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 Post subject: Dellorto + 853 ccm big bore
PostPosted: Mon Mar 18, 2013 8:43 pm 
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Joined: Mon Mar 18, 2013 8:05 pm
Posts: 13
Location: Denmark
model: 750 Sport
year: 1990
I have already read through most topics in the forum, and what a great source of information it is.

First of all, a short introdution should be in order. I just recently purchased a 750 Sport as my first ever motorcycle, and have been messing a bit with it since. It is fitted with the Dellorto PHM 40 conversion, and supposedly fitted with a 853 ccm big bore cylinder kit. I have no proof of this, other than the word of the previous owner. I have not really been driving very much, as I didn't feel it was running well at all.

First of all, I had some trouble getting the bike started. At first try, when using the choke, the engine flooded completely, to the point where gasoline was dripping from the exhaust. New plugs and a second try, this time without the choke. The bike started fine, but it was impossible to keep it idling, without using the throttle. At other times the idle speed would stay very high, after giving the throttle a little blip. I have now ended up dismantling the carbs from the bike, and this is where I could use some help. I do realise that my setup is not that common, but I am hoping for some pointers anyway.

Does anyone have any idea, what kind of jets and needles would be a good starting point for my bike? This is what is fitted at the moment.
Main jets 148
Slides 60/1
Needle K5 clip at top position
Atomiser AB265
Idle Jet 70
Choke Jet 60
Pump Jet 45
Needle valve 250

I have a feeling my idle jet is way too big, as the idle mixture screw was only about half a turn out.

Another question is, how do I adjust the accelerator pump? The screws were set different on each carb, and that seems a bit too random to me.

Pictures from the workshop will follow.

Cheers
Michael


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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Mon Mar 18, 2013 9:56 pm 
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paso grand pooh-bah
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Joined: Sun Jul 18, 2004 12:00 am
Posts: 5255
Location: southern Germany
model: 750 Paso
year: 1987
Michael, I cannot help but you´ll find some Dellorto files in the downloads
viewtopic.php?f=1&t=1551
The only 853cc kit I`ve ever heard of is the one for the 748.
I only know that you can take a 750cc 2 valver Duc to 804cc.

G.


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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Wed Mar 20, 2013 4:30 pm 
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Joined: Mon Mar 18, 2013 8:05 pm
Posts: 13
Location: Denmark
model: 750 Sport
year: 1990
As I said, I have no idea if the 853 ccm is for real or not. Anyway, I have now started assembly of the carbs again. Only change I have made is change the idle jet for a 65, so then we'll see how that works.

Another thing is, the carbs were only fitted with short inlet trumpets before, which I doubt did anything good for the performance. I have bought some 90 degree silicone elbows, which I plan on fitting. The problem is however, that the tank has been modified at some point, probably when the Dellortos were installed. The fuel pump, return line and breather line has been discarded, and the bottom of the tank has been welded flat. This gives very little room for proper air filters.

I plan on giving the ignition some attention as well. I have noticed that the coils are two different kinds, but I haven't measured them yet. What would be a good match if I were to find some replacement coils? I have read a lot about this, but almost everywhere it is stated that the standard coils have a 4 ohm resistance on the low voltage side, whereas the workshop manual says it is 40 ohm. I have the Kokusan ignition.

Cheers
Michael


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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Wed Mar 20, 2013 5:58 pm 
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paso grand pooh-bah
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Joined: Sat Sep 03, 2005 12:00 am
Posts: 1318
Location: SF Bay Area
model: 750 Sport
year: 1990
If you have the Kokusan ignition, then any coil that fits the SS or Monster series will work just fine. Dyna coils are the general default upgrade, or the ones that Ca. Cycleworks is selling.

I chased a problem with my Dellortos for years, and found that the previous owner had not installed the O-rings in the manifolds, but instead opted for silicone RTV, which works fine, for a while, then breaks down in presence of modern fuels. O-rings are measured by the ID and the thickness, and can be found on line in many places for a reasonable price. While you got it apart, it would be good to check it. Use some sealing grease when you install it.

For aircleaners, get two elbows and simply make a U-turn and lay the air filter next to each other above or along the carbs.

I've long wanted to modify my tank that way and get the extra fuel storage. How many gallons can you now carry?

Cheers, Phil

_________________
Duc in the Bay
1990 750 Sport x2-Rosso Blanko (900ss copy) & Nuovo Nudo (Scrambler project)
1991 907 -mostly stock
2002 ST4s - Lots of mods.


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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Wed Mar 20, 2013 9:55 pm 
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Joined: Mon Mar 18, 2013 8:05 pm
Posts: 13
Location: Denmark
model: 750 Sport
year: 1990
Sounds good with regards to the coils. I will check them out and measure them tomorrow.

I already read your post about the silicone on the inlet manifolds, so that was on my list as well, but thanks for reminding me anyway. :)

ducinthebay wrote:
I've long wanted to modify my tank that way and get the extra fuel storage. How many gallons can you now carry?


I have no idea, as I have not really ridden the bike, and only filled it up once, but only half a tank or so. I can see the point in having the bigger capacity, but the welds look really terrible. I will see if I can snap a few pictures from the workshop tomorrow of my project.

Cheers
Michael


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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Wed Mar 20, 2013 11:16 pm 
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Joined: Mon Mar 18, 2013 8:05 pm
Posts: 13
Location: Denmark
model: 750 Sport
year: 1990
Just a few pictures of me trying to wash the bike. It was too cold for that.
Image
Image

From the workshop
Image

New rear fender molded on a spare tire
Image


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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Thu Mar 21, 2013 5:28 am 
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paso grand pooh-bah
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Joined: Sat Sep 03, 2005 12:00 am
Posts: 1318
Location: SF Bay Area
model: 750 Sport
year: 1990
Yeah, I'd say that bike has been modified a bit. No sense going back to stock on that one.
Have you got a reasonable picture from the side?

Cheers, Phil

_________________
Duc in the Bay
1990 750 Sport x2-Rosso Blanko (900ss copy) & Nuovo Nudo (Scrambler project)
1991 907 -mostly stock
2002 ST4s - Lots of mods.


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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Thu Mar 21, 2013 10:04 am 
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Joined: Mon Mar 18, 2013 8:05 pm
Posts: 13
Location: Denmark
model: 750 Sport
year: 1990
ducinthebay wrote:
Yeah, I'd say that bike has been modified a bit. No sense going back to stock on that one.
Have you got a reasonable picture from the side?

Cheers, Phil


This is the best I've got, from when I picked it up. Btw, if I were to sell the faring, how much would that be worth?

Image


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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Fri Mar 22, 2013 2:26 pm 
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Joined: Mon Mar 18, 2013 8:05 pm
Posts: 13
Location: Denmark
model: 750 Sport
year: 1990
A few more pictures from the workshop. Now I am just waiting for filters and better weather.

Image
Image
Image
Image
Image


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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Fri Mar 22, 2013 8:25 pm 
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paso grand pooh-bah
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Joined: Sat Sep 03, 2005 12:00 am
Posts: 1318
Location: SF Bay Area
model: 750 Sport
year: 1990
Well, the previous owner liked shiny black paint that is for sure.
Rear frame section has been modified, probably to fit that older Sport tail section, which look good on it.
Besides that, it all looks there. You can cut and fit a 91-98 SS hugger to fit that swing arm. Not the same mounting pattern but close enough to call it.
Looks like a reasonable project bike. Between that and the Guzzi, you will be busy till it gets warm.

Cheers, Phil

_________________
Duc in the Bay
1990 750 Sport x2-Rosso Blanko (900ss copy) & Nuovo Nudo (Scrambler project)
1991 907 -mostly stock
2002 ST4s - Lots of mods.


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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Fri Mar 22, 2013 10:18 pm 
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Joined: Mon Mar 18, 2013 8:05 pm
Posts: 13
Location: Denmark
model: 750 Sport
year: 1990
You are right about the paint job, but i quite like it. I did think about modifying the seat section, to show more of the rear frame section. Cutting the bottom off of it, about 2-3 cm.

It is not all that clear, but the oil hoses going to the cooler is the original ones, which are far too long for the new mounting postion. Is it possible to fit hoses from a newer version, which had the oil cooler mounted near the horisontal cylinder?

EDIT: I just noticed that the newer versions oil hoses are a lot shorter than what I need. Any other ideas?

Cheers
Michael


Last edited by micap on Fri Mar 22, 2013 10:40 pm, edited 1 time in total.

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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Fri Mar 22, 2013 10:28 pm 
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paso grand pooh-bah
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Joined: Sat Sep 03, 2005 12:00 am
Posts: 1318
Location: SF Bay Area
model: 750 Sport
year: 1990
On my current Sport project, I am putting the oil cooler above the front cylinder head. I haven't completely sussed out the hoses or the routing, but if you look at several different Ducati models, you will be able to find hoses on e-bay, and adapters for the hoses to attach to the cases. Or you can source some new hoses through someone line Venhill or some such company. Its not a topic that has been discussed much here that I can remember.

I agree that the back end of the Sport frame should be more visible. I am doing the same on my current project.

Cheers, phil

_________________
Duc in the Bay
1990 750 Sport x2-Rosso Blanko (900ss copy) & Nuovo Nudo (Scrambler project)
1991 907 -mostly stock
2002 ST4s - Lots of mods.


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 Post subject: Re: Dellorto + 853 ccm big bore
PostPosted: Fri Mar 22, 2013 10:43 pm 
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Joined: Thu Oct 27, 2011 7:47 am
Posts: 448
Location: Wollongong,Australia
model: 750 Sport
year: 1988
I had the same problem with my MHR early in it's life.The idle would either be 2000rpm or it would stall.It turned out that my valves (shims) needed adjusting.Once I set the correct gap the problem dissapeared.Just a thought.

Cheers
Andrew


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