M74 Question
-
- Member
- Posts: 61
- Joined: Wed Jul 07, 2010 11:48 am
- Bikes: 1924 F
1929 F
1930 V
1942 WLA
1946 FL
1949FL
1957FL
1968 FLH
1984 softail
1993 Sporty (Buell engine) - Location: Australia
- Has thanked: 1 time
- Been thanked: 2 times
M74 Question
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
-
- Senior Member
- Posts: 6937
- Joined: Sun Feb 10, 2002 2:30 am
- Bikes: -
- Location: Central Illinois
- Has thanked: 112 times
- Been thanked: 310 times
Re: M74 Question
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? .....Cotten
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? .....Cotten
You do not have the required permissions to view the files attached to this post.
-
- Senior Member
- Posts: 6937
- Joined: Sun Feb 10, 2002 2:30 am
- Bikes: -
- Location: Central Illinois
- Has thanked: 112 times
- Been thanked: 310 times
Re: M74 Question
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
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