Bonneville America Forums Forums Technical Forums Performance Mods super lean

i have a 04 triumph america. I put on a set of bomber exhaust, k&n replacement filter with the bellmouth. i'm now running 155 main jets, 45 pilot jets, stock needles with 2 shims, and 3.5 turns on the air screw and the plugs are still running white. for kicks i put the stock air filter back in with the snorkle to see if cutting the air intake would make it richen up but no change. i now switched back to the k&n set up. before i changed the exhaust and filter the plugs were a pretty tan color so i don't think i have an air leak. jetted many a bike put this ones stumped me. any help

That's a lot of fuel available with that set up to still be lean, are you certain there's not an air leak at the manifold? With 3.5 turns at the air mix screw you're right on the edge of that adjustment not being useful and it implies the pilots are too small, so maybe you'd up those first and see.

I plan on trying 48 pilot jets. as far as an air leak like i said with the stock exhaust and air filter it ran near perfect on a dyno so i really din't know where a leak would come from

+1 With what oldroadie said.
Try the 48's. I've seen that work on some of these twins.

Not familiar with the bomber exhaust but with any restriction your jets would be too big with the 48s. Modern gas does not color the plugs like the old leaded non-alcohol gas did. Makes them much harder to read. Make one change at a time and test. Where you live has quite a bit to do with jetting, your elevation changes your jetting. Disconnect and ground one plug wire and turn the idle up just enough so the bike will run on one cyl. and adjust the pilot screw on the side you have the plug still connected on. Turn the pilot screw in until the engine runs rough then back out until the engine runs rough counting the turns between the 2 points. The correct setting is 1/2 way between those 2 points.I would remove those shims you have on the needles first and start over. Once you have the mixture right and adjustments made if you have a mid range lean spot then add shims or different needles. Each change you make effects the others since they do overlap as the throttle opens. I have straight pipes and pod filters and I run 48 pilots and 155 mains with no shims and my mix is nearly perfect across the board on a dyno. My mixture screws are about 2 turns out if I remember right.

One thing to consider is the type of jets you are using. Are they genuine Keihin parts or knockoffs?

As Ed stated, that's a lot of fuel for basically a stock intake with snorkel removed and bell mouth installed. Is it the Breath Bell mouth from TTP? Are you getting any kind of popping on decel?

With my ride (03 America) I had the straight through TORs installed along with a UNI filter, all 3 snorkels removed and opened up the filter retainer on top. I didn't drill out the bottom of the air box. I ended up with 135 mains, 42 pilots (never felt the need to change even though I had 45s available), Thunderbird needles with 1 shim and around 2.5 turns on the mixture adjustment screws. Plugs eventually ran a tan colour but you could smell that it was running rich at idle. No decel popping but I disconnected my Throttle Position sensor also which helped that a lot. FWIW.

One other item I forgot was to ask how it ran with the setup you described? Any bogging at mid range or indication it was running lean.

The reason I ask is that there is a vent hose for the float bowls that runs behind the engine. It is right beside the vent line for the fuel tank. If that hose is in a wrong location, it could create a vacuum in the float bowls which will cause a lean condition on the highway. The bike will be susceptible to cross winds causing the engine to bog. I mistakenly trimmed this hose before a trip to Edmonton a few years ago. I was getting a very lean condition and exceptional gas mileage. The plugs were white when I checked them. After checking everything for problems (and finding nothing out of the ordinary) I relocated that hose and fixed the problem.

I mistakenly took the "K&N set up" to be pods given the jets mentioned. If that is a K&N in the air box then those jets are enormous for your set up. The 45 pilot might be OK but not at 3 turns on the mixture screw and a 155 main and 2 shims with a stock air box you might as well just put your gas line right on the intake nipples.

thanks for all the input i'll re check everything and try all suggested. i never thought about no lead. where's reagan when you need him . god bless america!

mikej

Thanks for the info I guess my big concern is if i can ride this bike with this set up until i find out what's going on. right now after the feed back i've gotten i don't know if it's running lean or rich? if i knew how i would post a picture of the plug with the stock set up and the new plug after the changes?

mikej

If it's rich you will know it. You can smell it, the plugs will soot and the MPG's will drop off.

Bike doesn't have the crisp throttle response it had before the changes. Breaks down at around 7k. No popping when I back off. More worried about riding it to lean then to rich

Mikej

I'm not sure if this is the hose you are referring to but I looked under the bike and the hose coming from the tee fitting between the carbs was James behind a steel oil line and pinched closed.

Mikej

If that atmospheric vent to the float bowls is restricted the fuel flow dynamic is upset. It's the steady atmospheric pressure that pushes the fuel up through the jets as the pressure is lowered in the venturi, very much like a wing gets lift. Rob the bowls of that pressure and there's not enough fuel introduced into the intakes. You should get enough discoloration ont the plugs to see a difference, it's just way more subtle without lead.
You are correct, very very lean builds up a ton of heat and that's the enemy of air cooled motors. But a short ride on clean plugs should be okay and give you time to check it out.

That sure does sound like the float vent hose Ed mentioned. If it is plugged then it could explain why the bike might be running lean even with those large jet sizes. With the vent plugged, no atmospheric pressure will get into the float bowl causing a vacuum and a lean condition.

Now that it is unplugged, how does the bike run? I bet you it will now run rich.