High RPM Problems

[chuck]

My 72 125 six day is missing, belching, burping at high RPMs. Any thoughts on what might be causing this? I checked the main jet and it was clean. Is there anyway the PVL ignition could be going south?

Thanks for the help.



Chuck,


72 125 Six Days
74 250 Hare Scrambles
74 250 Maico
73 250 Honda Elsinore

[brian kirby]

Bing or Mikuni?

Brian

'72 Six Day (on loan from Ernie P.)

[chuck]

30mm Mikuni

Chuck,


72 125 Six Days
74 250 Hare Scrambles
74 250 Maico
73 250 Honda Elsinore

[wfopete]

If your PVL has been neglected and contaminated by moisture and corrosion, it could go quick. Mine PVL got me though a CC parade lap, then never lit off for the start due to the above neglect. Check grounds and all conections, shoot with WD40 and cross your fingers.

Pete Petrick
175 'Piner

[VICTOR MONZ]

Chuck:

What jetting are you using on the 30 mikuni?

Victor Monz

PS>  Donny Smith, if you see this I could use your help in jetting this 30 Mikuni.

Thanks.

Victor Monz

[chuck]

Victor,

230 main, 2.5 slide, 6F5 needle, 35 pilot, P5 jet. I've had the carb on for over a year and it has run fine. The last time I took it out it started missing bad at higher rpms. I'm down to the PVL as the culprit unless someone has some other ideas. I've checked all the jets for dirt, cleaned the carb. Cylinder and head gasket OK. I'll play with the PVL this weekend. Could a bad ground cause this at high RPM. I did have some moisture problems in the ignition earlier. Could be a delayed problem from that.

thanks,

chuck

Chuck,


72 125 Six Days
74 250 Hare Scrambles
74 250 Maico
73 250 Honda Elsinore

[Ernie Phillips]

Christopher's bike is a '72 Six Day with a 28mm w/180 main jet.  It is a little rich.  With a clean filter, it runs without missing on top end.  As filter gets dirty bike starts missing on top.  We need to rejet.

I would suggest removing the filter and running down the road to see if it improves. If so, clean filter and jet for conditions.

Ernie P.
Chattanooga, TN

[brian kirby]

quote:Originally posted by chuck

I've had the carb on for over a year and it has run fine. The last time I took it out it started missing bad at higher rpms.

I have a bike with a Mikuni that is doing the same thing. Its been on the bike a year and last time I raced it, it started to miss on the top and got gradually worse over the course of the weekend. I swapped all kinds of electrical stuff and nothing worked. As a last resort I swapped an old Bing and it ran better. I took the Mikuni apart and everything looks perfect, I cant find anything wrong with it.

Brian

'72 Six Day (on loan from Ernie P.)

[socalmx]

I am currently running a 30mm Mikuni with no problems at all.My two cents worth is that there is either something wrong with the jetting or the ignition is not up to par.

[hrbay]

try putting some better gas in it, gasahol may not agree with your motor.

GC

[TGTech]

Chuck,
The ignition can be an issue, but if it starts OK and works through the mid range, then the actual components are probably not the problem. The first thing that you should do, is to make absolutely sure that there is no rust or corrosion in the grounding path. This includes the coil to frame and the engine to the frame. Then make sure that the spade terminals are tight on the coil. If they are loose, that can cause issues. Finally, make sure that the spark plug cap is installed properly, where the plug terminal is connected correctly to the wire.

The carburetor can also be an issue, depending on the pipe and engine porting. If the engine isn't capable of efficiently flowing the amount of air that the carburetor will supply, then the jetting can be very tricky. As the amount of air increases, the air speed drops, and this will make the carburetion more tricky. You may have to mess with the slide, the needle, and the needle jet as well as the main and idle jets.

There is one other issue that you may be dealing with. Are you running one of the "G" series NGK plugs? I have NEVER had any luck with these plugs, so if you are, get rid of it and go to one of the V, VX, or IX series NGK plugs. My kid's 60 wouldn't run with the G series plug, but with the V or VX series plugs, it ran just fine. And I didn't change anything else.

Dane

[Ron]

Hi Chuck,
I'm surprised your bike ever ran clean with the jetting you have?
I went up to a 200 main in my 30MM before it started to stumble (to rich) and backed it down to a 190.
My throttle response is excellent with a N8 needle jet and 6DP17 needle (middle clip) and a 50 pilot jet. My idle wouldn't clean-up in 3 turns with a 55 pilot, but its at 1-1/4 turns with the 50 and it clears nicely.
I would think a 35 is way to small.
I also have a PVL and my bike starts on one kick cold and half a kick warm.
Hope this helps.
RonW

[chuck]

Dane,

You hit it on the mark. I checked the ignition wire and there was some wear, the outer sheaf was worn completely through. I taped it up and it seems to have cleared up the problem.

Thanks for the help.

Chuck,


72 125 Six Days
74 250 Hare Scrambles
74 250 Maico
73 250 Honda Elsinore

[chuck]

Ron,

I will definitely try different jetting based on you recommendation.

Thanks,

Chuck,


72 125 Six Days
74 250 Hare Scrambles
74 250 Maico
73 250 Honda Elsinore