Boylers11
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| posted on 18/4/16 at 08:36 AM |
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Wierd 893 Fireblade symptoms
Since rebuilding the carbs on my Locoblade, I've had some rather strange symptoms.
It was running reasonably well before the clean/rebuild, but I wanted to tune the carbs, so thought it best to start from scratch.
The mixture screws were only 1.75 turns out from lightly seated when I took it apart, so I reset them back to this.
Now, it starts without the choke with a few pumps of the accelerator, idles nice and quietly and the revs increase and decrease nice and quickly after
a dab on the throttle. It's also running much smoother and quieter than ever before, which is great!
I balanced the carbs:
But then found petrol in the little rubber caps on the vacuum hose nipples.
If I adjust the mixture screws, all that seems to happen is that the revs take ages to drop after a rev.
My main queries are:
1. Why is the choke not affecting startup?
2. Should there be a little fuel in the rubber caps for the vacuum nipples?
Any help would be great.
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mark chandler
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| posted on 18/4/16 at 07:11 PM |
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The little bit of fuel could be nothing, gravity will pool any liquid in these however a high float level will screw things up and allow fuel to flood
over, a fuel pump that pushes more than 2-3 psi will also create a similar problem.
The carbs do not have acceleration enrichment injectors so pumping the pedal will not make any difference, the same does not apply with Webers for
instance.
Are you sure the chokes are not held on? The plungers should be all the way down, in in doubt remove the metal slide that operates them altogether.
When you blip the throttle do the plungers all leap together, the rubber seals are easy to tear.
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Boylers11
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| posted on 18/4/16 at 08:44 PM |
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Thanks for the reply Mark.
I'm hoping to finish work a bit earlier tomorrow so I'll have another gander at it.
I'm pretty sure the plungers leap together, but I'll check again tomorrow.
When I try and start it without the vacuum nipple caps on, as it's turning over, little 'puffs' of fuel spray out, then once
it's running, even on a hard rev, there's no sign of fuel.
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mark chandler
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| posted on 18/4/16 at 09:50 PM |
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Fuel pump running, engine off gently lift the plungers and check that fuel is not dribbling out where the needles go in then ignore if the engine runs
properly.
Fuel should be dripping out the overflows before then anyway.
All that is happening on cranking fuel is being drawn out the carbs at low speed and falling to the floor of the inlet track, once running it stays
suspended in the air as there is a lot more draw from the engine.
I had some 40 Webers on a car, badly set up they dribbled fuel out he trumpets on idle!
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Boylers11
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| posted on 19/4/16 at 08:09 PM |
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quote:
Originally posted by mark chandler
Fuel pump running, engine off gently lift the plungers and check that fuel is not dribbling out where the needles go in then ignore if the engine runs
properly.
Fuel should be dripping out the overflows before then anyway.
All that is happening on cranking fuel is being drawn out the carbs at low speed and falling to the floor of the inlet track, once running it stays
suspended in the air as there is a lot more draw from the engine.
I had some 40 Webers on a car, badly set up they dribbled fuel out he trumpets on idle!
Thanks again Mark.
I've had a look tonight and there's no dribbling with the engine off and when it's running, everything seems to be in sync.
With the choke issue, it looks like I had a complete mare...when tightening the choke plate screws, the plate had jumped off the choke pins, so the
choke wasn't doing anything! What an idiot!
It's now functioning as it should, bar the small amount of fuel in the vacuum nipple bungs 
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mark chandler
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| posted on 19/4/16 at 08:44 PM |
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Ignore the fuel in the bungs, just gravity.
If you get the engine hot then it will evaporate out within seconds hence you will not find any after it's been on a run.
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Boylers11
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| posted on 19/4/16 at 09:10 PM |
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Awesome. Thanks again. I'd never have thought of looking at the choke if you hadn't mentioned it.
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