'87 Merc. XR2

[croSSed]

Just recently got this motor out of the shop because it has a hesitation issue. I found that when running WOT, and them backing off a bit I could feel it surging a bit. If I hammered the throttle then, it would fall on it's face for a sec and then roar to life. I even one time had it completely die doing this. The shop guy said that my timing was way advanced and that I'm lucky the engine held together. He said it was at 24* BTDC and he set it to 20* BTDC. He also did a link-n-sync. Now I look at the Merc shop manual and it says that it should be set cranking speed at 22* BTDC. Well, now I notice that the thing runs "tired". It isn't as throttle responsive. If I fire it up, idle away from the dock, and hammer the throttle there is an initial hesitation, then it goes. It used to roar like a violated ape as soon as you dimed the throttle. Somewhere around this site I have a vid I made last summer of my son driving my boat while I filmed. If you see that vid you can get an idea of how it ran: Flawlessly. It accelerated HARD from any speed, never hesitated. There is one more thing: This year I made the switch to CCMS reeds. Interestingly, these problems all showed up after I made that switch. I'm half tempted to put the stock reeds back in and see if the problem goes away. Besides that, I'm open to suggestions. I'd like it to run like it used to!

[skeeter91]

i had a almost the same problem with my 175 efi motor,ended up being the timer base.btw,did you lap the cages?

[skeeter91]

oh yeah,i run mine at 25deg wot advance.as per bob f(bob the builder).the tech that set yours put it where the mercury manual recommends for "safe" running.

[TEXAS20225]

today's gas aint good enough for 25 timing in my opinion check your trigger and watch it closely as you give it throttle make sure its not hesitating before it moves to advance i drove my self crazy trying to find this out , it was hanging just a tad but it was causing hesitation at the throttle( 23 is plenty of advance again in my opinion and im running 145 compression brucato ecu on a steel sleeve 260)

[j_martin]

Lead dress (how the wires lie and move) of the trigger is critical. Also, if anybody has messed with the stator, make sure there aren't any mounting screws protruding and interfering with the trigger. Sticky throttle linkage driving the trigger is most often the culprit.

Another thing to check would be fuel delivery. To check it, I pull the plug out of the bottom carb fuel galley, install a nipple, a hose, and a 15 psi gauge in my lap. If you have a plastic aftermarket bayonet connector on the motor, replace it with genuine Mercury, or bypass it completely.

I run an XR4 with 23-25 degree timing. No advance or idle modules. I run non-oxy fuel which is usually about 91 octane, and won't degrade like the ethanol blend if it gets a bit wet, just separates in the filter like it should, so fuel quality is always good. I've experimented with further advance at over 6000 rpm, and gained approximately nothing. Biggest problem with a vertical reed motor is fuel/air flow, so no surprise there.

If it idles, the reeds are fine. If not, you may need to lap the cages and flip em over or replace them. Ask Chris for advice here.

[skeeter91]

very good advice,stay away from that damn corn gas!

[croSSed]

UPDATE: Checked the timing yesterday and it was set at 18* BTDC at cranking speed. For a standard 2.0L 150 of that year that is the correct timing, but for an XR2 it's supposed to be 22* BTDC. I put it back the way it is supposed to be. Non ethanol gas is just about impossible to find around here. I run 92 oct. pump gas and then put Star-Tron enzyme fuel treatment in the gas. Although the thing is back to running "snappy", it still has the hesitation issue, and isn't predictable. It comes and goes. Very annoying. I'll do all the stuff suggested above and report back.

[croSSed]

Did some testing on the lake yesterday. I ran a fuel line straight from a 3 gallon remote tank to my motor. It still had the running issue. I can run it wide open, 6200rpm, then I drop the throttle back to about 4500rpm, I can feel it surging, I slam the throttle wide open and it falls on its face, then suddenly roars to life. So, running the fuel line straight to the motor, no quick-connects in between, same issue. It will run like a violated ape at full throttle, but back off from that and it will act like it's starving for fuel. Ideas?

[croSSed]

Hey everybody, it's close to a new season, and this issue is still causing me troubles. I had the boat out on the lake for the first time this year and same thing: fast cruise speed, kind of surging, slam throttle to WOT, boat falls on face and dies. It doesn't do this EVERY time, but most times it will hesitate before coming to life. I did check the trigger advance and all that; there were no hang ups at all there. Idle stabilizer is not present. To me it seems like there is a fuel delivery problem right at that point, like the carb fuel level is low - thus the surging, and when you open it up there isn't enough fuel present to deliver the needed fuel charge.

From skeeter91: "i had a almost the same problem with my 175 efi motor,ended up being the timer base.btw,did you lap the cages?"

What is the "timer base"? I did not lap the cages because they didn't need it. I closely inspected each reed seating surface and they looked almost new.

[pyro]

Does this motor have the factory advance module or not?

The reason why the spec timing advance is lower than usual is because the last few degrees of timing are not added in until the motor is running at the top of its RPM range. It doesn't kick in full advance until something like 5700 rpm.

If if the timing box has been removed, max timing advance is set to the actual WOT timing.

[croSSed]

Does this motor have the factory advance module or not?

The reason why the spec timing advance is lower than usual is because the last few degrees of timing are not added in until the motor is running at the top of its RPM range. It doesn't kick in full advance until something like 5700 rpm.

If if the timing box has been removed, max timing advance is set to the actual WOT timing.

It DOES have the advance module. What it doesn't have is the idle stabilizer module.

[rayhawk]

How are your fuel lines? I had slightly different symptoms but it turned out my brand new fuel line delaminated and was restricting fuel flow.

[Sparkieboat]

check your fuel pressure as suggested earlier, also make sure your carbs are clean especially the jets. Also make sure that you run good oil and gas. I would suggest trying a synthetic blend oil. Make sure you got the correct plugs. float levels need to be checked. some oil on your plugs during idle can cause hesitation. or if you have a carb overloading. I could have overlooked it but have you checked compression?

[mn808gade]

did I miss where u rebuilt lift pump?-th

[croSSed]

Lift pump? ?

Here's everything that has been done up to date, none of which has had any effect on this problem:
1. Changed all fuel lines.
2. Ran engine on remote fuel tank with separate fuel lines.
3. Checked compression, changed plugs, changed water separating fuel filter.
4. Checked condition of carbs (totally clean, floats at correct height. Though I will probably check this again if nothing else solves the problem).
5. Checked/corrected timing - 22 deg. BTDC in accordance with the shop manual that says this is the correct timing for this XR2 engine.

I run nothing but Mercury/Quicksilver Premium 2-stroke oil, and I run 89 octane gas usually from Union 76. Non-oxygenated gas is just not possible to get around here, so I run Star-Tron enzymatic cleaner in every fill up. This stuff is supposed to counter the effects of oxygenates in fuel.

I have NOT checked fuel pump pressure. One of the reasons I haven't checked this is that, in my thinking, if I did have a fuel pump problem it would run like crap at WOT, at least at times. It always runs balls-to-the-wall at WOT. It's that transition point between fast cruise and WOT where it is running inconsistently. It will cruise all day at slalom skiing speeds and below with no problems at all. It also never stumbles out of the hole. I can fire it up, let it sit at fast idle for a couple of minutes, idle away from the dock so that it gets warmed up a bit, and shove the throttle all the way to the stop and it storms out of the hole every time.

Anything else I can check?