Jetting on Super Combat

[Pep]

Does anyone have some numbers on their stock SC with an HT3 pipe?
This bike’s running pretty good, but seems like I could squeeze a little more out…
Idles good, clean in the low end, very good mid-range, but still a little lacking on top. Plug still a little dark.
35 Pilot, 159 Q6 Neede Jet, 6? Needle, Clip on 3rd, 3.0 Slide, and down to a 350 Main (stock = 410)
Leaning the main jet has improved things, just not sure if I’m getting into left field…
Any advice from you experts would be appreciated…
Like I said, the bike runs fine, just curious about what others have had luck with
Thanks!
-Laurie

[JayLael]

Laurie: My ported reed valved Combat Wombat with YZ 125 pipe and 34 mm mikuni carb, is running very well here with a 50 pilot and a 330 main jet. I think the only thing that makes anyone an expert is they have tried lots of stuff and made a few mistakes along the way. I say go leaner on the main jet if the bike is happy. Fuel/oil ratio and local conditions all come into play. I seem to always need a bigger pilot jet to prevent lean problems that occur once the bike is well and truly "hot". With this pilot I end up at around 3/4 turn on the air screw. Idle is the first step to a good running bike. Then work your way up.

[admin]

Laurie stock jetting for the Super Combat with a 32mm carb is what you show above except the needle jet was a R-9
Throttle position is extremely important to know what to change and how to do it. The HT3 pipes did not demand more fuel than a stock pipe.
So at 0- 1/4 throttle you are good ?
1/4 to 3/4 throttle still good??
3/4 to full throttle falls off ??

Thanks
Paul

[Pep]

Thanks for the advice Jay, I just put a 340 in and swapped the Pilot to a 40 just to see what happens. Hey, we went to a Corb Lund show in Austin a couple of months ago - what a great time! Thanks again for those road tunes back in Athena last summer - think of y'all whenever I hear him on the radio.

Paul, thanks - that's the needle jet that was in the carb, so I guess it's just a bit leaner than stock. Although, just now I looked up the specs and it shows the Q6 as stock? Maybe there was a change? Not sure that it would be a big factor - I suppose it will just mean nudging the other jets around.
As for throttle position, it's the 3/4 - WOT that's not perfect. Not bogging or hesitating, just not the pull I'd like to have.

I've got a fresh plug in and a sunny day outside - I'll keep y'all posted on results.

[admin]

I do remember specifically speaking with Harry about the R-9 Needle jets as I could not get them from Mikuni. Harry told me they were made specifically for Hodaka's and the Super Combat 32mm carbs. I grabbed two different sheets and both show a R-9
One is the Field Manual I keep next to me desk.

Your needle jet and needle feed the main jet. Try raising the needle one clip at a time and see if this works for you.
3/4 to wide open is a main jet issue but I think you might try feeding the main jet a little.
If the needle change works then we need to get you a larger needle jet so you can keep that clip on the needle in the middle (#3)
Thanks
Paul

[Pep]

Ok Paul, all I have is a repro of a SC owner's manual - you are definitely the source for the real numbers!
Test ride with the 40 Pilot/340 Main was a success - bike is pulling better than ever. Better from 3/4-WOT, still crisp down low and climbing hills well.
Once good and warm, I fiddled with the idle/air - the air screw is happy at about 1 3/4 turns out.
I'd like the spark plug to be more milk chocolate in color, but I might stick with this set-up for the weekend's race - a bit richer is safer...
This is the first race in what will hopefully be a good season for the bike.
Oh, and the HT3 pipe ROCKS!
Thanks for all the input - I'll report back any problems/changes
Laurie

[racerclam]

Hey Paul , the needle jet does not feed the main jet its the other way around the main jet feeds the needle jet and even if you raise the needle all the way up it wont give a clue the the main jet issue on top , BUT! will if the main jet is too small to feed the needle jet sufficiently at 3/4 and less throttle openings. And just a note On my origonal stock Super Combat ( except for the carb ) which is a 34mm I run a 420 main a 40 pilot a Q8 needle jet and a 6L1 needle a ns 3.0 slide . I hope this helps.

Rich

[admin]

Well thanks Rich I stand corrected. Two years ago when I was getting Billy's 175 jetted in for him here in Sandgate no matter how large a main jet I used it did not run right on top. I called Harry and he suggested for me to up the needle jet by several sizes. That helped. Then he had me raise the needle and the bike ran fantastic at 3/4 to full throttle. I eventually went to a larger needle jet so the get Billy's needle back in the middle position. Harry had told me then that the needle and needle jet feed the main jet but maybe I misunderstood him. Whatever he said and I did the bike ran fantastic !!

It was a very special thing when I would call him and ask advise over the phone . He would make suggestions and I would try things as he waited by the phone anxiously for my report.
Like when he and I were working on the HT series pipes.Harry did all of the design work and had all the ideas. Some folks have stepped up and claimed that they were involved in the project but that was not true it was ALL Harry. I miss the little white haired guy !
Have a great weekend everyone !!
Paul

[JayLael]

Laurie: It warms my heart that you like Corb Lund. He is our favorite singer bar none! The live shows are such a kick in the butt! I gave Paul a CD at Harry's funeral. I wonder if he ever had time to listen to it. I think Hurtin' Albertan is my favorite song. Reminds me of when I used to ride bareback horses.

[racerclam]

Thats ok Paul none of us is perfect if we were they would hang us an cross. Yep Harry is greatly missed we usually talked a couple times a week 8o(

[Pep]

Rich, thanks, yes that helps - bigger carb, bigger jets...extrapolation to a smaller carb kinda works out. And it will surely help someone out there with an identical set-up.
Thanks to both you and Paul for the carb tutorial - always learn stuff on this forum
Jay - HECK YEAH! We are Hurtin' Albertan converts! The show was at the Cactus Cafe and was just awesome. I always have his albums in rotation here in the shop - really gifted at nailing that lifestyle (as an ex-rodeo competitor myself) - plus the whole veterinarian connection is cool too. Can't wait until he's back in town.
Everyone have a great weekend,
-Laurie

[dirty_rat]

I just finished reading a new article on carb jetting for vintage bikes using Mikuni VM carbs. Good article, easy to understands. Here is a link to the article, it was on the Klemm Vintage web site. Here it is: http://www.klemmvintage.com/mikuni-tuning.htm

Hope it is useful to others.

Dirty Rat