I daily ride a well maintained 2001 FXD TC88, normally aspirated, only Stage I mod, and it just rolled over 65K miles. I changed the cam tensioners and all 4 cam bearings around 2000 miles ago.

About six weeks back, I noticed that the mid-high throttle response was off just a bit, not much but enough to be noticeable, and there was an slight increase with backfiring when it was cold. I'm thinking lean, so I pulled the plugs and they looked good so I went on. Then a couple of weeks back during a cross-town freeway run, the backfiring increased and was constant in decel...

I am thinking too lean so I pull the carb and go through and clean it but could not find anything wrong. I put it back together and the problem got worse to the point that it would not run without the enricher out, and even then it was really rough, backfiring, farting, just would not run. I go back into the carb, cleaned and rebuilt it with OEM part and it still ran like crap.

I am now thinking I have a massive vacuum leak so I pull the intake and replace all the gaskets and make sure that there are no vacuum leaks...and it still runs like crap. I have gone through the carb, replaced the intake gaskets and made sure that there are no vacuum leaks.

Now I am at the ignition system. I replace the MAP sensor (I had one laying around) with no success, replaced the coil and wires with no success, and ordered a new SE performance ignition module with coil kit. That came in on Monday and I am going to put in today and see what gives.

Is it possible that I have a top-end issue that is causing this problem? I have a big-bore kit and all the bits and pieces with big cams, new high compression pistons and cylinders, and CNC heads that I was saving for a different future project but I am at the point to where if the ignition module doesn't work, just do the build on this engine and ride on.

Is there anything else I should look at before I go full big-bore?

 

Bad lifter?? Or valve?? Any mechanical noise from the engine?

That’s a lot of miles on the stock lifters. Start by checking the lifters.

 

no noise, no smoke, nothing out of the ordinary except it will not run without the enricher out, warm or cold, and with the enricher out, it idles as it always has but now it will not respond to the throttle like it should when the enricher is out.

I thought about the lifters right after I changed the cam tensioners and bearings and kicked myself for not changing them out then. I am wondering if one has collapsed or is binding. I have decided that if I have to go back into the cam case, I am just going to rebuild the top end with the big-bore kit. I have everything I need except the push rod tubes for adjustable push rods.

We had some sub-freezing weather down here right before I noticed the fall-off in power...I was wondering if blasting down the road before allowing the engine to warm up sufficiently may have cracked a head or bent a rod or valve...

 

Have you checked for codes? Certainly sounds fuel related since it will not run unless the enrichener is open. I know you have been into the carb but it sounds like something is stuck in the emulsion tube. Sometimes blowing air through the passages will not dislodge a tiny piece of debris that has lodged itself in an orifice. I make it a practice to pass a piece of wire or whatever I can find that will fit, through the passages to make sure they are clear. Did you check the diaphragm closely for holes or frayed edges?

I would also take a look at the crank position sensor (CPS). I would not start a rebuild until I had solved the problem.

 

Did you replace intake seals?

 

I installed the new SE module and coil kit, put in new SE fat wires and new OEM plugs and it is still NFG. I'm starting to feel like the more I eliminate possibilities, the worse it runs.

It idled rough this time. I am starting to have a bad feeling about those original tappets I didn't change...

I did not check the codes. I never even thought about it. Probably should've, though. I read your suggestion and looked up how, and went out to do that and discovered/remembered that particular switch on my speedometer does not work and I never got around to fixing it. Murphy'd. Anyway, I did a bottom up rebuild on the carb and I am pretty sure it is not the problem. I have pretty much eliminated everything but the valve train and the CPS...maybe that is worth a shot considering the situation and alternatives. I don't have one of those laying around, though.

 

Sounds like an ignition problem. I know you have a cam position sensor, but not sure about a crank position sensor on your bike. Either can mess you up. So troubleshooting both using service manual diagnostics is where I'd start.

 

It just uses the crank position sensor and I think that is pretty much the last component in the ignition system that I have not changed from what I can tell from my books...

I'm guilty of just grabbing a wrench and heading on into things that I know pretty well instead of hitting the books first...that generally comes second...not a good thing sometimes, but not really an issue this time. Classic symptoms of a dirty carb/vacuum leak or ignition problem. BTDT. I am not over my head yet, just hoping that I am not overlooking something else that could be causing this before I start tearing into the cam chest and top end again.

I will pick up a new CPS and give it a try this weekend. I can always use it on the future build if it is not the problem...

 

I've had two CP sensors go bad in the past on different bikes. Typically run okay for a few miles and then leave you stranded. May just need to be removed and cleaned but at that mileage probably should be replaced for about $80 assuming that's the cause.

 

I doubt valve train is the problem unless a pushrod adjustor has backed off; if pushrods are adjustable I would check. Symptoms are not typical of a failing CPS but symptoms can be different. Pull it out and take a look, clean it up and try again. If there is improvement, replace it; if not, leave it alone.

Have you grounded plugs and checked the spark? Electrical is not my long suit but if the bike starts easily but won't run unless the enrichener is open, still leaning toward a fuel issue

You mentioned a "bottom up rebuild" on the carb but did you check the emulsion tube. The last bike I worked on had the exact symptoms yours is presenting. Pulled the carb, very clean inside. Looked through the slow jet and couldn't see any light on the other end. Ran a piece of copper wire through, put the carb back on, problem solved; just sayin.