I have an 84 fj 1100 that has the pods inplace of the factory air box. the p o installed a k&n filter on the gearbox vent but left the two ports between the carbs open shouldnt these be blocked or filtered to prevent debri from entering the carbs ? thanks.
Between carbs #1 and 2 ....and between carbs #3 and 4 there is a T. (2 T's total)
Those are the atmospheric vents to the carburetor's fuel bowls.
There should be a ~12-14" long hose on each T.
Run these two hoses down in back of your engine, pointing to the ground. Do not kink or pinch these vent hoses. Do nothing to impede the air flow within these vent hoses. No need to put a filter on the end of these hoses.
wasn't sure so figured I better ask. Was just going to put a small in-line filter on each one . Thanks for the information.
vents? not fuel overflow lines (i.e. for stuck floats )?
either way, certainly not to be obstructed
Both.
Under normal operating conditions those are vents to assure the air in the bowls stay at ambient air pressure.
Under abnormal conditions (stuck float) the fuel overfills the bowl and flows out the vent hose.
Think about the range of atmospheric pressure you can ride your bike through, from crossing the highest mountain pass at over 12,000' MSL on a hot summer day, to traveling across Death Valley at 280' below MSL in the cold winter, and everywhere in between. Pilots call this Density Altitude.
If the air within the carb bowl is not equalized with these conditions you *will have* fuel flow problems within the carb.
I'd never heard those lines described as vents, but clearly they do perform that function.
Of course they do not need to be as long as they are to do that.
Obviously, if a float bowl is air-tight fuel can not flow from it except in an ambient vacuum.
In practice I don't think ambient air pressure CHANGE is a factor though; equalization is the heart of the matter.
As the fuel level drops in the bowl, the air volume in the bowl increases and (unvented) the air pressure in the bowl drops. This creates a relative low-pressure in an unvented float bowl no matter what the initial base pressures were.
It is the relative low pressure that prevents fuel flow out of the bowl. A similar condition is more commonly experienced with fuel tanks and in extreme conditions can cause the collapse of a tank.
Same physics as imploding submaries at crush depth.
But, to stray back to the original topic, "vent lines" is as good a name as any.
Quote from: Burns on August 14, 2014, 01:32:40 PM
...In practice I don't think ambient air pressure CHANGE is a factor though...
Yep, I agree with you about the change of fuel levels in the bowl needing a vent, no question, but equalization at altitude is also a important factor. (of course, if you have one, you also have the other)
For example: Take a sealed bag of potato chips from sea level to altitude and see what happens to the bag.
I had the same thing happen to my Scott's gravity flow chain oiler. The vent line in the oil reservoir got pinched and when I rode from my home (at sea level) to Idlywild (5,500') the difference in the ambient pressure (vs. sea level pressure in the reservoir) caused all the oil to barf out on my back tire...on the twisty mountain road, it was a very exciting event. Not.
I made the mistake teeing together both vent hoses to run one longer vent/overflow hose on my '84 only to have it touch the top of my exhaust collector box. As the box heated up it melted shut the vent line...stupid I know.
What happened was the bike started surging on the freeway. My first thought was, the gas cap, tank venting.
I opened up the gas cap but the surging continued...I was on my way to the WCR in Hayfork (NorCal) and it was raining.
As I ride a bike that is misbehaving, I go thru a mental check list... Stopped at a covered gas station, pulled off my luggage, seat and side covers...looked for a pinched fuel line...nope not that (I know better)
So...not the gas cap...not the fuel line...what's next? Then I smelled it, the burning rubber smell.
A quick snip and all was fixed.
So the moral of the story is...If your FJ is surging, check your 1) gas cap 2) fuel line and 3) vent line.
yep, pinched lines are high on the "check this " list.
On the '90 Black n Blue that I'm rescuing I unknowingly pinched the fuel line putting the tank back on after cleaning it. It sat for awhile awaiting ignition plate/sender/rotor. When I replaced those parts it fired right up but quickly soured and stopped running. I figgered the carbs were dirty .... well a bit of wasted effort later I discovered the pinched line.
The old rule is "check the simple things first"
Seems I been relearning a lot of old rules lately.
It's all good though.
There are few sounds more beautiful than the song of a rescued bike running cleanly for the first time.
Quote from: Burns on August 14, 2014, 01:32:40 PM
I don't think ambient air pressure CHANGE is a factor though...
Yes it is... the delta between the venturi vacuum and the bowl pressure is what drives the fuel through the jets. Both of these "pressures" are relative to the same atmosphere when the bowl is vented to where the intakes are sucking from. Put either of those (vent or intake) in a different atmospheric pressure and the jets won't flow as designed. When you change altitude you'd get "surging" or other shitty running conditions due to a difference in the relative pressures long before you ever collapse the bowls due to excessive vacuum in them.
Bowl vents are what they are called because that's what they are. They keep the bowls and the intake at the same ambient pressure so the carbs meter fuel correctly... simple as that.
Frank
If a container is vented, the ambient (external) air pressure will equal the internal air pressure of the container. Any change in the former (e.g. a thousand feet of elevation) will be isomorphic with change in the later. I stand by my point that those changes are not at issue in a discussion of an obstructed vent (by whatever name you wish to call the vent) - the unvented bowl will not flow at ANY ambient pressure above zero (vacuum). You will be just as stalled at sea level as at the peak of your favorite mountain.
Also, I believe your discussion of the venturi is irrelevant to the subject of a vented float bowl - related, but irrelevant. The pressure of air is lowered when passing through a restricted opening ("venturi effect") and that is how fuel is pulled into the intake tract of the carburator (more accuratetly, the ambient air pressure PUSHES the fuel). The flow of air passing through the carb is generated by the low pressure area created by a descending piston (along with the inertia of fluid dynamics, but that is secondary).
Otherwise we are in heated agreement.
My pedantry drives me to make another reply to your comment.
The effect of altitude on carburation is largely a matter of density rather than pressure or velocity. The density of any given volumn of a gas increases with pressure, as is exemplified by the observation that compressing a given volume of gas into a smaller volume does not change the mass of the gas. The inverse should be obvious to the casual observer.
For each intake stroke the mass of air ingested lessens as altitide increases (less air gets in) and so the fuel-air ratio of the intake charge shifts toward rich and the effective compression ratio lowers.
Thank you for this didactic opportunity.
Remember my bag of potato chips analogy.
The same thing that happened to my Scott oiler will happen to the fuel within a unvented carb bowl.
That's it, I'm done.
We have no argument re:venting the carb bowl - ya gotta.
Our disagreement is with the effect of changes in ambient pressure.
With a vented bowl there ain't none. Those changes are the same for the air in the float bowl and the air you are breathing.
With plugged vents you have your potato chip bag situation.
Now I'm done.
nobody addressed the lower oxygen concentration at altitude. everyone agrees the bowls HAVE to be vented but the lower 02 levels
need to be compensated for at higher altitude.
I just purchased a performance ECU from Dale Walker of Holeshot Performance for my Ninja 1000. when we were discussing the Dyno sheet on his N1K he had explain that because of his shop being at 8000ft in Nevada the results were about 5-8 hp down from when his shop was at sea level in S.Cal.
back to the effect of lower ambient pressures on the carb.the engine is a positive displacement pump, every stroke of the piston will move
X-amount of air. that's on 1 side of the venture. if you reduce the ambient pressure on the other side of the venture the velocity across the the venture decreases. decrease the velocity and you decrease the fuel. the fuel mix is now lean.
at least that's the way I understand it, but what do I know, im just a smelly fisherman.
Scott
shit, I forgot to throw in the ambient temperature into the conversation...fuck it
Scott
Thanks for the replies. The information was valuable. Now I'm almost finished with the manometer, just curious , what would be more accurate on these home made meters ? Water ? or very thin oil ? Thanks again.
Quote from: klb on August 15, 2014, 10:26:26 PM
Thanks for the replies. The information was valuable. Now I'm almost finished with the manometer, just curious , what would be more accurate on these home made meters ? Water ? or very thin oil ? Thanks again.
As long as what ever you use stabilizes they will both be the same as far as accuracy. I use 2 stroke oil. Works for me and will do no harm if some gets ingested.
I would definitely not use water.... 2 stroke oil is cheap and easy to see.
George
(http://fjowners.com/gallery/2/1651_23_07_11_9_15_38.jpeg)
Quote from: klb on August 15, 2014, 10:26:26 PM
Thanks for the replies. The information was valuable. Now I'm almost finished with the manometer, just curious , what would be more accurate on these home made meters ? Water ? or very thin oil ? Thanks again.
Did you end up making a 2 or a 4 carb unit?
Noel
The liquid column will bounce around a bit as the pressure waves peak and trough; you need a bit of viscosity to get a decent reading ("stabilize"). As to "very thin oil" I've used 10-30 motor oil with gfood results. Like the fella said, whatever stabilizes and definitely not water.
Quote from: FJscott on August 15, 2014, 04:19:45 PM
shit, I forgot to throw in the ambient temperature into the conversation...fuck it
Scott
re: O2
I said "The effect of altitude on carburation is largely a matter of density" which addresses the 02 issue.
At altitude there is less O2 in the charge because there is less air in the charge. I don't think that the ratio of the atmospheric gases (Nitrogen, 02, CO2) changes much if any as a function of altitude.
You say that the air pumped on any given stroke is the same, but actually it is the volume of air that is constant. The mass of that volume decreases as the ambient pressure decreases.
It also decreases as the ambient temperature rises since hot air is thinner than cold air.
Power is all about getting as much air/fuel mix in the chamber as you can. Some drag racers ice down their intake manifolds before a run for a denser charge.
As to rich/lean. When you rejet for higher altitudes you go down on jet sizes and lean out the mixture. Lower altitude jetting will be rich at higher altitudes.
Cool and Low is the way to go.
The key to stopping the pulsing along with the oil viscosity is to restrict the air flow. In my picture you will see 2 black fitting in the line. They are restrictors from a Harbor Freight brake bleed kit (5.00).
George
Quote from: Burns on August 16, 2014, 10:44:08 AM
The liquid column will bounce around a bit as the pressure waves peak and trough; you need a bit of viscosity to get a decent reading ("stabilize"). As to "very thin oil" I've used 10-30 motor oil with gfood results. Like the fella said, whatever stabilizes and definitely not water.
I think we may have our vacuum lines crossed here. The guy with the fluttering vac on one cylinder is using gauges, not the one that's just built his own.
Noel
i put together a four bottle unit with vacuum restricters inline. am going to use 2 stroke oil for the fluid. Brother has an 1980 XS 1100. will see how this turns out. thanks
Tried to synch the carbs with the home made manometer, used plastic gatorade bottles and 2 stroke oil, bottles collapsed a fair amount. and was filling bottle two, to where the oil was getting into the vacumn tube, I couldnt keep up with the screw adjustments, shut it down and redistributed the oil evenly. bench synched the carbs again and ended up with the same results on bottle three, a lot of air bubbleing in the other bottles. Bench synched them again and ran it that way without the use of the manometer. Idles smooth. off idle stumbles, have to fan the throttle to get it reved and runs smooth at higher rpms. Am going to put together the 2 carb synch shown on here and try that.
Quote from: klb on August 17, 2014, 11:37:26 PM
Tried to synch the carbs with the home made manometer, used plastic gatorade bottles and 2 stroke oil, bottles collapsed a fair amount. and was filling bottle two, to where the oil was getting into the vacumn tube, I couldnt keep up with the screw adjustments, shut it down and redistributed the oil evenly. bench synched the carbs again and ended up with the same results on bottle three, a lot of air bubbleing in the other bottles. Bench synched them again and ran it that way without the use of the manometer. Idles smooth. off idle stumbles, have to fan the throttle to get it reved and runs smooth at higher rpms. Am going to put together the 2 carb synch shown on here and try that.
Something doesn't sound right here, bottles?
All you should have is 4 tubes joined to each other at the bottom, such as the photo below, or two pieces looped at the bottom with a connecting pipe between them, there is no reservoir as such.
You are balancing them against each other, not against atmospheric pressure.
The connecting fittings pictured are automotive vacuum line fittings I happened to have a box of but you could even use garden watering system fittings, anything that fits the tubing.
(https://farm6.staticflickr.com/5591/14952433521_be5c0558b1_z.jpg)
Some sort of restrictor to calm down the pulsations. The photo below shows plastic dowel cut into short lengths and a small hole drilled through the centre but you could use anything that has the same effect.
(https://farm4.staticflickr.com/3727/12704320625_b199fe60d3_z.jpg)
(http://or,%20if%20it's%20easier%20to%20grasp%20the%20concept,%202%20of%20Fred's%20joined%20together.%3Cbr%20/%3E%3Cbr%20/%3E%5Bimg%20width=558%20height=800%5Dhttps://farm4.staticflickr.com/3875/14771062889_bca506d9c5_c.jpg)
....and a board to fasten the tubes to, in this case a fence paling and electrical clips.
I used auto fluid, but once again it could be 2 stroke or old engine oil.
The other thing I did was add some sheaths near the carby end (pictured below) because if the engine is really hot the lines tend to get soft and collapse on themselves giving false readings.
(https://farm6.staticflickr.com/5072/7175620716_18860ab1a1_z.jpg)
The only thing I had to buy was the tubing, the rest was stuff I had lying around.
The only difference between a 2 tube and a 4 tube set up, other than being a PIA to use, is just ONE connecting tube between the bottom of the two loops.
(https://farm4.staticflickr.com/3875/14771062889_bca506d9c5_c.jpg)
If it makes it any clearer, just imagine two of Fred's joined together.
Something doesn't sound right from you post, can you post pictures of what you have made?
Noel
I must have screwed up. should have used glass bottles not plastic. I found the idea for 4 bottles on youtube. Several ways to make them. I abandoned the 4 bottle set up and went with the single line looped at the bottom and it worked great. Have in line vacuum restricters and is the set up for 2 carb synch. it is shown in the post above. Started at cabs 1&2 then 3&4 then 3&1. Like I said it worked great. Thanks all.