carb issue

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chris8686

New Member
May 2, 2013
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Bellingham
Hello, I am having a little carb jetting issue. The motor bogs 3/4-WOT. I am currently running opti2 mixed at 1.8oz per gallon or 70:1. The needle is in the leanest position and the main jet is a dellorto #62. I've rid the carb of all air leaks with seal all. The feel riding the bike says too rich and the plug color says leave me alone and ride me.

Here is a pic of my plug after doing a wot plug chop from this mornings ride.

The plug is a b8hs btw
 

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crassius

crassius

Well-Known Member
Sep 30, 2012
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what do you weigh? I'm finding that I can't tune out all the 4-stroking unless I ride uphill because my current weight won't put sufficient load on the motor on level ground - you could try lowering float a bit tho
 
2door

2door

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Staff member
Sep 15, 2008
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Littleton, Colorado
How many miles on the engine, Chris? If less that 200 I'll have to agree with what your plug said. "Leave it alone and ride it". They get better with age; like a fine wine :)

However I don't agree with running Opti-2 at your 70:1 ratio. You're a little on the 'oil rich' side. Why not mix at the recommended ratio?
Tom
 
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chris8686

New Member
May 2, 2013
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Bellingham
I weigh 180lbs. The motor has 750 miles on it. I am running it at 70:1 because I have quite a few 1.8oz packets of opti2 that I acquired from a friend. My older bike has 1500 miles running the same oil ratio. I recently did a total overhaul on that engine due to crank bearing failure. The engine had very little carbon build up and I feel very confident running 70:1.

When wot it flattens out and sounds like WAAAaaaaa
 
2door

2door

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Staff member
Sep 15, 2008
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Littleton, Colorado
Chris,
What carburetor are you using? NT? No matter really. If it has the needle raised by the throttle barrel the principal is the same. The needle only effects fuel flow from idle to about 3/4 throttle. From 3/4 to WOT it is main jet size that determines how much fuel enters the air stream.
If you're "bogging" above 3/4 throttle you might benefit from going a little smaller on jet size. I don't personally use published/advertised jet sizes due to the inconsistancy I've seen. I solder and drill the jets to satisfy the engine requirements.

You might want to explore going a little smaller but go easy, one step at a time. You do not want a consistent lean condition. Let us know, if you make a change, what happens.

Tom
 
Kioshk

Kioshk

Active Member
Oct 21, 2012
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Connecticut
I'm thinking a slightly smaller main-jet...
...wrote this, and just NOW re-read 2door's last post. Total agreement. Additionally, I suggest investing in a small precision drill-bit set. rejetting is actually really easy. You can hold the jet in a pliers, heat it up with a lighter or over a stove, and blip a bit of solder into the hole (I use flux to make sure it's clean). You can then patiently redrill the hole by hand (drill-bit rolled back and forth between thumb and forefinger). You can also used the bits to gauge your present jet; just go for a size 2-units less than your present one, increase by one if it's too lean. Also, don't forget to reset your needle to the middle setting.
 
crassius

crassius

Well-Known Member
Sep 30, 2012
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you can also chuck the jet into your drill press and feed the bit into it that way (little chance of snapping a bit like that)

I'm wondering if you're doing things right if you're spitting out mains at only 1500 miles.
 
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chris8686

New Member
May 2, 2013
85
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Bellingham
crassius said:
you can also chuck the jet into your drill press and feed the bit into it that way (little chance of snapping a bit like that)

I'm wondering if you're doing things right if you're spitting out mains at only 1500 miles.
Click to expand...
1500 miles with air leaks every mile. I think the bearing failure was a quality issue. When I pulled all 4 bearings one of the clutch bearings was on its way out as well.

The bike that I've been having trouble doing the jetting on had an air leak riding home yesterday. Half way home I came to a stop and it started revving up and the choke would not kill it.

Now that bike is going to sit and wait for its SHA to come in the mail and I will continue to play around with my other bike also equipped with an NT. This bike is jetted with a #64 main jet and the needle in the leanest position.
 
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