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To test if the new CDI (coil) that I put on my Duraforce a few weeks ago is causing it to run badly I'm going to put the old one back on tomorrow. The old has some rust on the metal parts that get bolted down and may have some on the contacts, which I plan to clean off first. Now my question, after I clean off the rust should I rub some WD-40 on the metal parts to protect them or will that interfere with operation? Thanks.

Never seen a need to remove rust from a coil. Have seen 30 year old coils coated in rust on SnowKing engines running just fine. You will never help or hurt the coil with WD-40.

A good coil should make a spark with just hand turning the flywheel with the sparkplug held against the engine head. Just an observation.

Phototone said:

A good coil should make a spark with just hand turning the flywheel with the sparkplug held against the engine head. Just an observation.

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Both the new and old CDI are/were producing a spark. The mower started running badly at medium to fast speeds after I replaced the fuel line, shut-off valve and CDI. Another member thought that it might be the new CDI causing it run badly as it never did before. The old CDI was replaced because I was having random problems with it starting, so it might be on it's way out. I'm going to clean the rust off the old one and put it back on to see if it makes a difference.

you need to take your carb off and clean it and drill, out the jets. On a duraforce if you have spark and it will not start in one or two pulls its almost all the time the carb needs cleaning.

beg said:

you need to take your carb off and clean it and drill, out the jets. On a duraforce if you have spark and it will not start in one or two pulls its almost all the time the carb needs cleaning.

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Cleaning and/or rebuilding the carb is on my list, after I've tried the other possibilities suggested to me. With the old CDI it would sometimes start and sometimes not. I checked it for spark 2 or 3 times and each time I had spark. When it did start it would start on the first or second pull. It starts on the first pull with the new CDI. I thought the CDI was going bad as this is the way the original CDI that I replaced 7-years ago behaved. Looking at the no start issue with hindsight I realize that the no starts may have been from the leaking carb causing it to be flooded. Yes, I know the carb needs to be cleaned and have the needle and seat replaced to fix the leaking problem permanently, but for now the shut-off valve is doing that job. Since it didn't run badly with the old CDI, I'm going to try putting the old one back to see if that takes care of the running badly.

well ok but my point was you need to clean the carb now that you have spark as the starting issue you mentioned is being caused by the dirty carb.you tried to get by without taking the carb off but are gonna have to.

Please explain to me how a dirty carb can cause a spark issue? In 40+ years of working on engines I have never heard this before. They are two separate systems with no connecting parts. One deals with fuel and the other produces electricity.

beg said:

well ok but my point was you need to clean the carb now that you have spark as the starting issue you mentioned is being caused by the dirty carb.you tried to get by without taking the carb off but are gonna have to.

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But I haven't had a starting issue since replacing the fuel line, shut-off valve and CDI. My issue since doing that is that it runs badly at medium to high speed, which I'll agree may be caused by the carb, but since it didn't run badly before replacing those parts I'm not fully believing that the carb is the only cause until I rule out the new aftermarket CDI.

In General the CDI either WORKS or DOESN'T WORK. If it works, it is not the cause of your poor running. You probably have carb issues, possibly less likely, but still possible seals or reed issues. The DuraForce engines are jetted at the very edge of running satisfactory (very lean), when fresh and new. Any, and I mean ANY slight build up of varnish, or any type of detrius in the jets will cause poor running, or NO running. Also you need to make sure you have a perfect seal between the carb and the reed plate.

Phototone said:

In General the CDI either WORKS or DOESN'T WORK. If it works, it is not the cause of your poor running. You probably have carb issues, possibly less likely, but still possible seals or reed issues. The DuraForce engines are jetted at the very edge of running satisfactory (very lean), when fresh and new. Any, and I mean ANY slight build up of varnish, or any type of detrius in the jets will cause poor running, or NO running. Also you need to make sure you have a perfect seal between the carb and the reed plate.

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Have you seen this YouTube video, LAWNBOY & TORO IGNITION COIL QUALITY ISSUES?