Bonneville America Forums Forums Technical Forums Performance Mods HP Confusion

I just got my 02 TBA back from the dealer today after addressing odd top end noises, which they resolved. They also Dyno tuned. I have the Freak, Bub Slashcuts, put in Thruxton Needles. They reduced my main jets to 138 as they said 160s were so rich they were pegging the sniffer.

My Bud Jango, has an 03 Speedy with a similar setup. He has been on the same dyno @ 68.8HP. Mine read 53HP.

My question is, would there be any difference between 02 and 03 that would account for this type of HP discrepancy?


With the mods I have done I would think there would be more of a kick in the butt than I am getting.

I'm thinking the Thruxton needles may have caused that rich condition. They are probably way too thin on the taper for the setup and were letting in a boatload of fuel. Did you tell them you had these in?

Have you tried the TBS needles instead? Thicker taper that the Thruxtons but thinner than stock.

Switching to the TBS needles and putting the 160s back (or even something in the high 140s) might be just what you are looking for.

Exactly what is Jango running?

I've dyno my car on the same dyno but on different days and have gotten different numbers. Weather plays a roll for when i dyno my car (it's a turbo though) and the same thing may affect your numbers on your bike as well. Just a thought.

-Josh

Phil,

Jango is running the 160s/42 with stock needles 2 shims.

The Thruxton needles went in while they had my bike.

The Mech. said I was way too rich at full throttle.

BTW - Jango tore his down to put the big bore kit in and had a significant amount of carbon build up at 6500 miles.

He was concerned.

Weather, tire condition/inflation, and chain condition/adjustment could account for some differences.

You mentioned that the exhaust sniffer showed too rich running WFO, was it running a reasonable mixture at less throttle? If so, you might want to try TBS needles. They seem to be a little longer, and that could make the difference.

Well, I have my suspicions, and I am gonna live with them.

Greybeard, the Dynos showed a good mixture with the Thruxtons in and consistant HP at WFO. Here is what I think.

When I got the bike back, it was waaaayyyyy too lean and popping on decel. A/F mix was at 2 1/4 turns which was the proper 13:1 ratio the mechanic was shooting for.

At that setting the thing is a real dog and is obviously not getting the gas necessary when cranked WFO on the dyno. I think this has resulted in the lower HP rating.

When I open her up to 3 1/2 pop goes away and a MAJOR increase in torque and accelleration.

I think if I were to go back and re dyno, I would be in the mid 60s HP...

That's my story, and I'm stickin to it...

I like the Thruxtons and will keep them for now....

Thanks to all.

That could easily be the problem. As I mentioned in another thread, many motorcycle carburettors use the idle and transition ports as a power enrichment circuit when the throttle is open wide and the engine is under a load. In the range above peak torque and near peak power, the mode of the intake system gets really interesting. The valve timing and port configuration start governing the air flow in that region, so the manifold vacuum starts dropping. There is a huge amount of air flowing through the carburettor(s) but not a lot of pressure difference from inlet to outlet. Since the speed of the air flowing over the ports is high enough able to pull fuel out of them as easily as the high vacuum at idle, you get the richening effect you need, unless the idle mixture is off.
On my America, when I took it in for the 500 mile service the wrench tuned for minimum exhaust popping. After the 1K mile runin was done, I followed the books advice to occasionally "ease" a new engine up to the rev limit, only it was in top gear, which I don't think they intended. I could barely top 100 on the speedometer. After readjusting the idle mix for fastest idle speed, I tried again in the same place under similar conditions and backed off after reaching 115.