The Opposite of Bogging FX-1/Super Jet

[E350]

1995 FX-1 with Single carb 701, MSD Enhancer, stock oem exhaust.

Throttle cable is not hanging up.

Runs fine at idle to slow ski-able speed but seems like there is no mid-rpm.

Rather, the ski goes from slow but ski-able speed to 3/4 WOT.

It runs fine at 3/4 WOT to WOT.

There is absolutely no hesitation.

There is no bogging.

It acts like there is a pipe on it which is tuned to have a "light-switch" throttle response which jerks your arms off.

There is simply no linear throttle response between slow ski-able speed and 3/4 WOT.

Throttle response from 3/4 WOT to WOT is linear.

I changed the carb to another known good carb last night.

And today . . .

Absolutely no change from above. The symptoms are identical with no change whatsoever, so likely not the carb.

Before I changed the carb I followed the Service Manual and warmed up the engine, checked the torque on the accessible head bolts (all were properly torqued) and then checked the compression with my Snap On gauge. 144 lbs. rear cyl. 146 lbs. front cyl.

I shined a pen light down the spark plug hole and everything looked normal.

After skiing today I checked the new spark plugs I installed after the ride two days ago in an attempt to fix the problem and this is the photo I just took of them:



When I put the original carb back on tonight, I stuck my inspection camera down the intake manifold, and the reeds look good to me in that they are all intact and there was no debris in there.

This is a symptom I am not familiar with.

Any suggestions?

 

[WFO Speedracer]

Yes you have the spark plugs put in the wrong way .

 

[E350]

Thanks WFO, probably why I was having problems attaching the cables to the electrodes.

It sure seems like a carb problem. like there is no mid-range before near WOT high-range. I guess it could be a carb problem since I was the one that has rebuilt the carbs over the years.

But I have never checked the pop off pressure on either carb.

But why would both carbs act exactly the same?

And something changed in the ski which I am not aware of which caused this problem to arise, and it arose slowly over the course of three rides.

Can something have happened on the stock exhaust which would cause these throttle symptoms?

 

[WFO Speedracer]

Have you checked the plastic reed valves on the back of jet plates , they can cause weird issues like this .

 

[E350]

I don't really know what those are.

Are they on the other side of the reeds which I can see from an inspection camera in the intake manifold?

If so, I can pull the intake manifold and pull out and examine the reeds both inside and out.

 

[kevbo]

Ive had that happen when the tank vent check valve stuck shut. It would idle and come to life near full throttle. It was confusing until I noticed that the tank was sucked in a little. If it happened slowly, make sure the tank is venting!

 

[WFO Speedracer]

I don't really know what those are.

Are they on the other side of the reeds which I can see from an inspection camera in the intake manifold?

If so, I can pull the intake manifold and pull out and examine the reeds both inside and out.

No inside the carbs on the plate that holds the high and low speed jets , remove the two screws on the jet plate and look on the back side of the plate , clear plastic reed with one screw and a metal plate over it.

 

[E350]

Well I found that the fuel tank intake vent air/water separator canister had 1/2" of water in it. So, I drained it and then disconnected the intake vent from the hose to that canister and blew into the vent and it was working fine.

But when I took the ski out for a test run today, it acted the same, even worse. Now the low speed is getting rough. WOT is still golden but mid-range and lower speeds are deteriorating.

Well, we used to be a jet skiing family, but since I am trying to also rebuild the pump in my wife's SN SJ, we are down to a single ski. She water skied today. I am confused. So, I will be researching these symptoms. And it looks like I will be wrenching tomorrow and for the foreseeable future.

But I shouldn't be whining, compared to Quinc's recent misfortune, we are fortunate.

 

[WFO Speedracer]

If it acts like a carb issue, usually it's a carb issue , have you pulled them off and gone through them yet , if not what's stopping you ?

 

[E350]

@WFO Speedracer What do you think about this approach?
I have a brand new, never used SBN 44 which I put on the 550sx.
How about I put that on the FX-1 and try it?
Won't that rule out any discussion of the carb?

 

[kevbo]

Try it out. Disassemble your old one and check everything., make sure the pulse line isnt leaking.. I like to run the tank completely vented, that little check valve can cause problems. You will need to drain the water separator more often if its removed.

 

[Myself]

Original fiberglass waterbox? Broken baffle blocking flow?

 

[WFO Speedracer]

@WFO Speedracer What do you think about this approach?
I have a brand new, never used SBN 44 which I put on the 550sx.
How about I put that on the FX-1 and try it?
Won't that rule out any discussion of the carb?

You want to know what I really think , ok here goes pull , the damn carb already, it's a single carb 61X , I know personally I could have it off in 5 minutes or less using hand tools , quicker than that with the 1/4" impact .

You have spent way more time typing here than it takes to go through a single 44 carb assy.

If that check valve. reed whatever you want to call it is damaged it will be a dead dog till it gets on the main jet , Yamaha doesn't even show it as a replicable part but it comes in all the Mikuni carb kits , number 12 on the second diagram.

 

[E350]

@Myself Yes it is the original water box. Should I remove the fuel tank and then shake the water box?

@WFO Speedracer I put a different known good carb on and the symptoms were the same. I can put the brand new SBN 44 on in two minutes and rule out my adjustments or any wear or obstructions in the carb. Wouldn't that be better?

 

[WFO Speedracer]

If you have already swapped carbs out then do what Myself suggested.

 

[E350]

Ok, a little bit of wishful thinking here, which I won't be able to test until Monday.

When I was removing the battery in preparation to remove the fuel tank to remove and check the integrity of the water box, I was surprised to find that the positive cable on the battery terminal was a little loose.

I had recently taken the stronger AGM out of the FX-1 to move it to the 550sx to see if the 550sx's starter would turn over with the FX-1's stronger battery and apparently the positive cable on the weaker AGM battery which I had swapped into the FX-1 loosened while riding.

Hmmm . . .

It likely is never that simple, but I will check Monday.

 

[WFO Speedracer]

Ok I have to ask this , mostly because no one else will , what exactly does a loose positive battery cable have to do with the ski not running correctly , I am just trying my best to follow your line of thinking here , honestly I cannot follow it at all , once the ski is started you could take the battery completely out of the ski and it would still perform just fine .
.
At any rate , have you checked the reeds , chipped edges on a set of reeds or reeds that are not sealing properly could be the issue and it would develop slowly and get worse over time .

 

[JC-SuperJet]

The MSD Enhancer is drawing power from bofth the Battery and Charging system...

https://forums.holley.com/forum/msd-powersports-forums/msd-powersports-troubleshooting/16632-superjet-enhancer-question#post150434

 

[E350]

Yes, I wondered if the problem was even the MSD Enhancher itself, but I wanted to run down all potential fuel issues before moving on to electrical.

But finding the positive cable terminal loose, maybe 3/16's loose on the battery post, makes me want to test first without touching more.

Wow, thank you @JC-SuperJet, "I've got a 92 Limited SJ with the Enhancer and recently I'd noticed a drop off in my bottom end pickup":



I think I will also remove the stronger AGM battery from the dormant 550sx and put it back into the FX-1 before testing on Monday.

Fingers crossed. Wish me good luck!

 

[WFO Speedracer]

The MSD Enhancer is drawing power from bofth the Battery and Charging system...

https://forums.holley.com/forum/msd-powersports-forums/msd-powersports-troubleshooting/16632-superjet-enhancer-question#post150434

Gotcha , I did not see that the MSD enhance was in play, however if it had enough of a connection to start the ski everything else on the ski would work just fine as the rest is all low amperage circuits .

I do fully realize that some ignition issues can mimic carb issues , I do have zero experience with MSD enhancers so I am not the one to speak on that subject .