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OMC Factory carb jets

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ridemywideglide

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"I'm hoping someone has &#

"I'm hoping someone has (or can link) the factory spec carb jetting info for a 1979 OMC 260.
I've been through the QJ twice, it seems well, but I replaced the original MR43t plugs with the NGK equivalent and I keep getting light black smoke at idle. Trolling for 45min totally ruined the new NGK's and they wouldn't even pass spark.
Had to put in some used auto plugs to get it running again.
Trying to pin down rather it's running rich=fouling plugs, or if it's incorrect plugs=fouling plugs.
I crossed the MR43t to the NGK BR6FS, this correct?
I've just never had bad luck with NGK's before, but since I changed the plugs (and tossed the originals) it's been hell..."
 
"Go back to the ac mr43t plug

"Go back to the ac mr43t plug gapped correctly. napa has them

Then do a vacuum test, and a compression test, this way we will know whats, what.

want to email me the result? You know the address.

but i personally would pop for the 9 bucks or so for a new set of plugs, the ac ones, never had problems with them, and with ngk i have seen burnt off tips, nothing left of the tip. seen deformed tips, all kind of stuff, even cracked ceramic right down the middle when i tried to remove them."
 
NGK plug are only good in ....

NGK plug are only good in .............................................................. Let me think now ???????????????????????????????????????????? It comming to me ?????????????????????????????????????????????????? Not a darn thing.

That's the luck I have ever had with NGK spark plugs.
 
"LOL.. I've always run th

"LOL.. I've always run them in my bikes, both dirt and street, and never had any issues.. I won't use them in the boat again..

Maybe I should send you the cash Chief, Napa wants $4.50ea for them here.. I'll check the others and see what I can find."
 
no i just bought 4 for under 1

no i just bought 4 for under 10 bucks i got change back from a 10 just at the beginning of the summer.

Napa and it's right next to a west marine i think they wanted more.

nj aint known for being cheap.
 
Napa in general ain't know

Napa in general ain't known for being cheap. I got down there and they said the number they gave me on the phone was for a cross-ref plug. I paid $2.09ea for the AC/Delco part. Maybe they quoted the rapid-fire on the phone....

I'll find out this weekend what difference they make.
 
"No doubt.. We'll see how

"No doubt.. We'll see how it does tomorrow. I'll check in sometime this weekend with the good or bad...

"
 
"Same result... 45 minutes of

"Same result... 45 minutes of trolling all but ruined the new mr43t's.. Hopefully I'll be able to clean them back up enough to run again.
Pulled the carb and I've got a 70/40 main/needle combination. I'm going to try "resizing" the needles to 44 and see how it does, then buy a set once I get close. It's clearly not the plugs, but the carb causing the issue.
Anyone have a source for used jets/needles for "170" quadrajets?"
 
what RPM do you troll at?

H

what RPM do you troll at?

Have you checked to see if the primaries' nozzles drip while trolling?

Were the idle tubes open when you were inside?
 
"It holds about 650 when the p

"It holds about 650 when the plugs are new. I've not noticed them dripping, and the idle tubes clear. I soaked it twice overnight and then followed with carb cleaner/air.

I just need less fuel on the low end at least, and possibly on top too, but that'll come later."
 
"You may be able to get a pair

"You may be able to get a pair of 42 rods easier than 44's.

Did you change the float? what is the float setting?

If the primaries aren't dripping, check the secondary POE outlets to see if they are dripping. Should be right under the forward edges of both air valves."
 
Everything is clean. The float

Everything is clean. The float is at .6" travel at the front of the float.

The idle mixture screws on the front have no effect what-so-ever. That and the fact that it constantly puffs black smoke while trolling pretty well leaves me at the needles.
 
"If the idle mixture screws ha

"If the idle mixture screws have no effect and your puffing black smoke, the idle loop is too rich. Changing the rods won't make any difference at idle but will help once the transfer slot is fully exposed.

Are you certain the upper ridle air bleeds are open??? How about the lower idle air bleeds?

What do you mean by "0.60" travel at the front of the float"?"
 
Maybe you should google some i

Maybe you should google some info on the quadrajet.
The needles ARE what controls the idle circuit.
The primary metering rod determines fuel mixture at cruise speed and determines responsiveness of the idle mixture screws and off-idle performance.
 
"Obviously, your knowledge of

"Obviously, your knowledge of the idle system in a quadrajet must exceed mine and by a substantial amount.

Maybe the third time thru yours will be "the charm" - good luck."
 
"It's not about "char

"It's not about "charming" anything. It's about my research to fix the problem.
This will be the FIRST time I've changed the jetting. But here's a little tidbit from Lars Grimsrud's papers on the Qjet... I'd suggest you google it and read up.

"The idle metering circuit on a Q-Jet is not an independent, stand-alone circuit. The idle mixture screws in the throttle plate receive their fuel through the main metering jets. Thus, a change in the main metering circuit (jets and/or rods) will affect the idle circuit. The idle mixture screws cannot meter more fuel than the main jets/rods will allow. Thus, if your Cruise Metering Area jet/rod combination is too lean, you may find that your idle mixture screws are ineffective. If your idle surges, is rough & unstable, and adjusting the screws seems to make no difference (but you can kill the engine by turning them all the way in), chances are good that your cruise metering area is too lean. You can verify this by running your mixture screws out to the point where additional turns have no effect on idle. Then cover the choke area of the carb with your hand. If idle speed & quality increases as you restrict the air flow, your jet/rod combination is too lean.""
 
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