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98 GTX limited cuts out above 10mph.

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bendychicken

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I have a 98 gtx limited that will not go above 10 mph. It starts and idles ok, but when you apply the throttle and get up to 10 mph it dies. It does not matter if you slowly increase throttle or just dump it, it will die at 10 mph. If the throttle is rapidly pumped it will go above 10 mph up to maybe 25mph for about 10 seconds and then it will start to die.

I pulled the intake off the carbs and the rear carb is not pulling as hard as the front carb is. All of the old grey fuel lines have been replaced with newer ethanol rated fuel lines.

I have not checked the compression yet and don't know what the range is. I'm hoping this issue with the rear carb isn't a blown ring on the rear cylinder....that would seriously suck as I was hoping to take this baby out in the keys on the 30th.

Could the high needles just be out of wack or gummed up or somthing? I can't see how any adjustments on the carb would alter the amount of air the cylinder draws through the carb though.

Any thoughts? Anyone? I've been playing with this thing for a few days and my trip date is coming up soon. Any help would be greatly appreciated. :banghead:
 
The carbs need rebuilt, and the fuel system needs cleaned (filter, select valve, etc)

You could have damaged the engine. It's a 2 stroke, and even if you have the oil injection hooked up... it needs the fuel to transport the oil. Also, a lean run on the 2-stroke makes excessive heat. So, to be safe... check the compression.

Speaking of the oil injection... since the carbs are gummed up... when was the last time the oil system was cleaned? You should probably think about servicing that too.
 
Thanks for your reply DR. Honda.

The oil system was removed by the previous owner and it just gets premixed fuel now (40:1).

I'm going to the shop today to check the compression. If the compression looks good, I'm going to pull the carbs and clean them out. I will clean out the fuel selector as well.
I think the fuel lines should be fine as they were all changed by the previous owner except for the pulsation hose and I just changed that last hose.

I have a clymer manual for reference. Are they fairly accurate in your experience? It's been a real pain working with that manual because they cover so many years and models in one manual it takes 1/2 an hour just to figure out which sections apply to the machine I'm working on.

Also, I pulled the fuel bowl (filter housing) and it had about 1/2" of water standing in the bottom of it. That was several days ago.

Again, thank you for your input.
 
I think its specifically the needles and seats in the carbs...they arent opening. its prob them or the diaphrams that open them.

Clymers manuals SUCK...find yourself a OEM service manual.

Rebuild with only GENUINE mikuni parts. Needles and seats are seperate from the kits. Change out the fuel line, and clean out the fuel selector valve.
 
Update: checked compression. Got 150psi.

Pulled the carbs and disassembled. They were filthy. Lots of grey gunky stuff in them with little black particles and water droplets.

I'm going to clean everything and re assemble with a rebuild kit and new needles. I think I'm going to leave the seats in though as they look perfect.
 
Replace it. they come as a kit, and they just pull out.

It sounds like your fuel lines need replacing. They all do, but yours def needs it. make sure to clean the selector too.
 
bendychicken said:
Update: checked compression. Got 150psi.

Pulled the carbs and disassembled. They were filthy. Lots of grey gunky stuff in them with little black particles and water droplets.

I'm going to clean everything and re assemble with a rebuild kit and new needles. I think I'm going to leave the seats in though as they look perfect.
Click to expand...

Use your old springs from the N/S assembly. Will save a lot of headaches later getting the correct pop off pressure.
 
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Minnetonka4me said:
Replace it. they come as a kit, and they just pull out.

It sounds like your fuel lines need replacing. They all do, but yours def needs it. make sure to clean the selector too.
Click to expand...

The fuel lines were already replaced for the most part but it looks like they didnt clean out the carbs or the fuel selector valve.
 
You are on the right track. If you are buying rebuild kits... buy oem Mikuni kits. The aftermarket kits cause problems.
 
Dr Honda said:
You are on the right track. If you are buying rebuild kits... buy oem Mikuni kits. The aftermarket kits cause problems.
Click to expand...

okay I'm getting really frustrated at this point. I completely by past the fuel selector. all fuel hoses have been checked. carb has been completely rebuilt. I put the thing in the water in it does the same thing. I disconnected the pulsator hose and felt the pulse until the engine died. reconnected the pulsator reprimed fuel system.

I just don't know where else to go in the fuel system ben back to front. I actually pulled the pickups out of the tank and checked them for obstruction.


if I pull a vacuum on the lower hose coming into the fuel pump I should get fuel right? and if I pull a vacuum on the hoes coming in from the top which I assume is the return, I should get no fuel correct?
 
I just swapped them out. I'm reading in the manual about the pop off test. So basically I screwed up the rebuild and I'm gonna have to tear in the whole thing down again and check the springs and levers via pressure popoff test.

Nice, so staying up till 1am rebuilding the carbs was all for naught.
 
bendychicken said:
I just don't know where else to go in the fuel system ben back to front. I actually pulled the pickups out of the tank and checked them for obstruction.


if I pull a vacuum on the lower hose coming into the fuel pump I should get fuel right? and if I pull a vacuum on the hoes coming in from the top which I assume is the return, I should get no fuel correct?
Click to expand...

Yes. That is correct.

bendychicken said:
also I played with the high and low needles and opened them up a bit. It runs richer but it still cuts out under throttle.
Click to expand...


That's not good. If the engine wont run around (close to) the factory settings, somthing is wrong.

Your ski shoudl be:

High:
PTO: 1/4
MAG: 0

Low: 1-1/4





bendychicken said:
I just swapped them out. I'm reading in the manual about the pop off test. So basically I screwed up the rebuild and I'm gonna have to tear in the whole thing down again and check the springs and levers via pressure popoff test.

Nice, so staying up till 1am rebuilding the carbs was all for naught.
Click to expand...

Let us know how it goes.

Just some tips:

The arm on the needle should be flush with the body. If it takes more than 1mm up or down to get your pop-off, you need to chance to a different spring.

While doing the pop-off... put some oil down in the needle to get a clean pop. Re-oil to re-test. Once you get a good pop-off... make sure you are holding pressure behind the needle. If you are, put the diaphragm, and cover on... and recheck that it holds pressure.
 
It's not unusual for one cylinder to be weaker or stronger than the other but that would not make it do what it's doing. I had what sounds to be the identical problem although it could be different. On our 2001 GTS I bypassed the fuel filter, pitcock and all the lines that went with all that mess and ran one fuel line from the reserve tube on the tank with a good inline filter straight to the carb. I made sure the return fuel line and the vent line were not restricted and I capped the line coming off the tank marked "ON" with a rubber cap. This eliminated a lot of fuel line. Now it runs great. When the fuel gauge reads empty I know I'm running on reserve. I just don't have to switch the pitcock to reserve if I run that low on fuel. I'm not sure if yours does but mine also has a filter in the carb. These can get also get clogged up if fuel sits in the carbs to long between seasons. Pitcocks can also get gummed up as well. Good Luck.
 
Re-rebuilt the carbs and adjusted the rocker arm flush with the body. Installed correct srpings for pop-off. Retested pop-off after carb assembly.

Ski is still doing the exact same thing.

How do I check the fuel return line? Can I just take the hose off of the carb and shoot some compressed air in it? How do I know that the return line is flowing. How much back pressure should I get from the return line? Can I just hook up a bicycle pump to it and check how much pressure it holds before flowing back into the tank? I'm running out of time for my trip and I just don't know what else to do.

The ski smokes like hell when it's running at higher rpm (which requires me to rapidly pump the throttle to get it up that high). I think I may have double mixed the oil though as the smoke looks like oil smoke not a rich mixture of gas.

I tried running it with the gas cap off and that didn't change anything. The fuel selector valve has been bypasssed so I know that isn't it.

Grrrrr.....
 
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What about the accelerator pump on the carb? It pumps fuel. I can see fuel running through the clear lines coming from the pump so it must be working right?

I don't think it could be the fuel pump just because it has been rebuilt and it's such a simple device. I disconnected the pulse line from the fuel pump to see if the ski would die, and it did so it must be working, no?
 
Checked the fuel return. Return is open.

The check valve on the vent is in questionable shape but the ski would not run even with the gas cap off so I doubt fuel system back pressure on the return is the issue.
 
After a casual look in the engine section of the FSM, I'm convinced it has to be the rave valves.......or more specifically the systems that control them.
 
I doubt that it is the raves, they don't cause this kind of problem. Have you changed your spark plugs and verified you are firing on both cylinders with good compression? The 951 will idle suprisingly well on 1 cylinder and get up to about 10mph, sounds to me like your running on 1 cylinder.
 
actually no, I just assumed it was running on both just by how it sounded. I guess I could just pull the plugs with the wires connected and the plugs grounded and turn the thing over a few times and watch for sparks.
 
Mechanic says it has to be the carbs. Guess I'll be taking them apart and rechecking the popoff pressures. I must have screwed up the pop off test somehow. That has to be it. I shot carb cleaner through all of the passages in that carb and watched it flow through.

One thing I'm seeing around the net is that I shouldn't have done the test dry, I should have added wd-40 into the inlet of the carbs and added some on top of the needle before pressurizing. I'll get it one of these times :redface:
 
I've been reading that there is suppose to be a plastic cap over the high speed jet screw. There are none on my carb. It that a problem?
 
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