Fun with TurboT's Gio Beast

[Weldangrind]

Yozalo, yes, it is the 125 Perormance Pit Bike muffler.

waynev, the quad has been nice and cozy in my shop for some time, without getting wet. It was running on the weekend after the 30mm Mikuni installation, but it hasn't started yet with the new pipe.

[anthonyfa18]

you just need to adjust the carb

[Weldangrind]

Success! It runs.

Prior to success, I had removed the carb and blown air through the passages, and tried the air / fuel screw all the way to 3.5 turns out. As previously mentioned, I think there was a spark plug wire issue, so I swapped it for an NGK cap and wire. Still no joy.

I took the carb off (again), and this time I removed the main jet and the idle jet, along with the float valve and seat to make sure that nothing blocked the passages. There was nothing in there; no dirt, no casting flash, nothing.

I read linuxman's post (http://www.chinariders.net/modules.p...ewtopic&t=8904) about his experience with a 30mm Mikuni, and it seemed reasonable that the 100 main jet was the culprit. After some measuring, I discovered that the main jet and the float valve seat are metric references (100 means 1.00mm). I'm not so sure about the idle jet, because it necks down inside, so you can't likely modify it by drilling it out.

1.00mm winds up right between a #60 and a #61 drill bit. Following linuxman's advice, I wanted to get closer to 1.05mm, so I drilled out the main jet to 1.04mm using a #59 drill bit (0.041"). A #58 bit would have opened up the jet to 1.07mm, and I don't want to go that far yet.

Upon adjusting the air / fuel screw to 2.5 turns out and re-installing the carb, it fired right up. It still takes the better part of five minutes to properly warm up, but it runs. Sounds mean with that new exhaust, too. 8)

[TurboT]

Sweet mate. Sounds good.

Good investigative work. I did a little hunting for jet charts, and found nothing useful to me other than suspected you were correct to need to jet it.

[PCD]

Originally Posted by TurboT

Sweet mate. Sounds good.

Good investigative work. I did a little hunting for jet charts, and found nothing useful to me other than suspected you were correct to need to jet it.

Was drilling out the jet a better soloution than moving the clip?

Even if you could have fixed it by moving the clip I would understand fixing the root cause first, that way you still have all your clip adjustment open to you. Am I on the right track or did you HAVE to do the jet?

Yes, i have a #41 bit

[TurboT]

Originally Posted by PCD

Was drilling out the jet a better soloution than moving the clip?

Even if you could have fixed it by moving the clip I would understand fixing the root cause first, that way you still have all your clip adjustment open to you. Am I on the right track or did you HAVE to do the jet?

Yes, i have a #41 bit

Hey Pete,

W&G can confirm, but I believe the clip was at it's richest setting when we first put it on... so there was no wiggle room there which left the jet.

I never looked at the clip, but I distinctly remember W&G doing so and saying as a reminder to himself and me it was at the richest setting.

Of course, now he'll come around and tell us that wasn't the case, and that I had been sniffing way too much gas fumes to remember my name, let alone the needle setting. 8O

[PCD]

Originally Posted by TurboT

Hey Pete,

W&G can confirm, but I believe the clip was at it's richest setting when we first put it on... so there was no wiggle room there which left the jet.

I never looked at the clip, but I distinctly remember W&G doing so and saying as a reminder to himself and me it was at the richest setting.

Of course, now he'll come around and tell us that wasn't the case, and that I had been sniffing way too much gas fumes to remember my name, let alone the needle setting. 8O

Right, thanks there Turbo, I totally forgot our Mikuni carbs already came on the richest setting. Bigger main or drill it out would be the next options.

Sigh..the older I get the more "seniors moments" I have....

[waynev]

One thing to remember on the mikuni carb is the main jet only controls the mixture from 3/4 to full throttle, that's it, and the only way to check if it's proper is a wide open run and kill the engine at full throttle and then inspect the spark plug.
Also most engines will like 1 main jet size up or down per 7 deg C temperature change, so if it runs good in the summer at 20C on a 100 jet, then when it gets to -1 you should be running a 130.

[Weldangrind]

Waynev, that's almost exactly what I was struggling with. It has been my understanding that the main jet controls the mixture at tip-in, but now I'm inclined to question that.

The main jet is (as we're all aware) directly below the slider needle. As soon as the throttle is opened, the needle is pulled up from the jet, uncovering the orifice. It seems to me that if the orifice is a larger diameter than stock, more fuel would flow upon opening the throttle (I think we can all agree so far). The thing that hadn't occurred to me is that since the idle speed screw simply lifts the slider, the main jet is uncovered even at idle.

To support this, I made no other mods and the quad fired right up. It still has a bit of a 'hunting' idle upon blipping the throttle, but I think that's something else. Maybe I just crutched it, I dunno.

I noticed a mis-match between the intake tube insulator and the new Mikuni, inside and out. A person would need to hog out the ID of the insulator to get maximum benefit from the new carb. The o-ring on the Mikuni isn't completely covered by the outside of the insulator either. The easiest fix would be an insulator that is designed for a 30mm Mikuni or Keihin round slider carb.

I'm not convinced that the stock insulator isn't creating a vaccuum leak. Anybody else have idle trouble?

Maybe a bigger idle jet will solve the idle issue; I'll see about picking one up today. The symptom remains that when you blip the throttle, it takes 2-3 seconds to come back to idle. That's despite re-routing the throttle cable to a more relaxed radius. BTW, it had the same symptom with the smaller carb, but it was worse.

Pete, to be clear, I used a #59 bit, which is 0.041".

Cheers!

[waynev]

Originally Posted by Weldangrind

Waynev, that's almost exactly what I was struggling with. It has been my understanding that the main jet controls the mixture at tip-in, but now I'm inclined to question that.

The main jet is (as we're all aware) directly below the slider needle. As soon as the throttle is opened, the needle is pulled up from the jet, uncovering the orifice. It seems to me that if the orifice is a larger diameter than stock, more fuel would flow upon opening the throttle (I think we can all agree so far).
Cheers!

Sorry W&G i can't agree with that statement, the larger main jet will not flow more fuel until you are over 3/4 throttle, it is the taper on the needle jet and the jet needle that controls the flow from 1/4 to 3/4's. Think of it this way your needle jet/jet needle is a 1/2" garden hose, even if you hook up a 2" hose to the 1/2" hose it won't flow any faster.


There's a nice explanation and a chart of throttle postions and what is the control for eash position here, http://www.iwt.com.au/mikunicarb.htm

[TurboT]

Originally Posted by Weldangrind

I'm not convinced that the stock insulator isn't creating a vaccuum leak. Anybody else have idle trouble?

Maybe a bigger idle jet will solve the idle issue; I'll see about picking one up today. The symptom remains that when you blip the throttle, it takes 2-3 seconds to come back to idle. That's despite re-routing the throttle cable to a more relaxed radius. BTW, it had the same symptom with the smaller carb, but it was worse.

Cheers!

Hey D,

Since we're on the subject of vacuum leaks have a look at where the intake manifold bolts to the head as well. While we were installing the carb I was looking around and noticed there seems to be a bad fit between those two items. I was looking at it and wondering if it was a problem, then got distracted by something else. It might be nothing, but might need a little goop there.

When I mentioned the racing idle and slow return to idle with Pop's, the first thing out of his mouth was vacuum leak, while we assumed it was the throttle cable I didn't think too much of it agian.

I noticed in your video the slow return to idle, but had assumed you had not rerouted the cable until I read this.

[anthonyfa18]

nice video good job on that exhaust mod

[Weldangrind]

Originally Posted by waynev

Sorry W&G i can't agree with that statement, the larger main jet will not flow more fuel until you are over 3/4 throttle, it is the taper on the needle jet and the jet needle that controls the flow from 1/4 to 3/4's. Think of it this way your needle jet/jet needle is a 1/2" garden hose, even if you hook up a 2" hose to the 1/2" hose it won't flow any faster.


There's a nice explanation and a chart of throttle postions and what is the control for eash position here, http://www.iwt.com.au/mikunicarb.htm

Of course your right waynev. I forgot about the needle taper.

I ordered a new idle jet today that is 22.5 instead of the stock 20. It should be in tomorrow, so we'll see if that helps.

T, I intend to remove the insulator completely, since the Hondas don't use one, and the o-ring on the carb should mate nicely with the intake. I'll check the intake to head relationship as well. Does anybody have a favourite method for checking for vaccuum leaks?

BTW, the quad wouldn't start this morning (I didn't try very hard). I made no changes at all from the last time it ran.

[PCD]

Ether, or that staring fluid you used to spray into carbs. The revs will increase if it gets sucked into a leak.

[TurboT]

Originally Posted by PCD

Ether, or that staring fluid you used to spray into carbs. The revs will increase if it gets sucked into a leak.

Hmm.. sounds like a neat trick.. we would have to get it to stop hunting for idle and racing sitting there too for that to work..

D, no worry on the spacer, could be the problem as it seems to be a bit of a flakey piece anyhow.

What is the jet worth?