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tshort2007
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Joined: 07 Jun 2009
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PostPosted: 18:56 - 07 Aug 2009    Post subject: Carburetter experts required!!! Reply with quote

Afternoon all. Having some MAJOR issues still with poor idleing, to the point where the slide is adjusted around 1/3 up jut to idle at 1400 RPM. Acceleration is sluggish, and plugs foul every 800 miles. I have tried all kinds of adjustments on the float height, with no difference. The carb is factory set with the idle air screw, as the casting is blanked where the screw goes. After i eventualy get the bike started, after a run, if i take the carb off, there is fuel al inside the spigot joint to the engine. If i pull even slightly on the choke when idleing, the engine cuts out, which i belive indicates a ric circuit, along with the black, wet sooty plug.

I am stuck for ideas, and cant really afford to get a pro to look at it. Anybody got any suggestions?

Cheers all
Tom
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Alex_H
Borekit Bruiser



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PostPosted: 19:05 - 07 Aug 2009    Post subject: Reply with quote

Your right, sounds rich. Make sure the air filter isnt all gunked up - did you do anything to the bike before it started doing this? What bike is it?
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P.addy
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PostPosted: 19:08 - 07 Aug 2009    Post subject: Reply with quote

hey..
my bike cold idles @ 1400, warm runs at 1750
its what my manual says, but i guess its different per bike.
Have you got any performance parts on there, 3rd party air filters, holes in ur airbox? jetted your carb?
i know thats what made me worry about popping and backfiring.. but again..could be my bike.
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tshort2007
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PostPosted: 19:32 - 07 Aug 2009    Post subject: Reply with quote

The bike is stock, apart frm a micron exhaust system, jetted from 100 to 105 to suit (still a little under, needs a 110) Bike currently runs with NO filter, as it just wont run at all with a filter on. My cousin has same bike, and his carb idles perfectly on my bike.
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Blue_SV650S
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PostPosted: 19:50 - 07 Aug 2009    Post subject: Reply with quote

Dude, is the main jet still 'in'?

Also take out the emulsion tube (the bit the main jet screws into) and check all the little holes are clear.

Also have you checked the needle jet is secure?

https://cv-performance.com/images/uploads/vortex_tube.jpg
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tshort2007
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PostPosted: 19:58 - 07 Aug 2009    Post subject: Reply with quote

Blue_SV650S wrote:
Dude, is the main jet still 'in'?

Also take out the emulsion tube (the bit the main jet screws into) and check all the little holes are clear.

Also have you checked the needle jet is secure?

https://cv-performance.com/images/uploads/vortex_tube.jpg


The needle is secure, and the needle jet is secure (te main jet clamps it in) the holes are all clear in both the brass jets. 3 observations -

1, I cant see any holes where the needle jet (emulsion tube) fits into the carb body inside the tube. Should there be any? (apart from the needle end and the main jet end, obviously!)

2, the needle is sloppy in the needle jet. how 'snug' shoud this be, and will it affect the idle?

3, there s a small jet i belive runs off the choke. this is split and damaged. will this make any difference if the choke ciruit is closed off
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tshort2007
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PostPosted: 20:37 - 07 Aug 2009    Post subject: Reply with quote

kawak ar125, 2t, single cylinder, rotary valve, mikuni vm 24 carb, cdi ignition.
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kungfupoodle
Renault 5 Driver



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PostPosted: 22:30 - 07 Aug 2009    Post subject: Reply with quote

Rich makes the plug sooty certainly.. but if its wet it could be an ignition problem.

Has the ignition timing slipped? Check it with a strobe at whatever rpm the service manual says to do it at.
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Blue_SV650S
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PostPosted: 08:58 - 08 Aug 2009    Post subject: Reply with quote

tshort2007 wrote:

The needle is secure, and the needle jet is secure (te main jet clamps it in) the holes are all clear in both the brass jets. 3 observations -

1, I cant see any holes where the needle jet (emulsion tube) fits into the carb body inside the tube. Should there be any? (apart from the needle end and the main jet end, obviously!)

2, the needle is sloppy in the needle jet. how 'snug' shoud this be, and will it affect the idle?

3, there s a small jet i belive runs off the choke. this is split and damaged. will this make any difference if the choke ciruit is closed off


I think you are getting confused over terminology. The 'needle jet' IS the needle itself (on/in the throttle slider) the emulsion tube is the bit in the pic above and is the recess/hole the needle valve goes into. The needle itself can be a bit wobbly in the slider yes, its up and down moment it shouldn't have.

As for holes where the emulsion tube goes - YES, it DOES need outside air - its how it works Wink ... {google fu for pic as states a thousand words}

https://www.datafan.com/TunersHandbook/2-strokefiltered_files/image080.gif

https://www.datafan.com/TunersHandbook/2-strokefiltered_files/image081.gif

So you need to check the airways are clear otherwise the fuel will not atomise correctly.

A bit clearer now? Thinking
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tshort2007
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PostPosted: 09:06 - 08 Aug 2009    Post subject: Reply with quote

Clear as the sky today! Am i right in saying the tickover does not use any part of the needle? and if i am coct (please correct if i am wrong) but there is insufficiant air pressure to draw fuel through the needle at idle?
OR
Because my idle circuit is so rich, having the slide 1/3 up just to tickover gives the air pressure required, giving a perfect mix from the needle jet but richening it from the rich idle circuit?

Could xcess fuel leak through the needle at idle speed?

Thanks for your help so far!
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Blue_SV650S
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PostPosted: 09:31 - 08 Aug 2009    Post subject: Reply with quote

tshort2007 wrote:
Clear as the sky today! Am i right in saying the tickover does not use any part of the needle? and if i am coct (please correct if i am wrong) but there is insufficiant air pressure to draw fuel through the needle at idle?
OR
Because my idle circuit is so rich, having the slide 1/3 up just to tickover gives the air pressure required, giving a perfect mix from the needle jet but richening it from the rich idle circuit?

Could xcess fuel leak through the needle at idle speed?

Thanks for your help so far!


If the plug is fouling every 800 miles, its rich when going along isn't it!! Wink

There are 3 phases/separate systems in a carburettor. First you have the idle circuit - which you already know about - this handles the first ~1/4 of throttle. Next we have the needle jet which controls ~1/4 to ~3/4, then it is mostly down to the main jet for the last 1/4! Now although we have 3 parts here that have the largest influence over things in 'their' stage, they are bound to effect/overlap the other stages to some degree.

As you have cleaned/checked everything else, I think your problem is a blockage in the holes in the FRONT of the carb. You can see the emulsion tube must have one, there is also one for the idle circuit.

Do you have/have access to a compressor?

p.s. I'd also second checking the ignition system!! Wink
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tshort2007
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PostPosted: 09:39 - 08 Aug 2009    Post subject: Reply with quote

Quote:
If the plug is fouling every 800 miles, its rich when going along isn't it!!


If i go for a good thrash, the pg gets browner. above 3000rpm, 1/2 throttle, the bike is a lot better, but not perfect

Yes i have a compresser (fantastic piece of kit Very Happy)

Ignition and timing seem ok, but unable to fully test without the correct readings tocompare too!

Still convinced its carb issue!
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Blue_SV650S
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PostPosted: 09:43 - 08 Aug 2009    Post subject: Reply with quote

tshort2007 wrote:
Quote:
If the plug is fouling every 800 miles, its rich when going along isn't it!!


If i go for a good thrash, the pg gets browner. above 3000rpm, 1/2 throttle, the bike is a lot better, but not perfect

Yes i have a compresser (fantastic piece of kit Very Happy)

Ignition and timing seem ok, but unable to fully test without the correct readings tocompare too!

Still convinced its carb issue!


Get it apart/off again and get the compressor on the little holes in the front of the carb! Thumbs Up

There are also tiny hole/s around the base of where the slider goes, this is the idle fuel hole - check this is clear - lots of compressed air is the way forward here!! Smile

p.s. a few detailed pics of the carb would help! (I can then turn the generic into the exact).
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tshort2007
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PostPosted: 10:20 - 08 Aug 2009    Post subject: Reply with quote

have blown through the 2 holes in the front of the carb on the air intake side, and both blow through into the emultion tube. by the holes in the bottom of the crb, i assume you mean the holes to the side of the top of the emustion tube, therse are also clear. how many holes are there inside the emulion tube (the casting, not the brass) from the air intake side?

i think poking with bristles from a brusare in order!!!

PS, will pop pics on later today, bike is at work at the moment. Bloody shame its runnin crap, as its a pefect biking day today Mad Mad
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tshort2007
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PostPosted: 10:46 - 08 Aug 2009    Post subject: Reply with quote

images below ( i hope Smile )
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tshort2007
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PostPosted: 11:19 - 08 Aug 2009    Post subject: Reply with quote

UPDATE - STILL NO JOY

Stripped the carb compleatly, scubbed all the crevicis wih cotton wool and carb cleaner. rebuilt, and nothin Sad

I have shown below a mod to the above image showing my idle circuit. the main feed in comes direct from the air jet in the intake of the carb. i assume it atomises as the emultion tube, so why is it still putting too much fuel in?

AAAAAAARRRRRRRRRRRGGGGGGGGGGGHHHHHHHHH
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garyd
Brolly Dolly



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PostPosted: 13:27 - 08 Aug 2009    Post subject: Reply with quote

Use your mates carb and ride the bike,if its now ok stop messing about and get a new carb.Then play about with that old one at your leisure Thumbs Up
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tshort2007
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PostPosted: 16:23 - 08 Aug 2009    Post subject: Reply with quote

Read my above post - funds are VERY low!! mates carb works fine, had it on for 3 days, cold starts, hot starts, wet starts, all fine!

SO i know its a carb issue, and cant afford the 110 for a new one Sad
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tshort2007
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PostPosted: 18:14 - 08 Aug 2009    Post subject: Reply with quote

More of an update

Blocked off choke
lowered float height below the standard setup (not as much fuel in the bowl)
unscrewed piolet jet 1/4 turn

Idles slightly better, at 1300 RPM with just the idle screw all the way in. No extra tension on the cable needed

So, lowered float height a little more, no further difference
then
unscrewed jet a littlemore, no differene
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baldy
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PostPosted: 23:20 - 08 Aug 2009    Post subject: Reply with quote

You should replace the broken jet. It may be letting a lot more fuel in than you think.

Does the needle valve work properly? It may be flooding the carb.
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tshort2007
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PostPosted: 07:58 - 09 Aug 2009    Post subject: Reply with quote

is it possible to block the needle jet off tempory to see if fuel is leaking through the top of the emultion tube? and is there a way to block off the idle jet slightly (by blocking one of the 8 holes in the side) to see if this betters things?

Thanks guys, your advice is invaluable so far
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Blue_SV650S
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PostPosted: 11:42 - 09 Aug 2009    Post subject: Reply with quote

tshort2007 wrote:
is it possible to block the needle jet off tempory to see if fuel is leaking through the top of the emultion tube? and is there a way to block off the idle jet slightly (by blocking one of the 8 holes in the side) to see if this betters things?

Thanks guys, your advice is invaluable so far


If you have swapped the carb over, then we KNOW its the carb, so we just have to keep trying.

So you have air-lined every jet and orifice?

Is the seal round the slider top cap good?

Are there any hairline cracks in the carb?

Put the float height back to stock.

If you want to isolate the idle circuit, all you need to do is block off the main jet. I guess the best way to do this is to put some blue-tac on the main jet??? not sure how that will react with the fuel mind you ...

If you have blocked off the main jet, I wouldn't run it too long - especially with a stroker.

Oh and just double check the needle jet is on the correct setting.

At the end of the day, if it won't idle, then it has to be the slow circuit we are looking at. By jamming the throttle 1/3 open, you are running the main circuit (controlled by the needle at this point) suggesting no fuel or too much fuel is flowing through the slow system.
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tshort2007
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PostPosted: 13:27 - 09 Aug 2009    Post subject: Reply with quote

Quote:
So you have air-lined every jet and orifice?


Yes, at least times with carb cleaner and 120psi air line

Quote:
Is the seal round the slider top cap good?


didnknow there was one
erm, no. its split, held together wih parcel tape and very perished
is this sigificant?

Quote:
Are there any hairline cracks in the carb?


No. WD all round, no bubbles or cracks

Quote:
Put the float height back to stock.


Done - nothing

Quote:
At the end of the day, if it won't idle, then it has to be the slow circuit we are looking at. By jamming the throttle 1/3 open, you are running the main circuit (controlled by the needle at this point) suggesting no fuel or too much fuel is flowing through the slow system.


fully agree, i belive its rich, but the bike will not start without the slide so far up, so i can only guess
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tshort2007
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PostPosted: 14:14 - 09 Aug 2009    Post subject: Reply with quote

WERE GETTING SOMEWHERE!!!!!!!!!!!!!

Plugged up the main jet, to prevent the fuel getting into the emultion tube. Idling at 1600 RPM with just the slide adjust screw about 2 turns out . but the bike revs up to red line when i twist the throttle.

gonna go an have another fiddle!
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Blue_SV650S
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PostPosted: 14:17 - 09 Aug 2009    Post subject: Reply with quote

tshort2007 wrote:

Quote:
Is the seal round the slider top cap good?


didnknow there was one
erm, no. its split, held together wih parcel tape and very perished
is this sigificant?
s


To be honest, we are running out of obvious things aren't we!! Wink

If it is perished, then it can let air in there, this could be playing havoc with the idle as the mix will be off - hence compensating with opening the throttle and bringing the main into play?? It could also be having strange effects on the airflow through the carb (imagine the air coming down through the slider/needle jet area).

I guess as a bodge/check, you can put some electrical tape round it (when it is done up) to seal it up and give it a try Thumbs Up Also the little rubber johnny that goes over the end of the cable bit on the same cap, is that ok?
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