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78 LM running rough, and it's my fault. But what did I do?

R

rustyrotor

Tuned and Synch'ed
Joined
May 11, 2009
Messages
59
My 78 LM is the bomb. love it. Want to be buried on it, except that would cheat the next generation, and that'd be wrong.

I redid the fuel hoses and filtration.
I redid the 4 spark plug cables and cleaned up the coil connections.
Also redid the starter connection after I let all the smoke out of the previous one.

Everything looks perfect. The bike runs as good as ever, if not better.

But:

Subsequently, it intermittently loses either spark or fuel to one cyl...but not, apparently, completely.
As in it doesn't seem to be running on one cyl, but 1.5 cyls. And it is very ON/OFF.

I have basic tools, and very basic knowledge...

So, please, help me understand, explain to me in terms a 10 year-old can handle,
how do I diagnose this, step by step?
 
Re: 78 LM running rough, and it's my fault. But what did I d

There is a dearth of information here.

The statement 'the bike runs as good as ever, if not better' is confusing - has it always run on 1 1/2 cylinders? It should n't be hard to sort with even the most basic of tools.

What did you change? Can you figure out which side is misbehaving? Four cables - is your bike twin plugged? Did you replace the cables with solid wire or graphite? Did you use resistance caps or straight throughs? Did you replace the plugs and if so did you use resistance plugs?

Does it use the fuel crossover or did someone get rid of it?

Note To Pete: I sent you an email chastising you for not giving me a bell on your last trip - you missed free cocktails and the best ethiopian cookery in toronto. Bad Man! I gather your puter went down and you didn't get it. I also gather you went in for some surgery and have survived?

Ta,

Chris
 
Re: 78 LM running rough, and it's my fault. But what did I d

Perhaps you could start by giving us the spec of your machine e.g. what ignition system, is it twin-plugged etc
 
Re: 78 LM running rough, and it's my fault. But what did I d

Chris R said:
Note To Pete: I sent you an email chastising you for not giving me a bell on your last trip - you missed free cocktails and the best ethiopian cookery in toronto. Bad Man! I gather your puter went down and you didn't get it. I also gather you went in for some surgery and have survived?

Ta,

Chris
Click to expand...

Sorry Chris, if we'd known how to get in contact we would of! We had to go to Toronto to vote and after battling through the gurning hordes at the Oz High Commission we could of done with a good feed and strong coffee!!!! :lol:

Surgery has been put off until July :evil: So this trip to the US I'll be hobbling around with a bloody stick like the grand-dad of the oldest man in the world!!!! :mrgreen:

Pete
 
Re: 78 LM running rough, and it's my fault. But what did I d

Sorry guys, work work work. Appreciate the interest.

It's a great US Raceco motor. Absolutely everything in the guts blueprinted, fancy, Ti. Manfred Hecht built it.
Dyna. Four plugs. 40's.

The bike runs great...when it's not displaying the symptom.

The power loss comes on suddenly, goes away ditto.

I've looked for all the obvious things again and again.
Dodgy plug contact, loose connectors to plugs, kinked hoses,
all negative to my eye. The crossover is present. As are big brass and glass
sintered metal fuel filters.

The spark plug cables are graphite with a copper core.
Caps? Don't know what they are. Came with the cables.
Which came from an automotive speed shop.

The plugs are conventional. Bosch. SOS.

Crap in the carb clogging main jet? What would make it intermittent?

Could the Dyna be going?

But this started after I renewed the hoses and cables.
 
Re: 78 LM running rough, and it's my fault. But what did I d

Which hoses and cables did you replace? I'd start with those. For ignition on these bikes, I prefer solid copper wires with NGK 5K ohm caps. I've never seen much if any benefit from automotive performance cables. The symptoms do sound electronic, but an intermittent fault is the most difficult to find. I'd start by making sure all connectors are tight. A little wiggle isn't sufficient. Take them apart and make any necessary adjustment to make the connections tighter.
 
Re: 78 LM running rough, and it's my fault. But what did I d

Crap in the fuel taps; check the filters.
 
Re: 78 LM running rough, and it's my fault. But what did I d

I prefer solid copper wires with NGK 5K ohm caps. I've never seen much if any benefit from automotive performance cables.
Click to expand...

It is not a bad idea to drain the tank and take out the fuel taps and have a boo - takes about 10 minutes.

Graphite with a copper core? Usually it is the other way around - a graphite core wrapped with stainless wire.

I am with John on solid wire plus NGK caps. The NGK caps are cheap as chips. Keep a spare in case your bike falls over.

The only thing to know is to run non-resistor plugs - resistor plus resistor can lead to strange behaviour. THe original metal shielded Bosch caps were a short waiting to happen.

Maybe you can use a timing light to check if and which side is not firing if it is electrical? If one side is not firing check the coils by switching sides. Then check the distributor connections to the Dyna.
 
Re: 78 LM running rough, and it's my fault. But what did I d

I can pretty much guarantee it's Dyna related.

Check connections and grounds again. Also if the grey sensor wire that comes from the distributor is moved excessively that can cause the plate to fail and will give the symptoms you describe. Try gently jiggling it with the engine running, you may be able to bring the misfire on.

Coils should be the black 5 ohm ones. Plug leads should be copper core. NGK caps and plugs are great. BP8ES.

Check your battery connection too :D

Been there!!
 
Re: 78 LM running rough, and it's my fault. But what did I d

Roger that. Will clean out the taps etc. But it really feels electrical. Will do that (AGAIN!).

Thanks.

Starting a new thread. Forks!
 
Re: 78 LM running rough, and it's my fault. But what did I d

I had a similar intermittent problem on a stock G5 with Dyna ignition. Ran great at times and poorly at others. It felt like fuel starvation but turned out to be one of the hall effect pick-ups in the distributor, a new pick-up plate and it went away.
JT
 
Re: 78 LM running rough, and it's my fault. But what did I d

Had a similar sounding problem on my 78 T3 some years ago. Turned out to be casued by in line fuel filters. Ditching them in favor of NO filter in the lined cured the problem. lack of filters in the lines after many miles since has caused-nothing. Or it could well be the Dyna, though mine have never casued me any problem whatsoever.
 
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