Mercury test wheel/propeller?

[pekstrom]

I am tinkering with my 1980 25HP Mercury and am suspecting that the WOT timing isn't quite right. I have the service manual and the process for checking WOT timing sounds doable, but the thought of leaning out over the transom at full speed doesn't sound like fun. I have read you can tie the boat to a dock and do it that way. But that sounds a bit scary as well. So I have been trying to find a test wheel for it so there won't be as much thrust but I haven't found any information. Does anyone here have any part numbers or information on which wheel would be the right one for a 25HP 2-stroke?

I have found info about making my own test propeller from an old, real propeller. But I would have to buy one anyway so looking to see if I can find a real test wheel.

Thanks!

 

[flyingscott]

Why do you think the timing is out?

 

[pekstrom]

Well, it has some real trouble idling, and it doesn't reach the WOT rpm even with just me in the boat. I can get it up to around 4500 rpm but according to the manual it should be between 5500 and 6000 rpm. I am also looking for a compression tester, anyone have any recommendations? When I got it, it seemed to run ok on muffs. As soon as I got it in the water it had idle problems where it would sputter and stall after a little while. By that I mean a minute or less. It stays running with some fast idle and I can get it into gear and get it going if I am quick. I have also noticed that at lower rpms it doesn't run clean and seems to not have as much power as it should. It will work the boat up to plane though, even with 5 people onboard, it just takes a little bit. And as it revs up, it gets to a point where it starts running clean and at that point it takes off. I don't have a tach in the boat so I don't know around what rpm that happens. I have been able to adjust it so it will stay running at idle but the rpm is way too high. It is up near 1000 rpm which I know isn't healthy for the gears in the lower unit.

I have cleaned the carb, fuel pump, new gaskets and diaphragm for those, put a new fuel line on it, checked the reeds and all new gaskets around those. New spark plugs, and the sparks look strong. Been adjusting the idle per the service manual procedure.

I have picked up a timing light so will be checking the idle timing on it. Figured while I'm at that I would like to check the WOT timing as well, if I can.

 

[racerone]

Timing rarely goes out of adjustment on these.-----Might to a compression test or inspect pistons through bypass covers on side of the block.

 

[pekstrom]

Compression seems ok on it. The top cylinder tested at 135 psi and the bottom at 130 psi. The small difference seems to indicate healthy cylinders, rings, pistons and gaskets, correct? I have seen comments about 90-120 psi being a good range and my service manual doesn't specify the compression. Is the 130-range a good range for this motor? I am assuming so since that's where it is. :lol:

So based on this, it seems worth it to put some money into trying to get it to run right?

 

[flyingscott]

Compression is good. I would look at the link and sync of the carb and timing. WOT timing has nothing to do with the idle. I would make sure the carb is opening all the way to 90/deg

 

[pekstrom]

Alright, so I have looked a bit at that too. But I only have a direct connected timing light and noticed that when I connect it up, it seems to cause problems with the spark on the cylinder it is hooked up to. So the engine runs rougher. If I disconnect it the rpm increases. So it makes it difficult to troubleshoot. So I’ll need to get me an inductive light instead. I did see though that the two idle timing dots are about half of an inch to the right of the timing mark. If I tried to get it to move to the left the engine died. Could have been because of the light. I’ll keep tinkering.

 

[flyingscott]

If ypu are trying to set idle timing without a tach that is useless. Do not worry about idle timing just do the link and sync and carb adjustments. You have to do the adjustments on a warm motor. You will be adjusting the carb and idle together until you find the balance between them.

 

[pekstrom]

Oh no, I know I need a tach. The outboard doesn't have the sender for that so I had one of those inductive tachs. It broke and shows a totally wrong rpm now so I am getting a new one. Once I get it I will take another look at the motor. Thanks for all the info.

 

[pekstrom]

Off the test wheel/prop topic, but possibly related to my motor not reaching WOT rpm. The Commander 2000 controller I got with the motor turned out to be a pull-throttle model while the motor needed a push-throttle model. So I figured out that the only difference is that the pull variant has the 850723A2 part while the push variant has the 850724A2 part. So I got me a 850724A2 and swapped it out. It works but I have noticed a gap/play in the throttle handle of between 1-2 inches. If I have pushed the handle forward to increase throttle, I have to pull it back 1-2 inches before the throttle actually starts decreasing. It is the same when I start pushing it forward. So now I am wondering if anyone here has ever converted one of these and know how to solve this problem?

 

[pekstrom]

Alright, I had some time this afternoon to pull the boat out in the driveway and tinker with the motor. Following the procedure in the service manual, I adjusted the throttle pickup and linkage as well as the idle screw as stated. It wouldn't start at first but after adding some fast idle I got it to start. But it didn't run very well, and stalled after around 30 seconds. So I adjusted the linkage and idle screw and eventually got it to run. But I have the linkage pretty much back to where it was. The picture shows where it is set.



It doesn't seem to have much power though. I have it idling around 800 rpm in neutral but it doesn't stay there. At times it revs up to around 1000 rpm and then drops back down. It drops below 800 rpm and some times stalls, and some times recovers and comes back up around 800 rpm. If I put it in gear it drops down to between 700 and 750 rpm. Just like in neutral, the rpm keeps varying and drops down below 600 rpm at times. If I rev it up with fast idle and then drops it back down, the rpm drops down below 600 rpm and it struggles a bit. Some times it stalls and some times it recovers.

In this video I am reving it up using fast idle, but of course it doesn't stall when I am filming it.

Oh, and with the inductively coupled timing light I did verify that the idle timing lines up when I got it to run at those lower rpms. So that shouldn't be the problem.

What should I try next? Is this an indication that I didn't get the carb cleaned properly? Or is it a sign I really should let a real mechanic take a look at it?

 

[flyingscott]

Sounds like it is running on one cylinder. Have rebuilt the carb and fuel pump with new parts? Have you checked for spark?

 

[pekstrom]

Hmm, I haven't checked recently, but I did check when I replaced the plugs last year after noticing the ones in it weren't the recommended ones (yes, I fought with this last year too). I found the ones recommended in the manual. The inductive tachometer I got does pick up pulses from both spark wires. I did rebuild the carb with new gaskets and membrane. I didn't get new mechanical parts. From what I could tell, they all looked ok. Your comment does make me wonder though. The fact that it runs a bit rough when I increase the throttle on the lake, and then at a point starts running clean and gets more power does sort of go along with the ignition, doesn't it? Could one of the coils be bad or perhaps the switchbox? How would I diagnose that? Would a weak spark cause this type of behavior?

 

[flyingscott]

Did you soak the carb and clean all the passages. Is the primer operating correctly on the carb?

 

[pekstrom]

I got one of those paint can looking containers with carb cleaner and a basket. I took the carb apart completely and followed the directions on the can. I think it said to soak things for an hour or so, so I did. I also had a couple of cans of compressed air that I used to blow through all the little channels in the carb body. And then I put it back together with all new gaskets, o-rings and fuel pump membrane. When you say primer I think of those rubber bulbs on lawn equipment. Is that what you mean? It doesn't have one of those. But I squeeze the bulb on the fuel hose until it gets firm before I start it.

Your comment about running on one cylinder got me thinking. It does run rough on lower rpms, and when I'm on the lake and speed up, it runs rough about halfway to planing. It doesn't sound quite right and there's an extra vibration in the boat from it. The best way I can describe it is that it has an rrrrrrrrrrr sound and vibration on the lower rpms and then halfway up that stops and you can feel a little kick when it picks up power. And that seems to happen around the same spot every time.

 

[pekstrom]

Alright, finally got back to looking at this. I went by the troubleshooting steps in CDI's guide for 1979-1996 Mercury's with the 114-7452A3 switch box. Per my research that's the one on my motor. In the steps they list both the OEM and the CDI resistance values you should find between the trigger wires (brown/yellow and brown/white). The OEM range is 750-1400 ohms and mine reads 789 ohm. So that seems to check out. Next, the voltage across those wires when cranking the engine should be 4+ volts. Mine reads just over 6 volts, so that seems to check out as well. What puzzles me a bit is that resistance should be infinite between each of the trigger wires to engine ground. I measure about 2Megohms and it increases slowly if I keep the meter connected. I'm not sure what that could indicate? A bad trigger or switchbox?

Also, it says I should have 150+ volts on the green wires to the ignition coils. It doesn't specify if it should be to engine ground or the trigger wires. If I measure from ground to each green wire I only get around 9 volts. If I measure from either trigger wire I get 110 volts on one and 98 volts on the other green wire. I don't have a load resistor so I can't test with the ignition coils disconnected. Based on the voltage to the coils being below 150v, I either have two bad ignition coils, or a bad switch box?

 

[pekstrom]

To keep this somewhat updated, I have worked with CDI Electornics support. Based on information from them I have done several tests on the ignition components (stator, trigger, switch box and ignition coils). The stator and trigger both operate within specs. The ignition coils are also looking healthy. The switch box on the other hand puts out pulses to the ignition coils well below the minimum voltage. So it appears the culprit is the switch box. I'll have a new one mid-week so we'll see.

 

[pekstrom]

While replacing the switch box helped improve the test results, it did not resolve the idle problem. So I went back to the drawing board and decided to go through another carburetor cleaning procedure.

I soaked all the parts in the carb cleaner bath for several hours and also used a spray can carb cleaner and blew it through all the tiny channels. Put all new gaskets and diaphragm on it and assembled it again. I double-checked the bolts holding the adapter plate and reeds in place, then put the carb back in place with a fresh gasket and made sure I tightened the nuts holding it properly. I did notice when I took it off that those nuts weren't tightened very much, so I may have had an air leak.

Another thing I noticed was that the timing link that goes from the choke/fast-idle adjustment arm to the trigger arm under the flywheel had slipped out of the trigger arm. So when the adjustment was changed the timing didn't follow. So I fixed that while the carb was off.

I pulled the boat out in the driveway and filled a tub of water for it to run in. And then I cranked it up. I am happy to report that it actually runs much better now. It idles pretty well and seems to do ok idling in gear as well.

Here it is idling in neutral and is hovering around 750-800 rpms:

Here it is in forward gear and hovers around 650-750 rpm:

It does still surge at times and then drops back down. At times it drops below 600 rpm and almost stalls. It usually recovers though. I'm not sure why it does that at this point. I'll have to analyze it a bit more. I have noticed that the bulb on the fuel line never gets that full feel to it. When I squeeze it, I can squeeze it about half way before I feel fuel flowing through it. So perhaps I need a new fuel line. I can't see anything wrong with it but I know that bulb should fill up after a few squeezes and get firm.

Now I need to take her out on the lake and see how it does there. And if it still runs rough on the lower rpms

 

[oldman570]

Test the coils as described in the manual to see if they are in limits. Replace the plugs with NKG brand BUHW and see if this helps. I have had similar trouble with motors, and have found that coils will break down under different loads, and other brand plugs will not work nor last over time.

 

[pekstrom]

I am happy to announce that the engine runs great now. It idles nicely even in gear. And it starts much easier as well. :lol:

For the primer bulb, the way the fuel line came assembled it had a short hose section going to the tank, and a longer section going to the engine. So the bulb basically hung off of the tank, which out it upside down. So gravity worked against the valves in the bulb. I took the fuel line apart and changed it around so now the bulb hangs down from the engine, right side up.

On our first trip to the lake I noticed that rather than getting firm as I squeezed it, the bulb collapsed instead. After a bit it expanded back out and the engine ran great on idle and low rpms. When I opened her up though, it ran for a couple of minutes and then died. And the bulb had collapsed again. So clearly a problem with the intake valve in it. Yes, the vent on the tank was open. So I ended up buying a new bulb rather than messing with the old one. And after swapping them out it ran great even on high rpms. And accelerating from idle it runs much smoother too.

I'm guessing my tub with water just didn't give it enough resistance for the exhaust because in the lake it doesn't seem to have the surge problem on idle.

So my conclusion is, clean carb, keep the bulb right-side up, and make sure you tighten the nuts holding the carb when you re-install it! :facepalm:

Thanks everyone for the advice I have gotten here!

I'm a happy camper!