CX100- do I need to change camshaft and valves with Dellorto 36mm upgrade?

[viggo51]

I have decided to go with bigger carbs on my CX100, 30mm stock to 36mm. I was going to just have the 30's rebuilt but I figured if I was going to spent the $ why not just get new 36's.

From what I'm reading on this forum folks are going to 36's for more performance. My question is do I need to change the stock camshaft or valves  or will these carbs work "out of the box" with jetting adjustments? The plan is to keep it looking stock with performance upgrades.

Thanks,
John

[blackcat]

http://www.mgcycle.com/index.php?main_page=product_info&cPath=279&products_id=179

This is about it and the next time you have a valve job, I would open up the inlets for the larger carbs but I rode mine without doing that for many years.

[geodoc]

Heh John,

I can only recount my own experience w/ small-valve round-barrels & 36's, though never installed them on a bike with a stock cam. As you've experience yourself, with the stock 30's it tends to run out of steam after about 5000RPM or so. I venture that even with the stock cam it will rev a bit more freely w/ appropriately jetted 36's. That said, at the very least you should remove the heads & valves and 'blend' the ports to match the new manifolds.

You'll probably see more improvement with a B10 cam that should require no valve pocket increase to provide adequate vale-to-piston clearance (check to verify on installation). One thing that does improve things is to modify the barrels to reduce the head-to-piston squish clearance. I've generally seen it at about .080" or so on Gilardoni 950 kits and decreasing it to about .040" makes a noticeable difference in smoother running, better fuel consumption and perhaps a little smidgen's worth of torque. To do this though, you'll need to measure the existing squish then remove the material necessary from the lower surface of the cylinder to bring the piston higher and close the squish clearance. All well & good and easy enough if you have a lathe and a bit of experience. If not, it will probably cost you $3-400 at a machine shop for them to make a centering plug to mount it in the lathe, etc.

I've never tried just using sealant w/o a base gasket, but it might tighten the clearance up a bit, though maybe there's other issues I'm not aware of that recommend against it.

As an aside, if you're going to order a set of carbs, Wolfgan Haerter at Columbia Laverda in Nakusp BC has the best prices and will set it up withwhat ever jetting you prefer.

http://www.laverda.ca/allitalia.htm

http://www.mgcycle.com/index.php?main_page=product_info&cPath=279&products_id=179

This is about it and the next time you have a valve job, I would open up the inlets for the larger carbs but I rode mine without doing that for many years.

[guzziownr]

Professor Dockray, just how thick is that base gasket?

My Eldo has an SP motor with 36 MM dellortos purchased from Wolfgang.  It has a "street" cam approximating a B10 and intakes blended to match the carbs/Delrin manifolds.

Mr. Dockray modestly does not post any of his work so if you are not familiar...

http://www.motorcycleclassics.com/classic-italian-motorcycles/moto-guzzi-v700-zm0z12jazbea.aspx

[bigbikerrick]

http://www.mgcycle.com/index.php?main_page=product_info&cPath=279&products_id=179

This is about it and the next time you have a valve job, I would open up the inlets for the larger carbs but I rode mine without doing that for many years.

I noticed they make these plastic manifolds for the 40 mm carbs as well. Anyone have any experience with these on a Le Mans IV? Or is it better to mount those big carbs with the oem rubber boots?
Rick.

[blackcat]

I noticed they make these plastic manifolds for the 40 mm carbs as well. Anyone have any experience with these on a Le Mans IV? Or is it better to mount those big carbs with the oem rubber boots?
Rick.

I used the rubber boots for awhile but they sagged so I went with the Delrin manifolds.

[Antietam Classic Cycle]

I noticed they make these plastic manifolds for the 40 mm carbs as well. Anyone have any experience with these on a Le Mans IV? Or is it better to mount those big carbs with the oem rubber boots?
Rick.

I used the rubber boots for awhile but they sagged so I went with the Delrin manifolds.

Y'all are talking two different types of rubber "boots" here. The CX/SP/G5 boot was a rubber elbow that attached to a flange at the head. Once the stock airbox was removed, they quickly cracked from age and the weight of the carbs hanging on them. Since these are no longer available (just ask "Groover"), Delrin manifolds are pretty much the only option.

The Le Mans (850, II, III, 1000) and many other models use a rubber sleeve to connect the carb to the flange on the head.

These do not sag from the weight of the carb - or at least not nearly as much. They do crack, but it's mostly superficial. Still available relatively inexpensively. Personally, I won't be changing out this stock flange and sleeve system for a pair of Delrin manifolds.

[geodoc]

I just measured one out of the gasket box and it's .026", so maybe .024" tightened down? Anyway, looks like it would help, but not get you all the way there if the stock squish was .080". Easy to measure and see.

Professor Dockray, just how thick is that base gasket?

My Eldo has an SP motor with 36 MM dellortos purchased from Wolfgang.  It has a "street" cam approximating a B10 and intakes blended to match the carbs/Delrin manifolds.

[Arizona Wayne]

Heh John,

I can only recount my own experience w/ small-valve round-barrels & 36's, though never installed them on a bike with a stock cam. As you've experience yourself, with the stock 30's it tends to run out of steam after about 5000RPM or so. it up withwhat ever jetting you prefer.




I'm the 2nd owner of my `81 CX100 w/PHF Dellorto 30 mm carbs.  It had 6K miles on it when I got it & K&N air filters.  No way has it ever run  out of steam @ 5k rpm.  In fact that's when the cam kicks in and it goes like a bat out of hell.   Since then I've put on Uni foam filters but that is all.   Far as I know my CX motor is stock except for the Gilardoni cylinders/pistons/rings it has now.  Maybe your weak CX had the stock air filter system of did it have square slide carbs?

[NCAmother]

Probably advancing the cam a few degrees will give you plenty of power up top, but you do lose a little bottom end.

[Simon_London]

I have done on this on my 950 small valve Guzzi (same engine as CX100).

Its worthwhile but actually not a straight swap.

There is no need to change the cam or valves.

You will need to open up the intake tracks to 36mm and get a pair of Le Mans or Delrin inlet manifolds. I would suggest removing the heads and getting this done professionally rather than taking a dremel to them in situ.

Jetting - everyone seems to have a different recipe. If you get as far as fitting the carbs, I'll tell you mine!

The most noticeable cost effective performance upgrade is probably a lighter fly wheel, but you do lose a bit of the Guzzi character if you go lighter than the Le Mans fly wheel. Not sure what is standard on the CX.

Making sure you have clean air filters is pretty basic but worth checking.

[Groover]

... (just ask "Groover"),

I've heard that guy is no good...   

Are the physical dimensions (other than the bore) the same between the 30mm and 36mm Dellorto PHF pumper carburetors? How about the threaded part? Would the factory "velocity stacks" from the 30 PHF screw onto the 36 PHF?

My '81 G5's current/factory setup:


Also, here are a set of 36mm which I think would be the correct ones for the upgrade the OP is asking. Not sure if that price is good or not (haven't compared)

http://www.ebay.com/itm/Dellorto-PHF-DS1-DD1-36mm-PAIR-carburetors-Moto-Guzzi-1000-SP-III-4676-4677-/172018620731?hash=item280d1bd93b:g:EFoAAOSwfZ1WYPK8&vxp=mtr

I put some holes in my factory Airbox (I don't have a photo with me), and I'm happy with the results. Gave the bike that little something it needed apparently.

[Arizona Wayne]

Your G5 setup is exactly what my CX setup was.  Now I have delrin intakes to my 30 mm PHFs.  Got them from MG Cycle who told me what I had to do to make the switch work.   Since the delrins aren't made to support your carb weight alone I use long zip ties to frame tubes to take the carb weight off the delrins.

[viggo51]

Grover,
Funny,  your link was where I bought my Carbs. Thanks for all the Info guys looks like I have a little more to buy before getting her running!