carb blowing out fuel/air mix

Forum rules
Please do not start new topics here, but here: New Panhead and Flathead topics
Post Reply
ed53-+
Posts: 24
Joined: Wed Nov 06, 2013 1:17 am
Bikes: 1948 fl ,2007 softail

carb blowing out fuel/air mix

#1

Post by ed53-+ » Wed Nov 13, 2013 4:00 am

just got the 48 ready to fire, have spark, have fuel, timing ? close enough i think. problem is when i kickstart theirs a vacuum
and then there's equal blow out. making me think i have a bad manifold leak or theres leaky valves , before i put the motor together i poured gasoline in the heads and had no leaks. compression feels acceptable , i certain that im gear timed correctly
bendix carb i rebuilt. any suggestions ? out there. thanks for the help



kitabel
Posts: 882
Joined: Tue Aug 03, 2010 7:10 pm
Bikes: 2008 96" Fat Boy TC
Location: Lynbrook, New York
Been thanked: 88 times
Contact:

Re: carb blowing out fuel/air mix

#2

Post by kitabel » Wed Nov 13, 2013 6:03 am

Compression test results?

ed53-+
Posts: 24
Joined: Wed Nov 06, 2013 1:17 am
Bikes: 1948 fl ,2007 softail

Re: carb blowing out fuel/air mix

#3

Post by ed53-+ » Wed Nov 13, 2013 6:32 am

yup,thats happening tomorrow alonmg with a manifold vacuum test

58flh
Posts: 3338
Joined: Sat Jun 26, 2010 1:54 pm
Bikes: 1958flh 1969sporty,had a knuckle but sold back to original owner
Location: NEW JERSEY
Has thanked: 195 times
Been thanked: 259 times

Re: carb blowing out fuel/air mix

#4

Post by 58flh » Wed Nov 13, 2013 1:50 pm

You want the Manifold leak test!,Vacuum is another entity.--After your tests,check valves for correct movement,also which Bendix do you have & was it a straight-up rebuild?----You probably checked,but lokk down the throat of the carb. & make sure the pump-shooter is streaming down the center of the manifold.I have seen them faced the wrong way & with a Aircleaner on you cant see anything until it spills back out!--Also the 3/8-hole on the top front of the Bendix MUST NOT be blocked by a custom cover!--If it is blocked by the numerous custom aircovers out there -Just drill it & fire away.Just something to check!-I have seen this blocked-off a lot of times over the yrs.--Respectfully---RICHIE

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

Re: carb blowing out fuel/air mix

#5

Post by Cotten » Wed Nov 13, 2013 4:57 pm

ed53-+!

You meant "pressure test" and not "vacuum test" the manifold, right?

....Cotten

steve_wood
Posts: 947
Joined: Tue Jan 08, 2008 12:32 am
Bikes: 56 FLH, 2007 FLHRCI
Location: Belleville, Ontario, Canada
Has thanked: 48 times
Been thanked: 27 times

Re: carb blowing out fuel/air mix

#6

Post by steve_wood » Wed Nov 13, 2013 5:40 pm

Ed53-+

The manifold pressure test the guys have mentioned is definitely important.

That being said, I seem to recall that my pan did the same thing when it was kicked through. But it fires up just fine. Something to do with the fuel/air flow behaving very differently at slow speeds.

Have you tried actually firing her up? Couldn't hurt to try.....

old.wrench
Posts: 516
Joined: Sun Apr 24, 2011 4:29 pm
Bikes: '54 FL and a mini-bike
Location: in the garage
Has thanked: 3 times
Been thanked: 80 times

Re: carb blowing out fuel/air mix

#7

Post by old.wrench » Wed Nov 13, 2013 6:41 pm

Ed 53,
I wonder if what you are experiencing is just what normally happens when the timing is off a little (advanced too much?). If your timing is off you will get some blowback through the carb when you attempt to kick the motor over. It sounds like this is happening during your first attempts to start the motor after putting every thing back together. If you are setting your timing with a test light, after you set your your point gap and then bring your timing mark into the hole with the front piston coming up after the intake valve closes and set your timer with the light, try rotating the motor through a few cycles while observing the test light and valve and piston position to verify that you've got it just right. First start ups on a new rebuild can be a little tricky. Good Luck!

Geo.

rrhawg
Posts: 93
Joined: Wed Feb 20, 2008 4:59 pm
Bikes: 59 Pan, 65 Pan, 45 Wl, 46 UL, 41 Chief, 48 Chief, 50 Chief, 53 Hummer, 53 Simplex, and misc. others
Location: Newport, Oregon
Has thanked: 2 times
Been thanked: 2 times

Re: carb blowing out fuel/air mix

#8

Post by rrhawg » Wed Nov 13, 2013 10:02 pm

It sounds like it's possibly a leaky intake valve. A compression test or better yet would be a leak-down test. You can put pressure to the spark plug hole and see if air comes out the carb, the valves must be closed. You can put it to top-dead center and hold the brake on or taking the pushrods out works also. It could be that a pushrod is to tight or the cam timing is off also.
Rich

ed53-+
Posts: 24
Joined: Wed Nov 06, 2013 1:17 am
Bikes: 1948 fl ,2007 softail

Re: carb blowing out fuel/air mix

#9

Post by ed53-+ » Tue Nov 19, 2013 1:20 am

well i did a cylinder compression, and intake leak test. bad news, 30 psi at cylinders, no leaks in manifold, also i discovered that i hadnt torqued several of the head bolts, ( forgot to finish up after pre-torque sequence) . so i pulled the heads today
poured gas into the valve ports had some minor leakage in the intake, and theirs cracks in the sparkplug c.bore area.
so being an inside machinist of 20+ years , i should be able to deal with this, a friend does the valve jobs, and ill make sure
the surfaces head/cylinders are flat. thanks for all of your input
ed

Post Reply

Return to “Carburetor/Fuel system”