'81 Hard to start when hot

[TopCatGr58]

There again TC, trading one issue for another.

The cooler the air that you can get to the intake the more power the engine can produce. Drawing air from just above the crank case and behind the cylinders is perhaps hottest air around the engine. That's one of the reasons the air box snorkel goes up and back under the seat.

With pods there is more airflow but when your going down the street or highway feel down there around those pods and see how hot the air is.

Cooler = more dense, so more oxygen molecules to combine with fuel vs. warmer air = less dense = less oxygen.

Well, Greg,

I guess I'm going to have to finally splurge and get one of those infrared electronic no touch laser aimed thermometers! My pods are mounted on velocity stacks which positions them much farther back away from the engine cylinders, closer to the battery, and without the airbox there, AIR circulates around that area much easier, so I feel I'm still getting fairly cool air from back there! Also, I know the airbox is made of plastic, but plastic does still collect, hold, and transmit heat thru it, so once the engine is fully warmed up, so is the air box, and so it will act a bit like a radiator and provide some heating affect to the otherwise cool snorkel air inflow.

Now, like you said, having the extra large holes drilled into the bottom of the AirBox are more proximal to the engine case and cylinders, so that air source I would agree would be hotter than the snorkel air. The snorkel air arrives from under the seat, which arrives from around the riders legs, and the Pods get similar air flow from around my legs and body, so I theorize that the Pod air isn't much warmer than the snorkel air....but I'll have to get a thermometer or two and place them in both locations to test it out.

T.C.

[BA80]

There is much more air flow behind the engine with the air box removed so the pods will get cooler air than the box with holes drilled in it.

The illusion is that if you can hear the roar of the intake you must be getting more power............WRONG!

The cooler air directed by the engineering of the box will create more power than the willy nilly direction of the pods. The drilled airbox will direct the air better but because of the placement of the drilled holes will actually reduce power because of the heated air being drawn in.

They both SOUND cool though............so do Harleys.

[TopCatGr58]

I wasn't trying to equate the "SOUND" of the pods vs. airbox to actual power.

I did a little bit more research on AIR density and variations with temperature, provided the other parameters remained the same, pressure and dew point/humidity. Here's the site I found and selected Imperial values, left the pressure/humidity the same, only changed the values for temperature.

http://www.gribble.org/cycling/air_density.html

I started with 85 degrees....a relatively comfortable riding temperature.
I then changed it to, 90, 100, 110 degrees. I'm going to have to get out my regular thermometer, and then measure the air temps at my Pods after riding for 5 minutes, and then again UNDER my seat also riding for 5 minutes, and see what the temperature difference actually is....and I would doubt that it will be more than 10 degrees difference...this will be measured with the bike actually moving through the air, so it will get actual air flow, not just stagnant air mixed with radiant heat!

From the values the website/calculator provided, the densities were the following:

Air density is ## kg/mm3

There is about 20% Oxygen, 78% nitrogen in AIR at sea level.
...................Air ..........Oxygen
85 degrees: 1.1674 0.23348 = Density
90 degrees: 1.1568 0.23136 = 0.90 % less dense
100 degrees: 1.1361 0.22722 = 2.68 % less dense
110 degrees: 1.1162 0.22324 = 4.38 % less dense

SO...if the air temp at the pods is even 10 degrees higher, it will still mean only ~1-2% less dense than from under the seat. That doesn't look very significant of a difference to me for regular street riding. Now if I were Racing, and hundredths of seconds mattered, then perhaps these differences could matter.

SO....the possible slight loss of performance from slightly warmer air with Pods vs. the airbox/snorkel compared to the easier starting when warm due to no place (OEM AirBox) to have fuel vapor collect and flood the air/fuel ratio during starting is probably neglible to the average rider! YMMV

T.C.

[BA80]

Suit yourself. I'm just stating facts from education and experience.

[motoman]

Besides what BA80 has stated bout overall running advantages of using the stock airbox, have you ever seen the 'dance' of those slides witout it? That is unnecessary wear on the slide needles since they DO float a bit off center at times. The airbox acts as a 'muffler', dampening the intake pulses. Think also of the additional unecessary movement wearing on those eight notorious points of the diaphrams that end up with pinholes..........JAT....for those that choose pods over stock.

[TopCatGr58]

Hey Brant,

Well, I can attest to the jumping affect of the vac. slides from my previous video I took years ago WITHOUT any air filters on there, and running the bike. However the air box isn't really restrictive to that extent...IMHO and so I doubt that there is much actual dampening affect of the slide bounce...would need to put one of those little spy cameras inside the airbox with a light, and record it's action under use....now My Missouri-ship is showing!

Back on the topic of TEMPERATURE. I went for a little ride today, ambient temperature in the shade was ~78 degrees. I mounted the thermometer just behind/right up against the POD end, and went for a 5 mile ride AFTER the bike was fully warmed up at 65 mph. I then quickly pulled to the side of the road and checked the temp...it was 90 degrees. I then put the thermometer along the side of the seat since I couldn't actually get it under the seat and have quick easy access to it. Rode another 5 miles and then checked the temp again....was 84 degrees.

The temperature of the air under the seat is not going to be as cool as still air under the shade due to heat from a variety of sources....the ROAD, sun, and still some radiation of heat from the cylinder fins into the air that flows towards the rear past the seat.

SO....even with taking a possible 80 degree under the seat temp, the behind the pods temp was only 90 degrees....a mere 10 degrees which according to the previous calculations I showed is only 1-2% decrease in air density....again, I doubt that it's seat of the pants performance sensible.
YMMV! And of course when riding in city traffic at slower speeds, the temps may vary a bit more, but the under the seat temp would still be higher as well, and I still feel that theres' some heating affect that occurs from the AIRBOX transmitting heat from the cylinders into the interior of the airbox.

T.C.

[BA80]

The cooler air directed by the engineering of the box will create more power than the willy nilly direction of the pods. The drilled airbox will direct the air better but because of the placement of the drilled holes will actually reduce power because of the heated air being drawn in.

People will spend lots of $ to attempt to increase HP by 1 or 2%. Just reducing intake air temp and shaping the flow will do more than that.

[motoman]

Hey Brant,

Well, I can attest to the jumping affect of the vac. slides from my previous video I took years ago WITHOUT any air filters on there, and running the bike. However the air box isn't really restrictive to that extent...IMHO and so I doubt that there is much actual dampening affect of the slide bounce...would need to put one of those little spy cameras inside the airbox with a light, and record it's action under use....now My Missouri-ship is showing!

Back on the topic of TEMPERATURE. I went for a little ride today, ambient temperature in the shade was ~78 degrees. I mounted the thermometer just behind/right up against the POD end, and went for a 5 mile ride AFTER the bike was fully warmed up at 65 mph. I then quickly pulled to the side of the road and checked the temp...it was 90 degrees. I then put the thermometer along the side of the seat since I couldn't actually get it under the seat and have quick easy access to it. Rode another 5 miles and then checked the temp again....was 84 degrees.

The temperature of the air under the seat is not going to be as cool as still air under the shade due to heat from a variety of sources....the ROAD, sun, and still some radiation of heat from the cylinder fins into the air that flows towards the rear past the seat.

SO....even with taking a possible 80 degree under the seat temp, the behind the pods temp was only 90 degrees....a mere 10 degrees which according to the previous calculations I showed is only 1-2% decrease in air density....again, I doubt that it's seat of the pants performance sensible.
YMMV! And of course when riding in city traffic at slower speeds, the temps may vary a bit more, but the under the seat temp would still be higher as well, and I still feel that theres' some heating affect that occurs from the AIRBOX transmitting heat from the cylinders into the interior of the airbox.

T.C.

Not the restrictveness as much as the airbox chamber acting as a pulse dampener.
I can tell you from other applications, that this affects smooth air flow ALOT more than you would realize.
If your familiar at all with large highway paint striping equipment, the big twin cyl. hyd. operated compressor which provides air tank pressure to paint and bead holding tanks does cause pulsations from reciprocating pistons that drasticly affects smooth bead flow out bead guns, unless a filter AND dampening chamber are front of system.
No difference in this case........still a big air pump.......just adding fuel and a bang to it.

[XJOK2PLAY]

My XJ used to be hard to start like this almost every time.
I'd have to do like Greg suggested, WOT while cranking.

After I installed the Dynojet kit, and played with the settings until I got it just right, it stopped doing that. My MPG's improved from 32 to 40, too.

Jet sizes, needle tapers, the needles being adjustable...
I think that is what helped mine.

But other's have installed the kit with different results. I know Trbig says he didn't see an improvement on his.

Bohn's XS is probably one of the best condition, best tuned 11's I've ever been around, and his starts hard all the time. But, his carbs are also stock.

I know on mine, that kit was one of the best improvements I made to mine.
Then, getting a proper synch was the next.

For the record...mine always had the stock airbox- no mods. Tod's has always had pods.

[stereomind]

My mileage is right at 32mpg at the moment.. It's good to hear that it could be improved a bit

My XJ used to be hard to start like this almost every time.
I'd have to do like Greg suggested, WOT while cranking.

After I installed the Dynojet kit, and played with the settings until I got it just right, it stopped doing that. My MPG's improved from 32 to 40, too.

Jet sizes, needle tapers, the needles being adjustable...
I think that is what helped mine.

But other's have installed the kit with different results. I know Trbig says he didn't see an improvement on his.

Bohn's XS is probably one of the best condition, best tuned 11's I've ever been around, and his starts hard all the time. But, his carbs are also stock.

I know on mine, that kit was one of the best improvements I made to mine.
Then, getting a proper synch was the next.

For the record...mine always had the stock airbox- no mods. Tod's has always had pods.

[motoman]

My mileage is right at 32mpg at the moment.. It's good to hear that it could be improved a bit

If intake and exhaust are all stock including carbs, that fuel consumption oughta' be in the neighborhood of 37-43mpg@ a constant 65-70mph.
Mileage of my Venturer to and from the rally was 31.5, and puky black to the point that noboby cared to follow me......just sayin'.

[XJOK2PLAY]

Stereomind,

The other mod I had done that also helped it to achieve 40 was the 850FD swap.

Other than that, it was a stock 11.

It also had a full Vetter 4 setup, including trunk.

It took a few times of pulling the carbs and resetting the rods before I finally got it.

11 carbs are just like people, though...they're all different.
You wouldn't think carbs would be, but they are.

I had issues before the DJ kit with them constantly... hard starting, high idle, stalling...you name it. Afterwards... cured them all.
Ymmv, though.

But, if you get them REALLY CLEAN, inspect everything well, go with a DJ kit, get the floats set right, get the adjustable needles set right for your bike, and do a FD swap, you can see 40 mpg realistically.

All mine would get, at best, when I first got it was 32.
8 mpg really makes a difference in a tank's range...(an extra 40 miles per tank, on a 5 gl. tank.)

There's lots of little things you can do to improve mileage on an 11, but the toughest thing to do is learn how to relax your right wrist...

[BA80]

Eh, I can get 40 too if I ride like grandma Bob.

[XJOK2PLAY]

Eh, I can get 40 too if I ride like grandma Bob.

Bubba,
Now that I ride a Connie, I can get 50!!

You couldn't do that if you coasted downhill both ways on your 11!

Oh, btw... It will still average 43 WOT...mach 2....

One thing I DO know about an 11...
The faster you go, the more fuel you consume, and the more oil you consume.
Fact of life...

Plus... I got a 6 gl tank to boot.

[motoman]

So did BillyRok..........no 'grandma' ridin there.....and even had ongoing running issues haunting the bike the whole trip......just sayin'.