Joe Reeves WOT timing Q, 1975, 50hp

[johnnynegaunee]

I read in the FAQ "The reasoning for the 4? difference is that when the engine is actually running, due to the nature of the solid state ignition componets, the engine gains the extra 4?." Does this pertain to the '75 CDI system?

My timing would then be 14-16 degrees, right? Spec.'s call for 18-20

Thank you.

 

[Joe Reeves]

Re: Joe Reeves WOT timing Q, 1975, 50hp

Yes, the 4? difference pertains to the 1975 system. If your full throttle spark advance is 20?, set it to 16? if using that method.

 

[johnnynegaunee]

Re: Joe Reeves WOT timing Q, 1975, 50hp

Thank you Joe

 

[bob johnson]

Re: Joe Reeves WOT timing Q, 1975, 50hp

would that apply to a 1988 48 special??

I am in the process of trying to time it...

running very rough at idle....wants some rpms...but seems to be a miss

I have the feeling it is the timing..

there is no adjusment of the carbs...no needles to adjust...


so it seems its all in the link and sync

bob

 

[Joe Reeves]

Re: Joe Reeves WOT timing Q, 1975, 50hp

Bob..... Best to start a new post/thread.

Yes, that method would apply.

The timing wouldn't change unless you changed it.

Carbs are not adjustable BUT have brass jets that can (and do) become clogged. This changes the mixture. The cure is to clean the carbs and manually and carefully clean the jets.

 

[bob johnson]

Re: Joe Reeves WOT timing Q, 1975, 50hp

Bob..... Best to start a new post/thread.

Yes, that method would apply.

The timing wouldn't change unless you changed it.

Carbs are not adjustable BUT have brass jets that can (and do) become clogged. This changes the mixture. The cure is to clean the carbs and manually and carefully clean the jets.

ok, I have one open....

the carbs were rebuilt, and the jets look great..i looked at them with my 5X loupes...clean and round!!

bob

 

[johnnynegaunee]

Re: Joe Reeves WOT timing Q, 1975, 50hp

I'm back with a couple more questions:

I had this 50 hp parked for 2 years, compression 160, 155, carbs were drained prior to storing, now has a fresh mix 50:1, high speed jets are clean. She runs good at idle and up into WOT, but after about 5 seconds and just after planing the boat, the engine starts to surge. I thought it was the timing, because I recall messing with the linkage before I parked it. Yesterday the surging was a lot less, but I had the timing set at 18 degrees without subtracting 4, as advised by Joe. I'm tempted to turn the timing back up, bad idea? Should I be on the fuel supply side? The primer bulb for the system does go soft to a point, but the engine doesn't die. I do not find any leaks, although I see it's a little wet with fuel around the bottom carb fuel bowl gasket. I just tightened it. I can over pressurize the fuel line quite a bit, still no leaking. It looks like the original fuel pump.

 

[Joe Reeves]

Re: Joe Reeves WOT timing Q, 1975, 50hp

A slow up and down surge (you don't say which...fast/slow) would be fuel. This could be a fuel restriction, a minor fuel/air leak at some point between the fuel pump and the fuel supply, or the throttle butterfly linkages between the carburetors is slighty set wrong...... one butterfly closed and one slightly open at idle would usually result in a surge at any throttle setting.

If using my method of timing and NOT subtracting 4?, you'll set up a pre-ignition condition which will melt a piston.

 

[johnnynegaunee]

Re: Joe Reeves WOT timing Q, 1975, 50hp

I'm a little confused Joe as to why an over advance in the timing would cause the surging to all but disappear.

Any tips in the search for the air leak- just renew suspect lines, replace clamps?

Replace the fuel pump?

Thanks again

 

[Joe Reeves]

Re: Joe Reeves WOT timing Q, 1975, 50hp

You still haven't said....... is this a slow type up and down surge?

To check fuel pump, have someone cunstantly pump the fuel primer bulb (acting as a manual fuel pump). If the problem ceases to be, replace the fuel pump.

Possible fuel restriction?....... temporarily try a different tank and hose.

Timing causing surge to cease?...... no idea BUT you absolutely DO NOT want the timing to exceed the factory specifications.

An air leak would be obvious as fuel would leaking at that point also.

Fuel restriction..... see the following.

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

 

[johnnynegaunee]

Re: Joe Reeves WOT timing Q, 1975, 50hp

The surge is about 1-2 seconds of higher rpms, then 1-2 seconds of the rpms dropping. I can throttle back from WOT slightly and it will run smooth.

I do note that the hose clamp at the inline fuel filter I installed is not particularly tight as i can twist the hose on the hose end. I replaced this clamp.

I do have those ball/O-ring valves at the fuel line ends, both are new this year. I run with removable OMC 6 gallon tanks.

You say "An air leak would be obvious as fuel would leaking at that point also." I thought this too, but could not see anything remotely damp, save for the bottom carb bowl which I have since tightened.

Can this style fuel pump weaken with age or do they just get a wear hole in the diaphram? I'm going to have to get someone to drive the boat so I can see if it runs better manually pumping the bulb. I think its likely to be the fuel pump, No?

 

[bob johnson]

Re: Joe Reeves WOT timing Q, 1975, 50hp

Bob..... Best to start a new post/thread.

Yes, that method would apply.

The timing wouldn't change unless you changed it.

Carbs are not adjustable BUT have brass jets that can (and do) become clogged. This changes the mixture. The cure is to clean the carbs and manually and carefully clean the jets.

well one reason people may be wiggling into other threads to get questions asked is that their questions goes unreplied to for so long!

my thread of my question about working on my 48 specials issues has fallen to PAGE 7!!! with zero replies...

while i didnt jump in JUST to get my question answered...

I do see a benefit of jumping in where there is a few people comversing on a very similar subject... they are all in the same room already!!! and they are on topic...can you blame someone for inviting themselves???

bob

 

[johnnynegaunee]

Re: Joe Reeves WOT timing Q, 1975, 50hp

The surge is about 1-2 seconds of higher rpms, then 1-2 seconds of the rpms dropping. I can throttle back from WOT slightly and it will run smooth.

I do note that the hose clamp at the inline fuel filter I installed is not particularly tight as i can twist the hose on the hose end. I replaced this clamp.

I do have those ball/O-ring valves at the fuel line ends, both are new this year. I run with removable OMC 6 gallon tanks.

You say "An air leak would be obvious as fuel would leaking at that point also." I thought this too, but could not see anything remotely damp, save for the bottom carb bowl which I have since tightened.

Can this style fuel pump weaken with age or do they just get a wear hole in the diaphram?

Went out again, with the primer bulb in one hand, boat controls at the other (15 footer). I kept the bulb full, went at full speed for at least a 1/4 mile then the motor bogged to about 1/2 speed. I stopped the boat, looked it over. I saw nothing different. Started it up went another 1/4, engine bogs.
This went on like this for a couple more cycles, then 1/2 speed was the best I could do.

I took the pump screen off, it's completely clean. I pumped fuel through the open line, gas gushes out like BP's oil wells. Can the fuel pump plug? Or is my best bet to look at the carb. float settings/needle?

I had the carbs rebuilt just before I parked it

Engine purrs along at idle and up to 1/2 throttle so it's gotta be a fuel supply problem, right?

 

[Joe Reeves]

Re: Joe Reeves WOT timing Q, 1975, 50hp

Assuming that the engine isn't overheating and it's firing on all cylinders, that sounds like a fuel restriction. However, if a fuel restriction, the primer bulb would have a tendency to go flat and stay that way.

The fact that the engine runs okay for 1/4 of a mile cancels out the carburetors UNLESS something is floating around in one of the float chambers which eventually would get drawn down into a high speed jet (I encountered this once on a V6).

 

[johnnynegaunee]

Re: Joe Reeves WOT timing Q, 1975, 50hp

I took out both carb bowls 2 days ago, they are clean, nothing whatever in them. I put an inline auto style filter in the supply hose to keep out the dirt, but that was before this problem.

Engine runs at normal temp, doesn't seem hot.

Could something be wrong with the timing advance, under the flywheel?

 

[Joe Reeves]

Re: Joe Reeves WOT timing Q, 1975, 50hp

At the full throttle setting, are both of the throttle buterflies both perfectly horizontal?

You state that the factory full spark advance setting is 18?-20?. I just checked my books and that is correct (19? +/- 1?).

 

[johnnynegaunee]

Re: Joe Reeves WOT timing Q, 1975, 50hp

Yes sir, both plates are horizontal at WOT, timing with your method 16 degrees (+4=20). Odd huh? The linkage that I can see looks tight and working ok. Could it be something in the fuel pump? High speed jets are clean. Every heard or have the float valve stick shut?