More compression = smaller jets?

[rerb]

Finally got the bike up and goin after raising the CR, fixing my blown seal and adding watermeth and an ignitech cdi. Huge difference!! Much better low end and it does wheelies without being spooled up now, and my 2 part iat gauge shows pre injection temps around 120 and post Injection at around 60. 

 

My problem is after the first gear or two, when you really lean into it, it starts bogging and missing around 7k, and completely hits a wall at 8. If you stay tapped the revs won't climb and the bike won't go any faster. Adding choke doesn't help, and the afrs are around 11 or so.

 

I'm having trouble finding the cause of this issue, currently thinking either I have a problem with my fuel return circuit, or the ignition is too weak. I'm going to try gapping the plugs down to .015" (.5mm), but I also wanted to ask if it makes sense that raised compression needs smaller jets? (Skimmed a mm off the cylinders). 

Is it more efficient and thus choking out from too much fuel? I asked a shop and they said usually when they increase compression they need to go up in jet size.

Curious what your experiences are, as it might help pinpoint the issue, thanks.

[no class]

is the pitot circuit up to par ?

 

[clivegto]

What main jets size. 

[Arttu]

Increased compression shouldn't affect on jetting. But water-methanol injection can affect. Methanol is fuel so it makes the mixture richer which can then cause misfiring. And even if it doesn't get too rich added water makes it harder to ignite the mixture. So you may need stronger ignition system or you can try smaller plug gap as first aid, like you planned. And if your tune is on rich side you may need to lean it to make it work with water injection.

Also increased compression needs more voltage from the coils to make sparks. So if your ignition system has been on the limit it may start misfiring now just because of higher compression. Again reducing the plug gap is a good first step for troubleshooting. Even if it doesn't cure the problem completely it should make some difference and give you a hint if the problem is there.

[rerb]

Mains are at 110, but yeah. Seems to be spark blowout. Gapped down to .015 and pulled out a few more degrees of timing and that seemed to solve the issue. Ordering some coils from ignitech and stepping down to 108 mains since my afr is mid 10s on meth. Didn't realize how much harder more comp and water was on ignition

Edited October 30, 2022 by rerb

[Arttu]

Good to hear you got some progress!

Just keep in mind that AFRs around and under 11 start to be at territory where you may get rich misfires. And detecting that can be tricky since unburnt mixture makes the lambda meter to read leaner than reality. So for example if you see 11.5 on the gauge you may really have that and engine running happily. Or you can be actually much richer and the engine is misfiring 20-30% of cycles.

[Reinhoud]

Connect a O2 sensor with AFR gauge, without it's guessing.

Sometimes too rich or too lean can have the same symptomes.

Edited October 31, 2022 by Reinhoud

[rerb]

Got to dyno it today, 260 HP and 150 Ft lbs. This is at 11 AFR flat, But Arttu raises a good point so we'll see how it feels on 108 mains. Felt good to hit my goal of 250 after a year or two lol. New problems arise, however: clutch slip! Currently using the Swedish conversion with 3 springs, I might try new plates and a 3rd HD spring first then get a lockup if necessary. Opinions on best clutch disc mfg for these bikes?

[Arttu]

A turbo Bandit that I tuned some time ago made a bit over 260hp and the clutch was holding fine with 2 HD springs and one stock. The plates were old but I blasted the steels with glass beads which improves the grip quite nicely. So I think the clutch should be able to handle pretty good power with those springs if the plates and everything else are in good shape.

[Gixer1460]

And the best manufacturer is the original OEM - even Funnybike drag racers use them in preference to any other!

A lock-up has the advantage that you can use std. springs for nice 'easy to use' normal riding with the lock-up adding clamp pressure when its required!