05 125 Pro Carb Jet Sizes

[jumbostu]

Hi

Just fitted a Delorto VHST 26 Flatslide to my sons gasser. The original carb was jetted: 105 main, 36 pilot, 268 emulsion, D36 needle, 200 fuel valve. The new carb I have rejetted to the same spec other than emulsion 270 - but the motor is now running very lean and have had to raise needle to max (clip @ lowest) so it doesnt bog out on big handfuls of throttle. Could anyone please post their standard specs or any that are known to run better??

cheers jumbostu

[hrc1]

Well, yesterday I fitted a VHST to my 175 Gasser. These come with same std carb/jetting as 125 (so one of 'ems wrong!).

It could be the float vlave, as I understand these need upsizing to 250 or 300 to work. See posts on this forum somewhere - lots on the Beta page.

The VHST uses the HE needle jet, I assume that's different than orig carb.

Anyway, I started with 266HE, D36, S37, 300 float valve & clip 2 from top. I only used the 266 as no 268s were available.

After testing, I lowered needle clip to groove three and then went to pilot 34.

I'm using Boyesen reeds and the small flywheel too.

Definately an improvement, before the 175 was a right wizzer, almost too much go. Now the go is still there when required, but the bottom half of rev range is smoother & has more torque, feels like a trials motor now! I could ride tight dry sections in 3rd & 4th now, not ideal, but a good test to see if you've progessed with the tuning.

Edited April 30, 2007 by hrc1

[jumbostu]

Hey Hrc

You dont mention your main jet?- tho I have just fitted a 300 fuel valve to my Jumbo along with a longer headed pilot jet and its definitely improved things on that bike - so was considering the 250/300 fuel valve for the Gasser - tho wouldnt expect a little 125 to want to gulp so much fuel that a 2mm fuel valve wouldnt cope. I cant believe how lean the bike was running with such a similar carb setup - do you think that slide cutaway has more effect on the flatslides?? smaller cutaway = more suction = leaner running??? Not sure either way. The plug was seriously dry with a hint of pink from ipone 2 stroke oil it uses - far beyond self cleaning. Also raising the needle to max to helped alleviate the bogging but suggests not enough fuel somewhere along the line - main jet as I mentioned is 105....

Thanks for your time

jumbostu

[hrc1]

I used the 105 main too. I suspect the float valve or, just maybe, the different spec needle jet as the problem.

What is the diffference between as HE & K needle jet?

Interested to see If you find cure.

[jumbostu]

Hi

Different needle letters denote different carbs that they fit

http://www.racecar.co.uk/dellorto/ check this site.

A D36 needle fits the phbl delortos and seemingly the vhst

Still not sure what my next step is tho lifting the needle def improved things . . .

Will post my success when it happens

cheers jumbostu

[hrc1]

Jumbo, try the bigger float valve - 250 or 300.

Also try the HE needle jet as this seems specific to the VHST

[peterb]

Hi Jumbostu,

I have no experience with the DellOrto flat silde carbs but many years on the standard round barrel PHBL's.

The 270 emulsion is richer than the 268.

200 fuel valve and 36 pilot should be fine.

Have you checked the float arms are parallel to the carb bowl mating surface when upside down?

105 may be too small for the main. Try changing this first (along with the float arm check) to 115 or 118 and see if there is an improvement - stay with the D36 at first, this needle did perform best in my 200, the richer D34 suits the bigger motors (particularly the 300).

Smaller slide cutaway gives less air, richer on the slide.

I experimented lots with my 04 200 and found the standard carb settings just fine, it was very susceptible to jetting changes and certainly did not run well with a 270K emulsion tube, nor a D34 needle.

Just remembered, the 03 280 uses the flat silde VHST 28 carb, here are the settings for reference:

needle D48

Main 107

Emulsion 272HH (That sounds richer already!)

Pilot 36

Slide not given, only a P/N MT280390022

Fuel v/v 270 (Bore it out!!)

Floats same as PHBL

Are riders still using Harwood Dale? My old riding ground for a few years in the 70's.

Bye, PeterB.

[jumbostu]

Hi PeterB

Thanks for your comprehensive reply - plenty to digest there thanks. Looking at the original carb as compared to the VHST - the inlet bellmouths are considerably different in size ie the VHST being much bigger so fitting the airbox rubber correctly whereas the original setup need a plastic spacer doughnut to make airboot fit down to carb size - this would surely restrict airflow a lot?? So I reckon the bigger bellmouth is simply supplying a largley increased amount of air and so will need re jetting more richly than first thought. I actually leaned off the pilot and main jets to original spec. When the VHST was first fitted it had the larher jets in but still bogged on full throttle openings - am sure lifting the needle would have cured this. Think I will revert to the original VHST jets 38 & 108 with needle lifted. Will let you know.

Me and my feinds go to Harwood Dale every week if we can, usually Thursdays - when its nice and quiet. They also hold a superb Pre 65/Twinshock sporting weekend soon - camping allowed - see 1st link

Scarbro DMC

Jumbo@Harwood

The 2nd link link is a pic of me on one of my Jumbos practising last year at Harwood Dale just up the hill on the right hand side as you go in - its all changed now with piles of rocks setup and some fine clearing out work in new gulleys, steps and warm up areas.

Best wishes

jumbostu

Edited May 5, 2007 by jumbostu

[peterb]

Thanks Jumbostu,

Those rocks wern't there in the 70's! We used to ride up the rivers and the rocky gullies (I was just a lad), was a great property. John Watson used to be one of the organisers there, may be he is still around.

Thanks for putting in the links.

Bye, PeterB.