Race 250 loses power on open throttle(help)

[mrdavies]

Its happened twice now... I'm speeding along with the throttle (wide)open ... not varying my speed and the scooter seems to loose all power. Both times have happened here in NYC, so its been hectic!
I pull over re-start it and its fine... off I go
Both times were at fairly high speeds.
Any answers out there for me?

This is on a new (160 miles) Roadrunner race 250

thanks

[scooterollie]

Your scooter is equipped with a fuel pump that it vacuum operated. There have been reports of folks having problems with vacuum pumps not delivering enough fuel at WOT. Engine vacuum is at the highest when you let off the throttle and at the lowest when you are wide open, thus not pumping much gas. I have a CFMoto engined 250 scoot and have never had that problem but I don't run wide open. Stan Jessup posted a link recently to a site selling higher quality vacuum pumps. Do a search of his posts. Some folks have replaced the vacuum pump with a low pressure electric pump but you must be careful that it does not over power the float valve and cause carb. flooding.

[WarrenS]

Also check the spark plug wire where it connects to the plug.

[roadster250]

I've been having the same problem with my new Rocketa 250. An electric fuel pump (universal type for a car) solved the problem completely but caused the engine to run way rich (and rough) and after a week, drained the battery to such an extent that it would not restart.

I bought the 'recommended' Mikuni vacuum pump and now the problem is back. I did an insulation of the fuel line near the engine (thinking it was vapor lock) without any change. So I would think the only culprit left is insufficient suck at WOT. I don't have an answer, but I'll share the solution.

Also - don't go on eBay and buy an cute Aprilla electric fuel pump like I did; the stinkin' thing has to be mounted in-tank to work.

Does anyone know of a better electric pump solution (lower pressure/lower draw)?

[scooterollie]

Check out this post if you haven't already seen it:

scootdawg.proboards59.com/index.cgi?board=talk&action=display&thread=1187181575

[maydog]

I have a race 250 and have exactly the same issue. It is due to poor fuel delivery at wot. I have posted some of my experience here:

scootdawg.proboards59.com/index.cgi?board=200cc&action=display&thread=1186460171

Do not use a electric fuel pump without some means of pressure regulation, I have tried with the smallest I could get my hands on - the engine ran too rich at part throttle and I made a mess (dumped about a gallon of fuel).

A straight bypass of the vacuum petcock should fix the problem, but you should probably have some means of turning off the flow.

I just purchased a fuel solenoid from Ebay (2 actually), I hope to recieve them soon. I figure I will power it straight from the regulator (the same as I had wired the fuel pump) and have a secondary feed from the switched end of the starter solenoid through a diode. This should allow priming when cranking the engine.

While you are under the hood, check that the power (red heavy gauge) wire from the battery is tied away from the engine, mine was not and had partially melted. Also my intake and exhaust manifold bolts were very loose after 1000 miles.

You must be doing some fast riding for continuous WOT. The problem seems, for me, to be pronounced by about 60mph - but I get power back by laying off the throttle a bit.

Top speed of the scoot measured by GPS thus far is 70mph, though I do think I have had it a bit faster. Riding is much more pleasant 55 and under.

Good luck

[roadster250]

My scoot also starts it's choking routine at a sustained speed above 55 or WOT on an incline.

Hey, thanks for the steer to the regulated electric fuel pump, Scooterollie!

I left an extra fuel filter (from the original electric fuel pump installation) and that is probably adding some back pressure that the Mikuni vacuum pump also has to overcome. I may try to yank that out just to see if I can avoid going back to the electric and the attendant charging issues it created...I'm getting better and better at taking the stinking body work off, on the positive side of the ledger...
Chris