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not sure of cause

  • Thread starter Thread starter terrylee
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terrylee

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Yesterday my sons' 79 850 wouldn't stay running, would start and run for few mins. and not rev up with choke on. Fiqured out it was getting gas, so checked volts to coils and one was really low (5-6 volts). Cleaned up connections(plan to due coil mod. this weekend) and bike started and run but not real well. Checked and cleaned points and set timing and bike ran pretty well, except wanted to backfire quite a bit. Adjusted air mixture on carbs (didn't mess with fuel mix) and bike seemed to run even better and not backfire as much. Today son tried to ride and it took nearly ten mins. for it to warm up and it backfired almost constantly till it warmed up and then just once and a while. Did a valve adjustment last season. What else might I look at? Ordered Morgan carb. sync. tool but maybe a while before I get it.(due to volcano). terrylee
 
Which way did you turn the air screws?

You might want to try adding a little fuel by turning the fuel screws out about 1/8 turn.

.
 
I'd get that coil voltage business squared away before doing anything else. And check the battery and charging system voltage while you are at it.
 
I have air screws at 1 1/4 or 1 1/2 out. (Had them out to 2 and seemed to not run as well). I will try turning fuel screws, any idea what might be a right amount of turns out to start? I do have it right, air screw in makes it richer (decreases air) and out on fuel riches (increases fuel)? I know on my 850 that has only one mixture screw, right makes it leaner and left makes it richer. I'm definetly going to do the coil mod. and check all elec. system this weekend. Thanks guys! terrylee
 
Coils need to be squared away before the carb playing. Otherwise you are chasing your tail. I know---I've done it
 
When you check the coil voltage the bike should be running or the points should be blocked open. Get that fixed first or your just spinning your wheels. Did you replace the condensers? Check to make sure you are getting a strong spark. Backfiring could be a coil failing. I had problems with my 850 would sometimes backfire (like a gun shot sometime) and quit. Personally I would get a set of dyna coils and be done with it. Get the three ohm green coils and use a 2 ohm ign ballast resistor from an old 70's Mopar with the points. Did mine 4 years ago..
 
Last edited:
I replaced the condensors and points last summer, and my son hasn't put alot of miles on it since. Will do the coil mod. Sun. and go from there. I have a couple of spare old coils from a 550 if we have one going bad.(of course have to tes them too since they came off a old parts bike. Wasn't aware about points needing to be open when I check coil volts. Thanks for the info. terrylee
 
Cleaning points can be difficult. A points file should be used for cleaning points: sandpaper can leave a glaze. Use contact cleaner to rinse them, and let the points close on a clean business card to blot away any metal dust. Make sure none of the wires are grounding/touching anything.

The voltage to the coils comes from the common orange white wires. Disconnect them from the coils before checking voltage.

You may have fixed the problem, but fouled a plug in the process. Check the temps of your pipes carefully. If only one pipe is cool, change that plug. If a 1-4 pair or 2-3 pair are cool, then you probably still have a problem with ignition.
 
Don-lo said:
Cleaning points can be difficult. A points file should be used for cleaning points: sandpaper can leave a glaze. Use contact cleaner to rinse them, and let the points close on a clean business card to blot away any metal dust. Make sure none of the wires are grounding/touching anything.

The voltage to the coils comes from the common orange white wires. Disconnect them from the coils before checking voltage.

You may have fixed the problem, but fouled a plug in the process. Check the temps of your pipes carefully. If only one pipe is cool, change that plug. If a 1-4 pair or 2-3 pair are cool, then you probably still have a problem with ignition.
Click to expand...

Now that there, is some VERY GOOD 'old school' advice, about cleaning and setting points and multi-coil setups.

I was taught using a match book cover. ;)
 
Thanks for the point advice. I used 400 grit sandpaper and very lightly pulled through points a few times. Then did clean with contact cleaner, didn't know about the b card trick. My son rode the bike to work and back and it run very well after warming up. And warming up doesn't seem to take so long. Still planning on doing everthing this Sun. terrylee.
 
Dave8338 said:
Now that there, is some VERY GOOD 'old school' advice, about cleaning and setting points and multi-coil setups.

I was taught using a match book cover. ;)
Click to expand...
You can still use a match book cover, just be aware that it's for a different purpose.

The business card is to blot away the dust from filing.

The match book cover is for setting the gap. The thickness of the match book cover is real close to the proper gap.

.
 
Steve said:
You can still use a match book cover, just be aware that it's for a different purpose.

The business card is to blot away the dust from filing.

The match book cover is for setting the gap. The thickness of the match book cover is real close to the proper gap.

.
Click to expand...

Works for me... ;) :D

It's been awhile since I've played with points. They can be charmimg. :-\\\
 
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