| Author | Message | ||
     Jeepurz |
ive been on this board using some info figured id join since it seemed like theres great info im freakin stumped. First im 55 and have riden and tinker with bikes since I was 13. the problem is im not up at all on new stuff. All my stuff is 70's bike wise & was purchased from barns for under 400 bucks.Yes Im cheap! I bought a blast last month 01 5K on miles. Purty much all the sudden no start, battery was weak so I popped a new one in. Still when it did start I got backfire through carb stumbles & dies. I studied up and checked the obvious putting in new plug, checked carb boot, and made sure carb was clean, checked spark , all good. I stuffed a rag in the intake and went back to research came back tried again, forgeting to remove the rag & it fires , see rag remove it , it dies. Im wondering if it could be the auto choke? I still havent checked intake manifold to head yet, is there a history of problems there? Were these carbs setup for accelpumps? on other hd's? (see pic).  thanks in advance for any input, I really like the bike & imo there underrated. Id really like to know about other carb options too. Down the road id either like to chop or cafe/fighter one. | ||
| Crackhead |
the blast doesn't use the accel pump. What jets are installed? and was the af screw messed with? | ||
| Jeepurz |
I didnt check jet sizes, just made sure they were clean, I will check the Air screw to see if its been tweeked, I picked up some starter fluid to see what a shot would do. Is AJ screw 1.5 turns out? I finally downloaded a manual but havent looked it over yet. | ||
| Gearheaderiko |
Welcome Jeff! Everything you've written points to the boot (aka: "Das Boot"). Did you take it off and inspect it (I see you've got the carb off)? Murphy's law says the crack will be where you cant see it. Is it a factory boot and not some other type of hose? Is it too tight or too loose? (its the same basic set-up as on many other bikes, but it fails at an alarming rate on the Blast. Only a factory boot will do). The Auto Enrichener is just an automatic choke. If its not working, the bike should run fine when warmed up. If its stuck half way, then the problem should still be minimal. But your description points directly to a sudden very lean condition (Das Boot). The slow Jet must be changed to at least a minimum #45 (unless you're at higher elevations). With a #46,or #48 the bike will probably start without the choke in the summertime (mine hardly needs choke with a 45, but its not stock so...). The main jet should be a #170 and thats good. Intake screw is 2 to 2 1/2 turns (but 1 1/2 is stock). There isnt a history of manifold to head problems, but it does happen. Yours sounds like a sudden problem which is usually boot, not manifold to head. Is the vacuum port on the carb plugged? (it may not have a vacuum port or the pipe may be solid since only CA Blasts used it) And you didnt do anything to the bike beforehand, it just happened? It could be electrical and everything else is just a coincidence. Pull the timing/points cover off so you can watch the LED on the module. No LED flash = no spark. Will it run if you warm it up? (as said earlier, #45 slow jet and 2 1/2 turns on the idle mix screw and it should run without the choke as long as you can get it started. Try warm midday, rather than cold am). FWIW: There are other causes, but most are gradual, not sudden. | ||
| Gearheaderiko |
PS #45 jet is stock on many HD's. Just dont tell them its for a Blast cuz they'll close the parts book and say they dont have it. Beside the accel pump, its virtually the same carb as on the twins. | ||
| Jeepurz |
thanks very much for that info, I did inspect the boot, but im bout blind, I will recheck it. It does look to be stock, I started it with ether, itll run without , I shot a quick vid that purty shakey cause im trying to keep it running, let off throttle it dies out, wont start again without ether. CLICK FOR VID.  | ||
| Swampy |
Welcome to the Thumper Forum Jeepurz! Sounds like you are runnning lean....Follow what Gearheaderiko said.. But..... Two things... Get a set of Superbike bars and disconnect the crank case vent so all the engine debris isn't running through your engine. | ||
| Gearheaderiko |
Change the slow jet to a #45. I dont like the "start changing parts" method of repair, but it has to be done anyway. That and 2 - 2 1/2 turns out on the mixture screw. Since you've got the tank off, do a compression test (with a gauge). Unlikely that your compression dropped all of a sudden, but it will cause your problem (and you've got the tank off anyway). | ||
| Gearheaderiko |
Did you find the vacuum port on the carb? (not that it makes all that much difference but..) | ||
| Jeepurz |
found it boot was tore, dont know how I didnt see it first time I bent it over and it opened up. next question any problem getting a radiator hose shorten it and go that route? another guestion on jets, If I were to open the exhaust up, im thinkin about cutting the pipe before muffler, adding a section, ive got a short red devil can Id like to add, Id also like to loose the airbox, and just stick a paper k&n filter boot. I can make bout anything but tuning carbs is not my strong point. I was hoping to wait till winter to do this but now im thinkin while its apart. thanks for all the input. | ||
| Gearheaderiko |
No, No, No!!! Use a factory boot. Anything else might get you home, but will fail (its been tried). And if it fails you'll be running lean and headed to certain damage. Stock exhaust is a little restrictive, but you can open it up if you want. Depending on the can, you might just end up being loud and nothing more (even less). Air filters have been just added on to the carb (no elbow, etc.), but might hit your knee. Dont spend a lot until you find out where your knee is. |
