Choke set up 180

[psg]

Surprised no one has mentioned the starter jet is the one with the rubber O-ring round it

(6) Choke or Starter Jet for Dellorto PHF carburetor 7746

Choke (or starter) jet for the Dellorto PHF carburetors. Where possible, we only supply original Dellorto jets marked with the famous diamond-shaped "Inc" logo. However, sizes that are no longer supplied by Dellorto themselves are manufactured for us at the exact same high standards. Available...

www.dellortoshop.com

 

[iis_iis]

Hi Jon. My Jota had 145 mains in it when I got it (PO evidently had little clue about carby tuning). It rode relatively OK (no flat spots or misses) but wasn't making much power and had atrocious fuel consumption. After a few dyno runs we (dyno bloke and I) settled on 120 mains, but the interesting thing is that on an experimental run with no main jets at all, it ran the same as it did with the 145s in it. The conclusion being that a 145 main jet is beyond the fuel flow range of the emulsion tube and needle/jet that sits just above it.

Yes Cam, there were anomalies with the 145 mains, seemed there were varied outcomes as the UK owners i dealt with could ride a 145. The issue i found had more to do with "flooding" the idle jet, weeks and weeks of adjustments that i could not get to behave in a predictable manner. 120 motors were quite different from the 180 series 1 carby jetting and adjustments. Ultimately the 180 series 1 with proper ignition came into the range of 120 motors.

Tinkering in the later 1990's with proper carby setup was required as fitting a proper ignition revealed the true crude jetting done at the factory to live with a BTZ two step ignition profile curve. Many an owner came back at me indicating issues they never had with carbies until the new ignition was fitted. Long hard road to uncover exactly what needed to be changed in jetting and settings. Few simple jet size changes, a rule of thumb fuel idle/cruise set screw ( 1 3/4 out from stop ) all seems common knowledge, anything but that as the old time mechanics kept telling owners what they wanted to hear.."its the new ignition that is causing all these problem with carbies"... pffffft what a load of rubbish... though i got the blame and the hard slog sorting the carby best basic setups... 120-122 mains, 50-55 pilot jet, K1@middle clip, 60/2 slides, standard airbox, with foam filter. 18m/m float, proper sealing plunger(s) and cable free play "choke".

My recommendation, post new ignition, pumpers turned off, the latter was at times by certain owners, used as cold enrichment cold crank start, ie the oft heard "three twists on the throttle" no choke, press starter, no indication as to where the pumper diaphragm operation travel was set... history behind the setup discussions. HTH j

 

[iis_iis]

Oh and BTW having a bag full of 145 mains on hand, used to solder them up and using number drills, have a range of "test" jets to get near the required new mains jet. Not surprised Cam the motor did not have any missing issues, maybe a fluffy overrich mixture could be felt, used to test for this by jetting up, finding a steep hill, ride until carby issues presented, bring on the "choke" see if it smoothed or was worse ( fluffy ) knew if too rich or too lean... got good at one hand under the tank and one hand on the throttle, semi prone on the fuel tank...must have been a sight...j

 

[Vince]

It's the exact opposite with my Atlas, everybody was saying there really lean to pass emissions and the 2 step ignition plus the lean jetting makes them a real pig to ride. I haven't ridden it much but we have some huge hills about here and I have a pretty tricky driveway and shed to get into and now with it all standard it's pretty dam pleasant in everything I have thrown at it. I am pleasantly surprised. Some bloke who constantly says" What Would I Know" suggested I try the standard settings first and apparently he does know some shit. Who Knew? He also said and here is another quote and it's a "Valid Point", the fuel in England and Europe is different to Oz fuel. Just my observation of current stuff. It's an odd Laverda World out there.

 

[Paddy]

. The conclusion being that a 145 main jet is beyond the fuel flow range of the emulsion tube and needle/jet that sits just above it.

This is highly unlikely the emulsion tube is 2.65mm so way bigger than any jet. also remember that the needle and emulsion tube are the same as a in a PHM40 on a 900SS with 300 needle valves. In my experience if there is a restriction in flow at the top end its nearly always fuel taps.
I think the point here is being missed.
The guy has a problem with the bike over revving on the choke. with the throttle shut. this is almost sure to be his choke jets but easily checked by starting on half choke if its set up properly..

 

[Vince]

My Pantah did the same, but it has a flip-up choke. It's either full-on or full-off. I think I got a smaller enricher jet, not choke, jet but it's been years so I forget.

 

[iis_iis]

Doing my bit to kill old mechanics dogma's around carby and ignition systems. While not exactly on topic of how to set up and start a Laverda. Remain resolute in a campaign to rid the general Laverda rider knowledge base of what can only be described as blind belligerence had to endure in the days of proper ignition, wasting my time pacifying customers about what happens when items are changed for older oem items. Well known two Laverda workshops in the UK were the worst, though we had a beaut out here. As any reader can decide upon to read or not read posts like this, the information is of great use to the cognizant owner reader alike.

How many times has there been posts about problem carbies/motor operation only to go through all the usual suspect issues, to quickly or slowly discover bowden cable issues with the fuel enrichment plunger and seat, small o ring sealing of the top flange... fuel enrichment off is more important than a over zealous enrichment rev to rev limiter instance.... turn the volume down a little next time, a wry smile here. j

 

[iis_iis]

It's the exact opposite with my Atlas, everybody was saying there really lean to pass emissions and the 2 step ignition plus the lean jetting makes them a real pig to ride. I haven't ridden it much but we have some huge hills about here and I have a pretty tricky driveway and shed to get into and now with it all standard it's pretty dam pleasant in everything I have thrown at it. I am pleasantly surprised. Some bloke who constantly says" What Would I Know" suggested I try the standard settings first and apparently he does know some shit. Who Knew? He also said and here is another quote and it's a "Valid Point", the fuel in England and Europe is different to Oz fuel. Just my observation of current stuff. It's an odd Laverda World out there.

Of note Vince, the HKZ on early triples as recounted to me, was more rider friendly than the clunk prone HKZ. May well be your latest ride has characteristics that reduce the effects of oem bosch ingnitions. Have you recorded the actual jets and settings on the Atlas, something i did automatically when a customers Laverda ( and ducks ) was brought to me, before i touched anything. Noting mechanical setups also.

Maybe and it seems so, you had a win, cannot have bad luck all your life...not possible, a large grin here. j.

*** oh and by the way we have or had summer and winter VOC fuel chemistry in Australia, direct from the lead Chemist at Shell of the day, as i recall, could have been other fuel refiner... jetting for altitude is another whole field on normal aspirated engines.

 

[Vince]

John, I have notes on every detail I find plus comments from other owners, according to Dr Karl it's not an experiment unless you record your findings and all data is valid, even incorrect data. I learn more from the latter.

 

[Paddy]

I get that people might have general info of interest but for people looking back with a "search" for specific problems in the future, then sticking on topic as described in the thread heading is helpful. It also helps whoever asked the question . Reading this now its quite likely that someone with a choke problem could think its related to over size main jets.

 

[Vince]

The search function works fine with the typical wondering chat at the pub thing we do here. If your search lists Thread Heading only then that will fail, keywords will come up anywhere in the thread. The strict moderating of sticking on topic lasted about a week when this forum first started and failed big time. Its fun to see where conversations can go. So Cam tried that no main jet thing and had something occur, you disagree. That's fine, it shouldn't cause a cuffufel. But it's an interesting exchange and something to think about. It's also fine to agree to disagree. Nobody is suddenly going to start pulling main jets out and riding without them, I bloody hope not anyway.

 

[hooksey]

The search function works fine with the typical wondering chat at the pub thing we do here. If your search lists Thread Heading only then that will fail, keywords will come up anywhere in the thread. The strict moderating of sticking on topic lasted about a week when this forum first started and failed big time. Its fun to see where conversations can go. So Cam tried that no main jet thing and had something occur, you disagree. That's fine, it shouldn't cause a cuffufel. But it's an interesting exchange and something to think about. It's also fine to agree to disagree. Nobody is suddenly going to start pulling main jets out and riding without them, I bloody hope not anyway.

Search function on here is exactly that............like a needle in a hay stack

 

[Vince]

The magnifying glass icon search function doesn't work too well, but the written Seach Forums one has succeeded really well for me. I hope that there is a difference and it's not wishful thinking on my part.

 

[Paddy]

If i wanted to start a conversation about main jets i would start a thread called main jets rather than hijack someone else's topic.
Its a waste of time me trying to help a guy if he has to filter out dozens of off topic posts , some quite misleading to the original topic.... but i get thats how you do it and I'm new here so learning..

 

[CLEMTOG]

"In my experience if there is a restriction in flow at the top end its nearly always fuel taps."

from Paddy above.
I can confirm this, when I was racing my 1200, the top end fuel starvation would show if the circuit had a long straight (eg the old original Snetterton, with its near one mile long straight) but any long straight, I always geared for max revs to come just after half way down the longest straight of any circuit, but maybe three quarters, this is when it showed up and starvation showed, it was very different if running a full tank, racing fuel consumption was (IIRC) around 18MPG it was very rare to run a full tank, as I made sure there would be next to zilch left at the end of whatever the race distance was, and this was while using 300 size float valves, I solved that by welding in an extra fuel tap boss and fitting a third tap, each carb had its own tap with carbs 1 and 2 linked and 2 and 3 also linked, I ran like it on the road for a while, and it cured the stutter when getting close to reserve, when you could (in the old days) ride at 100MPH with not much risk of a ticket, to all intents and purposes anything over this speed is a real hard chore, so it doesnt get done for more than a few seconds. these days, I get the same feeling at 80/85 that I did in the past at 100, that is me not the bike.
CLEM

 

[Vince]

Clem that's also very interesting but it's not on topic, where is the choke reference. O yer, it's again a conversation. I see how that works.