any carb experts?

alk

alk

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My inboard ski boat died on me last week, and having a hard time figuring out the problem. it ran fine a few weeks ago, but did stall once and took a while to restart. Let it sit a few weeks, now it will start right up, but won't idle at any speed.

It seems to be starving for fuel. The pump, lines, tank, filters, etc. seem to be fine. I get fuel to the carb, as evidenced by the fact that when I pump the throttle, I get nice spray of fuel into the carb. And it will start right up after a pump. But only way to keep it running, whether at idle speed or WOT, is if I keep pumping the throttle. Within second or two of letting throttle stay still, boat stalls.

So I figured the carb would be a dirty mess. But when I pulled it apart, looks very clean inside. Nothing looks clogged up, float is fine and adjusted more or less within spec. I sprayed it out with cleaner, replaced the filter, and tried again - but same. What could i be missing here?

Carb is rochester quadrajet, 17080562 series, on an sbc with mallory electronic ignition. I ordered a rebuild kit for the carb ($30), or I could take it for a professional rebuild at $200+, but not sure if I'm headed the right direction.

I was ready to bet that the anti-siphon valve on top of the tank was the problem, but replaced that with free flowing fitting until I get this resolved. No better. Tested the pressure and volume from the mechanical fuel pump, seems fine.

has anyone seen similar problem?
 
Have you taken a fuel sample to check for water / phase-separation or just old gas? Does it still smell really fresh/gassy?
You might try temporarily plumbing in a CLEAN portable O/B tank of fresh new gas to the fuel pump inlet before using the carb rebuild kit.

Is there any fuel in the semi-clear Tygon tube to the carb from the mechanical fuel pump safety outlet in case of bad diaphragm there?

What does the inside of the dist. cap look like? Flame arrester Clean? Spark plugs?

Is the carb-to-manifold gasket intact and carb bolted down tight?
 
I was thinking vacuum leak somewhere, but this motor has run flawlessly for me for past 15 years - albeit in another boat, with different ignition, but it ran fine after swapping to this boat for 1.5 years. So I don’t think anything like bad mounting of the carb.

I drained every last drop of old gas last winter, and blew out some crud from the tank with compressed air. I think the gas is good, because when running via pumping the throttle, it starts at barely a click of the starter, and sounds fine. But I do have an aux tank somewhere, will probably give that a try.

I only pulled the number one plug, to see if the timing was correct. It had what I think is a proper grayish tint to it, not too wet, or black,
 
Take a look at a spark plug, does it indicate rich (black, wet)? If so, could be a carb float problem. i.e. float is soaked and rides too low.
What kind of choke do you have? Make sure it's not malfunctioning and closing during operations.
Sandy has good input on the gasket.
Carb rebuild is probably in your future, but you could try to run some seafoam through the carb, I've heard of good results with this. Fill your fuel filter with seafoam and start the engine.
Do you have a vacuum gauge, or can you get a loaner from an auto parts store? Vacuum readings as engine is laboring and shutting down will give good info.
 
Sounds like the idle circuits are plugged up . May need a professional ultra sonic cleaning
 
quote:
Originally posted by alien1952

Sounds like the idle circuits are plugged up . May need a professional ultra sonic cleaning

Click to expand...


that's what I'm thinking. I did clean out every passage in the carb with cleaner, jammed some welding wire through the ones too small to spray the cleaner, followed with compressed air.

Assuming I didn't blind myself with all the cleaner sprayed back into my face, I'll put it all back together tonight, and give it a try this weekend running with new gas off clean tank. If no luck, I suppose the carb is off to a rebuilder. Which may be a season ending injury. thanks.
 
It’s a good thing I don’t make a living as a mechanic, or I’d be broke.

Put the carb back together after cleaning it out, with most of the parts from the rebuild kit. Back on the boat, and exact same thing, starts right up, but dies after one or two seconds. If I violently pump the throttle, stays running for five or so more seconds. Ran a piece of fuel line from a can of brand new gas straight to carb, no change.

So now I’m thinking it’s not fuel, and start yanking and feeling around the ignition wires. And the side of my coil is wet with oil, leaking out a crack in the top. Quick trip to the parts store for a new coil, and I’m back. Idles as long as I like at 700 rpm. Wasted a week, and few dollars for the carb kit. Worst part is that I must have run over something on the way to the parts store for the coil, because when I came out my tire was flat! The 200 for a tire was almost equal to the purchase price of the darn boat. Oh well,..
 
Well it's usually NEVER the coil...so you got lucky in that it was not some oddball problem no one can figure out. I also rebuilt my Q-Jet last summer and it runs 100% better. A good resource for Q-Jet information is:
www.cliffshighperformance.com
they have a good forum that you can ask questions on...
 
Alk- In spite of the flat tire part , that's good to hear you were able to fix it with a coil replacement .
For future reference, you can test the coil resistance in the primary and secondary circuits. Check the coil topic in GVP's Mechanical How-To forum here.

But feeling the leaky wetness is always a pretty good clue! :D
 
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