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Old 07-09-2013, 06:08 PM   #9061
alonzo
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carb update

Today I removed the 130 main jet and put in a 127.5.
Things are better... Much better. But, still not perfect. I've still got a bit of spit/sputter on full throttle near the top rpm (in pretty much all gears.)
I could really live with the way it's running because it's the best it has ever been and I don't usually run it that far up in rpm but, will continue trying to get it all right. Maybe tomorrow I drop in the 125 main or pull one of the shims.

-- alonzo
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Old 07-09-2013, 09:56 PM   #9062
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Quote:
Originally Posted by alonzo View Post
I've still got a bit of spit/sputter on full throttle near the top rpm (in pretty much all gears.)
Do you mean at wide open throttle?
Quote:
I could really live with the way it's running because it's the best it has ever been and I don't usually run it that far up in rpm but, will continue trying to get it all right.
A rich misbehavior means it's still way too rich. I would not leave it that way.
Quote:
Maybe tomorrow I drop in the 125 main or pull one of the shims.
Installing the #125 main jet makes sense in order to remedy the rich behavior at wide open throttle.

I would remove the shim simply because on this particular carburetor, installing a shim changes the mixture by lowering the slide rather than raising the needle (unless the slide is against either stop). If there was a lean issue at 1/4 opening, it would be better to solve it by raising the needle via machining extra clip grooves.

Regards,

Derek
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Old 07-10-2013, 03:37 AM   #9063
Tom S
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Quote:
Originally Posted by motolab View Post
... on this particular carburetor, installing a shim changes the mixture by lowering the slide rather than raising the needle ...
Looking at this I can see how it would lower the slide.




Still, it seems to me that with the needle higher in relation to the slide it would let in more fuel for the given amount of air at any slide position.
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Old 07-10-2013, 05:58 AM   #9064
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Originally Posted by motolab View Post
I would remove the shim simply because on this particular carburetor, installing a shim changes the mixture by lowering the slide rather than raising the needle (unless the slide is against either stop).
If placing the shim under the needle i don't understand how that affects the position of the slide at all? it would have the same result as moving it up if the needle had grooves. Not trying to be argumentative just cant really grasp how that would happen.
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Old 07-10-2013, 07:41 AM   #9065
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Originally Posted by rextec View Post
If placing the shim under the needle i don't understand how that affects the position of the slide at all? it would have the same result as moving it up if the needle had grooves. Not trying to be argumentative just cant really grasp how that would happen.
Look at item #3 in the diagram. The washer at the top. The spring pushes down on it and it pushes down on the circlip. If shimmed, the needle will be higher in the slide but so will that washer therefore more spring pressure pushing down on the whole slide/needle assembly.

The washer pushes on the circlip, not the top of the needle. If the needle has more groves then it is free to move up into the washer not affecting spring pressure.

-- alonzo

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Old 07-10-2013, 09:33 AM   #9066
alonzo
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carb update

OK. Back to the stock (125) main jet. Shim removed and a grove turned on the needle (had to grind a cutting tool from an old sabre saw blade - 0.017" ain't very wide.) With the circlip in the new groove the needle is raised ~0.060" (~1.5mm.)

I STILL get stumble at WOT at upper rpm. And actually, while running an indicated 70mph in 5th gear it would stumble at 5/8 throttle. In 6th at that speed it was pretty good.

Is the raised needle causing this. Guess it's easy enough to find out.

-- alonzo
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Old 07-10-2013, 02:56 PM   #9067
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Re-drilled the 1/4 inch holes with a 1/2 inch bit. Added 1 hole because some of the 1/4 inch holes were close together and overlapped. I'm only at 800 feet above sea level, so this should do it. It sounds great.

Thanks for your help Alonzo. I never understood the difference between diameter and area.

Given your experience, I may skip shimming the needle.

It's a shame you can't get the pumper carb kit for this bike any more.
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Old 07-10-2013, 03:04 PM   #9068
Tom S
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Quote:
Originally Posted by alonzo View Post
OK. Back to the stock (125) main jet. Shim removed and a grove turned on the needle (had to grind a cutting tool from an old sabre saw blade - 0.017" ain't very wide.) With the circlip in the new groove the needle is raised ~0.060" (~1.5mm.)
Did you do all that at once? You need to do one thing at a time to track down the problem.
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Old 07-10-2013, 03:26 PM   #9069
alonzo
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Originally Posted by Tom S View Post
Did you do all that at once? You need to do one thing at a time to track down the problem.
Yes. But i figured that changing from the shim to the circlip in a new groove in the needle (same amount of needle lift) that the difference would be minute.

But, you're right. Hard to track a problem when multiple things are changing. I won't ever do it again... ;-}

-- a
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Old 07-10-2013, 03:28 PM   #9070
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Quote:
Originally Posted by alonzo View Post
OK. Back to the stock (125) main jet. Shim removed and a grove turned on the needle (had to grind a cutting tool from an old sabre saw blade - 0.017" ain't very wide.) With the circlip in the new groove the needle is raised ~0.060" (~1.5mm.)

I STILL get stumble at WOT at upper rpm. And actually, while running an indicated 70mph in 5th gear it would stumble at 5/8 throttle. In 6th at that speed it was pretty good.

Is the raised needle causing this. Guess it's easy enough to find out.

-- alonzo
What altitude are you at? Have you checked to make sure that you don't have any leaks from the intake manifold or exhaust area?
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Old 07-10-2013, 04:28 PM   #9071
alonzo
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Quote:
Originally Posted by jspringator View Post
Re-drilled the 1/4 inch holes with a 1/2 inch bit. Added 1 hole because some of the 1/4 inch holes were close together and overlapped. I'm only at 800 feet above sea level, so this should do it. It sounds great.

Thanks for your help Alonzo. I never understood the difference between diameter and area.

Given your experience, I may skip shimming the needle.

It's a shame you can't get the pumper carb kit for this bike any more.
There was a guy over on xt225.com selling TM33 pumper kits but the link to his web site no longer works.

-- a
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Old 07-10-2013, 08:59 PM   #9072
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Originally Posted by alonzo View Post
There was a guy over on xt225.com selling TM33 pumper kits but the link to his web site no longer works.

-- a

I have a TM 33 pumper on my xt. I got the carb from ebay. I did buy the throttle cable adapter from muniac at xt225.com. I had to adapt it to work with my single cable throttle. I think someone with some mechanical skills could get the pumper to work without a special adapter. I do recommend a new rubber intake manifold. Mine split. The OD of the TM 33 is larger than the stock carb. A new manifold handled it fine and is still working great after 4+ years.
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Old 07-11-2013, 06:34 AM   #9073
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Quote:
Originally Posted by alonzo View Post
There was a guy over on xt225.com selling TM33 pumper kits but the link to his web site no longer works.

-- a
Before you give up on the mikuni, just for giggles, try adjusting the pilot/fuel screw in a little or going back to the stock pilot jet.

before everyone tells me I don't know how a carb works -- I do realize the pilot circuit usually has little to no impact on top end, but this carb responds different then almost any other I have tinkered with. I created and cured the exact high rpm stumble symptom when messing with the pilot circuit on this carb (was at 4,200' + altitude and I think the snorkel was in at the time -- its been awhile).
By the way the biggest improvements I got were from snorkel removal, backfire screen removal, 3/4" hole Z1 mod, and a (1) small shim on the needle (stock jetting/2007 model, and all above 4,200').

Backfire screen removal is a safety item and do it at your own risk. It also improved my DR650 throttle response, but that is a different story.




Rumlover screwed with this post 07-11-2013 at 06:55 AM
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Old 07-11-2013, 06:39 AM   #9074
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Originally Posted by Rumlover View Post
Before you give up on the mikuni, just for giggles, try adjusting the pilot/fuel screw in a little or going back to the stock pilot jet.

before everyone tells me I don't know how a carb works -- I do realize the pilot circuit usually has little to no impact on top end, but this carb responds different then almost any other I have tinkered with. I created and cured the exact high speed stumble symptom when messing with the pilot circuit on this carb (at 4,000' + altitude). By the way the biggest improvements I got were from snorkel removal, backfire screen removal, 3/4" hole Z1 mod, and a (1) small shim on the needle (stock jetting/2007 model, and all above 4,200').

Backfire screen removal is a safety item and do it at your own risk. It also improved my DR650 throttle response, but that is a different story.




haha, i bought the screen to replace the missing one on my bike.. hmmm wonder if i should just pull it back out?!?!
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Old 07-11-2013, 07:03 AM   #9075
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haha, i bought the screen to replace the missing one on my bike.. hmmm wonder if i should just pull it back out?!?!
I personally can't resist this kind of tinkering, but it is pretty subjective. improved response was quite noticeable on my DR (not as much on the XT), but it won't show up on a dyno. Just felt more responsive.
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