#35's or #38's? Need opinions on fuel mileage

[Bret SD]

After buying my 2002 Standard, I rebuilt the carburetors and installed #38 slow Jets. That was nearly 2 years ago, initially my fuel mileage was pretty poor until I discovered the rear brake caliper was hanging up.

After fixing the brakes and installing a Zeetex CT 1000 rear tire fuel mileage is around 29 miles per gallon when mostly freeway riding. When riding on the freeway my RPM's probably average closer to 4000 than not.
If I take my girl up into the mountains for a two-up trip, we probably average 3000 RPMs and miles per gallon is around 34+.

I regretted installing the #38's initially, but now it seems not so bad. I have a new set of #35's sitting in the top of my toolbox and have contemplated installing them. If I do go through the trouble of swapping Jets, what sort of increase in fuel economy can I realistically expect?

The bike runs flawlessly at sea level and at 5500 ft. elevation with great power through the entire RPM range, I'm just wondering if it's worth the effort at this point to change them out? 

[signart]

Speaking for myself, mine gets better mileage, starts better with less warm up time needed, better idle speed traveling through parking lots with 38's. Will not ever go back to 35's.

[Jess Tolbirt]

mine was stock and here in mid Tn. at 80 mph my mileage would drop sometimes to low 20's. 70mph low 30's, and 60mph high 30's.
never made it to 40 mpg.
I dont know what stock size is but if its .035 then i would leave the 38's in it.

[John Schmidt]

I had much the same experience with 38's. Never had mileage issues on trips, usually running in the low 70's on the slab I'd get mid-30's for mileage. At 4k rpm you're approaching 90mph which is a ridiculous speed at which to travel so mileage in the 20's is to be expected. Personally, I've never had mileage drop below 30. When I rebuilt the carbs this past summer the kit came with 35's so that's what I installed but the 38's had no bad effect on my mileage although I know others have said they did. The bike always started easy, even in cooler weather I seldom used the choke, and slow driving in city traffic it actually seemed to run better. I'm planning on swapping the rebuilt carbs from the old bike into the trike and while  they're out I'm debating reinstalling the 38's. That decision is way down the road this winter so have time to cogitate upon it. 

[signart]

Think about it, mileage drops come in play at higher rpms and or higher speeds, resistance etc. The size of the slows aren't going to factor in there. 

[turtle254]

Think about it, mileage drops come in play at higher rpms and or higher speeds, resistance etc. The size of the slows aren't going to factor in there. 

Slow jets affect across the board on fuel mix. 4 ports in carb for slow jet flow ... only one for idle .

[Bret SD]

Speaking for myself, mine gets better mileage, starts better with less warm up time needed, better idle speed traveling through parking lots with 38's. Will not ever go back to 35's.

My experience has been similar, thanks

mine was stock and here in mid Tn. at 80 mph my mileage would drop sometimes to low 20's. 70mph low 30's, and 60mph high 30's.
never made it to 40 mpg.
I dont know what stock size is but if its .035 then i would leave the 38's in it.

#35's are stock, I'm just mulling this over to see what the advantages and disadvantages are, thanks

[Bret SD]

I had much the same experience with 38's. Never had mileage issues on trips, usually running in the low 70's on the slab I'd get mid-30's for mileage. At 4k rpm you're approaching 90mph which is a ridiculous speed at which to travel so mileage in the 20's is to be expected. Personally, I've never had mileage drop below 30. When I rebuilt the carbs this past summer the kit came with 35's so that's what I installed but the 38's had no bad effect on my mileage although I know others have said they did. The bike always started easy, even in cooler weather I seldom used the choke, and slow driving in city traffic it actually seemed to run better. I'm planning on swapping the rebuilt carbs from the old bike into the trike and while  they're out I'm debating reinstalling the 38's. That decision is way down the road this winter so have time to cogitate upon it. 

Living in San Diego I literally never use the choke, I should probably use the old rule of 'if it ain't broke don't fix it', Lord knows I have plenty of other projects that could do :-)

[Avanti]

Read the post and reply #2

http://www.valkyrieforum.com/bbs/index.php/topic,75792.msg743575.html#msg743575

[98valk]

unless u have an aftermarket exhaust, stay with the 35s and tune the carbs. will get better mpg with the smaller PJ.  any PJ is good up to 4.5 turns open on the mixture screws if that is not enough then go up a size.
I have a modified air box, viking exhaust, ported and polished flowed heads with R1 cams and the bike only needs 38 PJs.

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,lower_rpm_engines.html

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_pilot%20jet,%20affect%20of%20size%20on%20idle%20and%20cruise.html

[Bret SD]

Read the post and reply #2

http://www.valkyrieforum.com/bbs/index.php/topic,75792.msg743575.html#msg743575

Crap! It's always more complicated 

[Bret SD]

unless u have an aftermarket exhaust, stay with the 35s and tune the carbs. will get better mpg with the smaller PJ.  any PJ is good up to 4.5 turns open on the mixture screws if that is not enough then go up a size.
I have a modified air box, viking exhaust, ported and polished flowed heads with R1 cams and the bike only needs 38 PJs.

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,lower_rpm_engines.html

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_pilot%20jet,%20affect%20of%20size%20on%20idle%20and%20cruise.html

Hmmm.. lots of figgerin to do I guess, If I remember right the pilot screws are turned out 1-3/4 turns on the bike right now. I should take a look at the plugs, it's been awhile since I last checked. The exhaust is stock and I installed pigs from Mark T as the PO had chopped them and drilled baffles.

I'm not sure if the timing wheel is stock or not, and frankly don't know how to tell if I were to open it up. The PO also had extra non-matching needle washers installed on it which I removed when re-doing the carbs. The AF is stock, I have the high flow filter which I removed when working on the carbs as well.

[98valk]

unless u have an aftermarket exhaust, stay with the 35s and tune the carbs. will get better mpg with the smaller PJ.  any PJ is good up to 4.5 turns open on the mixture screws if that is not enough then go up a size.
I have a modified air box, viking exhaust, ported and polished flowed heads with R1 cams and the bike only needs 38 PJs.

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,lower_rpm_engines.html

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_pilot%20jet,%20affect%20of%20size%20on%20idle%20and%20cruise.html

Hmmm.. lots of figgerin to do I guess, If I remember right the pilot screws are turned out 1-3/4 turns on the bike right now. I should take a look at the plugs, it's been awhile since I last checked. The exhaust is stock and I installed pigs from Mark T as the PO had chopped them and drilled baffles.

I'm not sure if the timing wheel is stock or not, and frankly don't know how to tell if I were to open it up. The PO also had extra non-matching needle washers installed on it which I removed when re-doing the carbs. The AF is stock, I have the high flow filter which I removed when working on the carbs as well.

for best mpg u want to be hwy cruise just using the PJ which is about 1/8-1/4 throttle. going more goes into the needle circuit which really eats the fuel.

[Robert]

Mid range is where you do most of your cruising and that is where you want the best mileage. You are not going to race down at low RPMs either. So keep the 35 up the top end to 115 and keep it as lean as you can at the mid and low range. You will feel a slight hold back but when you open her up she will scoot. So you get the best of both worlds, a good cruise and alot of power when you hit it. The larger top end will help it through the rpm ranges also.

[Bret SD]

unless u have an aftermarket exhaust, stay with the 35s and tune the carbs. will get better mpg with the smaller PJ.  any PJ is good up to 4.5 turns open on the mixture screws if that is not enough then go up a size.
I have a modified air box, viking exhaust, ported and polished flowed heads with R1 cams and the bike only needs 38 PJs.

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,lower_rpm_engines.html

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_pilot%20jet,%20affect%20of%20size%20on%20idle%20and%20cruise.html

Hmmm.. lots of figgerin to do I guess, If I remember right the pilot screws are turned out 1-3/4 turns on the bike right now. I should take a look at the plugs, it's been awhile since I last checked. The exhaust is stock and I installed pigs from Mark T as the PO had chopped them and drilled baffles.

I'm not sure if the timing wheel is stock or not, and frankly don't know how to tell if I were to open it up. The PO also had extra non-matching needle washers installed on it which I removed when re-doing the carbs. The AF is stock, I have the high flow filter which I removed when working on the carbs as well.

for best mpg u want to be hwy cruise just using the PJ which is about 1/8-1/4 throttle. going more goes into the needle circuit which really eats the fuel.

Judging by the sound, RPMs and feeling I'd say the transition occurs right around 3500 RPMs. If I were to cruise on the freeway at 3500 mileage would likely be low thirties, I was actually surprised getting close to 30 miles per gallon when cruising the freeways at around 4,000 RPMs.

[Bret SD]

Mid range is where you do most of your cruising and that is where you want the best mileage. You are not going to race down at low RPMs either. So keep the 35 up the top end to 115 and keep it as lean as you can at the mid and low range. You will feel a slight hold back but when you open her up she will scoot. So you get the best of both worlds, a good cruise and alot of power when you hit it. The larger top end will help it through the rpm ranges also.

This is something I'm going to have to put some time into, obviously, if I want to get it right. As it is now the bike idles smoothly, has no flat spots and will scream at higher RPMs.. When it's running this good I'm thinking its best I really take my time and try to figure out what to do before I start playing around. It would really tick me off if I created problems for myself at this time for no good reason.

[Robert]

Mid range is where you do most of your cruising and that is where you want the best mileage. You are not going to race down at low RPMs either. So keep the 35 up the top end to 115 and keep it as lean as you can at the mid and low range. You will feel a slight hold back but when you open her up she will scoot. So you get the best of both worlds, a good cruise and alot of power when you hit it. The larger top end will help it through the rpm ranges also.

This is something I'm going to have to put some time into, obviously, if I want to get it right. As it is now the bike idles smoothly, has no flat spots and will scream at higher RPMs.. When it's running this good I'm thinking its best I really take my time and try to figure out what to do before I start playing around. It would really tick me off if I created problems for myself at this time for no good reason.

I too would question the idea of getting into a job that is as time consuming as this when my bike is working well. Like the old saying goes, "if it aint broke don't fix it".  

I would normally get 35 MPG and when I first did the carbs I was as high as 40 MPG with no flat spot and no problem with acceleration. I am not sure why but on one trip I was at 45MPG and thinking something was wrong. I also did something most are told not to do mess with the air box. If you go back in the tech articles you will find that many had problems with jetting when they messed with airbox. That is because the air box gives a slight vacuum to the carbs. So when you take away the vacuum you need to compensate. Some were using 125 jets on the mains. 

[98valk]

Mid range is where you do most of your cruising and that is where you want the best mileage. You are not going to race down at low RPMs either. So keep the 35 up the top end to 115 and keep it as lean as you can at the mid and low range. You will feel a slight hold back but when you open her up she will scoot. So you get the best of both worlds, a good cruise and alot of power when you hit it. The larger top end will help it through the rpm ranges also.

This is something I'm going to have to put some time into, obviously, if I want to get it right. As it is now the bike idles smoothly, has no flat spots and will scream at higher RPMs.. When it's running this good I'm thinking its best I really take my time and try to figure out what to do before I start playing around. It would really tick me off if I created problems for myself at this time for no good reason.

to add,
do your road testing in third gear. no need to be in fifth and doing over 100.
in the factorypro instructions, u can't adjust the floats, since honda makes them non-adjustable.
a way around that is to use adjustable needles or stock needles and shimming them as needed, and different slide springs such as the I/S springs, which will make it leaner in the lower RPMs esp cruise and richer in the higher RPMs, both conditions due to the effect of the air velocity across the needle well.

[Led]

When it comes to Motorcycles, I never really worried about fuel mileage?   I may be an odd Duck on this.......

But if She performs superbly, at all levels for me.....I am happy.......and will dump in as much fuel as She wants!!!   

That is what Motorcycles are all about.....

[Bret SD]

Mid range is where you do most of your cruising and that is where you want the best mileage. You are not going to race down at low RPMs either. So keep the 35 up the top end to 115 and keep it as lean as you can at the mid and low range. You will feel a slight hold back but when you open her up she will scoot. So you get the best of both worlds, a good cruise and alot of power when you hit it. The larger top end will help it through the rpm ranges also.

This is something I'm going to have to put some time into, obviously, if I want to get it right. As it is now the bike idles smoothly, has no flat spots and will scream at higher RPMs.. When it's running this good I'm thinking its best I really take my time and try to figure out what to do before I start playing around. It would really tick me off if I created problems for myself at this time for no good reason.

to add,
do your road testing in third gear. no need to be in fifth and doing over 100.
in the factorypro instructions, u can't adjust the floats, since honda makes them non-adjustable.
a way around that is to use adjustable needles or stock needles and shimming them as needed, and different slide springs such as the I/S springs, which will make it leaner in the lower RPMs esp cruise and richer in the higher RPMs, both conditions due to the effect of the air velocity across the needle well.

Thanks 98, I appreciate the comment and will add it to the equation.. dunno when I'll tackle the project, first I'll have to engage in paralysis by analysis for an extended period of time.

When it comes to Motorcycles, I never really worried about fuel mileage?   I may be an odd Duck on this.......

But if She performs superbly, at all levels for me.....I am happy.......and will dump in as much fuel as She wants!!!   

That is what Motorcycles are all about.....

I like the way you're thinking here my man, sometimes the pursuit of perfection absolutely drives me crazy. Aside from all that my fuel mileage is not all that bad right now.

[Willow]

When it comes to Motorcycles, I never really worried about fuel mileage?   I may be an odd Duck on this.......

But if She performs superbly, at all levels for me.....I am happy.......and will dump in as much fuel as She wants!!!   

That is what Motorcycles are all about.....

That's an interesting perspective but generally improved fuel mileage also results in better performance.  Pouring raw fuel out the exhaust doesn't make you go faster.

[98valk]

[/quote]
I like the way you're thinking here my man, sometimes the pursuit of perfection absolutely drives me crazy. Aside from all that my fuel mileage is not all that bad right now.
[/quote]

another point. need to pick a temperature to tune at. per mikuni, whatever the perfect jetting is for max power and driveability at cruise, that is only good for plus/minus 25 degrees.

[Bret SD]

I like the way you're thinking here my man, sometimes the pursuit of perfection absolutely drives me crazy. Aside from all that my fuel mileage is not all that bad right now.
[/quote]

another point. need to pick a temperature to tune at. per mikuni, whatever the perfect jetting is for max power and driveability at cruise, that is only good for plus/minus 25 degrees.

[/quote]
Hmmm.. 70 degrees sounds about right for this climate in San Diego, I can tell my vehicles love cooler temps and run great. I have to say this summer when riding inland through Rincon Reservation temps were 112 and she still ran like a top. Probably more reason to leave well enough alone for now as I have zero issues with anything from temps, altitude and overall performance.