Riddle Me This

Discussion in 'Carb/Tuning' started by jimvette999, Oct 26, 2018.

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  1. Oct 26, 2018 #1

    jimvette999

    jimvette999

    jimvette999

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    Hello Gents...

    I just rebuilt the carbs on my 98 Vmax. Put everything in except the large diaphragms that look good. Everything includes the needles and seats, air cut offs, carb to engine boots. I soaked the carbs in carb cleaner overnight in Gunk Carb Cleaner. Set the floats to 16.5mm on the level bench using Vmax fuel pump. It runs great... the only problem is when I sync the carbs it would sneeze hard enough to blow the hoses off on 3 and 4 and couple times on 1. The Carbsync hoses have a restrictor/baffle on the hoses and that's where it would pop loose. Anyhow, after syncing the sneezing while syncing stopped but I still noticed once or twice while test riding....right as your kind of slowly/lightly accelerating from a stopped position ...... this is the reason I took the carbs off to rebuild in the first place. I'm using COPS, new NGK plugs, stock exhaust, and a K&N filter. This spitting/sneezing started about a year ago. Any ideas as to what the problem might be??? Could COPS be causing this?? It's the only thing really different to the bike in recent years. Pics attached for boredom relief.

    TIA!
    Jim
     

    Attached Files:

  2. Oct 27, 2018 #2

    mabdcmb@yahoo.com

    mabdcmb@yahoo.com

    mabdcmb@yahoo.com

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    Does this happen when the engine is cold or up to temp or both?

    I thought it was normal to get a sneeze every so often when the engine is cold.

    You could try to richen up the pilot circuit by turning the AF screws out a touch. You could try using the choke a bit longer.
     
  3. Oct 27, 2018 #3

    jimvette999

    jimvette999

    jimvette999

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    Thank you for your reply.

    Before the carb overhaul, it was indeed worse before fully warmed up. I've only ridden it once since the overhaul and it was already fully hot by the time I synced it. As soon as I eased on the throttle to go down the driveway it sneezed and again when leaving the drive. I flogged it down the street a few times and it ran really strong, couple more normal stop and go's after that and it was fine. Came back and turned the jets "in" half a turn...(wrong way) and called it a day. I was just really surprised to be having the same issue I was trying cure after a complete overhaul. While much improved, the sneeze was still there and I wanted to see what other causes could be so I can completely eliminate it. It didn't do this for the first 18 years of ownership. I'll turn the screws out a full turn and see if that helps.....again thank you!
     
  4. Nov 2, 2018 #4

    jimvette999

    jimvette999

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    STILL SNEEZING! New plugs, COPS, stock jetting, stock exhaust. Could the slide diaphragms be the problem? It does this right off idle.....by off idle, I mean low rpm under load, as in when you're just pulling away from a stop. It does it the worst when on a dirt road, 1st gear, going 5 mph or less.

    REPLY
     
  5. Nov 3, 2018 #5

    sdt354

    sdt354

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    I'd go less on the A/F adjustments. 1/8 to 1/4 turn at a time is prudent. And it will effect more than idle. I'd bet the pilot circuit is not clean enough. Nothing to loose doing a shotgun once or twice. Good intake boots are a must.
     
  6. Nov 4, 2018 #6

    MaxMidnight

    MaxMidnight

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    Yeh, wot he suggested.
     
  7. Nov 4, 2018 #7

    Hugh Jaynuss

    Hugh Jaynuss

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    mine does the exact same think when it’s cold, under load if I don’t let it warm up at low RPM’S. I was thinking of checking all of my valves. Has 19k and is past due for the task.
     
  8. Nov 4, 2018 #8

    lilredrooster

    lilredrooster

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    Personally I would leave it as it is, do not spend any more time, energy or money on further parts, labour or disassembly....

    Buy and try Seafoam, Seafoam Motor Treatment Part # SF16, mix it into your fuel tank at 2 fluid ozs of seafoam per gallon of fuel. Do not put it into the engine oil. Try 2/3 tanks full and see how it goes..... Don`t be shy in mixing it, you can go much higher ratio if required but this ratio should do it.....

    Low cost experiment, low energy, no labour, this stuff works wonders, highly recommended.....

    Try and avoid putting fuel with any likelihood or trace of ethanol in your bike....

    Not going to bore you with all the details, just try it for yourself......
     
  9. Nov 4, 2018 #9

    jimvette999

    jimvette999

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    I did the Seafoam for several tanks at high ratios before rebuilding the carbs. No luck. I may indeed leave it as it is but it does bug me. I soaked the carbs in carb cleaner 24 hrs and blew with compressed air 100 psi. They are clean as a whistle IMO. Thank you.

    I appreciate what you're saying...but can you tell me....if I'm lean and I need to get to rich to see if that's the problem....what's the harm/problem richening at 1/2 turns to get there to see if that's the problem. True...creeping up on it is great to get the proper A/F ratio but I'm after the problem and was trying 1/4 to 1/2 turns. At 4 and even 4 1/2 turns out...no change. Factory was 3 1/2 turns out. You did read that I soaked the carbs in carb cleaner 24 hrs and blew with compressed air 100 psi? I also did the shotgun several times along with Seafoam before the carb rebuild. Even used Chemtool at the prescribed dosage for a couple of tanks prior to rebuild. They are clean as a whistle IMO. I put new OEM boots between the carbs and the intake, no others. Checked for vacuum leaks with Starting Fluid.....nuttin. The boots from Airbox to Carbs not changed. Thank you.

    I had a noisy valve train when the bike was new...2000 miles. I went through the valves and re-shimmed to the tightest allowable spec in the book, I have a quiet valve train to this day... 42000 miles later. I have a hard time believing mine is slack in the valve lash but maybe??? Thank you.
     
  10. Nov 4, 2018 #10

    Fire-medic

    Fire-medic

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    When you did the carb disassembly/cleaning, could you see through the small pilot jet in the carb, the smaller of the two, in each carb jet block? That tiny hole has to be clear, and stay-clear, and any sort of particulate matter can soon plug it. That causes symptoms like you're describing, poor low-speed operation .
     
  11. Nov 4, 2018 #11

    jimvette999

    jimvette999

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    Yes, looked at the light through them. It runs great overall....just under load, light throttle get sneezing through different carbs....not just one...particularly 4, 3, & 2 ...2 only once or twice while syncing. It sneezes the worst on loose sand trail, low RPM, low speed...otherwise just occasional sneeze from a carb while say, low speed parking lot maneuvering while looking for a spot to park or pulling away from a stop slowly. The sneeze is below the throttle plates I assume because it blows the hoses off the vacuum ports I connect to. Not backfiring through the carbs air box I don't think....unless it's backfiring on the closed intake valve and the sneeze has no place to exit other than the intake tube???? Thank you.
     
  12. Nov 4, 2018 #12

    sdt354

    sdt354

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    Soaking won't always break up the crud blocking a pilot jet. I've had plenty of racks with pilot jets that needed to be cleared with a drill bit or guitar wire or just replaced. I'm missing what your trying to accomplish by cranking out the A/F screws so much at once,no load. Using the choke while riding it will let you see if enriching is whats needed.
     
  13. Nov 4, 2018 #13

    jimvette999

    jimvette999

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    Thank you for the reply. I might just pull them back off and check closely the jet's you mentioned to be 100% positive. The carb cleaner isn't the good stuff it used to be. As for adjusting the A/F, my thinking is if lean is the problem, why worry about sneaking up on it...just fatten it up, if it goes away, great, fine tune from there. Do you think it could be valve lash if not jets??? Do you think poor air box boot fitment could be the problem?? Thanks again.
     
  14. Nov 5, 2018 #14

    jimvette999

    jimvette999

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    How important are these? Mine were loose in the bore...I fashioned some stainless sheet metal in an "L" shape to hold pressure on them but now I wonder if they should have been be replaced.


    Untitled.jpg
     
  15. Nov 6, 2018 at 6:24 PM #15

    Fire-medic

    Fire-medic

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    They're cheap-enough, you can usually re-use them. As long as they don't fall-out, they probably are OK to re-use. They are held in-position by their jet block location and the carb body.
     
  16. Nov 6, 2018 at 8:56 PM #16

    jimvette999

    jimvette999

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    Cheap?? I dropped another $56 dollars shipped for those little bastards. I think Yamaha made more on parts than they did on the sale of the bikes. Mine were not a snug fit in the bores and I presumed they were meant to be so I bought em' since I'm going to re-inspect the jets and such. That was the only think not replaced except for the slide diaphragms which will require a second mortgage if I want OEM. Mine looked good, and they can be done without pulling carbs so I re-used those.
    Thanks for the reply.
    Jim
     
  17. Nov 6, 2018 at 9:34 PM #17

    Fire-medic

    Fire-medic

    Fire-medic

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    People have had good luck with the aftermarket diaphragm rubbers being replaced on the stock slides, there are a couple ways to accomplish the replacement. The plastic slides are fragile! Do not use too-much force or hammer on them or it's "all the King's horses, and all the King's men," trying to glue those slides together again. I bought a set, because the address where they were sold from was a business a 20 minute drive from me. However, I haven't had to replace any, I picked them up after I priced the diaphragm/slides from Yamaha. Four aftermarket rubbers for < the price of one diaphragm/slide. Worth the gamble. I did do one, I ground-off the inside keeper ring, and used epoxy to fasten it after replacing the diaphragm, though some people say that you don't even have to do that, you can use small dental picks to remove the stock diaphragm. Then you stretch the aftermarket diaphragm into-place.
     
  18. Nov 6, 2018 at 10:25 PM #18

    jimvette999

    jimvette999

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    Yes, thank you....I had read the aftermarket were a little stiff at first but got better. I'll be careful if I have to replace them. Can't believe how expensive OEM'S are.
     

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