69 FLH more running issues

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panhead_kicker
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Re: 69 FLH more running issues

#16

Post by panhead_kicker »

Just got back from a few miles to test the Zenith. Bike still has a hesitant idle.. not the rhythmic thump thump thump. I can sneak up to about 45 mph, but much over 50 will cause coughing out the carb. Weak acceleration to that point.
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Re: 69 FLH more running issues

#17

Post by RooDog »

Fuel delivery.....
Gas valve, filter, and hoses clear?
Tank gas cap vent clear?
Need a larger main jet? eBay is a good source, around &25-30
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Re: 69 FLH more running issues

#18

Post by 59Panman »

My bike would run fine until the vibration increased with throttle. Turned out the bar and the contacts on the ignition switch were worn. I figured this out by switching to the headlight position and all issues went away. Try running in the headlight position?
panheadrider1961
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Re: 69 FLH more running issues

#19

Post by panheadrider1961 »

Mark timing plate and pull it you still to me and I may be wrong have a broke advance spring or enlarged holes in weights thus giving you no advance in timing to run smooth
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Re: 69 FLH more running issues

#20

Post by panhead_kicker »

I'll check to see what the main nozzle size is stamped. Pulled the right fuel cap and cleaned out the vent porting a couple days ago, plus replaced a clear inline fuel filter with an in-tank filter on the top of the petcock. All new fuel hose (Auto stores around here having difficult time getting fuel hose!). So fuel runs well into a cup when I open petcock. But, I will say this... three carbs all behaving similarly? Hmmmm... I just don't know where else to look. A valve possibly? I did check compression the other day. 105 front and 120 rear. Looked ok to me.

I run the bike without lights, until I see a car and that reminds me to switch them on. There is no change during or after switch transition. Pretty certain the switch is in good working order.

I did pull the timer top to have a look at the weights; all clean and limber. The points cam easily turns to the advance position against the springs, and snaps back when released. I ran the bike above idle speed on the stand and strobed it, got the flywheel line dead center in the hole, after moving the timer head a hair. (And that’s with a 20 thou gap on the points, Robbie :) )
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panheadrider1961
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Re: 69 FLH more running issues

#21

Post by panheadrider1961 »

Ok good advance richen the mixture on the bendix it may be running to lean
RooDog
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Re: 69 FLH more running issues

#22

Post by RooDog »

You have to replace the jet tube that screws down through the top of the carbby to affect the mid range. They come in three size designations: A, B, & C, lean to rich. I had to go from an A to a B on my 1950 Panny to relieve a mid RPM stumble. If you have an adjustable main jet, I don't know what to tell you....
....RooDog...
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Re: 69 FLH more running issues

#23

Post by Mongrel505558 »

So far I haven't had any difficulty tuning the adjustable main jet, but since you have a fixed jet I won't go into that. One question that comes to mind is where did this particular carb come from? I ask because the Bendix carbs were also used on Sportsters in the early seventies. There were two standard sizes - 36mm, used on Sportsters, and 38mm, used on Big Twins. The idle tube for the Sportster carb is smaller.

The Bendix has a simple and rather interesting design. It doesn't have a low speed or intermediate jet. Instead there are four tiny holes (earlier had three) inside the top of the carb body near the butterfly. An internal passage connects these holes (Bendix calls them transfer ports) to the idle tube. The hole closest to the manifold has the mixture screw in it. The other three are uncovered in succession by the butterfly as the throttle is opened and engine vacuum draws fuel from the float bowl up through the idle tube into the connecting passage and out through those holes. That's how idle-to-intermediate operation is handled by the carb. By the time the fourth hole is uncovered there's enough venturi effect to start to draw fuel through the main jet (annular area around the idle tube). If those holes or the passage feeding them are in any way obstructed the motor will sneeze and miss, etc. Getting back to the idle tube - if it's too small it can't deliver enough fuel to those holes to meet engine demand. The "A" idle tube is 0.60mm ID and the "B" is 0.65mm. You'll find the letter stamped on the "screw head" of the tube on the outside top of the carb. The adjustable main jet is really just an idle tube with a taper and seat on the bottom. Raising or lowering the taper into the seat adjusts the main jet area.

Everything you wanted to know about the Bendix carburetor (thanks to Roo Dog for sending me the link many moons ago):

http://sportsterpedia.com/doku.php/techtalk:ih:carb01k

I know that's a lot of running on about the carb's operation, but I didn't know much about them until I decided to run one, and I like to know as much as possible about how things going on my bikes work. So far it's paid off with a smooth running motorcycle. Hopefully some of it will help you, too.

Jim
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Re: 69 FLH more running issues

#24

Post by panhead_kicker »

I think I bought this carb new in box back mid 90s. Don’t recall for sure. Here are pictures. Only the idle screw is available. Also a pic of main nozzle info. Are the two small holes in the end of the carb important? Look like blind ends, gasket covers them.
0844BAED-5DB8-4287-9522-E038D0960D19.jpeg
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Re: 69 FLH more running issues

#25

Post by RooDog »

I do not believe the two holes on the base flange do anything.
This is a newer production carb with the fixed mid range/low speed tube in place. I know nothing about these.
I got my older Bendix off of eBay for less than $50, and it cost very little to get it running with the original main jet, and changing the low speed tube, made it all happy and fuzzy feeling, but sorry, no unicorns & rainbows....
....RooDog....
How It Works, Idle Discharge.jpg
How It Works, Main Discharge.jpg
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panheadrider1961
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Re: 69 FLH more running issues

#26

Post by panheadrider1961 »

-72b big twin and sportster carb 38 mm fixed jet ,several oe used on ebay under 75 bucks ,yes drill holes blind spots, carb should be good for 74 cu richen mixture screw till you hear idle start to count as a shovel does ,turn idle screw to meet sound, have you checked free play in throttle? 1/8 travel before pull on cable tightens on throttle shaft, check idle air circuit on front ring of carb where air cleaner gasket goes may have something in it from sitting , and air cleaner what type ? needs to breath as much as possible with low restriction filter do you still have O.E. oval ? all this in consideration hope this helps
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Re: 69 FLH more running issues

#27

Post by panheadrider1961 »

one more thing pump roll pin usually ran in second hole on pump rod, is it free when opening throttle ?
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Re: 69 FLH more running issues

#28

Post by panhead_kicker »

panheadrider1961 wrote: Sat Sep 03, 2022 6:57 pm -72b big twin and sportster carb 38 mm fixed jet ,several oe used on ebay under 75 bucks ,yes drill holes blind spots, carb should be good for 74 cu richen mixture screw till you hear idle start to count as a shovel does ,turn idle screw to meet sound, have you checked free play in throttle? 1/8 travel before pull on cable tightens on throttle shaft, check idle air circuit on front ring of carb where air cleaner gasket goes may have something in it from sitting , and air cleaner what type ? needs to breath as much as possible with low restriction filter do you still have O.E. oval ? all this in consideration hope this helps
Ive not run a filter with the bendix yet, open to the breeze. Pretty certain i had the idle needle adjusted for smoothest idle. Started at 1.5 turns out, and that was very close. idled in very small range of needle movement. But like i said, hesitant ide and what i believe to be very lean mid range. I did find another nozzle in my stuff, has a " 24" printed on the bottom, cant read anything else. I may give it a shot. But still, it sounds like this carb and current nozzle ought to be sufficient for my .030 over but otherwise stock motor. As i recall, it ran ok on my 74" pan for several years. I even bubble tested my manifold again as a double check.
Bike has me stumped. ( Extra M74B on wall looks tempting, no manifold...)
Could a valve issue, say a collapsed hydraulic cause symptoms like this?
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Re: 69 FLH more running issues

#29

Post by RooDog »

Collapsed hydraulic is a non issue. Just adjust it like a solid, and move on....
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Re: 69 FLH more running issues

#30

Post by panhead_kicker »

RooDog wrote: Sun Sep 04, 2022 5:53 am Collapsed hydraulic is a non issue. Just adjust it like a solid, and move on....
Non issue as in it would not cause the symptoms?
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