ignition/tach
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ignition/tach
hi . I bought an 80 ironhead 1000cc. the other owners removed the electronic ign. and replacd it with points. they were fried so i bought through v twin dyna electronic points. everything is fine starts runs etc. Now the problem is the bike idles great 1000 rpm goes up to 4000 or so rpms and then the tach jumps from 4000 to 8000 and back again the engine does not seem to miss. I bought a new tach and the same thing happens. have i timed it correctly? If the timing was off would that do it ?or is there something in the coil screwing up? Im stumped can you help. thanks larry
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Joined: Feb 2006
Posts: 3,035
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From: Houston Texas
RE: ignition/tach
The ignition timing will not have any affect on the tach operation.
Is your tach a cable drive or is it electronic?
When you say it goes from an idle speed of 1000 rpms to 4000 rpms.....Is that what the tach does, or is that because you rolled on the throttle?
This almost makes me think your tach drive must be electronic. A mechanical drive using a cable would only do this if the drive ratio and the tach head you purchased did not match ratios. And, it would not be erratic as you describe it to be, but rather a steady reading of twice the rpms, or three times the rpms, etc.
On the other hand, if the drive is electronic then the problem is with your sender unit I would think........pg
Is your tach a cable drive or is it electronic?
When you say it goes from an idle speed of 1000 rpms to 4000 rpms.....Is that what the tach does, or is that because you rolled on the throttle?
This almost makes me think your tach drive must be electronic. A mechanical drive using a cable would only do this if the drive ratio and the tach head you purchased did not match ratios. And, it would not be erratic as you describe it to be, but rather a steady reading of twice the rpms, or three times the rpms, etc.
On the other hand, if the drive is electronic then the problem is with your sender unit I would think........pg
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Intermediate
Joined: Apr 2007
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RE: ignition/tach
hi again the tach i bought is electronic( after market) connects to the coil, power and ground. the bike idles at 1000 rpms and i can bring it up to 4000rpms with no problems. at 4000rpms thats when the tach goes ape, jumps between 5000 and 8000 rpms when i bring the throttle down to 4000rpms she is fine the engine does'nt seem to miss. at the higher rpms.
this problem just happened when i screwed around with the timing. so i thought i had done something wrong with the timing. can the coil be bad? this bike was neglected for a long time. thanks for all your help larry
this problem just happened when i screwed around with the timing. so i thought i had done something wrong with the timing. can the coil be bad? this bike was neglected for a long time. thanks for all your help larry
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
RE: ignition/tach
Hey Larry...
The tach must get it's signal from the coil impulses. Something there is causing problems in the picking up of the signal properly.
Let me admit right here and now that I have no solution for this. Your engine is going to turn about 6200 to 6500 rpms at maximum speed under load. If your tach operates properly from 0 to 4000 rpms, I guess you need to be happy with that.
All I can suggest is to return it to the shop where you bought it and see if they have an answer. If you bought it on line then you may have no recourse open to you. Having this happen when you were adjusting the timing had nothing to do with the tach.
If the bike does not miss, you can be sure there is nothing wrong with your coil. As I am sure you are aware of this, but I'll mention it anyway...every time the coil fires spark to the spark plugs, it does so on both wires at the same time. This is the way an ironhead is and this is referred to as a waste spark system, for obvious reason. Perhaps this is causing some kind of confusion with your tach head when it gets to 4 grand. But on that I am just guessing. Electric stuff can get squirrely, especially when it comes to impulse or pick up signals.
Wish I could help more. If you get an answer be sure to let us know.......pg
The tach must get it's signal from the coil impulses. Something there is causing problems in the picking up of the signal properly.
Let me admit right here and now that I have no solution for this. Your engine is going to turn about 6200 to 6500 rpms at maximum speed under load. If your tach operates properly from 0 to 4000 rpms, I guess you need to be happy with that.
All I can suggest is to return it to the shop where you bought it and see if they have an answer. If you bought it on line then you may have no recourse open to you. Having this happen when you were adjusting the timing had nothing to do with the tach.
If the bike does not miss, you can be sure there is nothing wrong with your coil. As I am sure you are aware of this, but I'll mention it anyway...every time the coil fires spark to the spark plugs, it does so on both wires at the same time. This is the way an ironhead is and this is referred to as a waste spark system, for obvious reason. Perhaps this is causing some kind of confusion with your tach head when it gets to 4 grand. But on that I am just guessing. Electric stuff can get squirrely, especially when it comes to impulse or pick up signals.
Wish I could help more. If you get an answer be sure to let us know.......pg
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