Thank you all for your replies, especially @im for that detailed guide, really helpful.

I followed some of the tips of @im guide. I revised this afternoon all the cable of the ckp, from the sensor to the connector. Is in one piece and seems good, even put some tape in the connector just to be sure it won’t separate.

I was working on the bike (as it has the exhaust “Y” was broken, welded this afternoon), and I can’t say what’s failing, but you can even see the flames in the admission on both cylinders, I’m attaching a video.


The lines under the tank looks good and they doesn’t seem to leak. I bet that the previous owner changed them at some point because they are in a very good shape to be 30 years old.




I changed the fuel filter the other day. Fuel lines of the tank were looking good.

I was thinking all this time that it has to be the sensor, I mean, even if the bike is not failing because of that it needs to be replaced - the beige goo it’s really melted. But to be honest it always has started good and at first try since I have it. So I kinda lost now.

Any help is useful! Thanks!

 

I’m posting YouTube link of the video so you don’t have to download it:

 

Okey, after trying a lot of things I discovered something interesting.

If I disconnect the temp sensor the bike stops doing that backfires and seems to run fine. I never thought that it could be the temp sensor, as the IAC seems to work fine (fully extended in cold situations and going back like in a 2 minutes of idle)

I pulled out the temp sensor after 2 idle minutes and it was at 400 ohms aprox. Following the temperature resistance table, it’s a temperature of 70-75 celsius degrees, what it seems reasonable with the real engine temperature.

Tried the sensor outside. It seems to be working as it should (at least outside of the bike), I heated it with a lighter and the resistance goes down to 100, and if i let it at ambient temperature resistance goes to aprox 2700k.

I don’t know if the bike is failing because of the sensor, but my tests make me think that maybe the sensor is not the problem, but it affects indirectly enriching the mixture or fixing somehow the bad synchronization of the ignition sensor.

The main problem is that I don’t know if the problem is coming from a bad synchro or a lean mixture.

What are your thoughts?

 

All right, I did more tests. I’m posting here every update so I hope it could help someone at some point.

Went to a electrical store and bought a couple of resistors to simulate an operating temperature of the engine, I bought them from 180 ohms to 480 (0,45€ xD) And… surprise! The bike has the same issues. Even with the one of 180 cranked like hell and needed some time to finally start, followed by a really low idle and dies if I don’t throttle it a little. I also pull out the temp sensor and, leaving it connected to the bike (but outside of it, at ambient temperature) and it runs fine, but I noticed that when the bike warms up to a high temperature starts to slightly fail again (not as bad as before), even with the sensor disconnected or outside.

So, as I suspected the temp sensor seems to be okey. But, if the bike runs in a richer mixture it works better for some minutes until it really warms up, that’s why when disconnecting the sensor, the problem of the backfires and low power is delayed and improved. Yesterday I’ve also tried disconnecting front and rear cylinder (one at a time) and it had the same issues, so I can almost discard the injectors or something like that.

At this point I think that the issue could come from the fuel line (lines, pump, etc.) or the already mentioned camshaft sensor. I don’t know if a richer mixture could cover up a damaged camshaft sensor, but I think it can do it on a slightly low pressure in the circuit.

Let me know your thoughts, I’ve already ordered a new camshaft sensor, crankshaft sensor (just in case), and I think I will order a new fuel pump and fuel lines. Even ordering all of these things is cheaper than carry a bike like this to the dealership. I know that the issue won’t come from all of these things that I’ve ordered, but I can always return the items or keep them to have spare parts.

I’ll keep updating the thread, thanks!

 

The purchase of additional parts without confirmation of performance can confuse things further.
From a distance it appears that engine temp sensor is functional.
The old CAM position sensor is functional.
The CRANK sensor is rarely a problem as long as the push and turn sensor near seat is held tightly together at the connector with a zip tie/tie wrap in a figure eight.
Your current fuel lines are the upgraded Goodridge HDFL005 and are known to be a good product.
You can remove those Goodridge lines to review and re-install. An inexpensive o-ring kit is available if needed but check them first.

I would re-install the OLD CAM sensor.
The placement of CAM sensor is critical.
BOTH standoff bolts must be installed on the CAM sensor.
Replace the 2 gaskets at throttle body to cylinder head. I believe it is part 26995-86B seal/intake manifold but reconfirm.
Should be less than $10 USA dollars total for the two gaskets since yours should be dirt by now if original.
Unmeasured air causes weird things to happen since it can cause a lean condition.
A garbage disposal allen/hex wrench will make removal and replacement of allen bolts at manifold easier.
The garbage disposal allen/hex wrench has the correct bend to reach those bolts.

 

Hi again!

Thanks for the tips. I didn’t post any update because I was waiting for the new spare parts to arrive, and started today assembling everything again.

This is what I’ve done:

-Cleaned the tank (had a lot of small pieces of that liner that Harley use to paint the inside of the tank. I had to repaint it when I have more time as it has some superficial corrosion)

-Pulled out the intake manifold and clean the inside. Also replaced gaskets too.

-Changed the fuel pump.

-Changed the fuel pressure regulator.

Today I assembled the essential parts and the bike seems to run fine! It still has the old camshaft sensor, so it seems that it wasn’t the problem, my bet is on the fuel pump or the intake gaskets. Anyway I have to try it better, as I’ve only tried it without give it a run, but if the problem is not solved, it seems to be definitely improved.

I’ll keep updating. Thanks!

 

Hi again!

Well, it seems that the problem is finally solved. I did some kilometers and the bike runs perfect, no backfires in the intake or power loss, I even feel like it has more power.

Anyway, I was curious of what was really causing the problem, and finally found out. It all started with the new fuel pump that I ordered on Amazon, it makes not only a much louder noise than OEM one but also sounds like there is something wrong at startup. I did a lot of tests and ending putting back the old pump again, just to try if that sound was coming from something that I hadn’t mounted as I should somewhere. The OEM one sounded good (as always had), so that sound is caused only by the aftermarket pump.


It’s true that the bike runs perfect and I don’t hear nothing strange when running, only at startup when cycling the pump, so maybe it’s normal for an aftermarket one (and I’m sure that is not the best quality unit, as it wasn’t really expensive). An important note is that the sound is better (not perfect) when I unbolt the tank metal plate and also improves if I remove the screen filter from the pump. I thought than maybe the vent was blocked, but it was good and even with the plastic cap off the noise is the same. Anyway, when I mounted the old pump back, I fired the bike up just for curiosity, and it started to fail again almost instantly. So it finally seems that the problem was the fuel pump. This is strange to me in some way, as I’ve always heard that a bad fuel pump is more noticeable at high rpms, and this bike was failing much more at low rpms and when it was hot outside, but who knows.

The good part of this is that I’ve learned a lot from the bike, spent a lot of hours with her and located (and cleaned) all the sensors and components. Even did a few upgrades, for example, the previous owner changed the OEM handlebar for a semi-ape ones, I love them btw. But this bike was the version that had a pneumatic suspension and anti-dive system, and the OEM handlebar was an air reservoir. Well, the hose was loose and simply capped with a bolt, and of course, with no air at all. I calculated aprox. the handlebar air capacity and fabricated a metal cylinder, relocated some things inside the batwing and I hid it there. It seems that the seals are not completely bad as it didn’t lose air (at least by the moment)



Another problem I went through is that I accidentally stripped the return fuel line thread under the tank in one of the multiple times that I unmounted and mounted the fuel lines. I solved it by using a M18x150 tap. I found this measure in this forum in one of @im ’s post (thanks again mate xD) went to buy it and with some patience it solved the problem, so I can confirm too that this measure is correct.

So that’s all for now. The only problems that I have now is that noise from the new fuel pump (I’ve contacted the seller and I’m waiting for a response to see if it’s normal) and also, the hot idle is good, but sometimes it jumps to 1200 or even 1400, will let it breathe for a few days (maybe the ECU is in a learning process) and if it doesn’t improve I’ll check where the problem is, but at least the bike runs real good.

Thank you all! I hope that someone find this thread useful. I’ll keep updating if there are any news, and if someone can help with these two minor problems would be great!

 

Thank you for returning with resolutions.
It might help someone else in the future.