Topic: No start...its spring...PD Carb

[Sdsbassist]

So had carbs off 5 times in 3 days. Thought I cleaned them really well. Used an air compressor to blow out holes.

When I put in fluid runs for 2 seconds than dies. Pulled out a plug and sparks great. No airbox on it right now, but will put it on when it runs consistently.

Someone enlighten me on what I am doing wrong. Seems no matter how many times I take these carbs off, I miss something

[Vinhead1957]

Check you petcock to make sure it is no clogged!   This can also be checked by removing one of the bowls to make sure it is getting fuel to that at least

[flybox1]

OK...how many threads are you going to start with the same subject? 
I just posted a bunch on another
stick to one thread so we're not jumping between several.

[flybox1]

lets stay on this one.

If those spray gas directly into the engine when you twist the throttle, that would absolutely affect starting wouldnt it?

DG

DING DING DING DING!!
we have a winner   

those are the nozzles for the accel pump.
In a functioning accel pump system, when you actuate the throttle, the pump squirts fuel out these nozzles into the carb throats.  it should be a forceful squirt.
helps with better accel from a stop, and also primes the carbs for cold starts.

dig into the accel pump system. 
start with carb bowl #2.  remove the smaller bowl on its lower edge.  note the path of fuel into and out of this small bowl, and how it gets to these brass nozzles.
note the check valves and which way fuel does and doesnt flow, and the path

[flybox1]

During normal startup it's not used. Only time it is "spraying gas" is during "QUICK" throttle use. On carb #2 there is a small "pump" that is part of the fuel bowl. It has an arm that runs up through the outside of carb #2 and is only activated during "QUICK" throttle twisting/usage. Hopefully others with way more knowledge will add to this.

during startup is SHOULD be used  so you're not relying on carb vaccum alone to start the bike.
one of the nice things about PD carbs 
choke knob pulled.
1-2 twists of the throttle to prime the carbs
kick it or hit the starter.
off and running 

[flybox1]

Its all part of the learning process...take your carbs off, and complete each of these.
ensure you have good flow of gas out of your petcock.
does your tank have debris in it? 
the bandaid argument for or against inline fuel filters you and others can get into later, but for now, add an inline fuel filter.  we need to ensure the gas your carbs are getting is debris free.
do all carb bowls fill with gas when you turn the fuel on at the tank? if no, find out why and fix it.
take off carb bowl #2.  your accel pump rod should have to slide out of the carbs as you pull the bowl off.
 is there a small oring on the top of the carb bowl? 
now, take the accel pump bowl off.
inside there should be a spring. under the pump diaphragm.  is the spring missing?

Carb Bowl #2 check valve
pick up carb bowl #2...look where the accel pump mates to it at the bottom.  there should be a tiny hole, that leads out of the top of the carb, where that tiny o-ring sits....can you spray carb fluid into the bottom of the bowl, and have it shoot out the top? this is to verify that the check valve at the top of the bowl is not clogged.  does it spray through?

accel pump bowl check valve
there is another check valve in the bottom of the accel pump bowl.
two small holes along the rim of the accel pump bowl.  one leads into the bowl, the other leads to the check valve. Indicated by the arrow.
spray into the one that leads to the check valve. carb cleaner should spray through

accel pump nozzles
between each carb body, there are TWO fuel lines.
the lines closest to the center of the carbs are the main fuel supply lines directly from the tank to the bowls.
there are three smaller lines, on the carb intake side, which feed fuel from the accel pump, directly to the accel pump nozzles.
each of these tubes have small brass inserts.  they are there to decrease the volume of the tubes allowing for a better nozzle squirt.  its a good time to remove these and ensure there is no debris clogging them.  I replaced mine with clear.
these tubes attach on each end to barbs.  spray carb cleaner into them and watch for spray out the nozzles. 

[flybox1]

Assuming that your pilot jets, main jets, and emulsion tubes are spotless, and free of debris, AND your floats are properly set....  we will continue

if BOTH of the check valves squirt clean
and
all nozzles squirt forcefully with carb cleaner shot at the accel pump fuel lines,
Replace all accel pump connector lines including the brass restrictors
Reinstall the acel pump bowl and spring onto carb bowl #2
Reinstall the small oring at the top of carb bowl #2 and install the bowl back onto the carbs with the rest of the bowls.
Without attaching the carbs back on your engine, attach your tank fuel line to them and let the bowls fill.
Actuate the throttle bell a few times, you'll see it depress the accel pumps brass diaphragm post... and look for fuel to slowly start priming the accel pump circuit. 
After 10-12 pumps, the circuit should be full, and gas should be squirting out the nozzles with each actuation.
If they do not, find out why.

Plenty for you to work on.
Dont put your carbs back on until this works perfectly!!!!

[flybox1]

keep us posted, then we can move on to the fast idle cam   

[flybox1]

So I am feeling like im missing the oring and the diaphram isnt too healthy either.







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Hey boss!
Two things to remember here on the forum.
First, Dont derail someone else's thread with your issues.  Start your own thread.
Second, start one thread, and stick with it until your issue is fixed.  Starting another, just makes us bounce back and forth and less likely to answer as you're all over the place.

As per your pictures above, that diaphragm wouldnt keep the prom queen from getting prego.  Replace immediately.

[flybox1]

insert your NEW diaphragm onto carb bowl #2, make sure the mickey mouse ears match up to the holes, then put the spring IN the accel pump bowl.  attach the accel pump bowl to the carb bowl with the three screws

[Sdsbassist]

Sorry didnt mean to hijack! I will clean up my mess later tonight and will post everything on this thread.

Airbox: am I missing the other o ring?



hanks all!

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[Airborne 82nd]

So I am feeling like im missing the oring and the diaphram isnt too healthy either.







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Hey boss!
Two things to remember here on the forum.
First, Dont derail someone else's thread with your issues.  Start your own thread.
Second, start one thread, and stick with it until your issue is fixed.  Starting another, just makes us bounce back and forth and less likely to answer as you're all over the place.

As per your pictures above, that diaphragm wouldnt keep the prom queen from getting prego.  Replace immediately.

  I must have missed something.
@ fly where did you get the clear fuel line with the restrictors from?
"Without attaching the carbs back on your engine" best advice so far. Quit putting the carbs back on. Do all your checks on the bench.

[flybox1]

THIS IS IMPORTANT!!!!!!!

FIRST.  your accel pump bowl is missing the check valve.  it wont work without it.
contact members harisuluv or SOHC Digger and see if they have an extra one to sell you.

SECOND, yes you are missing the o-ring at the top of your carb bowl.

 @ Airborne 82nd - the clear fuel line is generic fuel line, and the brass restrictors are ones i made because the PD carbs on my 750 had these removed at some point. 

[Airborne 82nd]

THIS IS IMPORTANT!!!!!!!

FIRST.  your accel pump bowl is missing the check valve.  it wont work without it.
contact members harisuluv or SOHC Digger and see if they have an extra one to sell you.

SECOND, yes you are missing the o-ring at the top of your carb bowl.

 @ Airborne 82nd - the clear fuel line is generic fuel line, and the brass restrictors are ones i made because the PD carbs on my 750 had these removed at some point.

What is the inside diameter of the brass and are they all the same?

[flybox1]

If you are missing the accel pump fuel line brass restrictor tubes, go buy some 3/16" OD brass hobby tube

Between carbs 2&3, you'll want two pieces @ .450" ea
Between carbs 1&2 (and 3&4) you'll want 1 piece @ .350" and 1 piece @ .450"
(1 short and 1 long in each fuel tube)

 

[Sdsbassist]

Its all making sense why this thing wont start...

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[Sdsbassist]

Its been said I am "missing the check valve."

I've done some forum searches and images..is it something Im missing from my first picture?

[Sdsbassist]

I think I have it, its just gunky. Heres a better picture. I can blows.air through, but not out.



If this is right I should just need the o ring and diaphram kit.

Any takers?

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[Sdsbassist]

I'm thinking this kit would be appropriate for what I need to fix?

http://www.siriusconinc.com/pro-detail.php?pid=&product_id=1094

Diaphram, O ring, spring?

[flybox1]

Yes, you have the check valve.  Couldn't see it in the first picture, but it's there.

That kit looks like the correct one.
Can you shoot carb cleaner through the check valve in the accel pump bowl?
Be sure it's not clogged.  See the arrow in my above picture.

Can you shoot cab cleaner up through the check valve in the top of the carb bowl?
Both must spray carb cleaner easily...

[Sdsbassist]

I will check it out and pick up the kit in the morning. Wish someone in the States sold the kit with the o ring.

Im hoping this helps get my bike started. Its getting too nice to sit in the garage.

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[flybox1]

I will check it out and pick up the kit in the morning. Wish someone in the States sold the kit with the o ring.

Im hoping this helps get my bike started. Its getting too nice to sit in the garage.

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The kit is sold by many vendors, but without the o ring.  Just go to an auto store and buy a $.50 viton o ring that fits...

CB750supply.com
4into1.com
Vintagecb750.com
Z1enterprises.com

[Sdsbassist]

Thanks everyone for the help. Ordered it this morning, should be here early next week.

In the meantime I will replace the cross tubes with new tubing, and clean the brass inside of them...then we will see what happens!

[pmurph1x]

Not sure about spraying carb cleaner where it can contact the diaphragm. I had a working accel pump and then sprayed carb cleaner into the holes to make sure all was clean. When I reassembled everything I found that the accel pump wasnt working. When I opened it up to Inspect I found that the diaphragm was all cracked and brittle. I have to think this was caused by the carb cleaner.

See this thread for pics: http://forums.sohc4.net/index.php?topic=122543.5

[Sdsbassist]

No im all kinds of screwed. thr thing was totally blocked so I PB blasted it the slowly worked it out and SNAP!



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