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I put a 80-81 Cdi on a 82 xlh, runs but backfires should I advance or retard

Posted by Barry Robak on


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Bill Boyd

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Probably retard it a bit but I don't think it is the timing
You say it runs and backfires but if the timing was too far advanced it would backfire on starting and be difficult to start
I suspect the fault to be electronic ---like a loose wire on the coil , faulty coil, faulty ignition control module, loose wire at ignition switch, loose ground wire , loose ground wire on battery
look for something that is making and breaking contact at random as that action induces a spark at the wrong time

Posted on Feb 27, 2016

Testimonial: "I replaced failed Cdi with used unit, the replacement is for 80-81, mine has 82a suffix replacement has 80 suffix, could the unit be designed with different timing curve?"


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I have a 2006 Suzuki C90,once it warms up, it constantly backfires unless at very low RPM's. Also does not run faster than 70 mph also while running rough.

Check ignition timing which is the cause of the backfire. Backfire through carb is ignition too advanced and through the exhaust is too retarded. It has to be just right.

Clean the injectors for 'running rough'..

Sep 04, 2018 | Suzuki Cars & Trucks

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Hi guy my kawasaki zxr400 is backfiring and not starting after l changed the CDI pliz help

Hi, Lyrical you may have your timing too far retarded the supplement manual I provided in your first question did not cover CDI timing but it was free you need a base manual that will cost $10 to download and why did you change the CDI in the first place? use the comment box below to respond For this situation I would call my local dealer or reputable shop's service/parts department and inquire about any possible quick fix, answers, or parts inquiry. For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
Kawasaki ZXR400 ZX400 1989 1999 Repair Service Manual PDF Download Manuals...
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Nov 27, 2016 | kawasaki Motorcycles

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Hi my malaguli 125 phantom max is backfiring threw exhaust wen let go and backfires threw card wen rev it plz cud u help

either your timing is not set right (retarded not advanced) or something in your fuel system ? possible water or dirt? you said it is backfiring when you let off the throttle, makes me point to the timing being to retarded.

Sep 19, 2016 | Motorcycles

1 Answer

I have a 80-81 Cdi on a 82 xlh, do I need to advance or retard to make it work? It runs but backfires

Hi, Barry if it is just the timing you need to advance it and check it with a timing light otherwise the usual suspects are:
1. A severely drained battery.
2. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
3. Faulty main circuit breaker and or connections.
4. Faulty ignition coil and or connections.
5. Faulty spark plug, oil or gas fouled, wrong heat range or service type, wrong gap, loose in the cylinder head, broken electrode or insulator.
6. Faulty spark plug cables, leaking or broken, internal damage.
7. Faulty ignition module, switch, CKP, MAP, CMP, sensor and or any connector in the ignition circuit could have corroded, loose, or broken pins/sockets
8. Burnt exhaust valve or air leak in the exhaust system.
For more information about your issue and valuable free downloads that you will need please visit the websites below and for specific information or questions, please feel free to contact me at [email protected] Good luck and have a nice day.
New electronic ignition system for my 82
Harley Davidson Manuals Mark Workshop
Owner Manuals Harley Davidson USA

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Feb 27, 2016 | Motorcycles

1 Answer

What causes the motor to backfire thru the exhaust? When I adjust the timing the carborator backfires?

Backfire through carb is timing too far advanced.
Backfire through exhaust is timing too retarded.

May 17, 2015 | Motorcycles

1 Answer


Check the cam sensor in the nose cone on the right side of the engine. These have a tendency to cause the type of problem you are having. Over time, the heat cycles the sensor goes through causes the epoxy to melt when hot, pulling the wires away from their contacts. After the bike cools, the wires again make contact and the bike runs fine until it gets hot again. Not a bad job to change the sensor, you just have to retime the bike after a new sensor is installed.

Aug 08, 2012 | 1979 Harley Davidson XLH 1000 Sportster

1 Answer

Hard to start then backfires through carb

Backfire through carb often means timing too advanced.

Mar 13, 2012 | 1993 Harley Davidson XLH Sportster 883...

1 Answer

82 Yamaha xs400 maxim. I keep burning up CDI. New CDI and bike runs great. If it goes on a long run (over 45 min), the idle speeds up and the next day the CDI is dead. I put and old one back that runs for...

The CDi usually breaks down when it gets an over voltage from the voltage regulator.
Try to replace the voltage regulator so that the CDi won't overheat.
Check also the ignition coil, it might have a short circuit it the connection terminal or the polarity is wrongly placed.
Thanks for using FixYa!

Jul 11, 2011 | 1982 Yamaha XS 400

1 Answer

I have a 1967 Harley XLH Sportster. I rebuilt the

"Backfiring" is a pretty broad term depending on where you live. Some people refer to backfiring as popping from the exhaust while others refer to it as the engine spitting through the carburetor.

I'll assume that you're talking about popping out the exhaust pipe. If it does this after you rev the engine and it backfires on the way back down to idle, this is typical of an exhaust system sucking air. The mixture is extremely rich under these circumstances and will not ignite. But, if your exhaust system is sucking air, it combines with the fuel air mixture already there and bring it to an explosive mixture thus the backfire.

You can check you valves but I've always found that if the valves on an Ironhead are too tight, it's extremely difficult to get it started due to the low compression on that cylinder.

Check you ignition timing and points setting. Also, what kind of condition is your mechanical advance in the distributor in? I'm assuming this is an XLH model and not the magneto equipped XLCH.

What type of carburetor is on the engine? Hopefully not the original Tillotson that it came with. If it's an S&S, the low jet should be a 28 and the main jet a 66 to 70.

Jun 10, 2010 | 1979 Harley Davidson XLH 1000 Sportster

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