New Mikuni issues on fresh motor MKIII

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pvisseriii said:
Coco said:
hoke and idle adjuster ect all make the carb run differntly when adjusted or turned so the circuits must all be working.

At this point it could very well be a faulty Trispark unit. I'm going to try a diffeent carb from a friend and see what that does. Then I'll try another Trispark unit.
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Do you have stock coil or a Dyna coil type, If dyna, You do know that these EI systems spark both sides at the same time so simply swapping a plug wire from the coil output will diagnose the unit. If the Tri or any other unit of this type is bad, neither cyilinder will fire.

What did that compression test show?
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I've got a Crane coil on there. I'm acually gonna try another Trispark unit before the carb. I have one coming to me so that will solve that once it shows up and I'll know whether I have a faulty unit or not. I'm thinking my unit is fine but at least I'll know.

Think a coil can crap out just under load and not at idle as well or even while I was timing at higher rpms?
 
Coco said:
Think a coil can crap out just under load and not at idle as well or even while I was timing at higher rpms?
Click to expand...
It is true that a marginal spark will be inhibited or stopped by high cylinder pressures, like under load. Had it happen when I was running a hot cam and high compression. The stock coil that had been sufficient wasn't up to it. Behaved like it was main jet trouble. Went to an Accell and it was fine.
 
Thanks for all the help so far guys. I'm sure I'll get things sorted pretty soon. I hope.

Cam timing seems interesting but as I stated earlier, bike ran completely fine for the initial break in, a test ride, then for 10 minutes into my first real ride. The problem came about after the bike was running fine so it has to be a defective ignition or something with the carb. Maybe a crapped out coil as well.
 
ludwig said:
Coco said:
..Think a coil can crap out just under load and not at idle as well or even while I was timing at higher rpms?
Click to expand...
I think it can .
reversed polarity is an unlikely cause , but this is an interesting article :

http://mgaguru.com/mgtech/ignition/ig104.htm
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Good article. Back in the stone age I was installing an American made coil in an Austin Healy.
Ruined two of them till I understood about positive ground. Each time it had the symptons of Coco's.
Run fine initially for a day or two, then start crapping out. Got the third one right. :wink:
 
Coco -

The most important jet in the carb is the needle jet (emulsion tube). It, along with the jet needle, control the mixture from 1/4 to 3/4 throttle. It sounds like the needle jet might be too rich, and maybe also the wrong needle. You did not give the numbers in your post for these two components; these parts all have numbers stamped on them. Who set up the carb for you?

See what is in there and let me know, I might be able to help you out.

Stan Smith
Morgantown WV
1975 Mk3 equipped with single 34mm Mikuni since 1982
1972 BMW R75/5
1970 M-G NF500 w/Velorex sidecar
2000 BMW F650
 
What number Needle jet do you run? Some people say p-2 / p-4 but that doesn't really help me. I think that is only half the number?? I am a bit confused by it. I have 166 P-8 in my carbs right now, but its runs a bit rich.

What does the 166 mean?

Should I get 166 P-4??? I tried looking up part numbers but everything seems a be vauge when it comes to needle jets for some reason.....Anyone have any insight??


Also is there someone who sells Mikuni parts up here in Canada, BC??
 
I'll stick my neck out and say theres only one place 6 volt coils belong , and its not on a motorcycle .Id expect problems with em on a Lawn Mower .

Any coil over 10 (8 actually) years old is suspect. probly 2/3 of em are knackered , and THATS 12 Volt ones. In NZ most cars had LUCAS coils .

A lucas SPORTS coil , with the checquered stripe band (paint ) could throw a 1/2 in spark , clean and hard . BLU and WHITE . youd get the odd
used 12 Volt that would , better ones are 15 to 20 mm ' jump ' some magnetos will trow 3 in . A 6 volt coil throwing 1/4 in. , on your lawnmower
itll play up . AS SOON as it gets warm , or any other time it wants . Insulation ( lacquer ) on windings is Suss ,The 6 volt was so itd start on a 1/2
flat battery , in the snow ( which is why its half flat , its COLD ). Ballast resistor burns of excess current . only got 6 Volt left. well , its only a 6 - Volt
Coil.
So if you start your bike after leaving it in the snow all night with a cheap battery , there O.K. .

For anything else there a DEAAD LOSS .If youve got a stonked up Motor , a 15 mm blue and white (1100 Deg temp) spark is a MINIMUM requirement.

Read the old ' CYCLE ' magazine " great coil test " , K mart one at 1/2 the price on the Cook Nielson ducati SS was about FOURTY times more powerfull.
Than the Commando that came dead last. how embarresing ! .The other 6 volt lucas coil Triumph trident was 2nd last. oh dear .

Then theres ' mikuni ' s ' or ' mikuni ', you could get the jets in America ,BUT. My pre unit Bonneville , d pull 8.100 rpm, magneto.amoungst other things.
Very reliable after the T-250 suzuki ( DONT mention the word 'coil ' please ). The Triumph ejected any 'forign' components.ordinarilly in a week. Once ,
arter about four tightenings , I tought I was getting a bit fetishish.But a few days latter , it'd fallen of .After that I relised it was throwing money away
fitting ' inferior '? forign 'pieces', so didnt.A hard habbit to brake. BUT , ive seen 40 D.C.O.E. Webers , on TWO triumph 500 daytonas, riden by wommbles
under interogation neither admitted to any problems , at all .Bar a bolt'd fallen out of the mount,but the Mechanic had fitted another.

As the blankety WEBER looks real smooth up in there on a Commando, I cant see why anyone would fit anything else. Choke sizes are Variable , so large
chokes in a 45 could lead to overreving, maybe the 40 would be fine for most road bikes.And cable pull (one only) would be light. The dellorotto D.H.L.A.
is similar.
Find em on old Lancias, Ducatti's , Porsches etc .not a bad carburetor.

sometimes I wonder if I woulve been dead now if the Commando had 'real ' coils . They made jetting impossible , and stopped crispness over 100 mph .
Mightve been half intentional ? design ' fault ' , like many others. Understeering cars as most drivers arnt competant in cars that DO handle .
 
DaveK said:
<<What number Needle jet do you run? Some people say p-2 / p-4 but that doesn't really help me. I think that is only half the number?? I am a bit confused by it. I have 166 P-8 in my carbs right now, but its runs a bit rich.

What does the 166 mean?

Should I get 166 P-4??? I tried looking up part numbers but everything seems a be vauge when it comes to needle jets for some reason.....Anyone have any insight??


Also is there someone who sells Mikuni parts up here in Canada, BC??
Click to expand...
>>

Mikuni carbs of different sizes and types use different series needle jets. The VM (round slide) 30 through 36mm carbs use a 159 series needle jet, for example,
159 P-0.

Contact Bill at Rocky Point Cycle, 800 351 5546. He can supply the jets you need.

Stan Smith
Morgantown WV
 
I have VM 34's but my needle jets say 166 P-8 on them.......strange.....They might be out of a snowmobile though :oops:
 
DaveK said:
I have VM 34's but my needle jets say 166 P-8 on them.......strange.....They might be out of a snowmobile though :oops:
Click to expand...


A 166 series is out of a 38 mm spigoted carb, the 30=36mm spigoted carbs use 159 series, but the flange mounted carb appear to use a wide array or jets
 
SKS3RD said:
Coco -

The most important jet in the carb is the needle jet (emulsion tube). It, along with the jet needle, control the mixture from 1/4 to 3/4 throttle. It sounds like the needle jet might be too rich, and maybe also the wrong needle. You did not give the numbers in your post for these two components; these parts all have numbers stamped on them. Who set up the carb for you?

See what is in there and let me know, I might be able to help you out.

Stan Smith
Morgantown WV
1975 Mk3 equipped with single 34mm Mikuni since 1982
1972 BMW R75/5
1970 M-G NF500 w/Velorex sidecar
2000 BMW F650
Click to expand...

Hi Stan. I actually got the kit from you (Colin G in Canada).

Needle is 6DH3, main jet is a 230 and slide is a 2.5 and I changed the pilot from a 40 to a 35.

Honestly, I'm doubting this is a carb issue and have doubted that from the get go but didn't know where to start looking. I'm betting on a faulty Tri-spark unit, or hoping anyway since I've run out of ideas. A new Tri-spark should be here this week so I'll report back once I swap that out and take the bike for a spin again.
 
Figured I'd update this. Bike still is not running quite right. Tried a new Tri-spark and that didn't work. I'm about to throw on a new coil and plug wires now over the next couple of days.

So far bike has been retimed about 6 times, carb ripped apart about 5 or 6 times (fuel flows excellent so carb is not the issue), two different Tri-spark units have been tried with no difference in performance and now I'm onto trying a new coil and plug wires. Lots of down time due to shipping time so I've checked over the wiring in the meantime and can't find any issues. Checked all connections ect Been raining for three weeks straight here anyway. Garden is full of slugs and my tomato plants are screwed.

If the coil does not solve anything maybe I'll try a new voltage regulator next? All I can think of besides a new battery but current one is new like everything else on this bike. :? :?: :|
 
Coco said:
Figured I'd update this. Bike still is not running quite right. Tried a new Tri-spark and that didn't work. I'm about to throw on a new coil and plug wires now over the next couple of days.

So far bike has been retimed about 6 times, carb ripped apart about 5 or 6 times (fuel flows excellent so carb is not the issue), two different Tri-spark units have been tried with no difference in performance and now I'm onto trying a new coil and plug wires. Lots of down time due to shipping time so I've checked over the wiring in the meantime and can't find any issues. Checked all connections ect Been raining for three weeks straight here anyway. Garden is full of slugs and my tomato plants are screwed.

If the coil does not solve anything maybe I'll try a new voltage regulator next? All I can think of besides a new battery but current one is new like everything else on this bike. :? :?: :|
Click to expand...

You can just disconnect the alternator to check the voltage regulator. Basically take the voltage regulator out of the equation. The bike will run without the alternator.

As I well learned from my little experience, and this is really crucial with a custom wiring harness, make sure it runs without going through your harness. This is the only way to verify that all the connections are correct.
 
Good point Dave. I'll be making a small 1 wire harness with a quick connect in the middle from battery to coil and see if symptoms persist after new coil is in. I'll have no way to kill the motor trying that hence the quick connect. If that solves it than I must have something amiss in the wiring like a bad connection I overlooked.

This is getting old fast and I'm watching the summer pass me by. I can only ride until around Oct 31 up here.
 
What is your neede jet? Not the needle, main jet, or pilot jet, but the needle jet.. It should be a 159 type and about a Q2. The Mikuni's are totally sensitive in this regard. Yes you will have to pull it apart again. It will slip out the top about the jet ring when you remove the main jet. This is NOT a main jet or pilot jet issue. This is a needle and needle jet issue. Your needle is proper( although i would put the clip at the top groove, lowering the needle. Also, make sure your needle is true. Roll it on a flat surface and observe closely for wobble.
As far as main jets go, I run a 300 with ease, a 350 to go fast, and a 280 for economy. That goes for 36mm vm or the 34 tm. Also your slide is too rich, you need a #3.

It's either that or pulling the head and and validating everything in it. Pushrods, inner and outer springs, valve to guide clearance, everything.
And what were the results of the compression test.
 
pvisseriii said:
What is your neede jet? Not the needle, main jet, or pilot jet, but the needle jet.. It should be a 159 type and about a Q2. The Mikuni's are totally sensitive in this regard. Yes you will have to pull it apart again. It will slip out the top about the jet ring when you remove the main jet. This is NOT a main jet or pilot jet issue. This is a needle and needle jet issue. Your needle is proper( although i would put the clip at the top groove, lowering the needle. Also, make sure your needle is true. Roll it on a flat surface and observe closely for wobble.
As far as main jets go, I run a 300 with ease, a 350 to go fast, and a 280 for economy. That goes for 36mm vm or the 34 tm. Also your slide is too rich, you need a #3.

It's either that or pulling the head and and validating everything in it. Pushrods, inner and outer springs, valve to guide clearance, everything.
And what were the results of the compression test.
Click to expand...

Interesting. I bought the kit set up for my sea level height by Rocky Point. He's been doing these kits forever and it should be set up for me. Even CNW said everything with my carb sounds right but I did switch to a smaller pilot.

What you're saying does not make much sense since the bike ran perfect with this very carb for thr first start up and timing session, initial 10 minute cam break in and 15 minutes into my first ring bedding ride. If the carb was off it would not have worked right from the start.
 
Coco said:
pvisseriii said:
What is your neede jet? Not the needle, main jet, or pilot jet, but the needle jet.. It should be a 159 type and about a Q2. The Mikuni's are totally sensitive in this regard. Yes you will have to pull it apart again. It will slip out the top about the jet ring when you remove the main jet. This is NOT a main jet or pilot jet issue. This is a needle and needle jet issue. Your needle is proper( although i would put the clip at the top groove, lowering the needle. Also, make sure your needle is true. Roll it on a flat surface and observe closely for wobble.
As far as main jets go, I run a 300 with ease, a 350 to go fast, and a 280 for economy. That goes for 36mm vm or the 34 tm. Also your slide is too rich, you need a #3.

It's either that or pulling the head and and validating everything in it. Pushrods, inner and outer springs, valve to guide clearance, everything.
And what were the results of the compression test.
Click to expand...

Interesting. I bought the kit set up for my sea level height by Rocky Point. He's been doing these kits forever and it should be set up for me. Even CNW said everything with my carb sounds right but I did switch to a smaller pilot.

What you're saying does not make much sense since the bike ran perfect with this very carb for thr first start up and timing session, initial 10 minute cam break in and 15 minutes into my first ring bedding ride. If the carb was off it would not have worked right from the start.
Click to expand...

How's about that compression test. I know it's a scary place to go but if it ain't the input (carb) or the output (exhaust) then it's something in the middle.
 
pvisseriii said:
Coco said:
pvisseriii said:
What is your neede jet? Not the needle, main jet, or pilot jet, but the needle jet.. It should be a 159 type and about a Q2. The Mikuni's are totally sensitive in this regard. Yes you will have to pull it apart again. It will slip out the top about the jet ring when you remove the main jet. This is NOT a main jet or pilot jet issue. This is a needle and needle jet issue. Your needle is proper( although i would put the clip at the top groove, lowering the needle. Also, make sure your needle is true. Roll it on a flat surface and observe closely for wobble.
As far as main jets go, I run a 300 with ease, a 350 to go fast, and a 280 for economy. That goes for 36mm vm or the 34 tm. Also your slide is too rich, you need a #3.

It's either that or pulling the head and and validating everything in it. Pushrods, inner and outer springs, valve to guide clearance, everything.
And what were the results of the compression test.
Click to expand...

Interesting. I bought the kit set up for my sea level height by Rocky Point. He's been doing these kits forever and it should be set up for me. Even CNW said everything with my carb sounds right but I did switch to a smaller pilot.

What you're saying does not make much sense since the bike ran perfect with this very carb for thr first start up and timing session, initial 10 minute cam break in and 15 minutes into my first ring bedding ride. If the carb was off it would not have worked right from the start.
Click to expand...

How's about that compression test. I know it's a scary place to go but if it ain't the input (carb) or the output (exhaust) then it's something in the middle.
Click to expand...

I'll try that after I swap the new coil and plug wires. I don't have the proper gear for a compression test and would have to buy it all.
 
I realized I never did post an update to this thread last year.

My carb was screwed right out of the box. Not sure what was up but a new carb sent on warranty solved everything in a matter of seconds. The bike runs like a scalded ape now.
 
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