Carb talk

Do you think there is a problem with the pilot jet size?

My Corsa runs 65s as standard.

RGS standard is 65, might suggest that is a bit big given the Corsa'a better state of tune.  The mixture screws were turned in a little which tends to suggest  a wee bit of richness at the bottom end, and it is a bit fluffy low down.

Reckon I've been riding round it up till now, but I would like to try go get a little more zing out of it, and maybe reduce the fuel consumption.  I'm sure that today's lighter fluid petrol needs smaller jets, I mean, the days of Jotas running 140s are long gone.

No point in going mad though- she runs OK, but there's work to be done inside t'mill...
 
As Janice Joplin once didn't sing:  "Oh Lord, won't ya buy me some Mikuni carbs..."

This is an interesting earlier post from John W:

Hello Lads,
                  Yes Paul moved house,  back on the coast again.  Though i liked the highlands ( "high" in Aussie terms :-) ).  Warmer in the day, which is nice. Thanks for the warm welcome back.

Re the 65 pilot jet on the RGS,  the 180 series 1 1000 factory seting  is 55 however the 1200 is listed at 65. The 1200 jetting is for the restricted air box though you wonder at the apparant going the wrong way on the pilot when the air flow is reduced. Possibly the reduced air flow also reduced the helmholtz ( venturi ) effect that enables fuel to be drawn up the emulsifier tube at low rpm.
Thus a bigger pilot jet may have been required.

Of all the Breganze triples the RGS was most afflicted with off idle/low rpm stumbles and almost incurable pilot jet to needle transistion variation in correct fueling ie it is either too rich or to lean or the 25 degree step on the ignition made it appear so.  If you try to adjust the pilot on a BTZ the motor will pink in hot conditions and stumble dangerously in slow hairpin turns especially uphill,  i know after nearly droping a Corsa!

The factory solution was to "smoother" the horrendous step of the ignition by gross overjetting on the pilot. Theory easly proved by fitting a decent ignition like mine or the Witt DMC,  fitting the 55 or 60 pilots,  reset the carby balence at cruise rpm of about 4000rpm ( forget balencing at idle rpm as whom rides around at idle rpm?? ). 80% of my riding is done on the pilots ( misnomer the phrase "idle pilot" as if that was so why does the fuel idle screw have an adjustment? ) it is the ever important pilot jet and transistion onto the needle/emulsifier that is soooo much more important than main jet size.

Paul B,  that point number 2 low throttle opening can be hard to diagnose. Though with some clever ideas like the one from Chris Pritt you can diagnose it very quickly on the road.  Find a straight low traffic area,  warm the engine up and start riding,  get the engine to "hunt" then pull the choke on slowly at first,  if the condition worsens then you are rich on that phase of the throttle if it gets better then worsens most likely your lean.  Over rich low throttle can feel like a lean out in the way the engine surges, though normaly you get other indicators for lean outs like carby spit backs and poping on the overrun ( provided the exhaust system is sealed against leaks ).  Make sure your air flow through the air box is adequate and near standard ( no snorkel! ).

One word of warning should you go for the 55 pilot, on the 180's here i find the closed or trailing throttle transistion to needle results on some engines,  a pronounced over rich on closed throttle to correct fueling when re opening the throttle. This results if riding close to the guy in front a "boost" of about 10hp and i find myself right on the front mans rear wheel in short order, bit disconcerting at first however i think it is great fun.  The reason i can only guess at however obviously the transistion phase is markedly effected.

HTH John

Thought I'd check under the airbox for holes, sure enough, they are there.  So, drilled airbox, drilled cans and large collector box and still feels rich, might try 105 mains, 58 pilots, see how it goes.
 
Dellortoman said:
I think you're being too fussy Lothar. You can often re-jet old worn out carbs to compensate for the wear. For example, if the needles and/or needle jets are worn it'll be running a bit richer than it's supposed to so just drop the needles a notch. It may not be a perfect solution but it will get the bike running better.

Whether a carb gets leaner or richer as it wears, there are adjustments you can make to compensate. I have an old Honda dirt bike with old carbys and I've had to drop the needles to the top notch to get it running right. It was going like the clappers. But thinking I should re-condition the carbs, I bought a full kit of (Keyster) jets, O-rings, gaskets, etc. that were supposedly correct for that model. I put them in and it ran like a sick dog. I tried the needles in every notch and it still didn't run right. Put the old needles in and it ran better. Put the old needle jets in and it's back to running like it should. Sometimes new jets aren't the solution - especially that Keyster rubbish.

Cheers,
Cam
Well said Cam I like the way you think about the problem and find a way round it.
                   Dave
 
Might be I am "shooting sparrows with cannons" here as we say, but the experience of 20 years with our Laverdas clearly shows: if you try to mask a problem, you will soon find yourself lost with to many variances and other problems.

I have done a lot of adjusting carbs like that. Last one was a 750 SFC replica that we found to be running rich all over the place, but especially in midrange. we dropped the needle to top notch/lowest needle position, put in smaller mains and pilots and it was still running a bit rich in midrange (needle jet was correct). It simply had worn out needle-jets and needles, but the owner was happy with the result and so be it.

However, completely refurbishing the carbs is a question of 2-3 hours of time and roughly 120? in total for the gasket-sets, the new jets and needles. Roughly 200? overall if the sliders are worn out, too. Hardest thing is to get access to an ultrasonic bath (which I happen to have...  :D ), but then it's fairly easy to do and gives you a way improved running bike.

Each to his/her own though.  ;)
 
Hope so!  In the end I decided that as some were running 55s or 60s, I'd split the difference and try 58s.  I'll leave the mains alone for now- must remember the golden rule to only change one thing at a time.  Have ordered a few O rings and bits and pieces which looked tired, should be OK for now. 
 
Well i think my thread has been hi-jacked somewhat but I took bowl 3 off today and it was apparent that the float was sticking.

It wasnt dropping like the other two floats. You could pull it with your fingers and it would click and drop to the level of the others.

Not sure why this was ???

http://www.motorcyclecarbs.com/images/dellorto/explview/PHF-ExplViewLG.gif

I think its parts number 69 and 8.

Perhaps I should replace them.
 
Moves freely on the axle, but doesn't settle properly. You have to flick it for it to drop properly.

I tried to move it up and down to make it move freely but it was still sticking.
 
fast_eddie said:
Moves freely on the axle, but doesn't settle properly. You have to flick it for it to drop properly.

I tried to move it up and down to make it move freely but it was still sticking.

So, if it's Not closing properly, you might have found the reason why it's running rich. That was why I said changing jets is just masking a problem... ;)
 
fast_eddie said:
Well i think my thread has been hi-jacked somewhat but I took bowl 3 off today and it was apparent that the float was sticking.

It wasnt dropping like the other two floats. You could pull it with your fingers and it would click and drop to the level of the others.

Not sure why this was ???

http://www.motorcyclecarbs.com/images/dellorto/explview/PHF-ExplViewLG.gif

I think its parts number 69 and 8.

I had exactly this problem with mine last year - took me for ever to discover what it was. You need to replace part 8... That has a body, a pin and a tiny spring. The pin is held captive by two tabs on the brass body. The two tabs had opened slightly allowing the pin to stick. Given the cost, it's best to just replace it.

HTH.

--
Dick
 
reggie3cl - no probs :-) More the merrier.  :P

Dick - do you know what the standard size for part 8 is in these carbs?

I guess I could take the old one off but im chained to my desk today and wanted to order one asap.

CHeers
Ed

 
A set of three runs about ?30 from Stein-Dinse. The choice is how much you want to fiddle fart around compared to do simply doing it right the first time and having a much better running bike which is actually fun to ride. Doing it right the first time usually takes less time than trying to troubleshoot problems with nackered parts too. Laverdas can be quite civilized if people would let them be and a lot of that is simply in the details.

Tom
 
Tom Eatman said:
A set of three runs about ?30 from Stein-Dinse. The choice is how much you want to fiddle fart around compared to do simply doing it right the first time and having a much better running bike which is actually fun to ride. Doing it right the first time usually takes less time than trying to troubleshoot problems with nackered parts too. Laverdas can be quite civilized if people would let them be and a lot of that is simply in the details.

Tom

  Should have this permanemtly scrolling across the screen in the tech section.  ;)


  Keith
 
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