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A2 35 kW restrictor kit

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stormbringer
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Re: A2 35 kW restrictor kit

Post by stormbringer on Mon 31 Oct 2016, 8:59 pm

Baddi wrote:I'll try and open the tank and then drive. Smile 
But I haven't noticied any venting hose from the fuel tank. Where should it be?
Tank left side; petrol tap´+ fuel hose + vacuum hose.
Tank right side; overflow hose, vent hose. Look at the tank underside. You should have had to unplug those two to get the tank off...
You can see the hoses on this picture, lower left corner near the fusebox/wiring loom:


Last edited by stormbringer on Mon 31 Oct 2016, 9:10 pm; edited 2 times in total
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Baddi
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Re: A2 35 kW restrictor kit

Post by Baddi on Mon 31 Oct 2016, 9:02 pm

stormbringer wrote:
Baddi wrote:I'll try and open the tank and then drive. Smile 
But I haven't noticied any venting hose from the fuel tank. Where should it be?
Tank left side; petrol tap´+ fuel hose + vacuum hose.
Tank right side; overflow hose, vent hose. Look at the tank underside. You should have had to unplug those two to get the tank off...
Nope, the only thing that was attatched to my tank was on the left side, so I guess someone already removed the overflow and vent hose. I'll look at it when I get time to remove the tank again.
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Alvi
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Re: A2 35 kW restrictor kit

Post by Alvi on Mon 31 Oct 2016, 9:59 pm

According to kepner tragoe (google it if you must, I had to do it when working as a service engineer for an American company many years ago), the first question is 'has something changed?', which makes the restrictor fitment the most likely cause. But.....it's worth checking a couple of simple things as well. Fuel heights? Essy to check with a bit of clear pipe led upwards on the drains with the drain screws opened. Also worth removing the air filter temporarily in case it's been damaged by fuel overflowing a carb - happened to me!
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eternally_troubled
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Re: A2 35 kW restrictor kit

Post by eternally_troubled on Tue 01 Nov 2016, 7:55 am

You can check that *some* fuel is getting to both carbs by using the carb-drain screws to check that there is fuel is both bowls.

You were talking about coolant:  as you've probably noticed the top of the cooling system (with its thermostatic cap etc) is under the tank - it's worth topping it up with distilled water if you think you've lots a bit, as well as making sure that the overflow tank (behind the air box) is also at the correct level.

As you demonstrated earlier in this thread, it is possible to synch the carbs 'by eye' if you can see the throttle butterflies and adjust them to act in unison.  It might not be quite as good as using the vacuum gauges but it should get them close enough to run, so if you did this previously I doubt that it is a problem now.

If you are concerned about the tank-vent-blocked problem you can test for it - ride the bike until it stops working then pop the petrol cap:  if a vacuum has been created there will be a 'hiss' as the air rushes back in.  If you get this then you have found at least one of the problems Smile

Good luck is solving these problems:  keep us up to date and we can try and throw some helpful information in your direction, or at least, provide some morale support!
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Baddi
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Re: A2 35 kW restrictor kit

Post by Baddi on Wed 02 Nov 2016, 9:39 am

I found and fixed the problem. And sorry for once again forgetting to take a proper picture of the restriction in place.

First I looked at the spark plugs and saw no soot, so that was not the problem. I then noticed that the right cylinder (spark plug on the left) exhibited no sign of a combustion taking place at all while the left cylinder (spark plug on the right) had some colour that I would connect with running a slightly rich mixture for a short amount of time. 



So the next thing was to check if my idea of the aluminum funnels in the intake was correct, so off with the air filter box. As I expected, they were loose. The one for the left cylinder was sitting loosely in its place while the one for the right cylinder had completely fallen off and into the air filter box. 



Funnels out, they look like this. Some wierd dents, but it is pretty soft aluminum, so I think that some previous mechanic has been a little rough. They said that the carburators had recently had gotten a complete disassembly and cleaning, but by the state of the sub-air filter and a few other things, I suspect that the person doing so was not a very good mechanic. 



The carburators look like this without the funnels. The left carburator was wetted with fuel but the right was dry.



I bent down the flaps so that the black plastic thing can hold on to the funnels better, but I think I'll have to be a lot more careful in the future as these will not take that much more bending forwards and backwards before failing as can be seen by the surface cracks in the bend and also because the thickness had thinned a bit at the bend.



This is what the carburators look like without the funnel or the air filter attatchment black plastic thingy. You can see that there are 3 air intakes and one that has the tiniest hole. 



Funnels back on and a close-up






So what is going on that is causing the carburators to stop functioning when the funnels fall off? 
Well, I've made a sketch. The carburator works because pressure differentials between the carburator bowl and the main air flow will press fuel through a nozzle and into the air stream.
The bowl of the carburator is connected to the air filter box outside the funnel by a passageway. The air velocity here is neglectilby small, so we say that the pressure in the bowl is the static pressure Ps. 
Then in the main air stream, we have a dynamic velocity larger than zero (Vd>0) and because of the conservation of energy (Bernoulli's equation) we have that if the velocity rises, the pressure will fall, so we have a dynamic pressure which is lower than the static pressure (Pd
As long as the float operates properly, the main jet will be submerged below the fuel level and the pressure difference will push the fuel up into the main air stream. The flow of fuel is then regulated by the pressure differential and the diameter of the main jet. 

What has happened here, when the funnel has fallen off is that air in the main air stream and the passageway to the bowl is not seperated, so the pressure in the bowl will no longer be the static pressure in the air filter box and thus the pressure differential is not great enough to force the wanted amount of fuel into the air stream and the carburator will not function as designed.



The motorcycle runs fine for now, but I guess I'll still have to balance and tune the carburators some time.
I hope that these pictures and discriptions will contribute to the forum, even though it got a bit off the main topic that started the thread. Smile 
All of the pictures can be found on https://imgur.com/a/tbQwm

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Re: A2 35 kW restrictor kit

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