Slight Misfire.....once....
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Laughing Gas
Joined: Aug 2008
Posts: 840
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Slight Misfire.....once....
I had a slight misfire the other day. Not a bang form crossfire, but more of a spitting sound from a single no spark situation. I'm a bit premature in posting this as I havn't done anything to check things out yet, but I have a question. Could prolonged idling around town cause enough carbon to build up that when I gave lots of throttle, some carbon got knocked loose and fouled a plug for a single misfire? That might explain why it hasn't happened since.
I usually drive the 5 miles to town at reduced rpms to warm the engine up and there was a lot of traffic around town so there was a lot of idling and just off-idle driving after getting there.
Last year I had a lot of ignition problems and changed plugs, wires, etc. Major problem was traced to a bad plug, killed by crossfire (old wires). I put another one in.....a good plug with hardly any use, but not new. RF9YCs seem to be hard to get vs the more common RF11YC and I had exhausted local stock, so used one of my used "good one's".
I havn't had a misfire since the one the other day, so although I will pull all the plugs, I don't expect to see anything out of the ordinary.
I suppose it could be fuel puddling on the intake manifold floor ...not sure about that one.
By the way, another question......is the Autolite R45 the common FE plug of choice these days? Seems to me it was the R44 which is no longer available.
I usually drive the 5 miles to town at reduced rpms to warm the engine up and there was a lot of traffic around town so there was a lot of idling and just off-idle driving after getting there.
Last year I had a lot of ignition problems and changed plugs, wires, etc. Major problem was traced to a bad plug, killed by crossfire (old wires). I put another one in.....a good plug with hardly any use, but not new. RF9YCs seem to be hard to get vs the more common RF11YC and I had exhausted local stock, so used one of my used "good one's".
I havn't had a misfire since the one the other day, so although I will pull all the plugs, I don't expect to see anything out of the ordinary.
I suppose it could be fuel puddling on the intake manifold floor ...not sure about that one.
By the way, another question......is the Autolite R45 the common FE plug of choice these days? Seems to me it was the R44 which is no longer available.
Thread Starter
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Laughing Gas
Joined: Aug 2008
Posts: 840
Likes: 8
Here's another thought, seeing how I can't find anything wrong with the ignition (not to say there isn't something wrong, just that I can't find it.....yet).
I did rebuild my 2 Holleys last year due to an internal fuel leak in one of them. I bought Holley re-build gasket kits (with PVs) and re-did both carbs. Normally they work fine. I forget what the symptoms were that led me to find that internal leak.
I used the 6.5 PVs that came with the Holley kits. I know the ones in the carbs were different. They had a microscopic stamp ( number about 1/32" high...very small) on the brass piece that holds the spring that said 5.5. Don't genuine Holley Power Valves have the number on the aluminum part you put the wrench on? I checked them with a Mity-Vac and they were both around 3 inHg. Think I am running about 14 inHg or a little higher, at idle. If the PVs are closing at a different vacuum than before, that may explain a bit about the "little hiccup" I sometimes (rarely) get when I let off the throttle a small amount, however that's beyond my experience to know for sure.
This more significant recent misfire seemed to be when I was accelerating moderately, but I may have also backed off the throttle a tiny bit when it happened. A single occurence, so all the facts arn't embedded in my mind.
I was out driving last night and I did some rather vigourous accelerating, which should have shown up with misfires if something like the plugs were weak, but everything worked fine.
EDIT: Doing a little research shows me I already asked about PVs here last year and it was suggested that 5.5 PVs would be more suitable, maybe even lower. My carbs are now done with blue gaskets (supposedly re-useable) so it may be fairly easy to try lower number PVs
I did rebuild my 2 Holleys last year due to an internal fuel leak in one of them. I bought Holley re-build gasket kits (with PVs) and re-did both carbs. Normally they work fine. I forget what the symptoms were that led me to find that internal leak.
I used the 6.5 PVs that came with the Holley kits. I know the ones in the carbs were different. They had a microscopic stamp ( number about 1/32" high...very small) on the brass piece that holds the spring that said 5.5. Don't genuine Holley Power Valves have the number on the aluminum part you put the wrench on? I checked them with a Mity-Vac and they were both around 3 inHg. Think I am running about 14 inHg or a little higher, at idle. If the PVs are closing at a different vacuum than before, that may explain a bit about the "little hiccup" I sometimes (rarely) get when I let off the throttle a small amount, however that's beyond my experience to know for sure.
This more significant recent misfire seemed to be when I was accelerating moderately, but I may have also backed off the throttle a tiny bit when it happened. A single occurence, so all the facts arn't embedded in my mind.
I was out driving last night and I did some rather vigourous accelerating, which should have shown up with misfires if something like the plugs were weak, but everything worked fine.
EDIT: Doing a little research shows me I already asked about PVs here last year and it was suggested that 5.5 PVs would be more suitable, maybe even lower. My carbs are now done with blue gaskets (supposedly re-useable) so it may be fairly easy to try lower number PVs
Thread Starter
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Laughing Gas
Joined: Aug 2008
Posts: 840
Likes: 8
I replaced the points with a Pertronix Unit some time. Even put a new one in last year during one of my not-so-good troubleshooting moments. There is no vacuum advance.
Basically, the only differences I have from when it used to work fine are the higher numbered power valves and the ignition timing. The timing may be the same, but as I previously had a slipping damper outer ring, I really don't know where the timing used to be.
In all likelihood, it is an intermittent igntion problem I haven't been able to identify yet.
Only other possibility I can think of is if :
6.5 PVs causes the mixture to stay richer longer as I let off the throttle and the vacuum starts to come back up, and the rich mixture sometimes causes a misfire.
Things I intend to try next are
1/ Check all sparkplugs
2/ Do the "midnight test"....looking for arcing or corona in the dark
3/ Put back the old Power Valves which are stamped 4.5 but open/close around 3 inHg
And then it may take a few weeks of driving to see if the problem is gone or not as it happens so infrequently.
Basically, the only differences I have from when it used to work fine are the higher numbered power valves and the ignition timing. The timing may be the same, but as I previously had a slipping damper outer ring, I really don't know where the timing used to be.
In all likelihood, it is an intermittent igntion problem I haven't been able to identify yet.
Only other possibility I can think of is if :
6.5 PVs causes the mixture to stay richer longer as I let off the throttle and the vacuum starts to come back up, and the rich mixture sometimes causes a misfire.
Things I intend to try next are
1/ Check all sparkplugs
2/ Do the "midnight test"....looking for arcing or corona in the dark
3/ Put back the old Power Valves which are stamped 4.5 but open/close around 3 inHg
And then it may take a few weeks of driving to see if the problem is gone or not as it happens so infrequently.
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