Mercury 175 slower than expected?

**mrichartz** · 08-30-2021, 12:00 PM

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** · 08-30-2021, 01:37 PM

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** · 08-30-2021, 02:14 PM

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** · 08-30-2021, 02:22 PM

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** · 08-30-2021, 03:03 PM

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** · 08-30-2021, 05:54 PM

Originally Posted by 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

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** · 08-30-2021, 06:22 PM

Originally Posted by blackmaxonly

Hey guys, as promised on Sunday I ran some more tests and got a couple of videos:
#1: Video of running
#2: Closeup of fuel line
#3: Water stream on top of engine?

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** · 08-30-2021, 06:25 PM

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** · 08-30-2021, 06:51 PM

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** · 08-30-2021, 06:52 PM

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** · 08-30-2021, 07:08 PM

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** · 08-30-2021, 08:09 PM

Originally Posted by 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!

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** · 08-31-2021, 06:04 AM

^^ 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** · 08-31-2021, 10:06 AM

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** · 08-31-2021, 10:30 AM

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