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djk
Joined: 20 Sep 2011 Posts: 141 Location: New Zealand
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Posted: Sat Oct 20, 2018 10:54 am Post subject: DB4 fuel vacuum pump |
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A little while ago about 4 liters of fuel got into my engine, i'm in the process of fixing and my question is when you take the tank off should fuel still be flowing from the hose that comes from the vacuum pump that feeds the carbs, it is a steady flow and not a drip. One mechanic i spoke to said it should be flowing a little and another said it shouldn't be flowing at all so i am a little confused. When i turn the fuel tap off it stops the flow so i know that part works. |
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2bims
Joined: 03 Apr 2010 Posts: 7289
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djk
Joined: 20 Sep 2011 Posts: 141 Location: New Zealand
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Posted: Sat Oct 20, 2018 11:47 am Post subject: |
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Excellent, thank you very much for the quick reply. i'll give that a go. |
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2bims
Joined: 03 Apr 2010 Posts: 7289
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Posted: Sat Oct 20, 2018 2:57 pm Post subject: |
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Just check the dimensions.....it should be a unbolt and plug and play same dims.....they are used on 2-stroke go karts for mikuni carbs......you can if you remove your old one check it for integrity by sucking on the nipple that attached to the plenum intake....it should cause a sucking of your finger onto the inlet and pumping on the outlet...if the round rubber diaphragms are intact that is.... |
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djk
Joined: 20 Sep 2011 Posts: 141 Location: New Zealand
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Posted: Sat Oct 20, 2018 8:55 pm Post subject: |
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I'll give that a go as well. Luckily we have a strong karting scene here in NZ so we have listings for this part on our local auction website. Again many thanks. |
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djk
Joined: 20 Sep 2011 Posts: 141 Location: New Zealand
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Posted: Mon Oct 22, 2018 2:53 am Post subject: |
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Did the sucking thing and it works like you describe, i opened it up anyway and everything looks okay and intact. I've got a replacement kit coming as well for piece of mind. |
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2bims
Joined: 03 Apr 2010 Posts: 7289
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Posted: Mon Oct 22, 2018 10:01 am Post subject: |
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Seals will deteriorate over time and go hard and not seal fully....which is possibly why fuel can flow through without engine running....hopefully the new one has more suction and power and seals correctly....at least its easy to check....should be just plug and play....its a shame the fuel tap on the DB4 isn't accessible to switch off when laying up without removing tank/seat cover and lifting tank......DB2 is easier....fuel tap can be reached without removing anything....just.... |
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GeeKay
Joined: 29 May 2009 Posts: 1767 Location: West Yorkshire
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Posted: Tue Oct 23, 2018 10:10 am Post subject: Re: DB4 fuel vacuum pump |
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djk wrote: |
A little while ago about 4 liters of fuel got into my engine, i'm in the process of fixing and my question is when you take the tank off should fuel still be flowing from the hose that comes from the vacuum pump that feeds the carbs, it is a steady flow and not a drip. One mechanic i spoke to said it should be flowing a little and another said it shouldn't be flowing at all so i am a little confused. When i turn the fuel tap off it stops the flow so i know that part works. |
How did the fuel get into the motor? Even if the fuel tap is passing, the fuel flow should be halted at the carbs by the needle valves preventing the float chambers from overflowing. You need to check both carbs needle valves and seals. _________________ Bimota SB6 and Benelli TNT 899S road bikes.
Beta Techno trials iron. Project bikes:- Suzuki V4 500, TS185 cafe racer, XR11/71, Kettle/Katana, TDRGV250, OR50, Gag125,Triumph T595 and a Triumph X75 Hurricane replica.
Too many projects............... |
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djk
Joined: 20 Sep 2011 Posts: 141 Location: New Zealand
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Posted: Wed Oct 24, 2018 8:37 am Post subject: |
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That will be the next thing to check, i'm just trying to eliminate what i can before giving the bike to my mechanic. The carbs do need further adjustment as well because it is still not running right. |
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GeeKay
Joined: 29 May 2009 Posts: 1767 Location: West Yorkshire
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Posted: Wed Oct 24, 2018 10:03 am Post subject: |
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do the carbs on your bike have overflow pipes fitted? They should be small-bore , clear plastic tubes that run from the carbs and exit under the motor or near the swing arm to allow over-flowing fuel to escape.
Only way fuel can get from your tank to the motor at standstill is via a leaking carb needle valve, though as mentioned above, it should run out to the floor via the overflow pipe(s). _________________ Bimota SB6 and Benelli TNT 899S road bikes.
Beta Techno trials iron. Project bikes:- Suzuki V4 500, TS185 cafe racer, XR11/71, Kettle/Katana, TDRGV250, OR50, Gag125,Triumph T595 and a Triumph X75 Hurricane replica.
Too many projects............... |
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djk
Joined: 20 Sep 2011 Posts: 141 Location: New Zealand
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Posted: Thu Oct 25, 2018 6:26 am Post subject: |
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This bike has 40mm Mikuni flatsides fitted, i just had a quick look and can't see any overflow lines. My mechanic is doing the work as a weekend thing and at the moment he has a lot of racing on so i'll take it around to his house probably weekend after this one. I'll either leave it for him to sort or hopefully figure it out then and there. He said to me that it has happened to other bikes and they have flushed the motor and it has never happened again. Hopefully it will be an easy fix. |
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