Which slides - 3 or 3 1/2 ? Also thoughts on a change to single Mikuni

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I have completely stripped and cleaned thoroughly (ultrasonic tank) my 2 x 932 Amals that were fitted to my 74 mk2a

the mods it’s had during my recommissioning include Pazon Surefire , new unbalanced exhausts and pea shooters, and a narrow K&N air filter. All in place of the balanced exhaust, black caps and plastic air filter

I‘ve now fitted 260 mains, 106 needle jets, new float needles, new 2 ring needles in the middle notch.

I have it up and running using the 3 slides, most of my running appears to be at barely more than a quarter throttle from what I can notice, apart from when I wind it on and get it to fly. It does appear to be running OK-ish but the plugs seem to show its a bit weak

Should I have also changed to the 3 1/2 slide as well? what difference would it make, and more importantly how would I recognise it’s different?

Part of me wants to scratch an itch and fit a single Mikuni 34 kit in place of twin carbs for ease of balancing ie none. I’d like your thoughts on this too m
 

Fast Eddie

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The 3 1/2 slides would be weaker than your 3 slides. Slides have most impact just off of idle.

How weak is weak? And are you sure it’s weak? Can you show us the plugs?

If you’re weak at 1/4 throttle I’d try raising the needle a notch (ie putting the clip on a lower groove) especially if you’ve got less restrictive air filter and / or exhausts (dunno what yer got).

The single Mik versus twin Amal’s debate has been done to death, just do a search on here. The key points as I see ‘em are:

Single Mik runs well, they’re very well made, and generally speaking a more precise instrument.

But they’re still carbs, they still need jetting and fine tuning. They’re more complex and precise than Amal’s. If you struggle tuning Amals, Mik tuning will be more challenging.

A single VM won’t feed enough to release full go above 5k rpm. This is why I took mine off, castrating a Commando just ain’t my idea of fun!

Twin Amal’s can be made to run perfectly sweetly AND deliver maximum go.

You will NEVER conclude this via a debate on the net! You will get totally convincing arguments from both sides !

The choice is yours.
 
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Can only comment on my own experience with the Mikuni..... Didn't like it!!
Main reason was the on/off start/enrichment/choke device. Fine if you have: A) Time to warm it up before riding, or: B) You can ride at a reasonably wide throttle opening from the get go, or: C) Your engine tune or ambient temperature negate the use of such a device...
Others will and do laud it, of course, so: 'yer pays yer money, etc. etc....'
 
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If you have not tuned the pilots but left them at the starting point of 1.5 turns out, the pilot circuit could be lean. If you have not already tuned the pilots for best idle do it know and maybe that will be enough to enrichen the low throttle openings.
 
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Part of me wants to scratch an itch and fit a single Mikuni 34 kit in place of twin carbs for ease of balancing ie none. I’d like your thoughts on this too m
As part of my recent engine rebuild with Combat cam, I've just finished removing the single VM34 and returned the Amals to service. So far the Amals are working well enough after a quick going through that I'm wondering why I ever took them off in the first place.
 
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I set my pilots with a warmed up engine at night using the Colourtune, as I've mentioned before, I would not be averse to setting them slighty rich more than one and a half turns out to make the engine run clearly on opening the throttle, however, if you need to open the pilot screw to say 2 turns, then a larger pilot jet would be on the cards.
 

Mart UK

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I set my pilots with a warmed up engine at night using the Colourtune, as I've mentioned before, I would not be averse to setting them slighty rich more than one and a half turns out to make the engine run clearly on opening the throttle, however, if you need to open the pilot screw to say 2 turns, then a larger pilot jet would be on the cards.
This confused me. That pilot screw is an 'air' screw. If you unwind it further, you're adding more air to the mix. So if you need well beyond 1.5 turns, would that not mean your pilot jet is delivering more fuel than you need and you could go down in pilot jet size, to get back to 1.5-ish turns on the pilot air screw?
 

Fast Eddie

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This confused me. That pilot screw is an 'air' screw. If you unwind it further, you're adding more air to the mix. So if you need well beyond 1.5 turns, would that not mean your pilot jet is delivering more fuel than you need and you could go down in pilot jet size, to get back to 1.5-ish turns on the pilot air screw?
You are 100% correct and this has been stated as clearly as humanly possible numerous times. Sadly it dos not stop incorrect posts appearing, which can create huge confusion for people.

Easiest way to remember what’s what is that the ‘pilot air screw’ is called an air screw cos it controls the air (its a very logical name for it). Therefore, winding out = more air / weaker. Winding in = less air / richer.

Jets, however, control the fuel, therefore bigger jets = more fuel / richer. Smaller jets = less fuel / leaner.

So, if your air screws require being out more than 2 turns, it means the engine is requiring more air to run correctly, this means the pilot jet is too big and the air screw is being used to over compensate. So a smaller jet would be in order.

The above is correct for Amal’s, other carbs do differ.
 
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This confused me. That pilot screw is an 'air' screw. If you unwind it further, you're adding more air to the mix. So if you need well beyond 1.5 turns, would that not mean your pilot jet is delivering more fuel than you need and you could go down in pilot jet size, to get back to 1.5-ish turns on the pilot air screw?
Sorry for my incorrect post, it will let in more air the further it is wound out, as you rightly point out.
 

cliffa

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I have completely stripped and cleaned thoroughly (ultrasonic tank) my 2 x 932 Amals that were fitted to my 74 mk2a

the mods it’s had during my recommissioning include Pazon Surefire , new unbalanced exhausts and pea shooters, and a narrow K&N air filter. All in place of the balanced exhaust, black caps and plastic air filter

I‘ve now fitted 260 mains, 106 needle jets, new float needles, new 2 ring needles in the middle notch.

I have it up and running using the 3 slides, most of my running appears to be at barely more than a quarter throttle from what I can notice, apart from when I wind it on and get it to fly. It does appear to be running OK-ish but the plugs seem to show its a bit weak

Should I have also changed to the 3 1/2 slide as well? what difference would it make, and more importantly how would I recognise it’s different?

Part of me wants to scratch an itch and fit a single Mikuni 34 kit in place of twin carbs for ease of balancing ie none. I’d like your thoughts on this too m
If you want to remove the hassle of balancing, you should consider a Don’s ( madass140) single cable / gantry setup. Once set I don’t think they will ever change.



 
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If you want to remove the hassle of balancing, you should consider a Don’s ( madass140) single cable / gantry setup. Once set I don’t think they will ever change.



I’m more concerned in actually getting them set to start with. I really don’t know what I’m doing. I’ll happily set up my Hayabusa throttle bodies, but I’m out of my depth with Amals
 
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I’ve revisited what I originally wrote at the top of the page.

my slides are actually 3 1\2 which is what the mk2a was originally fitted with.

my question should really be - do I need no. 3 slides in place of the originals? Looking at Fast Eddie’s answer it would appear that I would be well advised to change.
 

Fast Eddie

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I’m more concerned in actually getting them set to start with. I really don’t know what I’m doing. I’ll happily set up my Hayabusa throttle bodies, but I’m out of my depth with M
You’re obviously a competent mechanic, you just lack experience with Amal’s.
Read the link Steve put in post #2 and you’ll manage things just fine. At the end of the day, if you’ve got a fairly stock bike, you’ll need fairly stock settings, you’re not starting from scratch by any means.
 

Fast Eddie

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I’ve revisited what I originally wrote at the top of the page.

my slides are actually 3 1\2 which is what the mk2a was originally fitted with.

my question should really be - do I need no. 3 slides in place of the originals? Looking at Fast Eddie’s answer it would appear that I would be well advised to change.
Didn’t the mk2a have a black box filter and black cap silencers?
Is that what you have?
I run number 3 slides in 650 and 750 Triumph twins so struggle to think 31/2s are ideal in an 850.
 
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Thanks, yes. I have had a read of the article too, and it’s bookmarked for a longer read.

But, should I be fitting no. 3 slides to fully make it a mk2.?

edit, I’ve just seen the last reply. It did have black filter and black cap,silencers. Now it’s a K&N and pea shooters.
 
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But, should I be fitting no. 3 slides to fully make it a mk2.?
As LAB says all 850's came with 3.5 slides, the 3.5 refers to the cutaway and only affect the initial opening from idle mixture. The normal issue is a short hesitation as you first open the throttle, so as a test you can deliberately enrichen or lean off the pilot setting and then test to see if the hesitation is worse or reduced. So as an example if you enriched the idle and the hesitation reduced then you can look at fitting a richer cutaway slide.

If you have no hesitation or spitting back on initial opening of the throttle then leave it be.
 
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