1975 115 2-stroke inline 6 WOT problems

[randomguy8524]

Things I have changed

1. Dist cap
2. spark wires
3. fuel pump diaphragm
4. impeller
5. all rotten wires except for the 3 distrib wires and 2 stator wires
6. all fuel hose replaced with new 5/16 because the old 3/8 hose had 3 or 4 points of air leakage
7. pulse hoses changed to 50psi rated 5/16 fuel line
8. carbs disassembled. Squeaky clean. No stuck needles. Floats show no apparent defects.
9. checked timing is correct. set to 20 degrees max advance.
10. link and sync and set idle screws to 2 1/2 turns out.
11. verified tank vent working
12. put some ring repair in cylinders and then ran a 50 to 1 and seafoam tank
13. Plugged backdraft hoses

110-115 psi on all warm cylinders. tell tale is strong and cool water. no spark loss seen in the dark anywhere. every plug is firing.

I am running 50 to 1 mix on Normal fuel. I have 24 gallons of this mixed fuel then know now to switch to a premium or low ethanol alternative for the future.

I did not change the dist and stator wires because the seemed a pain to access if even possible.

I went to all 5/16 fuel line because fuel line setup when I got the boat was all kinds of rigged air leaks all over. The factory spec calls for 3/8 until the quick connect on the cowl then 5/16 from there.

From a stand I can put the hammer down and she takes off like a champion. If the tach is to be believed it will buck itself right up to 5krpm and sing for about 45 seconds to a minute and a half. It will then bog down to about 4k. A little bit of surging. If I ease back a bit it will run great at 4500 seemingly all day. And when it bogs down. I can ease back a moment and then just open it up again and she goes.

To check if it was overheating I ran it WOT (as much as possible) on a lake for 1 and half hours straight and when loading WOT against the trailer for 15 minutes. It was only able to reach about 4k rpm lugging under this load but the entire time it never sputtered or faltered. Tell tale kept a stream flowing good. Checked cylinders for melted presents or changes at all after the lug fest and none. So I don't believe it to be overheating.

Could overheating wires from the stator or distributor cause this?

What about the 5/16 fuel hose not being able to push enough juice? The filter will be nearly full when I prime. Then after some WOT action the filter will nearly be empty of fuel. I've seen it look so empty it honestly didn't look to anything inside other than air but the motor was running. The primer ball goes soft, maybe compresses halfway during use.

I plugged the backdraft hoses on the carbs and left the brass jet screws in. At last look the bottom carb lost its jet screw. Should I be looking to put it back in or am I safe to just take them all out?

Any help is appreciated. This thing is driving me nuts.

 

[demarko210]

From a stand I can put the hammer down and she takes off like a champion. If the tach is to be believed it will buck itself right up to 5krpm and sing for about 45 seconds to a minute and a half. It will then bog down to about 4k. A little bit of surging. If I ease back a bit it will run great at 4500 seemingly all day. And when it bogs down. I can ease back a moment and then just open it up again and she goes.

To check if it was overheating I ran it WOT (as much as possible) on a lake for 1 and half hours straight and when loading WOT against the trailer for 15 minutes. It was only able to reach about 4k rpm lugging under this load but the entire time it never sputtered or faltered. Tell tale kept a stream flowing good. Checked cylinders for melted presents or changes at all after the lug fest and none. So I don't believe it to be overheating.

The primer ball goes soft, maybe compresses halfway during use.

I had a 115 to me this sounds like a fuel delivery issue. Switching back to that 3/8 fuel line may fix this but not sure. With the soft primer bulb it sounds like the fuel pump also but you replaced that, double check.

 

[Chris1956]

What prop pitch and what boat? You may be simply over propped.

Squeeze the primer bulb at WOT and see if she will rev up higher. If so, replace the fuel lines with 3/8". However, I think 5/16 fuel lines are OK, but the fuel pump, if the "figure 8-shaped" one can be marginal. If primer bulb collapses, antisiphon valve, fuel tank vent or tank fuel screen are suspect.

You could try a 6Gal tank and std Merc fuel line to rule out permanent tank fuel restriction.

Stator only charges the battery. It has no effect on the engine performance. If the distributor trigger was bad, you would not have any spark, so that is fine.

 

[racerone]

The bulb does not stay hard once motor is running, very normal.

 

[randomguy8524]

I reopened the carbs and found that carb one had one needle lever that was not pressed correctly and found it riding on top of the float. corrected the issue and checked other carbs to be sure. Checked to make sure they were all in spec. Minor adjustments needed. Removed the other 2 back draft jets. Fuel pump check valves removed examined and check out so back in they went.

Its being starved for fuel. I ran her on the lake for a few hours this morning observing. I pulled the fuel out line on the fuel pump to verify operation and its kicking fuel out. Kind of sputtery and weak but certainly pulsing and kicking fuel. But its either not enough or perhaps some filter screens in the brass carb fittings I missed somehow in the carb dismantling. After fixing that needle lever it runs much harder and will pull the fuel dry in the filter and die out. Pumping the bulb does feed it and keep it going. I pulled the fuel hose off the tank outlet and ran it right down the fill tube to verify if the pickup was getting clogged. no change.

Weak pulse? Clogged in-fitting screens? Is it possible that all my tinkering and troubleshooting on muffs has ate the impeller already? The pulse fuel shots coming looked very weak but I have nothing to compare.

thanks for all the quick replies fellas!

 

[racerone]

If motor keeps running with the manual fuel pump you need to go over the entire fuel system.----Starting with screen in the fuel tank.

 

[randomguy8524]

If motor keeps running with the manual fuel pump you need to go over the entire fuel system.----Starting with screen in the fuel tank.

I ran a line that bypassed multiple fittings as a simplified circuit test of sorts. line ran down fill tube directly to bypass pickup as well. From tank to a ball, filter and then straight to the pump. No change. pulse pump is kicking fuel. But seams meager and cant pull enough to keep the filter from running completely dry.

 

[racerone]

I remember people complaining about filters on outboards looking empty 50 years ago.---Motors ran just fine.-----Just the way it is I think.

 

[ryan 98]

If its sucking the primer bulb in considerably I'd be checking the pickup in your tank first. They usualy have a little stainless screen that can get clogged up. I like doing things by narrowing them down one big chunk at a time. I'd just rig a small fuel tank straight to the motor and then you could eliminate the whole fuel system in one go. Also make sure your tank is vented well, if it isint it will run like a top for 5 mins then start struggling for fuel

 

[Chris1956]

Those motors never had a fuel filter. They have a screen in the fuel pump An inline filter might restrict fuel. I would remove it for testing and if she passes, install a 20GPH water separator.

There are also screens under the brass elbows and tees on the carb covers. They do not usually get clogged, but can.

 

[randomguy8524]

Thanks for the replies. It was a 5/16 thru fitting on the splash guard I somehow mistook for a being a 3/8 and a cheap 5/16 primer bulb that would suck air through one of its bulb clamps at high fuel draw.

2 air leaks fixed. She runs great!

Now onto the next project. Went to relocate my batteries more bow side after having a bit of trouble planing with a 2 person tube and noticed a bit of soft flooring. Currently got the nose flooring off digging out some waterlogged foam. Foam down the center channel was about 10% total waterlogged but the side channels are nothing but squishy mess. Between relocating 140 pounds of trolling batteries, replacing possibly 100ish pounds of waterlogged foam and propping down (currently on the backup 23p after spinning the OG 17p) I hope to have it screaming at 5500-5700rpm and cruising smooth.

With 24 gallons of fuel in 2 12 gallon metal tanks and the 2 deep cylces and then also the inline 6 motor all plopped smack on the stern, with the bonus of some heavy foam and a sasquatch leaning over to gander at it that I may have went about weight distribution all wrong. It may have dawned on me when me and 2 people were standing stern side and i noticed my transom was .5" under water lol. Not good. First boat. I'm learning though. Before the batterys that transom sat very comfortably so seeing the splash guard filling up had me anxious for a moment so I quick hit the bilge expecting a situation. Turns out I'm fat and the boat had to much junk in the trunk. She was bone dry.

Hope to have her back on the water within a week. Thanks for the suggestions fellas!