(this is on a 2008 Nightster)
Good afternoon yall. I just finished up my EFI to carb swap on my 08 nightster. I completely did my own harness, used a Thunder heart ignition (along with their coil and wires), new spark plugs, and used a brand new CV carb.

After setting everything up, priming the carb (I removed the white regulator section in the fuel pump assembly, bypassing it allowing for fuel to free flow without a 150 dollar pingle petcock- that I will buy later), and installing a brand new Die Hard battery- I cannot get it to idle. I was able to get it to run for about 10 seconds while holding in my starter switch and cranking the throttle- but it eventually died. It then started up again and back fired through the exhaust and died. So now it will only crank. On the TH, I have it set to "3" on the rotary switch. I do not have the air cleaner installed just yet, as I am wanting to verify that it is operating properly without issues- and I doubt that the air cleaner will make an operational difference in it turning over. I have the carb idle set to 1 turn and the AFM screw set to 1 and 3/4s turn.

I have read nearly every single forum post about this issue and none of them have matched- or helped mine.

I am going to try to start it with some starter fluid to see if that changes anything- but I doubt it.

It has all brand new seals too, but since it doesn't even want go turn over, I cannot verify for any vacuum leaks in the manifold.

I have verified spark on all cylinders, I know it is getting fuel because I can see it spraying, therefore I am stuck.

I am a master mechanic and run my own shop, this is a side project of mine that I am trying to finish up so feel free to shoot me your suggestions!

 

Just a couple of things I can think of. My bike is also carbureted, but I am still a newbie when it comes to its operation. Is your petcock vacuum operated? If so, is the hose connected to the carburetor? If the petcock is not vacuum operated, is the back of the carburetor, where the hose would go, sealed up?

Second, is the seal between the carb and the intake manifold the correct one, and is it sealing properly? What manifold are you using? What about the seal between the two intake manifolds and the engine?

 

I did my EFI to Mikuni HSR 42 swap about 75,000 ago. Might wanna double check the Crank Position Sensor wires for polarity. Inquiring minds want to know WHY a custom built wire harness. I run my Stand Alone off the ignition switch, separate from the ecu. All my EFI crap is tucked in under the tank. Why, you ask. The rest of the damn bike needs the ecu to run, like everything other than ignition.

 

Did my 07 Dyna EFI to Mikuni HSR42 about 75,000 miles ago. I run my Stand Alone off the ignition switch, bypassing the ECU. With TH Stand Alone EVERYTHING except the ignition is run through the ECU. THAT might be the issue, no ECU.

 

I wanted to rid the OEM harness to clean up the look and KISS - Keep It Simple Stupid. It was also easier for me to take the 3 hours of my day to make a 5 output harness with a few switches than deal with splicing stuff and it looking unprofessional

 

It was not the issue, an ECU is not needed at all once you have the proper relay and fuse box set up.

The issue was a leak at the manifold to head gasket between the cylinders. I took a 30 minute break and decided to look at it like I would a classic car with a carb.

I knew I was getting spark and gas, so it had to be an air leak. The only place that could be possible would be in that area. So I placed my palm over the intake on the carb and cranked her.

Lo and behold, she fired right on up and had a high idle- therefore I knew I had a leak in either of those three gaskets.

I tore it apart and noticed that one of the big orings where the mani meet the head- hadnt lined up properly.

I re-seated it and re-installed the carb and she started right on up.

She ran like a DREAM once I had her on the road.