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Post by Deleted on Mar 28, 2018 9:35:49 GMT -5
I recently rebuilt several (6) HDC carbs.Two of them I haven't been able to check yet as I'm waiting for parts to finish those saws.I have one more to put on the saw yet.One out of the other three works like a charm,the other two are starting to really get to me.One will only run on prime,just like before I rebuilt it,the other one won't even fire on prime.It has good spark,good fuel line & filter.When I put the carb in the saw after the rebuild I had it running tip-top (both of them) I let them sit for two days & this is what happened.Now I know why I've always been leary about doing my own rebuilds.
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Post by fossil on Mar 28, 2018 11:03:31 GMT -5
When I stop by next month maybe we can go through a couple of carbs. Once you get used to them they become second nature.
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Post by Deleted on Mar 28, 2018 11:13:16 GMT -5
Thanks Tim,meantime I'll try to figure things out beforehand.I don't want you to be wasting all your time here trying to fix my screw ups,I gotta be able to decipher stuff on my own.
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Post by fossil on Mar 28, 2018 17:18:35 GMT -5
I had lots of help when I started out in this hobby, and I mean lots. I'm always glad to share that info with anyone who wants it.
I'm certainly far from perfect. Still learning.
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Post by jerseyhighlander on Mar 28, 2018 17:48:20 GMT -5
I recently rebuilt several (6) HDC carbs.Two of them I haven't been able to check yet as I'm waiting for parts to finish those saws.I have one more to put on the saw yet.One out of the other three works like a charm,the other two are starting to really get to me.One will only run on prime,just like before I rebuilt it,the other one won't even fire on prime.It has good spark,good fuel line & filter.When I put the carb in the saw after the rebuild I had it running tip-top (both of them) I let them sit for two days & this is what happened.Now I know why I've always been leary about doing my own rebuilds. It's likely that some crud that didn't get fully removed from an internal passage during the rebuild finally broke loose after the fresh gas washed through it under use and is now clogging a tiny passage. May be necessary to go through it again with carb cleaner.
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Post by undee70ss on Mar 28, 2018 18:09:13 GMT -5
The saw that doesn’t fire on a prime, has other issues. Does it have a new plug? That one need to fire on prime first before messing with carb.
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Post by Deleted on Mar 28, 2018 19:05:43 GMT -5
A new plug isn't going to prime the carb.A couple of the saws have new plugs,the other ones have good used ones.When I pull the plug & ground it out against the muffler & it has nice spark,that tells me that the plug is good.I don't throw away perfectly good spark plugs.Most of the saws I got came out of a shop & were worked on before I got them,but that was yrs.ago,& a plug doesn't deteriorate over time.I have carbureation issues,not spark issues.Sorry,I misread your post,I'll check the plug in a.m.
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Post by lesorubcheek on Mar 28, 2018 20:20:40 GMT -5
....,the other one won't even fire on prime.It has good spark,good fuel line & filter.... If a saw has a spark with the plug removed and grounded but still won't fire on a prime, there's a couple things to check. First, it needs good compression. Another thing is the flywheel key may have sheared, or something else that would cause the timing to be incorrect. Also, sometimes a plug will spark under atmospheric pressure, but not under compression. I personally have never encountered this, but heard it said more than once. Pretty sure they sell spark plug testers that actually pressurize a cavity to make sure they fire under pressure. Another thing is too much fuel will flood it. Keep pulling enough and it'll finally thin out, assuming the only fuel is from the prime. There may me a few other things that can explain this, but that's about all that comes to mind at the moment. Dan
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Post by fossil on Mar 29, 2018 15:43:38 GMT -5
....,the other one won't even fire on prime.It has good spark,good fuel line & filter.... If a saw has a spark with the plug removed and grounded but still won't fire on a prime, there's a couple things to check. First, it needs good compression. Another thing is the flywheel key may have sheared, or something else that would cause the timing to be incorrect. Also, sometimes a plug will spark under atmospheric pressure, but not under compression. I personally have never encountered this, but heard it said more than once. Pretty sure they sell spark plug testers that actually pressurize a cavity to make sure they fire under pressure. Another thing is too much fuel will flood it. Keep pulling enough and it'll finally thin out, assuming the only fuel is from the prime. There may me a few other things that can explain this, but that's about all that comes to mind at the moment. Dan A little more info on the plug not firing under cylinder pressure. It's pretty much a linear relationship on pressure and voltage. A plug will fire at atmospheric pressure (about 14.6 psi at sea level) with about 3000 volts As pressure increases it becomes more difficult for the spark to cross through the denser air. Assuming an 0.025" plug gap and that the cylinder pressure is at 130 psi when the plug fires, it will take about 18,000 volts for the spark to jump the gap. It's difficult to pick a cylinder pressure without doing some more calculations because most chainsaw ignitions fire at 30 deg or a bit less before TDC. So, if the plug has started to degrade and the resistance is higher, it will take more voltage to fire that plug. I've had two plugs do that to me. One on a saw and the other on my ATV. Interestingly, both were NGK plugs.
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Post by sweepleader on Mar 29, 2018 15:52:47 GMT -5
It is not always easy to diagnose a bad plug on a 1 cylinder engine, mainly for the reasons fossil mentioned. Even putting in a plug from an engine that runs could be misleading for a number of reasons. That is part of why I like chainsaws, when they run it is a miracle!
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Post by Deleted on Mar 29, 2018 18:58:39 GMT -5
I put a new Bosch plug in it today & it still won't fire up.I got the other SEZ fixed - carb issues.This one the won't fire I'm suspecting low compression,but there's no way for me to test it because of the brilliant persons that designed the saw did so without any consideration to anyone who might have to put a compression tester on the saw.The thing that puzzles me is when I put the rebuilt carb in the saw,I primed it & it took off & I had the saw's carb adjusted properly.How can it suddenly develop flywheel key issues by sitting there idle for two days? I'm about ready to scrap this saw for parts.
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Post by sweepleader on Mar 29, 2018 20:58:40 GMT -5
Put a little oil in the plug hole and try it. That might raise the compression enough to fire. Get it on the rings so it seals better.
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Post by Deleted on Mar 29, 2018 21:08:29 GMT -5
I'll try it tomorrow so long as the 410 doesn't consume all of my time.
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Post by undee70ss on Mar 30, 2018 5:24:50 GMT -5
As a test, set plug gap closer ( .015-.020) and see if it will fire. Does this saw have the blue electronic ignition?
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Post by Deleted on Mar 30, 2018 9:32:33 GMT -5
No Greg,it has points & condenser.I'll try resetting the gap.
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Post by undee70ss on Mar 30, 2018 11:47:28 GMT -5
No Greg,it has points & condenser.I'll try resetting the gap. Ok. Do this test. Take a good plug and cut the ground strap off. Test for spark. If no spark, voltage is to low to fire under compression.
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Post by Deleted on Mar 30, 2018 13:27:03 GMT -5
How far away from the muffler to hold the plug while pulling the recoil?By doing this test will it determine that the condenser is bad,or the coil?I can also check the coil to see how many ohms it has.
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Post by sweepleader on Mar 30, 2018 13:56:13 GMT -5
Ground the plug to the saw, watch the gap. I use a wire with a battery charger size clip on one end and a small clip on the other. Put the plug in the big clip and the small one on the saw.
Like Greg said, cut the outer electrode off a known good plug for a tester so you get a huge gap. A good ignition will jump that gap. That compensates for the need for a big spark inside the engine with it at a .025" gap.
These tests will only tell you if everything is good, not which part could be bad. You have to test the individual parts to know about each one.
A resistance test of the coil really only tells you about continuity of the coil, not how much spark it will put out or if it grounds under load.
Without a condenser tester it can be very hard to know if the condenser is good or bad. Swapping parts from a running saw is the only low tech way to be sure and you must switch only one part at a time.
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Post by Deleted on Mar 30, 2018 16:43:47 GMT -5
I did something a little different.I put a hotter plug in the saw - a CJ-8 & opened the gap up on that to about .035.The saw fired up,but wouldn't stay running as per just about all my lousy carb rebuilds.
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Post by sweepleader on Mar 31, 2018 6:09:01 GMT -5
As a result of emission requirements over the years, car engines got leaner. The manufacturers opened the spark gap to get ignition of the lean mix. Because of that, it sounds to me like you are not getting enough fuel, too lean, if that is any help figuring this one out.
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