81 Darmah with 40MM carbs

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groover1
Cucciolo - the Lil Pup
Posts: 5
Joined: Sat Mar 01, 2014 2:15 am

81 Darmah with 40MM carbs

Post by groover1 » Sat May 03, 2014 7:07 pm

Hi all, hoping to get some info on Carbs for my Darmah.
I have an 81 Darmah with 40mm Carbs. The bolt spacing on the head is 58mm.
It runs rough and sometimes the front cylinder comes in and out above idle. I have found that the idle screw is screwed right in hard but does not idle high.
I have pulled the front carby off and found that there is a bit of damage where the idle screw contacts the slide on the slanted section. Also there is a bit of side movement of the slide on the locating pin.
I have read a bit on the forum here about swapping to new 36 MM PHF carbs but that seems to be mostly if the 32 mm carbs are fitted as standard
What I want to know is
* What do I have to do to fit new 36 MM carbs .(It has 40mm fitted at the moment)
* Any way I can use the 40mm Manifold or do I have to get 32MM manifolds with modifications to the bolt holes.
* Bearing in mind that the stud spacing on the head is 58mm
Or is that all too much trouble and should I just buy a new set of 40MM PHM carbies from Steve. I just thought 40mm carbies is a bit of an overkill.
Cheers

Spagjet
Mach 3
Posts: 79
Joined: Wed Jan 08, 2014 9:07 pm

Re: 81 Darmah with 40MM carbs

Post by Spagjet » Sun May 04, 2014 4:03 pm

I've got an '81 Darmah with 32mm carbies (original equipment), it runs perfect, good idle, no flat spot, all the power in the world, if the power curve was any sweeter it would pull my arms out of the sockets. 40mm carbies really aren't the best option for road use. 36mm carbies are off Pantahs I think (I thought they were off a 750S but they were 32mm), pretty much all v-twin bevels had the 32mm in stock form, even SS's. Everyone went mad for 40mm carbies but they are really at their best run at full noise all day which doesn't happen much anymore on the highway. 32 and 36mm manifolds are the same but 40mm manifolds are different.

The slide is damaged from people turning the idle screw in without lifting the slide first. Very common. There is always a bit of slop on the locating peg, shouldn't affect anything. Wear on the actual slide and/or carby body does affect things like idle and smoothness but they have to be pretty worn before it's a serious problem.

I swapped the 32's on my GTS for 36's years ago, it was a real pregnant dog to get the jetting and needles just right but once I did there was a modest increase in power and a bit less mileage.

have fun

groover1
Cucciolo - the Lil Pup
Posts: 5
Joined: Sat Mar 01, 2014 2:15 am

Re: 81 Darmah with 40MM carbs

Post by groover1 » Mon May 05, 2014 1:33 am

Thanks for the reply.
So what is required to change the manifolds as the stud spacing is 58 mm for the 40mm carbies that's assuming I can find a set

Cheers

Spagjet
Mach 3
Posts: 79
Joined: Wed Jan 08, 2014 9:07 pm

Re: 81 Darmah with 40MM carbs

Post by Spagjet » Tue May 06, 2014 11:48 pm

I think it's only the early seventies bevels that had the narrower manifold studs (bearing in mind that thinking is not actually knowing). I think this because my '81 Darmah (32mm) has got 58mm stud spaces, my '76 GTS had stock 32's which I swapped (carbies and manifolds) for 36's, swapped straight over, no dramas with the fitting, tuning was where the fun started. My other bike has got a late Darmah motor in it which the last owner changed from 32's to 40's, he had a lot of porting work done at the same time. He also had bigger valves put in so I'm not sure if the porting was to match 40mm manifolds with 32mm ports or if it was just something he had done to increase power. The 32 and 36 manifolds are the same item but the 40's are different. I just measured my GTS (36mm) stud spacing, it's 56mm.

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Craig in France
Cagiva Gran Canyon
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Re: 81 Darmah with 40MM carbs

Post by Craig in France » Wed May 07, 2014 12:51 am

On the stud spacing on Darmahs:
- 52mm up to engine number 903025
- 58mm after engine number 903026 (some time during 1979).

On the carbs:
- Standard was 32 mm. Initially AS/AD, after April 1979 CD/CS.
- 40mm was available as an option. Formally, this was as part of the 'Tuning Kit' :vroom: which was partly released in January 1979 and fully detailed in the 1980 parts book. The full kit included different cams, valves, Conti silencers and manifolds, these latter having part number 0799.88.007 (52mm heads) or 0765.92.580 (58 mm heads).

However, 40s were also available to order without the rest of the kit.

In addition, and according to which market the bike was sold in, your Darmah may have arrived with 40mm carbs:
1. Already fitted. This is what the UK importer did during 1978, calling the bike a "Darmah Sport". However these bikes still had heads with 52mm studs - and therefore the narrow inlet tracts that went with ... :?
2. With 40s in the crate along with 32s - sometimes with Contis too :shock: . There are reports of this happening in the States and in Oz .

On the manifolds:
52mm studs, 32mm carbs: 0755.92.585
52mm studs, 40mm carbs: 0799.88.007

58mm studs, 32mm carbs: 0799.92.583
58mm studs, 40mm carbs: 0765.92.580.

("Confused? You will be ...")

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