Bonneville America Forums Forums Technical Forums General Tech Rotten MPG

I'm going to throw this out there again. My '05 America is getting 25-27 MPG. I hit reserve at about 85 miles and put in 3.4 or so gallons. I just put the 42 pilots (were 45's) back in and it didn't help. The choke seems to be working right or at least the linkage is moving correctly. The plugs are black. As you can see from mods below it is not heavily modded. When I put the 42's back in I checked the floats for fuel inside and they are O.K. It runs good and starts fine and only has 1000 miles on it. I don't ride it hard by any means...in fact lately I've been very easy on it. I am at a loss. Anybody have any ideas?

According to Pats Jetting calculator, you should be running approx 126 mains with your current set up. Big difference from the 135s you have.

Also let me know if you want to sell your 45 pilots.

how many baffles removed ?
I think you should start at 130 mains
take a ride and then check your plugs.

my mpg was not that bad when i was running 175 jets.

If the plugs are black it would seem you are running way to rich. I would go back on the mains. If it is off, it would be better to be slightly on the lean side as the bike seems to perform better than slightly rich. I just went back on my pilots and mains and the bike is running great. I had a lot of other stuff done though. I would try 125s or 128s. My dealer tunes race bikes and says most all the bikes they redo for more power that have been worked on before, have too large a mains in them.

Nologic. I have a similar setup to you and I have the 130 main jets in. I am still running on the rich side. A dyno run showed I need to go back a bit more in the main jets.

25-27 MPG is still very bad mileage no matter what jets you are using. Our choke is not really a choke but a separate fuel circuit that allows more fuel into the carbs, rather like having a HUGE idle jet. Unless you have a leak somewhere I'd suspect a problem with the "choke." Either that or the heaviest throttle hand around.

I’ve noticed that when the choke is engaged the bike not only runs much faster at idle but engine braking is significantly reduced. If you’ve had a problem for some time you’ve probably gotten used to it. Try taking a dealer demo bike for a short spin and see if it feels much different. If it slows much faster at idle than yours that may indicate a “choke” problem.

The mains are not the issue. I have not been at WOT for quite awhile. I have been driving it very easy for the last few tanks. Haven't even been to half throttle. I believe this is something else. There is a slight increase in idle speed with the "choke" on. I used to notice when pushing the choke in after a few blocks that the bike would slow a little. It doesn't seem to do that anymore. This is much worse mileage than some here who have much bigger mains and many more mods.

I'm guessing but I probably get in the neighborhood of 40 to 50 mpg. The idle change with "choke" on is quite a bit if you are not getting that it lends credence to a choke problem.

I can't think of anything short of a leak (there is none)that would give worse mileage than that besides the choke circuit. The bike sat most of last summer due to my back surgery. Even though I put Stabil in the gas, maybe the choke valves are sticking open. I though maybe that I didn't hook up the TPS after jetting this spring but then I would have a drivability problem. But it runs great. I'll dig into it tomorrow.

The mains are certainly not more than a small part of the problem. The choke circuit acts as if you have giant IDLE jets. If the choke circiut is not shutting off it will be as if you had 60 or 70 IDLE jets. I'm just suggesting a ride on a bike with a known good choke to see if it has much better engine braking. If the test ride bike slows much quicker than your bike I would suspect you are getting way too much fuel at idle and the choke might be the problem.

I don't have the luxuery of another bike to ride. I understand what you are saying though. It seems to slow normally when letting off the throttle but like you say I may be used to it. I have noticed that the idle speed seems to be higher at times. Even when the bike is hot. I checked the choke linkage and all seems to be operating as it should from the outside. I am going to pull the air filter tomorrow to rule out a blockage in the air box. I don't have time today. This is eating me up!

nologic.

What air filter are you running??

Looking at your setup you should NOT have a shim under the needle and with those exhausts not even a 135 main jet.

That setup is wrong, sorry m8, but thats where your problem lies.

IF you are using standard needles then remove the shim, that will make a difference, if you want to use that shim then change your main jet to around 125.

TrOjAn

nologic,
How many baffles have been removed from your pipes? This is just a stab in the dark, but if the very front "baffles" or restrictors, were removed, then you will have lost the back pressure that your engine requires to properly run. Are you running with completely straight-through pipes?

But doesn't the main jet just come into play from 3/4 to WOT? I am running the stock air filter with no airbox mods. Just removed the snorkel.....nothing else.

singring: The last 2 baffles are removed and the third is drilled. The restrictor is still there.

I see. Thanks Phil. Maybe I'll drop to a 125 main and see what happens. I don't know what else to do now other than to bring things closer to the stock setup. The choke seems to be working right. (At least it does from a visual on the outside.) I pulled the air filter and there is no restriction there. It just seems like such a radical drop in mileage with the "small" changes that I have made. But I'll try anything.

I get rotten fuel mileage as well but I am running a Big Bore, Air Filter Mod, DBA Mufflers from Hermey's, 45 Pilots and if I remember right 145 Mains. She runs like a bear and I run it hard wherever I am going and between 90-95 miles I am switching to reserve like clockwork. I am sure that my riding style has something to do with it but I was surprised to see how poor of gas mileage I get with my BA, my Toyota 4x4 Truck with a V6 almost gets better fuel mileage than my bike. I am still wanting to try a set of Mikuni's but just have not had the time to get around to it. I need to contact Dinqua again and see if he has come up with a parts list for doing the conversion to Mikuni's.

What main would you suggest?

Why not just get a UniFilter or K&N free flow.. that will help get more air in.

For now I would definatly remove that shim

TrOjAn

I'd like to keep the stock filter for now. I ordered 125 mains. I'll try those. As far as the shim goes I put one shim in to eliminate a flat spot, which it did. Would I be better off going to TBS needles instead?
The sad part about all this is that the bike has never run and started better. If I start detuning it will go back to running less than perfect. I hope I can find a happy median between drivibility and MPG.

hmmm, like your nick theres no logic in keeping the restrictive air filter, I cant understand why you would rather mess with jets etc while still using the main cause of restriction... try playing with Pats Jet Calculator and see what you come up with.

http://www.dinqua.com/Triumph/Executables/PatsJettingCalculator.exe

TrOjAn

It shows no difference in jets between stock air filter and Uni or K&N. (124's) That doesn't seem right. I think it would still be too rich with 135's with the UNI or K&N.

Yea thats funny, must be the exhaust thats making his calculator come up with that.. O well, I tried.

All I can say is the shim and the 135 mains are wrong, but you must be happy with them so thats all that matters.. Your setup is just banging in fuel and it cant get out fast enough, too much in too little out.

Its up to you what you do about it...

TrOjAn

I appreciate your help. I think I'll throw the 125's in and see how it runs and what the mileage is like. I can always pull the shims if it isn't where I would like it to be. Thanks again.

When was the last time you changed your plugs? Change the plugs and wires, especially if you change your jets. Plugs are cheap. Wires are a little more, but they could make a noticeable difference. New plugs will show you if your setup is right and it might also help your mpg. The soot on the old plugs won't burn off entirely, and your plug reading will be misleading.

I wonder if coils can get weak. Anyone know of a way to test them?

I had a similar problem a couple summers back, and new plugs and wires helped a bunch. But then, that was just before my CDI went out. I don't know if they were related. Eventually I swapped out the coils too. Mine runs great now.

Cody

How is the acceleration?
You could swap sprockets.
After seeing this thread I got interested in my fuel usage and I get 30-35 with my speedy pretty regular. But I like having the off the line pop.

I run 2 shims with the stock needles .
I just could not get the thunderbird needles to tune right.
drop the main down and leave the shim.

unless you open the pipes up a good bit , the stock filter
will be ok.

can't put the air in any faster than you can get it out.
( with out a turbo anyway.)

First, the pilot jets are only effective from idle to around 3400 RPMs. They add a little bit of fuel running flat out, but they don't do much in between.
Your main jets may be too big, or your float levels may be a bit too high. It is also possible that the intake is restricted by a clogged air filter or something of the like.

Rick,
I can't imagine that jets, pilots, filter, shims etc would cause milage that bad. These bikes should get about 50-55 mpg from the factory. I'd be looking around the garage for that siphon hose. (By the way, nice bass, the Ricky)