PHF 40 carb accelerator pump question

[bigbikerrick]

Hello Folks, I am interested in experimenting with slightly reducing the amount of fuel sprayed by the diaphragm accelerator pump on my Lemans 1000 carbs. I have gone through the delLorto tuning guide, and it states that can be accomplished by the adjustment screws, on the rear of the carbs, that is held by a locknut.My question is in order to decrease the amount of fuel sprayed, do I turn the screw inwards, or back it out some?  I cant find that info in the tuners guide.  I thought I would experiment with that a bit, as I already have the jetting pretty close, and the bike is running nice, I just think that they shoot too much fuel out, and it blackens the plugs when riding around town, and cranking the throttle on, and off.
Thanks
Rick.

[Rolf Halvorsen]

When turning the screw clockwise - you will reduce the accelerator pump stroke, and thereby you will reduce the amount of petrol pumped extra into the carb.

Rolf

[bigbikerrick]

Thank you Rolf, thats exactly what I was looking for. Now I can go into the garage, and "tweak" the carbs to fine tune the throttle response!
Rick.

[lazlokovacs]

in theory at least!!!

I have some vague memories of trying to tune pumpers with a test tube catching the spray, on one side the screw made no difference at all..... PHM though not PHF

Let me know how it works out though, I currently have my pumpers disabled, but could be interested in re-connecting them if they can in fact be made to behave.

I think the pump comes into play too early IMHO. If you examine  the slides it seems that the different numbered slides spray for different amounts of time but all start at around quarter throttle or just before.... I'd have kept them if they sprayed from 1/2 to WOT for that extra kick when you're feeling  ....


 

[bigbikerrick]

Well, Here is what I did today. I took off both carbs, with float bowl full, I tested the "spray" of fuel with the adjustment screw all the way in, there was almost nothing. then 5-7 turns out, there was ALOT of spray, about 5" out the front of the carb. They were not set evenly before I touched them, so I tried 2.5 turns out from seated, a medium sized spray , so I tried it there and the bike hesitated a bit on rapidly cracking the throttle. Not too bad , just a bit. I turned both screws an additional half turn out to 3 turns,and could immediately notice an improvement. I also balanced both carbs with my vacuum tool, and adjusted the idle mixture. On a short  test ride this evening, it responded well, idled evenly, and pulled hard, with a very strong mid range, pulling hard to WOT. I am going to do a couple of plug chops, in the next few days, and see how  the plugs look.
All in all,I am happy with the results of todays tweaking, and it helped me understand these carbs a bit better.
Rick.

[lazlokovacs]

good stuff!

which slides have you got in there?

[Old Jock]

Link to Gregg's site with short article on the slides and how it affects accelerator pump, if anybody doesn't know about it

http://www.thisoldtractor.com/dellorto_carburetor_slides__what_do_the_slide_numbers_mean__--.html

[lazlokovacs]

/\ thanks for that...

having examined a /3 and a /5 I had assumed they all started early in the throttle opening...

I might try a /1 or /2 one of these days.

Assumption is the mother of all....

Cheers
 

[bigbikerrick]

good stuff!

which slides have you got in there?

I cant remember, I checked them out when I first got the bike a few years ago, and did some jetting changes. Thats interesting how the different "ramps" on the slides affect accelerator pump output. One thing is for sure, it sprays fuel from the time you barely start lifting the slide, all the way until its at wide open, then it still continues spraying for a second or two, after the slide is all the way up. These
reducing the pump output to 3 turns out from seated, seems to have worked out real good.. The plugs look great!
Rick.

[arbezc]

Hello, this is a relavent thread for me.

I have a 1980 Le Mans 2 that runs overly rich in traffic. I've returned the carburetors as close as possible to stock & set the acclerator pumps to 8cc / 20 stokes. I don't think reducing the output will have much effect at small throttle openings, only duration.

The LM2 supplement manual call for a "60 slide" (no second number). I assume they mean /1 as shipped in the LeMans 1. The bike currently has a new set of 60/3's. Does anyone know where I could find a set of 60/1 slides for PHF 36 carbs?

Thanks,
Charles

[bigbikerrick]

Is there an "official" procedure for actually measuring, and adjusting the accelerator pump output in the big 40s? I could not find it looking in the dellorto tuning manual. Another thing, I found incidentally, while working on the carbs, is the cable leading to the flip choke lever on the left carb, did not have adequate freeplay, and I think was allowing  just a bit of enrichment to take place. I realized this because in order to get the left cylinder idle mixture right, I had to turn the idle screw all the way in. After allowing a bit of freeplay in the cable, I was able to adjust the idle mixture the same as the right side carb, about 2-2.5 turns out from seated.
  Just another simple thing to look at when tinkering with carbs. Its the simple things that get overlooked by me sometimes it seems!
Rick.

[arbezc]

Hi,
I've never seen an official volume figure for the capacity of either PHF 36 or 40 carbs. I have read both 6cc & 8cc recommended by "experts".

Checking the flow is a matter of connecting the outlet jets to a small graduated cylinder with a rubber hose. With a full float bowl, you actuate the pump 20 times and measure the resulting volume. The stroke can then be adjusted as stated ealier. Mine were very close to 8cc / 20 strokes when the bike was bought.

[tetarabra]

Le Mans 850 with PHF 36 : 5 cm3 / 20 strokes / jet 38.

For information , Ducati bevel drive 900  with PHM 40 : 5 cm3 / 20 strokes / jet 50 . Could be a starting point of interest .

[bigbikerrick]

Tetarabra, and Arbezc, thanks for the info, guys. Just because I love to tinker, I am going to measure the ouput of mine .If I get it somewhere between 5cc and 8 cc on 20 strokes, I should be in the"ballpark."
Thanks again for the instructions/method on how to do this,
Rick.

[pressureangle]

This is precisely what I needed. Who carries all the different slides?

[arbezc]

Hello tetarabra, thanks for the feedback.

Is the 5cc / 20 strokes a Guzzi spec for the LeMans 1 or a figure you've found that works well? I'm not challenging your numbers, just wondering.
My carbs were set at 8cc but it seems overly rich when riding in town. All jets are set to original values. I assume that the effectiveness of accelerator pumps depends somewhat on riding style. I've you're not riding in a sportif style, ie, hard on & off the gas, they may not be of much advantage. I've considered disconnecting them but will try your setting first.

Also, have you ridden an 850 with the original #60 slides? Most bikes are now using 60/3 as a replacement. Is the difference in ramps noticable in the street? Both Theo Lamers & Stein Dinse in Europe sell a wide range of Dell'Orto slides include both the #60 & 60/1 for both the 36 & 40mm carbs. It would be good understand there operation before experimenting with more parts.

Thanks, Charles

[guzzisteve]

This is where I get all my carb parts-----http://www.herdan.com/

Hermy has it all !!    It helps if you have all the DelOrto part #'s.