RGS carbs

[ScorchLaverda]

Hey all

By now you all know that I am building this custom Laverda... 

Just finished the valves issue. Took me a long time to get the shims right, but now its all spot on. 

I am going to run trumpets, aka bellmouths, on the bike. I know its not the best option and we can get into long debate about it... But believe me, the standard airbox is just not going to look right on this custom. And its not going to fit, so its a no-go! So I need help on the setup I`m going to run it and what I have... At the moment I have a few sets of 32 Dellorto`s and a set of 36 Dellorto`s. I got the 36 Dellorto`s with a 1200 I bought a few months ago. The 1200 got 4C cams in. Well 2 inlet cams! :-\ ??? As far as I know the one inlet cam is modified to work as a outlet cam but its not done right. But thats another story for another time. Now I need to get the RGS custom bike ready first.

So my questions are... 32mm or 36mm? Which do you guys will work best? The RGS head only got 32mm inlets. What main jets size should I start with? (I know its most probably going to take a few tries to get it right) The motor got F1 cams in. This bike is not going to run every day. More of a special occasion bike.

Thank you

 

[jlo]

With 32mm inlets, stay with 32mm carb. Unless you live in the center of the Sahara, you engine will run just fine with the bellmouths. Just take the habit to close them with a ball or a tap when you you stop the bike.
With standard engine, I think that only 5 points more on the main jets would be enough to compensate the bellmouths, to be confirmed with the usual tests of course.

 

[Laverdalothar]

First of all: there is NO general rule that can be applied to my limited experience, as to many factors you haven't named do influence the choice of carb and settings:

-trumpet length and shape
-intake shape and length
-valve-seat shape, valve size and structure (polished, roughed, or?)
-valve stem thickness
-exhaust size and shape
-compression
-other carb settings (even the pilot jet does influence mixture at WOT)
-etc. etc. etc.

With 1200 ccm displacement and F1 cams, the engine will suffer a bit peak power wise by the 32mm intake. You can make the 36 run well by making the manifolds conically (36mm on the carb side, 32 on the intake) and smooth things out by that. But by nature, you will have the slowest airflow at the needle, increasing while coming to the valves. Not optimal for vaporization, but also not totally bad. You simply will not get peak power to the point as a 36mm intake would deliver (else optimal configuration assumed). But the drop in torque will be not as much recognizable as with the 32mm, as the difference between the bore and the slider size (38mm in both cases) is not that big on the 36mm, hence the airflow does not all of a sudden gets slower when the slider is opened more than 1/3 - 2/3. But that is caused by an overall potentially a bit lower airflow in lower slider opening... (slightly compensated by the bigger displacement and more under-pressure caused)

My guess is, that starting at 145 as a main on the 36 is on the safe side. you may go down to 135 potentially in small steps, eventually even down to 130, but that is something that needs to be controlled with a Lambda sensor on either open roads or on a braked dyno and totally depends on the factors above. Further down would be only possible according to the bikes I have seen and tuned with a 36mm SFC spec head. The configuration will lead to a maximum of roughly 95 HP and similar Torque. But that is just a very wild guess, based on other bikes with similar configuration. Flat-Slides would open up another roughly 7 - 10 HP and equivalent torque, but that's another discussion.

HTH