Flat spot under light throttle application.

[madkaw]

If you didn't update your coil with your electronic ignition then you need to. If you went pertronix you need a coil meant for that specifically . Probably measure near or less then 1 ohm. From what I have read the electronic coils are meant to have 12 volts continuous , but a points coil is not

[azriel_strife]

I have a hotspark conversion, it says to never use a a coil under 1.5 ohms.

This is the unit I got. http://www.hot-spark.com/Installing-Hot-Spark-Hitachi.pdf

It says I should have a 3 ohm coil with no ballast resistor. I overlooked this because I checked the voltage at the coil while the car was running and got around 9 volts, so I assumed the resistor was still in place.

I checked without the car running today and I have 11.95 volts at the coil power wire. So i know now that i don't have a ballast resistor.

I don't know for sure if this is a 12v coil or not, but it was working with the stock points when I got the car. So it is probably the factory coil made to run with the resistor.

I know running a coil with too low of a resistance is bad for the coil, but the coil doesn't seem to get very hot, and it's within spec for the electronic ignition i installed. I can't see this causing a flat spot only at a certain RPM/load.

[madkaw]

Actually--it says to have a 1.5 ohm coil for a 6 cylinder. Might double check all your ohm readings again just so you can cross this off your list.

It's also confusing to me that the instructions imply that you should see charging voltage at the coil--12-14volts, and you say you read 9volts running.

[azriel_strife]

yeah 1.5 ohm for the 6, but thats also assuming you have the stock resistor in place.

it says: "Check the voltage reading at the coil's + terminal, engine running, at 2,500+ RPM. If the voltage measures more than +14

volts, you'll need to replace the voltage regulator, install a coil with 3.0 Ohms or more internal primary resistance or install a

1.4 Ohm external ballast resistor between the ignition switch and the coil's + terminal."

I think i see 9 volts because the coil is constantly discharging, that and the coil is getting an intermittent signal because of the electronic ignition box sending pulses. I also never tried this at 2500rpm, just at idle.

[madkaw]

1.5 ohm is measuring the primary resistance of the coil- nothing to do with any resistor

What's the secondary resistance read?

The only running voltage test I see in the instructions is at 2500rpm which you haven't done.

[azriel_strife]

I just know the coil is getting 12v with the engine off and probably closer to 14 with the engine running., which means i don't have a ballast resistor.

secondary resistance is from one of the power leads to the spark output lead i assume? I never did check that, I just assumed the coil was good cause the car runs well aside from the flat spot.

I went to the local parts store today and they don't carry aftermarket coils that are 3 ohms. I guess i'll have to order one online. the only ones they have are like the blaster 2 with .7 ohms, far too low. Insurance is up on the car on the 30th anyway, it'll give me lots of time to give her the attention she needs, maybe new plugs and wires too, even though they look new.

Here are some pictures of her for reference.

[Zed Head]

You are really getting distracted by the coil resistance. If things were getting hot from too much current you would not see the results in the middle of the RPM range, and the results of overheating are usually complete failure or temporary complete failure which fixes itself when things cool down.

1.4 ohms is close enough. 0.1 ohms is not going to make a difference.

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[Stanley]

What rpm when it happens? Only at mid-range? Good acceleration from about 4000 to 5000 rpm and from 1500 to 2500?

I don't understand how ignition could cause a problem with light acceleration that would go away when accelerating at higher rpm or up a hill.

[zKars]

I would try to beg/borrow/buy a tail pipe AFR gauge and determine if the bog is the result a lean condition or not.

That will give a reason to pursue fuel or spark with better confidence.

Feels like either weak spark/bad plugs or fuel metering problem to me.

Edited August 26, 2014 by zKars

[azriel_strife]

You are really getting distracted by the coil resistance. If things were getting hot from too much current you would not see the results in the middle of the RPM range, and the results of overheating are usually complete failure or temporary complete failure which fixes itself when things cool down.

1.4 ohms is close enough. 0.1 ohms is not going to make a difference

I agree, but if the coil is not supposed to be getting 12v because it is a stock coil, this could be a problem. I know the coil is getting 12v, and this coil was on the stock points distributor, so I should be getting a 3 ohm coil regaurdless, just because that is what should be int here with no ballast resistor.

What rpm when it happens? Only at mid-range? Good acceleration from about 4000 to 5000 rpm and from 1500 to 2500?

I don't understand how ignition could cause a problem with light acceleration that would go away when accelerating at higher rpm or up a hill.

I don't think it is an ignition problem. But I was asking if it could cause this problem.

I moved my needles up about 4mm in the slides (so the seats of the needles are flush with the slide bottom, and set my fuel screws to 2 & 3/4 turns out, the bog is definitely reduced.

It occurs right around 3000rpm and it will remain there until I give it more pedal. the bog doesn't go away really. But to go any faster than 3000rpm on the highway, i need more pedal anyway. I can feel the bog come on in every gear if i let the car accelerate without increasing the throttle input. it just doesn't seem happy above 3000rpm unless i have it at 3/4 throttle or more.

I would try to beg/borrow/buy a tail pipe AFR gauge and determine if the bog is the result a lean condition or not.

That will give a reason to pursue fuel or spark with better confidence.

Feels like either weak spark/bad plugs or fuel metering problem to me.

I tend to agree. I think it is fuel related because moving my needles up in the slides has helped the issue, but it is a bit rich at idle now. I was hoping someone had a suggestion for other needles, because I have heard bad things about the SM needles i am running now.

Edited August 27, 2014 by azriel_strife

[Zed Head]

This is from the page I linked to in Post 31. Hot fire ignition.

[azriel_strife]

I see that, but it also states that if the coil is getting more then 14v when the engine is running that you need to either install a 3 ohm coil, or a ballast resistor. It is definitely getting more than 14v, since my battery terminal voltage is over 14v when the car is running, and the coil supply wire is switched battery power.