M74 Question

Linkert related issues
Post Reply
Johnno
Posts: 60
Joined: Wed Jul 07, 2010 11:48 am
Bikes: 1924 F
1929 F
1930 V
1949FL
1957FL
1942 WLA
1946 FL
2014 Ultra
Location: Australia
Been thanked: 2 times

M74 Question

#1

Post by Johnno » Mon Mar 24, 2014 8:15 am

I have a M74 on a 53FL & according to all info on how to tune low speed mixture screw should be 5 turns out as a starting point & adjust from there. To get it to idle properly I have it just over 2 turns out. Is this normal? Is it getting fuel through another port/casting fault, should I dismantle & blow out all the ports? I have bubble tested manifold & set float level 1/4". High speed mixture 1 1/4 turns. Points timing etc spot on. Bike runs well on road & will accelerate away in 4th gear from a low speed with no hesitation or miss. Just seems odd to have L/S screw so far in (anywhere near 5 creates black smoke & very rough idle). Thanks in advance. Regards Johnno



Cotten
Posts: 6911
Joined: Mon Aug 26, 2002 9:09 am
Location: Central Illinois
Has thanked: 100 times
Been thanked: 268 times

Re: M74 Question

#2

Post by Cotten » Mon Mar 24, 2014 12:06 pm

Johnno!

I send all M74 and later B carbs out at 3½ turns on the lowspeed, and 3/4 of a turn on the high.
The manual's suggestion of five to start was probably to accomodate vacuum leaks.

Does your M74 have a stepped highspeed needle like the one in the middle?
STEPTIP.jpg
.....Cotten
You do not have the required permissions to view the files attached to this post.

Johnno
Posts: 60
Joined: Wed Jul 07, 2010 11:48 am
Bikes: 1924 F
1929 F
1930 V
1949FL
1957FL
1942 WLA
1946 FL
2014 Ultra
Location: Australia
Been thanked: 2 times

Re: M74 Question

#3

Post by Johnno » Tue Mar 25, 2014 6:50 am

Hi Cotton
Mine just has a taper to a point, no step. Cheers Johnno

Cotten
Posts: 6911
Joined: Mon Aug 26, 2002 9:09 am
Location: Central Illinois
Has thanked: 100 times
Been thanked: 268 times

Re: M74 Question

#4

Post by Cotten » Tue Mar 25, 2014 3:56 pm

Johnno!

I haven't one handy to inspect, but I seem to think the seat orifice was smaller for the stepped needle. There may have been a mid-production change, but certainly the wider tip should still adjust.

But it also may account for a wider setting.
The HS needles are notoriously insensitive, so if you get any tuning responses while slowly adjusting at a constant highway speed, you are ahead of the game!

(Please note that the LS reverses itself at highway speeds, to meter air instead of fuel, so some back-and-forth adjustments between the two may be necessary.)

....Cotten

Johnno
Posts: 60
Joined: Wed Jul 07, 2010 11:48 am
Bikes: 1924 F
1929 F
1930 V
1949FL
1957FL
1942 WLA
1946 FL
2014 Ultra
Location: Australia
Been thanked: 2 times

Re: M74 Question

#5

Post by Johnno » Fri Mar 28, 2014 10:58 pm

Thanks Cotton. If it ever stops raining I will fine tune. Cheers Johnno

Post Reply

Return to “Linkert”