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DB4 fuel vacuum pump

 
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djk



Joined: 20 Sep 2011
Posts: 117
Location: New Zealand

PostPosted: Sat Oct 20, 2018 10:54 am    Post subject: DB4 fuel vacuum pump Reply with quote

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: 6206

PostPosted: Sat Oct 20, 2018 11:44 am    Post subject: Reply with quote

Sounds like the rubber diaphragms on the vacuum fuel pump have disintegrated......It works off suction from an air line attached to the plenum intake tube......if not replaced since original then they will be past their best....Its only around 8gbp for a whole new pump identical to the original so simply replace to check as its a cheap try.

https://www.ebay.co.uk/itm/Fuel-Pump-Carburettor-Replace-For-Rotax-Max-Kart-Carburettor-Mikuni-Carb-Chrome/362360393402?hash=item545e5cceba:g:e2EAAOSwd~RZVoiT:rk:20:pf:0
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djk



Joined: 20 Sep 2011
Posts: 117
Location: New Zealand

PostPosted: Sat Oct 20, 2018 11:47 am    Post subject: Reply with quote

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: 6206

PostPosted: Sat Oct 20, 2018 2:57 pm    Post subject: Reply with quote

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: 117
Location: New Zealand

PostPosted: Sat Oct 20, 2018 8:55 pm    Post subject: Reply with quote

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: 117
Location: New Zealand

PostPosted: Mon Oct 22, 2018 2:53 am    Post subject: Reply with quote

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: 6206

PostPosted: Mon Oct 22, 2018 10:01 am    Post subject: Reply with quote

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: 1721
Location: West Yorkshire

PostPosted: Tue Oct 23, 2018 10:10 am    Post subject: Re: DB4 fuel vacuum pump Reply with quote

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: 117
Location: New Zealand

PostPosted: Wed Oct 24, 2018 8:37 am    Post subject: Reply with quote

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: 1721
Location: West Yorkshire

PostPosted: Wed Oct 24, 2018 10:03 am    Post subject: Reply with quote

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: 117
Location: New Zealand

PostPosted: Thu Oct 25, 2018 6:26 am    Post subject: Reply with quote

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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