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LageB
Joined: 18 Jan 2010
Posts: 5
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 Posted: Tue Jan 19, 2010 6:07 am Post subject: Bing54 / Max height btw Fuel tank and Mikuni fuel pump |
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Hello everybody ,
This is my first post here. I am so sorry I do not have any Kolb, but hope you don't mind an outsider's questions. I found that my subjects has been up for discussions on this Forum before and hope for great input from here.
Background
Last year I came over a "Hydrocopter" (built aro 1960) as a fun project. Installed used Rotax 532 engine with Bing 54 carburator. The combo can be seen in this link: http://www.youtube.com/watch?v=qR6XSdwmnak
It was working fine aro 5-6 operating hours. Few weeks ago, it suddenly started to loose rpms and eventually stopped. I could sometimes get the engine started but never reaching top rpm and after 15-30 sec always stops.
- I opened up the carburator. Cleaned it, replaced Jets and needles etc.
(by the way, unbelievable thing, one needle looked like this:
http://i644.photobucket.com/albums/uu162/LageB/Rotax%20532/DSCN0930.jpg ...)?
YES - after installing the fresh carburator the engine worked well again ... for about 15 minutes.
In some occasions the plugs has been dry, other times, it seems the carburetor was flooding as plugs were soaking wet.
I suppose I could have a combination of problem. For the process of eliminating failure causes however, I want to find out whether the Mikuni impulse pump possibly operating on/under its limits. I have around 40 inch lifting height on my Hydrocopter. I can not move tank closer to the pump.
Maximum lifting height for the Mikuni
Does anybody here know official figure what is the maximum allowable height from Fuel tank to the Mikuni fuel pump?
Looking at the Rotax installation manual page.15, it says that:
1. If fuel tank is "considerably" lower than pump, an electric pump should be used. (unfortunately it does not specify what "considerably" is..)
2. Electric pump should be connected in parallel (with the impulse pump) to avoid fuel pressure to be excessive
I think Rotax' above information is somewhat fuzzy and trying to understand Point 2 I hope someone here could clarify physics (a)-(b) as under:
(a) What is the resulting pressure in the case Pumps are installed in series:
- Is it "Pump pressure_1" + "Pump pressure_2" ??
(b) What is the Pressure in the case of parallel connection?
May I understand that, the pressure (after the pumps) are basically same as from the the pump out of the two, that deliver the highest pressure for the moment? ( I guess the impulse pump's pressure varies with motor rpm)
So, for example, if assumption (a) is correct, I would have to make sure that the Electric pump and Impulse pump combined at no time exceeds 7 psi.
If the problem is that the impulse pump is not capable of the lifting height in the first place, then, would it not be more safe in that case just simply to have one Electric pump bypassing the Mikuni ? That is, isn't it better making sure I have one Electric pump strong enough that can fully cover pressure range required for my application by itself, rather depending on a combination of 2 pumps where each pump individually possibly are insufficient?
Lage
Stockholm / Sweden
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Tue Jan 19, 2010 6:45 am Post subject: Re: Bing54 / Max height btw Fuel tank and Mikuni fuel pump |
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I don't know the specific answers to your (good) questions, but some thoughts I have. Yes, 40" probably is too high for the pneumatic pump to lift fuel reliably. The vacuum generated by the pump isn't a whole lot. So I'd say you're probably in the "considerably" zone at that point 
An alternative to consider is a header tank located closer to the engine. You'd have to come up with some kind of arrangement to keep the header tank full (feed it with an electric pump and put some kind of fuel level regulation like a float switch or something like that in the tank), but that would be a way to get the fuel level raised to a place where the pneumatic pump could reliably draw fuel.
Also make sure the pulse line from the engine to the pneumatic pump is as short as possible. No longer than 12" at the max - too long of a pulse line is the most common installation error I've seen that puts 2-stroke powered planes down in the dirt than anything else. This will ensure the pump is working as hard as it's supposed to...
LS
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LS
Titan II SS |
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LageB
Joined: 18 Jan 2010
Posts: 5
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| Posted: Tue Jan 19, 2010 8:55 am Post subject: Re: Bing54 / Max height btw Fuel tank and Mikuni fuel pump |
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| lucien wrote: | I don't know the specific answers to your (good) questions, but some thoughts I have. Yes, 40" probably is too high for the pneumatic pump to lift fuel reliably. The vacuum generated by the pump isn't a whole lot. So I'd say you're probably in the "considerably" zone at that point
An alternative to consider is a header tank located closer to the engine. LS |
Thanks Lucien 
I am inclined to think same, i.e that 40" is probably in the risk zone for the Mikuni to suck & feed the Dual Bing 54 carbs
I have no space for a tank closer to the engine (it would have been best - I know). So, for me the questions are:
(1) Is it some way to confirm that 40" indeed is too much?
(2) If too much. Then no choice. An electric pump must be installed. either as:
- Stand alone ? -> If so, what pressure spec?
or,
- Series or parallel -> If so, what pressure specs (should be different depending whether parallel or series connection - right?)
Since this is not an Aircraft, I am thinking to adopt Stand alone option (by-passing the impulse pump) for simplicity.
Would a Automobile fuel pump 5.0 Psi, 130L/h work?
Edit:
Let me think about the Header tank though (interesting) but it would also add some complexity- anyway thanks for idea
Lage
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LageB
Joined: 18 Jan 2010
Posts: 5
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| Posted: Tue Jan 19, 2010 12:27 pm Post subject: Re: Bing54 / Max height btw Fuel tank and Mikuni fuel pump |
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Why are new threads on same subject posted ?
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NeilsenRM(at)comcast.net
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| Posted: Tue Jan 19, 2010 12:48 pm Post subject: Bing54 / Max height btw Fuel tank and Mikuni fuel pump |
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Isn't this getting a bit off the rules of our list? Lets keep it Kolb
related. A quick question is fine but.....
At least do not archive
Rick Neilsen
Redrive VW Powered MKIIIC
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LageB
Joined: 18 Jan 2010
Posts: 5
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| Posted: Tue Jan 19, 2010 2:50 pm Post subject: Re: Bing54 / Max height btw Fuel tank and Mikuni fuel pump |
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My apologies Rick Neilsen,
Kindly bear with me further (just in this thread) and I will be out of here after this thread
To Dana:
Many thanks for good advices. I will follow your recommendation and pull exhaust to check any damage 
May I understand you so, that in case "El.pump + Puls.pump" combination, the resulting pressure will be whichever pump's pressure is higher, actually regardless whether I connect in series or parallel?
If so, Rotax' choice of words are somewhat misleading when they say that pumps should be connected in parallel to avoid excessive pressure....
To Rickofudall:
Thanks a lot for informative links
LageB
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Tue Jan 19, 2010 8:29 pm Post subject: Bing54 / Max height btw Fuel tank and Mikuni fuel pump |
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> Isn't this getting a bit off the rules of our list? Lets keep it Kolb
| Quote: | related. A quick question is fine but.....
At least do not archive
Rick Neilsen
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Rick N/Gang:
I agree whole heartedly.
There is a Rotax List in Matronics to address Rotax questions.
We talk as lot about Rotax here on the Kolb List as they pertain to their
use in our Kolb aircraft.
john h
mkIII
DO NOT ARCHIVE
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John Hauck
MKIII/912ULS
hauck's holler
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