Bike whiz wanted.

[MidLifeCrisis]

Hi

Whilst in my youth i took many Ford pinto engine to bits, and welded many a sill seam, but i know nothing of bikes.

However, 30 years on, i thought it might be fun to get a quad bike, since 4 wheels good 2 wheels bad ( ;p )

I bought a Shineway Quad bike, it was cheapish, like most chinese stuff, and it almost works properly :S

The problem is this:

Its a 300cc engine, because i thought i might need a bit of power to tow small trailer back and forth to the allotment. However, if you run the bike in 4th gear at above 35 mph for more than about half a mile, once it warmed up, its starts surging. Its fuel surge, not electrical. if you stop the bike and wait 2 or 3 mins, off its goes again no problem, for a while, then it will start surging again.

Now, 30 years ago I was a bit of a whiz on carbs, and I still have a working gas analyser. the card is set up properly, ive checked and tweaked it.

Only twice have i ever seen fuel surge, on a car - once was a Bedford 6cwt van with a Vauxhall engine and weber carb, that was caused by a vacuum leak on the gasket. The other time was a Sierra which surged when hot, that was caused by the fuel line being too close to the exhaust manifold and vapour bubbles forming in the float chamber.

Niether of these causes is causing this surging. Ive also discovered if you keep the speed below 20 mph, it doesn't occur.

The only conclusion i can draw now is that this bike comes in 4 sizes - 200cc, 250cc, 300c and 350cc all with the same carb on, and the carb is too small to deliver sufficient amounts of fuel to the larger engine sizes.

Maybe what i need to do is figure out how to put a better quality carb off a 350cc motor bike, such as a honda or a suziki, something that can def deliver fuel to that size engine.

Id be grateful for any input, ideas or comments about this, and possible solutions.

[cb1rocket]

possible tank breather blockage, the tank is not venting and acting as a vacuum so the fuel doesn't flow.

Open the tank tap and ride and see if it cures it. If it does then you know the tank breather/vent pipe is block.

I assume everything else is spot on?

[MidLifeCrisis]

[The Artist]

[Frost]

Shineray sounds chinese to me. Buying a chinese bike is like buying a knife made of chocolate.

Check that the choke isn't sticking, or that the mixture screw hasn't been set too right in an attempt to get more power out of the thing or make it easier to start.

[MidLifeCrisis]

[nightshaddow]

did you buy it new or second hand,

if you bopught it new check the fuel lines these chinese bikes have poor quality stuff on them,

if scond hand i would check coil and the conecters there too..
____________________
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Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

[robocog]

Surging is more than likely a lean condition IMO

When you say you have set it up on a gas anaylser - we taking wideband lambda (looking at AFR)
OR
Gunsons type sniffer where your looking at HC's and CO2

Either way
/Some/ engines will happily run quite lean at idle or just off idle (to meet euro emissions and MOT requirements), but needs change with RPM /load not just being held at certain RPMs with no load

I know my DIY'd EFI'd lump in my kit car "wants" a slightly richer mix at certain cruise RPM's and low load than I was originally willing to give it
(I was aiming for a lean as possible idle through to cruise AFR, below stoich where possible)

Worked fine and dandy in cool flat conditions and I was rubbing my hands with glee thinking I had saved a packet on fuel for cruising to and from shows and gereral bimbling about and could perhaps start to be able to afford the siney shineys on offer when I got there (as long as I could keep my foot from stabbing the throttle pedal)

but on the first hot hot hot summers day out - as soon as the ECU took a bit of fuel away due to the air density algorthmn - and going slightly uphill it took to surging in an unpleasant sea sick inducing kind of way, added a couple % more fuel around the lean cruise bins and the issue hasn't re-appeared since
(though still waiting for an equivalently hot day to prove I have truly fixed it)

Has the engine got an air recirculation doo hickey?

Personally I'd just richen it up a tad via whatever you twiddled to get it spot on and see it fixes its surging

Do they check emissions on it at MOT time?
If not err or the rich side, as long as its not plug fouling it'll be reet

I suppose it depends where in the throttle range/rpm% its happening - which would help point to what part of the carb needs adjusting (assuming a CV jobbie)

(idle screw/needle height and profile / fuel float height or main jet..or a combination)

Also if its bitterly cold where you are- could be borderline icing causing a slightly lean mix?
(though my CV's used to spit and pop like an angry camel when they iced up and I'd get plain old missfires rather than surging...that was on a Pinto...shame they are so heavy, and it has to be said- they will tolerate a much wider variety of fuel mixtures unlike a more modern alloy tight tolerance lump as I found out when I first tinkered with megasquirt before going alloy 16v in the kit car)

Also agree on the points raised so far ref fuel lines/breathers
(also check its not a warped disk making it feel like engine surge..next time it does it clutch in and roll....LOL)


Regards
Rob
____________________
Needs a bigger garage...

[MidLifeCrisis]

[cb1rocket]

As you said do the tank breather first to rule that out. I'm betting money on it, hehe

[MidLifeCrisis]

OK, heres the results of this mornings tests

1. Breather ok, you lost your money.

2. Without adjusting anything, and because the weather conditions are indenticle to yesterday, i went for a test run down the long straight back lane i use, but this time keeping the speed below 25 mph. Result: no problems, no surging.

So maybe it is something to do with the carbing overcooling/icing up. I might try wrapping some hot water tank insulation round it, and then trying it at 40 mph.

[finpos]

Chuck a new spark plug in it if you have not already, you may be surprised. The single cylinder engine feels slightly different with an intermittent misfire.

Other thing to look at if you think it's being fuel starved is the fuel tap (assuming it's got one...); Put it onto "Prime" or "P" if it has such a setting, see how that goes.

f.

[MidLifeCrisis]

[Howling TerrorOutOfOffice]

Not had to strip my fuel tank, but believe the reserve setting draws fuel from the bottom of the tank and ON draws fuel from a few inches up.

[edit] stand to be corrected on this:
Suspect that because a motorcycle has a small tank, any buildup of water etc would be concentrated, and more likely to effect the carbs/FI. So Reserve in my book should be filling up time. Or keep your tank spotless by draining and replace filters as per spec. Often an overlooked job.
____________________
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The Harry Turner Project

[MidLifeCrisis]

Thanks for all the replies, I got some feedback for you all.

I found i could reproduce the surging by running at 35 mph+ and opening the choke. This caused the mixture to weaken and you could feel the onset of surging. if you then throttle back to 25 mph and close the choke a little to enrich the mixture, the surging dies away. It probably surges because its a single cylinder engine, and the block side vacuum isnt constant, as it is in a multi cylinder 4 stroke engine.

So its to do with the air/fuel ratio and the volume of air being sucked in, and the temperature of the air.

I think the problem is the carb is too small to cope with an engine that large. The bike comes in 50, 200, 250, 300 and 350cc sizes, and ill bet the same carburetor is used on all of them. It prolly works fine on a 200cc, but the 350cc just sucks too hard.

The solution in the end is to find a carb off a 350cc bike and adapt it . For the moment ill keep the speed down below 30 mph, and i can use the choke to vary the mixture.

Anyone got any suggestions for a better carb that might work, preferably something we've heard of, like weber or zenith.

[cb1rocket]

You can have a small carb or big carb regardless of engine size.

If they were all sold with the same carb, they would be set up to suit. No manufacture would just bang on a carb and hope for the best. They fitted it cos they know it works.

As you mentioned, the fuel mixture is weak and some choke is needed to enrichen it.

Getting a bigger carb would just be more headache - you have still got to set it up to suit and fit the correct jet. Zenith and Weber are car carbs, which I have little knowledge of and more likely will not fit without major modifications. Mikuni and Keihn are common OEM makes of bike carbs

I would go a for a bigger main jet and go maybe 2.5 - 5 up from stock. Reason being this is happening in the far end of throttle, and above 25 - 30 mph where the quad is nearing peak power output but the mixture is just wrong.

Can be sorted. Use would need to use the sniffer while dynoing the quad at the same time. Your get a better picture that way, than doing a stationary idle run.

[MidLifeCrisis]

[cb1rocket]

have you checked the venturi diameter of the existing carb, to the one your buying?

[cb1rocket]

hope your getting some luck, but a guide on carb tuning which I find is an essential read from another member