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 Post subject: Xr2 carb pressure?!?
PostPosted: Sat Jul 23, 2016 8:01 pm 
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Joined: Thu Nov 19, 2015 2:28 pm
Posts: 17
I have a xr2 race car which uses the Webber dft 32 34 carb.
I have been having issues with fuel surge which I believed was as a result of slosh in my tank around corners, and then sucking in air.
However I try to replicate this lack of fuel by removing the supply pipe when the engine is running at 4K revs and it runs on for a couple of minutes. This goes to show me that for the length of time the car is in a corner it can't be air travelling through the fuel lines because it's simply not using all the fuel that's in the line that quickly.
This brings me to suspect it could be an issue within the carb! What issue? I have no idea, and this is where I am hoping for some help. I thought it could be float height but that is set as per the Haynes manual reading of 35mm.
Anyone else have any suggestions?
It is running an electric facet fuel pump with an inline filter.
I am thinking about installing the old mechanical pump that runs off the cam! Does the meter the fuel exactly as the carb needs it?
What pressure is required to the carb for optimum performance on my type of carb? 3, 4 psi?
Is too much pressure likely to be an issue with these carbs?

I'd appreciate any advice!
Thanks for reading


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 Post subject: Re: Xr2 carb pressure?!?
PostPosted: Sat Jul 23, 2016 8:22 pm 
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Joined: Fri May 23, 2003 11:04 pm
Posts: 22291
Location: County Durham.
The mechanical pump pumps as the engine runs.
It pumps more as the engine runs faster, that is as close to being regulated as it gets.

As you say regarding fuel surge, it would have to run a long time sucking air to cause issues with the carb.
The carb has its own fuiel bowl that holds an amount of fuel in it. Like it's own mini fuel tank.

Try fitting a large inline fuel filter if you are sure fuel surge is the issue. But
I'd look at the carb needle valve under the float and see if you can check that the float or needle isn't getting stuck.

Have you checked fuel pressures?
Can the pump keep up with the demand placed on it?

Jason.


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 Post subject: Re: Xr2 carb pressure?!?
PostPosted: Sat Jul 23, 2016 8:38 pm 
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Joined: Thu Nov 19, 2015 2:28 pm
Posts: 17
Thanks for your reply.
That's exactly how I understand the mechanical fuel pump.
I've just decided to try a filter King I think after reading a bit.
It has a gauge so I can correctly setup pressure to the carb and a large filter bowl.
Not going to bother with the mechanical fuel pump now because I don't see anything wrong with my electric pump. That supplies around 7psi so as long as I setup the regulator on the filter King it should be ok I think?!? Hopefully.
If so, the only questions are, what pressure should my carb run at?
And, is there anything else within the carb which could cause the fuel surge issue.
Once again thanks for you reply!
It's only too often that you get a numpty, who has no clue, replying and your question goes missed by those with some knowledge.
Cheers


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 Post subject: Re: Xr2 carb pressure?!?
PostPosted: Sat Jul 23, 2016 8:57 pm 
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Joined: Fri May 23, 2003 11:04 pm
Posts: 22291
Location: County Durham.
OK.

Do NOT buy a filter king regulator with the glass bowl.
As mentioned in another thread here, seen too many classics go up in flames due to the glass bowl cracking.
If you must get a filter king. Get the alloy bowl type.

I run a Huco fuel pump. Runs around 3psi.
Runs my DMTR 34 on the zetec no problem.
Also, self regulates. So no need for the filter regulator setup.

Jason.


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 Post subject: Re: Xr2 carb pressure?!?
PostPosted: Sat Jul 23, 2016 11:40 pm 
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Joined: Mon Jan 04, 2010 8:11 pm
Posts: 400
Location: Northants
Sounds like float/ float valve issue to me, like Jason has already suggested.

Holding the engine at 4k while stationary will not use the fuel up like 4k with your foot buried into the mat whilst driving! That small chamber will empty very quickly and will only need to drop a small amount before you get fuel issues.
I went around Silverstone last year in mine and was ok, no issues with 34DATR carb and 1.8zvh engine and mechanical fuel pump. Used quarter of a tank mind...........

My brother had massive surge issues in the long corners and powering out. He is running a 1.8zvh also, but with the 28/32 tldm carb which has never been stripped or serviced as long he has had it..............10+yrs!!!
Which means it's long overdue....................................

_________________
XR2 1.8zvh
Nearly finished.... Just tinkering!


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 Post subject: Re: Xr2 carb pressure?!?
PostPosted: Sat Jul 30, 2016 7:57 pm 
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Joined: Thu Nov 19, 2015 2:28 pm
Posts: 17
Right, so I've installed the mechanical fuel pump back in and I did a rebuild of the carb stopping short of anything that would require rolling road setting up.
I have slightly changed the float level which I know will very slightly change air/fuel mix but float is adjusted up and there for slightly richer which should be safer.
Car started fine first time, but I noticed a lot of fuel jetting into the carb on idle!
Anyone have any suggestions as to why?
Could it be Purely because I have more fuel in the float chambers?
Many thanks


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