Bogging down on hole shot

[MASTER Brian]

My 1986 E-XP150 started acting up a little this weekend. It's on the back of my Ranger 373V fish/ski boat. The last few trips to the lake I've done more family stuff like tubing so I'm wondering if the plugs are fouling and i meant to check them before this last outing but ran out of time.

I have two props, one for towing and one for speed. I noticed it more on the speed prop, so maybe it's a prop issue.

Yesterday, i put the tow prop on and did some tubing and the boat ran fine, later i changed props to go do some fishing and didn't notice the issue right off the bat, but it started to have issues taking off. If I'd hammer the gas the motor would act as though it wanted to die. If I'd through it in neutral it'd Rev up fine. If I'd ease into the gas or idle for a while, it'd 'clean' out and then take off and run fine. This mainly seemed to happen after sitting idle for a while.

Any ideas?

 

[racerone]

The trouble shooting starts with a compression test.

 

[emdsapmgr]

Spark plugs are usually changed when the engine develops a slight miss at WOT. Revving the engine in neutral does not mean much. That engine will seem to run just fine when firing on only 4 or 5 plugs. Your ear can't tell how it's running. You need all 6 firing when under load in forward gear. You could do a test. When it seems to bog, have a buddy constantly prime the fuel hose bulb. That forces extra fuel into the carbs. If it runs fine as long as you constantly prime the fuel hose bulb, the engine may be running lean. Any signs of visible fuel leaks at any of the hose clamps?

 

[MASTER Brian]

The compression test will happen hopefully tonight or tomorrow. Just trying to round up a helper when I have time. I have a spark check board as well and I'll also check to see how the spark looks while doing the compression check. I'll also check for any fuel leaks, but honestly, I haven't had a chance to go back and look.

I know I've experienced this type of issue years ago, when I was into Jetski'ing but I can't recall what it was. From what I've read a slipping prop is normally at higher speeds, but it didn't seem to have any issue when she'd finally open up and run, only from take off and only with the high speed prop, which is a Raker 17. I did somewhat suspect the primer bulb, but it gets hard and seems to stay hard, but then again, I didn't reach back and try to prime when underway either. I am somewhat suspecting a bad fuel line or bad gas....maybe a vent/pressure issue with the fuel system. I'd be shocked if it's a compression issue as I've experienced a stuck ring before and this is totally a different feel to the engine. It seriously is like it's having an issue cleaning out or getting fuel, then it suddenly cleans out and goes. I am also planning on running a decarb mix through just to clean everything back up as it's been a season or two for that.

Since I don't want to further any damage, if there is some, my steps will be:
1) hook up the spark board to check spark and ground plugs to run the compression test
2) check all fuel lines for signs of leaking
3) most likely replace aging primer bulb and possibly some fuel line
4) i'll likely drain and refill the lower unit fluid to insure no water and it's been a while since it's been changed
5) maybe it's the fuel/water separator....it's been a few seasons since replaced as well...I'm actually really questioning this as the culprit as I think about it.
6) run decarb on the motor

Any other things to check if I haven't gone through this by the time someone thinks of something?

 

[MASTER Brian]

Pulled the plugs in preparation for the compression test. All the plugs were somewhat wet looking, but had black specks in the area between the insulator and the threads, I'm guessing a little fuel/carbon fouled due to too much low speed running. I'll see if I can shoot a good picture as well and get back. Other than that the tops of the pistons weren't too bad, they were a bit black, so I need to definitely need to run the decarb before it gets too bad.

How often should a carb tune up be done? This is an oil injected motor, but it still fouls up when lots of towing or low speed driving. I purposely did run the boat at 3/4 throttle, fairly rough water, for several minutes when I could to try to clean things out, but probably not enough to get it perfect.

 

[MASTER Brian]

Just to clarify before doing the compression test, it IS ok to unhook all plug wires and hook them to my spark test board, which will be grounded to the motor. Correct? Plugs will all be out and all grounded. Throttle position should not matter correct?

I always worry a bit when doing a test like this that I'll short out the electrics and the Sticky RE Compression says to unhook the fuel, jump to the solenoid, pull the laynard, etc.. My thought is using the spark board will kill two birds with one stone. Am I correct? Thanks!

 

[racerone]

Throttle position does not matter !!----Pulling the lanyard on the kill switch is one way to do this.----Leaving the key in off and using a wee jumper wire on the solenoid is another way to do this.

 

[MASTER Brian]

Finally got a chance to check compression. All 6 cylinders were right at 90psi, with one or two being about 88/89psi. All 6 had nice blue flame jumping about 7/16", at least I believe that's the gap I set the spark board at. It's whatever was required of this motor...been ten years since I rebuilt it.

Looking at the plugs, I believe they are potentially all fuel fouled as they are a black/dark blue color, with tiny deposits between the threads and the insulator. Top of pistons are the same color, but show no real carbon build up. I've been very religious about running seafoam through the boat early season as well as end of season and every other year, at least, I try to decarb it. I don't put tons of hours on the motor either.

What I think is happening is.....when I rebuilt the motor about 10 years ago, I had an issue with the gasket that goes between the power head and the midsection. Basically the gasket got somewhat compromised, I couldn't easily get another one, so we added extra sealer and all has been good...at least until potentially now. When I look over the lower motor shroud, it is somewhat oily/greasy towards the bow end...which isn't overly uncommon, but coupled with how the plugs look and a oily look in this section of motor, I'm thinking I have an exhaust leak, which at low rpm's is keeping the boat from going as it's flooding the motor out, when I get it to clear and can get to plain, I think I'm getting enough air into the housing to allow her to run.

At this point, I'm thinking of running a decarb, as that'll be done with the cover off and I'll see if I can see if exhaust is coming out of the questionable area.

Like I said it's been 10yrs, so my memory on all of this is a bit fuzzy, but how hard should it be to lift the power head, replace the gasket and go back down the road? Any ideas what a shop might charge as well? My neighbor has a hoist hanging from his garage ceiling if his rafters will hold this PH....forget the weight! I do think I have an extra gasket as I had one on order at the time, it was just slow arriving.

Thoughts?

 

[MASTER Brian]

I also forget, does 90psi seem low? A lot of what I read says 110-120, but I am also thinking this motor had lower numbers. She runs great at WOT and generally at idle. I'll see if I have the numbers after the rebuild. I was using a snap on gauge, so I know it's not the gauge, but I was using the shallower of the two plug adapters.