Question about Merc EFI 175 & 200 timing

[Bartman39]

Was looking in my manual and noticed the timing on my 175 XRI and a 200 XRI was slightly different...? It is 19 degrees advance on the 175 and 22 degrees on the 200 motor...? I have been told the blocks of the 175 and 200 are basicly the same (ports and timing) so is the main difference the timing and the fuel curve and possibly the tuner as they have different numbers as well...?

Reason I ask is I have a 200 tuner and of course I can adjust the timing to the 22 degree spec and have a digital ECU on its way also... I know I need to change the map sensor port for the digital ECU but what other changes...? Also wonder if any issues with changing the timing on this motor (the 175) to the 200 spec...? Also thinking of cutting the heads a little to bump the compression so any guide for material taken off to how much its raised would be a big help as well...

[j_martin]

Was looking in my manual and noticed the timing on my 175 XRI and a 200 XRI was slightly different...? It is 19 degrees advance on the 175 and 22 degrees on the 200 motor...? I have been told the blocks of the 175 and 200 are basicly the same (ports and timing) so is the main difference the timing and the fuel curve and possibly the tuner as they have different numbers as well...?

Reason I ask is I have a 200 tuner and of course I can adjust the timing to the 22 degree spec and have a digital ECU on its way also... I know I need to change the map sensor port for the digital ECU but what other changes...? Also wonder if any issues with changing the timing on this motor (the 175) to the 200 spec...? Also thinking of cutting the heads a little to bump the compression so any guide for material taken off to how much its raised would be a big help as well...

I'd be willing to bet that the x motor that's supposed to be set at 19 degrees has (stock) a timing advance module, or a combination idle stabilizer/advance module hooked into the bias circuit. That module is supposed to advance the timing at about 5000 rpm, and retard it at some higher speed, whatever the engine is max rated for.

Throw all that chit away and set it where it wants to be, unless you're gonna put hours and hours on it at half throttle. Then the slower timing might be easier on it at midrange.

hope it helps
John

[Bartman39]

Thanks for the reply JM... :) But my XRI EFI 175 does not have any modules on it just the ECU so nothing should affect the timing...? Really just wondering if changing the timing to the 200 spec (22 degrees) would hurt anything...? Possibly give it a little more topend...?


Also the tuner in my 175 is either broke or loose...? Had the lower off it awhile back and noticed it was moving around so I got a used 200 tuner (same year motor) and the gaskets to replace it...

[THEFERMANATOR]

According to the manual I have, your 175 should be like my 150. My 150 has the idle stabilizer module mounted over on the port side just above the linkage. Can't really help you out on the differences between the 2 though. I know the 200's had a detonation module on them as well as the timing module mounted on the port side above the cylinders.

[Bartman39]

This is an EFI XRI 175 not a carbed model so dont think they came with idel stabilizers or detonation modules...? Possibly some did but not on this one...

Mine had a warning module and a water sensing warning module but did not have an idle stabilizer nor did it have a detonation module... I verified these and still have them but have long since removed them and the oil injection setup and mix my own...

So back to my original question will it hurt to move the timing up to the 22 degree spec...?

[TheRickster]

I think everyone pretty much sets to 25* WOT with no extra modules andon the barb fitting i think the only time you have to channge them is on the HiPo (260's) when going from Anolog to Digital.. On the fishing motors it is plug and play...

Rick

[Bartman39]

Thanks Rick... :) Just the info I needed...

Were you out on the river yesterday...? Thought I saw your boat up around the saltwater barrier...?

[TheRickster]

Naa, we were out Sunday morning knockin some Crappie out..

Rick

[THEFERMANATOR]

Mine is a 95 150 XRI, and it has the idle stabilizer on it. Has the switch hooked to the shift linkage and the 2 wires that hook up to the switchboxes. The part number on it comes out to the idle stabilizer, not the timing advance module.