Mikuni Carb. . . To choke or not to choke

Bonwit · Apr 27, 2010

I thought I had a handle on this, but now I'm not so sure. It hadn't run all winter, but I was pleasantly surprised the other day when it started and ran beautifully on the second kick (full choke). Today though, I had more trouble. Full choke, no throttle. . . after several kicks, it finally fired (popped), but it felt as though maybe it was flooded. I turned off the choke and kicked many more times. It would fire, but not catch. Finally, it caught and ran fine, but I was left thinking that maybe I shouldn't have choked it in the first place. The outside temperature was in the mid-seventys.

I thought too that maybe my battery wasn't putting out. When I made that first successful start of the season, the battery had been on a maintainer, so I know it was strong. Since last week it hasn't been on the charger, though it measured 12.3 volts (no load) .

Any ideas on a good technique for helping to insure a quick start?

frank73x89 · Apr 27, 2010

One or two kicks before turning on the choke (34 mm Mik) and mine fires up easy even at 40 farenheit and below. Check that your spark plugs are not fouled and gapped correctly (.025-.032), that the float level is perfect and dont touch the throttle! It doesn't need choke when outside temp is warm. Make sure the innards of carb are squeeky clean!!!

mikegray660 · Apr 27, 2010

when the temperatures are rising (70+) i still use the choke on my mikuni when starting from cold, but not fully all the way choked- do you have the cable setup or the flipper on the carb ? - w/ cable setup ( easy to install) you can adjust the amount of choke - and do it with out having to play around directly with the carb under the tank etc - of course each bike is different but after screw around a bit you'll figure what works best
m

Bonwit · Apr 27, 2010

mikegray660 said:
when the temperatures are rising (70+) i still use the choke on my mikuni when starting from cold, but not fully all the way choked- do you have the cable setup or the flipper on the carb ? - w/ cable setup ( easy to install) you can adjust the amount of choke - and do it with out having to play around directly with the carb under the tank etc - of course each bike is different but after screw around a bit you'll figure what works best
m

Flipper. Tell me more about the cable setup. Is this a kit?

rick in seattle · Apr 27, 2010

Stan Smith at Rocky Point Cycle sells the lever conversion kit. You'll need to get a bar-mounted air valve lever as well; many Norton part guys sell them new. Works great here in Pacific Northwest winters. Just remember to ease the choke off after a few minutes to avoid fouling; easy to do on the handlebar.

rx7171 · Apr 27, 2010

Bonwit said:
mikegray660 said:

when the temperatures are rising (70+) i still use the choke on my mikuni when starting from cold, but not fully all the way choked- do you have the cable setup or the flipper on the carb ? - w/ cable setup ( easy to install) you can adjust the amount of choke - and do it with out having to play around directly with the carb under the tank etc - of course each bike is different but after screw around a bit you'll figure what works best
m

Click to expand...

Flipper. Tell me more about the cable setup. Is this a kit?

Check out
Item 2900
http://www.rockypointcycle.com/Merchant ... e_Code=RPC

rx7171 · Apr 27, 2010

mikegray660 said:
when the temperatures are rising (70+) i still use the choke on my mikuni when starting from cold, but not fully all the way choked- do you have the cable setup or the flipper on the carb ? - w/ cable setup ( easy to install) you can adjust the amount of choke - and do it with out having to play around directly with the carb under the tank etc - of course each bike is different but after screw around a bit you'll figure what works best
m

I thought the way the Mikuni "choke" works is really a seperate bypass for fuel/air and is either on or off, without any intermediate settings like the Amal type of carb.

In winter my bike would start first or second kick with full Mikuni "choke" set.
However now it's warmed up a bit here (60ish) I've found if it doesn't start after a couple of chocked kicks it will with the choke off and 1/4 throttle.

Bob

tpeever · Apr 29, 2010

rx7171 said:
I thought the way the Mikuni "choke" works is really a seperate bypass for fuel/air and is either on or off, without any intermediate settings like the Amal type of carb

Mikuni has a fuel "enrichener" circuit rather than a choke but I can get intermediate settings with mine. However, I only have the lever at the carb and it is really difficult to get it to stay at intermediate settings. Converting to an Amal-type handlebar lever should make finer-scale adjustments possible and I have considered doing this. My 1996 Triumph Thunderbird has Mikuni carbs and exactly the same enrichener plungers connected together and controlled by a handlebar lever. Very easy to have partial enrichment.

tpeever · Apr 29, 2010

Bonwit said:
I thought I had a handle on this, but now I'm not so sure. It hadn't run all winter, but I was pleasantly surprised the other day when it started and ran beautifully on the second kick (full choke). Today though, I had more trouble. Full choke, no throttle. . . after several kicks, it finally fired (popped), but it felt as though maybe it was flooded. I turned off the choke and kicked many more times. It would fire, but not catch. Finally, it caught and ran fine, but I was left thinking that maybe I shouldn't have choked it in the first place. The outside temperature was in the mid-seventys.

I thought too that maybe my battery wasn't putting out. When I made that first successful start of the season, the battery had been on a maintainer, so I know it was strong. Since last week it hasn't been on the charger, though it measured 12.3 volts (no load) .

Any ideas on a good technique for helping to insure a quick start?

My drill when completely cold is enrichener fully on and a first kick with no ignition. Then a second kick with enrichener fully on and ignition. No throttle until it fires up. Generally fires up on second kick. I run with enrichener on for no more than 30 seconds or so and then turn up the idle screw to maintain a fast idle. Takes me about 5 minutes to get warmed up. Once bike the has been started once, no need for initial kick without ignition in subsequent startups. I generally use the enrichener again if the bike has been sitting more than a half hour or so.

pete.v · Apr 29, 2010

Fuel on, let set for a few seconds to fill float bowl.
Choke on, 1 to 3 kicks.
Turn idle screw in and warm up with choke off.
Adjust idle to suit.

bpatton · Apr 29, 2010

tpeever said:
rx7171 said:

I thought the way the Mikuni "choke" works is really a seperate bypass for fuel/air and is either on or off, without any intermediate settings like the Amal type of carb

Click to expand...

Mikuni has a fuel "enrichener" circuit rather than a choke but I can get intermediate settings with mine. However, I only have the lever at the carb and it is really difficult to get it to stay at intermediate settings. Converting to an Amal-type handlebar lever should make finer-scale adjustments possible and I have considered doing this. My 1996 Triumph Thunderbird has Mikuni carbs and exactly the same enrichener plungers connected together and controlled by a handlebar lever. Very easy to have partial enrichment.

The plunger that regulates the enricher circuit has a rubber base that seals it when shut but it is possible to feather the effect. It's pretty much impossible to do with the carb mounted lever, it just won't stay put at any setting. The bar mounted lever setup is a great improvement in convenience, it will hold a setting, and it's inexpensive if you already have the Amal lever left over. You do need to get a new cable because the stock choke cable has a splitter. The conversion set at the carb is under $20, the cable can run much more and an Amal lever can bring it up over $100. Depends on how finicky your bike is to start.

highway · Apr 29, 2010

The problem with the choke/enrichener circuit on these round slide VMs, is they are jetted rich enough for 2 strokes that have weak signal compared to draw of a Norton twin.
I like to drill a tap the float bowls' enrichener feed hole and fit an Amal concentric pilot jet, a #30 (give or take a size) just as Amal series 2 have to adjust the enrichener circuit.
With a rocker it will start cold and fast idle @ 1800 to 2000. til the head warms up and you take the choke off
The way to go is the Mikuni cable adaptor, to your original choke lever, and you can modulate the amount of choke and fast idle. Rick

Nor72ton · Feb 11, 2014

Definitely full choke cold start with mikuni pilgrims,no throttle twist, my 72 combat starts first kick in this sequence, it can sit for months and still start first( sometimes second kick), but if I accidentally twist that throttle im there forever having a coronary seizure

WZ507 · Feb 11, 2014

Something smells fishy about your battery. If it was topped off to start the season (12.65 v) and dropped to 12.3 volts in 1 week it is nearing 50% discharge (12.25 v). A healthy battery would not behave like this. Try disconnecting it and jumping with a strong battery to see if that perks up the starting process.

Mikuni Carb. . . To choke or not to choke

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