Carb Tuning

[pearsonbe]

I remember reading here that part of the process of dialing in the carbs involves reading the header temps. Is that correct?

Also, does anyone have experience with Factory Pro's Finger Adjustable fuel screws? I'd like to know if they are worth the money.

[DonTZ125]

The idle mixture screws should be set to give the same response in each cyl; one of the easiest ways to check that is header temp.

[pearsonbe]

Thanks

[pearsonbe]

If one header is signficantly hotter than the others, that indicates a lean condition, right? And to correct that, I would turn the idle mixture screw counter-clockwise to enrichen the mixture?

[thatkid]

correct.

[pearsonbe]

Thanks, Nate.

[pearsonbe]

The infrared thermometer arrived today and after running the bike for a while in the garage, the max header temps I see are: 168, 589, 587, 155 (farenheit). Numbers are listed from left to right, standing in front of the bike. I don't know what normal temps are, but it's clear that the inner carbs are a lot hotter than the outer carbs. Also, I checked the numbers twice about 20 minutes apart and they tell me the same thing.

[thatkid]

cylinders 1 and 4 aren't firing.

[pearsonbe]

Do you mean not firing at all or partially? I wouldn't think it would run on 2 cylinders and feels pretty strong on the highway. I will check the ignition system again. Last fall, the coils and caps tested fine and there was a spark at each plug. The plugs are new.

[thatkid]

They may start to fire under higher load but at idle they aren't firing. I would guess a clogged jet or something with the carbs is off. They should all be at least 400+ depending on what you have in there.

[pearsonbe]

Ok. I will take a look at the carbs again, especially 1 and 4.

[pearsonbe]

Replaced the #1 and #4 pilot jets. Don, you're right. The inner diameter is small. Mine were not blocked and I couldn't visually see a difference between new and old. However, #1 header temp is better and #4 is much better - almost the same as #2 and #3. The idle is smoother and throttle response is pretty crisp. But the low end is still a little rough. Mid-range and top end are good. When I checked the temps, the bike was not completely warm and leaning on the kickstand. I will take another reading when it's warm and up-right.

[DonTZ125]

It doesn't take much to drastically affect the flow through a small orifice. A little plating, a little roughness, and suddenly the flow is almost reduced by half, and the cyl won't fire. This is also the reason why rodding these jets out with steel wire is such a bad idea; it doesn't take much scratching to completely change the flow characteristics.

Now that you have fresh pilots, adjust your idle mix and sync your carbs.

[willandrip]

Them Infrared temp guns are a great tool and cheap as chips (fries for you US guys) .
They are a great aid to carb tuning; everyone should have one.
The trick is to aim it at the same spot on each header.
I go for the bend on the pipe; it seems to give the most consistent reading between pipes.
Anyone got a better choice ?

[pearsonbe]

Yup. I love the infrared gun and that's a good tip on the location of the reading. I try to pick the same vertical location on each pipe. Next time I will use the bend to see if that improves consistency.