Jetting help VHB

[ritratto]

Hi all,

I have a '78 G5 with K&N pod filters and  Dustall replica mufflers. I am running VHB carbs with 130mm main and 45mm pilot (50 original, but ran too rich and flat between 4 and 5 grand).
So, here is the issue. It still idles a bit too rich and still has a bit of a flat spot between 4 and 5 grand.
There are also new plungers and seals on the choke.

Any help in much appreciated.

Thanks,
Ted

[not-fishing]

I tried the hit-n-miss rejetting a V50 III with pods being the only change.  It ran better but I just gave up guessing.

Then I bought a Colortune 14mm sparkplug system from England and used it.  My left side went down one idle jet and up one slot on the needle. 

Now the little V50 runs stronger than ever.

I'm really sold on the Colortune  otherwise known as a Poor-Mans Substitute for a Dyno-tune

Mark

[guzzisteve]

RPM makes no difference, it's throttle position: 1/8, 1/4, 1/2, 3/4, w/o

http://www.thisoldtractor.com/mg_manuals/dellorto_manual_a_guide_1.1.pdf

[canuck750]

I tried the hit-n-miss rejetting a V50 III with pods being the only change.  It ran better but I just gave up guessing.

Then I bought a Colortune 14mm sparkplug system from England and used it.  My left side went down one idle jet and up one slot on the needle. 

Now the little V50 runs stronger than ever.

I'm really sold on the Colortune  otherwise known as a Poor-Mans Substitute for a Dyno-tune

Mark

IMHO the Colourtune is a good guide for idle mixture, not so convinced it is accurate as rpm climbs, especially above 3000 rpm but still I have found it to be a useful tool.
I also bought a gas analyzer from the same company, fairly cheap on Ebay, a little more finicky but I found I could get a what I perceived to be a more accurate setting of the mixture screws, could be my imagination though.

I spent Sunday tuning my Laverda SF1, it has a DMC programmable electronic ignition. After setting the advance curve to a gentle curve adjusting the timing with a strobe at 3500 rpm made a very big difference to the top end running. After the timing was right the carb idle adjustments came way down and the mixture screws could be turned in to reduce the rich running.

What I am leading to with all this blather is that the interconnection between an accurately set ignition with a good spark and a proper functioning advance makes all the difference to the carburetor!

Once everything was set up the temperature of the exhaust headers at the head dropped by over 75 degrees F, and any sense of hesitation seems to have been cured.

[Chuck in Indiana]

What I am leading to with all this blather is that the interconnection between an accurately set ignition with a good spark and a proper functioning advance makes all the difference to the carburetor!

I've said many times that carburation problems are generally ignition. 

[guzzisteve]

Most all of the VHB's I have set up w/K&N's and Dunstal's needed 55-60 pilot, needle all the way up and 150 mains

[ritratto]

Most all of the VHB's I have set up w/K&N's and Dunstal's needed 55-60 pilot, needle all the way up and 150 mains

Thanks Steve.... Have you run one this way? It is stock at 50 and 130, needle in the middle.

[80CX100]

I've got the same engine and carbs in my CX100,,,with big oval K&N's & Lafranconi's,,, stock pilot & main were 50 & 125, I went to 52 & 140, clip stayed in the middle on the needle, but I put in the short euro mixture screws,,, for set up and fine tuning, I hooked up my homemade manometer and went back and forth from screwing in the mixture screw & lowering the idle screw to get the best combustion possible,,, indicated by the highest idle on my gauge,,, then finished the balancing throughout the rev range.

But I agree with Canuck & Chuck,,, the thing that really cleaned up my carb tuning and combustion, was redoing the electrical system,,, I kind of went overboard and did the full monty,,,but I get nice strong sparks,,,lol,,, I put in a rated? lol 450W alternator w R/R, ran relayed direct power to new Bosch Big Blue coils, condensors,points & plug wires,,, good clean big ground wires,,, and the last icing on the cake at the end,,, which KiwiRoy told me I'd need when I started,,, was a new ignition switch,,, when I couldn't get the damn thing to start,,,lol.

fwiw ymmv

Kelly

[guzzisteve]

Yes, my 850T and SP1 w/Bub's full system. I don't care w/stock is, I did plug chops after 2mi in the throttle opening on flat strait roads in IL. Put the same thing in many customer bikes. Make sure the timing is correct and advance isn't stuck.
Lean is mean but it will also burn your valves.

[Two Checks]

Based on my experience 50 pilots 142 mains (it could use bigger) middle notch on the needle and 265 atomizers.
For reference I am at aboutt 500' msl. Worked great with an 850 w/ Bubs and pods and on a SPII and Cal III with stock pipes and airbox.

[80CX100]

Yes, my 850T and SP1 w/Bub's full system. I don't care w/stock is, I did plug chops after 2mi in the throttle opening on flat strait roads in IL. Put the same thing in many customer bikes. Make sure the timing is correct and advance isn't stuck.
Lean is mean but it will also burn your valves.

Sorry for the thread hijack,,, but it's all on the same topic.

Steve, I have great respect for your expertise and input here,,, I've learned LOTS from reading your stuff over the years,,, 

Should I infer, that your opinion is that by setting up my mixture screw this way (manometer) that I may be too lean,,,I researched many different ways of doing it, sound, heat, pressure etc,,, none were really working for me,,, I researched the hell out of the colourtunes,,, but I was reading almost as many negative as positive reviews of them. (Apparently quality control has gone down and some guys have damaged heads with them?fwiw idk).

I debated raising the needle to the lower clip as you've done,,, actually had them set that way, but I thought I had read somewhere that would be too rich,,, so I switched them back to the middle.

My plugs have never looked hot,,, once started it likes choke for 1-2 minutes before it runs clean and strong,,, guzziology refers to this being a good thing, that if it ran without a choke right away,, you're too rich?.fwiw idk

I realize plug chops are the preferred method, but that can be a pita with roads and traffic being what they are.

tks

Kelly

[guzzisteve]

I use a Colortune for idle mixture only. I don't read Guzziology. I do have an old copy of it from the 90's. I just do things the way I learned, right or wrong. I don't read MC magazines either, it's irrelevant to my situation. I do get the GuzziNews since 81'  What I do doesn't mean what you should do, I just stated what I do. Whatever works for you is what you should do.
I have gone blasting on the interstate here in GA checking plugs, not to many strait roads.

[80CX100]

     Tks for taking the time to reply, I'll keep a closer eye on my plugs, will probably try raising the needles a notch,,, just for shits and giggles,lol.

      tks

      Kelly

[ritratto]

Thank for all the replies. I will be taking all into consideration over the next week or so and see how it turns out.

Cheers!
Ted

[chuck peterson]

I've seen 125s for a main on G5/vert...bottom notch on the needle and that's it for k&n....have you got the intake manifolds on? They have a bit of a choke on the inside and create some Low pressure/Venturi/whatever effect...might help...have a machinist turn down the outside to fit the k&n

But then, I've heard those intakes are getting rare.

Lots of different dist springs, too. I found a vert with lemans springs that couldn't get out of its own way, poor thing. Measured carefully and replaced per Guzziology, sprang to life reborn. Set the timing at full advance?

[ritratto]

Hi Chuck,

I'm guessing you left the pilot at 50?

[chuck peterson]

No idea...15 plus years...I remember the 125, because it wasn't a 130 I was expecting to see...