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Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

Old 08-17-2010, 10:12 PM
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fiery
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Default Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

To Pe:

A couple of months ago I bought a couple of carbs. from you for my MVVS 8 cc and 10 cc engines.

I put the smaller carb on my 8 cc engine.

I cannot get the idle needle set. I have turned it all the way in (it cannot be turned any further in) and it is still too rich ar low speed.

Should I shorten (snip) the spring that tensions the low speed needle so it can be screwed in even further?

This has me puzzled. It is as if the diameter of the low speed needle is too small, and fuel is getting past it even when blocking off the main needle jet.

Any suggestions for how to proceed would be appreciated.

PS

I have had this engine for so long it remembers when my hair was all there. Almost 15 years, huge compression still. It just never dies. I use castor lube at 20%. I think this may have helped its longevity. I love the nice, dense white vapour trail it makes.
Old 08-18-2010, 03:52 AM
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Default RE: Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

the shell of the idle needle should have a 1.2mm gap to the carb body (2 turns open)
The idle needle must protrude from the shell edge by about 19.0 mm correct any difference with the 1.2mm, i.e. 19.2 changes 1.2 into 1.4.
Idle needle tip is tapered. main diameter is 1.49 -0.02mm for the part that slides into the main jet.

With these dimensions all should be well, unless you run a very high tank pressure.
Old 08-19-2010, 01:31 AM
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Default RE: Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

Thanks Pe

That is most helpful information. I will check the measurements and report back.

Best Regards

Old 08-28-2010, 11:36 PM
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Default RE: Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

Idle needle is wound all the way Pe.

I'll send it back to you for a check-over.
Old 08-29-2010, 04:40 PM
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Default RE: Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

Meaning?
What are the spray bar measurements?
Is half throttle rich? In that case you can tap the idle needle further out of the needle body assembly.
Old 08-29-2010, 08:03 PM
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Default RE: Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

Hi Pe

I have removed the Carb from the engine.

I can tune top end, no problem. The issue is that it is impossible to tune the low speed (idle). Idle runs blubbering rich. Acceleration as throttle is opened is also not clean, due to being too rich.

The low speed needle is wound in as far as it can go; i.e. the low speed needle holder (shell) is hard up against the throttle lever securing nut.

I am unsure as to how the idle needle can be further adjusted, unless a portion of the end of the shell is cut off (so more of the needle enters past the jet?

Suggestions?
Old 08-30-2010, 05:00 PM
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Default RE: Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

Have you measured the dimensions I sent as reference?
I know it is rich because you tell me, I want to find out why so I can help you to cure it!
So measure needle and spraybar please?
Old 08-30-2010, 07:13 PM
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Default RE: Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

Thanks Pe.

Will do, I have a digital vernier caliper, which will be perfect for the task.

Will post findings shortly.
Old 09-17-2010, 10:50 PM
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Default RE: Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

Here are some measurements from the problematic carb Pe:

LS needle - 19 mm total length of exposed needle (exposed proud of the shell)

- first 12 mm of the exposed needle is 1.98 mm diameter

- last 7 mm has reduced diameter. First 5 mm of the 7 mm is 1.42 mm diameter, last 2 mm (tip of needle) tapers in a flat
top cone profile, 1.1 mm across at end of tip.

I hope this may shed some light on what is wrong.

Old 09-18-2010, 07:40 AM
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Default RE: Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

You need a new idle needle:
main diameter should be 1.49 -0.02mm for the part that slides into the main jet, yours is 1.42

If you are Derek, I have your address, and will send you one.
Old 09-19-2010, 05:00 AM
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Default RE: Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

Thanks for that Pe, you have correctly identified me.

I also recently bought a P&L set from you for a 2.5D, which I am pleased to say has bedded in very nicely. But that is a story for another day
Old 09-19-2010, 03:08 PM
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Default RE: Low Speed Needle setting on a 3rd Gen. MVVS TN Carb

idle needle coming soon.
Pls be sure to detach the muffler from the 2.5cc Diesel when not running it. The liner corrodes if you don't. Yes, I agree. Awsome engine. I made a conversion from a standard ABC glow engine. This produced a totally different engine, very smooth running in the high rpm ranges. Not like a diesel at all.

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