fuel to carb problem... I think

[China_Racer_1]

I was at at the Shanghai F1 rack today and wanted to bring out the 400 for a few sessions and get the suspension dialed in.


On the way there with our hired driver (We always use this guy 'cause he is the only driver we know with ramps and tie downs. ha ha)

However in order to do that I need to be going in a forward motion.
I got the bike around one lap and brought her in.

I thought initially that the jetting was way off.

with no spare jets I swapped carb banks for one I used in a race last season and I Figured were reasonably close.


Ah Xing (Pronounced Ah-Shing) is quite a competent mechanic and works on the BG-Performance Superbikes

but the issue persisted.

what I found was this.

The bike started a bit rough but once running it was pretty strong zipping up and down the parking lot.
Then it would simply DIE!

This happened with both carb banks so its not the carbs.

I could here the pump kicking in when I came to a stop. Then I would start it again go for a bit then it would die then I would hear the pump fl the bowls back up and so on .

So any clue?

I am stumped. Lines are new, filter is new, fuels pouring out of the hose I am clueless on this one. Frigin gremlins I guess.

Any help greatly appreciated.

Oh by the way she felt good out there on the F1 track when she was running. man I can't wait to get her going and pitch that bitch full bore into Turn 6 a long sweeping 5th gear wide open of a left hander whoo hoo!

[cad600]

Is the engine stalling out when you are slowing down / coming to a stop? If so, you need to sync the carbs and adjust your air mixture screws. That should help a lot.

One other thing to check is the wire harness. I know you cut the harness down to it's bare minimum, but you want to make sure that you do not have a wrong wire going into the fuel pump. Bmiller did this by sticking the rear brake plug into the fuel pump plug. Each time he hit the brakes, it would pop the fuse for the fuel pump.

Those are the only things I can think of right now.

Good luck.

[China_Racer_1]

Cad thanks but it was croaking out only after the bowls had emptied out.

Did not matter if I was going fast, slow, in between, throttle on, off, holding half way. it just croaked.

Also I kept the original plugs so they would plug right into each other. All I did was ditch the wires leading to the brake lights turn signals and such.

I will retrace the fuel pump wires though and put on new connectors as I saw the housing for the plug is cracked but I think that parts OK 'cause the pump works.

That's why I am scratching y head on this one. Why will the pump not work when I am moving and only work proper or at least work to refill the bowls once she has died out. Scratch... scratch....

[mrfreeze5]

Ok, here's a silly question, but Ive done this at least 3 times in the last week while tuning my bike.

Is the petcock open?

[China_Racer_1]

Freeze - Ha ha - Yeah I checked that. I also checked for a kink in the fuel line. Plus it would not keep re-filling the bowls if the cock was in the no go pos.

Nice looking bike you got there, by the way.

[China_Racer_1]

you know i got Modking to make this fuel cell and if he is not having trouble with his then it can't be the tank.... if I changed carbs and it does the same thing then it can't just be the carbs no mater how out of whack they are the fuel is just not getting to the carbs.

I will re plumb the thing with a larger diameter fuel line, remove the filter and see what happens. all this and tune the carbs in better as well.

Then see what I come up with.

Oh and I think I got Mr Yamaha Freak Dave Sadowski to rebuild me engine this winter. so it should scream in the spring. we are working out the details now to see if we can come to an agreement.

Oh and before I go... anyone know what carbs would work better for this bike.

I will have a bit of engine work to them and I have two sets of carbs,

One off a stock 40 the other off a 3EN model which I think they are the same as off a 600.

I would rather rebuild one set of carbs and work with them. so with that said where do I get a rebuild kit and a shit pile of jets? any discount places for such things?

[mrfreeze5]

Did you actually verify there is fuel flowing through the hose? It may have been running because it was trying to pump fluid and nothing was coming. It sounds like a fuel delivery problem to me. Check the pump and make sure its inlet isnt blocked, the pickup tube in the tank could be blocked, How long did your pump run? I know when mine is running, is makes a strong pumping sound, then kinda tapers off as it finishes doing its thing. But when its just pumping air, it stays the same and then just cuts off after a while. Have you tried actually drainging one of the carbs immediately after it dies to check for fuel?

Or the pump could be overactive and is flooding the carbs. If that is the case, I would start by checking the main relay for proper function.

So it will run for a bit, then die(hear pump pumping). Then it starts again immediately, or does it need to sit for a few minutes? After it dies, does it fire right up, or does it take some convincing-ie lots og choke or throttle, or a hard start where the engine is firing and the starter is running trying to make the engine turn over on its own?

[China_Racer_1]

yeah what its doing is this

it dies

I pull over and try to start it after I hear the pump run then tapper off from pumping hard to pumping slow to stop pumping when the bowls re full (I am assuming)

then yes it is in fact hard to start again. but its hard to start when cold in the same manner.

Like it needs to be choked or it starts and I have to still hold the starter button on as I feather the fuel on a bit then it eventually gets up to rev.

Did that make sense?

[mrfreeze5]

yeah what its doing is this

it dies

I pull over and try to start it after I hear the pump run then tapper off from pumping hard to pumping slow to stop pumping when the bowls re full (I am assuming)

then yes it is in fact hard to start again. but its hard to start when cold in the same manner.

Like it needs to be choked or it starts and I have to still hold the starter button on as I feather the fuel on a bit then it eventually gets up to rev.

Did that make sense?

Yes, makes sense. mine is doing the same type of start problem now, but for a different reason I think. My carbs are WAY out of synch and it is leaning out when I try to start it.

I am wondering if it might be a vacuum problem instead. I am assuming youve been through this already, but have you made sure your carbs are fully seated on the intake, the clamps are tight, the vacuum port screws are tight(and have crush washers), etc. Since mine is leaning out at startup, one way I could help it to turn over was to pull the filters off and press my hand on top of the carb sealing it off. It makes more vacuum and pulls more fuel in and starts up. Since my carbs are so far off right now, thats about the only way I can get it to start at the moment. But you might give it a try to see if it makes a difference. It probably wont solve the problem, but it might give you a clue to start narrowing things down. It will also let you feel the pull of the engine and maike sure its sucking like it should. I found that one of my carbs had a wekaer pull than the others and realized it wasnt quite seated all the way down on its intake boot.