Vapor lock

[kstevens]

I removed relay but won't get a chance to ride till Friday, I will bring extra o- rings in case the relay does cure the problem, thanks guys

[who_gives_a6]

I had similar problems during the summer that was fuel boil. Would get 5 or so laps at the track and then would start. So definately would consider that if you ride high rpm's alot.

[kstevens]

QUOTE (who_gives_a6 @ Nov 7 2012, 01:37 PM) <{POST_SNAPBACK}>

I had similar problems during the summer that was fuel boil. Would get 5 or so laps at the track and then would start. So definately would consider that if you ride high rpm's alot.

It happens on every ride, whether its fast paced trail riding or on a mx track

[Canniboomer]

Vapor lock can happen without the tank boiling. If there is partial blockage at the tank inlet screen, more vacuum is created in the feed line while the pump pulls for fuel. All liquids boil at a lower temp in vacuum. Once our stock fittings are gutted, there is no need for the inlet screen to protect the valves. We remove the tank-screens on every machine now. On highflow setups I send out with the internal tankclunker, that inlet screen is plucked off FYI (for the last 2 years anyway). You can let the fuel filter do all the filtering, and there is one less thing to worry about. If you have a rear-outlet tank?, make sure the line to the pump goes around the right side of the motor, and not over the top of the hot head.

But, your symptoms could also suggest the machine is repeatedly overheating. Does it have an auto-bleed impeller cover? and is the pump chamber primed?
It's a good check to watch the coolant bottle bleed inlet while blipping the throttle, to SEE some dribble of liquid backflowing to the bottle, to confirm it is pumping coolant. If nothing?, you can blow by mouth into that bleeder hose to detect blockage. If you can move air into the chamber, but there is no dribble flow into the bottle at revs?, then the impeller is stripped. If the bleeder airway is blocked, there is likely a trapped air pocket at the impeller. Or, maybe the radiator is mud-plugged.

If everything checks out fine, the pump may just be too weakened. Or, it is running extremely lean, or combinations of things. Curious to find out wazzup.

[kstevens]

I will check all the coolant items you mentioned tonight, as I am going riding tomorrow, it's hard to test as it takes a good 20-30 min for the problem to start then after the initial stalling and restart, it occurs about every 5-10 min of riding

[Catmochanic]

Probably wouldn't hurt to check your fuel pressure? Install a gauge before the regulator, should read 40-45 psi. (from what I read on here). See if it changes any when you are having the problem?

[MX Quad Dad]

Both of my quads are rear tank feeds. Both seemed to get weak after about 20-30 min. riding on warm days Both were hard to get refired if they were shut-off or stalled in this weak state. both were cured of it by rerouting the fuel line

I believe I found out about this from a Cannondale service bullitin

[kstevens]

Fuel lines have been rerouted for quiet some time now, I went riding today after the fuel pump relay was removed, and so far so good, the problem did not return ( knock on wood) it was a fairly warm day and fan seemed to stay on for a while so I know I was hot enough for the problem to occur, but all seems good at this point... Thanks guys and if anything new develops, I know were to come

[kstevens]

QUOTE (kstevens @ Nov 9 2012, 06:45 PM) <{POST_SNAPBACK}>

Fuel lines have been rerouted for quiet some time now, I went riding today after the fuel pump relay was removed, and so far so good, the problem did not return ( knock on wood) it was a fairly warm day and fan seemed to stay on for a while so I know I was hot enough for the problem to occur, but all seems good at this point... Thanks guys and if anything new develops, I know were to come

If the quad runs fine with no relay, why is there a relay in the first place?

[cannondale27]

It routes main power through the ECU rather than the key switch.This allows ECU to control things such as thr fan even with the key off.This also may prevent overloading the keyswitch or its wiring(hasnt happened to me yet).