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Carb Rebuild Complete - Dies on throttle

  • Thread starter Thread starter oohsam
  • Start date Start date
Hi,

Nice work on your carb sync. Yes, sometimes "close enough" is "close enough".

With the stock needles you normally have to raise them a notch. If you are not using the Dynojet kit then you'll have to shim the needles using small washers. The Dynojet kit needles have a special taper on the bottom and slots on the top to make the adjustments easier.

But you may want to perform some plug chops to check the air/fuel mixture at the different throttle openings. Then proceed as necessary.


Thank you for your indulgence,

BassCliff
 
Instead of doing plugchops, cant I just the color tune?

I think my carbs come with adjustable needles :)
 
Thanks Cliffe, read them all thoroughly!

Got home, thought I'd look at the color tune and see where my idle is.
It's sitting with a nice blue spark. When I rev it, the spark becomes orange (lean?) and it struggles around 3,000 rpm. So I think that means I need to adjust the Jet Needle.

Do I move the clip up or down?....

I'm unsure at this stage if I should increase the main jet to 142.5 and also increase the pilot jet to #45.
Will this require a resync with my carb tool?
 
OH I also did a plug chop. Took the bike up the road, hit it full throttle, it boggged out again about 3-4000 rpm then kept going. Killed the engine and had a look at the plugs.
They looked a little on the black sooty side but were sort of tanned.
Really hard to tell....

I'm pretty sure its felt like it wasnt getting enough fuel. hmm
 
Nice work on the sync! With the Carbtune you want them within 2 of each other (can't remember the measurement units) so that looks good to me.

With the Colourtune, yellow is *rich*, pale blue is lean, and a nice deep blue is spot on...

I hope to take some video when I get into using my Colourtune but I don't know when I'll get time yet. I need to do it soon as my bike is running like crap in traffic, bogs down off idle and I need to give it a wrist full of rev's to get moving and it occassionally stalls which is a tad embarrassing... driving me insane.

You can do the equivalent of plug chops with the Colourtune to a certain extent. Do the same markings of closed throttle, 1/8, 1/4, 1/2, 3/4, and full throttle. Just make sure you have a fan running getting lots of air flow and don't run it too long, just get it up to temperature so it idles without choke then do one check and shut it off for a bit.

My plan is to use the Colourtune to get all the readings on both carbs like the above, do what I can to correct it and check again, then do some plug chops to double check it.
 
oohsam said:
Thanks Cliffe, read them all thoroughly!

Got home, thought I'd look at the color tune and see where my idle is.
It's sitting with a nice blue spark. When I rev it, the spark becomes orange (lean?) and it struggles around 3,000 rpm. So I think that means I need to adjust the Jet Needle.

Do I move the clip up or down?....

I'm unsure at this stage if I should increase the main jet to 142.5 and also increase the pilot jet to #45.
Will this require a resync with my carb tool?
Click to expand...

Move the clip down one notch on the needle to allow the needle to "raise" sooner and supply more fuel

Start with the needles before you up the main jet size.

Remember, the main jet is only going to be working after about 5,000 rpm

Wish I could find that nice chart someone put up with the pilotjet/cutaway/needle/mainjet transitions

I've always found the Colortune to be more helpful at lower RPMs and less accurate at higher RPMs, just becuase it's hard to maintain a steady 7,000 RPM to get a good reading
 
pilot_jet_intro.gif


There it is, courtesy of www.mikunioz.com.

And everything refers to throttle openings rather than RPM too...
 
Forget the RPM - that's meaningless (my bike will hit 10k rpm on 1/4 throttle in neutral yet the jetting could still be a mile out). It's throttle position you are checking.
 
If you want to check performance/plugs while operating on the jet needle circuit, find a safe place to test. Mark your throttle grip and bar so you know where solid 1/3 throttle is (allow for cable slack). With the bike fully warmed up and on a level or uphill road run the bike a mile or so and note performance. Any surging or? Chop off and read the plugs too. Do what the plugs/performance say to.
At 1/3 to 1/2 throttle you are on the jet needle with no significant overlap from other jetting circuits. 1/3 works fine and will be safer due to lower speeds.
If you need to test the mains later you'll do the same thing except at full throttle.
 
Awesome! Thanks guys... Went to pull out the needles last night, didnt have the pliers to do the job so I'll buy that today and give it a crack tonight.
Hopefully this takes away the surging and I can spend my time doing plug chops..

Cheers
 
Oh and here is a cutaway of a CV carb. Little diff to ours but almost the same.

CV13.jpg
 
Ok I have some updates.
I raised the needle (moved the clamp down one slot) on all 4 carbs, and put them back together. Started the bike up and adjusted the mixture screws. I found that I have had to unscrew about 4-6 turns to get it to the highest idle. I think thats too much!
Anyway, got the mixture to what I think is right, and reved the bike. It had about 20 times the response it had before. wow. It didn't feel like it bogged when i revved it.

Took it out for a longer ride than usual, riding how I would normally about half throttle.

The bike bogged down a tiny tiny bit as I was going up a hill. Was alot less noticeable than before. Biked seemed very responsive. Until I got to the bottom off the hill I put it in neutral and the idle fell away and the bike died.
Couldn't start it back up again (and having a flat-ish battery didn't help! - damn those garage starts and no riding = no charge !)

Anyway walked the bike back home, pulled out the plugs, and they were a little white on the metal part of the plug. So I am thinking that I am still a little lean. Which means I probably need to up the jets to 142.5

Not too sure at this stage if my pilot needs upping. The pilot controls how much fuel comes in at idle right? If so I'll need to put the pilot up one size so I dont have to adjust the screws so much.

Oh this carb stuff is fun! :/

I feel as though I have almost got it though. I'm very worried about running my bike lean, dont want to damage anything.




So I'm thinking i was running lean
 
oohsam said:
So I'm running #40 Pilot, #140 Main jet and the stock air jet (not sure of the number!)

Not sure if I should try it with a #45 pilot... I will remove the needles tonight and have a look at my pin adjustment.
Click to expand...
If it were mine I'd try a 42.5 pilot.

Sam, excessive fuel can wash the colour off the spark plugs electrods. are you sure you're running lean?
 
To be honest I'm not 100% sure...I have alot of trouble with this lean/rich thing.
I've done a few plug chops and I pull out the plug and It doesn't look white, yet it doesn't look sooty black, but its not a lovely tan as it says in every article I read. Kinda blackish/brownish.

The Pilots only go up in increments of 5 after #40 :(
 
Why don't you use the Colourtune to get your pilot right? That way you know she'll at least be able to idle and you won't need to push her any more...

Don't forget to make sure to warm her up to running temperature to start with before doing any checks... she should idle on her own without choke.
 
I'm not good at this stuff!
I need to workout what is the right colour for the spark first...because there are different blues. lol...

Proof that tools dont make the man!
 
oohsam said:
I'm not good at this stuff!
I need to workout what is the right colour for the spark first...because there are different blues. lol...

Proof that tools dont make the man!
Click to expand...

Well they say "bunsen blue" is the right mix, so think back to high school days (huge struggle for me I can tell you!!!) and try to remember what the flame out of a bunsen burner looked like... if it's lighter than that then it's too lean.

I'll shoot some video (or try to anyway) when I do mine but I'm not sure when that will be yet...
 
Oh the things we used to do with a bunsen burner! was not that long ago for me lol so I still remember..haha...
I'll give this a crack tomorrow. Found a great vid on youtube which gave good info on this.

Its a car but its still valid.

http://www.youtube.com/watch?v=xEZ0-uN0NA4
 
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