| Author | Message | ||
     Jet_pilot |
I just realized that I posted this in the wrong section. Forgive the duplicate post I have a 2008 Blast that I bought from a friend over the winter. He used it once, layed it down and sold it to me. So, over the winter I put on a Firebolt fairing with HID lights, painted it to match and the wife is very happy (its for her). When I went to pick up the bike from the seller, it would turn start but not come off of idle without dying. Knowing that it had sat in his garage all summer, I figured the carb needed to be cleaned. Back at my house, I removed the carb and took it apart. The inside of the carb wasnt varnished or dirty, but I cleaned it anyways. The DAS boot was deteriorated so I replaced the boot and jetted the carb according to ezblast's post on the buell xb forum. The bike has a Jardine exhaust on it, I did the airbox mod, Iridium plug. The jetting that I have is: Pilot 48 main 175 Needle is the 27094-88 sportster N65C. I went with the needle instead of shimming the stock needle. Air Screw 2.5 Also has: Airbox mod and Jardine exhaust. Im at 800' elevation I did the carb work and the airbox mod and it fired right up. Idled perfect. When I blipped the throttle it would respond instantly. I never held the throttle at a steady hi rpm though. This was the middle of winter and I couldnt ride. After the carb work was done, I continued to work on the Firebolt fairing retrofit. By the time I got that done, It was nice enough to go for a little ride. Again, it started great, was on hi idle (choke) and I let it warm up for a minute or two until it came down to the normal idle. I went out of the driveway and started giving it gas and passed about 1/2 throttle it started to back fire. I brought the bike back in the shop, tore the carb apart to check everything even double checked the float). It was clean inside. I put the carb back on and same thing. This time I was running the bike on the lift in neutral and when it goes past 1/2 throttle it will start to backfire. I took the carb off again, put all the stock parts back in....same thing. I took the carb off AGAIN and put the other jets (mentioned above) back in as the jets were not the problem. I also passed low pressure air into the port on the front of the carb to verify that the slide goes all the way up. This time when it was running, I was watching the gas flow in the carb. At idle and up to about 1/2 throttle the gas sprays evenly out the jet needle. After 1/2 throttle, the fuel begins to spray out of the carb (away from the engine). Im assuming this is because the backfiring is creating a "wind" that is blowing the gas out. I should also note that when it is backfiring, there are "sparks" that can be seen where the exhaust pipe goes into the head. I checked the static timing next. The red light was not on on the LED. I moved the module about 1/16" of an inch and the light came on. Next I timed it dynamically. Other than getting a nice oil bath, the timing light is showing the two dots on the crank at 1200rpm. I checked the TPS next. The voltage is supposed to be .5v. Mine was 1.247v. The lowest that I can get the TPS to read is .85 so i set it there. I started the bike, same problem. Next I started the bike and sprayed starting fluid around the carb intake. No change in rpm. Then I did the base gasket. No change in RPM. Next I did the head gasket. The engine died! It started back up and when I sprayed the same spot, It dies again. I thought that this was weird considering that I did a compression test and the compression is at 130psi. A head gasket will usually yield a lower reading. So I went to my local Harley dealership and picked up the head gasket and a new rocker box gasket. Changed them both. Started the bike. Same backfiring. I ohmed the coil next. The primary coil is supposed to be .4-.6 ohms. Mine is at .8 to .9. The secondary coil test was within spec. Plug wire tested within spec. Just for the heck of it, I pulled off the cam cover and verified that the cams are lined up correctly. After I got the cam cover back on, I did the timing again just to make sure I put the module back in the same spot. I did notice that my timing light does not show a consistant pattern of flashes. There is a "dead spot" in the flashes every so often. Could be my light, but i thought id through that in here too. The only thing that I cannot test is the ignition module. Is it common for them to act up at higher rpm? From what I read, it does advance the timing in three different steps. So, I am thinking of replacing the coil as that was just outside of tolerances. Im also thinking of replacing the ignition module, but at $150.00, I want to do that last. And if I can find a tps, id change that too. I changed the TPS with a new one. Weirdly enough, I cannot twist it enough to get the voltage to .5. The lowest the new one will go is .947. Yes, I backed the idle screw all the way out. I also bought a NEW coil, no difference. I bought a NEW ignition module, no difference. I cracked the fuel cap open to make sure the vent was clear. No difference. For the first time in my 25 years as a mechanic, I had to bring a bike to the dealership. They still use Blast as trainers and have a couple mechanics that are supposed to be Blast experts, but havent offered anything that I havent tried yet. The only thing that I cant test is the stator. My experience with the stator is that they either work or not. I need the forums help here. I think that I have included everything that I have done. I have about 15 hours into this issue and its driving me crazy. I am an experienced mechanic so I will understand the technical stuff, if you have any ideas..... | ||
| Swampy |
Check that the diaphragm is not pinched. Take your time and work the diaphragm into the groove while you are putting the cover into place. Make sure your needle guide is under the emulsion tube not setting in the recess inside the throttle bore. |
