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 Post subject: Weber Carbs
PostPosted: Wed Jun 22, 2005 10:44 pm 
I just wanted to let everyone know...
The fuel pressure fix for the webers works awesome once you get it adjusted right. It was a huge pain trying to make them work and I couldn't figure out how to make them run right, so I even ordered new mikunis to put in. But, I had some motorcycle genious look at them and they run awesome now. So don't get discouraged if you have the webers, just keep playing with the fuel pressure.


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PostPosted: Thu Jun 23, 2005 2:04 pm 
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paso grand pooh-bah
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Joined: Wed Jan 19, 2005 12:00 am
Posts: 707
Location: CNY, US
model: 750 Paso
year: 1988
Ok, so ... what'd he do?!

I've about had it with mine. I'm this close from buying a pair of Mikunis from an m900 and toying with the idea of pulling the Mikunis off my m750 and buying a pair of FCRs that instead ...

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PostPosted: Thu Jun 23, 2005 8:23 pm 
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paso grand pooh-bah
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Joined: Tue Oct 26, 2004 12:00 am
Posts: 1304
Location: Kapiti, New Zealand
model: 750 Paso
year: 1988
faster, we have posts on the site re a suitable type of fuel pressure regulator (I think it was a slocum post) and the pressure to set it at. I'll leave you to find them, 'cause you're better at pooters than me, and it's too early in the morning for me.


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 Post subject: Weber Carbs
PostPosted: Sun Jun 26, 2005 7:23 pm 
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Joined: Wed Jul 21, 2004 12:00 am
Posts: 67
Location: Windsor, CT USA
If the float needle valve and seat are in good condition, they will stop the fuel flow from the stock fuel pump quite well. All that a fuel pressure regulator will do is prevent excess fuel pressure (>3.0 psi) from slowly bending the tang on the float, and slowly raising the float level. When I measure the ouput from my fuel pump, the highest pressure that I saw was about 3.2 psi, when I had the engine spun up to the point where the fuel pump was getting maximum voltage. The greatest benefit for making a Weber run better is to re-jet it and set the float level correctly. Yes, I do use a pressure regulator set at 2.75 psi (a Holley 0 to 7 psi adjustable version), but I only use it to save the trouble of re-adjusting the float level every month or two. When I first installed the regulator, I experimented with different pressure settings to see if fuel pressure alone would affect the way the bike ran (after first adjusting the float level to the correct 46 mm). I found that the only effect was when the fuel pressure was set too low (around 2.5 psi or less) the bike ran like crap in the transition from idle to larger throttle openings, and seemed to suffer fuel starvation when run near full throttle for any period of time.

I recently re-installed the stock exhausts (to spare the neighbors' ears), and am currently using the following jets:
idle jets: .060, idle mixture screws set at 2.25 turns out
main jets: .160
air corrector: .155
emulsion tube: F-36 (stock), with the top two holes sealed by epoxy compound.

I found that sealing the top holes in the emulsion tube helps tremendously in eliminating the mid-range "stumble".

If re-jetting your Weber doesn't make it idle and run better, at the very least in the low range from idle on up to half throttle, then you should check the intake manifolds for air leaks, and perhaps consider dismantling the carb for a good cleaning.


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PostPosted: Mon Jun 27, 2005 12:12 am 
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paso grand pooh-bah
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Joined: Tue Oct 26, 2004 12:00 am
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Location: Kapiti, New Zealand
model: 750 Paso
year: 1988
:thumbup:
Excellent, jfiore! Very useful and clarifies the issue. It would seem the pressure regulator is a good idea in any event.

Do you have any ideas as to the relative merits of DellOrto and Mikuni carbs?


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PostPosted: Mon Jun 27, 2005 1:35 pm 
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paso grand pooh-bah
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Joined: Wed Jan 19, 2005 12:00 am
Posts: 707
Location: CNY, US
model: 750 Paso
year: 1988
That is the kind of carb post I'm looking for ... great detail! I plan to put it to the test, because I've about had it with my Weber. Thanks for the excellent write-up!

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1988 Paso 750 #753965
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 Post subject: Weber Carbs
PostPosted: Tue Jun 28, 2005 4:39 pm 
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Joined: Wed Jul 21, 2004 12:00 am
Posts: 67
Location: Windsor, CT USA
If anyone is interested in greater detail on the Weber carb, and what I have found through my attempts to make them work seamlessly, send me an e-mail at j_fiore@sbcglobal.net, and I will be glad to share what I have found.

In spite of all of the jetting and emulsion tube combinations which I have tried, I have never been able to get the Weber to operate perfectly throughout the entire span of throttle openings and RPM. It's very close, but there's still difficulty in finding a balance between a transition from idle that's not overly rich, and a mid-range RPM/small throttle opening that doesn't have a "hole". I've opted for the overly rich transition from idle. My suspicion is that the stock 36 mm venturis flow too much air at small to medium throttle openings for the design of the emulsion tube. I've attempted to find 34 mm venturis for the carb, but the Weber parts distributor that I use has not been able to get them for me.

Regarding the Dellorto and Mikuni carbs, I have no opinion to offer on their relative merits since I've never had the opportunity to try them, nor ride a bike equipped with them.


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 Post subject: Re: Weber Carbs
PostPosted: Wed May 19, 2010 9:32 am 
34mm venturis for the 44 DCNF are no longer available in the UK. I'm told that some people simply make them ( a job for a milling machine) an this is not too difficult. James


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 Post subject: Re: Weber Carbs
PostPosted: Wed May 19, 2010 11:03 am 
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paso grand pooh-bah
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Joined: Mon Jul 19, 2004 12:00 am
Posts: 1714
Location: Eastern Shore, MD
model: 750 Paso
year: 1988
Wow, a thread with posts almost 5 years apart!


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 Post subject: Re: Weber Carbs
PostPosted: Thu May 20, 2010 7:15 am 
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paso grand pooh-bah
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Joined: Wed Dec 05, 2007 12:35 am
Posts: 1646
Location: Newzealand
model: 906 Paso
year: 1990
jcslocum wrote:
Wow, a thread with posts almost 5 years apart!

yeah Box ! couldnt you wait a few days :?: :lol: :lol:
If you havn't already seen Higgy's " webberology " you should have a look . Its here somwhere

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 Post subject: Re: Weber Carbs
PostPosted: Thu May 20, 2010 10:07 am 
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paso grand pooh-bah
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Joined: Tue Jul 29, 2008 9:50 pm
Posts: 3198
Location: Hilltown,Pennsylvania
model: 906 Paso
year: 1990
Weber doc can be downloaded at the following url anytime, check out the cam doc while you are there
http://mysite.verizon.net/vze2hw9t/index.html

Jetting in the weber doc is for the 906,but the techniques are valid for any Paso or Sport. On the 750's I would suggest you contact Jfiore as he is actively working on his Weber on the 750. I have plans to acquire a 750 Paso by summers end. Looking at a couple of candidates now

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If it ain't broke keep fixin it till it is
88 750
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92 907ie


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