Pocket bike idles, but doesn't rev under load

[Junkers]

Hey guys and gals, was wondering if anybody could help me as I'm stumped.

I have a 49cc pocket bike and have been having problems since day one. Currently the bike will idle but die if you give it a decent amount of revs under load. I can pick the bike up and rev the nuts of it and it will do that without any hesitation but as soon as it's under load it will die past half throttle or less. The warmer the engine becomes, the less throttle you can give it before it stalls. It doesn't really just die, it sounds as if the engine boggs down then struggles to idle.

I've tried replacing the carb and have already replaced the coil, although I think I may need another. The bike is also a pig to start which I presume will have alot to do with the problem. I removed the reeds yesterday and they seem to be sitting flush with the rubber pads so I don't think it's that either. Can anyone please help?

(Yes I've turned the choke off) I can't return it as I had to replace the starter within the first ten minutes of owning it and I live in christchurch :weep:

[98tls]

Fwiw i had a dirt bike once on which the coil shit itself when it got hot with the same response your getting though when cold it went fine in neutral or under load as you say,it only crapped out after a few miles.Wonder if its worth checking that the correct plugs in there,whilst at it i would test the lead as well sometimes its the stupid easy things we overlook.....i know this from my own experiances bugger it.

[Morcs]

Running rich.

My cbr had a similar problem.
http://www.kiwibiker.co.nz/forums/showthread.php?t=58146

We tried everything, and It took $1100 of shop bills to eventually find out it was rich as hell in the midrange.

I hope this helps. Find what jet sizes and settings your carb has, and work from there.

[BigAl]

Or not getting enough gas? Presume that you've checked your fuel line.
With the carb bowl off does the fuel stream out. The chinese filters aren't flash.

Presume you've tried a new plug, the original ones are crap. NGK6M from memory, $5 from repco.

What does the plug look like, black or white?

[Junkers]

Checked the gas line, pours like a fountain. I don't think it's running rich as I normally have to twist the throttle to start it and this is the second carb thats behaving exactly the same.

Had a look at the spark plug and that suggests a stoich mix, but has a black semi circular ring on the outer lip. I think it could be the coil producing a piss weak spark, when i turn it over at cranking speed it produces a very small intermittent spark. I'm thinking maybe when the throttle is wide open and the engine is under load at low rpm it "drowns" the little spark or the air becomes to dense for the spark to jump from the electrode. However when the engine isn't under load it flies up into the high rpm perhaps because the there is less air/fuel per cycle. Just my 2 cents anyway.

New coil is on the way. If you guys have any other ideas I'd really like to hear them. Cheers for the help. :2thumbsup

[98tls]

Cant help anymore but be sure and post up what the fix was eh.

[daytona 2]

ive had two chinese pocket bikes that have done that...the problem in the end was resolved by turning the fuel switch around that other way...but yes its because that carbs not letting in enough gas for that amount of rev's....if i was you i would buy a delloroto replica carb of trade-me wihch will deffinity fix the problem.

[Coyote]

Same problem happens to mine. I pick it up and it'll run fine until you put it back on the ground. Just takes a warm up and you need to push forward to get moving rather than rely on the bike to get you going from a standstill.

Though mine is second hand and it could have a few problems that I'll eventually fix :p Though it's been far, far, farrrrr more reliable than my Honda VFR, one of the most reliable bikes around supposedly...

I'm on my phat ride in my profile pic :D

[FLYMO]

being a 2 smoke no doubt id check the crank seals
maybe even pressurise the crankcase to see if theres a leak somewhere

[racefactory]

sounds like coil or carb to me...

and that carb is a piece of **** get a dellorto rep from newmanz.co.nz or trademe.

and i'd replace that chinese spark plug out in an instant mate... that solved much for me in terms of low end acceration. My b1 replica used to backfire under acceleration from a start and new plug fixed it...

good luck

[Junkers]

Cheers, yeah got a new plug and coil is on it's way. If that doesn't solve my problem then I'll invest in a replica carb.

[Junkers]

Well, got the new coil and plug in there this evening, got the bastard started after several pulls. Started idling, then I picked it up after it had warmed enough so I could take the choke off. Gave it a little gas while it was in the air and the rear wheel started to move so I thought "sweet".. sat it down then got on it, opened the throttle then it started playing it's old tricks again.. #@$!!!

I have a few questions.. What is the gap on the coil/flywheel supposed to be? Can using 95 instead of 91 cause any problems? And last but not least, if the coil layers becomes slightly 'smoothed' by the flywheel.. can this wreck the coil?

[racefactory]

hey mate... let me tell you i a similar problem with my C1 before.

are we talkign about a cag here?

Anyway... on my c1 i had a problem where when i applied the gas under load it started backfiring and would die. i had jsut installed a euro made wrist pin bearing and had put a ton of oil back in there before i sealed the engine up again.

i solved it by A- replacing spark plug..was major fouled. secondly... putting the bike on stand and revving the shiit out the engine for 5 - 6 seconds... managed to burn out the excess oil just sitting there inside. Also mate... i found a ton of unburnt oil and fuel inside the exhaust header which i emptied- check your exhaust header for liquid just pooled in bottom if you been running fat. so basically if youve been running the mixture real fat you could have caused some problems.

If its a cag- i seriously think its just plain crap carb (they suck those cag carbs) with a needle that you wont be able to adjust to fix or quite likely a clogged needle jet thats not getting fuel through... take carb apart and clean... that fixes many problems. also might want to play/clean with your idle jet if the bike dies at REALLY low revs ie the slightest throttle increase.

yeah clean the carb you may have a clogged needle jet or something.

oh and coil gap should be thickness of a business card..

good luck let us know how it goes.

[racefactory]

if not that then maybe this

often the chinese put the fuel filter on the wrong way and it means that your carb will never have enough fuel in the float chamber for high throttle settings, check to see that fuel flows nicely through the filter...

if not that then maybe its a kinked fuel line not giving enough fuel through there.....

one things for sure it all sounds like carb trouble one way or another.

[Junkers]

Sorry for the noob questions, but I don't know the difference between a cag and a daytona etc?

It's just one of those cheap trademe job's, I had the old carb apart and cleaned it all out.. removed the jet etc and blasted it with crc.. still kept playing it's old tricks. I know those carb's are crap, you can tell by just looking at them haha. I don't think it even has a independent idle jet.

The fuel line was kinked and turned solid so I replaced that about a week ago, there is definitely no fuel supply problems.

Now looking at getting one of those Dellorto replica carbs from ebay, fingers crossed. I will pull off the exhaust and see what I can find.. cheers for your help.

[Junkers]

OK.. Just been out there and took the regulator off the carb. Plenty of gas coming through, took the jet off and blasted it with CRC.. no clogs there. Then I took the exhaust off and found a decent amount of fuel/black stuff hanging round the exhaust port. I stood the bike up and a small pool of black oil/fuel came out the rear of the bike, like pitch black crude oil. Is this the result of running "fat"? (Do you mean rich?) What could be doing this?

Well I tried starting it with the exhaust off, didn't work. Not sure if they work with the exhausts off though, they rely on back pressure don't they?

Before I took everything apart I managed to get it going again, but it only lived for a minute before it died, then I would wait a minute to start it again and it would idle for about 5 - 10 seconds before stalling.

[CookMySock]

how are you getting on with this ?

What oil and sparkplug are you using ? What fuel/oil ratio are you running ?

Try heating the tip of the plug up using a propane torch or similar. You can get it pretty much red hot, so give it rings. Allow to cool a little and refit it as hot as you can. Choke, start, choke off, now get on it and RIDE IT HARRRRD. How does it go ? Don't doof around on it at all - just give it death, and certainly don't try to idle it around.

DB

[Junkers]

Been playing around with it some more and have put it down to the carb. My new Dellorto style PHBG arrived today but they gave me a watercooled adapter :mad:. I'm using castrol full synth @ 25:1 ratio.

I managed to start the bike the other day, and found out a interesting quirk. You can idle the bike with the choke on, take the choke off and give it a short blast. It will begin to roll happily and then suddenly surge and try to stall but the funny thing is.. if your quick enough and put the choke back on it won't stall. So I guess a lack of vacuum is not drawing the petrol out possibly?

I am going to try and make this watercooled adapter fit as I do not want to have to wait another 2 weeks. Let you know how I go.

[CookMySock]

You can idle the bike with the choke on, take the choke off and give it a short blast. It will begin to roll happily and then suddenly surge and try to stall but the funny thing is.. if your quick enough and put the choke back on it won't stall.Keep doing this and see how long you can keep it going for. Don't softcock it - give it heaps!! get the choke off as much as you can so it's running nice and clean. Get on it and ride it if you can, but give it some work to do and see if it begins to clear. Maybe once it has warmed up it will go now.

Also make sure your plug is nice and clean. Consider going up to 50:1 mix just until it cleans up.


HTH,
DB

[Junkers]

It's fixed! the bastard goes...

After a bit of mucking around with the adapter plate and trying to make the float needle seal properly, we got it going. Goes very well now.. until we lost the idle screw and the kill switch wire broke off. :whocares:

I am pretty surprised though.. the carb it came with was shot, the replacement was shot and the dellorto wasn't working properly either, got there in the end though so I'm happy, cheers for everyones help! :2thumbsup

[CookMySock]

yay for cheap chinese junk !! (we got two of them) ;)


DB

[BigAl]

Good stuff Junkers, perseverance eh!

[Junkers]

Good stuff Junkers, perseverance eh!

Spoke to soon :shit: The float needle on the new carb won't seal and shes pouring gas everywhere.. my bike must be cursed.

So my next question is, can genuine dellorto parts fit a replica carb?

[Gadgit]

Yip they fit no prob...
You've had a bad run with carbs aye I got 3 19 rep carbs but they never had any issues like that... but using the genuine internals will give you a better power...if tuned right the genuine emulision tube is a better design

[Junkers]

Well I fixed the carb up and had it running for a day. Came in the next day and tried to start it.. what do you know. So I've caved and bought a new engine. If this doesn't work then I'm going to have to fly up to Auckland and throw the bike at bargains direct and hold them hostage until I get a new bike. :crazy:

[racefactory]

hey mate glad you got somewhere.

yeah that oil in the header plays havoc if it builds up like that... good thing emptying it. was there tons??

hang on a sec... your using a 19mm rep carb on an air cooled cag?? thats way too much for those bikes i thought.

the air cooled guys come to the conclusion that the C1/B1 rep 39cc water cooeld 14/14 mm carb/ dellorto 14/14 is the best for the air cooled cags. try and find one of those if you can. a 19mm is overkill youll get crap all bottom end response on a air cooled cag- thats what ''they'' say.what was it like?

btw have you had a look at the plug again? maybe its running so rich/fat your starting to foul it again? check that mate. since you had it running for a while then it doesnt work again i have a feeling that MAY WELL BE the problem. scenario could be your running so fat (as indicated by your fuel and oil in header) plug is starting to foul again after a days use. since you using the 19mm dell rep carb yeah this sounds pretty likely to me...

damn man... hope you get it sorted.

ps... to solve the fuel leaking from unsealed needle problem.... get a hammer or something and give the carb a good tap with it... you can usually get it to seat again, at least on mine you can. i found that out when i crashed my bike one time.

[Gadgit]

Theres a few mod daytona's running round with 19mm rep carbs one is winning prody mod class and the other I put the 19mm on and it made a Huge difference... it runs 7-60 gearing and pulls my 95kg ass no problem. Also runs a 0.100 jetting and loves all the fuel you can throw at it lol

[racefactory]

cool man, good to know.

[Gadgit]

Yea well I was a sceptic of the 19mm till I seen Bretts bike haul ass... the standed B1 responds well to a 17mm upgrade too just a bit of usless info throwen in there

[orange]

bigger is not better
why are no open bikes running 21mm carb's?
I are now running a 18mm hole

[racefactory]

21 mm is overkill for these bikes you will lose all your bottom end.

19mm is what the mass say is the best carb for B1 water cooled, 17 and 18 and nice too bit more bottom end. i run a banshee carb which is 17.5mm

[Gadgit]

I know of one GP3 running a 21mm He shows up to Mt Welly track now and then and dominats... It's still all in set up and what you want the bike to do... throw a 19mm on a std day2 and I don't think it will preform any better... I do also recall the hillbillies running a 22mm carb on Kens Day1 mod and it was a real screamer but there was alot of custom bits in there to.. Still comes to what the engine flows like and ya riding style.. some like it easy some like it with a bit of restriction lol

[racefactory]

yeah that is true nice post

[orange]

just because it's running it doesn't mean it's running at it's best.

[Junkers]

Well.. back to the topic. Got my new engine and it goes, unbelievably I struck more problems but solved them with a little time ( fuel filter started to leak etc). Happy as larry now. Although.. that new dellorto style carb seems to be misbehaving, but I'm going to leave it alone.

Fixed my friends one at the same time, his is identical except he has a "race" clutch (has grey clutch material instead of brown). His seems to pull much harder than mine. Are they really that much better or could it be something else?

[daytona 2]

if you want real clutch push get a BZM :2thumbsup

[BigAl]

Are they really that much better or could it be something else?

More likely the difference in performance is the clutch setup. Try measuring his spring length and applying it to yours.