How to: High speed Chop test.

[Crazcnuk]

For those of you that use this as a test of your jetting, how long do you hold the bike at full throttle in high gear?

Keeping in mind that this will cost a fortune and a licence suspension pretty much anywhere, how long does it take to give a good reading.

I recently did this on my bike, flat out for 10-15 seconds. The plugs were perfectly clean, with nice indicators for timing.

This is with 120's in a bike that should need no more than 115's, but the test shows that 120's may be fine at wide-open throttle.

Right now, though the bike is very rich in the mid range, and bogs in the low end, although these can be adjusted.

According to my CV tuning guide, if you are within 2 jet sizes of correct you should be able to set the carbs properly.

This makes me wonder if it would be better to 1-2 sizes big than 1-2 sizes small.

[oseaghdha]

4th or 5th for about 15 to 30 seconds works for me.
Preferrably up a bit of an incline.
I happen to have the perfect spot, with a safe place to pull off about 5 klicks from my house.

[petejw]

i think the higher the gear the better
but that can be easily said than done,
as oseaghdha said, if u can find a slight hill even beter, if u can put sum load on the engine.
i do mine in third, wot till it reaches around 8000-8.5
dont chop the throttle till after u hit the kill switch,

if u hav a bit of colour on the plug u should b doing fine,
u could try changing the needle position?

u should b fine with 120s
the 81 came with 110 on the outside and 120 on the inside.

[81xsproject]

Right now, though the bike is very rich in the mid range, and bogs in the low end, although these can be adjusted.

Yeah... good luck with that. Let us know when you get that mid range leaned out (which you won't). You just go on ahead and drive at WOT all the time, then.

[psycoreefer]

I had a similar problem where mine was always rich in mid range and especially at idle, when I replaced my emulsion tubes that went away. I figure the tubes were worn and letting gas flow even when the needles were "down".

I think I remember from your other thread that you replaced your tubes though? I'd think that if you needles/tubes/idles jets are all stock then you should be lean at less then WOT, not rich. hmmm.... whats your float level set at?

[Crazcnuk]

No, I haven't replaced the tubes, yet, I have some on order.

Mine are just oval where the needle goes in, so I think changing them can't hurt.

81XS, I thought you knew a bit more about CV carbs...let alone chop tests.

You have to get the main jet right BEFORE you can tune the mid and low range.

As for adjusting the mid range... why not? I have new tubes coming and 5 steps on my needles to play with.

What amazes me is that it did NOT foul, even a little, with the 120s as I think they should be too large. I think the 115s, or at most 117.5s should be what this motor needs.

When I did the test I hit 6k crawling up to 8k, in 5th gear up a fair incline for 10-20 seconds (or somewhere in there) hoping to hell no cops were around.... and it takes a LOT to get my bike to 8k in 5th gear right now.

[DavesXS]

Drop your floats down 1mm and see if low and mid range clear up.
I has a similar problem and it was the floats. Took 3 times to get them just right.
BTW I am running 117.5's

[egsols]

Hey Craz,

I would have thought that the 120's may be a bit big too, based on your local altitude.

[79XS11F]

It does not matter what gear your in. It's the RPM that matters and the engine does need to be working. A slight incline will do that for you so on any highway the top of first gear will not get you a big ticket and have you in the higher RPM range. If no incline is available then just shut the engine down before it stops pulling.
Rob

[81xsproject]

81XS, I thought you knew a bit more about CV carbs...let alone chop tests. You have to get the main jet right BEFORE you can tune the mid and low range.

I do. In fact when I hit 8500 rpm at WOT, the AFR is 12.7:1. It doesn't get much more perfect than that.

I don't know how it is that you are going to use an adjustable needle on 80's carbs, but it sounds interesting. The new emulsion tubes may be the way to go for correcting midrange richness.

This is with 120's in a bike that should need no more than 115's, but the test shows that 120's may be fine at wide-open throttle.

I was trying to help you out when I told you this in your other thread. So, if you want to flame my words that is your deal.

I think the 115s, or at most 117.5s should be what this motor needs.

115's huh?

Good luck.

[tarzan]

Hey Craznuk,
I have an 80 too and I'm running 110's right now.BTW I'm about 80 miles south of Canada ,I dont know what elevation your at but were about 2000 feet abve sea level here.My bike runs great with these jets and I am also running pods right now.
It sounds to me like you could come down to at least 115's because the symptoms you describe with soggy bottom and midrange are on par with too much fuel.It doesnt sound like you need a throttle chop yet,I think you need to get it to run pretty good then do a chop.Good luck.

[Crazcnuk]

problem is I had the bog problem, in the low end, even with the 110's.

I have aftermarket slip on mufflers and a K&N filter in the stock box, so I didn't think I should need much in the way of jets.

However, all of this could be due to the weak coils. I hope it is a whole new ball game once I get the new coils in.