Mercruiser 233 Wonbt Start

"I have a 1975 Trojan with a t

"I have a 1975 Trojan with a twin Mercruiser 233HP 351 Ford Engines with Prestolite ignition. Before I pulled the boat for the winter, I was experiencing starting problems with my starboard engine. I would have to keep the starter engaged and pump the throttle until the engine eventually started. Once started the engine would begin missing when throttled up beyond 2000RPM. Once I pulled the boat I can't get the engine started to winterize it. I have tried the following lengthy diagnostics:

Replaced: Spark plugs (set@ .30), wires, distributor cap, rotor, coil and gas filter and water separator. Fuel pump was replaced 5 years ago. I rebuilt the carb and had the same problem. I swapped the port carb with the rebuilt and had the same problem. I ran a portable tank with fresh gas and had the same problem. Looking into the barrels of the carb, I can see I am getting gas while engaging the throttle.

I checked the timing by aligning the timing marks at 10 degrees BTC with #1 cylinder in the up position and the rotor aligns with #1 position on the cap. I removed the spark plugs, turned the engine over and all spark plugs were firing. Because the engine would occasionally backfire while trying to start, I loosened the distributor and tried to start it in different positions but no luck.

I performed a compression test and got the following results which I don't think would impact starting:

Cyl Dry Wet
1 125 140
2 120 135
3 140 150
4 130 140
5 135 145
6 135 145
7 135 145
8 140 150

The only thing that I am thinking now is that I may have a vacuum leak that is preventing enough gas to be sucked into the cylinders but I don't know how to test for this without the engine running.

I have reached the end of my rope and would welcome any suggestions."

"Worn out enngine? Backfirin

"Worn out enngine? Backfiring either from worn timing chain, burned valves or lean fuel mix. You swapped carbs so I suspect the chain, valves and rings are shot."

"Dennis Kooney
I'm not su

"Dennis Kooney
I'm not sure how you are setting the timing, but using a timing light is the only way to really time an engine properly. They can be "Power Tuned" but nothing beats a timing light to be sure.
Bert"

"[b]"Replaced: Spark plugs

""Replaced: Spark plugs (set@ .30), wires, distributor cap, rotor, coil and gas filter and water separator."

Ayuh,... What about the Points,+ Condenser,..??
And, as noted by Bert,... You still haven't Set the Timing...
Probably didn't get to Dwell either...

With the backfiring, I'm wondering about the placement of the New plug Wires...."

"I don't see nothing wrong

"I don't see nothing wrong with the compression numbers. Your getting good spark at the plugs.

Verify correct placement of plug wires.

As always Bond-o hit it on the head.

Post results after you do the above, and Bond-o's suggestions.

Still doesn't run then pull the timing chain cover.

My Dad had these engines in his cars all Ltd's forget how many i messed with, the timing chain does stretch sometimes, and you could have also have jumped a tooth easy to check."

"Thank you all for your sugges

"Thank you all for your suggestions and opinions. I would like to respond to them as follows:

Bondo/chiefalen/Bert Goodrich:
There are no points and condensor. The ignition is a Prestolite electronic ignition conversion kit. I inspected the internal components for wear and they were OK. I swapped the control unit from the port engine and got the same results. I verified the firing order and the spark plug wiring and it is correct. I laid out all plugs and they are all firing. The timing was set with a timing light originally but now that it is not running I had to verify same with aligning the timing mark on the harmonic balancer @ 10 degrees BTC with the piston in the up positon and the rotor does line up with #1 cylinder.

If the timing chain jumped wouldn't I see everyting out of synch if I performed the above test? How do I verify timing chain streatch or if it in fact jumped?

Guy Gaspar:
If the valves and or rings are shot as you suspect, wouldn't that show up in the compression readings which I don't think are too abnormal as listed in my original post.

Thanks again for all of your input."

"After cranking over for a bit

"After cranking over for a bit, have you pulled any of the plugs to see if they are getting wet or remain bone dry. Have you checked the oil after a lot of cranking to see if you have washed down the walls and had gas get by the rings into the pan.Any chance it`s just badly flooding?
There are usually only four reasons a motor won`t run, no gas, no spark, no compression or spark happening at the wrong time.
If you are absolutely sure you have gas, spark and reasonably sure the timing is close then I would, by deduction, start switching the electronic ignition components between one motor and the other. My "guess" at this point is that something is fubar in the distributor.If no results there, I would be pulling the timing cover and seeing where the marks on the gears line up. With a stretched chain it should still run, just not well.jumping a tooth would have a more serious affect.
My boat to the left has the same motor, only just one. Good Luck !!"

A stretched timing chain can c

A stretched timing chain can cause difficult starting. I have never checked a timing chain for stretch when not running.

What I have seen is when the motor is running and you put the timting light on the mark and rev to ~ 1500-2000 and hold it steady the mark will occilate and not hold steady.

See if some either can get it to fire and if so have all your test eqipment ready to go.

Also you can hook up a timing light and have someone crank it over and see where the light flashes. ( normally I do this with ONLY # 1 Plug in place) ( in your case it wont start anyway so just try it) If it does not flash every time or not near the timing mark (~6-8 degrees btc) then it may show something is wrong. I use this method for basic initial setting of timing when a distributor has been installed. It allows you to get very close when starting a new set up.

This motor should be a bit higher than 125 psi I would suspect that a 1975 motor would be closer to 160-170 psi so you have lost a lot of compression. Not that this is your problem but definatly a loss of overall power!!!

"Dennis:

I based my comment

"Dennis:

I based my comments on your findings and work performed. As Kghost said; the comp. numbers are not that great.

To check the chain manually, disconnect the battery and loosen or remove all the plugs. Take the dist. cap off and manually rock the engine a few inches back and forth. There should be no delay in the movement of the dist. rotor when rocking the crankshaft."

"Guy,
I get abount 5/8" m

"Guy,
I get abount 5/8" movement (play)in the crank before I see movement in the distributor rotor. Is that too much play to cause a starting problem?

I reset the timing as directed by KGHOST. She wants to fire off but still won't start. Plugs are wet when pulled so it is getting gas.

Maybe the spark I am seeing when the plugs are out and fired up is too weak?}

My last option is to swap the port distributor and electronic ignition components out as suggested by BARRY MERVYN."

"Weak spark or fouled plugs ar

"Weak spark or fouled plugs are a good possibility...spark should jump a good 1/2 inch...how about the inside of the distributor cap, coil and rotor...any cracks or missing components??? Is the battery in good enough condition to turn the motor over quickly and still provide enough voltage to the ignition system. Squirt a few drops of motor oil into each cylinder as you would during a "wet" compression test...this is meant to restore any compression loss caused by gasoline washing down the cylinder walls if the engine were flooded. Try advancing the timing a bit by turning the distributor a few degrees in the opposite direction of distributor rotation...you may be just a few degrees on the late side. If the timing chain had skipped several teeth, the motor would likely pump air out through the carburetor...if it skipped just one tooth, the best way to tell would, as mentioned, be a TDC check."

"Cap, rotor and coil all chang

"Cap, rotor and coil all changed. I had previously laid out all of the plugs on top of the manifolds and turned over the engine. Each plug did spark but they didn't "crack" like a strong spark should. The battery cranks over the engine but does get run down. Before I go out and buy a new battery, how would I test the battery to see if it is still providing enough voltage to the ignition system? This would be awfully embarrasing if all this is being caused by a weak battery, but I would be very happy at this point if it were the case."

"As I remember, 9.8 volts mini

"As I remember, 9.8 volts minimum while cranking, more would be better"

And you using what spark plug

And you using what spark plug firing order on this motor?
I/O`s or I/B`s
standard or reversed rotation?

"when cranking the engine over

"when cranking the engine over you should be getting full battery votage at the coil, ~ 12.4-6 VDC.

When running it will drop down to ~ 9 -10 vdc due to ballast resister in coli or on engine or in wiring.

Check to see if you are getting battery voltage at coil when cranking. I prefere a test light to see this. Get a test light and hook it up across the battery terminals and observe the brightness of the light. now do the smae at the coil, aligator clip to a good ground and the tip of light to coil +, Then to coil -. and compare.

The 12 volt signal comes from the solenoid when cranking. I believe it is the I terminal on ford solenoids. May be a weak connection at the solenoid or from it to the coil.

That ignition should be able to give you a good spark that will jump a 1/2 inch gap. It may not be bright blue but it should be white ish/yellow.

If the spark is a orange then it is weak.

Also is .030" gap for the plugs correct?

With the electronic conversion in there I would try .035 - .037 and see if it helps......

your dwell is much larger now than when it was points."

"Kghost...As I understand it,

"Kghost...As I understand it, if you were to put a voltmeter on the battery, there would be a significant voltage drop when the starter is engaged...the "I" terminal does provide full battery voltage when the starter is engaged but that voltage would only be around 10 volts due to the current draw of the starter. If battery voltage drops below 9.8 volts when the engine is cranked, you either have a bad battery or a defective starter which is drawing excessive amperage. You also would not have enough voltage to operate the ignition system. A "battery load test" involves using a device which draws current from the battery and a voltmeter to observe voltage drop under these conditions. This device determines the the condition of the battery and whether or not replacement is necessary."

That is all true but we are ju

That is all true but we are just trying a quick down and dirty test to try to solve the issue.

I have been using test lights for years and they are a great tool to test electrical stuff.

It is much more dificult to try to explain to someone (typing) how to do voltage drop tests and methods.

Not everyone is a good meter maid......

I have a load tester that I use all the time. Even have solved my own bad batteries with one.

Does he have one? Does he want to buy one?

A test light is only ~ $10.00

Also I was trying to give him some direction of where to look for "voltage drops" due to bad components or connections only using a test light.

Also I was not trying to determine if his battery was bad as he obvisously has more than one due having to two motors. He should actually have four! Two per motor.........in that boat.....I would.