The 38mm Mikuni VM you got from me should have a needle with 5 tiny grooves for the little clip to go in to. Pull that little puppy out and take a look again, I think you will find them on the needle. That is the stock needle that comes with a VM carb.
Regarding the main jet size. Since your experience and reports from several others with the new Mikuni VM carbs that have been in the carb kits recently, I have been revisiting the jetting of these carbs. There seems to have been some minor
looking changes the carbs and I believe some jetting affects as well. In any case, they are flowing a lot of fuel with the stock jets. I made the recommendation for your carb based on my own carb (an older 38mm VM) and then also using the Pocket Tuner slide rule for changes based on altitude and temp. The end result was a main jet that is still a bit rich for your engine as noted by the plug condition. Others have reported similar findings.
So what I have done is to order a new carb for my Savage and start at square one again and go through the jetting process. I found that the stock #35 pilot and #310 main jet on the 36mm carb was too rich. I dropped down to a #30 for the pilot which worked well, but that still had the adjusting screw at 2 1/4 turns out, so more ideally the pilot should be the #27.5 ...this is basically at sea level & in a high temp/humidity environment. The main jet ended up being a #250. These jet sets were on the new stock 36mm VM.
I then installed the UFO in the bottom of the carb slide and now have the jetting at a #15 pilot (with the needle jet top drilled to lean the slow speed curcuit further, the needle on the 4th groove/slot to richen the midrange, and the main is currently a #240 but will be going back up to a #250 or possibly #260... we shall see which is best.
For your situation, based on the reports and the jetting testing done witht the new carb, you might try ...
the 38mm VM comes with a #30 pilot stock, which may be OK for you if your adj screw is not turned out more than 2 turns out. If it is more than 2 turns out then drop down to the # 27.5 pilot and that should do it.
Your plug is black so the main is to rich ... come down one size at a time until the engine revs strongly at full throttle with no bogging down. At that point your plug should be looking the proper very light tan color. I suspect that you may end up somewhere around the #240 main jet.
Just remember that every engine is a little different, your location affects it, and jet and tune until the engine feels good and strong.
I have been puzzled by the difference in jetting between the earlier Mikuni VM and the new ones. Something has changed but I do not know exactly what it is. Regardless, we jet/tune until it is right.
vroom1776 wrote on 12/31/69 at 16:00:07:Lancer,
2 questions:
1) This is on a mikuni VM, right? The one I got from you (38 mm) does not have clip positions on the needle. Are you using a different needle (than stock w/ the carb)?
2) Why are you using such a small main jet? What size carb is it? For my 38 mm, you said I should be running a 310 at 4k feet... Using a 290 w/ decent results, but the plug is all black... (probably the pilot, IMO).
V
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