Old school Chevy motorheads

[Davy Crockett]

My boat has a 350 chev with quadrajet , It Idles ok with muffs on but as soon as I put it in water it won't run at a low idle and dies, Doesn't seem to load up with gas or anything it just doesn't want to run at at a low idle . Exhaust backpressure can be the only culprit but what counteracts that ? No vacuum leaks that I could find and anything above idle in the water it runs fine. Any ideas ?

 

[Petras]

does your qjet have the idle mixture screws exposed? or are they still encased? also, have you tried adjusting up your idle setpoint? another thing to try would be checking your timing. Wouldn't be too unrealistic if the distributor got bumped.

Also, what kind of rpm's are you seeing at an idle? Should be around 750.

 

[huffranger]

Does the boat sit at the same angle on the water as on the trailer ??

Maybe float bowl level or needle and seat change out ??

Did it run fine last year ?

Plugs ? wires ? cap and rotor ??

Timing ??

I could be way off base here but I have seen a potato in the exhaust of an old 350 shoot out like a bullet with the engine hardly missing a beat...

Fuel pressure ?? Old gas ??

 

[Petras]

Good questions Huff, my next question was going to be the angle of the boat. Does the front of the boat sit higher in the water or on the trailer or is it pretty much the same. Also, what part of the state are you in?

 

[Davy Crockett]

Idle speed is at 750 , Open adjustment , I tried adjusting some but I didn't have a flexible adjustment tool so I got in with a needle nose and 1/4 turn either direction either way didn't change things. I bought it two years ago and It had just been tuned up at the storage place, It idled fine at home with muffs but not at the lake in the water. I ran it that way all summer and when I brought it back home I hooked up the muffs and it idled ok. I drained it up and put it in storage and didn't use it last summer. Since it purrs so nice with muffs I didn't think about timing but It would be worth checking out. I ruled out float bowl by running it on the trailer at the same level with muffs as well as a in tub of water, same results.

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I'm up by Metigoshe but I'll have it in DL for the summer.

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I'll have to dive into it and refresh my memory this weekend but there are microswitches that shut off the spark when shifting. They sure don't help matters any.

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I wired the choke open once and that didn't change things either.

 

[PrairieGhost]

I am not much of a mechanic Dave K, but reading this thing about running with muffs, but not in the lake makes me think it's electrical. Is your boat aluminum? I am wondering if it's grounding through the hull when setting in water, or perhaps just grounding through the lower unit. I once had an old 18 horse Johnson that did what your talking about. There was a wear in one of the spark plug wires where the accelerate linkage wore through the rubber. When in the water and I went to idle the linkage shorted out the spark plug wire. Did it some up on the trailer, but run better.

I did have an old 1958 Chev wagon with a 348 and powerglide that I did all my own work on. Long long time ago though. Learned that it was tough on transmissions holding the brake and floorboarding it before releasing the brake. Especially on a car geared for top end and not 1/4 mile. Any other farm boys remember Saturday nights lined up in town with your hoods up so you could all check out what others may have done to their engine since last week-end?

 

[LBrandt]

Buddy in high school, about 1962 to 1966, had a 1961 chev belair station wagon 283 2 speed slush box. Family car, if his dad only new!!!!!! Would set up a run at the old 1/4 mile. You know the ones with the white paint across the start and finish put on with a paint brush. Would get there a little early and pull the fan belt, said it gave him an extra 5 hp and it ran better a bit to the hot side. Didn't lose many, man the good old days.

 

[2400]

Here's a few suggestions for you.

Do you have a fuel pressure gauge, vacuum gauge, dwell/rpm meter, timing light, feeler gauges, plug socket and gap tool or know someone that has them?

As my old shop teacher always said , always begin at the begining. Pull the plugs and look at them, all over them look for cracks on the porcelain, wrong gap, missing electrode, dirty, rusty. If in doubt it's time for a fresh set of correctly gapped plugs.

Check the plug wires for cracks, burned spots or just falling apart. When in doubt replace them in the correct firing order.

Check the cap and rotor for cracks and chips. Replace if needed with quality ones (Blue Streak). If you replace them make sure the firing order is correct and in the right rotation.

CHeck the coil for good voltage and replace if needed (Blue Streak). I've seen engines run fine with a bad coil and miss like hell under load.

Replace the fuel filter with a new quality (Wix) one and new rubber lines.

Pull the valve covers and check the lash and make sure the timing chain hasn't stretched.

Check the carb mounting bolts and the base gasket for cracks and leaks. Check the screws on the underside of the carb and make sure they're tight, then check the screws holding the top (cover) on. Make sure the choke is free and open. You might want to check the float level and weigh the float to make sure it doesn't have gas in it. Also check the needle valve.

THEN turn the idle screws in until they stop, back the out 1 1/2 turns. Static time the engine, make sure the carb has fresh gas in it. Crank it over, once it's running set the timing checking for best vacuum. After everything else is set and double checked adjust the carb. With the engine set the idle, then turn one of the idle screws in until it stumbles and back it out 1/2 a turn, then do the other one and recheck and adjust the idle to book specs.

If that doesn't help either post up here or PM me and I'll do my best to help you.

Have a great time on the water!

 

[Mort]

Just put a double pumper holley on it....effn quadjets...sheesh....

 

[Wild and Free]

Just put a double pumper holley on it....effn quadjets...sheesh....

Ha Ha I was thinking the same thing only I would go with 600 cfm Edelbrock, they are great all around carbs and require only minor idle speed and idle mixture adjustments when bolted onto a small block GM engine.

 

[Davy Crockett]

Thanks for the replies, I'll rumble them around in my head till I take a look at it this weekend. The boat was well maintained and stored inside, the engine and engine compartment plug wires and such look new. Guess the first thing to do is get a new carb adjustment tool and start adjusting, I also have an adjustable fuel pressure regulator to try on it if that doesn't work. I ruled out old fuel, It came with a full tank and I burned 80 Gallons and topped it off with no change, It has sediment bowls that are clean as a whistle. This is an old school early 80s Sea Ray so it shouldn't be that hard to figure out but I thought it maybe was something boat related that I was overlooking. Why it purrs like a kitten with muffs and won't stay idling with just a little back pressure is beyond me.

 

[Wild and Free]

Remember when adjusting the carb set the idle mixture first using a vacuum gauge on a "Manifold" vacuum port not a "Port" vacuum port. Set it to where you get the highest vacuum and then set the idle speed. Make sure "Base" timing is set first before adjusting the carb. Meaning the timing without the vacuum advance hooked to the distributor if it has it.

Make sure all adjustments are done at full operating temps too.

 

[Wild and Free]

Can't give up too many more tuning ideas or the next thing we will see from Davy is this.

 

[svnmag]

I'm seriously wondering WTH myself.

 

[NodakBuckeye]

That is a true tower of power.

 

[Davy Crockett]

haha, My boat is nothing like that although in my younger days I would have liked to had one.

 

[svnmag]

OK. I'm stupid. Is this an inboard configuration?

 

[Davy Crockett]

Yes it's I/O

 

[svnmag]

Home rolled? This is too freakn' cool to me.

 

[Davy Crockett]

It's a old school 26' Sea Ray with a full basement. My goal this summer is to video 45 MPH wind conditions on main bay , Had it out in 35-40 when the boat was still "new to me" and it was a blast. I don't have a picture of it but it makes a one ton dually look like a toy when you hook it up. Funnest camper I have ever owned. I also have a 77 Bayliner with aft cabin and bathroom, I'm selling that one if anyone is interested. Sink, stove fridge, freezer nice screened in canopy .