Author Topic: PHM 40 carbs question  (Read 2962 times)

Online bigbikerrick

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PHM 40 carbs question
« on: January 02, 2016, 01:36:35 PM »
Hi Folks, yesterday I was checking the needle clip position on my Le Mans 1000 carbs , and was surprised to find there were no springs on top of the slides.Apparently they were removed using the external springs only to return the slides. My question is ...is this "kosher" ? I was all ready to remove the external springs to decrease throttle effort, as some suggested, when I found the slide springs missing. What do you all recommend? leave it as is?, buy new springs for on top of the slides, and remove the external springs? or any other suggestions....
Thanks alot,
Rick.
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Re: PHM 40 carbs question
« Reply #1 on: January 02, 2016, 02:11:12 PM »
What's preventing the needles moving in relation to the slides if there are no internal springs???


Offline Aaron D.

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Re: PHM 40 carbs question
« Reply #2 on: January 02, 2016, 04:03:06 PM »
What Pete said, at the least. You should have springs there. I am very surprised you 1)feel the need for lighter springs if you have no springs and 2) that you haven't had a stuck throttle!

Have you removed the tops of the carburetors? Forgive me but I have to ask.

Online bigbikerrick

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Re: PHM 40 carbs question
« Reply #3 on: January 02, 2016, 08:24:55 PM »
Yes I did remove the ops of the carbs to change needle clip position.Thats how I noticed the internal springs were missing. as far as what holds he needles, there is a flat plate that drops down into the slide,on top of the needle, and there is a little spring loaded "rod" about 2" long that attaches the slide to the lever on the top of the carb. This rod moves the slide up, and also pushes it down, to seat, as you open and close the throttle.The actual cable end pulls on the lever.

To me, even with only the external springs returning the slides, the throttle feels hard to crank. cables are lubed , as well as grip tube, it snaps back well, when released. for comparison, it feels stiffer than both  the daytona 2 on my cal II,( PHF 30) and on my eldo ( VHb 29)

I cant even imagine how stiff the throttle on these bikes must be with both sets of springs in place!
Rick


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Re: PHM 40 carbs question
« Reply #4 on: January 02, 2016, 08:40:43 PM »
any chance of a pic? I'm having trouble visualising this???

Normally with PHM's the needle has a small clip then there is the plate on top of it and then a short, stubby cable that goes up to the bell crank. The plate keeps the needle in place but is itself kept in its location on the top of the slide by the main return spring. If that isn't there I don't see how the needle and plate remain in their correct location as the throttle is opened and shut.....

pete

Offline Aaron D.

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Re: PHM 40 carbs question
« Reply #5 on: January 02, 2016, 09:15:34 PM »
So it has bell cranks? And a rod with a spring inside?

Online Chuck in Indiana

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Re: PHM 40 carbs question
« Reply #6 on: January 02, 2016, 09:20:36 PM »
Strange stuff here..  :popcorn:
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Offline Tobit

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Re: PHM 40 carbs question
« Reply #7 on: January 02, 2016, 09:44:26 PM »
Looking at diagrams, the PHM with the flattops show a conventional spring on top of the slide.  The PHMs with bellcranks do not.  I haven't been into my carbs in a while but I did put softer springs in the carbs a long time ago and tossed the external springs. 

http://www.ducatimeccanica.com/dellorto_diagrams/phm_parts_list.htm

Tobit
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Online Antietam Classic Cycle

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Re: PHM 40 carbs question
« Reply #8 on: January 02, 2016, 10:41:39 PM »
The Guzzi parts diagram doesn't show an internal spring, only external.



Now you have me curious - I'll have to pull one of mine apart tomorrow.
« Last Edit: January 02, 2016, 10:42:53 PM by Antietam Classic Cycle »
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Vasco DG

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Re: PHM 40 carbs question
« Reply #9 on: January 02, 2016, 11:21:45 PM »
Where's Martin? He'd be all over this.

Offline jacksonracingcomau

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Re: PHM 40 carbs question
« Reply #10 on: January 02, 2016, 11:35:28 PM »
Where's Martin? He'd be all over this.

clue is PHM on LM 1000 not PHF, can't remember if all LM1000 were like this but certainly late ones were, funny rod, no jeesus clip on needle, plate (#31) instead
Guzzi steadily made throttle worse from orig LM , peaking with this one (also on 40mm carb 1000S), then over revving on 1100 Sport, the very worst

The answer as with all of them
Tomaselli 2C  throttle, flat tops, light springs deviators and teflon lined cables.

Throttle as light as a normal bike,

Offline Aaron D.

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Re: PHM 40 carbs question
« Reply #11 on: January 02, 2016, 11:57:04 PM »
I have PHM40s on the 1100, internal springs and the usual 1/2 turn throttle. Light on the wrist but I have to take two handfuls to act silly. Stock setup-never saw the LMIV setup.

Offline jacksonracingcomau

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Re: PHM 40 carbs question
« Reply #12 on: January 03, 2016, 12:16:20 AM »
I have PHM40s on the 1100, internal springs and the usual 1/2 turn throttle. Light on the wrist but I have to take two handfuls to act silly. Stock setup-never saw the LMIV setup.

Hey, if you're happy that's perfect, it's your bike, at time I couldn't believe what they'd done, so near yet so far.
If you ever get to try a 2C throttle with teflon cables and light springs you might change your mind, so don't, it'll cost
Sorry if I sound like I'm dissing your bike, not my intention, just comparing throttle action twixt models, factory never made perfect, they let us choose final bits, personal pref etc etc

Some on here changed the carbs, long way round fixing the issue IMHO but with good cables etc it does the job

Offline mrrick

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Re: PHM 40 carbs question
« Reply #13 on: January 03, 2016, 03:20:42 AM »
Sorry, deviators??   :huh:

Vasco DG

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Re: PHM 40 carbs question
« Reply #14 on: January 03, 2016, 03:40:09 AM »
Angled cable (?) manifolds to go into the flat tops. You can get them at a variety of angles from memory.

Pete

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Re: PHM 40 carbs question
« Reply #15 on: January 03, 2016, 05:01:58 AM »
clue is PHM on LM 1000 not PHF, can't remember if all LM1000 were like this but certainly late ones were, funny rod, no jeesus clip on needle, plate (#31) instead
Guzzi steadily made throttle worse from orig LM , peaking with this one (also on 40mm carb 1000S), then over revving on 1100 Sport, the very worst

The answer as with all of them
Tomaselli 2C  throttle, flat tops, light springs deviators and teflon lined cables.

Throttle as light as a normal bike,

Exactly what I did, difference is amazing on an LM1000. I also got the Guzziladen roller 90 degree cable pulley with a bearing inside and made cables from a set outta the local bike store

Works a charm and have not had any sticking open events either (I do have a kill switch in case it ever does manifest itself)




Offline mtiberio

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Re: PHM 40 carbs question
« Reply #16 on: January 03, 2016, 05:41:51 AM »
there is a difference between the bell cranks and the flat tops in terms of ratio of cable pull to slide pull. With the flat tops, the slide moves 1" if the cable is pulled one inch (1:1). With the bell cranks, you get "quick pull" action. I can't remember the ratio, but the ultimate effect is you get faster lift at the expense of harder pull at the wrist.

On top of all this is the pumper lever. When that hits the ramp on the slide and gets pushed into the diaphragm,  you can feel the effort go up substantially at least momentarily.  Add a quick turn throttle and you are really having fun.  Figuring out what kind of throttle you have isn't tough. Just compare the diameter of the barrel (usually plastic) where the cable wraps around it. The smaller the diameter, the slower (easier) the pull.

IIFC, the tomaselli 2C has a relatively small barrel compared to some. Some throttles have a snail (or cam) shaped cable run at the throttle for variable pull.

When I raced, I used the plastic flat tops mainly because they were lighter and had the pumps levers removed. I also used a 2C throttle. Interesting some folks associate the bell cranks with accelerator pumps. In reality they are not connected. I believe the bell cranks came into being to provide a quick throttle function, and to allow quick cable replacement.
« Last Edit: January 03, 2016, 05:45:07 AM by mtiberio »

Offline guzziart

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Re: PHM 40 carbs question
« Reply #17 on: January 03, 2016, 08:24:00 AM »
FWIW, my '87 LM IV has PHM 40 carbs with bellcranks, there are no internal slide springs.  The slide return springs are on the outside of the carbs.

Art

Offline Tobit

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Re: PHM 40 carbs question
« Reply #18 on: January 03, 2016, 08:50:50 AM »
I'm going to have to pull the bellcrank top off one of mine today and look. 

Way back when I bought a set of light internal springs from Steve Ford when he was running Parts is Parts.  The difference was negligible.  Then I tossed the external springs.  Much better action and I've never had the slides stick under vacuum.

Tobit
Roman, '86 LM IV



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Online bigbikerrick

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Re: PHM 40 carbs question
« Reply #19 on: January 05, 2016, 03:02:44 AM »
Lots of good info here ,guys. Thanks. Its re assuring to hear that the PHM 40s with the bellcranks dont have internal springs. Mine also have part # 31 to hold the needle down, along with the slide rod ,#15.
The setup with the bearing on top looks sweet. I bet thats nice and smooth !

I think I had better keep the bellcranks on mine to keep me from having to grab 2 handfulls of throttle to open the slides fully, as I remember the throttle tube where the cables wrap was of a fairly small diameter.
Rick.
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