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Message started by Super Thumper on 08/21/13 at 14:53:00

Title: Chinese Raptor petcock test
Post by Super Thumper on 08/21/13 at 14:53:00

I bought one of those cheap eBay Chinese Raptor 660 petcocks for $9.95 before I knew better. It has the plastic fuel tubes instead of the brass ones and the fuel outlet nipple is smaller at 1/4" instead of 5/16" as it should be. Then I got advised of my error by some members. Well, since I had it I might as well try it out.

Here are the results:

I have a 97mm Big Bore Kit, a Mikuni VM36 carb, a Web high lift cam and a ported cylinder head on it.

I thought it would starve for fuel at high RPM since the fuel outlet nipple is smaller (1/4") than the OEM petcock or the CORRECT Raptor 660 petcock (5/16")

I have a 210 main jet, much larger than the OEM carb has.

To my great surprise it works just fine.

Sustained (for over 2 miles) running at 95 mph and NO fuel starvation problem!! :o

Don't understand why the OEM & Raptor fuel nipple has to be 5/16" since that is the size fuel line I had on my Ford pickup with a 302 V8! :-?

Title: Re: Chinese Raptor petcock test
Post by Steve H on 08/21/13 at 15:23:37

At least part of the reason is it's a gravity feed system. No pressure to force fuel through the tubes / hoses.

Title: Re: Chinese Raptor petcock test
Post by Dave on 08/21/13 at 18:14:36

Yep....Gravity system. Super Thumper......since you have an O2 sensor....watch what happens when you are cruising along and the fuel level gets close to the "reserve". I was on the interstate cruising along at 65 mph and saw my mixture going lean. I switched the petcock to reserve and my mixture went back to normal. The fuel flow rate will slow down as the tank level drops.....long before the engine becomes lean enough to stop running and let you know that it is time for the switch to reserve.

Title: Re: Chinese Raptor petcock test
Post by mjs3790225 on 08/21/13 at 18:50:38

Now THAT is an pleasant side effect! Fuel meter!

Title: Re: Chinese Raptor petcock test
Post by Super Thumper on 08/22/13 at 08:17:03

Good point Dave...I will try that to see how lean it gets and post the results here with some A/F numbers.

Title: Re: Chinese Raptor petcock test
Post by Super Thumper on 08/22/13 at 17:06:26

Test for fuel starvation with a cheap ($9.95) Chinese knockoff of a Yamaha 660 Raptor petcock.

Ran the gas all the way down until it ran out and had to turn the petcock to reserve. Cruising speed.... 55 mph.

NO surging, misfires or anything before it just died from lack of fuel.

The OEM petcock would run sluggish and surge before it died.

The A/F fuel gauge went from 12.8 to one to zero at the same time, NO lean running, NO piston melt, just a sudden safe shutoff.

Main petcock: 2.4 gallons
Reserve: 0.4 gallons