I'm a Nebie and have done mods now won't run properly

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069Toolman

New Member
Hi my name is Tim and i have been into the motorbicycling scene for only a few months now. I bought an entry level model whioch apparently is an a80
here is the link to the engine i purchased.. i thankyou in advance for any helpful tips anyone can provide.

http://www.ebay.com.au/itm/Motowork...orcycle_Parts_Accessories&hash=item19d4ebf903

Intialy everything was ok, little bit of a burr at top end but that eventually went away and loved the full revs. Had already ported out exaust to increase flow.
Went to a mates place and found the intake manifold to be very restrictive so out with the dremmel and ported and matched that as well.

On the way home i noticed it to be a fair bit chirpier but still reach the same top speed of 53(well according to my speedo). when i got home i though mmm lets widen the manifold a little more.

I did so and then thought well now the most restrictive part is the venturi of the carb so i dremmeled that out a little bit. I didn't stop there. i decided to drill out the jet a tiny bit and also the seat(full revs it would eventually run out of fuel in carb after a while)

I then thought well if the needle is traveling up into the seat a little bit further then maybe i should drop the float a bit to compensate.

after all that was done all it would do is go burr(4 stroking possibly) through most of the rev range mainly after 20 kms an hour or so and would only reach a top speed of 43 and get real hot real quick. i adjusted float level notch on needle to all options with not much luck.

After ordering a speed carb and waiting a week for it to arrive(which was annoying because ebay said it would only be a couple of days and i have lost my liscence) i was stoked.

I thought it would end all probs, it didn't it still seems to run the same or worse. I tried a pw80 carb and boy did it rev but no power. everything i have tried so far has made things worse and my daily ride is no more. Any ideas to what i have done wrong?

It also backfires i think out the exaust leek which seems to be leaking a little bit. well i hope it is that and not a cracked head(is a cracked head common)

Also not long after having the motor i noticed a little bit of exaust smoke comming through holes on the right side of the motor(oil seals perhaps?) it had still been running fine since then.

Also after many hours looking through threads and trying their remedies i noticed one saying about a rubber o ring in the attatchment from carb to manifold. i wasn't supplied one of those but have been using plumbing tape to fix any possible air leaks. Now the engin gets that hots it litterally melts the tape.


Thanks in advance for any help that can be provided

Tim
 
OK!

I can see what happened here...

In your search for max HP, you have created an engine that is un-manageable.

It happens a lot to racer type engine builders...

What you must do is go back a step, or two, in your experiments, until you get to some point where it can actually be used, but have a bit less HP.

..the most HP will be achieved in a lean condition, but not for long... it just builds too much heat!

The chinagirls are a great package to experiment with because they are so cheap!

Best
rc
 
Thanks rusty for your replie, yes u are correct. thats why i got a new carb, going back a few steps going back to a stock carb. Being on a tight budget i opted for a Speed carb rather than the origanal Nt carb because i was planning on upgrading anyways and didn't want to buy two carbs. Has anyone had any problems with a stock speed carb? they only major thing i have done is enlarge the intakle manifold somewhat, it is still smaller than the throat of the speed carb.
Thanks in advance for any help that can be offered.
 
the smoke you mentioned could be part of the problem,as you may be experiencing a lean condition.would be a good idea to investigate the source of the puffs of smoke,a leaking seal can be a major issue.

your exhaust leak needs to be repaired too,the exhaust pressure is part of engine performance as well.
 
thank you tool junkie for your advice. i haven't noticed the smoke puffs for some while, only in the first week or two. i have now filed the exaust mount flat as it was a bit bent from being in a vice whilst it was welded into shape. everything has been running ok with the exaust. one thing i noticed today when checking the float level of the speed carb was.

I undone the screws on the bowl whilst it was still on the bike with petcock turned off. as soon as i loosened the screws petrol came out. is the fuel in the float bowl supposed to be avove the bowl level where it meets the carb?

Thanks again everyone in advance for their advice
 
also i have managed to get it running a little better. i am not sure how, first i removed head to see if there were any obvious suggestions of a leaky head.. not that i could tell. i also wrapped plumbing tape around the carb pettels underneath the clamp as well as putting more on the manif old itself. I am thinking more of th issue was as it was running hot i was adding lil by lil more oil and may have over done it.

Now it will idle pretty well. although i think four stroke through entire range but mostly loose power as well if i open the throttle completly.
 
the fuel shouldnt overflow when bowl is removed.
drilling the inlet valve may be the issue,lifting the tab on float should help.
inspect that seat closely,as the tiniest burr will cause it to leak.
when modding carbs,its usually best to blow them out with compressed air as well as a cleaning solution to rid it of any debris.one shard of metal can cause trouble if it gets caught in the jets.
 
thanks tooljunkie, drilled out inlet valve on old carby, using speed carby now with no modifications. must have been a once off, because it is now sitting below the bowl(scratches head) still sounds like a lawn mower going up through the revs but is better when throttle not open too much feels like it is struggling for fuel when i wot, backfires if i wot when it is cold. is there any way to tell if it is getting too much fuel or not enough? i removed air cleaner and it ran the same i think. also is there a way to check if oil seal is leaking,
cheers for any replie or advice
Tim
 
a lil success at last. I have mid range back again yay,
after swapping jets for the one i drilled out from n.t carby and put into speed carby and raing the float level as much as i could i now have some mid range power back although it took a half hour ride for it too come good.?
is this normal?
i did this after noticing the spark plug was nearly white(running way lean)
Still a bit rough in bottom end revs, might be a clip placement perhaps but have seen on different threads it is best to get the float and jet sitch right first then ajust clip on needle. 3/4 through the revs it goes burr.
Thinking it might be still running too lean and not getting enough fuel?
Might take it for a ride again first to see if it gets better before i drill out jet any further?
Thanks for any imput. I am getting there slowly.
 
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