My old timer firecracks

[FinTruder]

Hi all!
I tried to search but didn't find any topics about supertrapp muffler talk from here.
I have 1990 vs1400 witch i brought last winter. It has these supertrapp mufflers and it bangs and spits fire like Mot*******er i had to admit that i dont know much about aftermarket parts i only know that previous owner cleaned and synced carbs checked in and outtakes and it runs beautifuly but only that nuclear-war-tier boom blasting while decelerate.

So my question is that is this normal? And i have these discs and caps what supposed to go on mufflers witch are not in place so shoud those stop afterfire etc or is it just straight pipe broblem?

Thank you guys and sorry about my bad english and stupid question.
Cheers

[navigator]

FAQ
https://supertrapp.com/faq

[Designer]

Info specific to your problem that is in the Link Navigator searched for and posted;

Why do some aftermarket pipes backfire when you decelerate?

Backfire, or “lean misfire” on deceleration is primarily attributed to an improperly tuned engine. Under this circumstance, the low speed fuel circuit needs to be adjusted. On a street bike, the rule of thumb is to adjust the fuel mixture screw out in ½ turn increments to add fuel. If you reach 3.5 turns out and it still pops on decel then go up one size on the pilot jet and turn the fuel mixture screw back to one turn out from bottomed. Repeat this process until the misfire is eliminated. In some cases, this problem is an indication that the exhaust is too free flowing (i.e. Head pipes too large in diameter or muffler core is too large) for the motor configuration you have. As always, check your spark plugs to verify the tune is correct. The plugs should be a light tan in color if tuned properly. If the exhaust is too “free flowing” you will ultimately add too much fuel which will cause an excessively rich condition and foul the plugs.

Hope this helps.

[hillsy]

Plugs don't burn tan anymore with unleaded fuel - just different shades of grey nowadays.

I put a ST baffle in my V&H can in my LC and it was nice:



The baffle plates allow you to change the back pressure / flow to suit the application. You kinda want them.

[FinTruder]

Thanks answer's m8s. So i assume that if i want that banging out i need to start packing the paffles in first. If that wont help i need to figure out setups from pilotscrews, right?

[hillsy]

Thanks answer's m8s. So i assume that if i want that banging out i need to start packing the paffles in first. If that wont help i need to figure out setups from pilotscrews, right?

It's probably a combination of both, but putting in the baffle plates will be the easiest thing to start with.

[FinTruder]

Ok. I'm little bit afraid to toutch those mix screws one option is that i put slahcut mufflers on and toss those toypipes away xD

[hillsy]

Ok. I'm little bit afraid to toutch those mix screws one option is that i put slahcut mufflers on and toss those toypipes away xD

The thing about the screws is you turn them in and count the turns - so if you can't make it better at least you can bring it back to where it was.

You should probably be somewhere between 2.5 and 3.5 turns out depending on your mufflers.

[Herb]

Ok. I'm little bit afraid to toutch those mix screws one option is that i put slahcut mufflers on and toss those toypipes away xD

Adjusting the mix screws is easy to do. The best idea is before doing any adjustment turn the screws in until they lightly seat, do not over tighten, counting the turns as you go. Write down how many turns it took to seat the screws. It helps if you scratch the side of the carb to mark where you started. This way you can always reset the screws back to the original position.

Then turn out the screw half a turn more than it was at to start.

When I put the V&H Classic II's on mine I had to go out about 3/4 of a turn more than stock to get it to stop popping on decel.

[FinTruder]

Ok. I'm little bit afraid to toutch those mix screws one option is that i put slahcut mufflers on and toss those toypipes away xD

Adjusting the mix screws is easy to do. The best idea is before doing any adjustment turn the screws in until they lightly seat, do not over tighten, counting the turns as you go. Write down how many turns it took to seat the screws. It helps if you scratch the side of the carb to mark where you started. This way you can always reset the screws back to the original position.

Then turn out the screw half a turn more than it was at to start.

When I put the V&H Classic II's on mine I had to go out about 3/4 of a turn more than stock to get it to stop popping on decel.

Good advice, thanks. What if one cylinder stops popping before another, do i still adjust both screws same amount until both are silent?

[hillsy]

Good advice, thanks. What if one cylinder stops popping before another, do i still adjust both screws same amount until both are silent?

The screws won't necessarily be the same setting on each carb - 2.5 turns out is a guide to start with. Adjust each until the pop stops.

[Herb]

When I was setting mine I actually ran them out one at a time until the engine started to stumble then turned it in until it smoothed out. Ended up with one side at just over 2 3/4 and the other a just over 2.5.

The rear was 2.5 and it makes sense because the rear has a larger pilot air jet. even the carb specs call for 2 turns out on the rear and 2 3/8 on the front.

[FinTruder]

Packing plates to muffler didn't make much difference to banging, only now i sounds like sitting on fart while decel. I guess i have to collect some trust and follow the instructions here. I assume that i need to take tank off to get front carb mixture screw exposed? Wish me luck

[navigator]

Packing plates to muffler didn't make much difference to banging, only now i sounds like sitting on fart while decel. I guess i have to collect some trust and follow the instructions here. I assume that i need to take tank off to get front carb mixture screw exposed? Wish me luck

You do not need to remove the tank.
You should adjust the mixture screws with the engine warm and running.

[FinTruder]

Packing plates to muffler didn't make much difference to banging, only now i sounds like sitting on fart while decel. I guess i have to collect some trust and follow the instructions here. I assume that i need to take tank off to get front carb mixture screw exposed? Wish me luck

You do not need to remove the tank.
You should adjust the mixture screws with the engine warm and running.

Ok. So since I'm not familiar with these mikuni carbs i need to ask are these air/fuel mix screws? Picture is from my donor bike parts.

[navigator]

Yes and Yes.

[FinTruder]

I managed to reduce popping and banging. Now its almost gone, but i try to understand these carbs fully and can someone explain why the back carb created mostly all that banging in both pipes? Front carb adjustments were all good. I checked all possible leaks and didn't find any.

[Herb]

In order to meet emissions they set these up really lean. The reason the rear cylinder has larger jets is because the rear cylinder will run hotter than the front which causes it to run leaner. Keep in mind that the rear cylinder's intake is behind the engine and will cause it to run leaner too. Add in a freer-flowing exhaust and you end up with an even leaner running engine.

A lean burn means that when you let off of the throttle there isn't enough fuel in the cylinder to burn and the unburnt fuel goes into the exhaust where it condenses in the cooler mufflers until enough builds up and it is set on fire when it burns really fast, actually explodes, inside the muffler.

I had the same issues with both of my 1400's.

[FinTruder]

In order to meet emissions they set these up really lean. The reason the rear cylinder has larger jets is because the rear cylinder will run hotter than the front which causes it to run leaner. Keep in mind that the rear cylinder's intake is behind the engine and will cause it to run leaner too. Add in a freer-flowing exhaust and you end up with an even leaner running engine.

A lean burn means that when you let off of the throttle there isn't enough fuel in the cylinder to burn and the unburnt fuel goes into the exhaust where it condenses in the cooler mufflers until enough builds up and it is set on fire when it burns really fast, actually explodes, inside the muffler.

I had the same issues with both of my 1400's.

I almost have a heart attack when i configure those mix screws and did first test run. First bang came simultaneously with strong hissing sound from gas tank cap (hot day) and in split second i thought that now i broke something from carb
It's been over 20y when i last time operated with carburator based engines and now im learning basics again. Lot is forgotten, but i kinda love old engines mechanics and this baby brings lot of hidden memories from past days

[Herb]

In order to meet emissions they set these up really lean. The reason the rear cylinder has larger jets is because the rear cylinder will run hotter than the front which causes it to run leaner. Keep in mind that the rear cylinder's intake is behind the engine and will cause it to run leaner too. Add in a freer-flowing exhaust and you end up with an even leaner running engine.

A lean burn means that when you let off of the throttle there isn't enough fuel in the cylinder to burn and the unburnt fuel goes into the exhaust where it condenses in the cooler mufflers until enough builds up and it is set on fire when it burns really fast, actually explodes, inside the muffler.

I had the same issues with both of my 1400's.

I almost have a heart attack when i configure those mix screws and did first test run. First bang came simultaneously with strong hissing sound from gas tank cap (hot day) and in split second i thought that now i broke something from carb
It's been over 20y when i last time operated with carburator based engines and now im learning basics again. Lot is forgotten, but i kinda love old engines mechanics and this baby brings lot of hidden memories from past days

Had to go change your Fruit of the Looms, EH?

It is fun to work on simple machines, take something that doesn't work or doesn't work correctly, and get it to work the way it is supposed to gives a person a great feeling.

Since the first time I fixed a machine that wasn't working the way it was supposed to and made it run correctly I have been hooked on repairing things.