Board index Flathead Power-Technical Questions, Answers, and Suggestions Knuckles 76 knucklehead problem

76 knucklehead problem

Post Fri Mar 13, 2015 12:44 pm

Posts: 3
A buddy has a 76 kncklehead that runs great until it sits for 8 or moe hours then he has to pull a plug and prime it with a little gas then it fires up and will keep firing up until its sets for to long! He has taken it to ever repair shop he can think of and replace carbs ignition wiring ,anything and everything with no luck! Anybody got any thoughts, I got a bet goin I can find a fix! LOL!

Post Fri Mar 13, 2015 12:46 pm
Pa Site Admin

Posts: 6039
Location: Ohio USA

A 76 Knucklehead ? :?

Post Fri Mar 13, 2015 3:00 pm

Posts: 1687
Location: Interlaken, NY USA

Manifold leak?

Post Fri Mar 13, 2015 3:29 pm

Posts: 375
Is it not normal to prime a kickstart motorcycle?

Post Fri Mar 13, 2015 9:43 pm

Posts: 497
Location: Six miles East of Cheney, Wa.
Possibly he's never established the right "routine" for starting it when its' cold/been sitting? Most every bike has it's own preferences, and it often takes some experimentation to figure it out.

I assume it's an overbored (.060"?) 74 inch motor? For sure, never heard of calling an engine by it's true, or over-bored size. My UL is a "76" but I wouldn't want to confuse anyone by calling it that...I'd just say it was a 74.

I'm also curious that someone running a knuck would have other people work on it...leads me to believe he just may not know what he's doing, or how to start an old kick-start bike. I certainly would never allow anyone to put a wrench to my bike, air the tires, or even put gas in it for that matter. Sacred territory! Really...if you can't wrench on an old bike yourself, perhaps.....???

If he's taking out a plug, and pouring gas into the spark plug hole, and it starts, I'm thinking that he hasn't figured out how many priming kicks it needs. ???

Good luck, I would bet that it's pilot error, and not the bike that's at fault. Also curious as to what kind of "repair shops" would be qualified to work on an old knuck. I'm kind of thinking zero to none.

Hope none of that sounded too harsh. No offense intended.

Post Fri Mar 13, 2015 11:55 pm

Posts: 1729
I had a 61" Panhead for a while which defied anyone to start it when hot (cold was no real problem). It received the attentions of various experts, real and imagined, more seals, carbs and ignition parts than grandfather's axe and never WAS sorted out. A great shame, as it was the sweetest iron-motor Big Twin I've ever known when running... I eventually sold it in frustration. I have been told it that it is currently enjoying a career as a trailer queen in Scandinavia....
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sat Mar 14, 2015 11:27 am

Posts: 497
Location: Six miles East of Cheney, Wa.
One thing I've learned the hard way is to always replace the condenser if starting becomes problematic. But often that's the last place people look. Back in the day, I know I completely took apart more than one carb, when it was the condenser's fault.

k.

Post Sat Mar 14, 2015 11:48 am

Posts: 375
Basically what you have to do with a cold motor:

1 choke full closed, throttle well open
2 kick the engine around 2-3 times
3 switch on ignition
4 dont forget to retard timing, else you can break a leg ( happened to my father twice)
5 open choke to half
6 kick
7 ride?

Is this not normal? The knuckles we have need extensive priming too..

Post Sat Mar 14, 2015 1:25 pm

Posts: 497
Location: Six miles East of Cheney, Wa.
Sounds about like how my Knuck started, I guess if it was very cold outside I'd set the choke to 3/4. My Knuck was always a good/easy starter.

The Little Mistress on the other hand, does not like much, if any choke. The pump-shot (Bendix) seems to be more than enough. However, if it's been sitting for a week or so, she can be a bit cantankerous but you just have to stick with it. With her, seems like it floods easy, although I'm not sure how that much gas flows UP into the chambers. With an OHV, the gas loves to drip down into the cylinders. Then once she runs, she'll start easy all day, and easier the next day. So there is something to the "sitting for a long time, hard to start thing".

I'd still like to know, is this a 1976 Knucklehead, :) or a 76 inch Knucklehead?

k.

Post Sat Mar 14, 2015 8:12 pm
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Posts: 6039
Location: Ohio USA

I am really curious wam5519 . Could you by chance be Yogi ? I new a Yogi by the name of Bill Miller 40 years ago.

Post Sun Mar 15, 2015 5:56 am

Posts: 3
Ok guys my bad its a 1976 knucklehead , you guys are great ! I like the condenser idea , and thanks for the starting sequence. Heres the thing this old boy has tried everything himself and then to every little self owned shop like you guys might have ,god bless you, and left the bike with them with no results . he has boxes of replaced parts ,carbs, manifolds, ignitions etc. thers gas to the carb but if it sits to long it wont prime itself, so any sujestions are greatly appreciated . and no ive never been known as yogi sorry been called alot of other things though! LOL! Thanks again guys

Post Sun Mar 15, 2015 8:00 am

Posts: 1687
Location: Interlaken, NY USA

If it's a 1976 knucklehead, then we may assume it's an aftermarket build from repro parts?
If so, need to know the following things as they can affect startability :-)
Stock cam or repro with stock cam specs?
Stock flywheels or repro flywheels with weight equivalent to stock (ie, torque monsters)
Stock stroke, or stroker?
Stock manual advance timer? or is it repop auto advance timer.
Linkert carb, or aftermarket carb, such as S&S, CV carb from later HD, etc.
All of the above can affect startability, and not, be "broken, or bad"
On the Condenser, it's worth checking, but usually they fail with temperature, ie get warm, get worse.
So, here's the deal on the above list.
If motor is not stock wheels, cam, and timer, these items can work in combination to produce a hard starting motor. Light wheels, cam with little overlap can make it difficult to produce adequate kick speed at time of ignition.
Auto advance can easily malfunction by hanging and not returning to static advance timing. Further, many make the mistake of setting timing with an auto advance unit for spot on advance at running speed, rather than setting for optimum timing at kick speed. Something that isn't important on an electric start machine, but very important for ease in kick starting. Trust me, on a kicker, it's ease in starting that's important, not the loss of 1 or 2 horsepower because the full advance timing is off by a degree or maybe 2.
Usually, static timing with spark at TDC is a good place to start. Advance slightly from there to find optimum for any particular bike.
Carbs: Too large of carb (ie S&S), may make it difficult to get a flammable mixture into the cylinders at kick speeds. Especially when cold. When an engine is warm, you already have a flammable mixture in the cyls, waiting for a spark to set things off. The HD CV carb is a good carb, but I recently had difficultly getting one of those setup properly for kick starting.
Just a few more things to think about on your way to resolving your problem.
DL

Post Sun Mar 15, 2015 9:06 am

Posts: 375
Frankenstein wrote:
Auto advance can easily malfunction by hanging and not returning to static advance timing. Further, many make the mistake of setting timing with an auto advance unit for spot on advance at running speed, rather than setting for optimum timing at kick speed. Something that isn't important on an electric start machine, but very important for ease in kick starting. Trust me, on a kicker, it's ease in starting that's important, not the loss of 1 or 2 horsepower because the full advance timing is off by a degree or maybe 2.
DL


Auto advance units have different curves that can be chosen, with various retard curves. The top half of the rotor can be modified to retard the retardfunction further or less.. that is ofcourse if you are referring to V-tronic ignition, otherwise I have no idea. The auto advance units should under no condition ever "hang" there is a serious piece of software engineering in there. I know that if the processor of the vtronic unit malfunctions it will reboot and find the correct ignition point again within 2 revolutions of the engine..

Post Sun Mar 15, 2015 1:22 pm

Posts: 1687
Location: Interlaken, NY USA

Referring to mechanical auto advance units, not electronic. Sorry, my mind was in the 20th century, not the 21. :-)
DL

Post Sun Mar 15, 2015 1:27 pm

Posts: 375
Aye I assumed electronics, as mechanical advance usually has no place on a knucklehead:)

Post Sun Mar 15, 2015 2:31 pm

Posts: 3300
Location: Central Illinois, USA
Golly Samsup,

My mechanical advance circuit breaker works fine on my '37.
But it has been fudged a bit....

...Cotten

Post Sun Mar 15, 2015 2:55 pm

Posts: 497
Location: Six miles East of Cheney, Wa.
Cotton you have a '37? Could be the sister of the Little Mistress! (which would be consecutive serial numbers)

Aren't some of the electronic units set up for electric start...requiring the engine to turn over one or two times before the spark kicks in? I've heard of guys putting kickers on newer bikes, but they don't start well (or at all) because of the lag between when the engine starts to spin, and when the spark begins to spark. I could have that totally mixed up, and wrong. And I'm not sure that would have anything to do with the cold/hot/sitting situation.

I'm not sure what kind of ignition the 1976 Kuncklehead came with.

ken

Post Sun Mar 15, 2015 3:17 pm

Posts: 3300
Location: Central Illinois, USA
Ken!

They are all sisters..

Now that I think about it, my other '37 OHV has a mechanical advance as well, but much more OEM, for a '66 or whatever, and less novel than my conversion of a "manual retard" assembly to "auto-advance".
(Or is is really auto-retard?)

I have no clue about modern "electronic" assemblies, although I am sure they could work fine.
(Just don't expect to fix one under a bridge abuttment in the rain.)

....Cotten
Last edited by Cotten on Sun Mar 15, 2015 3:31 pm, edited 1 time in total.

Post Sun Mar 15, 2015 3:30 pm

Posts: 375
Modern electronics really depend. The Vtronic ones are designed for kickstart, and have proven to be really really helpfull on hard to start kickstart engines. In any case, I think OPS specific case it is simply a lack of knowledge on older motorcycle start procedures..

Post Sun Mar 15, 2015 10:01 pm

Posts: 3
WOW ! Did I ever hit on the rite sight ! You guys are awsome! I will be using all of your suggestions to figure out whats going on and will keep you posted on the results, my friend will be bringing the bike here to Williston,ND in a week and said if I can figure it out he wiil make me a key so I can it when I want! Sold my flathead trike years ago and really miss the old ones. Thanks again Guys!


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