Welcome to the Family.....

Sounds like it is running very lean...
You will most likey need to get into the Carb and find out whats in there (Jet Wise) and adjust accordingly.....
Get the Factory Pro Jet kit (Stage 3) and use that, easier to tune....

UNtill you/we know what the Jetting is, there is no way to diagnose...

What line is off & plugged??? Need more info...

 

Welcome to the Family.....

Sounds like it is running very lean...
You will most likey need to get into the Carb and find out whats in there (Jet Wise) and adjust accordingly.....
Get the Factory Pro Jet kit (Stage 3) and use that, easier to tune....

UNtill you/we know what the Jetting is, there is no way to diagnose...

What line is off & plugged??? Need more info...

Plug in the hose where it says "to carb" (screw with a clamp). And inside of hose is plugged with something where it says vacuum hose.

 

The pipes do get hot, wrapping them won't help.
DJ junk too small slow jet.
I'd reinstall Factory pro stage 1 or 3 jet kit and your problem should go away.
Common cause for decel pop is the acorn nuts are bottoming out on the exhaust flange befor becoming tight to the gausket and drawing in air there , add a flat washer under the acorn nut and they will tighten up fine. Csreful not to overtighten the studs and break them.
Donut/Doug

 

Vacuum line to both Petcock and PAIR system have been blocked..
You may have a leak at Carb where it is plugged, causing the lean/hot condition.


PEtcock apparently has been modified to Gravity only. Do you turn it to OFF when not riding?

Acorn nuts, as stated, could be the Popping issue with exhaust leak...

 

What intake do you have? Stock? Modified stock (decapped)? Shouldn't need much if any change in main jet for just exhaust without intake. Maybe just slow jet or just the A/F screw which you've done already. You're probably good as is. On the hot exhaust part, I have the Cobra Speedster Slashdowns and my side cover was melting. I removed the shield and wrapped with header wrap and it stopped the melting.

 

Update. I removed the pipes and replaced the gaskets. Acorns are not bottomed out. Still backfiring on decel. What is the function of having the vacuum line off of the carb? What happens when it is eliminated? It feels like fuel is dumping in and without the throttle open to bring air into the engine, it just burns in the exhaust.

 

The purpose of having the vacuum line to the fuel petcock is that the OE petcock design has it CLOSED when there is no vacuum. Then as the engine starts, normal vacuum opens the flow. The PO was evidently not happy with that arrangement and modified the diaphragm so that the vacuum feature is null. Now, you need to use the manual cut off valve whenever you park, or restore the diaphragm.

Sharp of you to replace the gaskets, that is where the air is usually getting in and with aftermarket muffs, I was expecting the old gaskets to have been used. ARE YOU ABSOLUTELY SURE that the PO did NOT leave the old gaskets in and put another set on top of them. They mash in so well that its easy to believe there are none there when looking. There are gaskets where the intake from carb meets the cylinder heads that are suspect too.

The PAIR bypass mod on your bike seems to be half assed. You need to get the block off plates and do the job correctly. It has been written up on this board since the dirt was put down.

prs

 

What you need to do is 1 thing at a time so

Start with pair valve write up follow the directions even as far as hooking all vacuum lines as they should be.

You already did new gaskets for pipes but if you did not put washers on then the acorns you will need to do this next.

Next step is to make sure all the band clamps to manifold are tight, loose is vacuum leak and lean running, you can do this when you do the pair valves.

Since the bike is relatively new to you I would also research valve adjustment and then jump in and do it just so as to have a base line to go forward.

now when you have all of this correct we can go on from there if problem still exist.

 

why do people rejet for pipes?????????????????????

 

What intake do you have? Stock? Modified stock (decapped)? Shouldn't need much if any change in main jet for just exhaust without intake. Maybe just slow jet or just the A/F screw which you've done already. You're probably good as is. On the hot exhaust part, I have the Cobra Speedster Slashdowns and my side cover was melting. I removed the shield and wrapped with header wrap and it stopped the melting.

Intake is stock.

 

The purpose of having the vacuum line to the fuel petcock is that the OE petcock design has it CLOSED when there is no vacuum. Then as the engine starts, normal vacuum opens the flow. The PO was evidently not happy with that arrangement and modified the diaphragm so that the vacuum feature is null. Now, you need to use the manual cut off valve whenever you park, or restore the diaphragm.

Sharp of you to replace the gaskets, that is where the air is usually getting in and with aftermarket muffs, I was expecting the old gaskets to have been used. ARE YOU ABSOLUTELY SURE that the PO did NOT leave the old gaskets in and put another set on top of them. They mash in so well that its easy to believe there are none there when looking. There are gaskets where the intake from carb meets the cylinder heads that are suspect too.

The PAIR bypass mod on your bike seems to be half assed. You need to get the block off plates and do the job correctly. It has been written up on this board since the dirt was put down.

prs

I'm sure that when I pulled the old gaskets out that there weren't any behind them. I had the petcock off and apart and it seems to be working as designed. I don't turn the valve off when I stop. I agree that the mod was half assed at best. I will try to get some pictures put up.
How much might the back pressure caused by the baffles play into this equation?

 

I'm sure that when I pulled the old gaskets out that there weren't any behind them. I had the petcock off and apart and it seems to be working as designed. I don't turn the valve off when I stop. I agree that the mod was half assed at best. I will try to get some pictures put up.
How much might the back pressure caused by the baffles play into this equation?

The back pressure actually gives you more low end torque

 

I had the petcock off and apart and it seems to be working as designed. I don't turn the valve off when I stop[/B].

That is impossible!!!
The Vac line turns the petcock ON & OFF with vacuum from the Carb...
With that line blocked off (as stated) you would get no fuel to Carb...

There is a Mod some use to bypass the Vac line by reversing the spring against the Diaphram in Petcock to hold it open and not use the vac line......

ON the Backfire, the Cobra pipes have a thinner flange and the Acorns 'will bottom out' with them in most cases.. Add some washers and re-torque them to make sure or change acorns for regular nuts..

All of this adds up to some shady backyard mechanics byt someone before you...

You/we will need to know what size and make of Jets are in the carb also......

You/we need a baseline/starting point to figure out whats going on.... :tools:





.

 

Plugs

If the plugs are fouled it is not running lean. Fouled plugs is a rich air/fuel issue. If bike is running lean engine would be running hotter and plugs would be white in color or less brown.

 

Backfiring on Decel

I've chased this for quite a while. I've done most of what you suggested. My question is this: Why does the backfire go away when I open the choke about 1/4"? The bike is an 06 VTX with V&H pipes and a non-stock air filter. Any thoughts? Running lean? How can I adjust without tearing down carb and replacing jets? Thanks

 

I've chased this for quite a while. I've done most of what you suggested. My question is this: Why does the backfire go away when I open the choke about 1/4"? The bike is an 06 VTX with V&H pipes and a non-stock air filter. Any thoughts? Running lean? How can I adjust without tearing down carb and replacing jets? Thanks

open the pilot screw about 1/4 turn

 

Post #3 the picture:: the vacuum is going to the Air Cutoff Valve.
Cuts air on throttle release==makes it richer.
To stop the pops.

Some MC they plug them.
I don't think anyone has messed with theirs here.
If the diaphragm is torn you may need a new one.