ESE's works engine tuner

[TZ350]

.Have had another thought on this running on problem. Maybe the Blow Down Time Area is insufficient at 10k RPM, leaving a lot of hot nasty stuff in the cylinder. The factory ran these engines to 8,500, with a similar size exhaust port (80atdc & 72%) and blow down I guess. I will have another look at this with EngMod2T.

Ok. EngineMod has the inlet, transfers and blow down peaking about 8,500 rpm and the exhaust port at 7,800 rpm. I had asked EngMod to design a pipe for peak HP at 9,500 rpm. Indeed the engine makes peak power at 9,500 rpm and will touch 10,000 but runs on. I wonder if the rpm mismatch with the exhaust is my problem? Residual hot exhaust gases making it run on. It may be I have to reconsider the expansion chamber and more closely match it's design to the ports potential.

Any thoughts on interpreting RPM figures in the right hand column of the EngMod screen shot would be greatly appreciated.

[TZ350]

When I initially setup the EngMod 2T model for the F81M. I chose 9,500 rpm for peak power. Looking at the target STA's and the STA's achieved. It looks like I will have to lower my ambitions a bit and accept that I my not be able make as high a reeving engine as I would have liked.

[wobbly]

Peak power at 9500 is perfectly achievable , send me the .pack as analyzing the thing needs way more than just timing and STA numbers.
I mean when did any engine making good Hp , since the middle of last century , have all the transfers opening together - that alone leaves a heap on the table.
Normal stagger pumps up the front side by default , and allows many opportunities to then re engineer the peak and overev characteristics.

[jonny quest]

Are you too rich?

I had an MX bike that would run on after throttle was closed. It was pilot jet being too big. It was enough fuel to feed engine through pilot passage.

[TZ350]

Peak power at 9500 is perfectly achievable , send me the .pack

Thanks Wobbly. F81M-RS10,pack file emailed to wobbly1

Thanks Again.
TZ350.

[TZ350]

Are you too rich? I had an MX bike that would run on after throttle was closed. It was pilot jet being too big. It was enough fuel to feed engine through pilot passage.

Thanks for the pointer. It certainly got worse the richer it was. Food for thought, much appreciated.

[wobbly]

Beta , just to be on the same page , was the 198* Duration you actually measured done with the CIK dead stop blade ( 0.2mm @ 45* = 0.28mm actual height change ) and
CIK rotary digital encoder.
I use a 0.7mm blade @ 45* as this gives exactly 1mm of height change on a 50mm digital gauge - easy to then calculate the real timing.

[husaberg]

i came accross this today i have not read it all.'

Step 1: DETERMINE THE CORRECT NEEDLE AND OR NEEDLE JET.

Whether or not your carburetor is a MIKUNI or a KEIHIN, it does not matter. This is the most important step in jetting your carburetor--period!

1. Remove the main jet.

2. Place needle clip in mid-position.

3. Start motor and run it on the stand.


Condition: Motor running and main jet out. Needle or needle jet is correct: Carburetor should run clean to approximately 3/4 throttle. From 3/4 throttle to full throttle, the motor should start to break up as a result of too rich condition.

Correction: None needed.

Condition: Needle or needle jet is too rich. Carburetor runs clean to approximately 1/2 throttle but breaks up before 3/4 throttle as a result of too rich condition.

Correction: Mikuni replace needle jet with next leaner and test again. Keihin replace needle with next leaner diameter and test again.

Condition: Needle or needle jet is too lean: Carburetor runs clean beyond 3/4 throttle and has an erratic throttle response.

Correction: Mikuni replace needle jet with next richer and test again. Keihin replace needle with next richer diameter and test again.


The emphasis here is to find the correct needle or needle jet diameter, which will allow more fuel to pass than is needed but not so much that the needle itself has no control below 3/4 throttle.


Step 2: DETERMINE THE CORRECT PILOT JET.


1. Make sure the bike is warmed up if at all possible.

2. Main jet out.

3. Needle clip in mid position.

4. Turn air screw all the way in then 1/4 turn out.

5. Start motor and run it on the stand.

6. Adjust idle so the bike will just barely idle.

Condition: Motor running and main jet out.



PILOT JET CORRECT:

With one hand on the throttle maintaining RPM at approximately 1/8 throttle, turn air screw 1/4 turn at a time clock wise until you bottom it out. Motor should become slightly erratic and you should have to play with throttle to maintain RPM. Start turning air screw counter clock wise, 1/4 turn at a time until you have reached 2 3/4 turns out. Between 1 1/4 and 2 1/4 turns, your motor should have reached its highest RPM maintaining a steady throttle. Adjust air screw again between 1 1/4 and 2 1/4 until you have determined highest RPM. Quick throttle response should be clean without bog.



PILOT JET TO RICH:

RPM does not reach a peak between 1 1/4 and 2 1/4 turns, stays the same or keeps rising out to 2 3/4 turns.

Correction: Mikuni replace pilot jet with next leaner and test again. Keihin replace pilot jet with next leaner and test again.


PILOT JET TO LEAN:

RPM does not become erratic and motor maintains throttle when air screw is turned all the way clockwise.

Correction: Mikuni replace pilot jet with next richer and test again. Keihin replace pilot jet with next richer and test again. Remember, with a steady throttle approximately 1/8, there should be a distinct difference in RPM from 1 1/4 turns to 2 1/4 turns if the pilot jet is correct. The emphasis here is to find a pilot jet that will run crisp without bog and without the main jet.


Step 3: DETERMINE THE CORRECT MAIN JET.

The main jet selection process is easy once you have the correct needle diameter or needle jet. You now only have to correct a rich condition from 3/4 throttle on up and you know what a rich condition sounds like. Your pilot circuit is correct and without bog.

1. Replace main jet with one that is at least two sizes smaller.

2. Needle clip in mid position.

3. Start motor and run it on the stand.


By replacing the main jet with one that is too small, you are looking for a condition that is too lean. You adjust your main jet from a too small to lean condition.

Condition: Motor running and main jet in.


MAIN JET CORRECT:
Carburetor should run clean and crisp to full throttle.

Correction: None needed.


MAIN JET TOO RICH:
RPM reaches a peak slowly with a deep sound. Excess fuel and oil mixture at end of silencer. Spark plug fowls easily and is dark in color.

Correction: Mikuni replace main jet with next leaner and test again. Keihin replace main jet with next leaner and test again.


MAIN JET TOO LEAN:
RPM reaches a peak quickly but erratic. A quick full snap open of throttle causes the motor to hesitate BEWAH sound or a complete bog. Motor sounds like it has a ring to it. End of silencer white. Spark plug is white in color.

Correction: Mikuni replace main jet with next richer until the BEWAH bog just barely goes away, then replace the main jet with the next richer and run it. Keihin replace main jet with next richer until the BEWAH bog just barely goes away, then replace the main jet with the next richer and run it. The emphasis here is find a main jet that is just rich enough to allow you snap the throttle wide open without the motor bogging as a result of the main being too lean. Should be a quick crisp throttle with no hesitation.



Step 4: DETERMINE THE CORRECT NEEDLE TAPER AND CUT AWAY.
This step in the jetting process can be made very simple if you remain close to stock. However, your needle taper is adjusted for 1/2 throttle to 3/4 throttle. Start off with a rich taper (shallow taper angle) and keep going leaner (steeper taper angle) until it will not maintain constant RPM at 1/2 throttle (runs erratic). Go back to the leanest taper angle that ran the smoothest at 1/2 to 3/4 throttle and that should be the correct taper.

The needle taper final test should be under track conditions with the greatest effect entering and exiting corners. Do not change the needle diameter or needle jet size during this process because that has already been determined. Adjust taper and throttle cut away only.

Throttle cut away effects from idle to 1/4 throttle. The correct cut away will maintain steady 1/8 throttle with quick throttle response. Generally the stock cut away is very close. Experiment with different cut away until it maintains the best response to 1/4 throttle.



QUICK TIPS:
Keep it simple, buy the optional OEM needles or needle jets that are available, as this may speed up the taper selection process. Don't skip any steps or you're just guessing.

[190mech]

husa, Thanks for sharing!!!

[HSuomi]

Attachment 353941

Why ......... with the best power main jet fitted. On straight Methanol this thing would run on after a full throttle 10,000 RPM dyno pull.

Does this mean that the engine RPM stays high after the dyno run when you pull the clutch?

I'm having similar issue on my 90cc methanol dragster and I'm wondering does it actually make any power in this situation? Im curious because I just built a DIY slider clutch and I wonder if the bike can be stopped with brakes after the 1/8 mile or does it just keep going? I have not tested if the engine stops with kill switch in this high reving situation...

[Grumph]

That's a good point. Clarification please Rob. Ignition on or off when running on after a dyno pull please.

My runaway Mach 3 was sitting on 9000rpm with all the plug leads off and only stopped when it ran out of fuel in the bowls.
Which was a giveaway it had another source of ignition.

[peewee]

hey guys let me ask a question. I had a 10mil billet crank made for my banshee engine. I sent four skf roller bearings (nj206ecp normal clearance) to the crank shop to have ring grooves machined then fitted on the crank. I received the crank and unboxed it to find the outboard clutch side bearing was a koyo of c3 clearance. ive not yet talked to the shop to hear their explanantion as theyre closed for the weekend but is this oddball c3 bearing going to cause me problems at some point down the road ? if so im going to demand they put a same type skf bearing on.
for some reason they sent the fourth skf bearing back to me (with groove already machined) and I don't see anything wrong other than the groove appears to be machined so the skf markings would be toward the webs and not visible but I don't see how that would affect anything ? so im stumped until I hear what they have to say

[F5 Dave]

They must have messed one up and got a local replacement.
Why weren't they all C3 as typical?

[peewee]

i didnt know they were supposed to be c3. figured normal clearance. and im not sure how much press fit the inner race has on the web pins. i asked them in a email what bearings i need to send and they said nothing about c3.

yes perhaps they screwed up the 4th bearing and got a local replacement. i hope to figure this out monday but i dont have a good feeling if all the bearings arent the same

[husaberg]

IME all are at least c3 not sure with horizontally split cases though...