Weber chokes and jets

PostPost by: iain.hamlton » Wed May 16, 2007 5:14 am

My +2 is a mongrel. Somewhere along the way it has acquired a big valve engine, but the power tails off at high revs - 4500 rpm and above, just where i would have though it should really pull. As regular readers will know, I have checked fuel delivery to the carbs, ignition dwell, timing etc, and feel I have sorted everything. But the other day I checked the main and air correction jets , and found 115 and 155 respectively. The big valve "should" have 120 and 150 according to the manual. From what I read, these should help the top end, so I have ordered them.

But it suddenly occured to me: what about the venturis? The big valve should have 33mm. Other engines have smaller ones, so if the carbs came from elsewhere, the chokes may be 30 or 32.

My question is where are the venturis marked? What do i need to dismantle to find out? How much less power would i get if it had 32s instead of 33s?

One day I'll go to a rolling road, but I'd like to get everything close first.

best regards, iain
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PostPost by: types26/36 » Wed May 16, 2007 7:57 am

iain.hamlton wrote:My question is where are the venturis marked? What do i need to dismantle to find out? How much less power would i get if it had 32s instead of 33s?


The ventruis are marked on the end and the number can usually be seen looking into the throat with the aux venturis removed first, the engine will have slightly more power at the top end with the larger venturis but you could loose tractability at the lower end, depending what type of driving you do its a compromise between all out performance and better lower end response.
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33mm delorto.JPG and
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PostPost by: iain.hamlton » Wed May 16, 2007 12:26 pm

Thanks Brian.

Is it possible to take a trumpet and auxiliary out without taking the carbs off? If necessary, can the venturis be changed this way too?


best regards, iain
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PostPost by: types26/36 » Wed May 16, 2007 12:50 pm

iain.hamlton wrote:Is it possible to take a trumpet and auxiliary out without taking the carbs off? If necessary, can the venturis be changed this way too?


Yes both can be removed with out taking off the carbs but there are a couple of things you should know.
Depending on which model of webers you have the aux venturis can be held in the body in a different manner, with the older carbs the aux venturi is a slide in fit with spring device which goes in an internal slot to locate it, the later carbs have a grub screw and locknut to locate it.
Once the aux venturi is out the main venturi also just slides out, it has a fixed pin which goes in a slot to keep it in the correct place.
If the venturis (aux & main) have not been desturbed in a long time they can get gummed up as corrosion builds up between the venturi and the carb body, they can be difficult to get out. If there is no gumming they will just slide out.
.
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PostPost by: types26/36 » Wed May 16, 2007 1:00 pm

and some locating screws on a 45DCOE
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PostPost by: iain.hamlton » Thu May 17, 2007 8:57 am

Brian, thanks for your help.

I was able to see the number on one of the venturis just by looking down its mouth. 32. Think I'll get some 33s so its the same as it says in the book.

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PostPost by: denicholls2 » Thu May 17, 2007 11:06 pm

If anyone has a couple of these venturi locating springs available, I've been having a hard time locating the replacements I need. Any help appreciated, even if it's a really good source for Weber bits, some others of which I also need.
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PostPost by: 264889socal » Fri May 18, 2007 3:29 am

They can easily be made from music wire or spring stock from a hobby shop. If you have the old ones and they have lost their tension, I used a hole punch close to the same diameter of the clip, some Viton sheet about 1/8" thick, and used the round bit stuffed into the original spring. Stiffened up the tension significantly. Now the chokes are hard to remove and they do not seem to leak.

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