Air and gas intake issues (Heart of the system) By motley (Read 1,075 times)

[motley]

Okay so on startup the scooter has a decent idle.

When the scooter is fully warmed up I loose rpms and I do not get enough gas to the fuel filter causing temporary weird break downs.

I tried playing with the heart of the system some more, Checking gas lines and adjusting the carburetor.  I even popped the hose off of the carburetor to the air-box and went for a run to see if I could get a lead.

Then I figured hey lets bypass the petcock to see it it's faulty 'Cheap and easy test'.

I put a manual on off switch on and shoved a screwdriver in the intake line.

I still had the same issue, But seemed not as bad...

But then I really needed that screwdriver. So I used it to adjust the carburetor, Then I forgot to shove it back in the intake line on the next startup.

BAM! The scooter had a amazing idle. I ran the intake line into the trunk and filtered it with pantie hose to prevent any suction of dirt during testing.

After a long run to the point I should break down I didn't, The Bike only gained a higher rpm idle.

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If anyone has dealt with a similar issue or happens to know what I need to do I would highly appreciate this!!!

I fear taking off the carburetor

[cyborg]

If you have the petcock vacuum line open and it runs good you are rich

[motley]

I had someone help me adjust the carburetor and we just could not get the right mixture no matter what we did.

I am starting to think my custom exhaust is letting out to much back pressure and not allowing what is refereed to the heart of the system to operate right, Maybe not...

And yes on a throttle let off I do receive backfires, So it is to rich, But it is nearly impossible to get the carb right.

I am starting to mainly think the carburetor needs a cleaning. This bike entirely hates cold weather and requires priming the carburetor. Which tells me there is possibly a fuel issue inside the carb somewhere.. The bike in general hates a fresh start. But mainly cold starts.


Could I be lazy about this and just run something safe in the gas tank possibly?

Other than that it will require bringing it to a shop.

I appreciate your response

[jct842]

Back fire on let off indicates lean. _{What main jet is in carb now?} You do know that if you put a pipe on you will probably have to up jet. Putting on a custom air filter also usually requires larger main jet too.

[motley]

I do not really know to much about the jets on this bike.

I have attempted to take the carburetor off but I'm to afraid of messing up the rubber intake manifold.

I will have to attempt to get it off today or tomorrow, So I can not really update anything on that until then.

The brand is a Walbro carb

Very similar to:

www.retrobikes.com/proddetail.php?prod=100-055

Maybe even the exact same one.

I am 100 % sure this bike has a bore kit as well other stuff done to it, I think the original owner did not go all the way through on this build, The 50cc valve name plate is still there , So maybe not, Bike simply hits 50 with no problem.

Also the same has been done hear with that P.A.I.R system
scooterdoc.proboards.com/thread/5990/crankcase-vent-tube-pics-added?page=1&scrollTo=46339

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On another note if this bike has been bored out is it possible it could go faster if the carburetor has not been adjusted etc?

I will update latter on the jet

[jct842]

Your way out of my league, the only thing I know about a walbro carb is it is whats on my chain saw! What is the engine number? (low down on left side next to the kickstand mount.

[jct842]

Do your self a favor before you get dirt and grime under your fingernails: scooterdoc.proboards.com/thread/5324/scooter-doc-gy6-manual :read riches scooterdoc manual. and then there is more in the library, it won't hurt a bit to know a little of what to expect when you get the wrenches out.

[motley]

LB1P39QMB

Seems to be part of the reason of the speed, If this guy is correct:



Do you Need the Number where the stars are ?

And I appreciate the pointer

EDITED

Well I got the needle out, It's non adjustable.

Never got to the actual jet, I will assume I should just look into a better carburetor as for some reason... The carburetor is actually lightly glued to the intake manifold.. FML why would someone do this.... I might need a new intake manifold when I actually reattempt to remove it as cracking from flexing acquired ..

Therefore it will just stay on as is..

If I had a lot of time on my hands I would just take it apart still attached to the intake manifold, Would be a pain but...

Might consider this or ordering a new manifold.. Kind of stuck now.. Might try dumping gas on the glue latter...

[jct842]

The rubber manifold is frequent fail, they crack and leak...... order one.
I am guessing the walbro was stuck on by some one other than the manufacturer. The picture of that walbro shows a non constant velocity carb. The constant velocity carbs are used on every chinese scooter I have ever ran in to. I think if it were me I would order the correct carb and a range of jets so you can tune to your engine. the top number, 139 type of thing is the number to go by when ordering parts for your scooter. If that carb was rednecked to your scooter be prepared to correct for mismatch of cables and choke/enricher. A new correct carb can run 20 to 35 bucks. Again do some reading before jumping in to the problem head over heels.

a cracked manifold can let extra air in and therefore cause a lean condition. might try it first.

[motley]

I did some testing and the manifolds fine, If I twist it there is only what I would consider stress cracks.

But I will consider ordering it : )

I will dig around for a nice carburetor, As well order a nice Jet kit.

I would like to think my issue is solved

[tvnacman]

are the vac and fuel lines from the china factory or have they been changed?

John(jct) is correct about the popping on decell.
a cracked air box or inter connecting tubing will allow air in that will lean things out. cover/restrict the air intake on cold starts see if it helps.

John