using your words it was burbling under acceleration with the 390 jet in first and second gear quarter throttle if this helps with describing it better
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using your words it was burbling under acceleration with the 390 jet in first and second gear quarter throttle if this helps with describing it better
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Your main jet has next to no effect on ¼ throttle opening operation. That would be your air screw, pilot jet and needle in that order. The main jet becomes the principal factor around ¾ throttle.Originally Posted by knipfeldustin
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Arm chair racerThe day begins with 3WW
It is not wrong per se, it is just not the best way or maybe the only way that it should be tested. There is A lot MORE TO READING a plug then you might imagine. the color of the porcelain near the tip can tell something about a different throttle position ir rpm etcc. The electrode strap thells you things. the outer ring or end of the threads tells you something but in the end if you have a peefect looking plug and your bike runs like cr_p then you still need to jet it. Unfortunately it is NOT something that is a pefect science that you can put in a box. It is just a general guide. Timing, plug heat range and oil ratio etc affect plug color. I don't obsess about it. As I mentioned, Kawasaki...over 200 championships...never cut the threads off a single plug.... The one exception might be Rob Muzzie and the road race team but i don't know. I can also pretty much guess that Honda was not out there at Unadilla or Hangtown during a National, hackin the end of Marty Smiths plug either.
Did it burble/sputter at wot?
What does the new plug look like with the 390?
no prob you're welcome, however, of course it's not caused by an air leak. Like I said...your bike runs with no electricity.
then just ride it normally as long as you can while trying to avoid what ever causes the problem so you can get some time on the plug.
You did not previously say it sputtered with the 370. the main is contributing little to the sputtering at that position. It is mainly the needle and the pilot. If it starts with no choke then maybe go down 1 on the pilot jet.
YOU SHOULD TRY DROPPING YOUR NEEDLE ALL THE WAY DOWN. IF IT IS ONLY 1 OR 2 CLIPS FROM BEING DOWN IT WILL NOT HELP MUCH BUT TRY IT ANYWAY. IT SOUNDS TO ME LIKE YOUR NEEDLE JET MIGHT BE TOO BIG OR YOUR NEEDLE IS TOO SMALL IR THE TAPER IS INCORRECT.
IT IS POSSIBLE THE CHOKE HEIGHT OF THE JET NEEDLE IS TOO HIGH ALSO. You need to give us all the numbers off it. or just post a photo of it in the carb for now.
your slide might also be wrong. we need that number.
It is likely big enough imo.
yes it did, this is why it runs with NO ELECTRICITY.
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I would do the following also.
The following gas level test eliminates the need to check the float level and can be more accurate. It should also be done PRIOR to jetting.
GAS LEVEL - Check the actual gas level first by doing the following:
1. get a small 10” long piece of clear plastic tube.
2. connect it to the float bowl drain fitting.
3. hold it close to the carb with the open end even with the top of the carb.
4. open the gas valve on the tank and drain screw on the carb bowl.
5. the gas in the tube should be from even with the bottom of the main carb body to 3/16” below it. If it is outside this range, I would correct it.
If your gas level is high but you have plastic floats you might need a new float or possibly heat that one and bend it.
Also if the level is high it can cause big problems and you will likely never get it jetted properly.
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I stated this because the manual for this model carb stated main jet affects 1/4 to wide open throttle. The mikuni vm super tuning manual by mikuni is what I printed off the web for the info I have on the vm model carb.
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The bike runs great at wot throttle until you let off and then it immediately starts the insanely high rev crap and continued for 7 seconds today, I originally stated it did this for 30 secs which was a overestimate I'd say the longest it's continued to run was 15 secs max
. I did not pull the plug after riding with the 390 jet as I only got to third gear and went to downshift to turn and as soon as I clutched engine began overreving so I pulled kill switch to get it to stop.
In my post I didn't mean it sputtered with the 370 jet I meant it ran very similar to running the 390 and was just a little sputtering in the bottom spectrum of things with the 390 jet only.
I did happen to notice today when I pulled my slide that the needle is all the way down(clip in top position).
I will get some numbers and pics of everything in the morning.
I actually went through the steps of checking the floats according to the manual and they both measured correctly. I will still run your tube test tommorrow and see what happens.
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.
Heir Knipfeldustin.
Does it still run with no electricity with the 390 main jet when the high rev situation occurs?
1. Yes.
2. No.
3. I don't know because I did not try it.
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Arm chair racerThe day begins with 3WW
Heir Knipfeldustin.
Did you lower the slide all the way and try it as Barn suggested earlier?
1. Yes.
2. No.
3. I don't know because I did not try it.
Did it stop immediately?
If not, how long did it run before it stopped?
Did it actually run with no electricity with the 390 main as you previously said?
1. Yes.
2. No.
If it stopped immediately, then we have cured your running with no electricity problem.
OMG...The pig is interrogating Knipfeldustin...Barn used the wrong photo..what a moron!
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Yes.......
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No I have not tried lowering the slide yet. (Will do today)
No it did not stop immediately it continued to run for 7 seconds(with no electric) at extremely high rev after I pulled the kill switch with the 390 jet.
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ok, let us know but i'm not holding my breath for a positive result.
son of a "bleepin" "bleep". WTF is its prob?
Try a 10 heat range plug today too if you have access to one.
i would not do a ton more with the main until you try that unless you have a bigger main or can get one easily. i know you said all you have is a 390. based on everything, i really "think" that is large enough but in your case it appears that we need to throw the entire book at it which is nuts.
some race bikes can tend to run on after the electricity is stopped but that's typically because they run near the edge of destruction to try and gain that tiny edge in hp, however, this should never occur on a non pro race bike because there is no point in running near the edge.
there was a guy on here several months ago that had a run on prob after it was turned off. he finally removed his head and it looked like someone had taken a center punch and hit the combustion chamber a zillion times. this was actually caused by detonation.
around the tiny dents were very sharp raised pieces of metal. i don't remember if he sanded them out or got a new head but i think he sanded them and it fixed the problem.
your bike does not detonate/ping now but it might have before you owned it which might have created the same prob inside your chamber. the ocurrence you have now is actually called pre ignition. some call it "run on" or "dieseling" these two latter conditions occur AFTER the ignition is turned off. i have never seen them cause a high idle after wot.
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I live in the middle of no where so I won't be able to get a plug besides the stock ones I keep around here. I was told ons.com that this bike was raced in the 80s and was even featured in some of the old dirt wheels parts ads. ( I've yet to track one down so I have no proof) everything on this bike is set for tt racing (wide axle,extended swinger, works rear shock in lowest mount setting, roost factory air box, dg head, 38mm carb) it's def a top end motor
What gets me about this is that if I drive around at say half throttle it does fine and comes back down fine when letting off it and won't cause any issues.
It's only at the wot throttle where it does it every time consistently.
Sometimes the rpms are extremely high and will fall just a bit then repeat until it stops (370,380 jets)
Sometimes the rpms just stay extremely high and don't fluctuate. (Yesterday with he 390)
I only tested onetime with the 390 due to being pissed and tired of screwing with it.
The gentleman I bought this from I believe is a member here maybe captain wheezy (not positive) he said he never really rode it he got from a family friend who passed so I don't know much history on it. I have no idea what all is done inside engine honestly....it's about time to find out I guess!
As I side note I tried a test of my own and I turned the choke on and left it on while I rode it through the gears this morning it did NOT do the death rev thing after wide open throttle....of course it was running like it was flooded but the bike let the rpms fall back down instead of holding them at wide open.......I'm not sure if this helps or gives us any usable info just an idea.
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Slide #
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if this is the case and it was raced in the pro class they were running race gas or they were getting their hieny beat.I was told on
yes we got that.
Ok, great thinkin. whish i would have thought of that.
It "suggests" [does not guarantee] that it is blazing lean. keep in mind, it burbles around 1/3rd throttle so it is RICH at that position not LEAN.
the extra gas might be enough to cool the cylinder below the point where it auto ignites the gas. the 10 plug will also reduce cyl temps but will not cause an excessively rich condition. hopefully you now see why i and others have been trying to reduce your cyl temps. the colder plug will do that, however, it might not do it enough. this is where timing and jetting etc.come in.
since you have no bigger main jet, I would try it with the fuel mix screw out one turn and then turn it in all the way. if it runs horrible or won't start with it in all the way, turn it out 1/2 way. one way makes it leaner all the way thru the throttle position and the other way makes it richer. at the very least i see a 400 - 410 main jet in your future sat the very least.
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I was wrong thought needle looked like it was all the way down but it is not I can move the clip up two more spots....sorry for the incorrect info
Needle says ... 6dpt Or 6dpl Hard to tell I'm leaning towards "t" as the last digit
Here's something I noticed on the carb cap this morning the underside of cap appears to have a sealant applied but is dried and not sealing anything .....could it be pulling air through this cap gasket after slide is closed allowing it to continue running ?? Idk just a though
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