VFR problem (1 of 2 possibilities)

[andym]

So I somehow managed to run out of petrol one day, and now the bike is acting weird:

Start bike and the revs will sit around 2.5k (with the choke off), after a couple of minutes the revs will drop until it cuts out (then it will keep cutting out every time it's restarted).

It appears to be absolutely fine when riding (even at higher speeds), and is only really noticeable when I stop at lights or pull the clutch in for more than a second, then it either cuts out or threatens to cut out.

So is it as simple as crap in the carbs, or is it possible there's some damage been done to the fuel pump? (1991 VFR)

[MarJay]

Doubt it's the fuel pump. It's going to be blocked pilot jets I think.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[ssray]

You can bypass the fuel pump, just connect the tank straight to the carbs

[stinkwheel]

If it was a fuel flow problem, it would be causing problems at high revs when demand for fuel is highest, not low revs.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Copycat73]

water in the fuel ?
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[ADSrox0r]

Mate had a '92 that did exactly the same thing. Unfortunately we never did track down the problem before he flogged it (And not to me the git, I would've had that luvverly 8 spoke off it for the 800)
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Pol Anorl]

if you ran out of fuel its probably sucked the shit through from the bottom of the tank, itll probably be blocked jets.
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[Robby]

When the bike is running, put your finger on the fuel pump. You'll feel little vibration when it pulses, about once every 2 seconds at idle, more frequently at higher revs.

Also check the charging system. It's a 90s Honda, reg/recs like to fail. It may appear to charge at idle, but not at higher revs.

I currently have an 87ish VFR 750. The fuel pump and reg/rec have both failed. It's fairly hard to get enough crap into the carbs to block them up, it runs a decent fuel filter.

[Polarbear]

Too much of a coincidence it has happened after running out of fuel. Shit in somewhere and would guess the carbs.
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[Major Doss]

[andym]

Tl;dr: I was just being a bit paranoid thinking the fuel pump could have been damaged if there was no petrol running through it

Haven't had a chance to check anything over yet.... still waiting to be allowed in my lockup to do the work (it's only been about 5-6 months after all).

The fuel pump was just me being a bit paranoid, I don't know if they work the same as submerged pumps (I really should look in to the workings of them), the pump was removed about 2 years ago for a partial strip after 1 of the connections had detached and needed to be resoldered.

As for the carbs, this definitely won't be the first attempt at cleaning a set, So far I've done 2 50cc scooters, GPz, ZXR and CBR and never had a problem with rebuilding them, just never done any from a V4 before so should be interesting.

The battery was replaced just over 2 years ago, the reg/rec definitely isn't the standard 1 that was fitted to the bike and the last time I checked the voltage was definitely normal.

Since I bought the bike (almost 2 1/2 years ago), the only problems I've had are as follows:
Battery died the day after I bought it (previous owner put £20 in to my account towards the replacement)
The chain adjuster had seized solid to the hub so required a full strip/clean/grease
Found fuel line was old and brittle (if that is the right term for rubber), so replaced with new fuel lines (after which the fuel pump shit itself and needed repaired).... all of this has been around 2 years ago.

The only thing that has been done recently (last couple of weeks recently) was finding out why it was rattling like it had a problem with the CCT, which somehow got worse when the bike leaned over to the right.... turns out it was a loose bolt in the clutch area.

For a 24 year old bike, it has been fairly problem free going by some of the stuff I read in The Workshop

[Robby]

There is no CCT, what with it having a gear train instead of a chain.

The fuel pump is a diaphragm type, and fairly tough mechanically. It is wonderfully crude, relying on contact breaker points (you know, things that can make a spark) to move a diaphragm up and down. The points get worn out over time, a replacement set is about £15. Mine died because it had been struggling along on knackered points for ages. When I fitted a new set of points, the much higher current being delivered down into the pump body managed to exploit an intermittent short and burn out the wires in the non-serviceable part. 30 year old insulation fun.

Major Doss is quite correct. The carbs are a pain in the arse, refitting is not fun. Probably easy with new rubbers, but who drops £80 on new carb rubbers on a bike worth under a grand just to make a job easy.

Oh, don't bypass the fuel pump. It would probably work on a full tank, but the carbs are quite high up and the lowest part of the tank is quite low. Fuel doesn't like to flow uphill.

[smallfrowne]

Silicone spray and a nice hot bath should help with the rubbers. V4 carbs can be amusing (for a masochist) to relocate.
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'90 VFR750; '89 NC30; '95 DR650; '89 CD250U; ~'82 CG125; ~C90

[kramdra]

[stinkwheel]

The carbs are a sod to remove. Gert a big lump of hardwood to use as a lever and watch the alloy casting doesn't fracture.

Never had a problem re-fittig them. Just clunked onto the rubbers one side at a time with a bit of a shove. A very thin application of WD40 to the inside of said rubbers smoothed the road.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[andym]

I'm no stranger to fighting with carbs, my GPz was an 82 model and probably still had original rubbers (on both sides)..... 2 days I fought with them..... TWO FUCKING DAYS

Eventually I just blasted the rubbers with the heat gun for a few minutes then used brute force and ignorance.... that worked

Then there's the CBR, now the carbs aren't difficult to remove or anything, I just begrudge buying tools for 1 job.... OK so it was only a few quid for a bike width screwdriver because some genius decided to have all the screws facing the same side of the bike because of the cam chain

[stinkwheel]

We're not talking airbox rubbers here. The airbox unscrews and just lifts off the top.

The carbs are sat down into the V of the engine and are very tight on the inlet manifold rubbers. I usually land up with a bit of wood under the edge of the carb assembly, levering one side then the other up against the rocker cover. Spraying WD40 round the join and rocking them up and down eventually gets the lube in there and they start to move. Once they start moving on one side, it's all over bar the shouting. You could easily lift the bike off the ground by pulling up on the carbs if they've been on there a long time so make sure it's somewhere stable.

If nobody has had it off before, the clamp screws are inteligently located for reaching with a screwdriver through holes in the frame.

Putting them back on is usually just a case of lining them up then pushin d down hard one side then the other until they "clunk" into position. Takes nearly my full weight though.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Vincent]

[Major Doss]

There was some cobblers in "practically rehashed articles about so called sportsbike magazine" last month about pretending to fix carb rubbers for about, ooh, till you sell the thIng..
If you like VFR's, then the £80+ will be a drop in the ocean. These are the little things that make a bike get loved.
If you are indifferent to them, there are lot's of us that do like them. Flip it before it costs more than a bean.

[mentalboy]

[stinkwheel]

Re-fitting the carbs after stripping is the work of minutes in my experience.

It's a job I've done a total of four times now on three different bikes. They all took around an hour of careful levering, sweating and cursing to get the carbs off. They all took 2 minutes to pop back on again. The rubbers are even labelled for orientation.

I believe VFR400s are trickier to refit the carbs on than the 750s.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[temeluchus]

Drain the float bowls and remove the drain screws. Give the carbs an almighty blast of cleaner up the drain 'ole, you might not have to remove the carbs at all.
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[stinkwheel]

[temeluchus]

[andym]