Fuel Tap possible problems

Moderators: trixynut, Mincehead, dicky, phuk72, Jak, Kevtrx849

Post Reply
maccers
TRX-Enthusiast
Posts: 14
Joined: Fri Nov 09, 2018 9:17 am

Fuel Tap possible problems

Post by maccers » Tue May 21, 2019 2:05 pm

Was out on the TRX today, pretty much for the first time since buying it, have done short rides but today was first long, fast one. Bike seemed to take a while to start which I found odd. Then it cut out just before getting home. Loads of cranking power, I cant recall the position of the fuel tap, but I put it to PRI then texted wife to see if she could possibly bring a spare battery, or collect my kit so I could push the bike home. Tried to start it, fired up fine, rode home...!

I assume there is a problem with the fuel tap. I know these are very hard to get, and are expensive new, if you can still get them. Probably not as expensive as the damage it may cause though..! Am going to test the vac pipe with the tank off. Assume riding with the tap in PRI will just let fuel flow, and as its being used and floats are good, should not leak.

If the vac is split, and therefore not working while engine running, would it also be the case its not locking off fuel flow when engine stopped?

User avatar
Snod Blatter
TRX-Enthusiast
Posts: 405
Joined: Sun Sep 16, 2012 8:40 am
Location: Worksop, UK

Re: Fuel Tap possible problems

Post by Snod Blatter » Tue May 21, 2019 10:45 pm

You are correct that prime just lets fuel run straight through the tap, but the tap needs vacuum as a signal to let fuel through so if there's no vacuum you'll get no fuel (unless the tap leaks which they all seem to do, when you'll get a dribble).

Might be that the vacuum hose to the tap has split or come off, so the tap only sends enough fuel on prime?
'95 4NX with K&N filter, Motad Venom cans, YSS PD valves, Ohlins fork springs, 530 C+S, Green CDI, 11/16 radial master cylinder, +30mm jack up dog bones. Enjoyable money pit.

User avatar
dicky
Site Sponsor / Administrator
Posts: 1051
Joined: Thu Jan 06, 2005 11:26 am
Location: Ruffy, Victoria.

Re: Fuel Tap possible problems

Post by dicky » Wed May 22, 2019 12:25 am

Replace the fuel tap with a simple On/Off/Res tap, they are pretty much interchangeable on most Yamaha's but search on here for ones that definitely fit.
Then block the vacuum port on the inlet stub so that the engine still runs properly.
The original fuel tap will leak eventually (some from new, its a crap design) and this has been the cause a more than a few broken engines as fuel will slowly dribble through the carbs and into the cylinders, causing hydraulic lock when you hit the starter. Bent cranks, rods or cracked heads is the usual result.
dicky
OOOSDC #5

maccers
TRX-Enthusiast
Posts: 14
Joined: Fri Nov 09, 2018 9:17 am

Re: Fuel Tap possible problems

Post by maccers » Wed May 22, 2019 11:43 am

Thanks for feedback there. The bike has been heavily restored before my tenure, so its possible the tap has been replaced. Anyway, I had the tank off yesterday on the bench. The Pri as expected lets fuel out. Res also works when slight vac applied via pipe and me pretending to be at mcdonalds. On did not work, however, I suspect I may have actually ran out of fuel in the main tank, and needed to use the reserve, as the tank almost ended up in next doors garden when I lifted it off the bike...! So, probably school boy error, but with the tank on the bench, I'm gonna fill it and try the On with a vac pipe and see what happens. Also will monitor it after to check for leaks. Managed to empty the tank anyway and stick the fuel in lawn mower...!

User avatar
dicky
Site Sponsor / Administrator
Posts: 1051
Joined: Thu Jan 06, 2005 11:26 am
Location: Ruffy, Victoria.

Re: Fuel Tap possible problems

Post by dicky » Wed May 22, 2019 11:57 am

If the fuel tap was replaced with another of the same type then it will still leak.
They all do, and sooner rather than later.
dicky
OOOSDC #5

maccers
TRX-Enthusiast
Posts: 14
Joined: Fri Nov 09, 2018 9:17 am

Re: Fuel Tap possible problems

Post by maccers » Wed May 22, 2019 12:13 pm

Yes, good call. It looks a genuine part, maybe even still the original one. I'll check out what I can use as a replacement.

So anything that will fit but crucially to eliminate the vac system so its just manual on/off/res ?

User avatar
HolerTogni
Site Sponsor
Posts: 700
Joined: Thu Aug 24, 2006 3:14 pm
Location: Germany - Munich
Contact:

Re: Fuel Tap possible problems

Post by HolerTogni » Wed May 22, 2019 8:45 pm

Hi maccers!

RGV 250 or left hand side XTZ 750 fuel tap fit.

Informating greets from Munich!
Image
Nothing against four cylinders:
TRX 850 & Racetrack-TRiXie :twisted: 8)

User avatar
dicky
Site Sponsor / Administrator
Posts: 1051
Joined: Thu Jan 06, 2005 11:26 am
Location: Ruffy, Victoria.

Re: Fuel Tap possible problems

Post by dicky » Wed May 22, 2019 11:43 pm

If you had read the thread titled Fuel Tap Problems, 2nd from the top in this section, you would see that the 2000-2001 YZF-R1 (5JJ) is a known good fit.
You should probably check that other items known to wear/perish have been attended to: Air-Cut valve cover on carbs, rubber boots between carbs and inlet manifold, needle jet inside carbs, spark plug leads.
Just look at the main thread here to get an idea of what starts to go wrong. Sticky threads are a good place to start.
dicky
OOOSDC #5

maccers
TRX-Enthusiast
Posts: 14
Joined: Fri Nov 09, 2018 9:17 am

Re: Fuel Tap possible problems

Post by maccers » Thu May 23, 2019 11:06 am

Yep, I looked at that thread that lists all the taps, will probably get the R1 tap. Its about £90 new - yikes!!

Tank still on bench this morning, filled it right up with fuel, set it level, and before I'd even tried the vac it was dripping - it had been dry overnight. So yes, it leaks. For the record, the vac in position On does work.

I put a small cup under the fuel out pipe, and in the time it took me to polish one side of my mini (literally, an old Austin mini..!) it had filled about an 8th of a small tea mug - aprox 30 mins. So garage now full of fumes I will empty tank back into jerry can, and seek out a new tap.

Previous to this incident, I had tanked the bike a few months ago, took if for an MoT and then left it. It ran fine until I run the tank dry and stopped, so assume I've not knackered up anything re locking up the engine with fuel? Tank off anything I can do to check this?

Thanks all ...! Safety first and all that

maccers
TRX-Enthusiast
Posts: 14
Joined: Fri Nov 09, 2018 9:17 am

Re: Fuel Tap possible problems

Post by maccers » Thu May 23, 2019 11:09 am

Actually come to think of it, the previous owner had replaced and serviced the carbs, so the floats would be fine and not let any fuel into the carb/cylinder space. Phew! New fuel tap on order!

User avatar
OzzieDave
TRX-Enthusiast
Posts: 91
Joined: Sun Oct 02, 2016 11:33 pm
Location: Woodcroft, South Australia

Re: Fuel Tap possible problems

Post by OzzieDave » Fri May 24, 2019 4:32 am

No need to buy a genuine tap from Yamaha, I bought one for $8 Aus, from AliExpress (and a spare) which works well.
Proudly Aspergian. Yellow 98 TRX850, Staintune mufflers, braided brake hoses, blue spot brakes, remote control ignition switch, Ignitech ECU. 17/42 525 chain.

maccers
TRX-Enthusiast
Posts: 14
Joined: Fri Nov 09, 2018 9:17 am

Re: Fuel Tap possible problems

Post by maccers » Thu May 30, 2019 10:37 am

I fitted an inline fuel on/off tap for now, had to turn the petcock round to give a bit more room and used some longer hose from the inline tap to the pump. Works fine, just have to remember to turn it on and off.

Post Reply