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Discussion Starter · #1 ·
quetion is its a 74' cone shovel mostly stock, dyna s ignition checkd the timing, plugs, fuel..Bike runs good until it really starts to rev and then it breaks up messed with the a/f mixter to bike was running great then it just startd to happen but low to mid range runs good..Havent checkd the pushrods, could that have anything to do with it still have yet to check them..
 

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dyna s are notoriously fussy regarding low battery voltage
No doubt check your charging system.If everything else checks out,what rpm are you seeing this happen at.
A broken inner valve spring are common and will give these symptoms at 3000 rpm up.
 

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Discussion Starter · #10 ·
Id say upwards of 3k, i could best describe it as it feels like its hittin a rev limiter it just breaks up..Thought it was the timin at first the waay it would kick back here and there but that all checked out..Runs strong like i said until you crank on it and the rpm's get up there and it just breaks up, the mech advance seems a tab worn were the pins touch on the base..
 

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Discussion Starter · #12 ·
Went over all the simple stuff first, starting to scratch my head trying to fig out what else to check, like i said runs good low-mid range once it gets up there it just breaks up hard..going to double check everthing again t n...
 

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If there's a circuit breaker on the battery, bypass it and then try it.
 

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FearNoEvo said:
dyna s are notoriously fussy regarding low battery voltage
I disagree. The 2K is fussy. I've had S ignitions still running at 7V. That's one of it's selling points for me. . . reliable on the road and durable even when your charging system craps out or your battery is on the way out.

It's only a hall-effect pickup. No computer chips.

Respectfully,
Jason
 

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79shovel said:
Id say upwards of 3k, i could best describe it as it feels like its hittin a rev limiter it just breaks up..Thought it was the timin at first the waay it would kick back here and there but that all checked out..Runs strong like i said until you crank on it and the rpm's get up there and it just breaks up, the mech advance seems a tab worn were the pins touch on the base..
Did you inspect the timing weight cavity when you serviced the weights? Look for marks of rubbing. The limiter pins and holes on the weight set get worn and allow the weights to travel too far outward. When they start rubbing the timing cover they'll give the results you describe. It's a short ride to totally bound up failure from there.

I've also seen aftermarket timing covers where the weight cavity is a little too small and will rub a set of weights that are in great shape. You can open it up a little with a die grinder easily enough. (Think CCI)

Otherwise, the broken valve spring as was mentioned sounds pretty reasonable if all else ruled out. With a broken spring, the valve will start to float/bounce at higher rpms giving your symptoms.

Jason
 

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I disagree. The 2K is fussy. I've had S ignitions still running at 7V. That's one of it's selling points for me. . . reliable on the road and durable even when your charging system craps out or your battery is on the way out.

It's only a hall-effect pickup. No computer chips.

Respectfully,
Jason
Its ok to disagree. Doesn't make you right. It may only be hall effect pickup, but its still an electronic ignition. Being an electronic ignition, it requires certain voltage levels to function correctly, to bias the transistors etc.

I run the dyna S in our gas drag bike, total loss electrical, no charging system, it gets below 10-11 volts and starts to act flaky at high rpm. In fact, one of the quickest ways for us to tell if that battery is full whack, is to listen to it going down track. Any misfires, popping etc is a quick reminder to charge the battery between rounds.
 

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I would imagine the drag bike is running a bit more compression than a stock '79 (7.5:1) Shovel.
 

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No doubt, but I have had the same problem on my 82 shovel with a dyna s.

May or may not be the problem, but its a quick, easy check to insure proper voltage where its needed.

For me trouble shooting any problem starts with the easy shit. Fuel, spark, compression, timing, etc etc etc. When the easy routes are exhausted, roll the sleeves up and start checking the harder stuff. I've seen many a bike torn asunder for very simple issues.

As a lark one time on a lawn mower forum, no shit, they exist too, I threw a question onto one of the diagnostic threads. I knew what was wrong because I had already fixed it, but I was interested to see where the so called experts would take me in trying to solve the issue. I described the problem as follows: Runs great at idle and up to mid throttle, starts to miss under load and full throttle.

Within about 3 posts, and going on for 4 more pages, they had me completely dis-assembling the engine. I finally let them off the hook and explained that cleaning and adjusting the points solved the problem in about 10 minutes.

Its easy to over look the obvious when frustrated, always start with the basics.
 

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FearNoEvo said:
Its ok to disagree. Doesn't make you right.
Not trying to be right. Just relating my actual experience with them.

Seems reasonable to me that 74" low compression motor with a stock 5 Ohm HD coil (my bike) might behave differently than a maximum-effort drag motor.

Mine ran down to 7V with the lights out. On a few occasions.

Jason
 
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