Board index Flathead Power-Technical Questions, Answers, and Suggestions Pans Hard starting when engine is hot

Hard starting when engine is hot

Post Wed Jul 26, 2006 1:43 pm

Posts: 180
Location: Nashville, TN USA

My '60 FLH starts on the 3rd kick every time when cold, but she don't want to fire when hot. I've been told that's typical for pans due to vapor lock in the lines but don't remember any problems in my younger days. At my age and weight, I can't kick the thing for an hour!!!!! Time for an ElectraGlide?

Post Wed Jul 26, 2006 5:25 pm

Posts: 646
Location: Detroit
If it's hot or even warm don't use any choke. If it won't start on 3 - 4 kicks vary the choke (maybe half way to full open) and hold the throttle wide open as if to start it like it is flooded. If you flooded it excessively you may have to pop your air cleaner cover off, too. Sounds like you carb is on the way out.
New Knuckleheads? Thank, you, Jesus!!

Post Sat Jul 29, 2006 7:55 am

Posts: 197
Location: Bucktown, PA
If the stuff that should work doesn't, you have to try some stuff that shouldn't work (what'd he say?).
All these things are different, and they all have their quirks.
Try a couple clicks on the choke, and/or holding the throttle wide open.
Try retarding the timing a tad.
You could even close the choke, open the throttle and give a couple prime kicks like you do when it's cold. This sometimes does it for me when Wilbur the Warthog ('64FLH) acts up when hot.
And check for intake leaks!

Post Mon Jul 31, 2006 5:39 pm

Posts: 87
Location: Finland, Europe
During our 38-year companionship my Panhead has always been tricky to start when hot or half warm/cold. It was the same when it was a rundown expolice bike, as after a first-time backyard motor rebuilt, and 16 years ago after serious blueprinting. First I give two strokes ignition off and throttle full open. Then I kick it slowly toward compression, turn the ignition on, and kick it, thottle in less than half open position. If she does not say anything, I give one more kick. If still no sign of life, I swtch off and do the same with 1/4 choke. I could kick all day if I just go on kicking. I always have to start the procedure again. If on the other hand she backfires or just runs putt, pufff... You just have to start over priming with 1/2 or 3/4 of the choke on. Gradually giving more and more juice finally bribes the old girl to fire up. But you have to be faster than a cobra to open the choke, as it does not run many seconds with the choke closed when hot. You can say that she starts on the first kick, if and when all things are in the right positions. The only problem is to figure out exact which positions are right for the time being. It never hurts to pat the old girl on the tank together with a few encouraging words, especially if there are a lot of experts gathered around. But these bikes are all different, which is part of the fun.

Post Tue Aug 01, 2006 9:14 am

Posts: 646
Location: Detroit
That sounds about right but I always use some retard, whether hot or cold, and more when cold. If you don't have stock bars with the advance retard cable a spring on the circuit breaker pulling it toward full advance works wonders.

The set up on Morris Mags is similar and is supposed to "auto" advance and retard through the use of the springs under the base. You initially flip it to retard, start the bike, and forget it. Mine, when I do use mags. works like Morris says it will.

You are right though, between hot and cold can be challenging: exactly how far between "hot" and "cold" is always the problem and part of the fun.
New Knuckleheads? Thank, you, Jesus!!

Post Wed Jun 06, 2007 1:00 pm

Posts: 3
Location: tulsa,ok
After reading the problems some are having starting their bike between hot/cold,thought I'd throw in my 2cents.I myself have been having problems recently.(28plus years riding/wrenching kick start bikes) I've began to wonder if the hard starts are due to my using HD's "H"cam. Both of my bikes(51FL and 58FL)act the same.Great starts when cold,but questionable when warm/hot.I believe I've eliminated ablut everything else. Anyone ever do comparisons between the cams? I'm 59yrs old now,and am willing to sacrifice some performance for more reliable starts!....walt

Post Wed Jun 06, 2007 2:09 pm

Posts: 2688
Location: Los Angeles, CA
How does a gravity feed fuel system vapor lock? With the carburetor below the tank any vapor would rise to the top of the line and enter the fuel tank through the valve. Vapor lock is an unheard of thing on a Model A Ford for the same reason.

Post Wed Jun 06, 2007 3:16 pm

Posts: 87
Location: Finland, Europe
Chris, the fuelline makes all kinds of curves on some models and then we have the fuel filter. More than vapor lock in the fuel lines I suspect the intake manifold which is very hot and the fuel fumes disapear.

Walt, I have used diferent cams in the 52 Pan. Originally a low power F motor. Always the same. My 47FL does not behave in the same way although the construction is very similar. It is a better starter as it is quite indifferent to engine temperature.

Krazy, yes I too always retard the ignition, just forgot to mention.


Post Wed Jun 06, 2007 8:49 pm

Posts: 3
Location: tulsa,ok
I also own a 47FL and have never had any hard starts.The cam is factory original,and,I've ridden it across country with no problem starts!I also run the same carb.(SU)On my Pan,I've tried three different ignition systems.(complete including coil/coils,both single and dual fire)I also worked various advance curves to no avail.(auto advance distributors)(Using a degree wheel and advance jig,I've varied the initial timing from 1degree to 20plus for starts)Currently,I've settled on approx 14degrees. (initial with 35 degrees total)I'm riding the 58 every night now and trying something different each night.Making one change at a time means it's time consuming,but someone has to do it!(I just don't like the"experts"watching an old man have trouble starting a real bike!)Sometimes,no matter who you are and how many times you've did it,one can run in the wrong direction!One of the guys commented to try something that shouldn't work....maybe I'll work my way there! the way,has anyone ever checked exactly how far the original advance mechsm(65-69 or even later mechanical advances) would retard the timing?

Post Thu Jun 07, 2007 1:06 am

Posts: 87
Location: Finland, Europe
I sincerely do not think retarding really helps starting itself other than avoid backfiring and undesired air trips. You can retard the ignition so much that it almost does not run anymore. If it won't run it won't start either.
Remeber that on a traditional motorbike you kick once and the motor turns over three times. On a Big Twin you kick three strokes just to get one of the pistons into position at the compression phase. At this moment the spectators anyway start laughing that it does not start. So with these cards on your hand you can't win.
A friend who has a restored '49 claims that the starting got better after installing one of those electronic breakerless pieces that go inside the early distributors. When we rode home from the national Panhead-Rally it started on first kick every time. But these are all individuals. I would not have it any other way.

Post Sun Jun 10, 2007 9:23 pm

Posts: 3
Location: tulsa,ok
Well,I've been out every night riding and starting my bike,and each and every time but once,it's started first kick with ign on!I followed your advice by holding the throttle full open,kicking thru until compression is found,then reduce throttle to approx 1/4,turn ign on and kick.
I once had a fellow mechanic tell me that one needed to have a special"sense",a certain"feel" for starting these machines.I've always had pride in how my machines start.(28 plus years of riding and kicking they better be good starters!)After trying numerious mechanical changes and not making any true headway the last couple of years or so,I thank you for getting me in the right direction on my routine for starting a warm/hot motor!...walt

Post Wed Jun 13, 2007 2:41 pm

Posts: 87
Location: Finland, Europe
Well done bro, it never hurts to have a serious talk with the old girl. When she agrees that it is in your both interest that she fires up on the first kick, you are there. I'm still arguing after 39 years...
Theory: Everything is perfectly right, but it does not work.
Practice: It works but you do not know how.
We combined theory and practice: Nothing works and nobody knows why!

Post Thu Jun 14, 2007 6:46 am

Posts: 32
Location: WV
Well if I can add to this conversation...I was running a Linkert 22 years ago, and was actually winning money starting this pig...then speed came along...put one of those fancy carbs on with all the things you turn, pull, push, and pray....hated it...hated riding, well stopping anyway...kicked my ass off...last summer was the killer...90 degrees, humidity was off the board, I was in the middle of a field, no shade kicking....lost 5 pounds that it home that day and bought a M74B....after a new top end his winter I put the newly purchased linkert on...cold...choke on, retard, 3 primer kicks, turn switch on and it fires...everytime...after that ALL day long...turn switch on and first kick...back to winning that I have told that story, I will probably never get it to start again...LOL...I guess my point being that I personally would rather have smoooooooooth starting and running than top end speed....nothing up ahead I need to see that bad....good luck guys......Skip

Post Thu Jun 14, 2007 10:50 am

Posts: 309
Location: Ohio
I also have been fighting with my 56 once the engine gets hot. Like the rest of ya. I start telling myself that I'm getting to old for this crap. It came to me with a Super-E shorty. Every time I'm kickin my but off I tell myself I got to try finding a linkert to put on it to see if it indeed would make any differance. It sure can't be worse. Right...?

Post Thu Jun 14, 2007 10:02 pm

Posts: 1038
Location: Ojo Caliente,NM,USA
when one won't start hot the first thing I check (usually by substuting a known good part) is the condencer. Then I check the spark with a sparkgap tool. When you can't fix the carb no matter what you do maybe it's not the carb!

Post Thu Jun 14, 2007 10:05 pm

Posts: 2688
Location: Los Angeles, CA
Hell, my Sportster won't start unless it feels like it.

Post Fri Jun 15, 2007 6:45 am

Posts: 3159
Location: Central Illinois, USA
Dusty wrote:
" When you can't fix the carb no matter what you do maybe it's not the carb!"

That's why I have enjoyed servicing carburetors:
I always suspect the manifold first.

(And Pans have been found to leak even at the valvecover screws over the intake ports!)

Back to the heat issue:
Cold motors require a much richer mixture when cold than warm. That's why chokes were invented.

If a hot motor is hard to start for no other reason than carburetion, then it should be suspected to be too rich. This can occur because the machine is tuned to maximize cold starts, without fully dialing in the high speed mixture. The Panhead carburetor's circuits will affect each other, and trimming to find a medium between the two takes alternating trials. (Referring to real Pan carbs, of course!)

Ideally, settings can be found that offer easy starting as well as highway performance.
However, the transition from low to highspeed circuits can be complicated by borewear from the throttledisc. When the eyebrow groove of wear into the carb casting extends as far as the idle bleeds, then idle and lowspeeds must operate under conditions that are no longer intimately controlled by the disc. So optimizing the low may conflict rather than compliment the high, especially if you are trying to fatten it up to cure the "flat spot" so often associated with excessive bore wear, loose venturies, etc.

Meanwhile, like Chris,
I think Harley gasline vaporlock is a myth.

(I truly vapor-locked a machine once, but it was a '62 Ford and it was the motor that stuck until it cooled down. Pressure within the cylinders wouldn't let the intake valves open.)

Just my opinions, for what they are worth.


Post Fri Jun 15, 2007 9:57 pm

Posts: 2688
Location: Los Angeles, CA
Meanwhile, like Chris,
I think Harley gasline vaporlock is a myth.

A vapor lock occurs when the fuel boils and turns to vapor. It is common on older V-8 engines where the fuel filter and line ran on top on the manifold. My 1964 Impala SS 409 car had a factory line that ran from the fuel filter back to the gas tank to allow the vapor to bleed out of the system. Harley put a thick insulator block between the carb and manifold to stop any chance of a vapor lock.

Post Sat Jun 16, 2007 9:28 am

Posts: 1536
Location: S.Calif.

My opinion about hard starting: A 61 or 74" big twin should start by the second kick (with the ignition ON). If it does not start, you've got some problem(s) somewhere: carb adjustment, valves not seating, air leak, or an electrical spook. [Note: A rarer problem occurs when both bushings in the timer are worn, which causes missing at higher than idle rpm. A symptom of worn bushings - is when static timing with a 2-wire socket light bulb, and the ignition "ON", the bulb should light (or go out, depending on how you have it hooked up) immediately, as soon as the timer is retarded. When the bulb won't light (or go off) immediately and indicates worn timer bushings.
Aftermarket coils can cause intermittent problems, or a lousy condenser. No way should you ever have to kick the machine over repeatedly, ever. They were designed to run dependably. And from 1936 to 1964, big twins were designed to require a minimum of effort to kick-through. The motors were only suppose to be a half-heartedly "bump" kicked, not jumped on like the longer stroke Shovelhead demanded.
If you put another carburetor on other than a Linkert, then the problem ratio is increased.
Stick with original engineering and components. People try to "improve" on original engineering and they get problems. What real good is a SU (sounds like a Volvo name) carburetor over a Linkert? Can you even feel any improvement? I don't think so. You just lose your internal throttle coil and control wire and muck up a terrific package trying to be different. Find the problem and fix it. All of the symptoms are in the '59-69 service manual.

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