer and back it in so it's deep enought to run. Have a friend crank it while you operate the choke and throttle. Warm it up at 1500 rpms's.When "warm" adjust the idle stop screw for about 800 rpm and then ajust your idle needle(s) in (one at a time) till the motor stumbles. Quickly backing it out 1/2 turn from "stumble" will usually save it from needing a re-start. Do that for all the idle screws. Re-set idle stop for 800.Now have your friend put it in gear (make SURE you are on the transom NOT in the water) and reset your idle stop for as low as you can get it. 500-600rpm is great if your old reeds will let it idle that low in gear. Now, re-adjust the idle screws, in to stumble, then 1/2 turn out. When you've gone back and forth with that a few times and have it "perfect" - adjust each one out 1/4 turn.Reset the idle stop so that it's about 700-800 out of gear and 500-600 in gear. Sometimes bad reeds won't let you get that low, you've GOT to get it under 1000 in neutral (worst case) to avoid beating up your lower unit when you shift into gear, even 1000 is "bad" but like I said "worst case".Now adjust (and hook up)the throttle cable so that with the shifter in neutral, there is light to moderate pressure holding the throttle arm against the idle stop.Take the boat off the trailer and go out in the water. Try the hole shot. If it falls on it's face try adjusting the idle screws out 1/4 turn at a time (all of them together) till you can get a hole shot. You can kind of do this on the trailer at the ramp, but it's not really safe for you, the boat, or the tow vehicle.You're done.-W
If the carb linkages can be moved manually and more power is achieved, then stop messing with timing until you get the throttle and shift linkage adjusted properly. Here is a short and simple version of the procedure. This procedure also assumes the control box (throttle and shift controls) are proper for the engine you have. Those boxes are not all the same as they have different "throws" (travel distances for the cables). If you know for certain you have the correct controls, here ya go!
1) Disconnect both the throttle and shift cables at the engine.
2) With the carburetor throttle linkage in its fully closed position, and the throttle control in NEUTRAL, bring the end of the throttle cable up to its attachment point on the throttle linkage. DO NOT push or pull on anything -- the point here is to see if the cable is too long or too short.
3) If the throttle cable does not line up exactly, adjust the trunion (the threaded barrel on the end of the outer cable sheath until the cable end and throttle linkage attachment points line up exactly.
4) Attach the cable.
5) Now see if the throttle opens fully. You can tell this because the throttle plate (not the choke plate) is perfectly horizontal in the carburetor throat. If the throttle still is not open, more cable adjustment is not the issue. You either did it wrong, the engine needs a link & sync procedure, the control box is worn, the cable is stretched, or it is the wrong box for the engine.
6). The shift cable is adjusted in exactly the same manner.
IMPORTANT: The key to these adjustments is that you not push or pull anything to get the cables attached. When properly adjusted for length the ends should line up perfectly.
baisicly that what it is.procedure is not that complicated,but will save you a gallon or two on gas and engine will run like a bee.observe how much throttle cable travels when attatched to linkage and when is "unloaded".idea is to check controll box is engaging properlyand the gears inside are not"jumping"