Another XR4 issue

[AstroGlide]

Hi guys, long time reader first time poster. I have just recently purchased a 1990 18' astro quickfire with its original XR4 150, the motor is in pretty good condition for its age. I say lack of maintenance has been it's worse enemy until I came along. I've taken the boat out a few times since I acquired it, I've run it at 40 mph @ 3800 rpm with wife and fishing gear. And again at 40 mph @ 4100 rpm with my wife and 2 grown kids plus gear. At 3/4 throttle the engine runs great, it's when I restart is where I run into a minor issue....idling. A quick bump of the key and she fires right up, but I have to either lift the high idle to keep her running or quickly drop her in gear. I bought a factory manual and I'm in the process of link and sync. I've changed the water pump, rebuilt the fuel pump and replaced the spark plugs. I haven't run it since these basic maintenance procedures, but one thing has caught my eye. As I pulled the plugs I noticed that No. 1 2 3 4 plugs had oil dripping off of them..completely fouled and the No 5 6 looked liked they there's good fuel/oil burn. Before running this motor in my test tank, I was wondering if anyone on here has anything to add that I may be overlooking.

 

[Iceman66]

Re: Another XR4 issue

I would try run it now after checking/adjusting the link and timing, and the replacement you already have done.
If still not idling, time fore a carb rebuild I guess.

 

[Dukedog]

Re: Another XR4 issue

Put in a fresh set of BUHW"s. Lose all tha baggage then get out there and drive it like ya stole it. Luggin' these things around is tha worst thing ya can do. If it doesn't straighten up after that ya might wanna look at tha carbs and/or ignition parts. Tha Quickfire is a "made ta run hull" and so is tha xr4. It needs ta be set up ta turn 5800 at very least when ya out by yourself for a "strole". Tha complete "set up" needs ta be maximized........jmo

Question? Still have tha original gearcase on it?

 

[James R]

Re: Another XR4 issue

I will never run a two stroke motor until I have stripped and cleaned the carbs and rebuilt with new kits. However a compression test is the very first test to see what I've got before spending money. A spark test is the next. These merc V6s suffer with power pack failures after a few years and produce erratic firing.Sounds like you are loosing sparks to one or more cylinders.

 

[AstroGlide]

Re: Another XR4 issue

Thanks for all the ideas guys. The wife and kids factor is the main reason why I haven't opened her up to WOT. I think my next test run will be solo with the gps to check my top end speed. Compression check had all cylinders popping at 112-115, the last owner had installed a full electronics package a year prior to falling ill and storing the boat (5 years ago). Resistance on coils and stator are within specs as well as timing which I verified at TDC on my dial gauge., exactly at .462 on the timing mark, the packs are throwing a spark a half inch long on my spark tester. The fact that my issue is not in high speed is pointing me towards low rpm fuel starvation, a lean condition which could explain the excessive amounts of oil on the plugs. Could an air leak at the carb base or in a random fuel line be an issue? Or possibly the anti siphon valve on my tank? The weather hasn't been pleasant enough for me to run in the test tank, so I am just snow balling on thoughts as to what else I can check. To answer the question on the lower unit, yes it still running the original lower unit.

 

[Dukedog]

Re: Another XR4 issue

Sounds like some kinda carb condition. Fuel drippin' off tha plugs means its not firin' or tha carbs or loadin' up those cylinders. Not lean. Lotta guys don't agree with me but I've done it way more times than I can count. A carb motor (especially tha wh's) actin' tha way you describe caused from settin up for a little while WILL straighten up "most" (not always) of tha time when its taken out and driven with both feet on tha floor and a finger on tha trim. Look at all tha fun you'll have doin' it. But really tha carbs probably need a good cleanin' and new gaskets through out. Somewhere along that year they went from tha wh's ta wmh's carbs. Does yours have accelerator pumps? Hope not! If they do, forget about runnin' tha dog outta tha thing. That type won't ever straighten up. They only had tha pumps a coupla years then pump part went away...............

 

[AstroGlide]

Re: Another XR4 issue

Thanks duke, the weather broke enough for me to drop it in the tank and fire it up. Idle condition was still rough, had to stay on the high idle lever to keep her running. Dropped her in gear to finish my link and sync and she would fall on her face each time. Grabbed the primer bulb and it was soft, removed the fuel line from the engine, push in the check ball and gave the bulb a couple of pumps... No fuel. Removed the siphon tube from the tank, it was clear... Removed the anti siphon valve....the check ball was jammed in the fitting. Twenty minutes and a punch later, I was able to free it up and remove it. Reconnected the fuel line and pick up assembly and bingo....no idle issues. Went WOT, and you were definitely right....that engine screams. Set the WOT stop to 5500 rpm, now I'm really excited for the solo run.

 

[Dukedog]

Re: Another XR4 issue

See that's what tha dreaded word "assume" gets ya. That's what I did with tha primer ball when ya mentioned tha fuel pump rebuild. Thought ya had any fuel issues "gettin' to tha carbs" taken care of. No mater, ya got ta do tha happy dance. Good for ya! Take care of that gearcase. Its tha weak link if ya abuse it but will last a long time when taken care of...........gl.

 

[AstroGlide]

Re: Another XR4 issue

It's always an assumption when your opening a can of worms. It would've been spot on ideas if we were dealing with a fine running engine that's exhibiting a certain problem. But here we have an engine that's running poorly and trying to repair multiple problems. I'm glad that the required maintenance was complete and the main cause found without running into other issues. I've heard horror stories of the lower units on these engines. While I was replacing the water pump, I did a runout on the main drive shaft and prop shaft. End play on the main shaft bearing was a little looser than I'd like but a quick shim and I was back in the ball park. The prop shaft has a slight wobble (still in specs) but I'll have a replacement coming within a few days from a local merc dealer. Thanks again for all the help, as always any info is appreciated.

 

[Dukedog]

Re: Another XR4 issue

If ya need any parts for that gearcase let me know. I've got a few! Just not anytime soon. We're retired seen' tha country right now. Yours being a '90 may be tha same as tha small xr6 case which has a little bit stouter drive shaft and bearing. Its my case of choice on my hot rods with a few "additions" and I always start in gear which helps 'em live. As long as ya don't run it to high in stock form it will be just fine. There's a few tricks ta make 'em last on stock apps. Make sure ya "snap" it in gear, don't just chop tha throttle at speed unless its necessary. Tha drive shaft is tha weak part. They tend ta break at tha pinion. Have a good one................