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PostPosted: February 2, 2014, 1:48 am 
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Joined: February 2, 2014, 1:14 am
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Location: san pedro, california
Ok, so I built a Book locost with a crossflow 1700 and a Type 9 gearbox. I love this car. Trouble is that I built it in Southern California and I can't find anybody to dyno tune my Weber DCOE's. Can someone refer me to someone who can. Thanks


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PostPosted: February 2, 2014, 9:46 am 
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I might mention that so many Crossflows have been built with Webers that I would think an hour on the internet will confirm what Weber settings to use.

I would suggest as a starting point;

F15 emulsions

4 x your choke diameter plus 10 for your mains (example 4 x 32 + 10 = 140 mains)

main jets + 50 for air correctors (example 140 + 50 = 190)

You may need to play with your idle circuit and accelerator pump stroke length from there but it's not rocket science.


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PostPosted: February 2, 2014, 11:34 am 
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Location: san pedro, california
Thank you Cheapracer. The settings are very close, I got the engine and carbs as a package deal from Vulcan engineering. It runs, it pulls like a train, but it spits and farts. I am just looking for a session on a rolling road as they say in England to very fine tune it, somewhere in southern california. Thanks again.


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PostPosted: February 2, 2014, 2:09 pm 
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Location: Vancouver, BC
I wouls suggest calling Dave Bean Engineering as they specialize in vintage Lotus race cars (most if not all these days run webers). I'm sure they could point you in the right direction.


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PostPosted: February 2, 2014, 11:34 pm 
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Joined: April 23, 2006, 8:26 pm
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Location: SoCal
I have a love/hate relationship with side-draft Webers. I had them on my Datsun 1200, and while it ran well, the one guy in SoCal really SOAKED customers for his services. Every time I hear people bitching about how expensive ECU tuning is, I just laugh, remembering how, for what this guy charged back then, it would have paid for an aftermarket ECU. Nope, me and carbs, been there done that. I suggest you learn to tune it yourself - the problem there is all the jets, bleeds, and chokes that are needed. The one saving grace now is the availability of wideband O2 meters. With one of those you can do the job yourself and likely save $$$, if not $$$$.

The over-charging guy I used was back in the 1980s, so I doubt he's still around.

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PostPosted: February 3, 2014, 12:30 am 
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carsea wrote:
It runs, it pulls like a train, but it spits and farts.


When does it spit and fart?


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PostPosted: February 3, 2014, 1:03 am 
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Location: san pedro, california
It spits from 2000 rpm to about 4000 rpm usually cruising never when I stomp on it, it backfires explosively when I get off a hard pull and let the transmission slow me down. Thanks for the help.


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PostPosted: February 3, 2014, 1:50 am 
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carsea wrote:
It spits from 2000 rpm to about 4000 rpm usually cruising never when I stomp on it, it backfires explosively when I get off a hard pull and let the transmission slow me down. Thanks for the help.


Air/vacuum leak? Everything tight? And was it tightened in the proper order so it didn't warp something?

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PostPosted: February 3, 2014, 5:40 am 
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carsea wrote:
It spits from 2000 rpm to about 4000 rpm usually cruising never when I stomp on it, it backfires explosively when I get off a hard pull and let the transmission slow me down. Thanks for the help.


Firstly this is the internet and I can only go by what you write so here's my answer based on the statement above ...

Cruising at 2000 to 4000 RPM on a small throttle opening is pulling heavily of the idle circuit still and it seems too lean. If that's so it also explains your backfiring which is being caused by the throttle plate closed and drawing mostly a very lean mixture from the idle circuit.

So we have 2 separate evidences that you have a lean idle circuit. Most DCOE I have ever worked with seem to have a F9 emulsion tube with a 45 idle jets, factory standard it would appear, so you can try 55 idle jets and/or F12 idle tubes if you can get them. Obviously the jets will be easier to get and try.

Also if it idles best with the idle mixture screws less that one turn out that also tells you it's too lean, that might be a 3rd evidence but this isn't always 100% accurate as a lumpy camshaft can also be the cause.

So I say go and fit some 55 idle jets and see what happens.

If that doesn't help enough then next step is try some F16 emulsion tubes (if you have F15 currently).

This is all presuming that your car accelerates reasonably well and it's just the cruise and backfire that's the issue.


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PostPosted: February 3, 2014, 9:34 am 
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Location: Cape Town, South Africa
I've only ever had experience with a Weber 36DCD, but the principals stays the same.
Agreeing with Cheapracer, that it sounds like a lean idle circuit.
It's actually surprising how far up the rpm range the idle circuit has an influence when cruising.


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PostPosted: February 3, 2014, 10:30 am 
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Joined: September 5, 2006, 11:00 pm
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Location: Columbia SC
Had three cars with DCOE's. The one i got just right was an X 1/9 that I drove a lot. Cheapracer is spot on with the tuning advice. I drove the X as a DD for a few years and had to retune during the summer and winter in Baltimore. One or two sizes on the mains and a tweak on the idle screws. If it was really hot, an idle jet change was probably in order. My car had a moderate cam and the F11 emulsion tubes were not the best. Changed them for maybe F9 or F15 I really can't remember . Took me some tweaking to get it right. The car had NOTHING below 3700.. Then bam.. just came on to about 7k. It was hard to get the low speed acceptable. Tune for one and the other would suck.

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PostPosted: February 4, 2014, 10:45 am 
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Joined: February 2, 2014, 1:14 am
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Location: san pedro, california
I appreciate all your answers, especially cheapracer. I didn't really want to become a weber tuner (too many variables) and I guess that what our brothers in England are able to do (rolling road session) is just a dream here. Thanks for trying to help me.


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