Carb/Exhaust combo..What is the best for higher gas mileage?

[Anonymous]

What is the best carb/exhaust combo for the following:

1. Higher gas mileage

2. Higher Horsepower

3. A nice compromise: A little bit better Gas Mileage...A little bit better Horsepower.

I'm really wanting to understand this. Please help!

thx!!

Rudi
San Antonio, TX
1980 GS1100E w/ 89,500 miles 8O

[Anonymous]

Re: Carb/Exhaust combo..What is the best for higher gas mile

What is the best carb/exhaust combo for the following:

1. Higher gas mileage

2. Higher Horsepower

3. A nice compromise: A little bit better Gas Mileage...A little bit better Horsepower.

I'm really wanting to understand this. Please help!

thx!!

Rudi
San Antonio, TX
1980 GS1100E w/ 89,500 miles 8O

Rudi it seems like you expect to find plug and play solutions--you are getting yourself into a never ending thing by modifying a stock bike.


You were given some sensable simple advice.--Tweak carbs--degree cams(not that simple)--performance exhaust

[Anonymous]

....

Well, I do not possess extensive knowledge of such things. So I'm trying to learn about it via this website.

[Anonymous]

Re: ....

Well, I do not possess extensive knowledge of such things. So I'm trying to learn about it via this website.

one thing at a time and after you find he exhaust and se that the plugs run a little lean, you will be adjusting your jets--after a round or two of that yoiu may want to leave the thing alone

[Anonymous]

so you are saying

So are you saying that it doesn't matter what kind of pipes/carbs you get? It matters most how one tunes them?

I was under the impression that getting a really nice set of pipes and carbs would help the performance on my bike. Of coarse, one would need to tune them properly....but up against stock pipes and carbs, the newer ones would out perform stock ones.

[Anonymous]

Re: so you are saying

So are you saying that it doesn't matter what kind of pipes/carbs you get? It matters most how one tunes them?

I was under the impression that getting a really nice set of pipes and carbs would help the performance on my bike. Of coarse, one would need to tune them properly....but up against stock pipes and carbs, the newer ones would out perform stock ones.

absolutely not--the pipes are the first thing to chose then you can tweak after they are on--without the performance pipes you will not be totally wasting your time but will be getting much less than you could and also not e leaving room for those flatslides which you will eventually want if you become hooked

[Anonymous]

I see...

I see...

So, correct me if I'm wrong, I should think about first getting a good set of pipes. It appears that Vance & Hines has the best selection of street legal pipes for my bike.

The part I'm fuzzy on is when to think about getting nice carbs. Some have mentioned the Minuki's.

Or should I simply keep my stock carbs and try to tweak them the best I can with the nice pipes?

[Anonymous]

Re: I see...

I see...

So, correct me if I'm wrong, I should think about first getting a good set of pipes. It appears that Vance & Hines has the best selection of street legal pipes for my bike.

The part I'm fuzzy on is when to think about getting nice carbs. Some have mentioned the Minuki's.

Or should I simply keep my stock carbs and try to tweak them the best I can with the nice pipes?

Some folks would do it all at once and enjoy it--im one of those test and tweak guys. You just said that V&H didnt have pipes for your bike????

[Anonymous]

No...

nope...they seem to have the best selection of pipes for my bike. I haven't checked with Kerker yet, though. I like the V&H pipes....they look good.

[Anonymous]

Re: No...

nope...they seem to have the best selection of pipes for my bike. I haven't checked with Kerker yet, though. I like the V&H pipes....they look good.

If i had it to do over again I think i would have chosen v and h i think they are a better quality although the look very much the same in most instances. I sure would like to know any information on the pipe quality.

[Jeff Tate]

First, to Slopoke. I've had a Kerker pipe and now have a V&H supersport and liked both alot. Quality was equal as far as I could tell. I just sold the Kerker and installed the V&H about 1 1/2 years ago because I liked the aluminum canister look, plus they have a set of restrictors of varying diameters that slip into the collector so a little more fine tuning can be done. I sold the Kerker on E-Bay just so everyone knows, and won't be trying to buy it. Now on to Rudi. I can only speak from my experience, but the best of all worlds is to leave it stock. This is just my opinion as far as mileage , power, and such are concerned. More power usually means a drop in mileage. Stock bike were jetted on the lean side to meet emission standards , so richening up the off idle response certainly won't hurt. If you decide to change pipes and carbs, beware that a lot of patience is needed to get it all sorted out. Very rarely have I heard of those mods being slapped together and everything works great together from the get-go. Sorry to be so long winded, but it isn't something to just jump into with out prior warning...believe me, I know. But I don't regret it either. You have to go slow to go fast!

[Anonymous]

Jeff...

Jeff,

Interesting....So you're saying that, for gas mileage purposes, it's better to keep things in their "stock" state? I would be aiming for better gas mileage as I plan to go on long trips.

That Super Chrome pipe from V&H's website looks like the stock pipes on my bike...only a hellva lot more shiny. Would you recommend those?

As with the carbs, and please excuse my lack of techical knowledge, are the original stock ones the best for achieving high gas mileage? Or would getting a newer set ALONG with those V&H's pipes AND tuning everything properly be better?

I hope I explained that well...

Bottom line:

Stock pipes + Stock carbs + proper tuning = better/worse gas mileage

or

V&H's pipes + Muniki carbs + proper tuning = better/worse gas mileage

Which choice wins?

Thanks!!!

Rudi

[Anonymous]

Ok, my turn - lol. Maybe it's best I don't get started on this one, but I'm bored right now waiting for my new front forks to arrive.

First, while there may be rare instances where this is NOT true (i.e a poorly tuned bike to start with), but for the most part you can have good gas mileage OR you can have performance, you can't have both simultaneously. The reason for this fact is that to get better performance you are squeezing more air/fuel mixture into the combustion chamber. The better exhaust pipes help clear it out so more can get in, and the bigger carbs allow more in. There are other components (camshafts, pistons, etc) that have a say in this process, but I only see pipes and carbs discussed in the previous posts.

Now on to the the air/fuel mixture. In a diesel engine this ratio is held constant. This explains why diesels get the same fuel mileage when they are towing and not towing. This is not true on gasoline engines. The air fuel mixture varies on loading, acceleration, and many other factors. By changing the pipes you are altering this ratio since more of the bad, spent combustables will exit the combustion chamber. This means that you will have to pump more of the good stuff in. As Slowpoke stated, you will be running lean. Lean is NOT good because lean engines run hot. This heat can harm your engine and make you wish you had never messed with it.

Carb re-jet or new carb? If you are looking for a slight performance upgrade, rejet your carb with the pipe you want. This will give you the looks and sound (may or may not like) without costing a ton of money. OR go whole hog and purchase the new carbs. Keep in mind, however, that you will still need to jet (or re-jet) them to get the correct air/fuel mixture. This will cost considerably more and I doubt that you will get much more performance since you are not altering any of the other engine vitals.

There is an old addage in racing - speed costs - how fast do you want to go? I'm relating this because new pipes and carbs really need better cams, more compression, blah, blah, blah. All of this costs lots of $$. Especially if you have someone else do the work and it sounds as if that's where you are. If you have lots of cash to play with go for it.

If you decide to do all the work yourself, the pipes are a bolt on - no problemo. To jet your cars properly, however, that is a bit of a trick, especially since we are dealing with 4 synchronized little buddies. First, syncronize them. Then go to a nice straight spot on the track, road, wherever and go flat out - open throttle. Then shut it down and read the plugs. They should be a light brown. If not then ad bigger jets if the plugs are white or smaller if black (I doubt if you will be rich to start with, but you may go too far). It's an iterative process and I'm not really doing the science justice here. Get a book, it will explain it in more detail with pictures too!

If I were you I'd either leave the bike stock or just add the pipes and re-jet. But I'm not, so whatever you do, good luck.

Steve

[Billy Ricks]

I'm running a Yosh Duplex and RS Flatslides on my 700. Right out of the box the carbs performed very well. In fact, ten years later I still run the carbs the way they came from Yoshimura. Gas mileage is not off much from what I got with the stock carbs. Performance though changed greatly. It absolutely rips even with basically stock motor internals. The RS Flatslides are easy to tune, but if they are set up as recommended by Mikuni I doubt you will need to bother much with jetting changes. I've got Cosworth forged 12:1 pistons and Vance & Hines modified grind cams yet to install. Add to that a head that has already had all 16 valves replaced, new springs, seats redone, intakes ports matched to the manifolds, and mild porting. When I get around to installing the pistons and cams the RS carbs will still be more than enough of a match for the mods. Some people swear by Keihin CRs, but the Mikuni RS's are hard to beat.

[Anonymous]

Ok, my turn - lol. Maybe it's best I don't get started on this one, but I'm bored right now waiting for my new front forks to arrive.

First, while there may be rare instances where this is NOT true (i.e a poorly tuned bike to start with), but for the most part you can have good gas mileage OR you can have performance, you can't have both simultaneously. The reason for this fact is that to get better performance you are squeezing more air/fuel mixture into the combustion chamber. The better exhaust pipes help clear it out so more can get in, and the bigger carbs allow more in. There are other components (camshafts, pistons, etc) that have a say in this process, but I only see pipes and carbs discussed in the previous posts.

Now on to the the air/fuel mixture. In a diesel engine this ratio is held constant. This explains why diesels get the same fuel mileage when they are towing and not towing. This is not true on gasoline engines. The air fuel mixture varies on loading, acceleration, and many other factors. By changing the pipes you are altering this ratio since more of the bad, spent combustables will exit the combustion chamber. This means that you will have to pump more of the good stuff in. As Slowpoke stated, you will be running lean. Lean is NOT good because lean engines run hot. This heat can harm your engine and make you wish you had never messed with it.

Carb re-jet or new carb? If you are looking for a slight performance upgrade, rejet your carb with the pipe you want. This will give you the looks and sound (may or may not like) without costing a ton of money. OR go whole hog and purchase the new carbs. Keep in mind, however, that you will still need to jet (or re-jet) them to get the correct air/fuel mixture. This will cost considerably more and I doubt that you will get much more performance since you are not altering any of the other engine vitals.

There is an old addage in racing - speed costs - how fast do you want to go? I'm relating this because new pipes and carbs really need better cams, more compression, blah, blah, blah. All of this costs lots of $$. Especially if you have someone else do the work and it sounds as if that's where you are. If you have lots of cash to play with go for it.

If you decide to do all the work yourself, the pipes are a bolt on - no problemo. To jet your cars properly, however, that is a bit of a trick, especially since we are dealing with 4 synchronized little buddies. First, syncronize them. Then go to a nice straight spot on the track, road, wherever and go flat out - open throttle. Then shut it down and read the plugs. They should be a light brown. If not then ad bigger jets if the plugs are white or smaller if black (I doubt if you will be rich to start with, but you may go too far). It's an iterative process and I'm not really doing the science justice here. Get a book, it will explain it in more detail with pictures too!

If I were you I'd either leave the bike stock or just add the pipes and re-jet. But I'm not, so whatever you do, good luck.

Steve

Steve...appreciate the time you took to write that. Great info!

Question: How can I tell if my original stock carbs are working perfectly. Is it out of the question to think they still work flawlessly? What is the point at which one really NEEDS to buy new carbs?

Where am I going with this? Within the next year or so, I plan on getting the engine glass beaded...as well as the carbs. Wouldn't want to waste the $$ on shining up my carbs if they were on the verge of needing to be replaced.

Thx !

Rudi