2003 SX Viper won't run below 2000rpm

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kurick

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Hey guys first post here. Have 2 vipers. One 2004 stock and one 2003 Mtn with bender triple pipes that will not idle. Starts on full choke only and runs great above 2000rpm(with choke off). Once it drops to 1800 it quits, unless I "massage" it back to life. Things I have done: Disconnected TORS. Reeds are good(not chipped). Ohm checked stator, good. Removed flywheel and sanded rust(wasn't bad at all). All new plugs. Swapped coil rack from good running viper. Cleaned carbs 3 times following mrviper's post in the tech section. The pilot circuit is clean. Adjusted TPS(even though I don't know how to set it, I was frustrated and needed to try something after the last carb clean). Makes no difference if the headlight is on high or low beam. 2000ft alt. 165mains. 55pilots. A/F screw 1 7/8. Compression is 100 110 110. A little low but it should still idle? I have a video on my phone I will try to upload, or if someone knows what's up I will email it to them direct. Thanks in advance. This site is great, just not finding that other fella with the same issue that already has a great thread about this.
 
They are under the float. Remove float (use a spring load punch) to remove pin. Then under float is a screen held in by screw. Seen these plugged a number of times. Worth a shot.
 
Yanked the carbs again. Had a centre punch like you had posted, perfect for removing the pins, thanks. Pulled the screens. Very little crud on them. Cleaned them with carb cleaner anyway. Sprayed carb cleaner thru fuel inlet port, no obstructions. Removed the small air inlet jet and sprayed cleaner thru there, was clean. The carb cleaner comes out of the pilot jet. Installed everything and started engine. Runs the same. Confirmed that pulling the choke at 3000 just bogs and dies like usual, like it's flooding. I believe I have ruled out the lean idle presumption? I've searched the forums looking for TPS diagnostics, can't pin point anything. Gotta be electrical?!
 
Things I would try. Put every thing back together airbox and tors wires than adjust throttle cable for some play if it is tight at carbs. Start with choke and let it idle don't touch the gas but set your idle at carbs with the idle screw.If you need to keep pulling the choke lever to make it idle it is lean and the pilot jets must be removed from carbs to be cleaned properly.
 
Does the sled act like it is running out of fuel by increasing in rpm then quitting or just wont run? You have to establish whether it is too lean or too rich at the lower rpm. Does it run with choke on at the lower rpm?
A few things come to mind:
-if the carb needle and seat O rings are hard or cracked they will leak fuel constantly and create a rich condition just like too high of a float setting...but it sounds like yours is lean not rich
-if your crankshaft seals are damaged, too hard, or cracked you will end up with a lean condition
-cracked pulse line from crankcase to fuel pump can cause lean issues
-fuel pump issue
-cracked carb boots will suck air and cause lean condition
 
Ok boys. Swapped carbs from good running Viper. Runs the same. While keeping it running at 2000rpm, I sprayed ether at both crankshaft seals and all the carb boots. No change in rpm. Put the carbs from the Viper that doesn't idle onto the other, runs like a top. It's like the ignition is being cut below 2000...
 
kurick said:
Ok boys. Swapped carbs from good running Viper. Runs the same. While keeping it running at 2000rpm, I sprayed ether at both crankshaft seals and all the carb boots. No change in rpm. Put the carbs from the Viper that doesn't idle onto the other, runs like a top. It's like the ignition is being cut below 2000...
Click to expand...

Fuel filter?
 
Well that rules out the carbs lol if it cuts out like the key is being shut off there is a tor behind the gas flipper might be stuck and try unplugging headlight tac and stuff.
 
Your 2004 Viper should have DCS so unfortunately you can’t swap CDI boxes
You could swap the spark plug wire boots... maybe you will get lucky.
I am wondering about a couple things:
- stator
- CDI
- Piston/ring damage
- crank bearings
 
Sounds almost like a cracked pulse line to the fuel pump.
Check that line closely that runs from the crankcase to the fuel pump.
If is has a small crack, it may only have enough suction to run the fuel pump at higher rpm.
 
-When i swapped the coils i used the coils, wires, and plugs from the 2004.
-Ran without the belt, same thing.
-Have not checked the suction fuel filter.
-When i did compression test i had the carbs out so i put the 3 hoses from the fuel pump into solo cups because they were pumping a lot of gas into the belly pan.
Thanks for the info about the CDI and DCS, i didn't know they would be different. Should a guy swap stators?

Thanks for your time guys.
 
bluewho said:
Well that rules out the carbs lol if it cuts out like the key is being shut off there is a tor behind the gas flipper might be stuck and try unplugging headlight tac and stuff.
Click to expand...

TOR switch under the throttle lever? I'll check it out! Will unplug headlights and tach as well.
 
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