full throttle bog

[Mekanix]

96 sportster.

Noticed max rpm was 6000-6400 and improved with half choke.
Actually everything improved with half choke.
Also feels lean at mid range. As in: rev up and down slightly at steady throttle.

Havent done anything yet.

Any Ideas before I start.
There is no throttle response above 3/4 without choke.

Thinking of running fuel line direct from tank for quick troubleshooting if its carbs or fuel selector.

 

[Waterluvr]

Outside of the carbs or fuel pump needing some help it's the usual suspects ~Selector valve, air leak at the o-ring on a water separator filter, and a new one to me that took hooking up an outboard tank and line right to the fuel pump was a crack lengthwise in the plastic nipple on top of the fuel baffle where the *ON* supply line to the selector valve clamps on.

That one had me stumped, it flowed fuel really well to my Mity-Vac with the recovery cannister hooked up and only caused a problem when the boat was underway and subject to vibration.

 

[Mekanix]

Found a rip in the separator o-ring. I have a feeling that's not all it is though.
What a pain its going to be to remove the selector and put that back in :s


Can I replace the fuel lines with 1/4 inch automotive style ?
It has... I don't know what it is but its very thick walled fuel line.

 

[Waterluvr]

I use A-1 USCG rated line but there's nothing wrong with 1/4" ethanol resistant fuel injection line that works well. Once you pull the knob and retainer off the front of the valve you can pull the whole thing to you from inside the engine bay, SBT has a pretty nice replacement valve for a fair price.

 

[Mekanix]

Cool. I was hoping to get lucky and not have to get into the fuel lines but might as well get into it now.

I find it hard to believe that the pump can pull fuel over that distance and through the water separator. Seems like that would be the first thing to cause a leak.

Another thing I noticed; while going straight I could keep the rpm's pretty steady but any movement left or right cause a 1000 rpm drop that stays there for a few seconds and then slowly recovers.
I wonder what would be affected that much by slight movement.

 

[Waterluvr]

That's a tough one really, pretty much speculation without having the boat here to work on but you're loading the crank just a little bit at cruising throttle (say 80%) and it's not keeping up when it drop's 1000rpm's ~So long as compression is up there where it needs to be and you don't have something like a bad wire or resistor cap it's almost got to be a fuel problem.

Plugs a nice tan color, insulators not looking like a vanilla ice cream cone?

 

[Mekanix]

Just finished break-in, Comp is still 155. Definitly fuel since half choke recovers power every time. Also its running on straight fuel now instead ofthe premix.

Plugs are black with slight tan coming on near the end while I was troubleshooting with the choke.

 

[Waterluvr]

Just for your own satisfaction since your taking the time to replace the fuel lines, cut a few of them lengthwise near where they were clamped on and have a look at what's happening to the inner linings of the hose, all your fuel up there has at least a 5% blend or more of ethanol in it and it wreaks havoc on fuel systems and the seals in the selector valves.

I do a lot of boat and carb work and anymore if the boat is ten years or older replacing all the fuel lines has become a routine part of most fuel system repairs as we have to deal with a 10% ethanol blend here, it destroys the inner hose lining and that all winds up in filters and pumps and makes a mess of internal carb passages.

Almost every week I work on carbs that have been to someone else's shop recently and still aren't right, there's all manner of garbage laying in the bottom of my ultrasonic cleaning tank afterwards and I believe most of it is dissolved solids from fuel hose linings.

 

[Mekanix]

This was a US boat until 2011 and still has all the original hoses and clamps. I can't imagine what the inside of the lines will look like
I usually don't run into issues like this. Wide open is usually just fine but low end and pop off are what I'm normally playing with. The only time I've seen this was with completely clogged internal filters.

Are these carbs supposed to run with the high speed closed all the way ?

 

[Waterluvr]

They ship that way and you'll see that as the specification in the BRP manuals, and yes they will run nicely with the high sides closed so long as everything on the fuel supply side and pump is good to go. Here's the issue, the pto cylinder is always running just a bit hotter and you can tune that out using the pto high side adjuster.

When I have a 2 stroke Rotax boat in for fuel problems I do a final water test and tune and run two temperature probes on each cylinder and tune the pto high side to get those operating temps close to evened out at cruising speed. They run famously afterwards tuned like that and it's usually not very far at all off of being seated (1/16 to 1/8 of turn on most boats).

 

[Mekanix]

You know I just happen to have a set of thermocoubples with spark plug rings just waiting for a purpose

Thanks for the tip. What do you normally see for a temperature ?

 

[Waterluvr]

That has a huge bearing on the water temperature your operating in, on a summer's day in 75* surface temp water expect 140-155* near the cylinder bases, you get a more consistent reading the lower you go on the cylinders and throttle response is better tuned from there when you dump it wide open from a dead on the peg idle.

 

[Sportster-2001-951C-Stock]

I think if you want to be safe you can just start at factory suggestion then go a bit richer till you lose 50RPM or so.

I'm thinking black plugs are indicative of hydrocarbon soot.

 

[Mekanix]

I'm using the cv tech breakin oil and running the oil injection and I fog after each run. I'm thinking that's why the plugs are black.
New set going In and ill see what the diff is.

Whar a pain to get to the hgh speed screws with the airbox on

 

[Mekanix]

Ok had it out today and man what a difference!!

Replaced the water separator with an inline filter and pressure tested the system. Held just fine. Selector was really clean. Lines were good inside, No gunk!!

I can hit 7000 now easily and hold as long as I want without any quivering. Still haven't set the pto carb. I have it at 1/8th out right now and both plugs are beautifully tan after a 45 minute ride!

I'm waiting for a gasket for the water separator and in the mean time I'll just run the filter and change that if necessary.


The new problem I'm facing is that the steering is way off.

In order to go straight I have to turn the wheel left to 11:00 and while under power. It feels like I'm pushing against the jet wanting to straighten the nozzle.

When I look at the jet wash in the back while cruising I can see the wash pointed to the right a little when I have the wheel straight but when i turn the wheel to 11:00 the jet wash is facing straight back and I go in a straight line but if I let go of the wheel it will return to center and I'll start to make a right turn again.

Why ?

Could my jet pump not be square with the hull ? Could it be the nozzle in some way ?

In theory I should be able to leave the wheel straight and it should go straight but I always have to hold left just a bit and it feels like I'm loosing a bit of speed because of it.

 

[Sportster-2001-951C-Stock]

I was hoping you were going to say the center electrode insulator is turning yellow, that's what I notice after the 1st half hour or so with a fresh set of plugs. The yellow then becomes cardboard brown from there, not grey, red, purple, tan or some other color.

Assuming your pump isn't installed upside down or something like that I'd say you're noticing the limitations of using a jet pump for propulsion. I'd estimate my 130HP Rotax pulls my butt out of the water on skis about as well as a 65HP Johnson outboard can, almost.

 

[Bonmotwang]

My boat is doing the same thing, go right under power. and mine is 10 o'clock I would say. And the water stream is same as you described too.


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[Waterluvr]

My boat is doing the same thing, go right under power. and mine is 10 o'clock I would say. And the water stream is same as you described too.


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It's perfectly normal guys, engine torque and the direction of impeller rotation are the cause. If you reversed the engine rotation and leading/discharge angles of the impeller it would pull you over to the left.

The same issue exists on outboard engines and inboards, that's why you see left and right hand rotation props to match opposing engine rotations on twin engine boats designed to balance that annoying steering issue out.

 

[Bonmotwang]

It's perfectly normal guys, engine torque and the direction of impeller rotation are the cause. If you reversed the engine rotation and leading/discharge angles of the impeller it would pull you over to the left.

The same issue exists on outboard engines and inboards, that's why you see left and right hand rotation props to match opposing engine rotations on twin engine boats designed to balance that annoying steering issue out.

Some jet boats do left and right too?

 

[Waterluvr]

Some jet boats do left and right too?

No, they can get away with running the same rotation side by side in jets because all of the steering force is supplied by the pump discharge. That wouldn't work at all on an inboard boat spinning two right handed rotation prop's in front of the rudders, and backing up would be a nightmare.

 

[Sportster-2001-951C-Stock]

Our boats can maneuver at low speed to make a 360 rotation in it's own length, no many prop boats can claim that.

 

[Mekanix]

True, And they can crab sideways in neutral

I noticed there was an improvement with a second person in the 3rd seat and with a full tank of gas.

Seemed to track straighter.
Also I cleaned the hull. Maybe that did something.