Author Topic: Boring out Dell'Orto vhb 30's?  (Read 1203 times)

Offline rutgery

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Boring out Dell'Orto vhb 30's?
« on: June 20, 2018, 03:51:28 PM »
I just had a visit from someone with a real 1972 V7 Sport and I noticed at the carb number ''vhb 30 cd'' the 0 from 30 was milled off and a 1 was stamped in. Unfortunately, the current owner of the bike couldn't tell me exactly what was done to the carbs but he seemed convinced the carbs were modified inside as well. Does anyone know if it is/was a common mod bore out the vhb carbs to 31mm?





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Online Antietam Classic Cycle

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Re: Boring out Dell'Orto vhb 30's?
« Reply #1 on: June 20, 2018, 04:02:49 PM »
Not "common" in my experience and I'm not sure it would be worth the trouble to gain 1 mm of throat diameter. There's virtually zero difference in flow between VHB 29s and VHB 30s and it stands to reason going from 30 to 31 would yield the same results.
Charlie

Offline mtiberio

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Re: Boring out Dell'Orto vhb 30's?
« Reply #2 on: June 20, 2018, 06:41:56 PM »
I believe Mike Rich did this for some of the “Production”  class v-7 sports. Only have to look production from the outside
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Offline John A

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Re: Boring out Dell'Orto vhb 30's?
« Reply #3 on: June 20, 2018, 07:38:38 PM »
if Mike did it, there was a good reason
John
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Re: Boring out Dell'Orto vhb 30's?
« Reply #3 on: June 20, 2018, 07:38:38 PM »

Online Antietam Classic Cycle

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Re: Boring out Dell'Orto vhb 30's?
« Reply #4 on: June 20, 2018, 08:14:13 PM »
if Mike did it, there was a good reason

Maybe in racing that extra 1 mm makes a small difference, but for a Guzzi used on the street? The cost would outweigh the benefits.
Charlie

Offline wirespokes

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Re: Boring out Dell'Orto vhb 30's?
« Reply #5 on: June 20, 2018, 08:19:22 PM »
I've wondered about boring out some PHF 30s to 36. Seems like the castings are all the same (30, 32, 34 & 36) it's only the bore that's different. True?

Perhaps the VHBs couldn't be bored any larger than 31?

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Re: Boring out Dell'Orto vhb 30's?
« Reply #6 on: June 21, 2018, 08:37:59 AM »
I've wondered about boring out some PHF 30s to 36. Seems like the castings are all the same (30, 32, 34 & 36) it's only the bore that's different. True?

Perhaps the VHBs couldn't be bored any larger than 31?

Not sure but... Thought that 30-34s have the same body size and 36-40s have larger bodies.

Offline John A

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Re: Boring out Dell'Orto vhb 30's?
« Reply #7 on: June 21, 2018, 08:52:18 AM »
 30's and36 PHF's have the same body, I have  a pair of 30's to bore out but I need a bike to use them on.
John
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Offline mtiberio

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Re: Boring out Dell'Orto vhb 30's?
« Reply #8 on: June 21, 2018, 09:01:00 AM »
have to agree with charlie, not worth doing on a street bike, but on a race bike that requires stock carb bodies, every little bit helps. AFAIK, the VHB's cannot be bored out further. The round slides can be bored out substantially. It also means that your flow is compromised with a 30mm bore as the diameter of the slide is 36.
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Offline rutgery

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Re: Boring out Dell'Orto vhb 30's?
« Reply #9 on: June 21, 2018, 09:05:08 AM »
I've wondered about boring out some PHF 30s to 36. Seems like the castings are all the same (30, 32, 34 & 36) it's only the bore that's different. True?

Perhaps the VHBs couldn't be bored any larger than 31?

That's most likely the case, as the vhb's only go up to 30mm. Unfortunately I don't know if this bike is ever used for racing..

30's and36 PHF's have the same body, I have  a pair of 30's to bore out but I need a bike to use them on.

The PHF's seem to use the same body. However, I found a post about boring out the phf 32's on the laverda forums, and it doesn't seem as easy as you might think..
http://www.laverdaforum.com/forum/index.php?topic=89062.0
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'89 V7 Sport replica from a Cali 3

Offline John A

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Re: Boring out Dell'Orto vhb 30's?
« Reply #10 on: June 21, 2018, 09:16:02 AM »
That's most likely the case, as the vhb's only go up to 30mm. Unfortunately I don't know if this bike is ever used for racing..

The PHF's seem to use the same body. However, I found a post about boring out the phf 32's on the laverda forums, and it doesn't seem as easy as you might think..
http://www.laverdaforum.com/forum/index.php?topic=89062.0



Thanks for that, I hadn't looked into actually doing it, I just put the carbs aside and thought I would chuck them up when I needed them.
John
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Offline guzzifan

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Re: Boring out Dell'Orto vhb 30's?
« Reply #11 on: June 21, 2018, 09:06:03 PM »
Bored some PHF 36's to 38's one day just for fun.  The tricky spot is the accelerator pump nozzle mounting spot.  I worked around it, and so can you.

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