Fuel starvation 75RD350

[Kawtriplefreak]

Last time I rode the RD350 a couple weeks ago:
Half tank of fuel or a little less running hard through the gears shifting at 9000. 1/2 mile from home headed uphill at the top of 3rd lost power and nosed over at 8500. I got out of it and shifted to 4th and ran easy the 1/4  mile or so to the driveway. Ran fine no noise. Revved normally with no load. Pulled plugs: coffee and creme. I parked it and hadn't messed with it since. I don't have fuel filters installed so it can't be that. I contacted M in SC and he said either petcock or vent obstruction. Then he told me the test I needed to do to confirm whether it was the petcock or vent. Fast forward to yesterday. Frank B stopped by and we checked it out with the test Mark gave us. Fill the tank all the way up.Crimp one fuel line (hemostats) Place the other line in a graduated container. Turn petcock on for exactly one minute with the fuel cap on. Record the fuel level and pour the gas back into the tank. Leave the fuel cap open. Repeat the test. If all is working as it should be and the timing is identical the fuel level in the graduated container should be the same. It wasn't. 2 ounces difference in one minute. Next step is to take the cap apart and very likely find the little vent hole plugged or compromised in some way. Thanks M in SC and Frank B. More to follow.

[m in sc]

glad to help. hopefully its just that simple. 

[dgorms]

I sure like hangin with geniuses!

[85RZwade]

I sure like hangin with geniuses!

Well, you've got the address and you've been invited...

[msr]

SCIENCE!!!

... and a clever, simple way to conduct the necessary experiments. Good one, Mark!

[SoCal250]

I like it when a test procedure indicates the likely issue on the first go.

[STLMike]

Good info!
I have a 4 wheeler I suspect is being fuel starved.

[m in sc]

just an easy cap vent test. works on.. anything TBH.

[Kawtriplefreak]

Well after fooling with it for a little over an hour and a call to M in SC for technical advice I am pretty certain it is fixed. Test ride to follow once the snow melts. We are getting snowed on right now, but it doesn't look like we are going to get the 5-8 inches forecast.
I took the cap apart and I didn't find any trash, but I did find the seal had rotated on the little inner washer and covered up the inner vent hole. I also took my scribe and ever so slightly opened up the main vent hole on the outer flange that the big seal goes on per M in SC. You have to keep everything in alignment while installing the big seal that goes against the tank itself and keep the three little nubs on the inner seal in the matching holes in the outer flange that orients the whole mess and then compress the spring to install the e-clip that holds it all together.
Next, I performed the flow test and here is where it gets weird. As before I used the same graduated container and pinched off the same line as before and opened the petcock to on for exactly 60 seconds. Before I got 3 cups of fuel in one minute with the petcock open and the cap on and two ounces more than that with the cap open. As stated before that told us we had a vent obstruction.
My 1st test with the correctly oriented parts for the vent and I got four cups of fuel in 60 seconds with the cap closed, vast improvement. I poured those four cups back into the tank as before. The follow up with the cap OPEN for 60 seconds should have been four cups but was only THREE. I thought briefly that I had lost my mind, so I repeated the test two more times, with the same results then called M in SC. Then I repeated the test while I had him on the phone, same results. Mark said to reverse the order and repeat the test and I did, same results. Mark said he can't explain it and nether can I. So, we agreed to take the win and ride it and see what happens. I observed the flow coming out of the line into the container and it is obviously stronger with the cap closed then open, which in my mind is the exact opposite of what it should be and furthermore the opposite if what it was before?   

[1976RD400C]

I notice when I wheel my bike out of the garage and jostle the gas in the tank you can hear it gets pressurized and vents out the cap. Once my cap vent was completely plugged, I think when I replaced the rubber gasket, and the bike shut off after a quick warm up and within the first mile riding.

[m in sc]

it was weird for sure. put of the sun! 54 degrees.

[Kawtriplefreak]

As it turns out, gravity and physics don't change. Today I did the test again. Same results. Then I shot a little puff of air into the line I had off. Repeated the tests and got 4 cups exactly in 60 seconds with the cap on and off. So I am draining the tank now to further investigate. Apparently something is blocking the stand pipe intermittently.

[Kawtriplefreak]

I took the tank off and inspected it with my borescope. I didn't find  anything. Took the petcock completely apart and other than the already known no screen or standpipe filters didnt find anything amiss. I will be ordering a new petcock from John at Economy Cycle along with some wiring stuff I need for the Zeeltronic setup on my Gray Ghost RZ.

[Kawtriplefreak]

I did electrolysis on this tank when the bike was first resurrected years ago. The inside still looks good. I filled it up today with Evapo-Rust full strength and I  will leave it in there until my Economy Cycle order arrives. I figure it is a good idea to make sure and already had the 5 gallons of Evapo-Rust on hand since the Gray Ghost tank job.

[Kawtriplefreak]

The tank after a week filled with Evapo-Rust full strength. I did a water rinse then put a 1/2 gallon of WD 40 in the tank and coated it thoroughly, drained that and blew inside the tank with the air hose.

New petcock from John at Economy Cycle prepped and just a touch of Gasoila on the threads, sealing washers and tank gasket. A bit of trivia, M in SC took me to the hardware store in Charlotte if memory serves in 2004 and we bought that can of Gasoila to seal the threads on the Pingel for the Phoenix Project. Still good after all these years

Another quality product from John at Economy Cycle Thanks John!!
Filled it up with gas. No leaks. Fired up on the 2nd kick. It was raining and cold so no test ride until later in the week. More to follow. Thanks M in SC for your guidance as always.