1996 mariner 115 holeshot stumble problem

[wycough]

Hey guys, thanks for looking. Let me give you the history.

1996 Mariner 115 on a 17ft ChampioN bass boat. Stored for a long time. Cleaned gas tank. New fuel. New plugs. One can of Berrymans. Lower unit lube changed. And she fired right off and has run for two seasons. Idled a little rough, but very useable. Good holeshot.

Last week. Had a guy clean the carbs and slight adjustment per him. Big problem! Or more mistake.

Now I've had it in the shop and here are the details. Link and sync. Timing adjusted. New fuel accelerator and new fuel pump re-build. New regulator. Bulb and line new last season. New fuel lines. New fuel filters. Throttle cable and hot foot new about 3 months ago. Throttle cable adjusted for completley closed and WOT. New plugs NGK and gapped. Engines been on dyno at the shop.
Tech took it to the lake and adjusted also. Oil pump adjusted with in spec line.

5000rpm's at WOT
48-50mph WOT
trophy 24pitch prop
water pressure 15-18 WOT
carbs at 1 1/2 turns out
tech stated a little rich
idle in neutral is 1000 and very smooth
idle in gear is 900 and pretty smooth with motor level
starts easy
timing set exactly to factory specs
these rpms are per a new teleflex sportsman series tach, may be just a bit off

Now remember I did have a good holeshot. But, now it will slightly hesitate then stumble all on itself from idle(900rpm's) until 2000-2100rpm's then off it goes smoother than ever. Mid range and top end range is great! But I really need my hole shot back. The stumble is killing me.

#1 and #2 carb seems to have a problem, but as soon as #3 and #4 kick in it's great. That is what I'm assuming. i believe they kick in around that rpm range.(2000-2200rpm)

What else can I check besides the shop doing a carb rebuild which may or may not cure problem? Am I missing something? What is causing the stumble and hesitation in the low end carbs and holeshot? Is there anything electrical that controls the #1/#2 carbs upon hammering down the throttle?

Please help quick? Thanks!

 

[studlymandingo]

Re: 1996 mariner 115 holeshot stumble problem

First off, it sounds like you are running too much pitch on your prop. I think the WOT on that motor should be more in the 5600 range. You should probably go to about a 21P.

Second, the "stumble", is it running out of gas or loading up?
Sounds like it might be a little on the rich side and is loading up, might try going about 1/8 turn in and see where that gets you. If that makes it worse, then go back to original and try 1/8 out.​

 

[wycough]

Re: 1996 mariner 115 holeshot stumble problem

Max rpm's is only 5250. I still have to measure how far below pad I am, i'm thinking 4.5 inches and gonna go 3.5 so that will take care of the last 200 rpm's. The prop has never effected holeshot in the past. The stumble is what is effecting the holeshot. I was happy with the holeshot prior to the carb cleaning.

It had the stumble day before when it was a little leaner. Now the screws are a little more out and still stumbling. Maybe I'll try another 1/8 turn out.

Forgot to mention, before starting all this the #1 plug was dark. Running richer than the other three. Will pull it and look at it in the morning to compare since adjusting.

Maybe this motor likes to run richer than the tech and dyno think it should. The oil pump had to be adjusted also. It was pumping a little rich before the cleaning.

 

[studlymandingo]

Re: 1996 mariner 115 holeshot stumble problem

What color is the plug, if it's light brown.. too lean, black.. too rich, dark brown.. just right.

If the one plug is black then that carb may be loading up, you may turn back the mix 1/8 turn on that one first.​

 

[wycough]

Re: 1996 mariner 115 holeshot stumble problem

Not sure what the plug looks like now, after the adjustments. It was dark before. I'll pull the plugs Thursday and see how the four look.

I'm thinking that this motor likes it a little rich. A good medium between smooth idle and good holeshot. I've been told that these inline fours can be a little tough to get perfect in both aspects.

Just because the tech thinks they are rich doesn't mean they are in perpective to how the motor was use to running. I think I will richen them just a tad if the plugs read like it needs it. Then check holeshot.

If no improvement then I guess that leaves me with a carb rebuild. OUCH! 400-500 dollars. I just don't have the time right now to do it myself. Gaskets, needles and floats could be the problem. But, I really think it's an adjustment issue. It's just that i'm running out of adjustments to try.