Hard start

capehorner · Dec 3, 2012

75 Norton Mark 3 - 125PSI compression cold after 3 kicks, carb is Mikuni single 34-rebuilt with .240 main jet as I live at 3500 feet plus. Pazon ignition new, timing is 28 Degrees dead on. This puppy won't start cold without starting fluid, once hot starts so easy I am amazed. Right cylinder exhaust is cold at tip of muffler but I pulled plug wire and there is a difference so I am pretty sure it's firing. Is there anyone near Stevensville, Mt who can help me. I have a kegerator filled with great beer. I am at a loss as what to do next and am a noobie but mechanically ok. HELP.

usefulidiot · Dec 3, 2012

i'm by no means an expert, but are you giving it any throttle when cold? all 3 of my nortons WILL NOT START when cold without 1/4 throttle at least while kicking. Also if it doesnt fire after 1-2 kicks i find i have to tickle again and it fires right away.

OldBalz · Dec 3, 2012

usefulidiot said:
i'm by no means an expert, but are you giving it any throttle when cold? all 3 of my nortons WILL NOT START when cold without 1/4 throttle at least while kicking. Also if it doesnt fire after 1-2 kicks i find i have to tickle again and it fires right away.

The OP HAS A MIKUNI on his bike ....you can't tickle a Mikuni!

The general consensus of Commando owners that have Mikunis is...No throttle when starting cold. That's the way it is on mine and I don't even give it throttle when hot-starting.....only when it starts.

mikegray660 · Dec 3, 2012

Are you sure your Mikuni choke systems is working? does the choke level actuate /lift the little piston in the carb and is the choke circuit clear. As mentioned with a mikuni you shouldn't really open the throttle or it defeats the purpose of the choke - the main jetting has nothing to do with cold start

rpatton · Dec 3, 2012

OldBalz said:
The general consensus of Commando owners that have Mikunis is...No throttle when starting cold. That's the way it is on mine and I don't even give it throttle when hot-starting.....only when it starts.

+1 My 850 has a single VM34. The choke (Enrichener Circuit) is an air/fuel circuit totally separate from the bore/slide the carb usually breathes through. If you set the enrichener by raising the plunger and then open the throttle, the enrichener doesn't come into play, it might as well be closed. What pilot jet are you using?

bill · Dec 3, 2012

as stated you CAN NOT open the throttle on a mik. also it is NOT a choke but an enrichener circuit. you might try raising the idle speed with the idle stop and DO NOT touch the throttle as you start it.

dynodave · Dec 3, 2012

1. make sure the bowl gasket is sealing the enricher circuit or fuel will not get pulled up.
2. make sure the fuel/float level is up to snuff....too low will make it hard to start.
3. if all else fails I would solder shut the upper two air bleed holes on the dip tube. (sorry- an amal MKII would have a changeable jet)

concours · Dec 3, 2012

Who did the "rebuild" on the carb? You? A pro? friend? Get them back on it.. It sounds like something is wrong in the enrichener circuit, as others have mentioned. The Mik enrichener ONLY works with a closed throttle. Your enrichener plunger is in good condition? The rubber tip is intact? (not stuck down in the well)
The engine has good (tested) compression? Checked for vacuum leaks around the intake manifolds?

radiofun · Dec 4, 2012

Hi Capehorner. I also have a Mik and the responders are right in that you should not use the throttle. The first thing to do is turn up the idle screw a bit. If that doesn't work, then check to make sure Mikuni choke lever is actually working.

PS. I live in Helena but I don't get over the Stevensville much otherwise I would take you up on the beer offer.

capehorner · Dec 4, 2012

I don't use the choke as it's way too much on the Mikuni. Carb was rebuilt by Rob Snow, local pro.

dynodave · Dec 4, 2012

capehorner said:
I don't use the choke as it's way too much on the Mikuni. Carb was rebuilt by Rob Snow, local pro.

drill and tap the bowl hole and put a #25 amal jet
then use the choke/enricher so it will start

radiofun · Dec 4, 2012

The Mik is desinged to use the choke lever when the bike is cold so If it was set up properly (by the pro) then its use should not overwhelm the system. Try truning up the idle and use the choke level, but immediately flip the level up once the engine starts.

mikegray660 · Dec 4, 2012

not using the choke/enricher at all at cold start is your problem , as mentioned you can turn you idle up a bit which should help too - try opening /lifting the lever UP part ways (if cable operated easy to do) or do as dave says

think radio means down - choke/enricher off = down once started

radiofun said:
The Mik is desinged to use the choke lever when the bike is cold so If it was set up properly (by the pro) then its use should not overwhelm the system. Try truning up the idle and use the choke level, but immediately flip the level up once the engine starts.

donmeek · Dec 4, 2012

a lot of good expert advice here. mikunis are easy to tune(must be if even i can do it). please remember the old adage that most carb problems are ignition related and vice versa

OldBalz · Dec 5, 2012

capehorner said:
I don't use the choke as it's way too much on the Mikuni. Carb was rebuilt by Rob Snow, local pro.

Well....Maybe your "local pro" doesn't know how to set up your Mikuni. There's a lot of good advice from the members here that have Mikunis.

You'll do a lot of kicking if you're not using the choke/enrichener lever on cold starts. Sounds like you might want to start listening to the comments that you are getting on this thread versus your local "expert".

It's kinda like if you don't like the answers then you shouldn't ask the question..........

Hard start

Similar threads