Mid-Throttle bog? By skooter (Read 4,484 times)

[skooter]

Well my Dino-Scooter with 13,159.9 miles on it is back together and so far so good.

I am however having a mid-throttle bog. It pulls hard off the stand still but then seems to bog in the mid range and then eventually evens out.

I don't think it's the variator weights because it didn't do this just a few miles ago. Now the air box is back together.

My friend borrow it to go to a friends house and he said... " he had to adjust the idle screw" ....

I think he may have adjusted the air/fuel screw on the side of the carb, and not the top idle screw.

My question is..what is stock for the idle screw? How many turns out/in. How about the air/fuel screw on the side of the carb?

It has a brand new stock carb on it.

[sprocket]

There is not stock position for the throttle... the A/F screw starting point is 2 -1/2 turns out...

Warm up the scooter for 5 minutes before adjusting the air/fuel (A/F)

Adjust the A/F screw in 1/4 turns and wait a count of 10. You want to get it so the
engine idle is at the fastest. Try going counter-clockwise to make it richer or clockwise to make it leaner...

Then adjust the throttle screw until the back wheel just begins to turn on the centre stand...
then back it off 1/4 to 1/2 turn...

[Bashan]

Perfect description of how to set the A/F by my good friend Sprocket. Having said that, the A/F doesn't do much after 1/4 throttle, it's for the low speed circuit. It sounds like a tiny vac leak is not pulling the needle slide out quick enough, check all your vac connections and the intake manifold. Rich

[sprocket]

>>it's for the low speed circuit.

Hey Rich...

I have always though this was the case also, however I was amazed recently about how much it does effect the mid-range ...

I had awful bogging mid-high and I re-adjusted the air/fuel and the bogging totally went away...go figure...

[Alleyoop]

Sprocket,
You are correct and I for one have been saying that over and over Contrary to what some keep saying that it is only for Idle and 1/4 throttle. And it is also written in some of the Carb tutorials as well. The Pilot Jet Feeds fuel all through the throttle range now mind you as the velocity of air increases as the throttle plate is opened less fuel gets sucked in from the Pilot jet but it still feeds fuel. I have gotten BRUPS out of the engine at WOT meaning it needs more fuel and I just crank the Fuel Ratio Screw about 1/4 turn and get more fuel out of the Pilot Jet and no more Lean condition.
Alleyoop



Here is a nice diagram of all the Air and Fuel Ciruits of a Carb and even the ACV ciruit. It is in Chinese or whatever but doesn't matter anyone that knows something about a carb will understand what is what.

[zugzug]

Well, every part of the carb works thru the whole throttle range. The idle jet and a/f mix is the main adjustment for idle and up to 1/4. The needle height/clip has the most effect in the 1/4-3/4 range and the main jet mainly affects the 3/4 to WOT. So if its good at low rpm and idle but lean/rich in the middle it would be best to adjust the clip on the needle instead of adjusting the a/f. Why throw one part off to get the other right? It doesnt make that much of a difference on scoots and small single m/c but it does come into play quite a bit with larger displacement engines that are frequently ran in the lower range.

[skooter]

Thanks for the info everyone.

I'll get it on the stand tomorrow, get it warmed up and then see if I can adjust it a bit.

I know this ole' dinosaur still has the guts because she ran well right before my friend tried to play mechanic.

I'll keep everyone posted, and also i'll check for a vacuum leak.

[sprocket]

Here is a little less complex CV carb diagram...

Alley as you say the idle jet is always contributing some fuel in the low to mid range. I suspect that as the main jet opens wider that the amount coming from the idle jet is reduced... but I don't know for sure...

However, in the lower to mid range it may give as much as 10% to 15% of total fuel..

This is just my experience and I agree with you Alley it does have effect on the low to midrange...

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[Bashan]

A great discussion with world class diagrams from some very intelligent people...what more could you ask? Rich

[sprocket]

Yes, those springs are critical. It probably depends on you much it was stretched.

It is only the air flow/vacuum that raises it and it certainly would prevent the needle raising all the way...