Detonation

[Alain2]

Here is my setup for my canadian RD400 Daytona Special (street bike):

Stock porting 2R9 cylinders
65mm Wiseco pistons, 120psi cold (after break in)
OEM CDi 2.0mm (OEM recommended)
B9ES (OEM recommended)
Foam pod air filters
OEM exhaust

VM28 carburetors
170 MJ

Mid range is running very good, but it started detonating around 7000 rpm at wide open throttle in higher gears.

At 2.0 timing my EGT were the following in 4 th gear w/o:

4000-5000 rpm: 800-950f
5000-5500 rpm: 950-1100f
5500-6000 rpm: 1100-1150f
6000-7000 rpm: 1150-1200f
7000-8000 rpm: 1200-1250f

I lowered the timing to 1.9mm and now the detonation is intermittent passed 7000rpm.
The EGT are now running 50-100f higher passed 6500rpm which confirms It now detonates less (right?), but dangerously getting 1350f at 8000rpm.

Spark plugs don't show sign of detonation.

I'm a bit puzzled at this point.

To play it safe I would have to go to 1.8mm and 175 main, but I'm afraid I'll loose power between 5000-7000 rpm, where it runs very good.

Is there a way to increase fuel only in the high rpm? Bigger carburetors?
Is intermittent audible detonation an absolutely no-go?

[m in sc]

try a 180 (me? it stuff a 190 in there 1st). always err rich then work down, especially if its throttle position related.

[Dvsrd]

What VM28 setup Are we talking about? RD type with bleed type needle jet, or R5 type (Dale A/ Dave F modded
That has a significant influence on MJ size, as you probably know. If ignition timing is the main ussue, then a ignition system with an advance/ retard curve should help...

[Alain2]

2r9 carburetors with OEM 284-o8 nozzle
5l1-2 needle
30 pilot

The 284 nozzle is like a 175, but shield. The carbs have factory by-pass boots.


Midrange is already tuned. I can ride highway no problem 1/2-3/4 throttle.

[Alain2]

I should add that with this particular project Im trying to reach maximum power, no trying to hit best reliability.

[m in sc]

i understand that, but start rich work down. bikes with holed pistons are slow ;)

always throw as much fuel as it can take and run clean. I still think you're at least 1 size too small. Nothing to lose going up and testing.

My method is go up till its fat, in 2 size increments, then drop a size down to get it to run crisp all the way. with an egt, you'll be able to monitor the temps so it should go fast. IF it can run a 180 and the temps stay where they are at the lower rpms where its running good, you've hit it IMHO

   

[Alain2]

Tested 190 main, max EGT was 1200.

Unfortunately I still get detonation +7000 rpm.

I now have to back timing to 1.8mm. The wiseco already took a lot of abuse.

[m in sc]

how was the power? and was it only detonating at WOT?

might still need to go up.    i know on 350s for example, going to pods alone with stock exhaust will bring you over 200 mains rest being stock.

[Alain2]

I think I underestimated the 2r9 cylinders. Weird because midrange is tuned leaner than my 1a1 RD400, buy high rpm need more fuel. I just put 210 main to be safe, will test in the next couple days.

[sav0r]

I've seen well over 1400F on EGT before. It inherently means nothing because none of use here have data to compare your numbers to. Also, the longer the straight, generally the higher the EGT. Factors like the position of your EGT in relation to the cylinder (distance from piston to probe) will drastically change the numbers you read. And just because your EGT reads 1400F doesn't mean your pistons are anywhere near that hot. If you are really concerned with detonation, get a detonation counter and data logger. If you can see detonation on pistons it's too late, but all engines have some detonation, it's unavoidable. That said, powerjets might fix your perceived top end knock. They work very well.

[SUPERTUNE]

Do you have the 3J7 head with the 2R9 cylinders? or STD 1A1 heads using a .50mm copper headgasket?
With foam pod air filters, the mid-range will be lean, because of the Euro/Canadian 2R9 bastard needle jet, its not a replaceable needle jet like the std RD #175. The #284 needle jet is a special one by Yamaha to use the Euro/Banshee crossover tube and intake manifolds.
I would either go back to the stock airbox or do a primary needle jet conversion so you have choices on the needle jet.
The 5L1 needle is a std oem RD400 needle (except 2V0 Daytona)
Chuck

[Alain2]

I have a 3J7 head with 0.5mm gaskets, same chamber size and CR than 1a1 heads.

[m in sc]

but at what throttle position 'at higher rpms' are you getting the audible detonation?

[Alain2]

Only at WOT.


I'm starting to think that the noise I get is not detonation. Something is wrong.

If I had detonation few pulls here and there (let say 10 pulls), would I see it the top of the piston? I pulled the head and there is nothing unusual.

Could the noise be the rings catching?

[m in sc]

if its only at wot, its fuel.  if you don't hear it at 8k under half throttle, then its not squish, or anything else mechanical IMHO.