Hoping for quick reply! - fuel problem *NOW FIXED!*

OK I have started having a running problem with the GPX (the previous owner must have been a right Shifty bugger ). Here is the gist of it:

The bike has started to run a bit strange. When I try to get up it to carve through traffic or whatever, its like it fuel starves or something goes wrong anyway when it gets up in the rev range. It just looses power completely, almost like it is cutting out (but doesn't stall or anything), but seems alright lower in the rev range. Thing is, I am not sure yet but it feels like the point at which this happens is creeping down the rev range, so I do not know where it will stop, and I don't want to get stranded or anything! So do you have any ideas, has it done anything like this to you before? Anything I should check out?

I pulled the tank off tonight and pulled off the fuel tap. It is one of those ones where it has a line connecting to the engine side of the carbs, which pulls vacuum and opens a diaphragm/valve or whatever to let the fuel flow through the line to the carbs. I had to suck on another line I set up(no jokes please ) to get it to let any fuel come out of the tap. Could some of the problem be this vacuum arrangement? Would it be unadvisable to gut this diaphragm so that fuel always flows? Will this fix the problem, or is it ok and the problem lies elsewhere?

I really want to get this sorted so I can ride down the coast tomorrow for AMAC (the Australian Music Association Convention - Wooohooo!) coz the car will use a heckload more fuel. I have to work Sunday so I will have no other opportunity to get it fixed between now and Monday's ride with Aussie Ninja.

Thanks in advance.

Drim.

EDIT: I forgot to add that the fuel bowls (well 3 out of 4 anyway, haven't checked the left carb yet) are completely dry. And I mean dry. The needles looked like they hadn't seen fuel in a while....

What does it all mean?

Last edited by HemiDuty on Tue Sep 13, 2005 7:55 pm, edited 2 times in total.

damn Drim- my wife gets pissed when i have to do a routine thing like oil change to the bike or brake pads or chain/sprockets.... "no, honestly, bikes are cheaper then cars... i just need another set of tyres"

how's your partner holding up with all your bike (mis)adventures?!

(if you don't mind me asking!!) oh, btw- i have no idea about fuel type stuff.... mine did dimilar when i ran outta gas once! clogged fuel filter after that due to shyte at bottom of tank..... but that's about it!!

Thanks for asking Yankster.

She ain't happy with a lot of it, she doesn't really understand why I want to go fast / race etc., but she puts up with it bless her.

Rule out fuel problem (from easiest to hardest):
1. Put in carb cleaner in tank and run it
2. Check fuel filters, air filters, clean them while you're on it
3. Balance/synchronize the carburettor (can use a piece of plastic hose)

Rule out ignition problem
1. Check/change sparkplugs
2. Check coil/stick coil (I found one faulty stick coil on mine)
3. KTRIC ?

These are quite common steps, though, so may not find a very specific problem.

sticking or worn choke sliders?

Hemi - sounds like you have a blocked vacumn line from the tap to the motor. Don't gut the diaphragm under any circumstance, this will just stuff the tap. If you want fuel to flow all the time just leave it on 'Prime*'

Check the line from the tap back to the motor, make sure it isn't blocked or split anywhere ( vacumn will leak out of split, and won't pull fuel from tank to carbys). You may also have a split diaphragm in the tap, be careful if you pull the tap apart to check this.....it will need to be replaced if it is stuffed.

Its losing power in the upper rev range because it is slowly starving for fuel. Once you drop the revs, some fuel will flow into the bowls, and you will keep moving ( just as you have described.)

One more thing to check - undo the tap completely from the tank, and check the internal filter - it could be partially blocked inside the tank, which can reduce the flow through the tap to carbies. *If you set it to 'Prime' and hardly any fuel flows out the tap, your internal filter will be chockas with crap, and need a good clean.

If all the above checks out OK, then you need to pull carbies off, and check for sticking needle and seat - if these are sticking, you will experience fuel starvation. Don't worry about needles looking dry, thats normal.

These 3 are where I would start to look.

Good Luck Mate !! Hope you sort it out for the ride

cheers
Dave

Thanks for the replies. Well my neighbour came over and checked it out too, and it looks like the fuel tap and vacuum junk is all ok. It doesn't have a prime setting either, just off, on and res. I pulled one of the bowls off and it had heaps of mud like stuff in the bottom, we cleaned it out and threw it back on. It hasn't made any difference, I just took it for a test ride then and it hates full throttle. This all started only a couple of days ago when I went over Mee with my neighbour.

I guess I will go and check out a few of the easier suggestions put forth here. I have the uncanny feeling that I won't sort it tonight though.

But I am still going to ride it to the coast tomorrow. Surely it wouldn't actually break down and leave me stranded? My Valiants never did that to me, even when they had lotsa problems.

Thanks again.

From what u've just said...I would check the plugs now.

the brown crap in the bottom of the bowls is fuel sediment - it is coming from the tank. Cleaning this out is good, but won't fix your problem.

I reckon if you got that tap off, you would find the same shit all round the internal tank filter ( its generally really small and just sits on top of the tube that runs from the tap up into the tank) - clean all this crappola away, and see if this helps. ( It may well be the first time that the tap has ever come out of the tank, in like, a very long time....)

The run up over Mt Mee may have dislodged some bigger pieces of gunge in the fuel system ? This is where you may have problems with sticking needles and seat.

Knock over the easy things first.

cheers
Dave

Entirely possible the insides of the fuel lines have swollen or clogged up with gunk. They don't last forever. I'd recommend a full replacement of fuel lines, filters, and a clean of the tank. Any join is a place gunk will collect and therefore restrict fuel flow. That would be a cheap, if somewhat time consuming start. After that, you will need to look more carefully at carbs.

I'd be a bit worried that maybe a decent run might end up with a lean condition that could potentially cause some overheating.

Yeah I am worried about it getting lean too, but as long aas I watch the temp hopefully should be ok. The tap was dirty but looked OK, I cleaned it up earlier. Its getting late now, and I have to make an early start, but I might go back down and check the plugs and stuff. That's if I have a plug socket that fits it......

Probably a bit late Drim but check that the tank breather isnt clogged. A quick way to do it is to unlock the filler and ride it under the conditions you get the problem, I had a suzi that did the same thing years ago and it was creating a vacuum in the tank which compromised the "free" flow of fuel.
Luck mate

Thanks John I will try that when I get it all back together. I pulled a couple of plugs and apart from looking very old, they didn't seem to be faulty. The area of the head around the plug threads looks bad too. Anyway it is all looking like a no-go for tomorrow on the bike, I will have to get a couple of hours sleep and bloody well drive the stupid cage down. Since the bike is all apart ATM I may as well hold off and buy new plugs, pull the carbs off completely and go right through it all.

So it looks as though I will probably miss the ride on Monday, sorry guys.

Getting some street-fighter thoughts going around in my head with all the gear off the bike......

EDIT: The filter looks good too, a bit dirty in places but clean in others, but isn't part of the problem.

well drim you have to get fuel flow from the tank to the carbys ( bleeding obvious) so pull out the fuel tap as someone said and check for crud on a strainer inside the tank and work your way back to the carbs looking for fuel flow along the way.

once you have flow at the carbs try to start it up and use the spit on the finger test on the header pipes, if the headers dont sizle when you touch them with your finger you have a problem with that cylinder.

Dont cook the end of your finger, remember your a vegetarian guitar player this is bad, and if you have a dead cylinder you know which carby needs the most cleaning.

Good luck.

Would come over and point and things and maybe open cans of beer or rum as necesary but i have to work.

Could also be your ignition breaking down. Plugs sometimes dont show signs that they're not functioning correctly.. I had 1 plug track along the outside of itself to the head at high revs, but at normal riding, it was fine. If it's JUST started happening, I would assume that something's failed, rather than a buildup over time.