New Rider
Currently Offline
Posts: 11 
Likes: 1
Joined: Jun 24, 2014 11:31:13 GMT -5
|
Post by zan on Jul 17, 2014 7:36:10 GMT -5
Here I am coming for help again.  So I've got my 72cc bike with a 16mm Dellorto PHBG. Occasionally at full speed, after several minutes of riding at top speed, she will cut out, almost as if the ignition has been cut. Pumping the throttle once or twice gets her back running and up to speed, but just one time she cut out completely and I had to stop and wait some moments until she would start back up, then she ran just fine for another hour of riding. I've got a long ride home coming up this weekend to help my mother move, so quick help would be appreciated. One more thing, she gets fuel from a vacuum pump. |
|
|
|
Post by wilds on Jul 17, 2014 10:16:47 GMT -5
Sound like it doesn't get enough fuel when your at WOT...
Have you changed the jets to bigger ones after 72cc?
Could also be that you have to set the float to a proper level.
|
|
|
|
Post by shalomdawg on Jul 17, 2014 11:15:54 GMT -5
howdy, also to check is tank vacuumn from cap vent not working to vent the tank.
lotsa miles and smiles to ya
ken
|
|
New Rider
Currently Offline
Posts: 11
Likes: 1
Joined: Jun 24, 2014 11:31:13 GMT -5
|
Post by zan on Jul 19, 2014 22:09:46 GMT -5
She still does it with the enricher turned on, and with the gas cap off. I got an idea however. The vacuum pump runs into a small cup with a run-off tube back into the tank and a gravity feed to the carburator, and the holes on the cup are tiny, maybe a millimeter in diameter. As I can pinpoint the exact points on certain runs where she cuts out, for example right before a certain curve on a certain road, I'm pretty sure that's the problem. The cup simply runs out of flow and the carb runs out of fuel. That theory also works on the bad cuts, where I'll have to slow down to 20ish kmh, or stop completely and crank the engine for several moments to get fuel from the pump, to the cup, to the float bowl, to the engine. I think I'll take the cup out and drill the fuel hose holes a millimeter or two larger to see if it works, and I'm fairly confident it will.
|
|
|
|
Post by alleyoop on Jul 19, 2014 22:22:34 GMT -5
I know what you have I just went through with another guy on how to take it off. I can't remember if it was on this forum or DOC or PROF with the same kind of fuel system. Then the pump will go straight to a fuel filter and to the carb no in between stuff. I will try and find the diagram for it.
Alleyoop
|
|
|
|
Post by alleyoop on Jul 19, 2014 22:24:33 GMT -5
I know what you have I just went through with another guy on how to take it off. I can't remember if it was on this forum or DOC or PROF with the same kind of fuel system. Then the pump will go straight to a fuel filter and to the carb no in between stuff. Alleyoop Found the Diagram of what I believe you have if SO: Take #2 hose put a Fuel Filter on it and go straight to the Carb and #3 to Vacuum to work the pump the REST YOU CAN TAKE OFF.  Take #2 hose put a Fuel Filter on it and go straight to the Carb and #3 to Vacuum to work the pump the REST YOU CAN TAKE OFF. |
|
|
|
Post by skuttadawg on Jul 19, 2014 23:00:32 GMT -5
A 16mm is small for a 72cc . The power kits come with a 21mm . What size main jet are you running ? I bet your are running lean and had a soft seize . Also what sparkplug are you running ? Too hot of a plug can also do this . Have you done a plug chop ?
I have heard of Roketas having a vacuum problem with the tank cap before . I had put on a Uni and ran it for two years and one day it died . I let it set but it would die fast . Well a hose that I just tucked away had not been capped but worked great for a long time . I covered up the hole with duct tape and ta da it was righteous again
|
|
New Rider
Currently Offline
Posts: 11
Likes: 1
Joined: Jun 24, 2014 11:31:13 GMT -5
|
Post by zan on Jul 20, 2014 4:44:51 GMT -5
The China-made carbs marked 21mm will be at best a true 18mm, and the Dellorto is a true 16mm. Others in Finland have even run 90cc kits on a 16mm PHBG. As for the fuel system, that's not what my bike has, here's the 'cup' the fuel runs into from the pump.  And the pump itself.  The main jet is a 75, any bigger and she starts bogging and spewing black smoke on full throttle. The sparkplug is the stock C7HSA. I recently took out the head for another, failed project, and the valves were a nice, healthy brown color. I looked up pictures on how a lean running head looks and that's not it. I'm going to drill the holes of the fuel primer bigger today, there's nothing to lose really. If I were to take the primer cup out completely, wouldn't there be lots of overflow through the carb from the pump pushing in more and more fuel even when I'm engine braking and such? |
|
New Rider
Currently Offline
Posts: 11
Likes: 1
Joined: Jun 24, 2014 11:31:13 GMT -5
|
Post by zan on Jul 26, 2014 8:42:18 GMT -5
Well, I removed the fuel primer entirely and ran the pump directly to the carb. The cuts are less frequent now, but still happen sometimes. Could the pump be running out of flow?
|
|
|
|
Post by jjoshua20213 on Jul 28, 2014 23:32:27 GMT -5
Try nrunning with the gas cap off and see if it still does it. And 75 main is too lean. try an 80 and adjust the carb and jeedle jet.
|
|
Freshman Rider
Currently Offline
Posts: 85
Likes: 3
Joined: May 24, 2013 22:49:43 GMT -5
|
Post by dakotafig on Jul 29, 2014 12:46:15 GMT -5
I have had the same sort of thing for a long time on my 150, although my cutout isn't that bad, it is just a momentary stall and then it is back up and going for another 30 - 45 seconds until it until it does the momentary stall again. All of this only happens at full throttle. I have gone through the same items, running without the gas cap, adjusted carb, changed carbs ect.
Never once have I adjusted the float level in the carb though, didn't really think of that. Is there a proper method to do that, does running out of fuel seem like the logical answer to this sort of stall?
Mine is a gravity feed system so I have a fuel valve and not a fuel pump, but otherwise same sort of momentary stall.
|
|
New Rider
Currently Offline
Posts: 11
Likes: 1
Joined: Jun 24, 2014 11:31:13 GMT -5
|
Post by zan on Aug 2, 2014 19:42:24 GMT -5
I moved the needle clip up by one notch, turned the air (fuel?) screw all the way in since it gave the highest idle, and switched the jet to 78. The next size up I have available is 82. Here are the results, with the engine warmed up. The point where the cuts happen has moved up a few hundred revs. Also, that puddle on the ground is gasoline from when I cleaned my air filter, not a leak. |
|
|
|
Post by alleyoop on Aug 2, 2014 19:48:59 GMT -5
It is to LEAN, you moved the CLIP the wrong way if you moved it up, you leaned it out more, You need to raise the NEEDLE move the CLIP DOWN.
Alleyoop
|
|
..BAD TO THE BONE..
