Bogs down under load?

[Piercee100]

My bikes revs fine in the garage but when I'm driving about it will get to around 7k and start bogging / Kangarooing until I change into a higher gear.

Noticed a hole the size of a 5p coin underneath my air box on one of the seams, looks like its been stabbed with something. Could this cause the problem with air pressure to the carb?
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Rides: Honda H100a (Retired), VT500e (Sold), Kawasaki ZX400 (sold), Kawasaki GT550 (Sold), Suzuki Inazuma (Daily), Honda CD185t (Broken), LML Star 2t (Last run edition).

[Martay]

What bike? Yes a hole in the intake system isn't helpful.
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Eat well, poo hard
Drives: Cavalier 2.0 16v
Rides: Slightly ratted Honda City Express

[Piercee100]

its my Vt500 again the hole is on the 40cm long junction box between the airbox and the carb. Think I will try and plug with some fibreglass and see what happens.
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Rides: Honda H100a (Retired), VT500e (Sold), Kawasaki ZX400 (sold), Kawasaki GT550 (Sold), Suzuki Inazuma (Daily), Honda CD185t (Broken), LML Star 2t (Last run edition).

[Fizzer Thou]

Sounds like fuel starvation (blocked fuel cap vent or fuel tap filter) or a problem with one of the main jets.

While checking the main jets,check the float heights and for any holes in the carb diaphragms.
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Just talk bikes.What else is there?

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[wilcox.ian]

i know it's a long shot... but my gsx400t used to rev to about 6.5k - 7k, then the cam chain went and i stripped her, set the timing back up currectly and sorted out the valve clearences... would then rev up to 9k, then dumped all her oil on the way to leicester forest east MAG run last september, and would all of a sudden rev right through the range, put fresh oil in (and a new case gasket) and she ran fine from then on
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[Piercee100]

The carbs have recently had new diaphragms fitted so I know they're good. Also new fuel tap (non vacuume type) blanking off the vacumme feed from the cylinder. Inline fuel filter fitted which is working well. The bike rev's cleanly whilst stationary but once on the move around 7k its not so much bogging as Kangarooing! Thought I had a puncture at first lol. I can get the bike past 7k but it feels like i'm nursing it through all the time, again runs spot on when not under load.

I'll check the pilot jet's as well, just bit of a pain due to the fact that it took me two days to get the carbs back on last time

Does WD40 work for checking boot leaks or will I need to buy some easy start?
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Rides: Honda H100a (Retired), VT500e (Sold), Kawasaki ZX400 (sold), Kawasaki GT550 (Sold), Suzuki Inazuma (Daily), Honda CD185t (Broken), LML Star 2t (Last run edition).

[Robby]

Revving up fine in neutral doesn't tell you a great deal, nor does it revving up with a large throttle opening - It's a CV carb, so you can whack it wide open, but the slide will still only open as far as it needs to.

It does sound like a fuelling problem. At some point on part throttle openings it isn't behaving. If you can nurse it past this point and eventually get to full power, then we know it is somewhere in the middle. It's working fine at full power, when the slide is fully raised and the main jet is regulating the fuel slow. It's working ok on small throttle openings, when the idle circuit, lower part of the needle and lower part of the needle jet/emulsion tube are doing their thing. The problem is at medium openings, so the needle and needle jet/emulsion tube as doing the work.

My first step would be (unusual for me, since I tend to avoid removing carbs) to pull the carbs and check that they are clean, particularly inthe emulsion tubes, and that everything is within factory spec - so that's idle screw settings, needle height, float height. Also make sure the diaphragm is correctly fitted, they are often fitted poorly. There is usually a small locating lug on them.

When stripping them, drain them fully into a cup and look for any evidence of water, which will bead up and sink to the bottom. A VT500 is old enough for the rubber sealing ring on the fuel filler cap to perish, a new one doesn't cost much from Honda. Was a problem on one of my old CB250RSs.

Carefully inspect the inlet rubbers for cracks, or corrosion where they mount onto the engine causing a poor seal. If there is an O ring where they mount onto the engine, it may need replacing. At least give it a smear or engine oil, good at plumping them up and helping create a good seal.

Holes in the inlet before the carbs shouldn't cause major running issues like this, but should be sorted. A hole on the bottom of the airbox is usually for the crankcase breather vent.

My expectation would be to find a dirty emulsion tube or water in the carb. Take your time stripping them down, use proper carb cleaner with a straw nozzle to blow it into all of the small holes, and make sure you have a workshop manual to hand with the correct settings for reassembly. Get the bodies good and clean too, aids clean reassembly.

[Piercee100]

Thanks Robby and others for the advice. I've done most of that and it have some of those symptoms and she's running better but still not perfect. So far-:

*New carb Diaphragms.
*New Fuel (did find a bit of water from a leaky petrol cap seal).
*New Fuel line with inline filters (found a pinch between the carbs).
*Carbs stripped and cleaned to a high standard, settings checked.
*Airbox repaired.
*Checked boots for leaks with easy start.

I took her out for an hour this morning with the wife on the back, starts and runs lovely. When I hit around 3k I noticed a bit of a misfire, only very slight to around 7k. She's reving fairly freely up to around 10k (limit) but seems to have half the power from 7k onwards.

When I got back to my garage I noticed the rear carb flooding which soon stopped on its own when left to idle for a few seconds. Could the coil be failing under load? Again sweet as a nut whilst not under load and at slow speeds is great but I think I would struggle to keep up with cars over 60mph. I'm now wondering if its electrical.
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Rides: Honda H100a (Retired), VT500e (Sold), Kawasaki ZX400 (sold), Kawasaki GT550 (Sold), Suzuki Inazuma (Daily), Honda CD185t (Broken), LML Star 2t (Last run edition).

[dungbug]

Sounds similar to the fault I've got with the GN, also suspecting that it's an electrical fault when under load.

[Budgetboy]

Sounds like a coil breaking down,fouled plugs or your battery is weak.
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[i.p.phrealy]

BUMP!!!!!

Did you fix the issue?
noticed my VT500E has a weird issue, it will rev to 8.5k on 3rd and hit 75-80* but knock it into 5th and it behaves like it's running out of petrol.
going to give the carb a good clean once this smog has buggered off!


*on a private road, honest occifer!
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Finally allowed a big bike 19/03/14!