Volvo 5.7 Idle Creep

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Guest

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My buddy has a 1998 5.7 Volvo 5.7 GS with an Edelbrock mid rise, and an 850 double pumper. (this was the engine that ingested water due to dieseling)

The ingestion issue has gone away, but after idling thru a no-wake zone after about 5 or 7 minutes, the engine, on its own, will start to increase idle rpms all by itself, without touching the throttle.

There is no vacumm lines to leak, becuase the Holley 850 has mechanical secondaries, if there was a manifold or car base leak, the engine would not idel well at all.

My theory is this:
Since the double pumper keeps the secondary bowls full at all times, even at idle, Could a float be sticking to the point its starts to dribble fuel into the intake? thereby increasing engine rpm without any advance on the throttle?

When the engine is shut down, it diesels, but not to the point of water ingestion.

Am I on the tright track? or am I all wet?

Again, this engine had none of these symptoms last year, it ran great with no issues.

So I don't see how the timing could effect it,

One last thing guys, can somebody please tell me what adjusting the "dizzy" is?
 

Scott Danforth

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or your buddy could have the rear floats set too high.

since the boat is on an angle, you need to set the rear bowl float lower than the forward bowl.

the other issue is with too large a carb for the motor, or too small a motor for the carb, at idle the air flow "signal" is too small to accurately meter fuel.

all dieseling is bad, and if it diesels, the last few coughs are the motor spinning backwards.

dizzy is an old-school name for distributor, as in the aluminum thingy with the plastic cap on it that has all the wires going to the spark plugs.
 
G

Guest

Guest
I think you're on to something with the rear bowl float level, Scott.

Since this engine ran beautifully last year, I'm wondering if the rear float is hanging up, causing increased dribbling into intake manifold, increasing the engine speed with no throttle.

If thats the case, he needs to take apart the rear bowl asembly and check for crud.
 

Scott Danforth

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newer holley's use a rubber check valve on the accelerator pump. once you pull it thru the casting, you need to take a side cutter and remove the pull *** or it hangs the float up.

not to mention rear bowl in a boat, especially on hole shot gets surge-flooding from the sloshing in the bowl

another thing to check is the accelerator pump squirter check valves
 
G

Guest

Guest
I should also point out that the carb is not an 850, but a 750, (still a big slurpee for mouse motor, IMHO)

Could the accelerator pump squirter check valves, and the rubber check valve you mention, get bunged up from sitting during winter storage? It sems to ake sense that they would.

I laos tend to think his idle is too rich, which should stop the dieseling.

This much I know, my buddy loves doing hole shots because the engine has so much balls.
 

Scott Danforth

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yes.

my carb has the traditional ball type check valves and I had to pull the bowl off to free up the check valve in the accelerator circuit as the fuel in the bowl evaporated, leaving behind a bit of varnish which gummed up things. also had to pull the squirter and free up the check under the squirter

I have seen the rubber check valve get debris under it as well.

if his power valve is too small, it will run rich as well. since this is a reman'd motor some tuning would need to be done if its a pre 1992 carb, if there is a backfire, the power valve diaphragm usually ruptured. in 1992, the check valve was added. (there is a kit to update earlier holleys)

your buddy should have #64 or so primary jets and about #76 secondary jets as my first guess. would have to read the plugs.
 
G

Guest

Guest
This carb he has is, only a couple of years old. I'll have him check the float and and check valve.
As we both know, evaporated fuel over winter can reak havoc on carb internals.

Heres a quick question, can a carburator be rebuilt twice? I've heard yes and no on that subject.
 

Scott Danforth

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you can "rebuild" a carb until you break something. on a holley, you can buy any part of the carb.

there is not limit of number of times the carb can come apart for cleaning.
 
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I've got a little Holley 2bbl on my Volvo SX 5.7, (1998) I had it rebuilt and flowbenched once, the boats been idle for a few years. so I'd like to do it again. Thats why I asked.
 
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