Supertrapp Megaphone 1997 Backfire / Pop issue

[Decayism]

Hello All,

I have had an ongoing issue with my 1997 V-Max which “I think” could be related to my installed Supertrapp Megaphone series slip-on exhaust system, but at this point, i'm not sure....

When I first got the bike several years back, the supertrapps where already installed and the bike worked fine for the first few years… no issues.

All of a sudden, about three years back, the bike would start cutting out just a little between 5200 – 5500 rpm, right before V-boost would kick in. operation above or below that rpm range was OK. So… I brought my bike to a friend of a friend mechanic and he told me that there were different sized jets in the carb with could be the cause, so.. “we” decided to rejet the carbs to larger jets and all the same size (larger as in, not stock size). Now, my gas mileage when down (no big deal), and the cutting out disappeared (ya!), but a new problem was introduced. Now, when coasting along, not giving or taking away throttle, it backfires or pops; same thing when decelerating. After a year of that, I said, screw this and brought it to a local Yamaha dealer. They told me that the jets that were installed are not correct along with the typical “that’s what you get for using a backyard mechanic attitude”, and installed factory spec jets. Well the problem didn’t go away, and I’m still living with it. I brought it back to that Yamaha dealer, but they seem unwilling to help if I’m not willing to shell out $$$$$ I don’t have…

My supertrapps have 6 discs installed, factory jets and no modifications to the air box.

The carbs have been sync’d at Yamaha at the time of the factory jet install “im assuming” and once more after that. No difference.

I have another person I know that I’m going to visiting in spring who has a v-max and sync’s his own carbs, just to try it again.

Any thoughts about what I can do to solve this?

Any advice would be appreciated.

 

[Traumahawk]

Do you know the size of the jets that are currently in the carbs?

Also, richer is not always better on a Vmax.....but usually if its too rich, it wont pop or backfire, it will just be lazy?

 

[Redbone]

It could be an exhaust leak and/ or an intake leak. Try checking the boots that the carbs are connected to, while running spray the boots with some canned air or maybe wd40 and while doing this listen for changes in the idle that would indicate an leak.

 

[Decayism]

Not sure on the carb jet sizing, but i'm sure they put the stock size it... would have to look it up online.

Tried spraying the boots late last year and didn't notice a difference, will definitely be trying that again once the weather warms up.

Do you think that the Supertrapp Megaphone slipon exhaust system requires jetting or should a stock setup work fine?

 

[Traumahawk]

The stock set up with slip ons, should work just fine. If it was put back to stock....it should be 152.5's.

You can rejet for slipons.....but its not required. If you do rejet, you should go 1 to 2 jets sizes LEANER, but its not required.

 

[Decayism]

At this point, I don't want to rejet if it will run fine.

So.. once spring rolls around.. i'm going to check Intake and exhaust leaks and get the carbs sync'd.

I've also come around information suggesting that the bike is running to lean on the low end and that adjusting the a/f screw could help?

Also, The carb diaphrams could be bad?

Thanks for all your input guys.

 

[Traumahawk]

The air fuel screws typically cover the rpm range from 0-4000 rpm. Older settings on mine were all 4 3-4 turns out. Please make certain to using the correct fitting screw driver, and I would spray PB blaster in them, and walk away for about 2-3 hrs, and then see if they will turn. The air fuel screws are brass, and it is easy to strip them out if your try to turn them....and they are frozen in place.

 

[Traumahawk]

Really the only way to see if the diaphragms are bad....is to take them out and physically look at them. It is easy to do....if you feel mechanically up to it.