Hard Starting Mikuni on a '62 XLCH

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Hard Starting Mikuni on a '62 XLCH

Postby jOe » Sat Feb 02, 2019 12:03 am

I need some help with a hard starting '62 with a new Mikuni VM83..Run of the mill XLCH , new rings,timing set ok,no issues. When it runs,all's well, but it's really hard starting. Generally sputters on every kick. Sudco said to replace the .033 jet which it came with with a .035--which I did. Same symptoms. Any insights as to how to use the choke? Air screw is backed out 1 1/4 turn. I have the exact same set up on a '65 XLCH and with the choke it usually starts on the first kick. Any ideas?
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Re: Hard Starting Mikuni on a '62 XLCH

Postby 55panman » Sat Feb 02, 2019 2:21 am

The choke is just an enrichener and I don't think it richens it that much. Give it a couple prime kicks before you turn on the ignition. And don't touch the throttle when you kick it to start because that opens the throat and instantly leans it out. Always worked on my Pan. Pull the slide out and see what the cut away is marked on the bottom of the slide next to where the needle comes through. If it's like a 4 it's too lean. I always run a cut away that's less than what they come with. Get like a # 3 . Running a low number cut away richens the mixture up at low throttle openings. It also helps to keep the engine from stumbling if you crack the throttle off idle. My dirt trackers always came right off idle without a stumble cracking the throttle wide open because I run as low a cut away as I can get. You may have to lean that primary jet out again.
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Re: Hard Starting Mikuni on a '62 XLCH

Postby thefrenchowl » Sat Feb 02, 2019 6:08 am

Joe,

Would you mind telling us what's better in a Mikuni compared to a Linkert DC?

Patrick
Flat Head Forever
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I'm the one who has to die when it's time for me to die so let me live my life the way I want to...
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Re: Hard Starting Mikuni on a '62 XLCH

Postby jOe » Sat Feb 02, 2019 10:23 am

Are you talking about the center needle? 5 grooves and the Sudco tech said to keep that in the middle for now. ( groove 3). I put the .035 jet in- slightly better. I started with the air screw out 1 1/2 and went in about 1/4 when it was running. When it runs, it seems normal- just really hard starting . I may pull a few degrees of timing out of it and see what happens. Out of the box it had the .033 jet. Maybe it’s just a case of getting the starting procedure dialed in.

Linkert DC?- I’d rather see them saved for original configuration restorations. This ‘66 is not any sort of candidate for restoration.
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Re: Hard Starting Mikuni on a '62 XLCH

Postby 55panman » Sat Feb 02, 2019 12:28 pm

Joe, I'm talking about the throttle slide itself. That is the round barrel down the center of the carb that controls the throat opening. If you pull that out turn it over and look in the center you will see a marking 3 3 1/2 4 whatever. That is the size of the eyebrow cutaway that controls how much air can enter the carb when the throttle is shut. If you look at the slide the bottom back side is flat and it cuts off air flow. the front side bottom has an arc cut away. Less arc allow less air into the carb when throttle shut (richer), more arc allows more air into the carb when the throttle is shut making it leaner. This has the most control over lean or rich when the throttle is shut. The number corresponds to more arc cut away or less arc cut away. Try getting a slide with the least number cut away you can. I run 2 1/2 or 3 in my XR750 Harley 38mm dirt tracker. As far as carb internal from one bike to another you can build 2 engines exactly the same and use the same carbs and settings on them and they can run completely different.
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Re: Hard Starting Mikuni on a '62 XLCH

Postby jOe » Sat Feb 02, 2019 1:06 pm

Yeah, the bottom of the slide is marked 2.5. I put the .033 jet back in, took about 1 degree of timing out of it, gas, and it started up reasonably easy . Twice in a row!
I guess I’m ok for now. My goal is to get it to start as easily as my one kick wonder ‘65.
Note- when I took the slide out, I noticed on the raised curved area below the slide, in the main carb body, that there were areas that didn’t look fully polished. Is that typical? Again, this is a brand new unit.
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Re: Hard Starting Mikuni on a '62 XLCH

Postby jOe » Wed Feb 06, 2019 9:18 pm

A short post script. Out of the box, apparently the Mikuni VM38 is set up for use with the K&N air filter. Once I put it on, things starting a lot more normally. I installed the air cleaner, 34 jet, left the air screw at 1 1/2, lowered the slide a bit and now it starts just like any other temperamental XL. I'm still trying to dial in the best starting procedure, but the air cleaner seems to give it enough suction to draw the correct amount of gas.
I called Sudco to get some advice which was a wasted phone call. The carb came with 31,32,33(installed),34 and 35 sized jets. I asked the person who claimed to be tech support about the sizes and he told me they weren't marked as such (although I was looking at those numbers when I was talking to him) but are identified by 2.5 increments. I don't know if he was thinking of the slides or the jets, didn't matter, no help there anyway.
What was really throwing me off was my my '65 with the exact same carb set up(velocity stack) starts on the first kick with the enrichment lever down. 5 feet away, the same set up on the '62 wouldn't start with a velocity stack.

Thanks for all the tips. I learned a lot.
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Re: Hard Starting Mikuni on a '62 XLCH

Postby 55panman » Wed Feb 06, 2019 11:09 pm

JOe, If you run a Mikuni without an air cleaner you are ASKING for a FIRE!!! Sooner or later it will, especially on a Sportster, it will backfire through the carb and if it does there's a good chance of it blowing gas and a flame out the carb throat. Then your carb is on fire. Just saw a guy on a Brit facebook site that burned his Triumph down when it backfired with no air cleaners on his Mukunis. Beware!!
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Re: Hard Starting Mikuni on a '62 XLCH

Postby jOe » Wed Feb 06, 2019 11:39 pm

Yes, that’s absolutely solid advice. I’ve had an M-53 and a Tillotson catch fire- both times I got lucky. Especially with the Tillotson- that was on a ‘56 KR. Both times I ripped off my shirt and smothered them out.

There’s an old saying around Northeastern Nevada and Southern Idaho -“You’re as wrong as if you burnt your shirt “. It goes back to cattle branding, but I guess it’s applicable here.
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Re: Hard Starting Mikuni on a '62 XLCH

Postby 55panman » Thu Feb 07, 2019 1:43 am

JOe, Yeah, back when I was younger and dumber, (than I am now), almost 50 years ago, I had a Mikuni on my 1955 Panhead with no air cleaner. Anyone who has ever kicked a Pan to life will know that they can kick back occasionally. So at bar closing we're heading to a party and there's a few people standing around watching me kick start the Pan after bragging it's a one kick starter. Of course about 6 kicks later it pops back with a belch of flames and blows the carb off. The people holler and jump back and the carb, on fire, is swinging back and forth on the throttle cable from the apehangers. Needless to say I put an air cleaner on the next day.
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