Ironhead Can't get past 4000 rpm

[85mm]

Be careful reading the plugs after just running the engine in your driveway. You need to get out on the road and run it hard, then chop the ignition and read.

Also, your idle circuit could be rich and your intermediate/main circuits could be lean. You need to know the mixture at all points in the operation of the carb.

[Kingrabbit]

Point taken on the plugs reading, you are right.
But am I safe to assume that given the symptoms noted above there is something amiss? If the rear cylinder is missing I am not sure if running the bike on the hiway will help. Given the heat in the front cylinder from idling for 5 minutes I am cautious about damaging things.
Is it possible (given that I have checked the timing and pushrods, installed new plugs and air filter and cleaned and adjusted the carb) that my issue (poor running; more on one cylinder than the other) that this could be electrical? The coil maybe?

[ezmerf]

You can determine that by switching plug wires.I have a 74 and the rear most of it's life wouldn't fire right unless I unsnapped the boot and just let sit and hang on plug let it warm up and then snap wire back on.BTW if U get shocked U need plug wires.Anyway I did this for yrs just never could figure it out.

[85mm]

Lots of things can go wrong with points ignition. I can't comment, as I have Daytona Twin Tech on single fire mode. Equal points gap is essential, I do know that. And the advance mechanism can be bad, bad connections, bad wires - lot's of things. Plugs could be bad. Both plugs are the same, right?

With one cylinder overheating, have you done a compression test yet?

[Kingrabbit]

ezmurf that is a weird one but I will try that trick. Who knows? Gremlins?

85mm I will do another compression test and report back - I did it awhile back and they were the same values.
I will also go over points gap, timing etc. again. Maybe I missed something, which is entirely possible.
The plugs are the same. NGK B-6L. I got these other plugs from the Harley dealer (can't remember the number right off) and they were about 1/4 longer in the thread, which seems wrong - I know there's not a lot of clearance between the plug and the valve in there.
This bike fooled me at one point into thinking my plugs were dead. It wouldn't fire up so I pulled the plugs tested each one against the engine. They did not spark across the gap, just between the plug and the bike frame. So to me this meant there was lots of juice in the wire but the plug was dead. I replaced the plugs and the bike fired up. Then a few days later the same thing happened - bad starting, crappy performance. Now the new plugs seemed dead. Just for kicks I really cleaned up the old plugs i had just replaced and put them back in - lots of spark across the gap.
I doubt the plugs have to be perfectly new or perfectly clean all the time.

[trappnman]

get air filters at about 1/2 price from any lawn mower shop if you are talking just the foam

agree with mick- its not gas in my experience- any gas item, is going to give you sputtering, or at least like mick, everytime I've had something gas starved as a problem, it sputtered.

as you modify the engine, often times the STOCK petcock is simply not efficient enough and if its being gas starved, getting a good free flowing petcock like a Pingles will often cure it

I read here many times that "take off inline filter and use screen in tank".

really? a micky mouse screen over top of petcock as an efficient filter? Given a choice of either or, I'd rather take off that silly screen, and replace it with a good inline- I run both btw.

often times loss of acceleration can be cured with a simple good tuneup- including valve adjustment, etc because many things only break down or occur at higher rpms

[plucinskid]

Just my personal experience on magneto bike, I had a bike that would overheat and miss fire badly on the rear cylinder. I have timed many ironheads and became complacent by using the timing mark on the flywheel only. My problem was the flywheel had two marks and not one, I was timed 180 deg off. Chasing the gremlins and changing more than one thing at a time can generate more problems. Fix or change one thing at a time and if it doesn’t work go back to what you had. I would put the exhaust back the way you had it and or try the lollipops stated earlier. That is if this all started after the exhaust mod. Also, dump that Clymer and get a Factory manual when funds are available.

Ironhead Sportster points and timing - YouTube

Ironhead Sportster points and timing - YouTube

[Kingrabbit]

Thanks guys. Plucinskid thanks for the Youtube link. I have used this exact video while setting points and static timing. My flywheel has the dots and one line like in this video so I am thinkimg I am not 180 degrees out. I hope.

[ezmerf]

have u tried lifting the boot off and see what it does?Just curios.

[Kingrabbit]

No I will give it a try - the only time the rear cylinder boot came off was on the highway once. It was blowing round and zapping me. I couldn't pull over fast enough.