Carb question for SBC

[pronstar]

The Volvo-Penta 260 in my boat is just a SBC 350, rated at 260hp.
It came with a Volvo-ized Rochester Q-Jet carb from the factory, and the one that's on there was rebuilt a while back.

The previous owner - a friend of mine - had used Q-Jets on the boat for years. He'd put a new one on ever few years, instead of rebuilding the carb.

Recently, the boat developed an idle issue (refused to idle, just stalled), but ran great from 1,100 rpm on up.

Checked the usual stuff...vacuum leaks...distributor...MSD box. Nothing helped.

We put two different Q-Jet's on, no matter what we tried it still wouldn't idle.
For shits and giggles, we put a Carter AFB on and now...runs and idles like a champ.

I'm glad I've got a boat that runs well, but this one has me stumped. I'm just curious at this point.

Any thoughts on WTF was going on?

[Racey]

sounds like idle circuits in the carbs are out of adjustment, or are clogged up.

Take it off the boat and Berryman brand carb cleaner every port on the thing, readjust the idle air bleed/idle mixture screws, watch your eyes when spraying that thing :D.

I'm no carb guru, but they are pretty simple deals, usually it's a dirt issue, or simple adjustment issue.

Berryman is the shit, the other brands of carb cleaner are doodoo usually

[pronstar]

I'm no carb guru, but they are pretty simple deals, usually it's a dirt issue, or simple adjustment issue.

That's weird the thing...we put two "new" freshly rebuilt Q-jets on, wouldn't idle on either of them. Cleaned the Q-Jet that was on there...no idle.

I'm sure we overlooked something, but it's a head-scratcher. Especially since it idled great once the Carter was put on there.

[Racey]

That's weird the thing...we put two "new" freshly rebuilt Q-jets on, wouldn't idle on either of them. Cleaned the Q-Jet that was on there...no idle.

I'm sure we overlooked something, but it's a head-scratcher. Especially since it idled great once the Carter was put on there.


Were the idle circuit screws all the way turned in? usually on almost every carb you turn them till they are bottomed out, then back out between 1 and 2 full turns (these the are screws with springs on them to hold tension). tighter is leaner on the early model quadrajets, i think the later model smog ones were the opposite.

[pronstar]

Were the idle circuit screws all the way turned in? usually on almost every carb you turn them till they are bottomed out, then back out between 1 and 2 full turns (these the are screws with springs on them to hold tension). tighter is leaner on the early model quadrajets, i think the later model smog ones were the opposite.

Yeah, we mucked around with these as well.

I bought the boat from a buddy, just odd that carbs he'd used for years - right out of the box - just didn't want to work anymore. We got the Q-jet to idle at about 1200 rpm...not particularly useful.

I'm going to chalk this one up to "owning an old boat". I hopeit runs well on the Carter, because at anything but idle, the Q-Jet ran great.

[Racey]

Yeah, we mucked around with these as well.

I bought the boat from a buddy, just odd that carbs he'd used for years - right out of the box - just didn't want to work anymore. We got the Q-jet to idle at about 1200 rpm...not particularly useful.

I'm going to chalk this one up to "owning an old boat". I hopeit runs well on the Carter, because at anything but idle, the Q-Jet ran great.
Very strange, hopefully someone pops in here with the answer to your question.

Another thought, maybe its a combination of butterflies being too far open or closed on top of the idle circuit.... damfino :D

[Yellowboat]

when you say fresh rebuild, did they use the wrong gasket set on them?

I had the same prob, took the carb apart to find a gasket blocking the idle circiuts.

[SS 201]

Years ago if the carb had backfired enough times it ruined melted a cam bushing or something.

[pronstar]

when you say fresh rebuild, did they use the wrong gasket set on them?

I had the same prob, took the carb apart to find a gasket blocking the idle circiuts.

We bought newly remanufacturered carbs, didn't do the rebuilding ourselves.

I'm guessing that both reman'd carbs had something going on with the idle circuits.

[DaveH]

had a boat the other day that idled like crap, turned out to be the plugs.

how old are your plugs? what does your ignition system look like? old wires, cruddy distributor cap and rotor?

not saying this is it, you just need to be certain you ignition is working 100%.

[pronstar]

had a boat the other day that idled like crap, turned out to be the plugs.

how old are your plugs? what does your ignition system look like? old wires, cruddy distributor cap and rotor?

not saying this is it, you just need to be certain you ignition is working 100%.

Plugs, wires and distributor were OK. Swapped them out and no dice.
MSD box was OK, hooked another one up and no dice.
Plus it all works fine with the Carter AFB on there.

[racerden]

The Volvo-Penta 260 in my boat is just a SBC 350, rated at 260hp.
It came with a Volvo-ized Rochester Q-Jet carb from the factory, and the one that's on there was rebuilt a while back.

The previous owner - a friend of mine - had used Q-Jets on the boat for years. He'd put a new one on ever few years, instead of rebuilding the carb.

Recently, the boat developed an idle issue (refused to idle, just stalled), but ran great from 1,100 rpm on up.

Checked the usual stuff...vacuum leaks...distributor...MSD box. Nothing helped.

We put two different Q-Jet's on, no matter what we tried it still wouldn't idle.
For shits and giggles, we put a Carter AFB on and now...runs and idles like a champ.

I'm glad I've got a boat that runs well, but this one has me stumped. I'm just curious at this point.

Any thoughts on WTF was going on?The thing that's interesting is your statement of installing another Q-Jet and it not idling either. Then the AFB worked...Either something was 'disturbed' when you installed the AFB or you definately have (2) internal concerns w/the QJ's. Contrary to belief, the QJ is quite a good carb especially for pleasure marine applications. Volvo Penta used these carbs almost exclusively and it's always best to retain the carb that came with the powertrain because of correct jetting, CFM etc. Best professional guess is it needs to be taken apart cleaned & calibrated correctly. Let me know if I can be of assistance. Shoot me a PM for futher details of overhaulng one.
Denny
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