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Blocked idle circuits

J

jackman

Contributing Member
"Idle circuits choked up/block

"Idle circuits choked up/blocked on Quadrajet carb' on Mercruiser 228 engine. If I was to take the carb' off, lay it on its side and spray WD40 into the needle adjustment holes and leave it soak for a while and then blow through with an airline would I achieve anything?"
 
"I soak the carb after disasse

"I soak the carb after disassembly, in a good soak solution bought at any auto store maybe berry's. Let it soak for a good hour or 2, blow dry. Can of carb clear with the jets out all thru every freekin hole, blow dry, repeat the carb cleaner and blow dry.

The kit your using should be carb specific and a new bearing maybe, the accelerator pump new, with the kit needle and needle seat new.

Check the float that there is now pin holes or rusted thru make sure.

Set it right the float with the included ruler and reassemble.

Inset the adjustment screws gently when they go all the way in gently do DO NOT BEND THE ENDS.

Out a turn and a half to start and then your ready to set the carb.

Set the gaskets dry.

Good luck !

Let us know how you made out."
 
"[b]"would I achieve anyth

""would I achieve anything?"

Ayuh,... Probably Not....

There's No short cuts to be taken when a carb Rebuild is in order..."
 
Frank
What symptoms are you e

Frank
What symptoms are you encountering with the engine that leads you to suspect the idle circuit.
Bert
 
Thank you all for your help. S

Thank you all for your help. Symptons are that adjusting idle mixture needles has no effect on revs. I'll follow the advice and disassemble the carb rather that try a short cut. Can't get to it for a couple of weeks though but will post a message when job done. Thanks again everyone for the advice.
 
That's a good indicator of

That's a good indicator of an idle circuit issue; full overhaul is probably in order.

Pulling the idle tubes is the best way to ensure those passages are clear in the main body. You can poke them out with wire if not varnished solid. Compressed air afterwards with the main jets out is the other needed task.
 
"The idle rpm is down under 65

"The idle rpm is down under 650 when you tried to adjust those screws, wasn't it??"
 
If I back down to 650 idle eng

If I back down to 650 idle engine cuts out. Have to idle at 800/900 revs or engine cuts when I engage gear. It ticks over at 650 in gear. Its an old engine 1978/80 from memory.
 
"Yes, they are old.

Did you

"Yes, they are old.

Did you try the screws in gear or at 800-900 rpm?

Very possible, at 900 rpm +/-, the transfer slot or main system are turning on. when that happens, the mixture screws will do little if anything.

You can always back the idle speed down to make the adjustment."
 
"frank norris
Shut the engine

"frank norris
Shut the engine off, back off the idle speed and reset the idle screws out 1 1/2 turns from being seated. Keep the idle speed as low as you can and then set the idle screws."
 
"My rule of thumb for carb idl

"My rule of thumb for carb idle adjustment is this.

If you can set the main idle screw adjustment so the engine will idle at or near 400 rpms without stalling then your carb is typically OK.

Not to say the accerator curcit may be bead but the overall idle curcit is ok.

I would adjust the main idle to Aprox 500-550 rpms. Now try to adjust the idle mixture screws one at a time.

Turn in slowly until engine stumbles, then turn out until max rpms are reached. repeat for other screw.

If you can not idle down to ~ 500 rpms then you have an issue. If you do idle down and still no reaction when adjusting a/f screws then you have an issue.

When you have the main idle set to high you may not get a change when adjusting a/f screws."
 
"Kghost:

Think most of us c

"Kghost:

Think most of us concur on your receipe.

What are you getting at with "Not to say the accerator curcit may be bead but the overall idle curcit is ok." ?

When the idle speed is too high, you won't get any control with the mixture screws as the bulk of the fuel will feed from the transfer slot and/or the lower idle air bleed. With BBC's, this usually occurs by 900 rpms, a definite at 1000."
 
"Makomark,

I was referring

"Makomark,

I was referring to the idle may work and be affected by A/F mixture screws but under acceleration you may get a burp or hesitation that would indicate a bad accelerator circut/pump.

I was kinda thinking a bit ahead of myself and saying if the idle is ok there could still be some other issues......I had a lot going on today as I was doing parts research on line/and by phone for my Harleydavison motor build I am starting and also dumping my land line phone while transfering my land line phone number to my cell phone and notifing all my cell phone contacts that it was changing etc etc etc.....

I was a bit rushed.............and not paying strict attention to all my words vs thoughts........LOL

I'm a bad speller and to damn lazy to spell check I guess!!"
 
Thanks for the info' kghos

Thanks for the info' kghost and makomark. As I've tried all suggestions I'm going to take the carb' off and rebuild it.
 
""""idle a bbc at

""""idle a bbc at 400 rpm's ???"""

Not as a final setting but when doing a integrity testing, it should idle that low, If not then there is something wrong (vaccuum leak etc.etc.)

At least they have for me in the past...........

Besides a 454 or 502 with thru transom exhaust and NO mufflers idleing at around 500 rpms sounds coooooool!!"
 
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