Help diagnose a sick RX warrior!

[smokingcrater]

So my wife's sled was running a little strange last spring. Didn't idle well and was down on power. Assumed it just needed a carb cleaning, so finished that up this last weekend, and... here I am!

Took the carbs apart, like I have done for the last 8 years or so, and cleaned all jets. Nothing unusual, carbs were all fairly clean. Put it back together, fired it up, and same thing. On a cold start, it runs well for about 3 minutes, and then all of a sudden falls flat, up to the point it will die. Through elimination (new plugs, swapped coil packs, problem doesn't move), it is definitely the second cylinder from the clutch. I can unplug that coil pack while it is running and have almost no affect on it. (also verified good spark on that hole with the spark plug resting on the block)

Also did a compression test and came up with exactly 120 on each cylinder, and yes, I know that is low, but it could a completely cold engine, the cheap HF tester, or the fact I only held the throttle at WOT and didn't hold open the vacuum slides on each carb. In any case, all holes were the exact same.

So... I'm not a carb guy! What in a carb would potentially cause this type of problem? Where it seems to starve out after a couple minutes of idling?

 

[ToddMeister]

Is the fuel pump working properly?

 

[pdiddy]

Pretty interesting that CYL2 runs well cold but not warmed up. Are you sure it's starving when warmed up? I think the ECU drops the idle down at that point so that might be a factor. Maybe swap the carb next and see if the problem follows it? Keep in mind those pesky pilot jets are hard to clean. Actually, it might even be easier to swap the jets than the whole carbs.

 

[smokingcrater]

Is the fuel pump working properly?

The RX's have dual fuel pumps, feeding each end of the fuel rail. In theory a single pump is more than enough to run on. So i wouldn't think that would affect it too much but I haven't tested them.

 

[smokingcrater]

Pretty interesting that CYL2 runs well cold but not warmed up. Are you sure it's starving when warmed up? I think the ECU drops the idle down at that point so that might be a factor. Maybe swap the carb next and see if the problem follows it? Keep in mind those pesky pilot jets are hard to clean. Actually, it might even be easier to swap the jets than the whole carbs.

The more I think about it, I don't think actually ever runs well on that cylinder. I think the high idle is masking it. Once it is warmed up and out of fast-idle, it sounds more or less normal at >3000 rpm if I hold the throttle. The miss is still there, just much harder to pick up.

And yeah, I was already thinking that my next step is probably to swap the parts of carb #1 and carb #2 to see if the problem moves or not. (really hoping it does!) Breaking the carb rack apart doesn't look like much fun. Some part of me thinks there is no fuel in the bowl even, so might have to concentrate on that area of it.


As far as my get cleaning routine, I run fishing line through anything that I can, and then dunk the bowls and jets in a heated ultrasonic cleaner at 60 degrees C for 10 minutes, and finally send a shot of carb cleaner through them. I'm reasonably confident there was nothing left in them., but... (also spray carb cleaner through every hole I can find in each carb)

 

[RobX-1]

You mentioned you removed and cleaned the jets but did you also remove and clean each needle valve assembly as there is a small screen underneath the needle seat that could be plugged/gummed up. There is also a very small jet in the mouth of the carb that I also remove (to the left as you're looking into the mouth) that can be removed and cleaned. It's in a recessed hole where one of those pocket screwdrivers will just fit to unloosen it. The other side of the mouth of the carb has a hole too but it's blocked off.

I know you stated that you've annually disassembled and cleaned the carbs for the past 8 years but I wonder if you're now having a similar issue I ran into a few years back. I had posted this about my RX-1 with 11,000 miles in a different post about someone having an issue with their RX carbs so thought I would mention it here as it might have some bearing on your issue.

Throughout the years, I never had an issue with removing and cleaning the carbs (ie. soaking jets in Napa's parts solution as well as spraying with Gumout carb cleaner) annually and even bought a mercury carb sync'er to finish the job right; which could also be the root of your problem if it hasn't been done. Two years ago after doing the yearly maintenance, I could not get the carbs to sync like I had been able to do where all four lines of mercury were at the same level. In this state, the RX-1 idled fine but ran like crap; especially at full throttle. I can't tell you how many times I had the carbs off but still could not sync all four carbs together. I even bought a fuel pump rebuild kits (not so much as I wanted to but buggered up one of the gaskets during disassembly ). I honestly did not believe any of the jets needed to be replaced as I could see thru all orifices in the jets. I came to the conclusion that due to the age of the jets, they possibly tarnished up but not something noticeable to the naked eye. Since I hadn't replaced the needle and seats, when I did, I also replaced all of the jets, o-rings and such and also replaced the in-tank fuel filters. They are pain to replace but if you have one of those flexible bolt grabbers, you can snag the fuel lines and just barely get the filter out to replace with new. I did have one of the tank filters practically fall apart, the stem the fuel line connects to and the round filter the stem passes thru came apart, so this maybe something to consider as well. Once I did all of this, the ole beast was back to its old form to the point I could now sync the carbs and get a consistent level across all four carbs and the issue of running rough when getting into the throttle was non-existent. Not saying you need to do all of this but just letting you know what resolved mime.

As pdiddy mentioned, you could always try just swapping the internals from one carb to other rather than splitting the carb rack and swapping the entire carbs to determine if the issue follows the carb.

 

[smokingcrater]

You mentioned you removed and cleaned the jets but did you also remove and clean each needle valve assembly as there is a small screen underneath the needle seat that could be plugged/gummed up. There is also a very small jet in the mouth of the carb that I also remove (to the left as you're looking into the mouth) that can be removed and cleaned. It's in a recessed hole where one of those pocket screwdrivers will just fit to unloosen it. The other side of the mouth of the carb has a hole too but it's blocked off.

I know you stated that you've annually disassembled and cleaned the carbs for the past 8 years but I wonder if you're now having a similar issue I ran into a few years back. I had posted this about my RX-1 with 11,000 miles in a different post about someone having an issue with their RX carbs so thought I would mention it here as it might have some bearing on your issue.

Yep, removed/cleaned everything on the bottom side of the carb that is removable, including that little round screen thing under the float pin. (#11 in the pic) That was the only screen I found so I'm assuming that is the one you are referring to?

 

[RobX-1]

Yep, that's the screen on the needle valve assembly (#10) I was referring to. And, #29 is the small jet I had mentioned. Have you also confirmed the pilot screws are all adjusted the same.

 

[MrSled]

Could need a valve adjustment!

 

[smokingcrater]

Could need a valve adjustment!

Not impossible, but this is a REALLY low mile warrior that was relatively easy driven for its life. My wifes sled, groomed trails only, and it has around 1400 miles on it.

 

[1nc 2000]

Check wires rubbed thru near battery area on chassis.

 

[smokingcrater]

So, update...

Just to verify fuel, I was careful removing the carbs and drained them into a container one a time. All had roughly equal amounts (about 10 seconds to drain each) Also tested each fuel pump, hooked up an old brake bleeder reservoir to the fuel lines one at a time and held a gloved hand over the respective intake to build vacuum. Both pumps pumped about an inch of gas into the container in 5 seconds or so. (I was mistaken above, there isn't a common fuel rail, one pump feeds carbs 1,2 the other pump feeds carbs 3 and 4.

Next was the teardown, and noticed one thing, possibly two. Normally when I clean carbs I don't take out the pilot screws, just check them. When I cleaned earlier this week I had taken them out, and somehow apparently got two of the microscopic washers on the pilot screw for #2 and #4 had none. (hey those things are tiny!) Although that might not have had much effect, it wasn't helping either. Straightened that out and reset to 2 turns out.

The other thing that was a little strange that I can't really confirm... I swapped all the parts on carb 1 and 2, and checked everything closely when reinstalling. When I blew through the pilot jet, sometimes there was almost like a momentary valve inside it that would sometimes engage. It was a perfectly circular, clear hole looking through it though. My only guess is maybe a tiny flap of varnish/gunk that was stuck to the side would sometimes flip up to obstruct flow. Blasted it with compressed air, a bunch of carb cleaner, and then more compressed air, and I couldn't recreate that effect after that.

(also removed/checked those air pilot jets inside the throat of the carb. Yeah, they had never been removed, only cleaned with carb cleaner shot through them, but they were all perfectly clean. Those things have a massive diameter comnpared to the fuel jets.)


So... everything is back together, will hang the carbs back on the sled tomorrow and see if I solved anything! At a minimum I just hope it moved to cylinder #1 at least.

 

[RobX-1]

I believe those washers on the pilot screws are used to keep uniform pressure on the rubber o-ring when pilot screw is tighten and the spring compresses on the washer. Without the washer, I could see the spring just compressing into the o-ring and not creating a good seal. Now that you got that resolved and cleaned the carbs again, am curious to know your results. You can't clean these carbs enough as this emoji was created just for situations like this

Are you planning on sync'ing the carbs once you get this squared away?

 

[smokingcrater]

yeah given how much I've played with the carbs I'm going to resync. (ATF in a tube stapled to a board method!)

Also, REALLY liking my EFI Nytro at the moment!

 

[MrSled]

Not impossible, but this is a REALLY low mile warrior that was relatively easy driven for its life. My wifes sled, groomed trails only, and it has around 1400 miles on it.

I thought you had posted it was up in miles.. you are correct I would guess not needed. Sorry my bad . Usually the Vectors, Rages and the RX1 if the pilots don't get pulled and thoroughly cleaned or replaced they run like crap.. it don't take much tp plug those pilots as you know based on the size of the holes in them.