1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

[bassboy416]

Hey,
So I recently took out a boat I just purchased for the first time. I noticed a few things about it and am not sure if they are interconnected or not but my main question is why is it when I checked the 4 spark plugs that the upper two were white and the bottom two looked pretty normal???? It looks as if there are 2 carbs and 1 is for the top 2 cylinders and 1 is for the bottom but im not sure. So, heres some symptoms. The boat ran great at higher speeds and once warm ran better than before, but it seemed to have a high idle in nuetral. It would rev a little higher than I'm used to out of gear but once put in gear it would often times die. If you put it into gear hard it would run just fine and go like crazy. It ran very well, and I was able to easily get it on plane, but white spark plugs tell me that something is getting hot. Before I cause damage, I'd like to find out if anyone has ever seen something like this before. Why are only two spark plugs running hot?
Jimmy

 

[jerryjerry05]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

White plugs, running lean.Pics?
Clean the carbs.Check for sucking air somewhere.
Start it and spray some starting fluid round the base of the carb and the intake.
If it makes the motor change speed it's got an air leak.
Set carbs at 1 turn out. Where are they now?
Compression test?
Any water on the plugs?
Check timing.

 

[Frank Acampora]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

White plugs? Does your engine have electronic ignition or battery and points? If it has electronic ignition and it has bent electrode plugs, replace them with surface gap- Champion-L20V or NGK BUHX.

White porcelain insulators (Inside the shell) Indicate hot, lean running. This is dangerous for the engine.

Watch the tutorial on timing and carb synchronization and also read the sticky on synchronizing carbs and timing. Following instructions on these should solve idling and running problems IF the engine has good compression. SO: First check compression on all four cylinders.

 

[bassboy416]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

As of yet, I have not done a compression test on the motor. There does not seem to be any sign of water in the plugs or any loss of power or symptoms of serious engine problem. I am more inclined to believe that the difference stems from the upper carb. There are 4 cylinders. The top two look to be connected to one carb and the bottom two to the other carb. Both carbs are tillotson carbs. The top 2 plugs are white (not the porcelain just the electrode) after 1 trip out, and the bottom two plugs look perfectly fine. Do I need to go out and buy a compression tester, or can I start by running some sea foam through the gas or intake and adjusting the idle mixture screw? If this is a problem that has been there before I bought the boat, what damage could there possibly be if the engine still runs great at speed and gets on plane no problem?

 

[jerryjerry05]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

If the plugs are running hot so will the hole you burn in one maybe two pistons.
Seafoam is a waste of $
Use Mercs Powertune or Omc's Engine Tuner.
The seafoam I bought and tested didn't remove ANY carbon.
Bring it by and I'll do the comp test for free!!!
Unless your in Africa and then you can send me a ticket and I'll be there Monday
Kidding, I'll be there Tue. Kidding again,fill out the profile and location.
You MIGHT be close to someone who can help.
Any auto parts store will loan you a tester.
Best is get a good one.You can spend 10$ and get 10bucks worth.
Spend a few more and have a tool that will last forever, I paid 160$(really good set) in 1986.Still works like new.

 

[bassboy416]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

UPDATE:
I've always been the kinda guy too learn things the hard way.... Here's whats happening now. I found a place to rent a compression tester and will try to get it done ASAP.... I'm afraid I did burn a hole in a piston. I bought the boat from a gentleman who did not do regular upkeep. He said it ran great for 6 trips over 2 years until the last time he took it out when it kept dying and barely made it in. Said it was missing and having issues. Never changed the impeller while he had it. He replaced the plugs and told me the old ones were bad and way over gapped and barely any electrode left. He said he had talked to a knowledgable person who recommended he put in a certain type of plug. When he would start it for me it idled perfectly but generally would backfire before starting which didn't worry me. I took it out after changing the lower unit oil one time for a total of 6 hours on the water and about 3 of those total drive time only about 30-45 minutes at higher rpms. I came home and read spark plugs to find what i found. So today I went back to check the carb syncronization and see how it would run with surface gap plugs. I also adjusted the air fuel mixture screws so they matched on both carbs. Once i started it, it ran horrible backfiring all over the place, so I turned it off and put the old plugs back in. It fires up like it did before, but now it will idle fine for a minute then have a huge backfire out the exhaust hole and kill itself. If I keep it at higher throttle it idles evenly not missing or anything but sure enough it keeps backfiring and dying eventually. Did I burn a hole in the piston? Where in the hell could I even find a 1976 chrysler 1209 hd piston for a 120 outboard? I'm done ignoring the idea that a compression test isn't needed. I'm thinking its the first thing I need to rule out before replacing coils and what not.. what PSI am I looking for and how do I perform the test? any ideas on whats going on? burnt piston crown?

 

[Frank Acampora]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

First of all, these multi- cylinder, multi-carb engines will start and idle on only 2 cylinders. It almost shows nothing.

Until you get compression results, there is no use talking about anything else.

You still need to tell us what type of ignition the engine has and what type of plugs were installed.

Compression numbers should be over 120 PSI with all cylinders within 10 PSI of each other.

Backfiring indicates a lean condition so you definitely need to remove and clean both carbs. While you are at it, replace the fuel pump gasket and diaphragm.

Pistons are easy to find--Force 125 HP ( 3.3125 diameter cylinder bore) pistons will fit.

 

[jerryjerry05]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

Don't panic. YET!! These motor are real simple and the parts are all over and they are easy to fix.
Like I said fill out the profile and loction.You might be close to someone who can help??
When doing the comp test,make sure you remove all the plugs.
The actual comp readings will vary with the different guages.
Like Frank said the difference shouldn't be anymore than 5-10# between the cylinders.

 

[bassboy416]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

Thank you all for your help. This is an ongoing process, and will continue to update so that hopefully someday somebody with the same problems can use this for help. I have a starter with a gear that has been shearing metal like crazy. I went yesterday and removed the starter and am ordering a new one. In the mean time, I checked the timing and looked through the spark plug hole at all 4 pistons. The top two were more brown/grey while the bottom were more black (not badly caked but slightly). No holes spotted from the plug hole. Timing was right on the mark. I have access now to a compression tester, but I do not want to keep running this starter because it is beginning to put marks on my flywheel (not bad just barely but it flings metal everywhere every time I start it). On the top of my motor is a place for a pull cord. Can I pull my engine with some nylon cord to get compression test readings? I'd really like to see what I'm looking at compression wise first before I start spending money elsewhere. I have a mechanic friend who is willing to help me. He has suggested that he believes it to be ignition or carb related, but he also advises to start with a compression test. If I test with a cord I won't be able to do the test with pulls in secession. it will take me a minute to re string the line and pull. Can I do it this way? Would I do it at Wide Open Throttle? What PSI am I shooting for?

 

[jerryjerry05]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

Yes you can pull for a comp test.
Turn key OFF.
Uses about 6ft of line.
Then remove all plugs.
Doesn't need to be in foward or full throttle.
Will be easier to turn/pull over in N
The readings: they will vary from guage to guage.
My motors are about 150# on each cylinder.
Some motors are 165# some at 140#
What your shootin for,is that all cylinders are within 5-10# of each other.

 

[bassboy416]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

Just a follow up to a prior comment about filling out my profile. In case it didn't work, I'm located near sonora, ca in a place called Arnold. I am fully employed as a painter and am willing to pay gas for anyone who is able to come out and help me out. I'm borrowing a compression tester tomorrow and will try to pull it with a cord on top of the flywheel. I am not sure how accurate the reading will be, but it will tell me how close the cylinders are to each other and if I have any that don't match the others. If I can find the parts, I would imagine it would be cheaper to learn how to fix this engine myself than to buy a new 120 hp motor. I have worked on dirtbikes and vehicles but never done any piston work before. So far, this has been the easiest motor I've ever had the chance to work on... Just hope to find it repairable. It did run great for me for the only outing i took it on.

 

[bassboy416]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

Did a compression test today. Did not have a starter, only a makeshift pull cord. Throttle was not wide open and engine was cold. Top two cylinders (the ones that were running lean) read about 140-150. The bottom two read about 120-130. Whats the next step?

 

[jerryjerry05]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

Don't add more posts this one has good info in it. Ask a mod to run them together?

 

[bassboy416]

Re: 1976 Chrysler 120 HP 4 cyl with 2 white spark plugs and 2 normal whats the deal

The carb solved the problem. Bought a new starter, and did carb rebuilds. Aftermarket kits sucked. Got gasket material and made most myself and replaced bowl gasket with O ring. Ran better than ever with excellent idling and throttle response. Must have been sucking air somewhere. What an incredible difference. Don't give up hope if you're reading this. It might not be as bad as you think