High revs at startup

[Lutz]

Hi everybody.
I've been meaning to ask this for a while, but I just haven't until now. When I start my bike when the engine is cold, as in not warmed up yet (not cold outside, although it does happen when it is cold outside as well), it will rev up very high for a few seconds (maybe several seconds).

I'm sure this is a jetting "problem," namely with the pilot jet/circuit. Everything in the top end was new as of last spring, and I didn't ride much over the summer. I do have the bike jetted pretty well: it runs cleanly, no bogging (lean or rich) anywhere. I did play with jetting a lot over the summer, and as I recall my jetting for the summer was 152/cel#3/40. This was in 75-85 degree or so temperatures and about 600 feet or so of elevation.

The problem, as I said before, only occurs when the engine is cold. A dirty air filter seems to aggrevate the problem. Also, the choke has little to no effect on the problem.

So my question is, is this an indication of an overly lean pilot jet? Or could some other part of the jetting circuit (air screw)? Logic seems to dictate that it must be a lean pilot circuit, but as we all know, logic isn't always correct. Most of my confusion comes from a very foggy memory of a thread that 'maybe' said that too fat a pilot could have this result.

I never did any testing to find a jetting combination that made the motor not rev up when cold-started, since it usually isn't that bad- I only jetted while the engine was warm. Sometimes, though, the motor revs up so much that it scares me: I don't want a cold seize!

Short end to a long thread: will too lean a pilot make an engine rev high when started cold?

Thanks in advance for the help.
Regards,
Lutz

 

[know_fear]

I'm guessing that your bike is a newer 220 with the RB carb mod, am I right?
That's what mine is with almost identical jetting (38 pilot) and with the same characteristic/problem. I was never able to find the cause but I wasn't too worried since the bike ran fine. I'm hoping that a cold seizure would only occur from high load on a cold engine rather than from high revs but maybe someone else could enlighten me.
While this was going on with my bike I noticed that I was getting more spooge and that my plug was fouling even though the cooler temps should of had me running leaner. I went to leaner jetting (35, CEL/2) but the plug stayed oily so I went back to the richer settings before I did some real damage. At this point I suspect leaking main seals but I'm still testing.
I realize that I'm only adding more questions to this thread but you can take some comfort in knowing you're not alone.

 

[Tom Ludolff]

Mine did that when I had the pilot circuit too lean. A 1/4 to 1/2 turn in on the pilot air screw should help.

 

[Lutz]

Nope, my bike's not a newer 220. It is/was a 1995 200; however it is now a 225 ala Eric Gorr. Mo-better porting, stock 35mm carb, Pro-Circuit pipe, V-force Delta II reed cage. I currently run pump gas, but I'm seriously considering switching to a race/pump mix, for various reasons. My bike doesn't produce excessive spooge, very little actually, and like I said before it runs very cleanly once warmed up. Warm starts result in the bike going to normal idle right away.

Another thing that should be noted is, as I recall, the bike did this in bone stock form as well-before any of the mods.

As I began writing just now, I began to wonder.... I am running pump gas, which has relatively high evaporation points. I wonder if this could mean very little fuel is vaporizing at initial startup, effectively leaning out the mix until a little bit of heat gets into the motor. Just a thought. Maybe Rich will read this and have some imput on that thought.

Thanks again.
Lutz

 

[Lutz]

Thanks for the reply Tom, it wasn't there when I started writing. I'll try that whenever I get a chance.

 

[Jim Crenca]

Fishead had reported earlier that a lean pilot can cause runaway idle at cold start up (with or without choke on). My 94 with the RB mod & 38 pilot has this same intermitent problem. One day when cold it idles too fast, the next day it doesn't. Tapping the kill button while you franticaly lower the idle rpm screw works OK, but then you have to reset idle after warm up. I too believe that pilot jetting is good but haven't check air screw as I'm happy with it's current, critcal setting. BTW, my intermitent cold idle has occured with different ambient temps, with pump gas and C-12; float level is right on the money and I can't find any vacuum leaks. :(

 

[canyncarvr]

A simple answer to your simple question (at the end of a long thread ;) )

Yes.


BUT....so what? I've found that if I jet for what the bike wants when I actually RIDE it, it will have the high rpm thing goin' on when I START it.

I use the kill switch to regulate the 'over-rev' situation. As you say, it only happens for a little bit. THAT depends on start method. I've taken to a NEW method myself.....a slight variation on what I've generally done before. I'll kick it real slow (with not much more than foot weight on it) several times before I smack the kicker good enough to start it. I can feel it 'burp' after a couple of slow strokes..that tells me it's ready.

When I do that, it's only a kick or two to start it...and I don't have so much of the 'overrev'.

I used to kick it (normal speed) with the kill switch 'on' a couple times, then try to start it. The 'slow kick' method works quite a bit better.

Still, a few taps of the kill button takes care of it anyway.

The bike runs perfectly when at temp......a little bother when it's cold is, well....not bother at all!

 

[Lutz]

Thanks guys. I figured this wasn't really much of a problem, and something that is easily dealt with, which is just why it took so long for me to ask about it. I had maybe forgot about using the kill switch to control revs, or maybe I just do it subconciously. I know I never let the revving get to out of control until I do 'something' about it. Just needed some confirmation, as they say.

CC, thanks for the starting suggestion. I pretty much do the same thing already, with one usual difference. The first thing I do when starting the bike cold is tip the bike to the left a bit and wating until fuel enters the float boal over flow tube. Then I know the carb is full of fuel, and it is right there for the engine when it needs it; then I follow the basic starting method you described. Starting usually takes just one or two kicks, more often one.

My Christmas break starts soon, and I'm hoping to get some good winter riding in. Some serious rejetting will be in order though. The bike was last jetted around 80 degrees F; now the good old sub-freezing winter temps are the order of the day. I also hope/plan to stud an old rear tire using carriage bolts too, for some decent traction. Should be fun, since I haven't ridden since September.

Regards,
Lutz

 

[canyncarvr]

To tell the truth...I hadn't used the kill switch to control the revs until someone else suggested it (I fergit who..O&S or 23jay maybe?). I figgered that would load the thing up so bad I'd have plug problems.

Not so.

I'd used the clutch to pull the revs down. Switch works better...wears the clutch a whole lot less!