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2003 RX-1 Stumbles Off Idle

mg_sxviper

Newbie
Joined
Sep 20, 2023
Messages
13
Age
59
Location
Chelan WA
Country
USA
Snowmobile
RX1 and SX Viper
Got a 2003 RX-1 that starts right up with choke on, then idles perfectly. When I hit the throttle it stumbles (and will die if pressed). If I put the choke half on, it will rev up so it's definitely a lean issue. I have gone through the carbs multiple times, all jets are clean, new pilot jet o-rings, even tried new pilot jets. They are stock sizes and I'm at 3400' so if anything it should be rich. Pilot screw set at 2 turns out, also tried 2.75 out to see if related, no diff. The rubber piston valves are not warped and seated good. The o-ring in the piston valve cover is ok. The carbs are seated good in the intake boots, the airbox boots are seated good as well. It feels like it's a vacuum issue that should be raising the piston valve on accel but don't know what happens in the process of accelerating. In the attached photo, I don't have the top vents connected yet, could that possibly be related, don't see how but asking anyway? I did not separate the carbs from each other, could there be o-rings between them or choke valve o-rings leaking air? I'm at a lost as to finding this and appreciate any help in advance.
 

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I have you checked the throttle free play to ensure it's not a TORS issue preventing the engine from reving up? Knowing the condition of my in-tank fuel filters when I replaced them on my RX-1, have you inspected yours to ensure they are not plugged/gummed up? When you had the carbs disassembled, did you also remove the needle valve and inspect those little screens?
Screen.JPG
 
I have TORS bypassed. I replaced the needle valve and inlet brass screen as well. I have not removed the in tank filters, good suggestion...
 
Not sure if they could be related to your issue but something to check. They can be a PITA to get to but if you have one of those flexible grab tools, you can fish them out but you will find there is not much slack in the fuel lines to completely remove them from the tank. I also had to rebuild one of my fuel pumps as I buggered one of the diaphrams when troubleshooting an issue. Although Yamaha does not list a rebuild kit for them, this is the kit I used.
 
Something else to check, knowing they were an issue on the 03-04 RX-1, are the coils as they are known to arc between coils and have led others to believe they had carb issues when in fact it was the coils. I had to replace two of mine and when doing so, ensured they were the superseded part number: 8FA-82310-00-00 Superseded by 8FA-82310-01-00 - IGNITION COIL ASSY

To check for arcing coils, just turn off the lights and fire it up and watch between the coils.
 
Got a 2003 RX-1 that starts right up with choke on, then idles perfectly. When I hit the throttle it stumbles (and will die if pressed). If I put the choke half on, it will rev up so it's definitely a lean issue. I have gone through the carbs multiple times, all jets are clean, new pilot jet o-rings, even tried new pilot jets. They are stock sizes and I'm at 3400' so if anything it should be rich. Pilot screw set at 2 turns out, also tried 2.75 out to see if related, no diff. The rubber piston valves are not warped and seated good. The o-ring in the piston valve cover is ok. The carbs are seated good in the intake boots, the airbox boots are seated good as well. It feels like it's a vacuum issue that should be raising the piston valve on accel but don't know what happens in the process of accelerating. In the attached photo, I don't have the top vents connected yet, could that possibly be related, don't see how but asking anyway? I did not separate the carbs from each other, could there be o-rings between them or choke valve o-rings leaking air? I'm at a lost as to finding this and appreciate any help in advance.
Were the carbs disassembled 1
Got a 2003 RX-1 that starts right up with choke on, then idles perfectly. When I hit the throttle it stumbles (and will die if pressed). If I put the choke half on, it will rev up so it's definitely a lean issue. I have gone through the carbs multiple times, all jets are clean, new pilot jet o-rings, even tried new pilot jets. They are stock sizes and I'm at 3400' so if anything it should be rich. Pilot screw set at 2 turns out, also tried 2.75 out to see if related, no diff. The rubber piston valves are not warped and seated good. The o-ring in the piston valve cover is ok. The carbs are seated good in the intake boots, the airbox boots are seated good as well. It feels like it's a vacuum issue that should be raising the piston valve on accel but don't know what happens in the process of accelerating. In the attached photo, I don't have the top vents connected yet, could that possibly be related, don't see how but asking anyway? I did not separate the carbs from each other, could there be o-rings between them or choke valve o-rings leaking air? I'm at a lost as to finding this and appreciate any help in advance.
were the carbs disassembled one at a time?
 
Got a 2003 RX-1 that starts right up with choke on, then idles perfectly. When I hit the throttle it stumbles (and will die if pressed). If I put the choke half on, it will rev up so it's definitely a lean issue. I have gone through the carbs multiple times, all jets are clean, new pilot jet o-rings, even tried new pilot jets. They are stock sizes and I'm at 3400' so if anything it should be rich. Pilot screw set at 2 turns out, also tried 2.75 out to see if related, no diff. The rubber piston valves are not warped and seated good. The o-ring in the piston valve cover is ok. The carbs are seated good in the intake boots, the airbox boots are seated good as well. It feels like it's a vacuum issue that should be raising the piston valve on accel but don't know what happens in the process of accelerating. In the attached photo, I don't have the top vents connected yet, could that possibly be related, don't see how but asking anyway? I did not separate the carbs from each other, could there be o-rings between them or choke valve o-rings leaking air? I'm at a lost as to finding this and appreciate any help in advance.

Got a 2003 RX-1 that starts right up with choke on, then idles perfectly. When I hit the throttle it stumbles (and will die if pressed). If I put the choke half on, it will rev up so it's definitely a lean issue. I have gone through the carbs multiple times, all jets are clean, new pilot jet o-rings, even tried new pilot jets. They are stock sizes and I'm at 3400' so if anything it should be rich. Pilot screw set at 2 turns out, also tried 2.75 out to see if related, no diff. The rubber piston valves are not warped and seated good. The o-ring in the piston valve cover is ok. The carbs are seated good in the intake boots, the airbox boots are seated good as well. It feels like it's a vacuum issue that should be raising the piston valve on accel but don't know what happens in the process of accelerating. In the attached photo, I don't have the top vents connected yet, could that possibly be related, don't see how but asking anyway? I did not separate the carbs from each other, could there be o-rings between them or choke valve o-rings leaking air? I'm at a lost as to finding this and appreciate any help in advance.
 
Yes each one but kept the
Yes each one but kept the bank together.
not trying to be a jerk but are you sure the jets haven’t been mixed up? Its easy to do& have seen it many times, the rx1 carbs are finicky & they run exactly as you described when carbs are dirty,also what is the history of the machine?did you just purchase it or did it run fine last year?
 
The fact it revs up when giving it choke would seem to indicate dirty carbs but as the OP stated, he just cleaned the carbs and even replaced jets/needle valves and such. That's why I suggested he check his in-tank filters as it's possible one or both are starting to disintegrate and continually dirtying his carbs. I know the one I removed practically fell apart when I removed it from its fuel line. Just something to check and/or eliminate as a possible issue.
 
Each time I remove the bowls the fuel is clean and I've removed the needle seats to see if new junk on the screen and they were clean. That being said, I'm going to check the filters this weekend and smoke the boots for leaks.
It's history... Got it from a friend this summer, has 900 miles, had been sitting for a few years with no fuel in it. First thing I did was clean carbs, they weren't bad, jets were not clogged. It starts immediately and idles perfectly smooth, so weird.
Thanks for all the responses so far.
 
Each time I remove the bowls the fuel is clean and I've removed the needle seats to see if new junk on the screen and they were clean. That being said, I'm going to check the filters this weekend and smoke the boots for leaks.
It's history... Got it from a friend this summer, has 900 miles, had been sitting for a few years with no fuel in it. First thing I did was clean carbs, they weren't bad, jets were not clogged. It starts immediately and idles perfectly smooth, so weird.
Thanks for all the responses so far.
Assuming you pulled the main jets out of the carb throats? And your sure the 2 similar jets in the bowl area didn’t get mixed up on one of the carbs? It’s classic rx1 carb symptoms with choke needing to be on & not revving up, the old saying on rx1 carbs is clean the carbs& then clean the carbs, even varnish that is hard to see causes problems, I haven’t seen any issues with the in tank filters or carb boots( mine is an 03 with original boots & changed in tank filters once probably 5 years ago when i had the tank off doing exhaust donuts, if you change the in tank filters I suggest adding extra hose to them as you cannot get them out from the factory as the hose is too short& if you ever want to change them again it will make your life much easier
 
You make a valid point. As much as I think that I removed a jet, cleaned it, then put back one at a time, I could have screwed that up so I definitely need to recheck them. If I indeed swapped the jet named power jet in parts diagram/starter jet in svc manual and main jet that would do it.
 
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Only other suggestion is to sync the carbs. Maybe one or multiple are out of adjustment. Syncing really only helps the initial step in of the throttle which sounds like the issue you are having.
 
if all else is checked and good check carb sync as suggested. one other thing, I know you think it’s lean but being too rich with the pilot screws causes exactly the same thing. Im at about 1000 ft and mine ended up around 1.5 turns out. It was last year when I last set them. But at two I was seeing very rich mixture. Some thing like 10.9-11.0:1. At 1.5 turns its about 14.0:1. Yes, I use a portable wideband left over from my EFI tuning days.

And one last thing. Have the CV springs been changed? Aftermarket springs dump fuel in a bit quicker on tip in. They require a bit leaner idle mixture much like I run mine and perfect sync. Even then there might be a small miss on tip in. My theory on that is the aftermarket springs are very light and may not all be the exact same calibration making them not all open exactly on time. Adjust sync with a slightly elevevated idle speed. About the rpm you tip in at. This might help minimize these variable.

What really needs to be done for best tip in is to properly adjust each pilot screw for best idle on each cylinder while the engine is hot. I have not been able to accomplish this. The screws are simply impossible to access with a hot engine.

I’ve found that to get the smoothest running engine is to run stock jets, stock airbox and stock CV springs. My sled showed up with all of the usual mods. As I fixed everything I found that most of the reason it ran crappy was due to all of the mods.

thanks.
 


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