[stinkwheel]

Got a few runs in. Starting to get cold and dark now.

Tried the P4 needle jet and 6DH4 needle and there was a definite improvement, little to no pinking up to 1/2 throttle now.  A little more improvement raising it a notch, more still going up a main to 230.

The needle is much fatter than the previous 56FP17. I do wonder if this is counter-productive. On the assumption the midrange is lean, would i be better to have more of the main jet uncovered sooner? I'll give it a try tomorrow.

May just about be in a position to try a couple of larger mains to see what they do.

One thing that's clearly noticeable is it's faster.

[Mr_84]

G’day stinkwheel

Glad to see your deep into , with the 6DH4 needle on my 505cc and StreetKleaver’s 535cc the needle clip like to be 2nd from the top other wise it will try and foul the plug , but have a play round and get out and give it a thrashing, remember now that you have this new setup , to only change one thing at a time and go test
Happy tuning

[Mr_84]

Stinkwheel

It might be worth noting this carb has most likely been running rich in the mid now your close and it been tricking you into thinking it’s pinking , go 2nd clip from TOP yes that’s leaner  , go out and run it a 60mph on easy flat roads , that should have you running on the straight or flat part of the needle still, stop and pull the spark plug , if it isn’t to light of colour you needle is good , move on to main jet and thrash it

[stinkwheel]

There's definately detonation still, you can hear it and if you open the throttle more, it's worse and no more power is produced. I don't think I'd dare run it at more than half throttle at the moment but I was going to try going bigger on the main and see if I can crack it open wide.

When you say 60 on the flat, are we talking say 3rd gear, half throttle? I'm generally hooking 4th at about 55-60.

I'll do the needle first as you suggest and see what effect it has.

I'd do some video of these runs so you can hear the engine noise but I struggle to get decent sound that's anything but wind noise with either of my cameras. Maybe I'll try putting my bullet action camera in a sock or a bag of some sort.

[Mr_84]

G’day

 60mph in top gear that will be your cruse speed , I’ve just realised you have a 4 speed, but top gear is top gear , any heavy throttle opening will be testing more or the main jet.
These TM’s like the mid sorted then go for the main after ( I have a TM32 on another bike ) .
The best way to test is always pull the plug and look 👀 these dam TM’s can trick you into thinking they are lean when the opposite is happening , the only way to be sure is look at your plug .
Do a cruse ride that will help indicate the mid ( needle) thrash will indicate main .
The mid is so important on these TM’s everything evolves from there

[stinkwheel]

Hmm. Lowering the needle made it worse. I've done a video to show the noise I'm hearing but it'll take a bit to upload/process. It is very much related to both the load on the engine (more load = noise worse and at smaller throttle openings) and the throttle position (more open throttle = noise worse).

I can't think what it would be other than pinking, especially when you can get rid of it by retarding the ignition.

Plug looks lean to me. Admittedly, I haven't cleaned it for a while so I'll do that now. With the retarded ignition it was dark brown and a little oily. Looks to me like it's burned off all the oil residue that had been on it.

[stinkwheel]

Here's the video. Fast forward to 1:50 for the actual noise. I put a graphic up on screen on a few of the occasions where it starts making the noise. This is directly related to me opening the throttle.

https://youtu.be/Q1PJeP6WKzw

Off the clean the plug, drop the needle back down to the centre notch and try a larger main.

[stinkwheel]

Ok, found something unexpected. I upped the main jet half a size. This jet was a little tighter on the threads so I had to use a small amount more force to screw it into the needle jet and it felt like it took an extra 1/4 turn.

Next run out, bike pulling reasonably well from 1/2 to full throttle. No obvious pinking noises. Running like a dog with fleas up to 1/4 throttle with bogging, misfiring and 8-stroking. Less badly from 1/4 to 1/2 but still not great. Came back to find oil dripping from under the seat?! Turns out it spewed a load of oil from my rocker cover breather which has never breathed a drop of fluid before. Presumably as a result of the misfiring at low revs forcing gas up the valve guide. Plug black as hades.

I don't think my needle jet was fully seated. I suspect the needle jet has never been fully seated.

Went back to baseline main and pilot jet, still pulling reasonably well from 1/2 to full but with a hint of pinking at wide-open under load. Still god-awful at low revs. Tried dropping the pilot size which was better but not fantastic, Plug sooty and black.

I think I'll try the P6 back in it.

[StreetKleaver]

Hi Stinkwheel. If your new to these engines, they can trick you with what's detonation vs valve train rattle. Especially if you come from other makes like Japanese models etc.
My Iron Barrel gets a valve train rattle up at a certain rpm then goes away. Every gear, doesn't matter what load. It's more profound since it has Samrat Alloy rocker boxes and a alloy barrel. The noise resonates through the less denser material than the standard Iron Barrel.

There's a bit of a valve train clatter around 1500rpm and then around 3500rpm on my bike. You soon learn what "Enfield" noises vs detonation is. Haha.
Which at first I thought was detonation and like you tried to tune it out.

From the looks of your plug you're still very rich.

These Mikuni TM carbs are a little more sensitive to changes. More of a race bread carburetor than a set and forget type.

Before you get carried away and possibly chasing your tail.
Firstly make sure your ignition timing is spot on. There's plenty of publications and steps how to do it correctly. If it's not right, these things won't run great at all. The detonation zone I found is around 2800 to 3200 on these main if you have short shifted it and have it a bit loaded up.
If it is detonating around that area. I mark on the housing where the set point is with a fine line permanent marker. Then retard the timing a whisker at a time until the plinking is acceptable and only present when you "force it". IE a fistfull under load around 2800 rpm.


Next would be start off back to basics. Make sure your float height is correct.
Then go back to basics and start from the beginning.
The correct procedure is as follows.
#1 Set the pilot
#2 Set you Main
#3 Then fine tune your needle last.


Pilot circuit.
Your pilot jet should be around 20, 22.5, 25, 27.5. Possibly 30 but that's getting a bit rich and TM flat slides meter very well at slow air/vacuum speeds.
Its usually 22.5, 25 to 27.5 in most cases.
Set your air mixture screw 1- 1/2 turns out.
Get it running. Warmed up to operating temperature.
Set the tick over/idle slow so if your turn the idle screw out 1/8 of a turn it will stall.

Start by winding the air mixture screw out 1/4 of a turn and count to 10 listening if the idle improves or lack of improvement.
Example. It's slowly ticking over and you've started at 1.5 turns out. You turn it out (more air leaner) 1/4, wait... Turn it again 1/4 and hear the Idle improve by 250rpm. That's 2 turns out. That would be set.
If turned in (richer) by x2 1/4 turns to 1 turn out in total. Means the pilot jet is on the smaller side, you're taking away the air for it to run.

Rule of thumb you want between 1 and 3 turns out with the correct pilot jet with the idle at its healthiest (idle increasing ever so slightly from the slow tick over).
Each pilot jet change affects the whole throttle range since its always open. That's why its important to get it sorted first.
If the airscrew is less than 1 turn out, Pilot jet is too small you need to go up a size.
More than 3 turns out its too rich, you need to go smaller.

Another method is set the idle about 250rpm higher than you would usually. Use the same above method with the air mixture screw. Record where the mixture ends up and compare your results from both methods.
The high idle method isn't as accurate since the carburetor is starting to pull from the needle/needle jet circuit.
Once happy set your idle back where you want it. I set so it has good throttle response and no idle "hang".

The pilot and needle are really important to get right on these bikes because you spend most of your throttle openings there. Since the throttle is still sitting on the straight section of the taper around 1/3 throttle.

I'd start with the jetting MR_84 has suggested. Since his motor is closer to yours. The 6DH4 is the suggested correct needle taper for a 500 single 4 stroke engine. Taken from Mikuni's jetting database.

Start with
25 Pilot
P4 Needle
6DH4 needle. 2nd clip position down from the top.
210 main (But have a 190, 200 and 220 on standby)

Get your Pilot set, then main with plug chops. Then on to the needle. But that should give you a base.

Good luck!

Ben

[stinkwheel]

Thanks for that. Yeah, I've been running enfields for about 12 years now and this noise isn't the usual rattle and clatter. The fact it goes away if you retard the ignition timing suggests it is detonation.

It appears that the needle jet wasn't fully seated from when the carb was new. With my current "baseline" settings -which it's done a few thousand miles on- it ran very well at low revs up to about 1/2 throttle and acceptably well at higher openings with the ignition retarded, albeit a bit on the flat side.

Having changed that main up and the jet seeming to screw in a little further, it started running very badly indeed at small throttle openings and hasn't gone back to how it was when I went back to the previous jet. Main jet hasn't caused this, pilot jet is fine. Must be that the hole in the needle jet wasn't aligned properly so the bike has been running lean through the midrange. Only other reason I can think of is that the timing has moved, I'll check that but I think it's unlikely, never happened to me before on a bullet.

It's obviously running outrageously rich at the moment, if you think that plug tip looks rich, you should have seen it after the last run!

I very meticulously set the ignition timing this time round. Degree wheel on crank.

So yeah, it's a case of back to the start and walk the settings in. I'm quite pleased I found this really, it was starting to frustrate me because things didn't seem to be working as they were expected to work.

[stinkwheel]

Quick update.

After an awful lot of testing, I've concluded that the compression is just too damned high, there's no way to get this running well on pump fuel without either detonation or retarding the ignition past a reasonable point. I've ordered some gaskets and I'm going to put a 2mm compression plate back in on top of the 3mm which should take it back down to 9:1.

The midrange gains from swapping about the needle jet and needle should make it a whole lot more tractable than it was before anyway. If I was racing it, then it would probably be great as-is because I'd have the revs way up all the time (where it doesn't detonate) but sitting at 80mph in third is not feasable for on the road.

[Adrian II]

I do wonder if this is a case for twin plugging the head? Not normally a lot of use on ab old Bullet engine, but it might just improve the combustion while allowing for a slightly later ignition timing. You'd lose the decomp valve, though I gather it can be relocated to the top of the head, Tim NZ on the old Hitchcock Forum did this successfully, I might still have some saved pictures/drawings somewhere.

Would a shorter con-rod (if one is available) allow you to dispense with spacers under the barrel?

A.

[stinkwheel]

I think I'm just pushing it a bit too much. 9:1 should be more than sufficient compression anyway. It was running on that when I first built it with no detonation. I feel twin-plugging is a lot of work chasing a marginal performance gain I probably don't really need in the grand scheme of things. The performance gain from fitting the TM32 carb is noticeable but bumping the compression to 10:1 was a step too far. I've also ironed out a couple of other issues since then. Hopefully with all the work I've done on the carb and ignition side, it should just bolt on and go. Then i can put it away and get the 350 on the bench ready for the trials season

The newer 612 cranks are made to not require compression plates but I think fitting a plate which I already have in a weekend at the cost of a head gasket is probably an easier and more cost effective solution than a crank rebuild and binning a perfectly good steel conrod. There is JUST enough clearance to get the head on in the frame and the tank on without fouling the rocker covers with 7mm of compression plates.

[Adrian II]

The point of a twin plug system set-up in your case would NOT be for increased performance, but to make what's already on there cope with the high compression better. By the sound of it you already have all the power you want at WOT, I suggest it purely as an anti-pinking measure. 

A.

[stinkwheel]

What I was getting at is the current state of tune probably isn't worth the faff of twin plugging to maybe make it work. It needs dialling down a notch.

I can't even get to WOT on standard ignition timing as things are, probably 3/4 before it starts detonating, earlier if under load. I honestly don't think anything would sort this short of using higher octane fuel. I've been through all the permutations of main jet and needle position and anything I do from here makes it worse. I could boost up a tank of fuel with royal purple to prove the point but I really want it to be able to run on pump fuel.

On the plus side, if they start doing E85 fuel at the pump any time in the future, I'm all set to take advantage of it.