predator 420 jet with VC kit

[rammunition361]

what jet is normally used with the vegas carts kit? i tried 42 and it isnt big enough

[rammunition361]

45-46 main for future searches.

[slonomo]

Originally Posted by rammunition361

what jet is normally used with the vegas carts kit? i tried 42 and it isnt big enough

How do you know it isn't big enough? What method of testing are you using?

[raydhd]

IMHO A lot easier way to tune is to use an adjustable main kit from either NRracing or ECcarbs. You can dial the engine right in quickly and adapt to any change of conditions.

[rammunition361]

how is it adjustable? and slo, i can tell when an engine is lean. it would run on choke but not off. no air leaks. runs ok on 45 so far but not perfect. i will get the adjustable kit.

[rammunition361]

Originally Posted by slonomo

How do you know it isn't big enough? What method of testing are you using?

what are some methods you use? id like to dial it in real nice. Also it seems like on top end the speed doesnt match the rpms. almost like the belt is loose or its "missing a gear"

[slonomo]

These carbs were designed to run at 3600 rpm contant. Out of the box they won't idle, unless you have one with an adjustable idle circuit. They usually will run lean at 4500 rpm and above. So tuning them is tricky. If you tune the main to work at wot and use plug reading to dial that in, you might be rich in the middle say 2000-3600 rpm. They tend to load up when cruising at a steady rpm with no load.

The reality is, while you can get one of these carbs to run decently at wot, you'll sacrifice low speed drivability. If you tune it for low/mid rpm, then the wot will be lean. It's tricky, time consuming, and they will never run like a Mikuni slide carb that's designed for that kind of driving.

The old fashioned way is to install a new main jet, install a brand new spark plug, then start it up and do one full wot run. Take the plug out and look at it. There are photo guides all over the net about what a good plug will look like vs lean vs rich. Obviously black soot is rich. Once you reach black soot, you back down to the previous jet. That's the way I've always done it.

Running at idle is a whole other process. The idle circuit screw is usually blocked off from the factory, so you have to dig the plug out and play with that. Most times it's set up decently anyway. Starting point is 1.5 turns out. Adjust in 1/4 turn increments until you find the sweet spot.

If it only runs with the choke on, then your idle circuit is lean. Some idle screws will adjust air, some will adjust fuel. Either way, you have to adjust it so it will run without the choke. I always tune mine so it starts without use of the choke in warmer weather like 70 degrees. Winter use is a different topic.

[slonomo]

Assuming your rpm is correct, your speed may be related to your clutches, belt, and tire size. What is your current setup?

If you use a stock secondary, 780 primary, 1 3/16" wide kevlar type belt, 22" tires.....at 4500 rpm you should be in the 25 mph neighborhood.

If your clutches/belt are slipping look for heat on the clutches and belt. A burning rubber smell will also indicate slipping. Wear marks on the clutches too.

To check for full shift: use a black sharpie marker and draw several lines from the center of your clutches to the outer edge. Drive the clutch to top speed. Check the lines. Where your belt rides the lines will be rubbed off. This will show if your clutches are shifting all the way. Ideally at full shift, your belt will ride to the very top of the primary clutch, and all the way to the bottom of your secondary clutch.

[rammunition361]

Originally Posted by slonomo

Assuming your rpm is correct, your speed may be related to your clutches, belt, and tire size. What is your current setup?

If you use a stock secondary, 780 primary, 1 3/16" wide kevlar type belt, 22" tires.....at 4500 rpm you should be in the 25 mph neighborhood.

If your clutches/belt are slipping look for heat on the clutches and belt. A burning rubber smell will also indicate slipping. Wear marks on the clutches too.

To check for full shift: use a black sharpie marker and draw several lines from the center of your clutches to the outer edge. Drive the clutch to top speed. Check the lines. Where your belt rides the lines will be rubbed off. This will show if your clutches are shifting all the way. Ideally at full shift, your belt will ride to the very top of the primary clutch, and all the way to the bottom of your secondary clutch.

it isnt performing full shift after its warm. any ideas?

[rammunition361]

27" tires, 780, stock driven, belt that came in vegas kit