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Leaky carb

charles d cannon jr

Active Forum Website User
VOC Member
I know this is recent thread for a Comet, but we're all special, right? When I come home after a ride on my twin the conical K and N filter on my front carb is wet on the underside with gas (petrol). It is a Mikuni VM 28 mm carb. I'm using the correct manifold and the carb is angled out so it doesn't foul the head, at least at rest. I have set the float level to factory specs (15-17mm). I am getting no overflow through the overflow pipe, and I have set the bike on the side stand with the fuel taps on and filter removed and seen no overt drip after several minutes of observation, even after putting the choke on, thus it appears I have good seating of the float needle, at least at rest. Admittedly I am running the bike a bit rich with a 200 main and the needle second slot up from bottom, because I am paranoid about seizing (only 400 miles on rebuild). The rear carb is set up exactly the same though, and the filter is dry. I use the choke levers to start,but take the chokes off promptly. Could this be frothing due to vibration? This has really got me puzzled. All comments appreciated, thanks.
 

Albervin

Well Known and Active Forum Website User
VOC Member
The filter is wet on the "underside" but that is not necessarily indicative of the source of petrol. It could come from above or within. When you say "correct manifold" do you mean "original"?
 

charles d cannon jr

Active Forum Website User
VOC Member
I am assuming it is leaking from the opening of the carb, back into the filter and pooling at the inferior part of the filter.. The external aspect of the carb itself, appears to be dry. The Spares co sells intake manifolds with rubber adaptor sleeves for carbs like Amal Mark 2's and Mikunis that use spigot mounting instead of flange mounting. That is what I am using. Thanks.
 

chankly bore

Well Known and Active Forum Website User
Non-VOC Member
There is a lot of specific Mikuni information on the Internet. Mikuni advise not to use enrichment over 68 degrees Fahrenheit (20 Celsius). Is your "choke" plunger seating correctly?
 

charles d cannon jr

Active Forum Website User
VOC Member
best I can tell,it is seating. when I peer into the carb throat into the choke orifice it is occluded by the brass plunger when the choke is off, and when the choke is on, it is open. I have also taken the choke apart and the rubber seal at the bottom looks ok. I have reread Albervin's post and am wondering about leakage from the overflow outlet that is occurring at speed, but not at rest. I'm going to attach some absorbent material to the pipe, ride it and check that after the ride. if it is wet, I may readjust my float to the lower end of the factory recommended range as a trial. I also may lower my needle one slot. Thanks.
 
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