Topic: starts easy, runs good... park for 10 min... won't start. WTF!

[1974blaze]

i am at the end of my rope with this little cb125s.  i finally have it running pretty good all in all, but this damn starting then no starting thing is bull#$%*.  i have a fuel filter in or i would suspect the idle jet plugged, i would suspect no spark, but i'm felling like i've sorted that all out now.  i drained the bowl thinking it was overflowed.  what makes a hot bike not start?

please, someone... be my hero.

[Alan F.]

Maybe the threads on the CB650 hot start issue will help?

[1974blaze]

did a search earlier and seemed a little different but i'll have another look.  thanks.

[Frankenkit]

Are you using the electric starter?

[Ernie]

make sure your gas cap is venting and not creating a vacuum lock effect. if good, check for spark while hot, maybe bad condenser

[dusterdude]

or coil

[1974blaze]

yeah, i had hoped to have eliminated those.  tested coil and condenser at the shop.  seemed to be working fine, but of course they weren't hot when tested.  gas cap vents, fuel flows.   kick start only. 

is it possible that the valves need adjusting? like they are not opening when hot, i heard this might be the cause on another board, but i dunno.  also, i'm in colorado, so how about jetting thoughts?

[w1sa]

Marginal or inadequate valve clearances can cause the valve(s) to not fully close/seal when hot. This lowers compression and can make hot starts more difficult, often requiring better and faster 'kick' technique.
So, check the valve clearances for surety and tune-up purposes , anyway.

A higher altitude might require some carb tuning if not already done, but you need the rest of the engine tune-up to be done before properly assessing carb adjustment requirements.

[Frankenkit]

yeah it's the opposite of my hot start problem- I was just fine in ten minutes, but starting immediately was the problem.

[1974blaze]

i'll do the valves this evening.  then after i run it, assuming it starts, i'll recheck for spark, all with the petcock closed to stave off vapor lock. sound about right?

[Uncle Ernie]

I trust you will re-torque the head bolts before checking the valves...

My humble experience is that older bikes- especially singles, load gas up and flood EASY.  When hot, try opening the throttle almost all the way.  This puts more air in there to balance out the gas build-up. 

Also, what does the plug look like?  You can usually hasten the starting process at the gas station by just putting in a new plug. 

[1974blaze]

please explain more on t tightening head bolts?

i adjusted the valve clearance, seems a little tight, a touch noisier now, but nothing crazy.

bike started on second kick.  let it warm up, rode 5 miles through all gears.  a little puttery or lurchy like it was missing or running put of gas, but none the less running and up to speed. 

left the engine running when i pulled into the garage, got out the timing light and checked the timing. of course, i stalled it in adjustment and guess what... yup, with timing back where i started (static setting) it wouldn't start.

went out for breakfast.  came back, started on 3rd kick.  turned off the key, turned back on, tried to start, nope...

as a side note or clue, i feel like it idles high after it's fully warmed, like ridden for a little bit, regardless of idle screw turned out. 

this flooding theory feels plausible to me btw. but i'm giving no gas at restart and it does like being choked at cold start.  full choking after that will kill it.

[Uncle Ernie]

First; head bolts.  From time to time- depending on the dactory recommended intervals, the head bolts need to be loosened and re-torqued.  One at a time, in a cross pattern;  12 o:clock, then 6 o:clock, then 10, 4, 2, and 8.  I don't know why, but you're not supposed to just go around in sequence, one after the other.  The reason is that even head bolts get out of adjustment, and when they get out, then the valve adjustment will never be right.  You need a decent torque wrench to do this.  Find out what the recomended torque for YOUR head bolts are supposed to be.  As always- no points for being a gorilla.

If the idle screw has no efect on your idle, you may want to try messing the the mixture screw to lean it out a hair. 
When you twist the throttle, many people think you are giving it gas.  You are not.  You are opening the throttle which lets more air in.  The air then draws more gas.  So, different chokes work differently, but you should use the choke without twisting the throttle when starting. 


When the bike has been running (expecially rich), it is coated with gas.  The spark plug will probably be wet.  By opening the "throttle", you are letting in a lot of air with tends to dry out the plug and get it to work.  It won't kill you to try it.  Open the throttle all the way and kick through TDC. 

It doesn't sound like timing is an issue at this time.

Get a manual for tech specifications.

[Uncle Ernie]

Well?

[1974blaze]

i'm attaching a plug pic. looks a little hot/lean, but not THAT bad right?

tried the open throttle trick to no avail.  i believe the high throttle had to do maybe with needle clip in wrong position, centered it and seems to be fine now, thought i wouldn't have thought that would matter in idle.  still haven't done the head bolts, i have to get a decent torque wrench for it and , well...

my next idea is to post a video and see if it looks to anyone like i'm doing something weird in start.  or...

ride to my mechanic's garage with a six pack and offer it up to the first guy who can start the bike in the first 20 min i'm there.

[1974blaze]

update.

i think i'm on to something.  in a discussion with my mechanic we realized that i have the airfilter screen in but no filter, so, she's lean. 

i bought some foam from him and wrapped it around the screen, still haven't sealed it with weatherstrip and sprayed it with oil, but...

i was able to ride down the block, come back and.. with a little finesse... start it back up.  twice. 

so, i will finish the filter and re-set up the carb to suit the new air situation.  then we'll see.

[1974blaze]

update.

things went back to how they were after a tune up.  and it was time to timecert the spark plug hole, so i brought her down to mech shop to have that done.  brought her home and with kick all i got was the nastiest backfire i ever heard.  sounded like a dwarf cracking a bullwhip inside my muffler.  ouch.

time for a new tune-up with proper spark plug fit anyway.  went through it all again, tappets (.002) carb (cleaned idle jet, set floats) timing (static check looked good as is)

kicked... and.... nothing. didn't even try.

so i pulled out the air filter. 4 kicks and a little giddy-up.  couldn't keep it going though. 

theory, there are multiple issues at work here.  but mostly, it's all about the carb. 

it's worth pointing out that i had it running last summer quite well with little starting probs.  never a problem warm. 

[Uncle Ernie]

Where did .002 come from- is that the manual stetting?  Seems kind of skinny to me, but if that's what the manual says...   Torque the head bolts yet? 
What is different from last summer?