750SF Iding

Laverda SF

Laverda SF

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One thing my 71 SF does is that it's starts perfectly with the Enrichers but once warmed up with the enrichers closed it will "BAFF" and STALL after about 2 minutes of idling with Cyl-Heads at temp of approx 340 F, if I don't tweak the throttle - Sometimes an inconvenience at traffic lights when the bike has been ridden for awhile, if I forget to tweak the throttle.

Should I go to a larger size of Primary Idle Tubes. It's always done this - Basically stock with 2 into 1 Pipes and 30 Main Jets that work great up to 8000rpm, open VHB 30A's. Float level seems to work good at any speed.

Minor inconvenience - BUT - I want Perfection. Really thinking about going to Mikuni 34 CM's and running an Air Filter.

Just noticed I can't spell "Idling" in the Post - LOL
 
If you suspect the idle mixture is too lean, try opening the idle mixture screws a bit before replacing the idle jet. You'll know if you're going the right way because the idle speed will increase. Adjust for maximum speed then re-set the speed to where you want it with the throttle stop screw. If you end up with the mixture screws more than a couple of turns out to achieve a reliable idle, then you may need bigger jets.
 
Fit a digital electronic ignition and see if it helps.
Sorry, I just couldn't resist  :-\
My experience with Dells on any bike is that they like to be on the rich side of perfect (roughly exact).
The sweet range where the idle is fastest starts from a lean point e.g 1 1/4 turns out, and extends to a rich point e.g 1 3/4 turns out before it begins to drop off again. They usually like to be just inside the rich point, say 1/8 of a turn in from where it drops off the rich side. I have found this to avoid the symptom you mention. It is quick to try it.
Another cause of that is air leak into the manifold, can be very slight.
 
I had this with a 750 for years, bought new by me in 1973, was not fixed under warranty,(two attempts) crashed in '79 and rebult into an Egli, whereby it still did the same thing, I just sufferred it, and then about ten years ago I was lucky enough to get a Yamaha carb balancing guage with a four way tap, one gauge, reading on whatever cylinder the tap is turned to, my SF, became easier to start (was never a problem) very easy to start from a hot stop (no enritcher needed at all) an most of all would tick over for a fornight if you left it.
maybe your carb balncer is obsolete (I previously used  a bank of four gauges  by Davida) or the method,
how do you balance your carb slides?
CLEM
 
Hi Clem -1st get engine hot -  I make sure there is free play enough to let the slides fully bottom out with the adjuster screws wound out. Then adjust each screw in until the slide just starts to lift - then screw in the screws the same amount each until you have a tickover of about 1300RPM - turn each mixture screw in or out until the engine is revving its highest - but if too high - reset both adjuster screws a tad looser (always same each) until RPM range returns. Equally turn out the adjuster screws to get the tickover you require. Adjust cable free play equally and i often turn out mixture screws about an eighth of a turn so it's a tad rich - this helps avoid any tendancy to stall pulling away at low RPM. This method does require the motor to be running equally on each cylinder - timing - compression - jets etc. I've found that if I can't get it right this way - then i start to look for other problems - regards - Phil
 
First of all thanks for some very constructive Info:

I believe I have the sliders and throttle cable draw set equally on both carbs. I use a specific "allen wrench" as a gauge to set the position of the sliders equal in each carb and both Idle air screws are presently set 1 turn off seat. The engine does seem to idle verily rich at 800rpm and is constant and strong but after approximately 2 minutes it "BAFF's" and quits.

The Engine starts, like with one touch of the Starter Button, and I have very good throttle response pulling away all the way through the RPM range in every gear.

In other words, other then "Baffing" after 2 minutes of Idling (which isn't a good thing to do in the 1st place), the engine works perfect. The Bike has always done this and just seems to be it's nature.

I haven't used Air Velocity Gauges since the 60's when riding Norton's - To me Carb Air Velocity Gauges were never perfect over my own ears.

I will try turning the Idle Air out another 1/8 or 1/4 turn to say 1 1/8 off the seat but I believe I've been there before to no avail.

Here's other Data:

POINTS set at .4 - .5mm or .018?

Timing is slightly RETARD as I run 91 Pump Octane = 95 RON

NGK B8E S ? Gap at .7mm or .028?

Main Jet #130 ? K2 Needle Position 2nd Notch ? Idle 800rpm

I'm half pituded, NOT riding today, and probably not making sense ;o)
 
:D  :D  :D

Not trying to start another punch-up Cosi.
It's just that sometimes I find Laverda SF's style of writing a little hard to fathom. His use of words like "pituded" is a perfect example. I even tried googling it - to no avail.
No offence intended SF.

Cheers,
Cam
 
"I'm half pituded, NOT riding today, and probably not making sense ;o)"

I haven't been pituded for 18 days, Dry July!

If that's not what it means, can I have a second guess.

I haven't pituded for months, I'm married!
 
The word 'pituded' is a good way of dumping some those low scoring consonants in a Scrabble game... a paltry 11 points for a 7 letter word is atrocious. Get rid of them and make way for the K,J,X, Q and Z
 
"pituded" is an Irish Canadian expression for being 1/2 way between Corked and Skunked ;o)

Any I did open Idle Air another 1/8 turn and it didn't Baff at idle but I didn't hit many Red lights today.
 
"pituded" is an Irish Canadian expression for being 1/2 way between Corked and Skunked ;o)

Man, that didn't help one bit:

Corked?????????? (like a wine is corked)
Skunked??????????? (like, pissed as a skunk)

Cosi, you didn't text me the address.
 
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