Should I or not?.............Timing Set

[Bulldawg69]

I have an 88 Larson 24' with 350 magnum 4bbl Holley carb. This all came about because I purchased this boat a few months back. The owner told me the carb had been rebuilt a few years back and last season his mechanic suggested he replace it this season, which I did. I tuned it by ear on the lake with it idling in gear. Well I didn't like the performance adjusted it a few more times ran ok as long as you eased into it, if you hammered it to pull up a wakeboarder it would sputter but pick up. So this week I decided to put a vacuum gauge on it to tune the carb, have done this on cars for years, ( I have been teached). I get steady readings but nothing over 13-13.5. To me this would indicate slipped time unless it was in a high perf. motor with more overlap in the valves. Timing stays steady at 8 degrees. Should I tear into the front and change it or not? If I do would you advance the cam for more bottom or leave it at 0? Is this engine high perf.? And which 350's came with roller cams? Asking a lot on my first post...huh? Thanks guys for any and all help. P.S. new plugs also.

 

[RogersJetboat454]

Re: Should I or not?.............Timing Set

I have an 88 Larson 24' with 350 magnum 4bbl Holley carb. This all came about because I purchased this boat a few months back. The owner told me the carb had been rebuilt a few years back and last season his mechanic suggested he replace it this season, which I did. I tuned it by ear on the lake with it idling in gear. Well I didn't like the performance adjusted it a few more times ran ok as long as you eased into it, if you hammered it to pull up a wakeboarder it would sputter but pick up. So this week I decided to put a vacuum gauge on it to tune the carb, have done this on cars for years, ( I have been teached). I get steady readings but nothing over 13-13.5. To me this would indicate slipped time unless it was in a high perf. motor with more overlap in the valves. Timing stays steady at 8 degrees. Should I tear into the front and change it or not? If I do would you advance the cam for more bottom or leave it at 0? Is this engine high perf.? And which 350's came with roller cams? Asking a lot on my first post...huh? Thanks guys for any and all help. P.S. new plugs also.

If it were me I would be doing a compression test and cylinder leak down test first.

Ripping the timing cover off to mess with the timing chain sounds a bit hasty. On top of that, in order to remove the timing cover you will need to drop the oil pan and replace the pan gasket. Not an easy task in a boat or in most cars for that matter.

You say your timing is right on, what about the idle screws on the carb? Have any adjustments to those been made?

If you do eventually get to the point where you are pulling the timing cover off and replacing the chain, leave the cam advancement at 0. You don't have a race motor, and sacrificing top end for better bottom end is not a good compromise especially in a boat where you only have 1 gear forward.

I believe '87 or '88 was the first years for the GM rollerized small blocks in passenger cars. That being said, unless your block has been changed out to something newer, there is probably a good chance your engine is a standard flat-tappet cam as most heavy duty applications (trucks, boats, etc) did not receive this upgrade during this time period.

P.S. Welcome to Iboats!

 

[Eric 3.7LX Alpha 1]

Re: Should I or not?.............Timing Set

Where did you take the vacuum readings from, as marine carbs don't have any ports on them?

 

[Bulldawg69]

Re: Should I or not?.............Timing Set

Where did you take the vacuum readings from, as marine carbs don't have any ports on them?

Holley has one large one on the back of the baseplate and a small one up front for the choke pull off. I took mine from the large port on the rear.

 

[Bulldawg69]

Re: Should I or not?.............Timing Set

If it were me I would be doing a compression test and cylinder leak down test first.

Ripping the timing cover off to mess with the timing chain sounds a bit hasty. On top of that, in order to remove the timing cover you will need to drop the oil pan and replace the pan gasket. Not an easy task in a boat or in most cars for that matter.

You say your timing is right on, what about the idle screws on the carb? Have any adjustments to those been made?

If you do eventually get to the point where you are pulling the timing cover off and replacing the chain, leave the cam advancement at 0. You don't have a race motor, and sacrificing top end for better bottom end is not a good compromise especially in a boat where you only have 1 gear forward.

I believe '87 or '88 was the first years for the GM rollerized small blocks in passenger cars. That being said, unless your block has been changed out to something newer, there is probably a good chance your engine is a standard flat-tappet cam as most heavy duty applications (trucks, boats, etc) did not receive this upgrade during this time period.

P.S. Welcome to Iboats!

So you believe a cylinder or ring problem would cause below normal vacuum readings? Yes that is also with the mixture screws adjusted for max readings. Also, when starting, it will crank and not start till you release the key, just keep cranking.

 

[wca_tim]

Re: Should I or not?.............Timing Set

Are you sure you don't have a vacuum leak? and your last is confusing to me? it will turn over, but not fire until you let go of the key? electric fuel pump? that aside, I would focus on making sure the carb is right, check compression, valve adjustment, etc... the basics, before tearing into things further...

 

[Bulldawg69]

Re: Should I or not?.............Timing Set

Are you sure you don't have a vacuum leak? and your last is confusing to me? it will turn over, but not fire until you let go of the key? electric fuel pump? that aside, I would focus on making sure the carb is right, check compression, valve adjustment, etc... the basics, before tearing into things further...

I don't believe there is a vacuum leak, will dbl check today. Mechanical pump. It has started that way since I got it, even with the old carb. Fires right up, pump throttle once crank and turn loose.

 

[ENSIGN]

Re: Should I or not?.............Timing Set

spray some carb cleaner along the edges of the intake manifold and the base of the carb,you'll notice a difference in rpm's if you have a leak.also sounds like a bad key switch

 

[wca_tim]

Re: Should I or not?.............Timing Set

I believe I would check for vacuum leaks and then carefully rebuild the carb...

 

[Bulldawg69]

Re: Should I or not?.............Timing Set

I believe I would check for vacuum leaks and then carefully rebuild the carb...

The carb is two weeks old, new Holley 650 marine. I will check for leaks.

 

[mkast]

Re: Should I or not?.............Timing Set

when starting, it will crank and not start till you release the key, just keep cranking.

Your ignition switch needs replacing.

 

[fossill]

Re: Should I or not?.............Timing Set

Vacuum leak or timing not set right.

 

[RogersJetboat454]

Re: Should I or not?.............Timing Set

So you believe a cylinder or ring problem would cause below normal vacuum readings? Yes that is also with the mixture screws adjusted for max readings. Also, when starting, it will crank and not start till you release the key, just keep cranking.

Could be.

Think of the engine as what it basically is, an air pump. Worn/damaged rings, and cylinders make that engine less efficient at creating a vacuum. A timing chain thats jumped (as you think), a cam shaft with rounded lobes, bent push rods, or rocker arms out of adjustment will do the same as well. A compression test and cylinder leak down test will give you clues if any of these could be the case. Suggestions made by the others should be followed too. A vacuum leak on a freshly installed carb is with out a doubt possible.

 

[Bulldawg69]

Re: Should I or not?.............Timing Set

Ok, finally got to check for vacuum leaks there are none. And changing the switch didn't help it still starts the same. Have not got to do a compression check.