Carburetor Tuning for MPG - VTXOA
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post #1 of 49 (permalink) Old 03-25-2019, 09:13 PM Thread Starter
JPT
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Carburetor Tuning for MPG

So, I need a little help, I am not quite sure where to go as my mpg is way too low. I have the following:

2009 VTX 1300R
Batwing Fairing
Speedo adjusted matches GPS at all speeds
Roadhouse Classic 2:1
Arlen Ness Big Sucker (very open)
Factory Pro Jet Kit
Choke Cable removed, Ace hardware spring

Current Carb Settings:
Fast/Main Jet 220
Slow/Pilot Jet 58
Needle 4.5 (E clip at 4 with a #4 washer under)
Glenís garage A/F screw at 2 from lightly seated

Tests
2nd gear from 45 mph through governor - pulls strong, no noticeable issues

4th gear 50 mph hard throttle - no bogging or choking or hesitation, pulls strong

Cold start requires throttle, RPMís are low until warm. Will sputter (pop, or backfire) on a hot start.

MPG 25-28. Granted we likely still are on winter formula gas, but I think I should still be getting in the mid 30ís at least.

Thanks!

2009 VTX1300R
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post #2 of 49 (permalink) Old 03-25-2019, 09:20 PM
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what exactly do the spark plugs look like ???????


that is where you START with tuning the carb..


that is HOW you find out what and how its burning......
RBS, leroys73 and Harkon like this.



2005 VTX1800 F, type II, Silver Tribal, 86,000 Miles, Purchased Feb, 2005.
MTC clutch & springs.. K&N Air Filter. Garmin 2597 GPS.
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post #3 of 49 (permalink) Old 03-25-2019, 09:31 PM
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If you're able to run without ever using a choke, then the bike is way too rich. Did you follow the FP instructions by trying several mains, several clip positions? Is the slide spring stock or was it cut.
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post #4 of 49 (permalink) Old 03-25-2019, 11:15 PM Thread Starter
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I went through different mains, and have a good balance of power. I tried a few different clip positions but we really havenít had stable warm temps yet.

Here is a picture of 1 front and 1 rear plugs:

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post #5 of 49 (permalink) Old 03-26-2019, 07:25 AM
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my opinion..

the plugs are glazed... then covered with Rich fuel burn..
get new plugs and try again


order of investigation.
check for air leaks at the engine to intake and intake to carb. small cracks.. or LOOSE clamps.
check the vacuum diaphragm for cracks... very little cracks..
check the spark Timing...
check valve adjustment
check camshaft timing.

you are only a little rich... not 25mpg rich..
.
unless that thing attached to the throttle is a switch.. on/off/on/off....


side note.. Honda considers the vacuum diaphragm to be retired after 6 years... racers replace them every year.
its rubber.. heat/cold cycles... fuel vapors.. for a part that NEEDS to be very flexible and sealed.


if stiff and or leaking air.. you will NEVER get Full Throttle...
its a vacuum controlled carburetor



2005 VTX1800 F, type II, Silver Tribal, 86,000 Miles, Purchased Feb, 2005.
MTC clutch & springs.. K&N Air Filter. Garmin 2597 GPS.

Last edited by chuck_VTX F; 03-26-2019 at 07:33 AM.
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post #6 of 49 (permalink) Old 03-26-2019, 08:33 AM Thread Starter
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Quote:
Originally Posted by chuck_VTX F View Post
my opinion..

the plugs are glazed... then covered with Rich fuel burn..
get new plugs and try again


order of investigation.
check for air leaks at the engine to intake and intake to carb. small cracks.. or LOOSE clamps.
check the vacuum diaphragm for cracks... very little cracks..
check the spark Timing...
check valve adjustment
check camshaft timing.

you are only a little rich... not 25mpg rich..
.
unless that thing attached to the throttle is a switch.. on/off/on/off....

I will replace the plugs, cheap enough. What is the best way to check for leaks?


Quote:
Originally Posted by chuck_VTX F View Post
side note.. Honda considers the vacuum diaphragm to be retired after 6 years... racers replace them every year.
its rubber.. heat/cold cycles... fuel vapors.. for a part that NEEDS to be very flexible and sealed.


if stiff and or leaking air.. you will NEVER get Full Throttle...
its a vacuum controlled carburetor
The diaphragm is very soft and flexible, I did not see any cracks. I plan on lowering the needles to 3 1/2 when I get home tonight, and if that doesn't play well, I'll raise it up to 4. When I have the diaphragm out, I will double check for cracks.

Right now, it runs amazingly well at all throttle positions (except on initial start), just this mph is horrible...

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post #7 of 49 (permalink) Old 03-26-2019, 09:44 AM Thread Starter
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Also note that my odometer/mpg is off by about -4%. So in reality I am getting closer to 26-27 mpg. Still not an acceptable range, but more accurate for this discussion (and anyone having similar issues).

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post #8 of 49 (permalink) Old 03-26-2019, 09:44 AM
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.
hold diaphragm up to a bright light.. a light pull and see if light pass thru..
rotate 90 degrees and do it again... till 360 degrees are done.



2005 VTX1800 F, type II, Silver Tribal, 86,000 Miles, Purchased Feb, 2005.
MTC clutch & springs.. K&N Air Filter. Garmin 2597 GPS.
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post #9 of 49 (permalink) Old 03-26-2019, 09:56 AM Thread Starter
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Quote:
Originally Posted by chuck_VTX F View Post
.
hold diaphragm up to a bright light.. a light pull and see if light pass thru..
rotate 90 degrees and do it again... till 360 degrees are done.
Will do. Since I have to change the needle position, it will be a good time to check.

I was also double checking it by reaching through the air port with the diaphragm cap. I lifted up the bottom of the diaphragm by the needle to see if there was pressure. There was a good amount of pressure, so I assumed no tears or leaks. But obviously this is not a very scientific approach.
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post #10 of 49 (permalink) Old 03-26-2019, 11:48 AM
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I wasn't having problems but replaced the diaphragm. It was flexible and soft. However, when I held it up to the light a very small pin hole was in it. Glad I replaced before trouble.

BTW: I always get between 35 and 40 mpg running interstate speeds (honest 70 & 80) with a full load of touring gear unless I am fighting a wind, then it is still above 30.

Mine is pure stock except for a K & N air cleaner.

My VTX as used on Race Tech site.I'm70 rode 07 Black Cherry VTX 1300R to 49 States+DC & 11 Provinces, 138,000mi+Yamaha RSV,37,000mi,both w/aux tank & Race Tech SuspensionIBA:Mile Eater Bronze &Silver,SS3000,3xSS2000,EclipseSS1000Gold, 20SS1000,6xBB1500,3TX1000,NPT 29/76; Lake Superior Circle Tour 15 to 20K per yr between the two MCs
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