SV engine sputtering - suggestions?

Discussion in 'Technical Forum' started by racer51, May 27, 2013.

  1. racer51

    racer51 Active Member

    Joined:
    Jul 7, 2009
    Messages:
    313
    Likes Received:
    1
    Real Name:
    Rick Newcombe "Duke Nukem"
    Hi, Everyone. I'm seeking the wisdom of experience in solving a problem with my SV Gen1 engine.

    Symptoms:
    1. No power, engine struggles to rev starting at about 5k rpm.
    2. First detectable issue was that the fuel tank was pressurizing. Performance was "notchy" to start with.
    3. As soon as bike was leaned over in a corner, it seemed as if all power was lost and almost sounded like it was running on one cylinder.
    4. Sunday morning, bike turned over about 1/2 a revolution and "locked up" so that the starter would not turn it over. I managed to "unlock" it by putting it in gear and manually rotating the rear wheel against the seeming locked up engine.

    Troubleshooting:
    1. First two laps on bike on Sat. morning, engine seemed to perform fine. Would easily rev to 10k. Laps 3+ performance got progressively worse. Got a total of 7 laps in Sat.
    2. Although it did not appear to turn over more than a millimeter, eventually the engine "released" and I could crank it over with the starter.
    3. Pulled starter and it spins freely. So far this peculiar seizing problem has not returned.
    4. Once going, during practice engine performance deteriorated gradually to the point it would only pull about 5k rpm.
    5. Removed ball valve from vortex gas cap, which helped for about 2 laps. Added new plugs and checked fuel lines.
    6. Checked all electrical connections and cleaned petcock valve.

    Looking for solutions on where to start troubleshooting next.

    Thanks in advance for any suggestions you might offer.
     
    Last edited: May 27, 2013
  2. Dean

    Dean Active Member

    Joined:
    Jul 14, 2009
    Messages:
    198
    Likes Received:
    0
    I had a similar issue on mind, where after about 8k, it felt like it was running on 1 cylinder. It was awesome the day before, but after 3 laps in the wet, it was dying. I checked for water in the plugs and both were dry. I filled the connectors with dielectric grease just be sure, because, well, I race at Mission, and it's usually wet. When I pulled the front plug, I could see a slight grounding burn on the outside of the plug. My front plug cable was pulled to the side too tight, and only when under load, would it arc to the engine and not the plug.

    Once I fixed that, it was back to full power.

    Is this a gen1 or gen2 bike? If gen1, you might want to try a harley petcock for the tank. They work well, and don't plug up.
     
  3. Fireman

    Fireman Well-Known Member

    Joined:
    Jul 4, 2009
    Messages:
    834
    Likes Received:
    15
    Sounds like a fueling issue for the most part rick. The "running on one cylinder" sound could be fuel starvation. Dean knows his SV's and I am certain that there are a few other guru's in the club (Steve Robertson maybe?)

    Good luck. I am sure it will be something easy (or silly) it almost always is.
     
  4. Arctic Donkey

    Arctic Donkey Active Member

    Joined:
    Jul 4, 2009
    Messages:
    147
    Likes Received:
    1
    Real Name:
    Steve
    Well I'm certainly no mechanical guru but as Dean has already mentioned SVs, particularly Gen1 bikes can have issues of water getting around the front cylinder spark plug. While I didn't hear the noise you mentioned when I was with you in the pits I did hear when we were on track. I can't tell what the cause was but it certainly wasn't a good sound. I would start off with the easy things, check for spark/fuel/compression in both cylinders. I've never had one apart but doesn't the Gen1 use a mechanical fuel pump that operates off of engine vacuum? Maybe it has a diaphragm with a tear in it??? After that you might want to get into the carbs and check your linkages and the diaphragms in there too.
     
  5. jetfixer15

    jetfixer15 Active Member

    Joined:
    Jul 4, 2009
    Messages:
    129
    Likes Received:
    0
    Real Name:
    Aaron Cluff
    Is it a Gen 1 or 2 SV Rick?
     
  6. racer51

    racer51 Active Member

    Joined:
    Jul 7, 2009
    Messages:
    313
    Likes Received:
    1
    Real Name:
    Rick Newcombe "Duke Nukem"
    Gen 1

    She's a Gen 1. It's been suggested I take a good look at fuel pump output.
     
  7. racer51

    racer51 Active Member

    Joined:
    Jul 7, 2009
    Messages:
    313
    Likes Received:
    1
    Real Name:
    Rick Newcombe "Duke Nukem"
    Could jetting cause the sputter?

    I'm going to pull the carbs this week and will report on jet size. Could it be a simple as the bike being jetted for sea level?
     
  8. jetfixer15

    jetfixer15 Active Member

    Joined:
    Jul 4, 2009
    Messages:
    129
    Likes Received:
    0
    Real Name:
    Aaron Cluff
    From my Gen 1 SV combustion related Experience:

    FUEL: I ran my Gen 1 SV at Stratotech and Mission without making any jetting changes. The stock jets are 138's I believe. I had 152's with a BMC Race (the one with the wider top opening) air filter, when I ran at both tracks. If any of your carb vent tubes are blocked, a problem like the one you describe can occur (I have had this happen to me - it was the one that goes from the carbs to the gas tank). Making sure all the internal carb passageways like the main and pilot jets are clean and flow fuel is always the best place to start along with the integrity of the rubber diaphram. Carb syncronization is a must for any carb equiped bike. I have found the OEM petcock to be adequate for fuel flow ( I use 200 main jets with pod air filters), but they can get fouled ( a good cleaning can remedy that normaly. Dean mentioned a Harley unit for replacement as it will flow more fuel, as will a Pingle petcock, if your OEM one is beyond salvage.

    SPARK: Measure the spark plug gap and make sure its to spec. Check the structural integrity of the spark plug too as I have seen the insulation layer seperate from the main body. The spark plug colour can give you information too. Check each plug and see if they are the same and what they look like. If one is wet with fuel then no spark is occuring. You can meter the plug wire and coil if you have a multi meter or replace the plug first and see if the plug remains wet. After that, go to the plug wire and then coil. As Dean also mentioned, water inside the plug hole will cause problems with the sparkplug, which I have had happen.

    AIR: Make sure the gap between the top of the air filter and the underside of your gas tank is adequate. As long as you have the OEM tank mounting hardware in place, it will be. There are tank risers available but I have never used them. I mentioned the carb diaphrams and checking their integrity which ties into the air side as well.

    -The rubber boots that attach the carbs to the engine need to be air tight on the engine side and the clamps tight on the carb side (don't go crazy on those small phillips head screws though).

    I hope this helps.
     
  9. Jason Henton

    Jason Henton Active Member

    Joined:
    May 31, 2011
    Messages:
    192
    Likes Received:
    10
    I had a similar issue with the cylinder dropping out on me. Ended up it was shorting out the plug wire, through the insulation to the frame. Changed the plug wire and the problem went away. Also, with my machine, if the battery is not close to fully charged %80+ then it has a hard time turning it over, if at all. Hey wait a minute.. Arnt you faster than me? Nevermind, its just bad gas! :)
     
  10. sand.man

    sand.man Well-Known Member

    Joined:
    Oct 23, 2009
    Messages:
    554
    Likes Received:
    20
    Real Name:
    Ryan M
    So this is why I almost mated with you in one of the races on Sunday! Haha, hope you couldn't hear me screaming at you in my helmet, race anger and all that ;)

    Hope you get it sorted out.
     
  11. racer51

    racer51 Active Member

    Joined:
    Jul 7, 2009
    Messages:
    313
    Likes Received:
    1
    Real Name:
    Rick Newcombe "Duke Nukem"
    Pylon patrol

    Sorry about that! The bike didn't start to really act up badly until the Middleweight twins race. I worked on what I could before Sportsman, but then after one warm-up lap, chose not to gird specifically because I didn't want to be a pylon for the other racers. I'd never endanger others on purpose...maybe because I'm slow...but that's not on purpose! :)
     
  12. racer51

    racer51 Active Member

    Joined:
    Jul 7, 2009
    Messages:
    313
    Likes Received:
    1
    Real Name:
    Rick Newcombe "Duke Nukem"
    Awesome information - plug lead ZAP

    Thanks Aaron, this is some great information obviously gained through experience. Now I have someplace to start looking (and buying new parts...LOL).

    Just FYI, both plugs were a light brown. They were the first thing I changed. In testing I was getting a good ZAP from holding the front spark plug lead...is that normal if you're holding the rubber part??


     
  13. racer51

    racer51 Active Member

    Joined:
    Jul 7, 2009
    Messages:
    313
    Likes Received:
    1
    Real Name:
    Rick Newcombe "Duke Nukem"
    Location of fuel pump

    Hi, Team. First let me thank you all for your advice and suggestions. Next year I'll be a little more knowledgeable at SV tuning, but right now I'm a newb.

    Where is the fuel pump located on a Gen 1? Is it inside the gas tank? I see a "good" replacement on eBay for $68+- that has been recommended by some riders on http://svrider.com along with many comments about the original crapping out after extremely hard use...like 10 yrs of racing.
     
  14. Jason Henton

    Jason Henton Active Member

    Joined:
    May 31, 2011
    Messages:
    192
    Likes Received:
    10
    Fuel pump is on the right side, on the inside of the top frame rail. From what you said about getting shocked, I would be changing your plug wires and caps first.
     
  15. racer51

    racer51 Active Member

    Joined:
    Jul 7, 2009
    Messages:
    313
    Likes Received:
    1
    Real Name:
    Rick Newcombe "Duke Nukem"
    Little balls of red goo

    Hi, Everyone.

    Thought I'd let everyone know what I found when I disassembled the fuel system and carbs.

    Starting at the tank, the fuel filter was clear but the petcock was gummed up. Disassembled and did a thorough cleaning.

    Fuel pump was working but again not in as good of shape as I would normally prefer. Did a thorough cleaning.

    Float bowl on front carb was likely the source of my problem. They were both dirty with layers of gum but the front one had little red balls of goo about the size of the head of a pin in the main jet. They were definitely too big to flow through the tiny orifices in the carb. The tube that the needle jet sits in was also very gummed up particularly where the needle seats in the jet.

    Miraculously... I got it all back to together and it fired after pulling fuel into the system. Seems to rev freely now so I'm hoping I found and resolved the problem.

    Thanks everyone for your help and suggestions.
     
  16. Arctic Donkey

    Arctic Donkey Active Member

    Joined:
    Jul 4, 2009
    Messages:
    147
    Likes Received:
    1
    Real Name:
    Steve
    Good job Rick. I'm sure your neighbors won't mind some test runs up and down the street to make sure all is well :)
     
  17. racer51

    racer51 Active Member

    Joined:
    Jul 7, 2009
    Messages:
    313
    Likes Received:
    1
    Real Name:
    Rick Newcombe "Duke Nukem"
    SV jetting questions

    Hi, Team.

    My carb problems persist, but at least I'm getting more knowledgeable every step of the way.

    From more discussion with other riders and the advice provided so far, I believe I'm running the wrong main jets. They read "160" and the stockers are listed at 137.5. I'm tempted to go back to stock but I do have a BMC race filter, so a little larger is likely a good idea. Aaron mentions running 152's at both Mission and Strato with no problems. I'm likely only going to run in Edmonton so I wonder if I shouldn't try something between 137.5 and 152. Anyone have thoughts on this?

    Also came across a tuning article from Factory Pro where they suggested running 2 sizes larger on the front cylinder. Is this necessary or even wise?

    Notes: The lack of power and feeling of "bogging" at full throttle along with the "burbling" sound and regular backfires, indicate to me the carbs are running too rich. Also discovered the muffler was void of any packing material. I have repacked the can with new muffler packing glass. (wow, much more quiet and easier on the ears.) I'm hoping the increase in back pressure adds to the necessary forces acting on the system.
     
  18. sand.man

    sand.man Well-Known Member

    Joined:
    Oct 23, 2009
    Messages:
    554
    Likes Received:
    20
    Real Name:
    Ryan M
    You should speak to Doug Clavier @ Ronin Motorcycle Works in Sylvan Lake... He can have your bike singing in perfect harmony. He's also racing an SV.

    I'm under the impression that making the bike breathe better with air filter and exhaust actually draws more fuel from the carbs, as they work under the venturi effect of a high speed charge of air passing over the main jet opening causing a vacuum which draws fuel up from the float bowl.

    The faster flowing air draws more fuel, which, as I've been told, requires you to run smaller main jets.
     
  19. jetfixer15

    jetfixer15 Active Member

    Joined:
    Jul 4, 2009
    Messages:
    129
    Likes Received:
    0
    Real Name:
    Aaron Cluff
    A very common set up for the Gen 1 SV carbs is a BMC or K&N air filter (with the wide top opening), 152.5 main jets (up from stock 137.5), 17.5 pilot jets (up from stock 15), air fuel screws turned out 2.5 turns. If your air filter is aftermarket and has a small opening on the top you can widen it by cutting the material away, otherwise go to the stock jetting (if the opening is small). With BMC filters, the ones designated 'race' have the wide opening. I wouldn't concern yourself about running a bigger jet size on the front as that's more for when you run pod filters with 200 or 205 size main jets.

    Try running the bike with no air filter. If it runs better then it is running rich, and you need smaller main jets.

    Here is where I get my main and pilot jets:
    http://www.pjmotorsports.com/mikuni-jets.html#main jets
     
  20. racer51

    racer51 Active Member

    Joined:
    Jul 7, 2009
    Messages:
    313
    Likes Received:
    1
    Real Name:
    Rick Newcombe "Duke Nukem"
    SV jetting questions

    I spoke with Doug and am working with his advice. He's the one that mentioned that you do need some back pressure and that a burned out can will not provide enough back pressure to allow for "scavenging". LOL, regardless the bike was obnoxiously loud and it sounds better with the can re-packed.

    Aaron, you've been a great resource, thank you! At what clip setting do you run your needle jets? Do you know what type of needle jets work best? I think this bike's been done up with FactoryPro stuff. I have a BMC race with the full opening.

    The descriptions I get of the bike running worse as it warms up, the stumbling when going off throttle and sputtering at 1/4 to 1/2 throttle roll-on, fit my situation, again leading me to believe I'm too rich on the mains.
     
    Last edited: Jun 24, 2013

Share This Page