VT500 Airbox Modifications...

[J6G1Z]

I recently decided to attempt to improve the airflow through my airbox.

First I had to clean it up real well. There was a bit of oil & grime trapped in the bottom of the airbox.

[J6G1Z]

I removed the rubber intake snorkle & cut the round base of it off with a razor knife. I kept the base to re-install in the airbox inlet.

[J6G1Z]

I then took a spun aluminum velocity stack that I had picked up at a swap-meet & tested it for fit. I ended up wrapping the velocity stack with one wrap of 3/4" masking tape to act as a cutting guide. Then I took a good hack saw to the velocity stack & cut it along the tape line.

[J6G1Z]

After cutting the velocity stack so it would be shorter & dressing up the cut. I re-installed the rubber ring that I had cut off the rubber intake snorkle & then pressed the velocity stack into the airbox air inlet.

[J6G1Z]

Now the incoming air has a slightly larger intake opening with a nice radius to it to smooth that air flow.

I simply peened the interior side of the velocity stack to not only hold it firmly in place, but to also guide the filter cage into the center of the opening.

While I was at it, I drilled out the 3 rivits & removed the screen that is mounted inside the airbox. I filled the holes with some black RTV. Hopefully I will have the time to install the airbox back into the bike & test it out later on today.


Good luck
J.

[scottly]

I had just been thinking that the snorkel might be the major restriction on the FT, even more than the VT since it ingests twice the air in a single gulp. I don't think there would be that much more resistance from a foam filter to the K&N I'm using, but my bike needs a MUCH larger jet than the stock airbox. I'd try just popping the snorkel out of the FT and taking a test ride. If my theory is correct, the bike will have a flat spot between about 3-4K.

[J6G1Z]

I had just been thinking that the snorkel might be the major restriction on the FT, even more than the VT since it ingests twice the air in a single gulp. I don't think there would be that much more resistance from a foam filter to the K&N I'm using, but my bike needs a MUCH larger jet than the stock airbox. I'd try just popping the snorkel out of the FT and taking a test ride. If my theory is correct, the bike will have a flat spot between about 3-4K.

My first FT Ascot must have been previously owned by someone from the Yahoo Ascot Owners Group. When my FT Ascot came to me it already had about 4 of the common FT modifications performed. The petcock had been swapped to manual operation, the carb jetting had been changed, the air filter had been converted to an oiled foam filter & the airbox intake snorkle was missing. These mods are all discussed in the FT Tech Section.

Thanks
J.

[J6G1Z]

I have replaced the Ascot filter & cage assembly with an '85-'86 Shadow filter.

The Shadows filter element is much larger than the Ascots & is all one piece.

J.

[Luke]

Nice work... I love these kind of mods.

Interested in your post installation thoughts 

[J6G1Z]

Well, it upset my jetting & I have been installing larger jets. I'm almost there, but still have a bit of a dead spot around 7K RPM. I bought a DynoJet kit & it cannot handle much modification to the air box. Once I have the jetting corrected I can share the jet sizes, but unfortunately DynoJet has their own jet sizing ID that does not correspond with Keihin jet sizes.

Between the dual exhaust & the air box clean up, there is much more air moving through the engine. I just need to add the appropriate amount of fuel.

One of the members from across the pond, says he is using two #125 Keihin jets. Which sounds about right. The OEM jetting was a #112 in the front cylinders carb & a #120 jet in the rear cylinders carb.

I will update when I have more information.

Thanks
J.

[Luke]

Thanks ... guess I'll keep my tinkering hands away from that for a bit.

Until you figure it all out for us anyway

All the best,

[J6G1Z]

I performed the exact same intake modification on my first VT Ascot & it ran fine without changing the jetting. It was lean, but it ran. My first Ascot had a MAC dual exhaust on it though. I also used to run a K&N filter back then. I have now switched to UNI filters. I think the exhaust that I have now, flows more than the MAC exhaust did. Eventually I took that bike to a shop that had a tail pipe sniffer & they changed the main jet to two sizes larger. I don't know exactly what jet size they used. I would try the #125 jet in each carb & see where that puts you.

Good luck & please let us know what works for you.
J.

[Dibingo]

Well, it upset my jetting & I have been installing larger jets. I'm almost there, but still have a bit of a dead spot around 7K RPM. I bought a DynoJet kit & it cannot handle much modification to the air box. Once I have the jetting corrected I can share the jet sizes, but unfortunately DynoJet has their own jet sizing ID that does not correspond with Keihin jet sizes.

Cause Dynojet is a large commercial joke. All and nothing in their kits.
I know it to have turn their parts in all directions ! 

Between the dual exhaust & the air box clean up, there is much more air moving through the engine. I just need to add the appropriate amount of fuel.

One of the members from across the pond, says he is using two #125 Keihin jets. Which sounds about right. The OEM jetting was a #112 in the front cylinders carb & a #120 jet in the rear cylinders carb.

I will update when I have more information.

You're talking about me ! 

In the carbs of the Europe VT500E, not the same OEM jetting. ! OEM is 118 in front and 125 in rear.
In the carbs of the VT500C (shadow) same OEM jetting than Vt-Ascot.

VT500C et VT500E have not the same final transmission. (more longuer on the VT5E > top speed higher)

I ask me the question to know if the VT-Ascot have the final transmission of the VTE or the VTC ?

About your case John, in my VT5E I put two 125 jets, but my airbox is OEM. Just a homemade foam filter.
With your airbox like that, I think jets must be higher than that. Probably like 2x130.

[Dibingo]

We absolutely have to tune the exhaust and the air filter together.
The carburation adjusts then.
Logically, more there is of air / gas which returns and goes out, more the carburation must be rich!