Dellorto question

[canuck750]

I have Dellorto carbs on all of my Italian bikes, most are Guzzi with VHB style, similar on the Benelli 650S. I have always stuck with the original dark green plastic Dellorto floats, the new white plastic options are not as good IMHO. I don't care much for the Dellorto float adjustment design and I have heard various opinions on how to adjust the floats. The Dellorto literature says to set the carb on its side so the float assembly is vertical. I have found a few degrees of back tilt to the point the needle just makes contact with the seat but no more.

Up to this point I find most Italian Motorcycle forums agree, it's the adjustment part that seems to vary.

Reading to the Dellorto carb adjustment page it says bend the float arms until desired height is achieved. To me this would mean taking a needle nose plyer (or your fingers) and bend each brass arm from the plastic float to where the brass arm meets the main brass body through which the float pin passes. Now some folks interpret this as not bending the individual brass arms, ever, just manipulating the little tang that the needle is hung from (as is the case on all plastic float assemblies such as Harley Davidson carbs used on some models).

I raise this because I am sorting out the troublesome running of my Laverda SF1, same Dellorto round slide 36mm pumper carbs as used on the Lemans MKI, 18mm float height. I know the correct float height is critical to getting the bike to run right, I probably have the timing off a few degrees and need to set up a degree wheel and piston stop to check the factory marks (known to be less than perfect).

I am curious to hear the consensus from the Guzzi folks.

[Antietam Classic Cycle]

I have Dellorto carbs on all of my Italian bikes, most are Guzzi with VHB style, similar on the Benelli 650S. I have always stuck with the original dark green plastic Dellorto floats, the new white plastic options are not as good IMHO. I don't care much for the Dellorto float adjustment design and I have heard various opinions on how to adjust the floats. The Dellorto literature says to set the carb on its side so the float assembly is vertical. I have found a few degrees of back tilt to the point the needle just makes contact with the seat but no more.

Up to this point I find most Italian Motorcycle forums agree, it's the adjustment part that seems to vary.

Reading to the Dellorto carb adjustment page it says bend the float arms until desired height is achieved. To me this would mean taking a needle nose plyer (or your fingers) and bend each brass arm from the plastic float to where the brass arm meets the main brass body through which the float pin passes. Now some folks interpret this as not bending the individual brass arms, ever, just manipulating the little tang that the needle is hung from (as is the case on all plastic float assemblies such as Harley Davidson carbs used on some models).

I raise this because I am sorting out the troublesome running of my Laverda SF1, same Dellorto round slide 36mm pumper carbs as used on the Lemans MKI, 18mm float height. I know the correct float height is critical to getting the bike to run right, I probably have the timing off a few degrees and need to set up a degree wheel and piston stop to check the factory marks (known to be less than perfect).

I am curious to hear the consensus from the Guzzi folks.

I bend the tang, never the arms.

I've found conflicting information on how to set float heights on the PHF carbs - one source said carb on it's side, spring loaded bit of the float needle not compressed. The Dellorto manual says carb inverted completely, spring compressed, 18.5 mm float height. The latter is what I use.

[Bazil]

I too am confused, I reset float heights on the LM4 ( PHM 40s) a while back and still don't know if I did it right !

In particular, at the designated height ( which varies depending on if you look at the Dellorto manual or your friendly Guzzi manual), what should be happening ? Is it  that point at which fuel should shut off (easy enough to check), or is the point at which the plunger is just kissing the inlet ? There quite a bit of travel between those two points - which one is right ?

P.S -  I checked it with floats hanging vertically, spring compressed / fuel shut off. Still think it's causing enrichening. Might need to have another crack at it.

[Dave Swanson]

I was going to grab my copy of Guzziology to see what Dave has to say about it but we are in the dark.  Power outage from a storm yesterday

[Frenchfrog]

This is of great interest here...my bike seems to be suffering fuel shortage just after a hard acceleration...one idea is that the floats might be set too low or that the filters are clogged even though the tank and everything is brand new.When I installed the carbs i swapped over to the old style black floats as the white ones are reputed to leak and they were not the correct weight for the PHF 36's according to the original LM spec...maybe that's changed though ?

[SED]

The LMIII supplement and the Dellorto PHF&PHM pamphlet I have give the same info height = 17.5-18.5mm when carb body is on it's back and float arms vertical - "so that float arm is in light contact with the needle and the valve is closed."  In my experience this compresses the spring plunger very slightly and is enough to restrict or cut off the fuel.

It then goes on to say to bend the arms, but does not specify where or weather they include the center tang.




Guzziology says do not bend the arms though he says that the factory seems to do it that way.  My interpretation is this means bend the tang as Charlie does.  It's the way I do it.  Also check that both floats are at the same height and the assembly not twisted.

Another snag is that I've seen a white plastic float pivot bind slightly - something to check.

I've just about worn out my PHFs adjusting the float level and trying brown, black and white floats at different times.  Nothing has solved the running problem and I've read that float level is a coarse adjustment - that it is not critical to fine running. You can get an idea about how sensitive an engine is to float level by shutting off the fuel and letting it run out at idle.  If mixture adjustment is correct it should run for a couple minutes and then die without revving up or faltering.  This suggests that engines are not very sensitive to float level (at least at idle when vacuum is high).  Another indicator is that gasoline density varies from 0.71-0.78 g/cc.
http://www.kyoto-kem.com/en/pdf/Application/EDAA-11002D.pdf

All this suggests maybe looking for another cause and that may be too little fuel in the mid-range.  I've recently raised the needles in the LMIII a notch above stock and it seems to run better and had stopped pinging and the plugs look better.  (still need to get it dynoed to confirm the mixture)  Similarly Guzziology's solution to poor running stock V65 carbs is to drill the 268 atomizers to 271 and the Monza runs really well this way and gets over 50mpg consistently.  In both cases the stock factory settings (with new parts) were too lean for the fuel I get around here.

Let us know what you find.

[wirespokes]

Guzziology says that bending the arms (not the ones on the floats) is't always accurate, but doesn't go into it any more than that.

Here's some data from Robert Fleischer's airhead site - the float data is about half way down the page. https://bmwmotorcycletech.info/dell.htm

Since the end result should be a correct level of fuel in the bowl, it would be nice seeing where it's at. One of those clear float bowls could do that, or possibly modify a bottom nut with a hose fitting. Attach a clear hose and run it up the side of the bowl and then the level would be visible.

[canuck750]

I spent the day trying to get my Laverda SF1 to idle, not there yet but I am eliminating things one at a time

Back to the carbs I used a digital caliper to check the accuracy of the float gauge and its bang on. 18.5 mm, carb on its side the floats just making contact with the needle. 



The needle valves I am using are viton tipped but do not have the sprung damper hanger. I don't know if that makes a difference on the 36mm Dellorto carbs?

The issue I am having with my Laverda is that it starts up just fine on choke, once warm I can shut off the choke but the idle is very high around 3000 rpm, if I wind out the idle screws and drop the idle it will die around 2200 rpm, it just sputters and giving it gas just bogs and dies. It will restart right away with choke, and the same thing happens again. The bike has a DMC programable electronic ignition and the TDC, 10 degree and 40n degree full advance come on as they should with a strobe light. I don't believe there is an air leak at the intake boots, I have checked them several times and used some RVT sealant to be sure.

The carbs are new Dellorto 36mm pumpers, not rebuilt units, I could not get it to run right with the old carbs so I fitted new ones. The engine has been rebuilt by a Laverda expert (Wolfgang Haerter in B.C. Canada) spark is strong, compression is strong etc... Jets are stock, 60mm idle jet.

Plugs look a little rich and sooty



My generator light is staying on. The generator is rebuilt and it has a new voltage regulator, maybe just a wiring issue??

[SED]

Sounds like the idle circuit is not working at all.  Does it stay running with the choke on and warm?  It's a flip choke? 

The flip chokes will flood my LMIII after just 30-60 seconds of running, even on a cold day.  They would quickly stall it when warm at idle. If it runs when warm on the choke it is probably very lean (air leak) or the idle circuit is not passing gas - 

Sounds like you've checked for air leaks - and it would have to be a big leak to cause that problem so it may be idle circuit.  However, when I first started working on my LMIII it took someone on WG to tell me that it had ports to check carb balance - they are low and I didn't know to look for them.  If the screws were not replaced in those ports it would run very poorly. 

Only other thing I could imagine is a ignition failing at low rpm - timing light can probably show that.  Or valve timing is off...

[canuck750]

Sounds like the idle circuit is not working at all.  Does it stay running with the choke on and warm?  It's a flip choke? 

Sounds like you've checked for air leaks - and it would have to be a big leak to cause that problem so it may be idle circuit.  However, when I first started working on my LMIII it took someone on WG to tell me that it had ports to check carb balance - they are low and I didn't know to look for them.  If the screws were not replaced in those ports it would run very poorly. 

It will remain running with chole on at around 2000 rpm, with chokes off it needs to be above 3000 rpm.

I will look for those ports, did not recall seeing them, these are a new set of Dellorto carbs abs they are very similar to the originals but not identical, the idle screws are a different diameter and the intake manifolds mate to rubber boots not the old style aluminum manifolds.

Some on the Laverda forum suspect the timing chain may be off a tooth, I will see if I can check the marks with a bore scope, otherwise the motor needs t be dropped to remove the engine top cover.

[SED]

spraying starting fluid around the base of the manifold usually shows air leaks quick.

[canuck750]

My Dellorto carbs do not have the ports for the sync take offs, too bad, I was hoping this would be the cause.

After trying all else I dropped the motor and pulled the head cap, I have the timing off by 1 tooth!!

[Chuck in Indiana]

Thanks for the resolution..