Plug chop....whats your take on these???

[1978GS750E]

Did my first plug chop on the GS1000 this afternoon. This is after about 20 minutes of fairly steady 30 MPH riding out in the country.


To me it looks like cylinder #1 is very rich, #2 & #3 are lean and #4 is about right. What do you carb guys say???




Any ideas about how much to richen the fuel screws?

Thanks,
Ron

 

[Guest]

Did my first plug chop on the GS1000 this afternoon. This is after about 20 minutes of fairly steady 30 MPH riding out in the country.


To me it looks like cylinder #1 is very rich, #2 & #3 are lean and #4 is about right. What do you carb guys say???

View attachment 57888


Any ideas about how much to richen the fuel screws?

Thanks,
Ron

I'm not sure that is considered a plug chop, but I think your assessment of the plugs is right.

 

[Steve]

"Steady 30 MPH" does not describe the conditions well enough.

Was that at 1/8 throttle, 1/4 throttle, 1/2 throttle or wide open?

And the only place you are going to be able to do ANY speed that contantly for that long is going to be a closed course, like a race track that you have rented.

Yes, #1 looks incredibly rich, but you have no idea which part of the carb was doing that.

.

 

[1978GS750E]

So Steve, how long do I need to stay at each throttle position to see accurate results? My 30mph was out on the backroads and was not a constant throttle position, so I guess these plugs don't really tell me a lot huh?

As you can tell, I am new to all things carb related but have tried to absorb as much as I can from the tutorials and this website. Any help is greatly appreciated.

 

[Big T]

What Steve is alluding to is that a plug chop consists of riding at a steady throttle position for a few miles, then killing the motor, coasting in and checking the plugs

It needs to be done at 1/4 throttle, then half, 3/4, full

Something is way off on #1

 

[Steve]

Actually, it doesn't take very long, no "miles" involved.

The first thing to do is to get some new plugs, then find someplace where there is a safe spot to pull over and inspect the plugs. The top of a small hill would be ideal. Mark your throttle and housing so you can see where the various positions are. See picture at end of post. Warm up the bike so it is running well, and not on "choke" at all. Replace the plugs. Start the engine, let it idle for a couple of minutes. Turn the bike off, inspect the plugs. Pictures are wonderful. You have just tested the pilot circuit. Now you can go for a ride through the neighborhood. HOLD the throttle at 1/8 as long as you can, try to get a minute out of it. If you are accelerating too quickly, upshift. It won't accelerate as well in fourth gear. It is throttle position, not engine speed or road speed that is important. When you get to your safe spot, pull the clutch and hit the kill switch at the same time. Coast into the safe spot, inspect the plugs. Repeat at 1/4 throttle. You will have to upshift sooner. As long as you are not lugging the engine, 1/4 or 1/2 throttle in fifth gear is just fine. 20-30 seconds should get decent color on the plugs. Finally, the fun part. For this one, you will need some open road, where you can get up some speed. Use third or fourth gear, starting about 20-25 mph, hold the throttle wide open. Before you run out of road, pull the clutch and hit the kill switch, coast to a safe spot, inspect the plugs.

The important things to remember are to hold STEADY throttle, so you are only using one carb circuit, and kill the engine cleanly. Don't finish your half-throttle run with the engine idling as you coast into your safe spot, you will have just ruined the color on the plugs by idling. Clutch and kill, so the engine was last running at the throttle setting you are testing.

Here is how I marked my wife's throttle:

Idle setting is easy. Just line up the marks. Full throttle is also easy, just make the mark on the housing where the throttle grip stops. Measure the distance between those marks, draw lines at 1/2, 1/4 and 1/8.

.

 

[RichDesmond]

How far from a stock configuration are you?

 

[1978GS750E]

Currently has the stock airbox and filter with what I was told is a Vance & Hines Street Pro 4-into-1 exhaust that is only slightly louder than the stock pipes. Went back to the original #95 jets and it ran better than the #105's that were in it when I got it with the exhaust and the "dreaded pods"!

 

[RichDesmond]

Currently has the stock airbox and filter with what I was told is a Vance & Hines Street Pro 4-into-1 exhaust that is only slightly louder than the stock pipes. Went back to the original #95 jets and it ran better than the #105's that were in it when I got it with the exhaust and the "dreaded pods"!

Something very close to stock jetting ought to be in the ballpark. If the plugs look bad with stock jetting (especially if they look rich) you have other problems to solve before messing with the jets.

 

[Tom R]

At 30mph you're still in the float height range. Check the fuel level in your bowls.

 

[Steve]

At 30mph you're still in the float height range.

Huh??? :-k

You are ALWAYS in the "float height range".

In fact, the FIRST thing to do when checking jetting is to ensure proper fuel level.
Start by setting float height, verify with a clear tube outside the carb.

An out-of-spec float height will affect ALL circuits in the carb. If other "adjustments" have been made, they might be compensating for the improper fuel height, making diagnosis difficult on the other circuits.

.

 

[Tom R]

Huh??? :-k

You are ALWAYS in the "float height range".

In fact, the FIRST thing to do when checking jetting is to ensure proper fuel level.
Start by setting float height, verify with a clear tube outside the carb.

An out-of-spec float height will affect ALL circuits in the carb. If other "adjustments" have been made, they might be compensating for the improper fuel height, making diagnosis difficult on the other circuits.

.

Granted, but it’s more pronounced at lower throttle position.