BritBike Forum logo
BritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorThe Bonneville ShopBritBike Sponsor
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
ShoutChat Box
Comment Guidelines: Do post respectful and insightful comments.
Buy BritBike staff a coffee
Buy BritBike's staff a coffeeStill here since 1996 serving BritBike enthusiasts..
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
Member Spotlight
dandruff
dandruff
Los Angeles
Posts: 29
Joined: July 2015
Show All Member Profiles 
Newest Members
rudi, Derek, Psychorider, Shedengineering, Shayne Brown
10860 Registered Users
Top Posters(30 Days)
franko 172
reverb 64
DavidP 63
NickL 59
Popular Topics(Views)
1,005,930 mail-order LSR
a word from..
Forum Statistics
Forums34
Topics67,747
Posts679,990
Members10,860
Most Online14,755
May 5th, 2019
Who's Online Now
48 registered members (Adam M.), 363 guests, and 593 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 1 of 2 1 2
Wierd jetting issue Mikuni #775804 06/06/19 9:11 pm
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
I installed a pair of Mikuni 32mm TM flat side carbs on my T140D.. They are on both my race bikes so I'm familar with them..Easy swap, the slipped right on with no changes to the cables or inlet rubbers...
The engine idles nicely,pulls smooth at part throttle, and wide open is great... BUT,,,at part throttle, various RPM's depending on jetting it runs very rich ,dah, dah,dah like the cold start enricheners were left on, but they are not on...What's wierd is the problem is not load or throttle opening dependent...With a certain needle and jet it does it at 3500 RPM, change the jetting and it does it at 4500 rpm ot 5500...This is always at steady throttle in the lower gears,open the throttle and the engine responds and pulls good to redline...I thought it was maybe reversion since the engine is not stock...I put a "lollypop" in the mufller exit to change exhaust tuning but not really any change...The air filters on or off have no effect on the problem.
Kevin Roberts is sending me an air fuel gauge and sensor, I welded in a bung for 2 into one stock T140D header...Hopefully when ithe problem occurs I will see a change in gauge reading...

[Linked Image]


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Support Your #1 BritBike Forum!

Check out British motorcycles for sale:
British Motorcycles on e-Bay UK
British motorcycles on e-Bay North America
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #775844 06/07/19 2:07 pm
Joined: Dec 2013
Posts: 4,741
kevin roberts Offline
DOPE
Offline
DOPE
Joined: Dec 2013
Posts: 4,741
that oxygen sensor is in the mail to you. it's set for AF ratio, but there's another face plate and a toggle on the back if you want to make it read lambda instead.

the advantage of the AF gauge is that it removes ambiguity. you'll be able to creep up on the problem while looking at the gauge and then actually see what the mixture is doing right when you enter the problem zone. then you can change stuff and see which direction it's going even if the change is too slight to feel accurately.

the only thing i don't like about the gauge is that it's digital, rather than analog. i realize how hard it is to make a needle gauge respond quickly to a digital input, but what happens is that you have to average changing digital readouts in your head, which for me is harder than gauging an average needle position.

there's an analog color band around the perimeter of the gauge, but i've never found it much better.


every day you do not take a chance is a day of your life that you will never get back.
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #775847 06/07/19 2:23 pm
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
Kevin, Thanks....The engine feels good going through the gears at moderate or full throttle...But hold the rpm at about 1/4-1/3 throttle in the lower gears and it starts what guys here call "8 stroking"...At least that's what I think is going on.. If it is, the gauge will show a big change to rich...If it's ignition, I don't think it is, the gauge won't show a lack of oxygen, yes?


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #775849 06/07/19 2:43 pm
Joined: Dec 2013
Posts: 4,741
kevin roberts Offline
DOPE
Offline
DOPE
Joined: Dec 2013
Posts: 4,741
the gauge only reads what passes by the oxygen sensor in the exhaust pipe. if you have an ignition misfire up front that lets unburned fuel run out the pipe, the gauge will read that as rich, even though the problem is ignition.

it isn't intelligent. if you have weird valve timing that gives you best horsepower while shooting fuel out the pipe, it will read that as rich as well.

and if the exhaust pipe is hot and unburned fuel is igniting as it runs along the pipe, then the sensor will read rich up front and lean towards the end, depending on where in the pipe you put it.

i don't believe in using the actual gauge numbers for tuning. but for looking at relative values and changes, it's priceless.


every day you do not take a chance is a day of your life that you will never get back.
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #775867 06/07/19 7:12 pm
Joined: Oct 2009
Posts: 532
P
pushrod tom Offline
BritBike Forum member
Offline
BritBike Forum member
P
Joined: Oct 2009
Posts: 532
Interesting........very interesting. First. If you have an ignition misfire the gauge will show lean. I would guess that if it is rich where the 8 stroke is then the plugs would be sooty. If thats the case then maybe the needle jet is too big?
In order to keep the armchair tuners happy keep us posted. Cheers, PRT

Re: Wierd jetting issue Mikuni [Re: pushrod tom] #775874 06/07/19 8:37 pm
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
Sooty plugs....sometimes... If I ride " normally" , the plugs look ok.If ... I've tried three needle jet and two needles...One change at a time...More than anything it feels like reversion...The cam timing and exhaust are not stuff that invites reversion.... Right now it has a 22.5 pilot, 6DH3 needle ans a 175 main...


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Wierd jetting issue Mikuni [Re: pushrod tom] #775893 06/08/19 2:41 am
Joined: Dec 2013
Posts: 4,741
kevin roberts Offline
DOPE
Offline
DOPE
Joined: Dec 2013
Posts: 4,741
Originally Posted by pushrod tom
Interesting........very interesting. First. If you have an ignition misfire the gauge will show lean.


i have way little experience with AF gauges. i forgot that the sensor is reading O2 and not fuel.

so if there's a misfire, then the unburned fuel moving past the sensor would be accompanied by unburned O2 that would normally indicate a lean mixture.

thanks for pointing that out.





every day you do not take a chance is a day of your life that you will never get back.
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #775902 06/08/19 6:55 am
Joined: May 2013
Posts: 5,876
Allan Gill Offline
BritBike Forum member
Offline
BritBike Forum member
Joined: May 2013
Posts: 5,876
I’m curious how the O2 fails to burn, unless it has what been carried through on overlap. Once an ignition is present (even a flame) it will continue to burn all the oxygen available.
Fuel on the other hand is different and more so with a carburettor than F.I. If the fuel isn’t atomised correctly then it will fail to burn, I’m not sure what temperatures reach a combustion chamber from memory but I would say around 600°c (someone will tell me if I’m wrong) it might take a further 500°c to break that carbon chain and so the fuel passes through un-atomised and unburnt. That would give a lean misfire if I’m not mistaken


(...... now open to being shot down)


beerchug
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #775916 06/08/19 11:02 am
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
Oxygen is the oxidizer for the fuel combustion...As far as I understand, the oxygen by itself doesn't burn..............I'm going to take out the bike today for more trials....


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #775917 06/08/19 11:36 am
Joined: Oct 2009
Posts: 532
P
pushrod tom Offline
BritBike Forum member
Offline
BritBike Forum member
P
Joined: Oct 2009
Posts: 532
Patience will prevail!! PS On board A/f is a great tool but just keep an eye on the road.

Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #775919 06/08/19 12:37 pm
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
Tom, I live in a rural agricultural area so there's many two lane roads with no traffic and few houses...But at this time of year a huge tractor hauling a 20 foot wide array of cultivating equipment may be over the hill or around the bend..and clumps of mud from tractor tires or the occasional cow....Yes, a bit of caution, lol


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #775920 06/08/19 12:46 pm
Joined: May 2013
Posts: 5,876
Allan Gill Offline
BritBike Forum member
Offline
BritBike Forum member
Joined: May 2013
Posts: 5,876
Originally Posted by Hillbilly bike
Oxygen is the oxidizer for the fuel combustion...As far as I understand, the oxygen by itself doesn't burn..............I'm going to take out the bike today for more trials....


If you light a candle and place a jar over it (sealing it) the candle will continue to burn until all the oxygen has been used up. Basic fire triangle being fuel,oxygen,ignition. Take away anyone of these and there is no flame.

The ratio of oxygen to nitrogen in the atmosphere will also change the combustion delay by even 1%.


I think I’m taking this away from your original question.


beerchug
Re: Wierd jetting issue Mikuni [Re: Allan Gill] #775929 06/08/19 3:40 pm
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
Originally Posted by Allan Gill
Originally Posted by Hillbilly bike
Oxygen is the oxidizer for the fuel combustion...As far as I understand, the oxygen by itself doesn't burn..............I'm going to take out the bike today for more trials....


If you light a candle and place a jar over it (sealing it) the candle will continue to burn until all the oxygen has been used up. Basic fire triangle being fuel,oxygen,ignition. Take away anyone of these and there is no flame.

The ratio of oxygen to nitrogen in the atmosphere will also change the combustion delay by even 1%.


I think I’m taking this away from your original question.


We are talking two different things Allan...Oxygen by it's self does not burn , try lighting and oxy acet torch with just the oxy turned on...But it is necessary to support combustion as you say....

I took a few 10 miles rides on the bike..with the jetting mentioned...Riding normally as in using no more than 1/2 throttle or so and below 5500 rpm the engine is a real sweetie, instant response to small changes in the throttle, nice idle and it runs smooth for a Triumph. I did open it through second and third and it pulled good to 6000 rpm..The plugs are dark but not sooty...I raised the needle clip one notch and will take a longer ride to "recolor" the plugs...The plugs are NGK Competition # 7 , one step colder than normal for a T140E...
Sometimes I need to walk aways from this tuning [***] and then it seems better after a day of not fussing with it..


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #775953 06/08/19 11:44 pm
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
I took another ride for about 45 minutes ,the engine performance is quite good overall....There's still a bit of funny business during throttle but it's very brief and easy to power right through it...When the O2 gauge is hooked up I may have a better idea...
The right side plug is a little darker than the left..The insulators are dull white the but shell shows signs of a mixture a bit richer than it needs to be,,The ground strap shows only 25% heat discoloration...Usually means the plug is too cold...The plugs are one heat range colder than normal....I was running a .035 plug gap I closed down to .030...It may be the ignition is not happy with a larger gap..Probably should screw in the correct heat range...


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #775959 06/09/19 1:20 am
Joined: Jan 2014
Posts: 371
N
NickL Offline
BritBike Forum member
Offline
BritBike Forum member
N
Joined: Jan 2014
Posts: 371
Just thought i'd chime in here,,,,,,,, The Rita has a very short spark time (around 500us) this is considerably
shorter than the normal 1-1.5ms that most ignitions of this type use. It allows a greater dwell at higher rpm but the short
spark time may make it more sensitive to mixture setups.

Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #776046 06/10/19 11:54 am
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
Nick I closed the plug gap to .028.I believe that wider gaps can shorten spark duration,thanks for the reminder....Yesterday I rode for an hour chasing a friend on his 950 Guzzi cafe bike...The engine pulls very nicely at 3/4 throttle to 5500 through the gears,..Full throttle at higher rpm in the upper gears is not what I expect it to be but it will pull 6500 rpm .Not misfiring...I believe it goes rich despite what seems like a small 175 main jet. The spark plug ground strap color looks good,The insulator is dull off white and the shell appears to show decent mixture.No signs of detonation..It was warmer yesterday, 80F...Like all Triumphs, flogging the engine for an extended period brings on all sorts of clattering..
Despite often said statement that the main jet stands alone,it's been my observation doing all the needle, needle jet ,pilot jet and main jet work on this engine, a change in one effects all the other circuits to some degree...


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #776074 06/10/19 8:59 pm
Joined: Dec 2013
Posts: 4,741
kevin roberts Offline
DOPE
Offline
DOPE
Joined: Dec 2013
Posts: 4,741
i don't believe anything in these old carburetors work all by themselves.

it's always a mixed-up head scratcher.

fuzzy logic, we used to call it.


every day you do not take a chance is a day of your life that you will never get back.
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #776077 06/10/19 9:14 pm
Joined: May 2013
Posts: 5,876
Allan Gill Offline
BritBike Forum member
Offline
BritBike Forum member
Joined: May 2013
Posts: 5,876
Originally Posted by Hillbilly bike

Despite often said statement that the main jet stands alone,it's been my observation doing all the needle, needle jet ,pilot jet and main jet work on this engine, a change in one effects all the other circuits to some degree...


Very much so, every change I’ve done on my bike has resorted to doing the full rejecting sequence from Idle mixture to WOT main jet then finishing with idle mixture again. Each jet will influence the one before it and when you don’t have a great deal of free time it becomes a real chore. I had my lightning setup pretty good, bike would pull 110, when I decided to strobe the motor I found it was well over advanced.... the previous jetting is now too lean for the spark advance so need to go through that sequence again. Although it should rev a little harder with less spark advance from my experience.


beerchug
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #776082 06/10/19 11:13 pm
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
Yes, a little less timing can make more top end power......Carburetors as we know it were in form around 1900...It's something from a different place and time, a device that responds to the natual laws of the universe....it needs no power source....it's so simple it's confusing...


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #776092 06/11/19 2:00 am
Joined: Mar 2005
Posts: 10,250
J
John Healy Offline
BritBike Forum member
Offline
BritBike Forum member
J
Joined: Mar 2005
Posts: 10,250
Many of the Mikuni range carbs the needle never leaves the needle jet orifice. This makes changes at lower throttle openings effect, and what on an AMAL would have no effect on the main jet, change the effect of the main jet.


Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #776111 06/11/19 11:29 am
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
Yes, the needle is always in in needle jet orfice.I had marked the needle originally to see what goes on..there is about 8 needle jets and 14 different profile metering rods for this type Mikuni.Today I'l have the air fuel ratio gauge on the bike...The actual readings aren't so important as the change in readings past 2/3 rds throttle. The old standby of listening for 8 stroking or rolling back the throttle a bit to check for too lean doesn't seem to give any feedback..On my race bike with the same but larger Mikuni TM's, on the dyno, power fell off about 2 HP with one jet size leaner or richer than optimal..


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #776127 06/11/19 3:40 pm
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
Ok...I have been running the bike around with the air/fuel gauge installed...The O2 sensor is located on the two into one collector about 10 inches past where the two pipes merge and about 32 inches from the head port...It's a bit cool right now, 60F.. I fire up the bike and wait a few minutes to warm up the exhaus system...The bike is very lean with the chokes off, 17-1 and running a bit rough...Pull on one choke and the gauge drops to 13-1 ,so it's working..I take off down the road at a moderate pace to warm the engine...The engine acts lean and the gauge is 16-1...After a few miles the engine is running smoothly at part throttle and the gauge is around 14-1 at 50 mph...I roll open the throttle slowly in high gear , the gauge drops to 10.9 and climbs up to near 12 as the engine winds out...I stop in deserted section and full throttle it through the first three gears to 6500 rpm, the gauge reads 12-1.I did it several more times to confirm....Open the throttle in fourth ,the gauge drops to 10.8 during the longer pull and creeps up near 12 at 6000 rpm....On the way home I mess with shifting up and at part throttle to check the gauge reading...
My conclusion is the air/fuel reading are actually reasonably accurate from the way the engine responds... To sum it up...It's too lean at 1/8 throttle,just a touch lean at 1/4 throttle and the rest ok...the full throttle today felt strong and the air/fuel ratio is where it should be I believe .....The engine going rich when the throttle is rolled open in the higher gears at 4000 rpm may be a bit of reversion, or????


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #776146 06/11/19 7:16 pm
Joined: Aug 2015
Posts: 1,431
A
Andy Higham Offline
BritBike Forum member
Offline
BritBike Forum member
A
Joined: Aug 2015
Posts: 1,431
Something that happens in high performance 2 stroked is "triple loading". When the engine is out of its resonant range, air is sucked in through the carb picking up fuel, then pushed back through the carb picking up more fuel before being drawn back into the engine picking up yet more fuel on the way.
I wonder if something similar is happening to your bike? have you got wild cams in it?


BSA B31 500 "Stargazer"
Greeves 200 "Blue Meanie"
Greeves 350
Greeves 360
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500 sprint/LSR bike "Deofol"
Jawa 500 "Llareggub"
Aprilia RSV Mille "Lo Stregone"
'35 & '36 OK Supreme
Kawasaki ZZR1400 "Kuro no senshi"
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #776148 06/11/19 7:29 pm
Joined: Dec 2013
Posts: 4,741
kevin roberts Offline
DOPE
Offline
DOPE
Joined: Dec 2013
Posts: 4,741
that gauge has a lower display limit of 10.0, so it will read the same at 10:1 and richer.

appears that the pilots are lean, the mains are about right.

10.9 seems rich for what you're getting, because you're showing 12s at open throttle.

on my street bike i got best power when everything was at 11.5, more or less all the way up from the slide cutaway.

maybe tom has some thoughts in the numbers.

can you see any fog at the carburetor mouth blipping the throttle?


every day you do not take a chance is a day of your life that you will never get back.
Re: Wierd jetting issue Mikuni [Re: Hillbilly bike] #776150 06/11/19 7:46 pm
Joined: Oct 2012
Posts: 4,591
Hillbilly bike Online Content OP
BritBike Forum member
OP Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 4,591
No wild cams in this bike..Stock T140 intake timed at 100 degree lobe center..,3134 type exhaust timed at 103...I'm interested in why with the throttle held wide open the air fuel ratio above 4000 rpm in the upper gears is richer than the lower gears...

Kevin thisThis T140 e type head combined with tight piston to head squish might have leaner fueling requrements...so 12-1 might be good..


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Page 1 of 2 1 2

Moderated by  Alan_nc 

Home | Sponsors | Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons | DVD- Manuals & Parts books
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Powered by UBB.threads™ PHP Forum Software 7.7.3