Topic: how the hell do you do a WOT plug chop legally?

[paulages]

from the FAQ's:

1.  Pick the main jet first.  You can take a plug reading at wide open throttle.  Accelerate over a long distance (preferably uphill) getting into 5th gear and keeping throttle fully open.  When fully tapped out, grab the clutch and hit the kill switch.  The motor should stop immediately, then look at the plug.  Should be tan, but not too dark.

i have a good location, right by my shop to do my plug chops. slight uphill, about a half mile in length, and no lights. however, if "fully tapped out in 5th gear" by the 1/4 mile, i'm going about 95-100mph. i've done WOT chops in a lower gear for the same distance with the same results. in any gear, it's screaming at WOT at that distance. good thing there are no houses on this street...

[eldar]

Not sure why getting into 5th makes any difference. 5000 rpm is 5000 rpm no matter the gear! So you can scream at 20mph!

[mlinder]

Not sure why getting into 5th makes any difference. 5000 rpm is 5000 rpm no matter the gear! So you can scream at 20mph!

Load is different.

[paulages]

it's not RPM specific, but throttle position specific. i ride around at 5K quite often (good balance between engine braking and pickup). screaming is 9-11K. 

it's hard to stay at WOT without going pretty damn fast. even chopping at 1/2 throttle in 2nd gear gets me pretty fast (and screaming).

[jdamman]

I heard  a rumor that there wasn't a speed limit on on ramps...
Or just rent a little time on the salt flats, only costs a few dollars

[theunrulychef]

Having a 1/2 mile strip out in front of your shop is a luxury Paul. Try doing a WOT chop in between stop signs a block apart.     I've got the bigger problem that we don't have any straight roads in Philly that aren't so loaded with stop signs & lights that my only local option is the highway.  Then I've got my choice of I-95 which is always full of cars & I-76 which is always full of cars.   

I'm gonna have to take a trip to PA Dutch country with a toolbag sometime.  Perhaps that's a good excuse to take a nice long ride.

[eldar]

Load is different? My ass dont weight any different at other gears!

[mlinder]

Load is different? My ass dont weight any different at other gears!

True, but wind resistance rises exponentially. The engine is working MUCH harder to get (and keep) you at redline at 110 mph than it is at 55mph.

[ohiocaferacer]

You can do a plug chop in any gear....whatever your comfortable with. I usually do them in 2nd wot for a few seconds.

Remember.....all you wanting to do is get the needle all the way out of the main just to let the max amount of fuel(for a particular jet size) to come into the combustion chamber and determine the proper fuel/air ratio. Load really doesnt come into it......just a smooth steady burn on the insulator.

Cant remember if this was mentioned before or not......best to use new plugs when doing this. If you use old plugs...you will just be running in circles....not saying it cant be done....just easier with new ones.

Also.....remember float heights can play with your mixture too. I've chased many a main jet....only to find my floats were set too low(lean).

Later,
Greg

[mlinder]

I would think load HAS to come into it. When you get your bike dyno tuned, the dyno adds appropriate friction for proper load testing.
Wind resistance quadruples between 55 and 110mph. This increase in load is enormous. It requires 8 times more horsepower to top out at redline than it does to reach redline at half the speed.
I would have to think that these conditions would very much change what's going on with your fuel system, even though they are running at the same RPM.

/edit : (I could be very wrong about assigning importance to load for checking fuel delivery and spark, so just tell me to shut up if I am, but I cant imagine why a dyno would simulate load for tuning otherwise, and it really seams logical that it would make a difference. It's a completely different environment for the engine at redline in top gear than it is in second)

[eldar]

I was being funny there!

But I think ohio is correct. You are mainly trying to get the mains into play, does not matter the speed just the needle position.

But there has benn some discussion on whether or not plug chops are very practical. many feel they are a way of doing a rough tune and thats it. So it is hard to say. A dyno is probably better, I think a O2 meter is probably the best.

[mlinder]

I think an o2 meter would show different results at redline under load than under no load :/

[eldar]

It might but you cant tune perfectly for every condition. not with mechanincal carbs anyways. You are looking for a happy medium. But I doubt that the difference between wot in 2nd and wot in 5th is going to vary by that much.

[paulages]

i always understood that it was important to stay at WOT (or whatever appropriate throttle range) for long enough to "treat" the plugs to whatever conditions may be present. seems a few seconds wouldn't be enough. i've never managed to get a 5th gear WOT chop to work for the stated reasons. it works if you go straight through the gears really quickly, then stay at WOT (making the bike work harder to get fast). my strip is in a 45 zone. i break that even in second gear at WOT, because it becomes so torquey so quickly. so far, no smoky waiting at the top of the hill (knock on wood)...