low end bogging

[sblankert]

Hi folks,

I rescued a 2003 VMX12 from a guy's barn a last year with 6k miles on it, and have fixed all it's problems but the following:

When I first start it and lean back on the throttle, it bogs, and I have to rev it up to get it out of this funk to be able to go forward. If not it will stall out, especially when its cold.

I took it to a Yamaha shop and they took the carb apart to clean it (or so they say they did) but it still does the same thing.

It also "pops" a bit when it idles and at low speed. I don't hear it at high speed. The front right hand cylinder plug gets fouled easily, but even after putting new plugs in it still pops. I'm pretty sure its running rich, since the gas mileage is around 33 mi/gallon whereas my other VMX12s have gotten 37-40 mi/gal depending on how much throttle I'm using on the highway.

I'm not sure what it could be.... is it a bad coil? Or do I need to adjust the fuel set screw? How do I go about troubleshooting this? I'm going to take a day off work to fix this problem and need to be surgical in going about it, since this is my main mode of transportation at the moment and it will need to be back up and running the next day.

Thanks for any suggestions you may have, and keep the rubber on the road (low wave).

SB

 

[Traumahawk]

So very first question to ask, is it stock, or does it have a jet kit?

 

[sblankert]

It was stock but when the carb was cleaned at the shop they convinced me to put in a stage 1 kit. It didn't fix anything and it runs the same as it did before the kit was installed

 

[caseyjones955]

Did they give you the old jets, springs and needles back along wih the unused parts of the stage 1 kit? If not your going to want to get that stuff back from them. Stock exhaust?

 

[blaxmax]

Did they give you the old jets, springs and needles back along wih the unused parts of the stage 1 kit? If not your going to want to get that stuff back from them. Stock exhaust?

My guess is that they didn't put one in.

 

[caseyjones955]

My guess is that they didn't put one in.

Im not one to trust dealerships but if they charged him the $130 or so for it they must have passed him the little white pillbox looking container with all the cool brass doodads inside. Hopefully so...

If they talked him into a jet kit I can only assume that their rational was a full aftermarket exhaust already installed on the bike.

 

[Traumahawk]

Ok, well if they didnt give you the old parts back, you will need to get the old stock parts from a member on here. Sean and Kyle are good sources for that. This forum can walk you thru everything to make it run well.

If you do have an aftermarket exhaust, you can go with a different jet kit (stage 7 or Seans) your halfway there, and then the bike will run how its supposed to run with a jet kit.

Hate to break it to you, but the only usable part of the stage 1 kit is the needles, and then if you set them lean.

 

[caseyjones955]

Even when mine had the full stage 1 kit the only time I had bogging and popping at low rpm was before I had the carbs synched and AF screws set correctly. I wonder if this dealer just failed to get it dialed in. Mine doesnt have to be very far out of synch before the idle and off idle suffer notably. Im afraid I agree with what Eric just said about the only usable parts of the stage 1. If they set it up by the directions it will be way rich all over the rev range.

SB, do you have a set of carb synch gauges you can throw on to check their work, or lack thereof? Do you have the rest of the stage 1 kit and old jets and needles they removed?

EDIT, anything Trauma says trumps anything I say, he spent a decent chunk of time helping me get mine sorted which ended with almost all of the stage1 gone and a vastly improved performance.

 

[sblankert]

It came with a set of Supertraps and the carb was stock. That was their rational for suggesting a jet kit, and I agreed with them.

I do have a carb sync guage, I will try that next. I'm wondering if doing the shotgun method of cleaning might help too. Whatever it is, I'll have to do it in one afternoon.

To be honest, I do not know if they did anything to my carb but take my money. They did not give me the stock jets. In fact, they pulled out my platinum spark plugs and put cheap ones in, and said they threw them away so they couldn't return them to me. The bike stalled all the way home, and they had to come get it to take it back to their shop. When I got it back, it seemed like all they did was turn up the idle.

I haven't had much luck with the dealerships in North Carolina, to be honest. I wouldn't doubt that they did nothing whatsoever to my carb.

But that just leaves me with the same problem that needs to be fixed.

Oh, and let me add that if I put the choke on a little bit, it revs the engine to a higher tach reading and I don't have the bogging problem, but it still pops.

 

[caseyjones955]

Are the supertraps a slip on deal or is it a full exhaust? I learned here that only the added flow of a full header can benifet from a jet kit. If you slide one of the slides out of a carb you should quickly be able to see if its an OEM needle or a stage 1 and at the same time you can see what size the main air jet is (PAJ2 i think) its right behind the diaphragm, mine was the stage 1 size DJ150 which made it insanely rich. Trauma had me put back to he OEM air jet and the difference was significant. I think you can see the needles by popping off your air box lid to. There is a pic here somewhere of the different needles but cant get it on my phone. If you find they charged you for a kit you didnt get now is the time to discover that.

 

[Traumahawk]

The supertraps are slipons.....so they probably put in a stage 1 kit, with slipons. Slipons by themselves wont make the bike bog, so I would be willing to be the jet kit was put in.

You can see the needles by taking the airbox lid off, but its really hard to tell what they are. Its easier to get into the carbs.

The cheap NGK's are the best plugs to run in a Vmax....4 for 10-12 dollars at OReillys.