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October 01, 2014, 02:44:38 PM

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Author Topic: Mikuni TM-32 fittment  (Read 2919 times)

DanB

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Re: Mikuni TM-32 fittment
« Reply #30 on: May 19, 2014, 03:53:34 AM »
...
My issues: 
1.  The pilot and cold starting.  I've been completely unable to use the choke at all.  The 30 pilot fouled the plug very fast.  Dropped to a 27.5;  still acted too rich. Now at a 25, about 2 turns out.  Once the engine is warm, its smooth as anything at an idle.  Cold starts have been a challenge.  She'll catch if i ever so lightly hold the throttle; like just taking the play out of the cable.  Anything more and she coughs badly!  It'll idle at about 700 rpm, with my air screw and idle screw set warm.  Trying to roll on the idle sometimes results with the engine stumbling & spitting back into the carb.  Again, once warm, no worries.  I tried a 20 pilot, just for giggles... didnt really notice anything different. So my starting procedure has become: Give idle screw a 1/4 turn in, a couple of kick thrus, hold throttle gently, kick it, and give it a bit of quick revs until the engine holds... slow to warm up, once warm drop the idle screw back to 1000; wondering if changing the air jet or slide would make a difference.  Any ideas or suggestions?

Plug at idle (from cold start):


Plug chops at 1/4 and 1/2 throttle have about the same results to the plug:

Disregard the brown spots... some type of weird flash effect

It looks to me to be lean.  But no pinging, no flat spots and she really does perform well.  With the s-cams, my mids are so much stronger!  Between 30 and 70 mph is just a joy!  When I ran with the P6, i noticed a number of flat spots.  The P4 smoothed those out, but i think i need to raise the needle a clip or two; but raising the needle really wouldnt have that much of an impact at 1/4 to 1/2 throttle, right?  Again, suggestions most welcomed!

3/4 to WOT: She flattens out between 75 and 85.  The RPMs in 5th are between 4000 and 4800.  I'm going to try a 195 in there, but i havent done a chop yet at WOT.  Just need to find a good stretch of road for about 2 minutes with no police.

How lean can an AVL-leanburn be happy with?
Suppose I were an idiot, and suppose I were a member of Congress; but I repeat myself. ... Mark Twain
2006 AVL Electra

ace.cafe

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Re: Mikuni TM-32 fittment
« Reply #31 on: May 19, 2014, 10:05:55 AM »
You can go as far as 3 turns out on the air bleed screw, according to Mikuni. So you can get an indicator from that. If it  gets better all the way to 3 turns out, then you might try the next leaner pilot jet.
You already have the leanest throttle slide.
The needle jet and needle have about equal effect at half throttle, so changes on the needle should be noticed there.
Raising the needle makes it richer. Putting the clip in a higher groove lowers the needle and makes it leaner.
Did you put the silicone sealer on the manifold/head joint instead of a gasket?

The plugs look rich compared to other AVL plug chop photos that I have seen.
The choke is "on" with the plunger knob pulled up. It is somtimes stiff, and difficult to push it all the way down to the "off" postion.

Did you need to retard your  S Cams intake cam by a tooth to avoid contact with the piston, or not?
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DanB

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Re: Mikuni TM-32 fittment
« Reply #32 on: May 19, 2014, 05:12:31 PM »
Thanks Ace.

Quote
Did you need to retard your  S Cams intake cam by a tooth to avoid contact with the piston, or not?

No, I did not need to retard. They are 'on the dots'. Although, it is acting like it has been retarded. 

Quote
Did you put the silicone sealer on the manifold/head joint instead of a gasket?

No gasket; just sealer on the joint.  No leaks at all.

The choke is certainly down all the way, but I assumed that the new carb was internally clean.  I never thought to check it out.  Maybe there is a blockage somewhere.  Thinking I probably should check the passages and disassemble the choke.  The plunger button is down all the way, and it shows a bit of 'rod'.  Hard to describe what I'm thinking in my head; i need a photo.

Can you help me with the reading of plugs?  You say the chops look richer than other AVLs.  Can you tell me what you're looking at? Here's the plug...


1.  Ground strap shows the heat index / timing of the engine.  My heat band comes up onto the strap onto the flat of the strap... it's not on the apex.  I think its ok, but it may be a little 'cold' (photo is crappy)
2.  The fuel ring.  Too dark and sooty?
3.  When I look inside the plug on the metal screw shell wall, i see the same darker deposits.  Am I looking for a lighter tan  /brown here?
4.  The porcelain is mostly clear.  I think i can make out a brown band towards the middle of the insulator.  It doesnt go all the way around. 

Should I be looking at the threads as well on the plug?  Like 2 to 3 threads discolored?

Trying to decide my next move; Here's what Im thinking in order of sequence (please let me know if I'm way wrong here):

1st. Lean out the pilot circuit - try 22.5 if the 25 taps out at 3 turns.
2nd. Move clip one leaner (drop it), and see what I get.   
3rd. P2 Needle

Regardless - need my 3/4 & WOT reading.

I use this site as a reference; I know its for cars, but it helps me to visualize what i should be looking at... http://honda-tech.com/showthread.php?t=3063102

Thanks Tom, as always!!!! ;D
« Last Edit: May 21, 2014, 02:52:05 AM by DanB »
Suppose I were an idiot, and suppose I were a member of Congress; but I repeat myself. ... Mark Twain
2006 AVL Electra

ace.cafe

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Re: Mikuni TM-32 fittment
« Reply #33 on: May 19, 2014, 05:33:27 PM »
I think the ignition timing looks a little too retarded to me. If you can advance it a little, it might do better at higher rpms.

I think your plan for the pilot jet sounds good to me.
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

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DanB

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Re: Mikuni TM-32 fittment
« Reply #34 on: May 19, 2014, 08:11:17 PM »
Thanks again Tom.

Can I ask, what are you looking at that makes you suspect retarded timing? 
Suppose I were an idiot, and suppose I were a member of Congress; but I repeat myself. ... Mark Twain
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Re: Mikuni TM-32 fittment
« Reply #35 on: May 19, 2014, 08:45:51 PM »
Hi Dan,
 Looking at your pictures of the plug chops, I would say your idling colours are what you want to see for larger and full throttle readings. The plug picture you show for larger throttle openings looks way too weak for my liking - better to go too rich to begin with and work down from it gradually, to be safe. Unfortunately, I don't know enough about Mikuni carbs to advise jet sizes, but I had the 36mm Amal MK II running on a 280 main jet for my tune up, if anyone can translate that into Mikuni speak.
 B.W.

Adrian

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Re: Mikuni TM-32 fittment
« Reply #36 on: May 19, 2014, 10:30:22 PM »

DanB

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Re: Mikuni TM-32 fittment
« Reply #37 on: May 20, 2014, 04:23:05 PM »
Thanks Adrian and BW.  I need to think about the next steps.  I think Im close as the bike just runs soooo nice (except for the cold start issue).

Adrian, that reference document between Amal and Mikuni really doesnt work.  The cross reference for a 280 mains Amal mapped out to a 150 Mikuni mains... Unless im ready the table wrong.  That would be way to lean. 

I'm thinking next...

1.  play with Pilot (air screw and 22.5)
2.  I'm going to put a 200 main on.  See what that does at 1/2 to 3/4 throttle.
3.  Adjust the needle.

Then reevaluate. 

Mikuni Question:  How the hell do people wrestle with that damn spring??  God its a nightmare.

Suppose I were an idiot, and suppose I were a member of Congress; but I repeat myself. ... Mark Twain
2006 AVL Electra

ace.cafe

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Re: Mikuni TM-32 fittment
« Reply #38 on: May 20, 2014, 06:03:43 PM »
One thing I would comment on is that the idle should be at about 1000 rpm. Trying to get a very low idle speed is often a cause of stumbling type issues, and it is not recommended, nor IMO is it desireable.
So, I personally would recommend avoiding that 700 rpm stuff, and concentrate on the running performance.
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DanB

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Re: Mikuni TM-32 fittment
« Reply #39 on: May 21, 2014, 02:09:29 AM »
Agreed.  the 700 is what it cold starts at, and coughs if i try to give it more, unless i twist the idle screw.  1 or 2 minutes in and I can apply the throttle, and the idle picks up from there and will settle into a higher rpm idle (I should have clarified that... the 700 rpm tick over is scarring me and my sprag!).  She chokes on any throttle when cold...  The bike actually likes about 1100 at warm idle.  I have a small digi tach that 'sort of' tells me what its doing.

I interpret that as a) the pilot is rich; b) when cold, its HATES the idle to 1/8 throttle transition as its too rich for it.  I think you're right Ace; the bike's timing needs a bit of advance... not sure how or why it is this way (I noticed a similar prob last year but not as pronounced).  Also not sure how to advance it unless i do the woodruff key thing. ALternatively, I may try a performance elec. ignition box to go with the cams :)
Suppose I were an idiot, and suppose I were a member of Congress; but I repeat myself. ... Mark Twain
2006 AVL Electra

ace.cafe

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Re: Mikuni TM-32 fittment
« Reply #40 on: May 21, 2014, 03:01:16 AM »
On the Iron Barrel models, it usually will need the choke for any cold start, and will need at least a couple or three minutes of warm up before it will ride off cleanly. We always set the carb when hot, so it will remain stable at operating temps, and deal with the cold nature on cold starts. We can never ride off cleanly when cold

They might work a little differently due to different thermal character of that engine.
But  I have not seen any real difficulties with the TM32 on the AVL so far. The need for such a lean pilot jet at your elevation is unusual, and I don't know if the cams would affect it that way or not.
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DanB

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Re: Mikuni TM-32 fittment
« Reply #41 on: May 22, 2014, 02:31:39 AM »
It is interesting and wish I knew more about what's happening in there. I'm thinking it's not right. If I can't get the pilot set, I've decided to question my assumptions: 1) the carb passages are clear. 2) I did indeed put the cams on the dots (although I have a photo I took that I swear was right). 3). Check out the primary side sensor and make sure it's in place.

Would a retarded timing impact the cold start in such a way? The Harris Scrambler was also retarded 1 tooth I believe.... Did see anything like my situ.
Suppose I were an idiot, and suppose I were a member of Congress; but I repeat myself. ... Mark Twain
2006 AVL Electra

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Re: Mikuni TM-32 fittment
« Reply #42 on: May 22, 2014, 08:43:03 AM »


Would a retarded timing impact the cold start in such a way? The Harris Scrambler was also retarded 1 tooth I believe.... Did see anything like my situ.
Hi Dan,
 No, The original testbed machine had 32mm Amal MK I, followed by Amal 34mm MK II and finally Amal 36mm MK II [which gave the best power right through the rev range, incidentally] ran all sorts of cams and timings, finishing up with the 'S' cams timed 'on the dots' and it started and idled well in all cases. 'Asbo' 11, an Electra X with Dellorto 32 mm carb has 'S' cams fitted, with the inlet retarded by 1 tooth and also starts and runs fine. Both these machines were running the upgraded CDI [TCI] box, which later became available from Hitchcocks.
 I think your carburettor settings may need some fine tuning  ;)
 B.W.

DanB

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Re: Mikuni TM-32 fittment
« Reply #43 on: May 22, 2014, 01:59:53 PM »
Thanks again Paul.  Very good information... Reminds me to not over think / over engineer and focus - think basics.
Suppose I were an idiot, and suppose I were a member of Congress; but I repeat myself. ... Mark Twain
2006 AVL Electra

ace.cafe

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Re: Mikuni TM-32 fittment
« Reply #44 on: May 22, 2014, 02:12:07 PM »
Thanks again Paul.  Very good information... Reminds me to not over think / over engineer and focus - think basics.

 To set idle on a carb, I warm it up at around 1000 rpm, and then use the air bleed screw to find the fastest idle that I can find by turning in both directions, Then, since that usuallly will increase the idle speed, I bring the idle speed back down to around 1000 with the idle speed screw.
That usually does the trick.
Sometimes, if it coughs off idle a ilttle after that, I will give the air bleed screw another 1/8 turn in to richen it just a tad.
Then when it is cold starting, it would normally need the choke knob pulled up. But on warm starts, it wouldn't.

It should always get a 2-3 minute warm up before riding off, and that should be normal practice, not just for carburetion, but for getting the oil warmed-up, and bringing all the metal parts at least partially up to operating temperature before giving it any significant throttle. If it's not warm enough after 3 minutes, then give it 4 or 5 minutes to warm up. That AVL head has a lot of alloy metal in it, and it takes some time to warm that up.
« Last Edit: May 22, 2014, 02:16:26 PM by ace.cafe »
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

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