Mercury 175 slower than expected?

[blackmaxonly]

Hey guys, long time lurker but decided to finally dive in and get some opinions.

I have a 1983 Checkmate Eluder 18.5' with a 1978 Mercury 1750 175hp motor (crank rated, ~150 at the prop). I just recently got it put on the hull and am surprised by the lack of speed I am seeing on the GPS. The motor turns at ~4900-5000 WOT and the top speed I got on the gps was 44 or 45mph. Does this seem correct? For reference I have a 1991 searay 160 with a 1991 merc 115 that also does 43-44mph.

Research online tells me the hull is 1100lb unrigged, and close to 1800lb all said and done. The boat idles just fine, it has some hesitation / bogging when you put the throttle down so you have to ease into it, other than that it seems to run just fine. I also installed a clear piece of hose to look at the fuel after the bulb, and it looks like a solid stream, a few bubbles here and there but very very small.

Let me know what you guys think, or if I'm just being unrealistic with the speed I was initially expecting out of it

[Capt j]

Your dealing with a motor that's over 40 years old. It might only make 100 hp these days. Sounds like your overpropped. Those old 2.4's needed to make RPM's in order to make power. Try getting RPM's up towards 6000.

[blackmaxonly]

Yea the motor is really old, just had new rings put on. I fear I was overpropped, even though it seems like it should handle a 19" aluminum prop

[David - WI]

Either the boat is heavy (water-logged or full of unneeded junk) or the motor is not making power... gotta be a 60 - 65 mph boat. :confused:


https://m.youtube.com/watch?v=PdwQS-iMFwU

[blackmaxonly]

Either the boat is heavy waterlogged or full of unnecjunk) or the motor is not making power... gotta be a 60 - 65 mph boat. :confused:


https://m.youtube.com/watch?v=PdwQS-iMFwU
Thats one of the videos that I got my prediction from! It seems like everyone with a similar setup is running atleast mid 50s, and 60+ with a jackplate. Meanwhile I'm struggling to hit 45 with a simple 19" on castle rock. Brand new stringers and deck, glassed over as well So I can confidently say there is 0 water in the hull. Im thinking maybe a cylinder or 2 are down at WOT, but I have clean spark at idle

[Revenge22]

always mystifies me when mechanics re-ring an already tired motor. bore/hone for a motor that old I say... could have terrible leakdown. not that yours was tired , just a possible explanation !

[tlwjkw]

comp?.. leak down?.. all 'lectrics checked?.. carbs clean with all new gaskets?.. fuel delivery after mech pump?.. link/sync?.. all these things need ta be checked/done.. if they are good go here for initial motor set up.. Frequently asked questions and answers about Boat Propellers, Custom Props and Boat Propeller (stevescustomprops.com) (http://www.stevescustomprops.com/faq.html#How_do_I_adjust_the_Prop_shaft_engine_height_) look for a min. of 5800.............. jmo.

thats a 2.0 motor and with its age needs all tha help it can get.. do ya have an OEM manual for it?

[blackmaxonly]

Comp is all 110-115 across all 6 cyls, carbs were fully cleaned and new gaskets in all, and timed with a light according to the manual (20* max, 14*atdc idle). Im thinking its a miss but it doesnt sound like anything is wrong at speed. I will get to testing this weekend and see what I can figure out!

[tlwjkw]

is idle stablizer still on it?.. if so it probably needs go away... as for tha idle hesitation do this.. with all adjusments done you need ta have a very slight gap between tha throttle cam and roller.. this can vary depending on what you want it (motor) ta do.. this will allow advance timin' a tad before carb throttle.. helps a little with some and a lot with some.. also set "idle timing" with boat in tha water, in gear under a load.. numbers here will not mater.. jus whatever it ends up that makes you and tha motor happy... gl.

really sounds like its runnin' on 5 instead of 6 for whatever reason.. should spin tha 19 alum. easily if all else is close..

[tlwjkw]

because it actually works....... if your way works for you then thats great...

[tlwjkw]

never said it was tha right or wrong way.. jus said it works..

[tlwjkw]

Please show me in a mercury manual where it says this.


best i remember it says in tha water, in gear.. ta me that would be under a load.... can be on tha trailer.. doesn't need ta be goin' down tha lake.... ya jus guessin' ta start with anyway.. it gives ya about 8 ta 9* ta play with on idle timin'............

[Whaaaaat]

best i remember it says in tha water, in gear.. ta me that would be under a load.... can be on tha trailer.. doesn't need ta be goin' down tha lake.... ya jus guessin' ta start with anyway.. it gives ya about 8 ta 9* ta play with on idle timin'............

I was 100% wrong. My apologies. I skimmed what you had said and confused it with a thread from not long ago where a guy was telling people to adjust wot in the water in gear. I should've read your post completely.

Manual does say to verify timing adjustment of base idle in gear and warm. Adjust to stable idle .

I'm going to delete my previous post, I don't want to confuse anyone.

[tlwjkw]

no problem bud.. it happens... jus as guilty of it as tha next guy... don't remember if its in all are jus some of tha manuals...

i can see where doin' that would be a big problem...

[mrichartz]

I was 100% wrong. My apologies. I skimmed what you had said and confused it with a thread from not long ago where a guy was telling people to adjust wot in the water in gear. I should've read your post completely.

Manual does say to verify timing adjustment of base idle in gear and warm. Adjust to stable idle .

I'm going to delete my previous post, I don't want to confuse anyone.

Which that guy mistook for omc motors ? They need WOT in gear unload at rpm... Thats omc.

[Baker343]

Love these years of the 2L. Exhaust chest and dump was opened way up by mercury. Built for top end back in the day.
These motors can take a beating with the block built around the steal sleeves. We run these 40 plus year old blocks over 7k in roundy round races and just under 7k for 4hrs running Enduro's.
Compression looks good. Check all your ground connections especially your coils.
My guess would be the carbs. If original, I think they came with foam type floats. If one or more of your floats are heavy or out of adjustment your carbs might be puking fuel out the emulation tube and getting sucked back into the intake causing you to run fat. Floats could be breaking down and soaking up fuel and messing with your fuel level in the carbs. If your still running the stock air box, remove it and start it on a hose and see if it's puking.
Awesome and simple motors that still have a lot of potential to rip, even being in their 40"s.
Compression, spark/grounds and carbs

Listen to Tlwjkw he's been beating on these first and second generation motors for a long time

[johnboy 88 vegas]

Which that guy mistook for omc motors ? They need WOT in gear unload at rpm... Thats omc.
Why just OMC? Bout 8 years ago watched another mechanic rebuild a motor three times because of a bad idle box advancing the timing and burning up pistons on a stock 200 Merc. The timing was going off the chart on the flywheel once the motor was up and running. I'll take the wot at the boat ramp to be sure with a timing light on Merc or OMC after a rebuild or any changes to the electrical system.

[Baker343]

I don't believe the early 2L had timing advance modules.
Could be wrong

[tlwjkw]

I don't believe the early 2L had timing advance modules.
Could be wrong

yeah, they've been on tha V6 since its '76 show up time.. jus took some time for guys ta figure out they sucked.. called 'em "idle speed control"... took 'em (merc) a few years ta figure out that "stabilizer" sounded better......... :reddevil:

[Glastron1987]

Did you check the plugs after a hard run to see if one of the cylinders is at fault? Could be electrical or fuel.

[blackmaxonly]

Thanks for all the responses guys! I just did some electrical tests with the voltmeter and the stator / trigger / coils all were within spec of ohms (I dont have a DVA to do 'proper' measurements). My model does not have an idle stabilizer, maybe the previous owner removed it but there is no indication of one ever being on this motor. They do have the original foam floats, so I will order those after I try another new set of plugs. I will get a fresh look at the plugs after a hard run and see if there is an indication of anything. I will also run it with the airbox off to see if fuel is coming back out! Will keep you guys updated when I get around to it again on sunday

[mrichartz]

Why just OMC? Bout 8 years ago watched another mechanic rebuild a motor three times because of a bad idle box advancing the timing and burning up pistons on a stock 200 Merc. The timing was going off the chart on the flywheel once the motor was up and running. I'll take the wot at the boat ramp to be sure with a timing light on Merc or OMC after a rebuild or any changes to the electrical system.

I didnt say just omc.. but omc definitely have to be because unload wot they can pickup over 4 degrees of timing...I haven't worked on a merc in years so i dont remember exactly why but for sone reason they dont need to be... BUT im not commenting on the timing or giving advice on mercs.. And like baker said Tlwjkw been running these and knows..

[Whaaaaat]

Anybody know why omc would spec this. I'm curious. I can't think of a reason timing would change from loaded to unloaded unless some part of the crank was made out of gumby rubber.

[mrichartz]

Anybody know why omc would spec this. I'm curious. I can't think of a reason timing would change from loaded to unloaded unless some part of the crank was made out of gumby rubber.

Its electrical not mech why.. I honestly cant/dont remember.. to be honest i vaguely remember but not positive so...
I will say that when i use all digital cdi 8500 rpm it doesn't happen...
BUT I WILL STILL check under load every damn time to much time and $$$ not to.
Why i cut props up etc to make it easier

Not really helpful but

[blackmaxonly]

Hey guys, as promised on Sunday I ran some more tests and got a couple of videos:
#1: Video of running (https://youtu.be/CbRsorhMzUY)
#2: Closeup of fuel line (https://youtu.be/DGxc8a_H20M)
#3: Water stream on top of engine? (https://youtu.be/FJtWFrQisHk)

I also retook compression on all cylinders (cold) and they were higher than I mentioned, the lowest is 111 and the highest is 117.

#1: The first video may be an indicator to someone if they have a better trained ear / eye than I do. I confirmed there is strong spark at all 6 cylinders
#2: Would this amount of air cause the issues I am seeing? The fuel lines are brand new, including a new filter and pump ball. The air is coming in from either the ball, which is the 2nd new one Ive tried, or from inside the fuel tank itself, which I am not sure how I would end up fixing.
#3: As a bonus maybe someone can answer this: Where is the water line from the top of the engine supposed to run to? It is NOT on the water flow diagram in my manual, and came without any tubing connected. You can see I ran some tubing to just below the cowling for it to drain to, it is a strong stream. The telltale does not work unless the engine is at temp.

I did not have any fuel puking from the carbs when I took the airbox off.

[David - WI]

3. to the water pressure gauge on your dashboard.
2. the air itself doesn't hurt anything... the carb bowls are vented and floats / needle & seat will keep them full BUT it looks like you have a leak in the suction line somewhere; so you might not get enough fuel flow at WOT?
1. sounds normal to me.

[tlwjkw]

another thing ya might wanna check.. night time, remove cowl and run it while ya take a long screw driver and run it along spark plug wires ta ground.. try it with all wiring..

[mrichartz]

Yea if those are the old plug wires.. x2 on checking at night
I would change them either way if they are old
Need to find out why your sucking that much air in the fuel line most likely a cracked line.
Its amazing how SOMETIMES its just something small.

[mrichartz]

Oh do you have a water pressure gauge hooked up yet?
I would get that hooked up too sooner than later.. you never know... Easy enough to do since its already in the block.
The plug wires if they are cracked or leaking they could be fine while sitting there checking but when you start moving (driving it around) the cracks in the wires will start leaking and losing spark..

[blackmaxonly]

I will try at night to see if there is an issue with the wires. They were replaced in 2016, as well as both switchboxes. While cranking there is a clean jump across 1/2 gap from my tester on all wires. My hull does not have a water pressure gauge - should I install one or can I just cap off this water flow? I plan to get a small 6gal tank and try to see if there is any air in the line after that, as I have traced it to be before the primer bulb

Thanks for all the great information and stuff to test

[mrichartz]

Do you have a jackplate? Definitely install one
You have a working temp gauge? Can get away with out

its still a good idea to have water pressure gauge
But if you at least have a temp gauge you will have an idea.. ive had temp gauges stick too just make sure its working.
Water pressure will tell you before it gets hot rather than after or while its getting to hot..
Can always install it in one of the metal brackets for the
2 1/8 gauges..and not have to drill into your dash if you dont want to.

[Revenge22]

random interjection here, but at the beginning of the season I shelled out $250 for a GTC - 505 Ignition analyzer. the thing is absolutely incredible for diagnosing bad plugs/something wrong with ignition to rule out a fuel problem. its so easy to use and completely wireless, measures voltage at the plug wires AKA end of the ignition to see whats going on. no more pulling plugs for a drop test! also extremely handy for setting forward idle RPM in the water... no wires and battery terminals to mess with.

[blackmaxonly]

Jackplate is in the plans assuming I can get this engine running well. I do not have a temp gauge either, only speedo / tach / fuel. I will get a water gauge for sure

[mrichartz]

If you're putting a jackplate on i would install both.
Even if you're not jacking it up to where it could lose water pressure its worth the price to have them..

[tnelsmn]

I was running the exact engine for the first half of this season. Was able to run it to about 70 on a Hydrostream Viking. I was able to spin it to about 6k. There's more left in yours, just gotta find it.

Have you confirmed your timing pointer with a dial indicator to be true TDC? I had to make a new pointer with a piece of scrap aluminum since my flywheel cover is long gone. I also had to mark my flywheel since my new one didn't have markings.

Not trying to beat a dead horse on timing with yours but you'd be amazed how much it can change it. I tried to just set mine with the length of the linkage from the trigger to the throttle arm and was off by 10 degrees when I put a light on it. That was night and day. I then added another 2 degrees looking for more speed later.

What's the condition of the harness to your stator and trigger? Mine were junk and both had to be replaced. The wires on these old Mercs are junk.

For a reference this is mine 10 degrees retarded from where it should be. https://youtu.be/jgUFaLdjBV4

[blackmaxonly]

I was running the exact engine for the first half of this season. Was able to run it to about 70 on a Hydrostream Viking. I was able to spin it to about 6k. There's more left in yours, just gotta find it.

Have you confirmed your timing pointer with a dial indicator to be true TDC? I had to make a new pointer with a piece of scrap aluminum since my flywheel cover is long gone. I also had to mark my flywheel since my new one didn't have markings.

Not trying to beat a dead horse on timing with yours but you'd be amazed how much it can change it. I tried to just set mine with the length of the linkage from the trigger to the throttle arm and was off by 10 degrees when I put a light on it. That was night and day. I then added another 2 degrees looking for more speed later.

What's the condition of the harness to your stator and trigger? Mine were junk and both had to be replaced. The wires on these old Mercs are junk.

For a reference this is mine 10 degrees retarded from where it should be. https://youtu.be/jgUFaLdjBV4


My arrow was broken off as well, I had to make a makeshift one to set TDC. I used a method I saw where you screw a TDC stopper in the sparkplug, mark on the flywheel where it stops, then rotate the flywheel the other way and mark where it stops in that direction. Then you split the difference and thats your true TDC. My linkage broke from the throttle arm to the trigger so I had to get a new one and set to the factory spec of 11/16". The trigger and stator both seem to be just fine, all wires are in good enough shape, the stator could have some wire issues in the future, but they both passed the electrical tests within spec.

Can you clarify the steps you took to set the length of the linkage between the trigger and throttle? I put a timing light on mine, and at both idle / WOT cranking speeds they are at the correct timing of 20BTDC / 14ATDC

[Glastron1987]

Hey guys, as promised on Sunday I ran some more tests and got a couple of videos:
#1: Video of running (https://youtu.be/CbRsorhMzUY)
#2: Closeup of fuel line (https://youtu.be/DGxc8a_H20M)
#3: Water stream on top of engine? (https://youtu.be/FJtWFrQisHk)

I also retook compression on all cylinders (cold) and they were higher than I mentioned, the lowest is 111 and the highest is 117.

#1: The first video may be an indicator to someone if they have a better trained ear / eye than I do. I confirmed there is strong spark at all 6 cylinders
#2: Would this amount of air cause the issues I am seeing? The fuel lines are brand new, including a new filter and pump ball. The air is coming in from either the ball, which is the 2nd new one Ive tried, or from inside the fuel tank itself, which I am not sure how I would end up fixing.
#3: As a bonus maybe someone can answer this: Where is the water line from the top of the engine supposed to run to? It is NOT on the water flow diagram in my manual, and came without any tubing connected. You can see I ran some tubing to just below the cowling for it to drain to, it is a strong stream. The telltale does not work unless the engine is at temp.

I did not have any fuel puking from the carbs when I took the airbox off.

#2 Yeah, try an external tank and line you know is good and see how it runs with that. I've had several internal tanks go bad on me. Usually the pickup clogs or the anti-syphon valve goes bad.

[tnelsmn]

Ok, that sounds like a true TDC in that case. Or close enough for what we're trying to do here. I just used a ruler to measure following the manual to set the trigger linkage. Sounds like you did the same. Then I used the stop bolts on the throttle arm to set WOT timing.

It may just be how you typed it, or how I'm reading it, but I want to clarify that you're setting WOT timing at 20BTDC while cranking. Then you can adjust idle timing based on how it runs. I just left it strapped to the trailer backed into the launch. I don't have my manual in front of me but I believe its says you want 6-800 rpm idle in gear, but don't hold me to that.

Here's a video I shot once I got the timing issue figured out. https://youtu.be/oXHx6ZPmTDg

[blackmaxonly]

Mustve been the way I worded it, but you are correct in the steps that I took. 20BTDC at cranking speed, i think manual states that is the equivalent of 18 at 5500RPM. Do you think its safe to run higher than that? 21 or 22degrees? I also set my timing to 14ATDC for idle on the muffs, but on the water I had to adjust and its at roughly 12-13atdc to get the correct RPM range in gear. I do believe I have it at the higher end of that range, around 750-800RPM or else it will stall if I kept it at 14atdc. Glad to see you have a strong running motor and hopefully what I am going to be able to have

[blackmaxonly]

I just got a 6gal from a buddy that I know works well, so I will hook that up next time Im on the water. What did you do to fix the internal tanks? I have a 32gal tank that seems customized to this hull, and I dont think 6gal will last me a full day on the lake!

[tnelsmn]

I'm not an expert by any means, but I put that same question forward a while back on here and most everyone said 22 should be safe, but is starting to push it. I ran mine like that for a month or so. But I wouldn't go there yet until you get it running right. I swapped my motor for a 225ProMax so now the 175 is in mothballs.

[Glastron1987]

I just got a 6gal from a buddy that I know works well, so I will hook that up next time Im on the water. What did you do to fix the internal tanks? I have a 32gal tank that seems customized to this hull, and I dont think 6gal will last me a full day on the lake!

All internal tanks I have experience with have a pickup tube screwed into the top of the tank that goes down close to the bottom. The tube can get eroded with pinholes part way down or the tube can get clogged. In either case fuel flow can get interrupted so the engine does not run properly. One of mine even had a screen filter within it that got very clogged from lack of use for years. In any case, if you have access to this fuel outlet from the top of the tank, your can take the fuel line off and unscrew the tube and take it out and examine it.

Also, attached between that tube and the fuel hose may be an anti-syphon valve. It too can become clogged or malfunction in some way interfering with fuel flow. It has a spring and ball mechanism inside it.

It is easy to unscrew the fuel tube if the access to it is good.

Using the external tank will make it easy to rule out whether or not the problem lies with the internal tank. If the engine runs good with the good external tank but not with the internal tank, then the internal tank is at fault. Otherwise you have ruled it out as causing the issue.

[Whaaaaat]

^^ even a brand new anti siphon valve can restrict flow enough to pull in air. If you have one throw it in the trash and replace with normal barb fitting. Hairline cracks can be in the head of the water separator filter. Improperly mounted primer bulb, trash in primer bulb.

Use a section of clear hose and move it. Start at tank to next fitting in line, keep moving towards engine until issue is found.

[Glastron1987]

Forgot you have a water separator filter too. That too can be a point of failure. I actually never use those and never had a water issue.

[blackmaxonly]

I will test out on a second tank, see if that solves my issues or not. My setup does not have a fuel / water separator, so thankfully I do not have to worry about any issue there. I will more than likely end up buying a new siphon valve and pickup tube anyway, as my tank is original from 198x. Thanks for more info guys, I will keep you posted

[Whaaaaat]

Don't use an anti siphon valve. It will create more problems than it will solve.

[blackmaxonly]

Hey guys I'm back, a couple new updates. I got new plugs to be safe - BU8H, and they look fine after running (I have the BUZHW in there prior), no problematic symptoms. I switched to an external 6gal tank, and while there were virtually no bubbles, it ran the exact same. So I will still be ordering a new pickup tube and anti-siphoning valve because I can atleast get rid of the bubbles. This leads me to the one thing I completely forgot about - the fuel pump. I will be ordering a kit and rebuilding it asap to see if that solves my issue. The boat will idle / rev in neutral all day but fail to do anything once its put in gear, and if you do manage to get going its not that fast.

[David - WI]

Hey guys I'm back, a couple new updates. I got new plugs to be safe - BU8H, and they look fine after running (I have the BUZHW in there prior), no problematic symptoms. I switched to an external 6gal tank, and while there were virtually no bubbles, it ran the exact same. So I will still be ordering a new pickup tube and anti-siphoning valve because I can atleast get rid of the bubbles. This leads me to the one thing I completely forgot about - the fuel pump. I will be ordering a kit and rebuilding it asap to see if that solves my issue. The boat will idle / rev in neutral all day but fail to do anything once its put in gear, and if you do manage to get going its not that fast.

You can have somebody pump the primer bulb slowly while you drive.

[Glastron1987]

Sounds like some good progress. The fuel pump was the next thing I was going to mention. I took what David said about having someone pump the primer bulb as humor, but I think actually when you have a bad fuel pump you can actually get buy doing that, so you might actually want to try that as it may make is more evident that the pump was the problem.

[blackmaxonly]

Absolutely I should have had someone there to try that. Everytime I went back there it needed to be pumped again and was soft. Should it stay hard normally? I feel like the suction would prevent it from holding a strong pump. It should probly be replaced anyway even if it's not the issue, one more thing to eliminate - otherwise I supposed the carbs will be coming out, even though I soaked all 3 in solution and put a generous amount of compressed air through each oriface + new gaskets

[Glastron1987]

The bulb won't be too hard when the engine in running, not like when you first pump it, but it shouldn't be deflated either. If it gets deflated then there is a clog somewhere before the bulb. That's what happens when you forget to vent your tank, the fuel ball gets deflated. Of course that is only if your pump is working as well.

Another thing I do to check for clogs is take the connector off the end of the fuel line that goes to the engine and then pump the fuel bulb with the end of the hose in some sort of container. If pumping causes a nice stream of fuel to come out then likely there is no clog.

Also on many hoses there is an internal liner that can clog your lines if you don't center the fitting into them when attaching. That caused me some issue until I figured that out.

It seems though if the engine runs the same with the external tank (and I assume a good fuel bulb and line) that the problem lies somewhere after the fuel line. So pumping the ball with it running is a good test to see if the failure is alleviated.