Dear Randy: Petcock question.

fintip · May 31, 2013, 12:47:51 PM

How hard/impossible would it be to just fab up/manufacture an adapter plate that would make the 89 petcock work for the 87 and earlier bikes? Even if it were $50 per unit, that would be a huge savings. Hell, even at $100 it would make sense.

Would still love a rebuild kit, of course, if that ever happens in the distant future.

Country Joe · May 31, 2013, 02:37:21 PM

pdxfj · June 01, 2013, 09:40:53 AM

I don't believe the needle and seats in early models are enough to hold back the entire fuel tank, thus the vacuum petcock. Go with the 84-85 petcock on your 86.

Remember the later models have a fuel pump which basically shuts off fuel flow when the bike is not running.

fintip · June 02, 2013, 09:30:25 PM

Of course, the fuel pump. That's why the petcock design is incompatible.

Then again, considering the cost of replacement petcocks... I wonder what the cost of an adapter plate + fuel pump + carb conversion kit would be? Probably more expensive, but then you'd get a performance gain as well.

FJmonkey · June 02, 2013, 09:41:16 PM

Kyle, get the 84/85 petcock. It works with fuel pump while on Prime and can be shut off on Run. It is also half the price of the 86/87 unit. I spoke with George at the WCR and he was working on a FP upgrade on the cheap (used and proven by KTM riders) that he will post up soon I hope. I may take this project over as he has other higher priorities that he wants to get done first. I have had recent issues and they made me start thinking of doing this upgrade. Long story, you need to buy the beer to hear it all...

fintip · June 02, 2013, 09:55:06 PM

Hey, anytime you want a beer and we're in the same city, it's on me. Which reminds me, I owe you money on Paypal. Fantastic quality, those brackets. I knew they'd be good, but sheesh. I totally understand how they saved a guy's leg.

As far as running a fuel pump on other petcocks, when I think about it, I should be able to mod my '86 to just be an open-flow petcock and use a fuel pump in theory, yeah?

Look forward to that post. Still, the '84 petcock is $156 vs the '86 at $180... Have prices changed or something? 'Cause that's definitely not half price.

FJmonkey · June 02, 2013, 10:04:41 PM

Quote from: fintip on June 02, 2013, 09:55:06 PM
Hey, anytime you want a beer and we're in the same city, it's on me. Which reminds me, I owe you money on Paypal. Fantastic quality, those brackets. I knew they'd be good, but sheesh. I totally understand how they saved a guy's leg.

As far as running a fuel pump on other petcocks, when I think about it, I should be able to mod my '86 to just be an open-flow petcock and use a fuel pump in theory, yeah?

Look forward to that post. Still, the '84 petcock is $156 vs the '86 at $180... Have prices changed or something? 'Cause that's definitely not half price.

Ok, not half, feel free to search for others that will bolt on. The 86/87 has no way to shut off besides the vacuum function, fix that and you are there when you fit a pump. Maybe an add on valve, not as safe because hose and clamps can fail. Think worse case, if not, then think Darwin Awards. Its fuel, it has been the demise of a few FJs, I hope you and your FJ will join us at a rally some time soon....

movenon · June 03, 2013, 09:35:01 PM

Quote from: FJmonkey on June 02, 2013, 09:41:16 PM
Kyle, get the 84/85 petcock. It works with fuel pump while on Prime and can be shut off on Run. It is also half the price of the 86/87 unit. I spoke with George at the WCR and he was working on a FP upgrade on the cheap (used and proven by KTM riders) that he will post up soon I hope. I may take this project over as he has other higher priorities that he wants to get done first. I have had recent issues and they made me start thinking of doing this upgrade. Long story, you need to buy the beer to hear it all...

I will get that information on to you just as soon as I get caught back up. Still trying to get "loose"

George

FJmonkey · June 03, 2013, 09:43:35 PM

George plans to post his notes on what the KTM guys are doing to get a fuel pump (similar to what the FJ needs). Talking to George it sounds like a real good option to put a FP on a pre-89 bike. He might even offer to sell his project to another that will continue it and post it. I expressed interest based on my recent issues. I have found my root cause and ran home with zero fuel delivery issues, (Thanks Randy).... Can't find your Kookaloo with a plugged (buggered up) fuel cap....

fintip · June 03, 2013, 11:49:24 PM

Worth hearing more about; my gas cap was 'singing' the other night. Does that indicate a gas cap problem, or should I still assume it's a petcock problem?

FJmonkey · June 04, 2013, 06:51:23 AM

Quote from: fintip on June 03, 2013, 11:49:24 PM
Worth hearing more about; my gas cap was 'singing' the other night. Does that indicate a gas cap problem, or should I still assume it's a petcock problem?

The singing is not a problem, that is the flapper valves allowing air in as the tank cools and fuel contracts. It is only a problem if the flappers get clogged up and prevent air from flowing in (vacuum lock). I had vacuum lock issues but not from the flapper valves, I left parts that I should have removed when I did my Flapectomy. Parts are now gone and my FJ runs like STINK now. If you don't like the noise you can take them out. If you chose to remove them, take the the entire plastic part that has the orangeish/brown silicone valves out.

racerrad8 · June 04, 2013, 11:46:01 AM

Okay, the 84-88 petcock are truly a petcock. They are both vacuum operated for open fuel flow operation while the engine is running.

The 89+ "petcock" is really just a shut off valve used to remove the tank.

The later model bikes use the fuel pump as the shut off portion of the fuel supply system. They also use smaller needle seats in the carbs with a single inlet source since the fuel is now under pressure. Plus the fuel pump is controlled by the late model ignition control box to prevent constant running if the engine is shut off.

So, the thought of making an adapter might be great, but in order to convert over to use the "complete" 89+ system, you are going to need to address many things.

Petcock fitment (whether by adapter or late model tank)
Fuel pump
Fuel lines & filter including filter mounting
Late model ignition box to control the fuel pump
Possibly some wiring modification to make the late model ignition box to work
Carb inlet fitting
Carb needle seat

So until, if or when a rebuild kit becomes available for the O.E. petcock, you have the choice of using the two O.E. petcocks, the aftermarket manual petcock or some other variety of petcock that can be cobbled onto the bike.

For simplistic measures, bolt on the right one and ride.

Randy - RPM

fintip · June 04, 2013, 11:58:01 AM

Well, shucks. Didn't realize that the ignition box was part of the equation for the fuel pump. It's a lot simpler on my '89 750 ninja, and that's the only fuel pump I've ever messed with.

Last shot:

An adapter plate for some other true petcock from another gravity fed bigbore bike that has cheaper petcocks? I'm not sure what this would be, but ideally some measurements for fuel flow and hose size could be determined and some cheap aftermarket petcock could be found and an adapter made to fit?

Anyways, thanks for the response Randy, just shooting the shit.

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Dear Randy: Petcock question.