Touring On A Meriden Bike

[NM Bonny]

flat-slide or round-slide? either way, mikunis are an excellent choice for a 650 or 750 triumph. theyre easy to mount, easy to tune, and give excellent performance. but the VM version is a long carburetter compared to an amal concentric. if thats what youre fitting, you may end up having to modify your sidecovers again, although flat air filters will fit between the bellmouth and the old airbox brackets.

Round slide, I believe. Here's a picture of the kit...

Glad to hear you've had good experience with them.

The manual says they're pre-jetted for a stock engine operating at sea level to 3,500 ft. I've got a stock engine internally, but as you may know with Dunstall replicas, and daily drive is 6,000 ft (home) to 5,000 ft (ABQ).

 

[speedrattle]

ive been buying stuff from marino perna for 45 years. his stuff is first-rate.

when you get these carbs, take them apart and inspect the inside. post the initial jetting here. i am really interested in what MAP is putting in their 30mm carbs.

 

[NM Bonny]

ive been buying stuff from marino perna for 45 years. his stuff is first-rate.

when you get these carbs, take them apart and inspect the inside. post the initial jetting here. i am really interested in what MAP is putting in their 30mm carbs.

Oh, cool, excellent to hear Marino knows his stuff.

Okay, I'll inspect and post the data whenever the Mikunis get here--and thank you so much for the fine-tuning help.

Ashton, OR, is at 1,950 ft. So, it'd be cool to have a 'low elevation' kit I could carry on trips to swap out if my excursions dip into some low elevations that could endanger my exhaust valves and pistons.

 

[speedrattle]

ive been running VM mikunis in various british machines for 40 years. i can help with the jetting.

but first, expect it be set up rich as it comes to you.

 

[NM Bonny]

ive been running VM mikunis in various british machines for 40 years. i can help with the jetting.

but first, expect it be set up rich as it comes to you.

Okay, the 30mm kit comes with a 210 main jet installed, and a 25 pilot jet.

The needle is a 6DH3 set to the middle groove of 5 positions.

They also provided:
- mains 190, 200, 220
- pilots 30, 40

Question: before we get to your initial jetting advice for 5,000~6,000 ft, the carbs seem to have an overflow hose and two (count 'em) vent hoses for each float bowl. Am I mistaking the function of those?

I have to say that the quality of this Japanese carb is far better than the Amal (see pics), at last as to some components like the slide.

The only real disappointment thus far is shown in the last photo. Bummer...

 

[NM Bonny]

I want to mention that I've left the detour into carb tuning here--rather than on my main restoration/modification thread--because some trips involve potentially dramatic changes in altitude.

So, while determining what tools I need to carry, I'd also like to assemble a low-altitude carb-tuning kit that I can drop in at [x] altitude, and also have mixture screw settings on a card (or note in my phone) to enable a 'swap-and-go' setup.

Hope that makes sense, and will be useful to others contemplating similar trips--or even better, planning to join me for some portion of my trip to Ashland.

 

[speedrattle]

excellent

unscrew a main jet from the bottom of the needle jet and gently push up on the needle jet with a blunt phillips screwdriver (or a piece of wood if its at all tight) to pop it loose into the venturi. dont twist it- theres a locating pin. you should most likely have a 159-P2 or a 159-P4. see which it is.

look on the bottom plate of the slide. you probably have a 2.5 cutaway.

last there is a tiny and fragile brass air jet inside one of tbe air horn holes. see what tbe number on tbat is. use a very small screwdriver in very good condition. if its tight leave it alone. you wont need to change it but im curious as to whether is a 1 or a 2.

 

[NM Bonny]

excellent

unscrew a main jet from the bottom of the needle jet and gently push up on the needle jet with a blunt phillips screwdriver (or a piece of wood if its at all tight) to pop it loose into the venturi. dont twist it- theres a locating pin. you should most likely have a 159-P2 or a 159-P4. see which it is.

look on the bottom plate of the slide. you probably have a 2.5 cutaway.

last there is a tiny and fragile brass air jet inside one of tbe air horn holes. see what tbe number on tbat is. use a very small screwdriver in very good condition. if its tight leave it alone. you wont need to change it but im curious as to whether is a 1 or a 2.

The needle jet is 159-P0.

The slide is indeed a 2.5 cutaway.

I haven't got a small enough, high-quality screwdriver to remove the air horn jet.

Shall I go ahead and commence the idle speed and mixture settings? Or is the 159-P0 needle jet a problem?

I won't be able to perform the main jet testing until the kickstand is fixed per the main thread...

 

[speedrattle]

the 6DH3 is a slightly richer needle than 6DH2. i usually use it with a 159-P2.

im surprised at the 159-P0. i have been unsuccessful running a needle jet that lean. but try it.

but the first thing to do is make it idle. the 25 pilot works well at my elevation. ive gone down as low as 22.5 in thinner air. 30 will likely be too rich.

but test. set the airscrews at 1.5 turns out. if you can get tbe best idle within a half turn of that using the 25, youre good. if you have to turn the screw out to as far as 2.5 out, you should go down to a 22.5 or even a 20. 30 is a sea level pilot jet, i think. 35 is usually so rich it smokes.

i think you will be raising the needle to work with that needle jet

more later im dumping a truck

 

[NM Bonny]

the 6DH3 is a slightly richer needle than 6DH2. i usually use it with a 159-P2.

im surprised at the 159-P0. i have been unsuccessful running a needle jet that lean. but try it.

but the first thing to do is make it idle. the 25 pilot works well at my elevation. ive gone down as low as 22.5 in thinner air. 30 will likely be too rich.

but test. set the airscrews at 1.5 turns out. if you can get tbe best idle within a half turn of that using the 25, youre good. if you have to turn the screw out to as far as 2.5 out, you should go down to a 22.5 or even a 20. 30 is a sea level pilot jet, i think. 35 is usually so rich it smokes.

i think you will be raising the needle to work with that needle jet

more later im dumping a truck

Thanks very much for taking the time in the midst of a job.

I'll try it out--but again, will only be doing the idle mixture adjustment and pilot jet test for now, due to the kickstand...

Also: I'm ordering a 6DH2 needle, 159-P2 and 159-P4 needle jets, and 20 and 22.5 pilot jets, to have in my kit.

Seems useful--and good to have some tuning flexibility for whenever I install the Morgo 750cc kit down the road.

 

[speedrattle]

you should set the idle first so the machine can run. next will be the main jets, setting the needle rich so it doesnt restrict the mains.

200 is what i use in 32s and 34s in normal weather at 1300 feet. 210 in cold weather. but with low density air ive run as low as 180 for years. at high elevations you might end up with the 190s.

then last you can try raising and lowering the needle to work best with that needle jet.

im really surprised at the 159-P0. when i tried them on a 34mm they were so lean i turned around after 50 feet and took them out but 6DH3 may work with them. or maybe even 6DH4. at your elevation they might be perfect.

the 2.5 slide will be fine, and the air jet is so subtle i dont mess with them.

order an extra pair of main jets. you are going to destroy them by drilling them out to about a size 300 in order to set your needle jets. or you can just take the old main jets out of your amal mk2s and use those. theyre exactly the same jets, as mk2s and VM mikunis were designed by the same people.


that will likely do it for jets, unless you discove that you need to go even leaner at high elevations. at 10000 feet, my 72 would only go 40 mph with the stock concentric main jets, which i think were 200s.

do you have that morgo yet? theres a waiting list right now. when tbey get enough people theyll cast another batch

 

[NM Bonny]

you should set the idle first so the machine can run. next will be the main jets, setting the needle rich so it doesnt restrict the mains.

200 is what i use in 32s and 34s in normal weather at 1300 feet. 210 in cold weather. but with low density air ive run as low as 180 for years. at high elevations you might end up with the 190s.

then last you can try raising and lowering the needle to work best with that needle jet.

im really surprised at the 159-P0. when i tried them on a 34mm they were so lean i turned around after 50 feet and took them out but 6DH3 may work with them. or maybe even 6DH4. at your elevation they might be perfect.

the 2.5 slide will be fine, and the air jet is so subtle i dont mess with them.

order an extra pair of main jets. you are going to destroy them by drilling them out to about a size 300 in order to set your needle jets. or you can just take the old main jets out of your amal mk2s and use those. theyre exactly the same jets, as mk2s and VM mikunis were designed by the same people.


that will likely do it for jets, unless you discove that you need to go even leaner at high elevations. at 10000 feet, my 72 would only go 40 mph with the stock concentric main jets, which i think were 200s.

do you have that morgo yet? theres a waiting list right now. when tbey get enough people theyll cast another batch

Okay, sounds good. Here's my MAP cart right now:

Needles: 6DH2, 6DH4 (6DH3 in carb)

Needle jets: 159-P2, P4 (P0 in carb)

Pilot jets: N224.103/20, 22.5 (25 in carb, 30 and 40 in carb kit)

Yes - per the main restoration/mods thread, I snatched up a Morgo 750cc kit when they became available (only a few, as you say).

 

[speedrattle]

there was a NOS morgo on eBay, but i was too slow. im building a 650 T120 sidecar tug, and it would have been perfect. ive been kicking myself.

i have a 1972 T120 morgo, some head work, slightly bigger cams, oversize intake valves, 32mm VM mikunis at the moment. this is what i run in it at 1300 feet:

-- 25 pilots
-- 2.5 slide
-- 159 P-4 needle jets
-- 6DH2-2 needles (second clip position from the top)
-- 200 mains, maybe 210 or maybe 220 in cool weather.
-- 2 air jets

^^^these are a workable solution, but there are others that will also work. i have found that until your get really fussy, you can mostly use the same settings between instruments that are 2mm apart. amal concentrics too.

i used these same settings on the same machine with 34mm carburetters, except i used a 2.0 slide and a 35 pilot, both quite rich, in order to overcome an off-idle stumble from the big carbs.

6DH2 and 6DH3 are essentially the same needle, but with the same taper positioned higher on the 6DH3, which makes it richer. 6DH4 is different, slightly leaner on the straight section and then much richer on the taper. overall a richer needle.

where you are at 5000 feet or so, you are going to need leaner settings all around than those i use at 1300 feet. probably the 2.5 slide will work, but you can go as lean as 3.5. thats as lean as they go. for your lower elevation settings, you can just start clicking richer from what works higher up. there will be a noticeable difference between 6000 and 1900 feet.

the needle jet/needle situation is simple. 159-P0 is pretty lean for my air density. i have found that using a lean 159-P2 with a rich 6DH3 is indistinguishable from a rich 159-P4 using a lean 6DH2. they work out the same, and you can consider them a middle solution.

but the lean needle jet with the lean needle is quite different from the rich needle jet with the rich needle, a much leaner combo and a much richer one. so you have three levels to test, if theres something awkward about what you have.

so do this: set the pilot air screw so it idles around 800 or 1000, and go out and ride it around just like you got it, to get a baseline. it may be so rich it will blubber anywhere in the operating range. thats good because it tells you what you need to adjust. or it may be close, and you will have to look more carefully.

you must mark your throttle with tape and a pen. wrap a loop of tape around the throttle barrel, and put a stationary piece on the throttle housing. then mark a line on the tape on the housing. close the throttle completely, and mark a zero line on the throttle barrel. open it all the way, and mark a WFO mark on the throttle barrel. in between , mark 1/4, 1/2, and 3/4 throttle. these are the positions you will be evaluating, because they correspnd to different circuits controlling the mixture.

go out and warm up the bike, then find a stretch of road where you can open the throttle for a few seconds, under load, like slightly uphill. which is easy in albuquerque.

to test the main jets, run the bike at WFO for three seconds or so for the mixture to stabilize. then close the throttle about 1/8, per the tape on your throttle barrel. if the bike speeds up for a second or two, that jetting position is lean. go a step richer. if there is no change, its okay or a bit rich. to test the needle jet/needle/needle position, do the same thing at about 1/2 throttle. its gets a little messier in there because youre looking at three things at once. same thing, but maybe less obvious.

the reason for this is that fuel has mnore inertia than air. when you close the throttle, the airflow instantly decreases, but the fuel coming into the venturi from the float bowl will still run a few milliseconds, so the mixture fgoes rich for a second or two. if the bike speeds up, then richer is what it wants at that throttle position.

this technique is not as exact as timed runs with a stopwatch or using an AF meter, but it is almost as good and you can do it anywhere, anytime. it works best for main jets but if your e careful, it can pick needle position too. its hard these days with modern gasoline to evaluate mixture using spark plug color. you can do it, but it takes a lot of learning. on my race bike, i use an AF meter to get in the ballpark, and then timed runs on an airstrip or the track to zero in. on my street stuff i use the roll-off technique.

you will need this to make sense of the marked throttle:

notice everything overlaps a bit, but each circuit has its major region. thats what youre looking for.

what youre doing by getting serious about carburetter tuning will be super rewarding. the difference is running will be very noticeable, and you may eand up with summer and winter settings that are slightly different. the mikunis are easy to tune, and once you set them, you can mostly forget about them. they dont plug up, they dont wear out, and theyre easy to fix if something goes screwy.

but its not just mikunis. everything ive said about them here mostly applies to amals too, which are very similar, especuially the mk2s. theres some differences, and each is better than the other in a few areas. so what you learn with the mikunis is directly applicable to amals, if you end up running those in something

cheers!

 

[NM Bonny]

there was a NOS morgo on eBay, but i was too slow. im building a 650 T120 sidecar tug, and it would have been perfect. ive been kicking myself.

i have a 1972 T120 morgo, some head work, slightly bigger cams, oversize intake valves, 32mm VM mikunis at the moment. this is what i run in it at 1300 feet:

-- 25 pilots
-- 2.5 slide
-- 159 P-4 needle jets
-- 6DH2-2 needles (second clip position from the top)
-- 200 mains, maybe 210 or maybe 220 in cool weather.
-- 2 air jets

^^^these are a workable solution, but there are others that will also work. i have found that until your get really fussy, you can mostly use the same settings between instruments that are 2mm apart. amal concentrics too.

i used these same settings on the same machine with 34mm carburetters, except i used a 2.0 slide and a 35 pilot, both quite rich, in order to overcome an off-idle stumble from the big carbs.

6DH2 and 6DH3 are essentially the same needle, but with the same taper positioned higher on the 6DH3, which makes it richer. 6DH4 is different, slightly leaner on the straight section and then much richer on the taper. overall a richer needle.

where you are at 5000 feet or so, you are going to need leaner settings all around than those i use at 1300 feet. probably the 2.5 slide will work, but you can go as lean as 3.5. thats as lean as they go. for your lower elevation settings, you can just start clicking richer from what works higher up. there will be a noticeable difference between 6000 and 1900 feet.

the needle jet/needle situation is simple. 159-P0 is pretty lean for my air density. i have found that using a lean 159-P2 with a rich 6DH3 is indistinguishable from a rich 159-P4 using a lean 6DH2. they work out the same, and you can consider them a middle solution.

but the lean needle jet with the lean needle is quite different from the rich needle jet with the rich needle, a much leaner combo and a much richer one. so you have three levels to test, if theres something awkward about what you have.

so do this: set the pilot air screw so it idles around 800 or 1000, and go out and ride it around just like you got it, to get a baseline. it may be so rich it will blubber anywhere in the operating range. thats good because it tells you what you need to adjust. or it may be close, and you will have to look more carefully.

you must mark your throttle with tape and a pen. wrap a loop of tape around the throttle barrel, and put a stationary piece on the throttle housing. then mark a line on the tape on the housing. close the throttle completely, and mark a zero line on the throttle barrel. open it all the way, and mark a WFO mark on the throttle barrel. in between , mark 1/4, 1/2, and 3/4 throttle. these are the positions you will be evaluating, because they correspnd to different circuits controlling the mixture.

go out and warm up the bike, then find a stretch of road where you can open the throttle for a few seconds, under load, like slightly uphill. which is easy in albuquerque.

to test the main jets, run the bike at WFO for three seconds or so for the mixture to stabilize. then close the throttle about 1/8, per the tape on your throttle barrel. if the bike speeds up for a second or two, that jetting position is lean. go a step richer. if there is no change, its okay or a bit rich. to test the needle jet/needle/needle position, do the same thing at about 1/2 throttle. its gets a little messier in there because youre looking at three things at once. same thing, but maybe less obvious.

the reason for this is that fuel has mnore inertia than air. when you close the throttle, the airflow instantly decreases, but the fuel coming into the venturi from the float bowl will still run a few milliseconds, so the mixture fgoes rich for a second or two. if the bike speeds up, then richer is what it wants at that throttle position.

this technique is not as exact as timed runs with a stopwatch or using an AF meter, but it is almost as good and you can do it anywhere, anytime. it works best for main jets but if your e careful, it can pick needle position too. its hard these days with modern gasoline to evaluate mixture using spark plug color. you can do it, but it takes a lot of learning. on my race bike, i use an AF meter to get in the ballpark, and then timed runs on an airstrip or the track to zero in. on my street stuff i use the roll-off technique.

you will need this to make sense of the marked throttle:

notice everything overlaps a bit, but each circuit has its major region. thats what youre looking for.

what youre doing by getting serious about carburetter tuning will be super rewarding. the difference is running will be very noticeable, and you may eand up with summer and winter settings that are slightly different. the mikunis are easy to tune, and once you set them, you can mostly forget about them. they dont plug up, they dont wear out, and theyre easy to fix if something goes screwy.

but its not just mikunis. everything ive said about them here mostly applies to amals too, which are very similar, especuially the mk2s. theres some differences, and each is better than the other in a few areas. so what you learn with the mikunis is directly applicable to amals, if you end up running those in something

cheers!

Wow... this is really generous. Thank you!

I got the carbs installed, cables adjusted properly (both slides initial rising in synch and WOT equalized), but realized the fuel fittings are different enough that I had to order 90-degree pipes for the petcocks.

I'm not a huge fan of the pancake filters but they are the reusable/oiled type and I've got leftover K&N cleaner and oil. And the look is kind of growing on me...

Looks like due to my compact side cover design that I could maybe fit some K&N cones in there, though, as these photos suggest.

Okay, I'll proceed with the idle mixture portion when the fuel pipes arrive, fix the kickstand, and report back with results. Very excited to be riding the bike before winter blows in!

 

[NM Bonny]

Sorry for the interim silence. Finally warmed up enough to motivate me to get out to the garage and weld on the new kickstand. So, I'm hoping to finish that job this weekend (needs a little extension to dial in the lean angle) and get these Mikunis tuned for this elevation.

 

[Sparkdiver]

Weather is fine today in Utah...1970 T120R, headed out at 0700 at 31 degrees...defrosting over breakfast. 39 degrees now and got a blueberry pancake for insulation! Let's roll bro. Welded her up.

 

[Vector]

Weather is fine today in Utah...1970 T120R, headed out at 0700 at 31 degrees...defrosting over breakfast. 39 degrees now and got a blueberry pancake for insulation! Let's roll bro. Welded her up.

We may be riding to the Stagecoach Grill for lunch Sunday. I will be riding up that way on Tuesday. I'll text you.

 

[NM Bonny]

Weather is fine today in Utah...1970 T120R, headed out at 0700 at 31 degrees...defrosting over breakfast. 39 degrees now and got a blueberry pancake for insulation! Let's roll bro. Welded her up.

Whoa... brrrr! Man, wish I could join you guys!

Got her all done, so ready to start futzing with the Mikunis tomorrow or Monday. It's going to be in the low '60s!

 

[atomsplitter]

Once you get it all dialed in should be a great scoot to ride on. Last time I was in Albuquerque I couldn't believe how much it changed in the 50 years since I lived there. Ride safe.

 

[NM Bonny]

Once you get it all dialed in should be a great scoot to ride on. Last time I was in Albuquerque I couldn't believe how much it changed in the 50 years since I lived there. Ride safe.

Yeah, it started right up this morning but I think the way I've got the fuel lines routed due to where the inlets are on the non-handed Mikunis, and the limited space in there, it's not feeding fuel properly. So, after lunch I'll reroute things and see if I can get the idle dialed in... and just maybe I'll have a chance to go bed in the front disc pads and see how she handles in the canyon. It's a gorgeous day.

Albuquerque is unrecognizable. On the west side of the river where we used to go dove hunting when I was a wee lad, there's this thing called Rio Rancho--urban sprawl on steroids. Lots of people fleeing CA, TX, OK in substantial numbers, judging from the license plates. I'm lucky to live in the countryside out of town--but as cities go not awful, I guess...