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frans(at)privatepilots.nl
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 Posted: Fri Apr 23, 2010 2:25 am Post subject: Rotax carb choke problem |
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Gentlemen,
Recently, after a few months of winter inactivity, the starboard carb
was flooding. I took the carb out, cleaned the bowl and float valve, and
put the carb back in. Problem solved.
Except... I have cold start issues since then. It appears that the choke
of this carb is since this time no longer working. At a cold start, the
engine appears to run on two cylinders for a while (confirmed by the
EGT: only cylinders 2 and 4 produce heat), and if I manage to get the
engine running without choke so I can throttle up, then cylinders 1 and
3 finally join the party.
After that, the engine runs normally. I just checked the carb balancing
(mechanically and pneumatically) and the setup is perfect. The carbs
open and close at the same time, and manifold pressures of both
manifolds is perfectly equal. Starting if the engine is somewhat warm
(without choke) is perfect as well.
The problem is definitely choke related: it appears to me that the choke
is not working at all.
(And yes, the choke cable is attached, and confirmed to fully open the
choke if I pull the knob).
Before I go through a time consuming trouble shooting and disassembly of
the carb, has anyone an idea what this can be? The problem started when
I disassembled the carb, but I haven't messed with the choke or any
inards above the float bowl.
Any ideas appreciated!
Thanks,
Frans
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rlborger(at)mac.com
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| Posted: Fri Apr 23, 2010 5:08 am Post subject: Rotax carb choke problem |
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Frans,
My first guess...
If you had the float bowl off, check to make sure that the little hole down in the corner and associated plumbing in that corner is clear.
http://www.europaowners.org/forums/gallery2.php?g2_itemId=64633
I'm not sure if you are aware, but the "Choke" isn't really a choke in the classic sense. Pulling the "Choke" cable rotates a set of valves in the carb which enable a small enriching carb. The enriching carb receives its fuel from the float bowl through that small hole and associated plumbing.
You will also want to make sure the associated plumbing is clear.
http://www.europaowners.org/forums/gallery2.php?g2_itemId=64636
and the brass pipe that you see sticking down out of the carb and which goes into the float bowl.
http://www.europaowners.org/forums/gallery2.php?g2_itemId=64639
There may be some sort of blockage in that system preventing fuel flow to the enriching carb
Hope this helps and you can get back to flying your time machine.
Best regards,
Bob Borger
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rparigoris
Joined: 24 Nov 2009
Posts: 791
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| Posted: Fri Apr 23, 2010 8:07 am Post subject: Rotax carb choke problem |
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Hi Frans"At a cold start, the engine appears to run on two cylinders for a while (confirmed by the EGT: only cylinders 2 and 4 produce heat). Any ideas appreciated!"I agree with Bob, check very careful the enriching circuit passage on the bottom of the float bowl. I have a BMW R-100GS with type 64 carbs and these are the first things to get "carb snot" when it sits for a while. Not the easiest thing to clean, you have to go out of your way to make sure they are completly free. BTW best replace the float bowl gasket, if they leak on a 914 you can leak out airbox pressure faster than it can come in, hence run out of fuel or at least lean when you boost. The carbs are a pain to take off on the R100GS. If out on a trip if you discover that engine won't start because it got colder than normal in the morning, it isn't easy to hand choke. Blowing into the float bowl vent "primes" enough to get started. The 914 is a little harder to get to vent but if you were stuck somewhere and couldn't or didn't want to disassemble carbs could probably get you going if enrichment circuit failed. Best have a fire extinguisher handy if you do so.Good LuckRon Parigoris [quote][b]
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frans(at)privatepilots.nl
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| Posted: Fri Apr 23, 2010 8:09 am Post subject: Rotax carb choke problem |
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On 04/23/2010 03:07 PM, Bob Borger wrote:
| Quote: | If you had the float bowl off, check to make sure that the little hole down in the corner and associated plumbing in that corner is clear.
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Ok, this makes sense. I will take the carb out again as soon as I know
for sure that we are not going to fly.  And then check that this
little hole is still open.
| Quote: | I'm not sure if you are aware, but the "Choke" isn't really a choke in the classic sense. Pulling the "Choke" cable rotates a set of valves in the carb which enable a small enriching carb. The enriching carb receives its fuel from the float bowl through that small hole and associated plumbing.
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Ah. I was wondering about that. Noticed on the schematic that there is a
"start jet" and I presume this is also something I need to check to get
the choke working again.
| Quote: | There may be some sort of blockage in that system preventing fuel flow to the enriching carb
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I think you are right.
Thanks for the info!
Frans
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kevann(at)gotsky.com
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| Posted: Sat Apr 24, 2010 6:28 am Post subject: Rotax carb choke problem |
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Hi Franz,
When you recheck your float bowls for the choke problem you are having, you
can just pull the bowls without removing the carb from the engine? At least
that's what I would try first because I'm lazy!
Kevin
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