I need jetting help....

[n_green]

2011 Gasser 300EC. Fitted with a 36mm carb.
Prior to having the head modded I run with a 38 pilot, JD Blue needle clip 2, 168 main. Temps about 20 deg C at 1000m altitude. The bike run great. Prior to this I'd had a really flat top end, this jetting woke it up and made it a lot better. A mate and I were of the opinion that possibly this main was even one size too large hence the needle in clip 2 as a shortcut but I was really happy with it so was happy enough to leave it in there as it was.
Economy was roughly 10l per 100km.

Recently got the head modded, squish is now corrected and is 1.28mm, compression ratio has been lifted from 12.2:1 to 12.7:1. Cylinder was lifted by .55mm, so there is now 2 x .5mm base gaskets.

I can not jet this thing now

Started out doing seat of the pants WOT runs started with same pilot and JD Blue in clip 3. Run from 180 main all the way down to 168 and settled on a 172 main. Still felt rich up top. Went for a 50k spin and used 6.2l of fuel.

Went for a ride today and prior to the ride did a heap of WOT runs using plug chop method. Pretty sure I was doing this wrong.
Started from almost idle in 4th gear on an medium uphill slope. Pinned it WOT and let it go until it was singing for 100m and then killed it, pulled in the clutch and shut the throttle.

I started with a 168 main and went all the way up to a 180 main before the brand new plug showed any colour at all, and even then it was only just off white. So, would 100 - 200m of WOT be enough to colour the plug?
The 168 main felt the best, but after seeing the plug so white it scared me so I left the 180 main in all day. Top end was CRAP. Broke up and pretty much refused to rev past 3/4 throttle which was really only an issue on the firetrails but still annoying. 50k's of riding, 9l of fuel used This was at 25 deg C 1100m altitude.

This is bugging me, prior to this I thought I knew a little bit about jetting but now I'm triple guessing everything I thought I knew.

My main questions:

1) Did I do the plug/throttle chop wrong as asked above?

2) Can anyone with a 36mm carb give me a baseline to go off. Even a different Suzuki needle. Only results in the jetting thread are Simmo's and they are a good baseline but more opinions would be good.

3) Should I just run the same jetting as prior to the head mod, does a head mod actually require any richer mains, or is it usually just a richer pilot? (Pilot circuit is gold with a 38, as is 1.5 turns out and works.)

4) I want to try a Suzuki needle. I own an NEDW, NECW, NEDJ, NECJ. Which one would generally work best and with what baseline jets?

4) Do different needles result in different economy? For example, say I run a JD Blue needle jetted perfectly and then a Suzuki needle, lets say NEDW jetted perfectly. Would fuel economy be the same??

Thanks for any input, this really is doing my head in. And whats worse is I'm yet to install my oval bored 36 x 39mm carb which I'm assuming will require jetting changes again...

[Jakobi]

You ran with a 180 main in a 36mm carb You made my day!

Regarding the plug chops. Your method is good. You don't even have to have the engine rpms high. Its all based on throttle position. You also won't colour up a new plug in a single run. There are basically 2 approaches here. You either use an old plug thats already coloured and read the tip. As you jet down, the leaner runs will turn any previous colouring from brown, to tan, to grey, and then finally white and ashy. You are looking for a coffee colour. The other method requires doing a single run on a new plug, pulling it out, taking it home, cutting the threads off the plug and reading the fuel ring around the base. Some good info available by googling on it. Thumpertalk has some decent threads too, but at $5 a plug its something you'd only do once you're close and seeking perfection.

If you are happy with the idle circuit, leave it as is and move on to clip position. If not start over. If you are going to use a NEDW then you'll probably want to go several sizes up on the pilot to maintain the fuel mix that you have now. The W diameter is closer to a JD Red. An F or G diameter will be closer to the Blue. If you wanted to try the Suzi needle I'd suggest a 40/42 NECW#3 165 for a starting point.

With the clip position its as simple as starting in clip 3. Move a clip richer, and it'll either get better or worse. Repeat moving the clip chasing the best performance. Once the performance stops you've gone too far. Applies in both directions. I'd imagine for us in Aussie land, clip 3 or 2 will be on the money.

You do know a lot about jetting and that you are trying things and questioning is only going to improve your skills. Don't stress about it. Its all positive.

In my experiences the needles are where you will find economy, as they cover the largest throttle range, including the throttle ranges we spend the most time using. If a bike was jetted perfectly with one needle to the next it would be the same economy, but different needles have different tapers, and provide different fuelling at different throttle openings. This is how it changes the power delivery. Basically a rich condition will be more torquey and mellow, where a leaner one will be cleaner and snappier. A transition from rich to lean will give a 'hit', where a leanish bottom end that gradually gets richer will give you a nice linear power delivery. Its all compromise really. My personal preference is the N3xx needles. I use a lean diameter with a bigger pilot. I end up with a smooth bottom end with a strong transition in the mid range onto the pipe.

[n_green]

Thanks mate, thats where I was going wrong was using a brand new plug and it just refused to colour up

Oh well the current plug has been run for 50 k's with a 180 main so it should be nice and black and make step downs easier to read. (And yes I know I was a moron for running a 180 main but after stuffing round for half an hour I just couldn't be bothered and rode it that way as punishment

I might try jetting the blue needle correctly and then later jet using a Suzi needle. I'm wondering if the blue needle is also partly to blame for my 'boring' top end?

[Jakobi]

What do you mean boring? What are you comparing it too? What won't it do? Can you provide any more info on how its boring it might help.


My power signs off well around truly around low 9200rpm, but will rev out further will a smaller main, going by the trailtech tacho. It'll still happily pull the front wheel up in 5th gear in band with 13-50 gearing though. It might be the 36mm carb throttling the engine. You'll know for sure once you slide that oval bore in. I've never had to jet one so no idea what size main you'll be looking at.

[n_green]

By boring I mean it just seems to sign off and die up the top of the rev range. And not right at the top either, from about 3/4 onwards. Even when I had it jetted at its best prior to the head mod (38p, JD Blue #2, 168m) the top end was better but still obviously weak compared to the awesome pull off the bottom and through the mid.

Put it this way, 4th gear wheelies whilst high in the rev range required a fair bit of clutch and even then lacked the power to lift the front anywhere near balance point. Even if I had the front wheel up there once it got towards the top of the rev range it lacked the power to keep it up.

The first ride I had with the modded head (38p, JD Blue #3, 172m) the power was noticeably stronger everywhere and the top end was improved but still 'boring'.

I'm comparing this to my old KTM300 and 2 mates KTM300's. My bottom end and even mid craps all over the pumpkins, but the difference in top end is silly.

Then when I rode the '11 Gasser six days the other day it was really obvious what I was missing out on in terms of top end. That thing was awesome.

So I figure it is definately the carb to some degree, but could the JD Blue needle also be responsible for this 'boring' sensation up the top?

One way to find out I guess, jet the JD needle, then re-jet using a Suzi needle. Then throw in the oval bored carb and start again

[hannesd]

have you thought of the fact that that '11 six days might have had a 39mm carb instead of yours the 36mm?
that carb could give huge difference in top end.
+ more compression allso focusses more on low to mid torque...maybe combination of those 2 factors might "choke" your top end power

[Jakobi]

While you slightly increased compression ratio its not enough to kill your top end. I believe you also reconfigured the port timing to favour the top end which should have compensated for the slight increase in CR.

The needle won't have all that much influence in the 3/4 - WOT area. Its predomidantly the main jet working there. I personally think you've probably been a bit rich on the main the whole time. Any easy check would be to drop a 165/168 in and see how it runs. If its a noticable improvement its telling you something.

The head work in theory will have also improved the engines efficiency, this could actually result in smaller jets being required as the fuel is now being placed where it needs to be and burning entirely.

[Jakobi]

I also think that the 36mm carb is holding it back substantially.

[n_green]

Originally Posted by hannesd

have you thought of the fact that that '11 six days might have had a 39mm carb instead of yours the 36mm?
that carb could give huge difference in top end.
+ more compression allso focusses more on low to mid torque...maybe combination of those 2 factors might "choke" your top end power

Yep that's what I was getting at. The six days had the 38mm carb. Really opened my eyes as to what the top end should be like.

[n_green]

Originally Posted by Jakobi

While you slightly increased compression ratio its not enough to kill your top end. I believe you also reconfigured the port timing to favour the top end which should have compensated for the slight increase in CR.

The needle won't have all that much influence in the 3/4 - WOT area. Its predomidantly the main jet working there. I personally think you've probably been a bit rich on the main the whole time. Any easy check would be to drop a 165/168 in and see how it runs. If its a noticable improvement its telling you something.

The head work in theory will have also improved the engines efficiency, this could actually result in smaller jets being required as the fuel is now being placed where it needs to be and burning entirely.

I do agree with you. Even with the 168 main a mate and I were both convince it was probably still 1 step too rich. My problem is I've had a lean WOT seizure before so err big time on the side of caution. Admittedly that was mainly due to a blown stator side seal but since then I've been hesitant to step down too far on the main.

In reality say how bad would one or two main size too small be? Would it/ could it cause a lean seizure?