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Re: Mikuni s and some hesitation [Re: reverb] #770833 04/12/19 9:19 am
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If the idle is not even and just a "sput" sound on one side then the carbs are not synchronised.
Adjust the cables so that both slides clear the top of the venturi equally, then use the throttle stop screws to get the idle even between cylinders.

The parallel section of Mikuni needles are all the same diameter, the tapers differ in length and angle.
If you are running rich at 1/4 throttle the needle jet is too big
If it is ok at 1/4 throttle and then gets richer between 1/4 and 3/4 throttle then the needle taper is wrong (too rich)
If it is rich at 1/4 throttle then ok at 1/2 to 3/4 throttle the needle jet is too big and the needle is too weak


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Re: Mikuni s and some hesitation [Re: reverb] #770851 04/12/19 2:32 pm
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...I had them in synchronicity; that problem started after I advanced the Pazon and the idling speed went higher. I will remove the tank etc to see.
Hope is that because could be something in the cylinder. The valves are doing too much noise.

I only have the 6DH2 needles as spares but no smaller needle jets. For these spares I waited 5 months...

Also the decisive test is to test the Pazon at 38º but I did not received a response from they yet, regarding if it s possible to do it with these coils etc.

Re: Mikuni s and some hesitation [Re: reverb] #770855 04/12/19 4:05 pm
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As previously mentioned, twin plugs like to be used with the ignition retarded.... 2 plugs burning the mixtrure much faster than 1. Your advancing the ignition has also proved that advancing ignition will allow the engine to run leaner.


beerchug
Re: Mikuni s and some hesitation [Re: reverb] #770861 04/12/19 4:52 pm
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To me it sounds like the carb set-up is wrong, I would try making the following changes to make it run leaner:-

- change the air slide back to 3 or 3.5, note that the lower the slide cut-out number the richer the mixture will be. A bigger cut-out will allow more air flow and lean the mixture.
- change the needle for one with thicker diameters D-1, D-2 & D-3, see This Link for guidance. I think you could maybe try something like #6DH7 instead of #6DH2. This should also lean the mixture as the needle is thicker and will lessen the fuel flow.

It's worth studying the diagram in the link above as it shows two types of needle, one with a single taper and one with a double taper. I don't know which is best but maybe others can advise.

Last edited by gunner; 04/12/19 5:06 pm.

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Re: Mikuni s and some hesitation [Re: reverb] #770868 04/12/19 5:18 pm
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Hi Allan, I had it retarded at 30 32 and 34 but no good in any so I am advancing little by little to see.

Hi Gunner, 6F5 is the leaner man, that s what I have.
The STD for Mikuni s 32 slides is 2.0 or 2.5 slides, I changed for the 2.5; the slides are correct.
The carburetor problem in low could be the pilot jets and /or the needle jet, that I have the STD that all put to the 32mm but possibly need the other leaner.

The best test as suggested is to put the bike in 38º but I do not know if I let the other coils wires hanging out there would damage the coils or something else, hence I still did performed it.


Re: Mikuni s and some hesitation [Re: reverb] #770869 04/12/19 5:43 pm
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Quote
6F5 is the leaner man, that s what I have.


Yes but leaner where in the throttle position?

If you compare the diameters at D-1, D-2 & D-3 between the #6F5 and say #6DH2 needles you get the following differences:-
- D-1 = 2.515 vs 2.511, that's -0.004mm difference
- D-2 = 2.456 vs 2.511, that's +0.055mm difference
- D-3 = 2.454 vs 2.466, that's +0.012mm difference

As can be seen the #6F5 is slightly thicker (leaner) at the top of the straight section but then is narrower (richer) compared to a #6DH2 needle in positions D-2 and D-3.

This may account for the richness at the lower throttle openings.

For what its worth, I had a similar richness problem on my B44 when using a JRC PWK 28 carb (Keihan PWK copy). After much experimentation the problem was finally cured by using a leaner needle and slide cutaway. I don't think your issue is timing related but may be wrong.

Last edited by gunner; 04/12/19 5:49 pm.

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Re: Mikuni s and some hesitation [Re: gunner] #770905 04/13/19 12:25 am
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Quote
[quote] And very posible that the surefire cannot delivery ríght for the 4 plugs in some ranges.
But again, I do not know how to test it with these coils.

It's extremely likely that a pazon /Boyer / etal , will fire 4 pluggs just fine ... thery are good to 5 amps .
But this is only part of the equation .

The less happy news is
It's unlikely that the stock Advance curve ...for any single plugged iignition ...will be optimal for any duel plugged engine .
Why ? , because the dual plug head has 2 Flame fronts ... in an effort to quicken combustion time .

... All ignitions fire before tdc ... to reach a peak flame at around 15° ATDC .
( we think of it as an explosion , but there is a time factor as the flame propagates .)
the stock triumph Hemi combustion chamber is a slow burn configuration ,
So it starts at 14° BTDC ... at idle speeds
And must advance way up to 38° BTDC ... at full advance ... to have a peak-flame at around 15° ATDC

the stock pazon/ Boyer boxes are , for the most part , following the same stock-points start and stop advance marks
... using this stock pattern ... with a duel plugged head ... will diminish some of the advantage That the
duel plugs bring to the table ... especially at lower/medium RPMs .
any ignition will work at full advance ... if timed at full advance... but it's the partial advance that matters at lower rpms
And matters ... as a possible cause ... if you have a stumble or hesitation .

If your dual pugged engines runs best with a full advance of 30 degrees ... it really needs a qiucker more compressed advance curve
... then what is offered by any stock ignition
---------------------
If ...your dual , dual-coils ... are wired in series... ( as i suspect ) there is an easy way ... by moving 1 wire ... to disable one of the coils
And still have the bike run on the other coil .
-----------------

If the bike runs better on either "single" dual-coil ... it could confirm ...that the stock ignition box mapping is not ideal
For your custom 4 plug bike .

It would be a shame to lose the advantage of the extra plugs ... but a stock ignition is mapped for 1 flame front.
if the goal is a reliable daily Rider ... the hod-rod-mods may not be the best fit ... until you can invest time and money into a custom ignition.

... anyway , just an easily tested theory.

.





Re: Mikuni s and some hesitation [Re: reverb] #770915 04/13/19 4:48 am
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...hi Gunner, I put the 6F5 s due to they are leaner in all the parts (D1-D6) except in D3 and the sooty problem is at idle and 1/8 open.

The timing problem could be another problem cause the bike does not respond crispy and fast with all the mods that has.

Hello Quinten,

Yes I know that can fire the 4 plugs I was referring if it can fire them right or better expressed, if the "curve" does not let me too retarded at low RPMs and possibly mid range RPM; and that is what all use in the streets and freeways, up to 130km/h (cruising speed not for a few seconds) Nobody in the world except in racing (in 2 or 3 countries...) use these old irons to commute at constant speeds of 160km etc...and that s the problem with all these EI and the technical data etc, all is biased to the races; however, most use these bikes at 90-110km/h!! I am one of the few that use these bikes to commute at constant speeds of 110-130km/h for 3 hours or more without shutting down the engine.

Do not know, but year ago when I bought it, the bike was more "free" and easy to go in that mid range (the plugs were sooty in that time too)
I think that the PO never timed at 5000RPMs like me; very possibly that he timed it at 3500 or so, hence the bike free in some speed and then "iron out" or stall at higher speed
Possibly the bike can free up to 6000 but is way too much speed in fifth gear for the roads here, also these bikes are tall and not so much stable (I changed the forks stuff and have new rear shocks and new tyres but do not help) so is a bit dangerous no doubt. Again, I always referring to CRUISING speed, so constant mid range speed (up to 130km/h)

-As mentioned, it does not run best at 30º.
-The chambers as you see in those photos, are now squared.
-Not so sure to use only one coil to fire the system and do not [***] up the other coil (what I do with the connections) or the system; Pazon goes always with 2 coils.

Re: Mikuni s and some hesitation [Re: reverb] #770920 04/13/19 6:42 am
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The red earth and red box lead goes from the last coil onto the first, the bridging wire between the two is disconnected. You would need a ballast resistor if your running coils with a resistance of less than 3 ohms.


The other thing to note is that if your problem is at cruising speed, your black box could be getting tired, and that could be from running a coil resistance range close to its limits??? The reason I say that is my own bike was flatting out at a certain load, I did have coil issues which I swapped which made a difference to it flattening off, I later changed the black box for my new spare and a lot of power was restored. It might be if you do have to change then you also get the kit designed for twin plugs. (Quintens right in what he says), there is also very little difference between race and road application, both need to burn the fuel at the right time to get the optimum burn profile= performance.


beerchug
Re: Mikuni s and some hesitation [Re: Allan Gill] #770926 04/13/19 10:28 am
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Originally Posted by reverb
...hi Gunner, I put the 6F5 s due to they are leaner in all the parts (D1-D6) except in D3 and the sooty problem is at idle and 1/8 open.

The timing problem could be another problem cause the bike does not respond crispy and fast with all the mods that has.

Hello Quinten,

Yes I know that can fire the 4 plugs I was referring if it can fire them right or better expressed, if the "curve" does not let me too retarded at low RPMs and possibly mid range RPM; and that is what all use in the streets and freeways, up to 130km/h (cruising speed not for a few seconds) Nobody in the world except in racing (in 2 or 3 countries...) use these old irons to commute at constant speeds of 160km etc...and that s the problem with all these EI and the technical data etc, all is biased to the races; however, most use these bikes at 90-110km/h!! I am one of the few that use these bikes to commute at constant speeds of 110-130km/h for 3 hours or more without shutting down the engine.

Do not know, but year ago when I bought it, the bike was more "free" and easy to go in that mid range (the plugs were sooty in that time too)
I think that the PO never timed at 5000RPMs like me; very possibly that he timed it at 3500 or so, hence the bike free in some speed and then "iron out" or stall at higher speed
Possibly the bike can free up to 6000 but is way too much speed in fifth gear for the roads here, also these bikes are tall and not so much stable (I changed the forks stuff and have new rear shocks and new tyres but do not help) so is a bit dangerous no doubt. Again, I always referring to CRUISING speed, so constant mid range speed (up to 130km/h)

-As mentioned, it does not run best at 30º.
-The chambers as you see in those photos, are now squared.
-Not so sure to use only one coil to fire the system and do not [***] up the other coil (what I do with the connections) or the system; Pazon goes always with 2 coils.


Yes , I think we're kind of on the same page . .. there is no guarantee that timing is your problem ... the bikes symptoms only make it a possibility .
there is a fairly simple process to investigate these possibilities .

1. At what advance setting does it run best "full advanced at" ... once you find this top spot ...you can use this point to work backwards from .
Say it runs best ...full advanced at 30° at 5000 RPMs ... this is a start ... ignore any hesitation at other RPMs ... thats for later.


2. Its not a secret or anything special.
I can , and im sure others could too ... walk you through a simple ... one wire move change ... that can isolate either dual coil to run the bike ...
Its easier to do... than it is to explain.
*** as i have never seen the wiring , certain assumptions will be made ... that you would need to verify , clarify or dismiss .

3. Whats the primary value of each dual-coil ?




Re: Mikuni s and some hesitation [Re: reverb] #770951 04/13/19 7:08 pm
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Hi Allan, yes, could be possible, hence I want to test the stuff at 38º to decide the big bucks spending.

Hi Quinten, regarding point 1, I still do not find the best spot.
Do not know the coil values; I do not know the brand too; came with the bike. Looks like the ones that Tri sparks sells.
Yes, I am all ears about step by step how to s.

Re: Mikuni s and some hesitation [Re: reverb] #770967 04/14/19 12:24 am
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Reverb , you're killing me ... give me something to work with ... buy a cheap ass voltmeter .
.

Re: Mikuni s and some hesitation [Re: reverb] #770970 04/14/19 1:00 am
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...man, I can borrow a good voltmeter; killing you?
do not know; I do not want to [***] up the stuff. Now, that the pre unit magneto does not want to spark, this is my daily driver and the shops here do not sell these coils and of course the Pazon. I am like walking on eggs.

Re: Mikuni s and some hesitation [Re: reverb] #771012 04/14/19 1:51 pm
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Reverb, if I can jump in here, what Quinten is asking in number 3 is, what is the ohm reading through the primary side of the coil.
The coil actually has two coils in it, one called the primary, and the other called the secondary.
The primary is the one that your points/control box hooks to, and the secondary is the one that the spark plug wire hooks too.
Take your good meter, and set it on the lowest,/smallest number of the "ohms" scale. (That's the one with the horse shoe with splayed feet emblem)
Touch the two meter leads together and see what the meter reads. It should be zero, but some meters aren't that good. What ever the reading is, make a note of it. you will subtract it from the next reading. Disconnect the wires to the primary coil terminals, and put the meter leads on the two terminals, one on each terminal.
Write down the reading.
Subtract the reading that you got when you touched the two meter leads together from the reading that you wrote down.
Tell Quiten what that number is.
Just to show Quinten that you are trying, set the meter on the 20,000 ohm setting, or the highest setting that the meter will read.
Put one lead on a bare metal spot on the coil mount, and the other lead on the metal inside the cap that clips to the spark plug.
Tell Quinten what that reading is.
Go to the library and get a book on basic Direct Current electricity. Study it, until it makes some sense. It will serve you in good stead when working on old British bikes.
Electronic ignitions (EI) are another more complicated subject, but just remember that the EI box takes the place of the points and condenser, and if you know how they work, you have the concept.
Good luck

Re: Mikuni s and some hesitation [Re: reverb] #771064 04/15/19 12:39 am
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I don't know, maybe I missed it, but it seems that you are playing with the needles, pilot, ,slides, and main jets. But do you know what needle jet it has in it? Investigate the size it has and go from there. Also make sure both carbs have the same needle jet size. Ive seen them sold as matched sets but were different. Sounds like you need to lean out the needle jets. If they have the P0,P2.P3,P4's or bigger, start going down. Keep in mind timing needs to on the mark, valves set correct for camshaft and so on. Ive always had excellent results with Mikuni's, but in the beginning it took a little time to learn how to dial them in. Victory library, tuning mikuni carbs for English Twins is a good book to purchase and read. Mikunis on BSA's A65's, Triumph 750. Haven't touched them since.

Re: Mikuni s and some hesitation [Re: reverb] #771067 04/15/19 12:48 am
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Obviously I meant the P style needle jet markings. If at has a P4 in it try a P2 and see what happens. Or go down just one size to a P3. If they are labeled in a different marking then still go down two or one size.

Re: Mikuni s and some hesitation [Re: reverb] #771072 04/15/19 1:38 am
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...hello Jerry, I will borrow the meter tomorrow after a ride with more Brits.

Sloppyoil, I have new 159P4. Valve light is equal both sides because have the same camshafts
Ignition timing is something that I mentioned, I am testing due to still do not find the sweet spot.
Yes, Kevin R here sent me that booklet.

I do not have the possibility to buy these stuff here, so a guy mentioned why not solder one of the holes and see; if that do not cooperate, I can heat the solder to remove it...

Sounds good?

Thanks

Re: Mikuni s and some hesitation [Re: reverb] #771090 04/15/19 5:09 am
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Originally Posted by reverb

I do not have the possibility to buy these stuff here, so a guy mentioned why not solder one of the holes and see; if that do not cooperate, I can heat the solder to remove it...

Sounds good?

Thanks

Solder one of the holes? You mean the holes in the side of the needle jet? Those are air bleed holes, closing them will only make it worse.


Stepping on others doesn't make you stand tall.

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Re: Mikuni s and some hesitation [Re: DavidP] #771115 04/15/19 12:12 pm
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Originally Posted by gunner
A bigger cut-out will allow more air flow and lean the mixture.


Not strictly true, whilst having more cut away will have an effect causing a leaning mixture between closed and 1/4 throttle it won't allow more airflow, dont forget the front end of the slide hasn't changed so no more air can flow through the carb than with a leaner cutaway, but instead the pressure impulse on the needle jet isn't as great. less vacuum means less "suction" or draw on the jet so less is drawn through with the bigger cutaway.

Its important to remember that jets will send through as much fuel as the vacuum applied to it asks for, Needle jets (on amals at least, can't speak for mikuni round slides but they are MK2 amals under licence anyway) are measured in size, a 106 needle jet should measure 0.106" with a "go-no go" gauge when fitted into the jet holder. A 250 mainjet will proved 250cc's of (air presumably - what ever the flow bench tests with) when at a certain pressure. Change either Density, viscosity or pressure (vapour pressure of the fuel or the vacuum pressure applied to the jet) and the flow through that jet will change.




Originally Posted by DavidP
Originally Posted by reverb

I do not have the possibility to buy these stuff here, so a guy mentioned why not solder one of the holes and see; if that do not cooperate, I can heat the solder to remove it...

Sounds good?

Thanks

Solder one of the holes? You mean the holes in the side of the needle jet? Those are air bleed holes, closing them will only make it worse.


Agreed, you'd be better soldering both or none for a start, and if you need to lean it you want to enlarge the holes, Speaking of amals.... The transfer holes in the needle jets are 0.035" you can use a twist drill to open the jets out anything up to 0.039" (1mm) anything more than that will have detrimental effect on vacuum.... As above, your bleeding off the vacuum applied to the jet at low throttle openings, in this case the transfer point between slide and needle jet. It should be tunable without touching this, however running open mega's for example can have an effect at this point, in that instance they need to be soldered up to enrichen the setting. If your drawing too much vacuum then you may need to increase the transfer bleed holes.


beerchug
Re: Mikuni s and some hesitation [Re: reverb] #771125 04/15/19 2:04 pm
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Oh God, DO NOT START SOLDERING HOLES UP!! If you have P4's in the carbs I would suggest going to p2's. If it is that heavy or fat and you have been experimenting with needles, the needle jet is the next item you have to change. The reason I say go from 4 to 2 is it sounds like it is way fat. If the plugs are that sooty and you are having difficulties in starting and performance and you have experimented with the other components well?? The problem with jetting is that it is difficult to pinpoint over the internet. I mean, an individual has to hear, see, and ride, you know, a drivability test. I had a 750 I did for a person and of course the carbs were MATCHED to his motor. It was a lean situation, upon disassembly the carbs had P0's in it, changed to p2s and zoom, right on the mark. Those numbers make a big difference. And yes, I understand, most of the time you have to order them to try. Perhaps if you have a good honda shop or dirt bike shop near. They still utilize many Mikuni parts in stock, and just maybe, if you talk to one of the mechanics he may v
have a bunch of them in his box when he jets one for a customer. I know, I have lots left over when tuning and you cant send them back, once you buy they are yours. Good Luck.

Re: Mikuni s and some hesitation [Re: reverb] #771145 04/15/19 5:49 pm
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Everyone knows you don’t solder up the bleed hole.

You force a piece of cocktail stick into it!


Amateur Loctite enthusiast.
Re: Mikuni s and some hesitation [Re: reverb] #771320 04/17/19 7:54 pm
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...hi, I took some measurements.
I put the meter in 200 Ohms, disconnected the spark plugs caps, disconnected the wires that are in the low part of the coils.
The reading is: 02.7 or (8) in left coil and 02.7 in the other.
Then I put one lead inside the spark plugs caps and the other touching the metal part of the each coil mount. but at 20K do not read anything, only at 200M! reads but ONLY in one coil...
Started to read 19.75 then dropped quickly between 17.7 and 19.4 then dropping to 15.4 etc
I have the plugs wires crossed so I checked each one, but only the reading is in the Right coil wires.
Do not know about these numbers. I tried to follow what Jerry mentioned.

I moved the air screws, now are about 1 3/4 turns or 1 7/8, the electrodes look ok now but the ring or the firsts threads of the plugs are sooty.

Thanks

Re: Mikuni s and some hesitation [Re: reverb] #771403 04/18/19 4:59 pm
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Originally Posted by reverb
...hi, I took some measurements.

Excellent , ... not all meters are auto-zeroing ...
did you remember to short the two meter leads together.. as part of determining a Baseline ... for the meters resistance.
.. this number
Is then subtracted from what you are trying to test . ?
Your numbers suggest... maybe not ?
Quote

I put the meter in 200 Ohms, disconnected the spark plugs caps, disconnected the wires that are in the low part of the coils.
The reading is: 02.7 or (8) in left coil and 02.7 in the other.

I was expecting 1.8 ohms or 3.6 ohms ... as these are what i see on the web for coils "that look like yours"
So much for expectations ... that they test the same is a good sign... and 0.9 ohms (extra) could be the meter lead error ?
Im left with 2 suppositions.
you have 1.8 ohms coils ... and meter lead error ... of 0.9 ohms
Or
2.7 ohms coils ... with no meter error .

What you are measuring is just the 2 working ends of one wire ... formed into a coil .
The problem is
it is a low resistance test ... at the lower range of the meters reliability ...where meter error can be
too-high of a percentage of the total reading
( the pressure contact of the probes can even affect the reading ... your looking for an average)

Any chance you can confirm the low side readings again ...
And this time ... include measuring the meters resistance ? ( resistance of leads touched together )
all i really need are good numbers for the low voltage side of the coils












Last edited by quinten; 04/18/19 5:14 pm.
Re: Mikuni s and some hesitation [Re: reverb] #771404 04/18/19 5:03 pm
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barncobob Offline
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74 850 Commando, Mikuni carb..bike ran ok..had an intermittent miss 3000-4000 rpm,,,wasnt the carb it was the Pazon going bad..mechanic put a Boyer on it and it starts easily, runs great and the miss is gone..

had him put a Boyer on my 69 BSA T, never ran better..

Re: Mikuni s and some hesitation [Re: barncobob] #771405 04/18/19 5:23 pm
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quinten Online Happy
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Originally Posted by barncobob
74 850 Commando, Mikuni carb..bike ran ok..had an intermittent miss 3000-4000 rpm,,,wasnt the carb it was the Pazon going bad..mechanic put a Boyer on it and it starts easily, runs great and the miss is gone..

had him put a Boyer on my 69 BSA T, never ran better..


Does either your Commando or Thunderbolt run 4 spark plugs ?

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