ready to give up

[mh11]

ok, I am ready to give up.

1978 galaxie 22xl chevy 350 merc 260

had stuck exhaust valve, fixed it.
did compression test, all looks well
set timing 6 degrees btdc
dwell and advance are in spec
fuel pressure was tested, all good 5 1/2 lbs when you start motor
temp runs 140 to 160 all day long
bottom of hull is clean
throttle plates all the way open
idles 600 rpm nicely
tach was tested at shop, said was fine

questions:

1) tach reads only 3200 rpm max with 17p prop this does not seem correct at full throttle, tach also bounces when you get to wot, could the tach be off 1k rpms?

2) boat always backfires the minute you get get to wot, back off a little, and runs cleanly. i richened the secondary metering rods two stages, and it stilll backfires? help please

3) water is getting in the bilge from somewhere, there seems to be no water leak with the motor, can it be some of the lines going to the outdrive?

this boat is really cool, but it seems the backfiring problem is the one I really need to fix right now, can someone please help?

thanks!!

 

[Silvertip]

Re: ready to give up

Lifters adjusted properly??? If this is an air valve secondary style carburetor there is a spring adjust for the secondary air valve. If that spring is broken or the adjustment is wrong, the engine goes lean at higher throttle settings because the air valve won't open or opens too late if under hard accelleration. You need a service manual to set this correctly.

 

[erikgreen]

Re: ready to give up

I'm gonna post the simple questions

Is your engine newly rebuilt? How many hours on it? Is it all marine parts? How long since the carb and electrical system has been serviced? Did it run well before this, or did you just buy the boat?

Erik

 

[Fishermark]

Re: ready to give up

water is getting in the bilge from somewhere, there seems to be no water leak with the motor, can it be some of the lines going to the outdrive?

On the water question, here is a picture of an Alpha transom assembly - I think yours will be similar. Note there is a hole leading into the drive bellows area. If water gets into the bellows, it will leak into the boat. It is also possible that the transom is getting soft and allowing water to leak in around the assembly. (Not good!) Another common area is the exhaust tube - where it connects to the transom assembly.

 

[mh11]

Re: ready to give up

Here is the info,

110 hours on crate motor, checked the serial number, it is a marine engine.

Just bought the boat a year ago.

Quadrajet carb, i would assume by looking at it, it has never been rebuilt, it looks old.

Always ran around 3900 to 4000 rpms with the dead cylinder before, now only runs 3200 before it backfires with the valve issue fixed, and richening the secondary rods two increments......

Yes lifters are adjusted properly,

A person that I know that used to drag race said maybe the cam could be flat.....would that be likely with a motor with only 100 hours on it??

Thanks for the help!!

 

[proxyx]

Re: ready to give up

carb was never touched... hmmm, are you sure it's ok? try swapping with another from a rebuilder (borrow)

 

[Friscoboater]

Re: ready to give up

I am going with the carb thing too. I was having similar issues and I put in a new coil and it got better, but when I got the new carb, it was a whole new boat!

 

[dr_bowtie]

Re: ready to give up

when it back fires does it do it only once...?

more than once...?

if more than once is it a consistent backfire? or spuratic...?

a lobe on the came will be very consistent....

fuel or timing with be very non consistent....all over the place...

you mentioned fuel pressure at idle but what is it at WOT? you need to know that too...if it is lean enough to pop/backfire you need to know if it is delivery or carb...

 

[wca_tim]

Re: ready to give up

I'll go with carb too. if it is popping right away when you give it gas, would bet is in the carb, if takes a couple could be supply. either way, i would clean fuel filters change water seperator (whatever you have) and either replace the carb or do a thorough rebuid. If it's really ratty, you might just be better off to buy a new aftermarket and drop it on. Either way, sure sounds a lot like leaning out as others have mentioned. sounds like you already suspect the carb... and I would suspect you're right

 

[bruceb58]

Re: ready to give up

try sparaying carb cleaner around the edge of the intake manifold to see if it affects the idle. I wonder if you have an intake manifold vacuum leak.