Mukuni Hard Start

swooshdave · Feb 20, 2020

My Interstate is getting really difficult to start when cold. The last couple times it's taken a lot of kicking. Last summer it was one or two kicks when cold.

But it's been mostly sitting for a few months and we know how crappy the gas is around here.

Is there a pilot jet or specific circuit that may need cleaned?

Yesterday there was gas pouring out of the overflow. I tapped the side of the bowl and that seemed to work, or a least it did something. When I finally got it running it idled just fine and started first kick when hot.

Obligatory bike picture from last year:

Leonc · Feb 20, 2020

My A75 had been progressively getting harder to start over the last few weeks all it took was a fresh set of plugs to fix it. At 1500 miles the BP7ES's were shot.
Was hard to start but ran ok, and started ok when it warm.

gnolan · Feb 20, 2020

There is a small orifice in the bottom of the float bowl - it is not removable. It is probably clogged up. It can be cleaned with small diameter wire or welding tip cleaner.
Take the float bowl off and inspect carefully, you will see it.

RoadScholar · Feb 20, 2020

I tend to agree with your thought about the idle jet, should be a #40 and much easier to just replace. I suggest that you purchase at least 2. Unless you have an ultra sonic machine the idle jets are near impossible to clean.

Before you buy idle jet(s) try the following:

Shut off fuel taps
Drain the tank
Drain the float bowl
Turn the idle air trim screw in to a gentle seat, counting the number and fraction of turns
Remove the air screw
Squirt Gum-Out, or equivalent, but NOT brake clean
Hit the vacant air screw hole with compressed air, repeat at least 2 more times

You may be good to go, mix Techron with new fuel, it will do the rest.

Best,

bill · Feb 20, 2020

If you have to replace plugs in that short of milage you either have a tune issue with the carb/carbs or an oil control issue.

Leonc said:
My A75 had been progressively getting harder to start over the last few weeks all it took was a fresh set of plugs to fix it. At 1500 miles the BP7ES's were shot.
Was hard to start but ran ok, and started ok when it warm.

Peavey Jeltz · Feb 20, 2020

Two Commandos with VM34 kits. Both had #35 pilots installed with #30 and #40 in the bag of extras. Might depend on who put your kit together. Weather here in Portland, Oregon is pretty nice today. Commando started right up and off down Skyline we went.

Dave, message me if you want some VM jets hand delivered via Norton express. Gotta ride to the next meeting, I wimped out last two months.

Fullauto · Feb 20, 2020

I'm sure it will be something simple. I've never had to clean a pilot jet, ever. Most run their bikes too rich. So far my VM 34 has outlasted around four pairs of Amals. If you really want tp know what's happening with your tune, fit an O2 sensor and an A/F ratio gage. Very enlightening and you will learn a lot.

swooshdave · Feb 20, 2020

Peavey Jeltz said:
Two Commandos with VM34 kits. Both had #35 pilots installed with #30 and #40 in the bag of extras. Might depend on who put your kit together. Weather here in Portland, Oregon is pretty nice today. Commando started right up and off down Skyline we went.

Dave, message me if you want some VM jets hand delivered via Norton express. Gotta ride to the next meeting, I wimped out last two months.

The carb has been on the bike since I bought the bike... a LONG time ago so I don't think different size jets are the answer.

I sure hope I can get to the next meeting.

swooshdave · Feb 20, 2020

RoadScholar said:
I tend to agree with your thought about the idle jet, should be a #40 and much easier to just replace. I suggest that you purchase at least 2. Unless you have an ultra sonic machine the idle jets are near impossible to clean.

I'll stick the bowl in the ultrasonic cleaner and see if that helps.

gnolan · Feb 21, 2020

the starter jet (some call it the enrichener, it is not a "choke") is not the same as the pilot jet. Starter jet is in the float bowl, is not removable.
Pilot jet screws into the carb body, is removable and replaceable.
If the pilot jet is dirty, it will affect starting as in the lean condition will cause it to run rough or die AFTER the enrichener is turned off.

swooshdave · Feb 21, 2020

gnolan said:
the starter jet (some call it the enrichener, it is not a "choke") is not the same as the pilot jet. Starter jet is in the float bowl, is not removable.
Pilot jet screws into the carb body, is removable and replaceable.
If the pilot jet is dirty, it will affect starting as in the lean condition will cause it to run rough or die AFTER the enrichener is turned off.

I’m I correct that if it idles fine that the pilot jet is probably not the issue rather it might be the starter jet?

Hortons Norton · Feb 21, 2020

Sounds correct to me.

gnolan · Feb 21, 2020

That's where I'd look. Since the float was sticking per your first post, there is probably some dried up junk in the bottom of the float bowl, too.

RoadScholar · Feb 21, 2020

swooshdave said:
I'll stick the bowl in the ultrasonic cleaner and see if that helps.

The bowl doesn't have any jets in it, but you can check the vents, probably not worth an ultrasonic cleaning, up to you.

If you PM me the jetting package I may be able to suggest some alternatives, happy to help.

Also, a #35 or #40 can work, you may have more leeway with the idle air trim with the 40. I look for the air screw to be no less than 1.5 turns out from seat and no more than 2.5. If you ride in temps less than 55 (f) you'll have the bandwidth to richen the idle mixture (turn in) or above 85 (f) where you can lean the mixture.

Best.

swooshdave · Feb 21, 2020

RoadScholar said:
The bowl doesn't have any jets in it, but you can check the vents, probably not worth an ultrasonic cleaning, up to you.

If you PM me the jetting package I may be able to suggest some alternatives, happy to help.

Also, a #35 or #40 can work, you may have more leeway with the idle air trim with the 40. I look for the air screw to be no less than 1.5 turns out from seat and no more than 2.5. If you ride in temps less than 55 (f) you'll have the bandwidth to richen the idle mixture (turn in) or above 85 (f) where you can lean the mixture.

Best.

Considering how well it use to start before sitting I’m not inclined to change any jetting.

Fullauto · Feb 21, 2020

No wonder you can't tune it. You can't even spell it.

swooshdave · Feb 22, 2020

Fullauto said:
No wonder you can't tune it. You can't even spell it.

Yeah, I pretty much tap out my intellect trying to spell Amal.

Bernhard · Feb 22, 2020

swooshdave said:
Yeah, I pretty much tap out my intellect trying to spell Amal.

DYK that Amal is also a girls name?

gnolan · Feb 22, 2020

Here is the starter jet in the float bowl.

swooshdave · Feb 22, 2020

Bernhard said:
DYK that Amal is also a girls name?

Who wants to be the first to tell George that his wife Amal will one day look like her mom?

Mukuni Hard Start

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