Carb Sync

[Jason2tpa]

1998 S115TLRW

New to me issue I encountered after re-installing carbs following annual pull and clean (disclosure...I've done this countless times w/no issue). Launched the rig intending to run for bit then make fine tune adjustments to idle and speed. Start engine and its idle jumps up to high 2k. I immediately cut it off, cause that's never happened. Verified speed screw wasn't even in contact w/throttle lever, so r/o this wasn't causing the opening of the throttle valves (hint...if speed screw wasn't holding open valves soo much to cause this then something else is).

Followed the exact same procedure you see pictured, then started engine. Same result, but this time I kept engine running and pushed up on lower carb throttle lever. Rpms dropped, as expected. I'd release my thumb from the throttle lever, rpms jumped back up. Cut engine off. Loosened upper carb throttle lever securing screw (#3). Then while applying upward force to the lower carb throttle lever, tightened #3. Started engine and rpms steady at spec. But....here's where it get's strange.

I hadn't fully launched boat....so I put engine in fwd gear and increased throttle. Sounds good, no issues. Drop throttle and gear into neutral....but the rpms remain same...they didn't decrease as I reduced throttle. It's like the throttle lever isn't springing back to close the valves. Weird. I went back and forth w/removing #4, adjusting #3 so valves are closed, reinstalling #4, start engine, for about an hour then called it a night.

I reckon it's possible the spring loaded throttle lever(s) are gunked up, preventing these from springing back to close position. Plan on spraying these down w/PB blaster tomorrow and see if this remedies the issue. One other idea I had is if the oil pump's lever arm is too short it would hold the lower throttle lever open, which in turn would open upper throttle lever by #4. But....I didn't shorten the oil pump lever when removing carbs. And prior to me pulling carbs I experienced zero issues w/idle.

Anyways....if y'all think of something I might be missing or have any other suggestions...all are welcomed.

[TownsendsFJR1300]

As you've done this before without issue, I would check each carb, linkage disconnected to make sure the return spring (for each butterfly) is not broke.

You should be able to wind it tighter just to see if the spring coil is busted.


I just had a machine (Stihl high end back pack blower) that the return spring busted in the center of the "coil".



.

[Jason2tpa]

UPDATE

Nothing wrong with the carb throttle lever or springs. The oil pump rod was catching on the oil feed hose, which rests on the surface of the bottom cowling. So that's solved.

However, I've now a sync issue, probably from all the adjusting I did to the levers. Can barely get on plane...deep throaty when throttling up...no power. Then once on plane w/throttle still at WOT, motor stumbles w/****ing up down rpms until it gives in, then motor runs at top end. Having just cleaned carbs/jets, I know that ain't the issue. Highly unlikely bad fuel/debris (never experienced and fuel sits no longer than 1 week). Need to reset sync from start to finish and r/o fuel pump. Rain came today, couldn't finish.

[99yam40]

life sucks sometimes.
might want to make sure the timing is advancing when it should
2 things cause loss of power
lack of fuel and no timing advance

Oh yeah, I have cleaned carbs before and had something hit a main jet plugging it up.
maybe from pump or line.
had to take them back off at the boat ramp again to get it fixed.

[Jason2tpa]

life sucks sometimes.
might want to make sure the timing is advancing when it should
2 things cause loss of power
lack of fuel and no timing advance

Oh yeah, I have cleaned carbs before and had something hit a main jet plugging it up.
maybe from pump or line.
had to take them back off at the boat ramp again to get it fixed.

The same thought did cross my mind...pull'um again. Once I figured/fixed the throttle valve mishap, it took quite a number of cranks to turnover, which is unusual. Had me wondering....do the jets play a role with starting motor? If so, which ones?

[ChuckB1954]

Probably doesn't apply to you. but I verified my carb problems when I pulled off one plug wire off at a time while idling. My problem was probably only in the idle circuit. Never tried it when the engine was in the upper RPM range. My boat would struggle to plane though. One plug wire didn't make a difference as did closing the air adjusting screw for the same cylinder... Plugged up #4 carb.

[Jason2tpa]

If Im reading you right....by pulling off one plug coil at a time you isolated which of the 4 barrels was the culprit?

[Jason2tpa]

life sucks sometimes.
might want to make sure the timing is advancing when it should
2 things cause loss of power
lack of fuel and no timing advance

Oh yeah, I have cleaned carbs before and had something hit a main jet plugging it up.
maybe from pump or line.
had to take them back off at the boat ramp again to get it fixed.

Installed new fuel pump and filter cause it was due for change...synced carbs to spec...starts and idles good...no power under load. Deep throaty sound at throttle up. Enough to get on plane and run at half speed. Primer bulb is full and flowing. Gonna pull carbs/jets and start again from scratch. Gotta be a re-clogged jet. The only other possible fuel related issue is water in the fuel....but same tank of fuel i was running before pulling carbs w/o this issue.

[TownsendsFJR1300]

If Im reading you right....by pulling off one plug coil at a time you isolated which of the 4 barrels was the culprit?

That's correct..

If the cylinder is making power, pulling the spark plug wire (killing the cylinder), SHOULD show a drop in RPM's.

If pulling the wire doesn't change the RPM's, you now know that cylinder is dead.

Whether it's the carb, compression, ignition, etc, further investigation is needed..


To answer about the "barrel" of the carb, yes, that barrel feeds THAT CYLINDER.


I would ground the wire to the block just so you don't damage any electrics..