99 700SX backfire/dead throttle spot

S

spaceman99sx

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Joined
Feb 15, 2009
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12
Age
54
Location
Ottawa, Canada
I have a 99 Vmax 700SX that is giving me problems this year. Hopefully someone can help.
The symptoms are:
- it fouls the clutch side sparkplug (which is usually wet)
- burns a lot more gas
- sputters/backfire around 40km/h,
- at times it has a big dead spot in the throttle around 60-80 km/h.
- it still has top end power and idles fine
- the odd time it is only running on 2 cyclinders
- at times it runs perfectly normal
- it is worse in warm weather

Things the dealer tried:
- replaced the sparkplug wire boots, cleaned the carbs
- tested cdi and coils

Things I tried:
- swapped spark plug wires and drove for 5 hours and the same cyclinder fouled
- cleaned the carbs again (they were spotless)
- cleaned and checked the primer plunge
- verified the floats were in spec and the shutoff was working
- tested compression on all 3 cylinders: 125psi
- swapped the main jets on the 1st and 3rd cylinder and swapped the reeds on the 1st and 2nd cylinder, after a 15 minute ride with sputtering (lack of snow right now), the clutch side plug (1st) was wet

I'm running out of ideas, any thoughts would be greatly appreciated.
Thanks.
 
I had the same problem i on ride last weekend and it was the plug beleive it or not. Try going to a small engine repair place and get to right plug for your sled. Mine is a BPR9ES and only use ngk plugs. Now the reason i say to go to a small engine rapair place is that the plugs are packed seprit for each other and not grouped together in a plastic pacage and the kid at the canadian tire or what ever is in the states does not care if he dropes the box of spark plugs on the cement but the guy at the small engine shop should take care of his spark pugs and not play football with the box.
 
i have had better luck with champion plugs,,,,n2c. in ngk the r stands for resistor they also sell a bp9es that is a better plug i think, anyway is a cheaper way and easier then pulling carbs all the time if you know they are clean,,, try new plugs and see what happens.
 
I started the season with new plugs (BR9ES .028 gap), the dealer changed the fouling one when I first brought it in (after 3 days or riding), and I've changed them since but no such luck:(
 
Try changing the reeds. Or if you want swap out center and the one you are fouling and then see if you start fouling the center.......if so replace all the reeds.

Tod
 
I've always ran BR9ES in all our Yamaha's...we never foul one out...usually put in a new set at the beginning of the year...I currently have about 1300 miles on the same plugs
 
Ok lets get back to the beginning here.

Is your sled stock? If so try

1. stock plug meant for sled

2. recheck the carbs like everyone said. Are they stock jets? in the right places and are the numbers correct? Are the needles at the stock location? Is your fuel screws set right?

3. How is your oil pump set?

4. What gas are you using?
 
Tod said:
Try changing the reeds. Or if you want swap out center and the one you are fouling and then see if you start fouling the center.......if so replace all the reeds.

Tod
Click to expand...
Or at least check the reeds. I just fixed my friends T-cat that was running like crap, fouling the center plug, pretty much all the stuff that OP was talking about. Center reed was blown back towards carbs, so I replaced it with a set of V-force 3's (brand new, in the box of spare parts that came with the sled) now it screams like a banshee.
 
To answer some questions:
- my sled is stock
- pretty sure (not positive) the jets are stock but they all had the same number on them (forgot to write down the numbers though)
- I haven't check the needle locations yet (it looked like a pain to get at them)
- the dealer did adjust the oil pump. How do you check that?
- using 87 octane gas
- I assumed the dealer set the fuel screws but I'll have to verify.
- I have presently swapped the reeds on the bad cylinder (they looked okay) with another but I've only been able to do a ride around the lawn due to the 24hours of rain we just had. But from my 10-15minute ride the same plug looked wetter than the others.

I've owned the sled 5 years and this is the first time it's acting funny. So my original thought was that it wouldn't be the needle location or jetsizes or it would of been doing it all along. However at this point I'll have to go back and check.

Thanks for all the replies, I really appreciate it.
 
the jets on that thing should not be all the same. You should have..145 in #1 cyl. and 143.8's in the other two!
 
yammy said:
the jets on that thing should not be all the same. You should have..145 in #1 cyl. and 143.8's in the other two!
Click to expand...

Didn't notice that - the numbers are so small I didn't see the difference. Which cylinder is #1?
 
spaceman99sx said:
Anyone have any instructions on how to remove the needle?
Click to expand...

It is not necessary to remove the carburetors from the machine or from the rack to change the needle position. You will need to purchase a BONDHUS 2.5mm ball nosed allen wrench (the long one)to do this procedure. If you do this very often you will want to purchase a set of knurled thumb screws from Northern Lites @ http://nlites.com/ to replace the screws that hold the top covers of the carburetors. They look kind of cool anyway and work great!!

1. Remove the two screws that hold the top cover of the carb you wish to adjust. Put them someplace safe. Remove the top of the carb.

2. Remove the Phillips head screw that holds the arm to the shaft. Make sure your screwdriver fits this screw nicely. Don't strip the head!! The slide will now move freely up and down but you will not be able to lift it out.

3. Using the new BONDHUS tool, reach down on top of the slide and completely loosen the two allen headed screws that attach the linkage from the arm to the top of the slide. Don't try to remove the screws individually.

4. Very carefully lift the arm and linkage to the slide, with the allen screws in their holes, up and out of the carburetor. IMPORTANT! Watch for the plastic needle shims that may be stuck to the bottom of the linkage!!

5. Flip the link over and let it hang with the screws in it. Keep your fingers on the screws while you do this so they don't take off. If you don't you will hate yourself!!

6. Lift the slide out of the carb and make your needle adjustment, noting the placement of shims according to the Yamaha Needle Jet adjustment chart for your machine or any instructions you might have received with aftermarket performance parts.

7. Place the slide back in the carburetor. Don't drop it in. The needle may jump out.

8. Now flip the arm back over with your fingers on the screws and let the linkage down on top of the slide.

9. With the BONDHUS allen wrench tighten the two screws that attach the linkage to the slide.

10. Replace and tighten the Phillips headed screw that attaches the arm to the shaft. Don't over tighten it. They seem to be a little soft.

11. Reinstall the top of the carburetor and tighten the two screws that hold it down.

12. One down and two to go!! This may seem like a pain, but after a couple of practice runs you'll be a PRO at it.

Oh, one last piece of advice. When you get a chance, buy a few extra of the allen head screws that hold the linkage to slide, a few extra plastic washers for the needle and a few spare circlips for the needle. That stuff is CHEAP and the day comes when, yes you guessed it , one of them disappears. Put them in a plastic bag in a secret place that only you know about or your buddies will want to take advantage of your stash. Good luck!!
 
I checked the jets and all 3 are 143.8?!?! As yammy mentioned the #1 cylinder is supposed to be 145. The previous owner must of changed it for some reason. Now how a jet that is too small can cause the cylinder to flood has me a tad confused???

In addition:
- the needles are set in the middle (stock position 3) with 2 washers underneath
- fuel screws are 1.5 turns out from full
- all 3 cylinders tested at 125 psi
 
I run 142.5s and the clip dropped 1/2 a position all the way across like the write-up in the tech section says, but I have considered going back to the 143.8s but in all three, not using the 145. I fouled the #1 plug this weekend, but then found that I had a loose plug wire at that coil. The plug fouled after riding on the trail for about an hour, but had been fine all year up to this. I have a 98 Vmax 700sx.
 
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