1975 75HP Chrysler - occasional hard starting

thomasando

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Edit - Ooops - motor is a 1977 75HP!

I've done a bit of reading on this already, but not sure what it may be.

This has happened now twice, both times with the motor warm. The scenario - starts perfectly when cold, runs absolutely fine for quite some time out to the first fishing spot. Move a couple of times throughout the day. All of a sudden, go to start it to move and it won't start. Both times it happened it was only about 20-30mins from shutting the motor off to trying to restart, and the weather was not cold (30deg C plus).

The motor turns over fine but won't fire straight away. After a few goes, it will 'pop' (or backfire, maybe) and the starter will disengage but the motor will not start. Try to start again, same situation. This goes on a few times until eventually it will start. When it starts, it idles rough for a few seconds and then is fine. There's no lag or issues when putting the power on. Both times it happened, I moved locations, shut it down and it started perfectly (first touch of the key) for the rest of the trip.

Both times it happened it was the same scenario. The first time took about 8 tries to get it to start, second time was 3 or 4. The first time I thought I might have been out of fuel so switched tanks and it started straight away. The second time, I knew I had enough fuel and switched tanks - it did not start, so I switched back.

I also had some issues starting it cold (yes, used choke) on another occassion however I think that was due to not priming properly from the front fuel tank (I've had some issues getting it primed).

This is my first boat, I've only owned it for about 4 weeks. The motor has less than 200hrs since a full rebuild. I bought it off my uncle (a small engine/marine mechanic) and it is in excellent shape. He has owned the boat for ~20yrs with the same motor and did a lot of work on it for me before I bought it, to ensure it would be trouble free.

Any tips on some simple diagnosis I can do next time to try and track the issue? Could a bad fuel pump diaphragm exhibit this behaviour?
 

thomasando

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Re: 1975 75HP Chrysler - occasional hard starting

Something interesting just happened.

The boat has been sitting for about 1.5 weeks and I plan on going out tomorrow so thought I'd start it on the muffs.

Primed the bulb for the front tank, which I know has some fuel in it (not much, probably!) but the bulb wouldn't get hard. Never had it get real hard anyway, and it got as firm as it's been before. Started and ran for a few seconds then died like it was out of fuel. Wouldn't start again.

I changed to the rear tank and primed it up (bulb got very firm very fast). Started and ran fine (turned over a few times first, though).

Switched back to front tank, ran it at idle off the front tank for a good 5 minutes with no problem. The primer bulb still isn't firm, though.

Is it possible it's just an issue with the fuel line (occasional air leak?) from the front tank causing all of this intermittent starting trouble?
 

jerryjerry05

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Re: 1975 75HP Chrysler - occasional hard starting

If the bulb won't get hard? Then the squeezie could be bad or the fuel pump might be bad?
Easy to pull the pump apart to check.
It's possible the inline connection is bad, but it probably wouldn't run at full speed.
Try replacing any inline connectors. Try changing to OMC/Johnson connectors.
The Chrysler ones can/do go bad. I removed mine when I got the boat in 88.
As far as poor starting, change/clean the plugs.
Do a compression test.
 

thomasando

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Re: 1975 75HP Chrysler - occasional hard starting

Thanks Jerry for the pointers.
If the bulb won't get hard? Then the squeezie could be bad or the fuel pump might be bad?
Replaced the squeezie when I couldn't get it to prime at all with the original one. Couldn't get the new one to prime either, ended up having to do it by syphoning and the bulb firmed up somewhat and boat ran fine.

However, this squeezie is near the front of a long fuel line, and the line level does go above the top of the tank. It gets firmer during priming, but nowhere near as hard as the one for the rear tank which is on a short line (it goes almost rock solid). The rear tank has brand new hose and squeezie, the front tank has older hose but new squeezie. Could the location of the primer bulb on the hose make a difference?

Tested the old and new squeezies out of the boat, both do exactly what they're meant to.

Would the fuel pump being bad show up as problems off either tank? I would have thought it should?
Try replacing any inline connectors. Try changing to OMC/Johnson connectors.
Already got Johnson ones on it :joyous:
As far as poor starting, change/clean the plugs.
Do a compression test.
Plugs are brand new. Done about 10 hours now, but were new when I got the boat.
I haven't done a compression test myself - but it was done just before I bought the boat when my uncle did the head gasket. Not sure what the figures were but I know for a fact if it wasn't right he wouldn't have let me take it. He is so particular with everything, he changed some decals on the boat because a few of them were weathered! Doesn't make a difference to the running but he wanted it to be perfect for me.

Anyhow, I went out today, all was fine. I did run out of fuel in the front tank after only a few minutes thought, but it started with absolutely no problems whatsoever all day from the rear tank. So, I'm thinking it's an issue somewhere between the interconnect (pre filter) and the pickup in the front tank.
 

jerryjerry05

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Re: 1975 75HP Chrysler - occasional hard starting

Position of the two tanks, Where is the pickup tube? Turn tank around???
Compression can go bad in a minute. The first step to trouble shooting any problem is a compression and spark test.
I always suggest doing one, just to make sure??? Possible the hose is soft weak?
In the US were stuck in most cases running Ethanol. It ruins hoses and some of the rubber. You don't have it but if your putting in additives they might affect the rubber? Too much of a good thing,like Seafoam, or Powertune can cause trouble.
Also check the air screw,top/center/front of the carb. Initial setting, one turn out from gently seaated.
Start and warm up. Then turn in the screw till it just kicks,bucks,stutters. then back out 1/2 turn. Idle about 750-800 in gear, motor warm.
 

thomasando

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Re: 1975 75HP Chrysler - occasional hard starting

Thanks again Jerry.
Position of the two tanks, Where is the pickup tube? Turn tank around???
The front tank is up under the bow, it's custom made to fit right up in the nose so it doesn't take up too much space. The second tank is at the stern under the rear seat.

Possible the hose is soft weak?
Yes quite possible - doesn't really seem to be to me, but it's possible. I also read earlier that the orientation of the bulb can make an impact. The fuel flows the correct way, but it's downhill - could explain why I haven't been able to prime it well. I can't quite get it to be vertical with the outlet at the top due to not enough slack in the hose where it is. The bulb is probably 1.5m (say about 4.5ft) from the front tank, and the hose runs another 3m (9ft) to the rear interconnect.

I think I can reroute the line so I can move the primer bulb to be vertical while priming. I'll try that before I go out next to rule out any issues with bad priming of the system.

In the meantime, I'll get hold of a compression tester and check the air screw as you've said.
 

jerryjerry05

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Re: 1975 75HP Chrysler - occasional hard starting

My tank is under the center console. Probably 10-12 ft. of hose from the tank to the water seperating filter.
Then from the filter it splits to each motor. The squeezie is only about 1-2 ft. from the fuel pump.

I had a 18gal small tank as a backup for the main tank(100gal)under the console. The main tank went bad so I changed to a bigger tank under the console. When I removed the hose from the smaller tank it was all blown up like a balloon and real soft.It's a wonder it didn't leak it was so bad.But again that was primarily from Ethanol.
 

foodfisher

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Re: 1975 75HP Chrysler - occasional hard starting

Anyhow, I went out today, all was fine. I did run out of fuel in the front tank after only a few minutes thought, but it started with absolutely no problems whatsoever all day from the rear tank. So, I'm thinking it's an issue somewhere between the interconnect (pre filter) and the pickup in the front tank.
You're sleuthing and mine are the same. May be some debris in the tank blocking the pickup tube, or an air sucking connection. Try the known good primer bulb on the problem tank.
 

thomasando

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Re: 1975 75HP Chrysler - occasional hard starting

The squeezie is only about 1-2 ft. from the fuel pump.

Do you find it any harder to prime from a completely empty tank with the line back to the tank being so long? With such a massive tank it might not get empty though?

You're sleuthing and mine are the same. May be some debris in the tank blocking the pickup tube, or an air sucking connection. Try the known good primer bulb on the problem tank.

Thanks. I'll replace the line and primer, and pull the tank out and have a look. The fuel gauge on it isn't working either so something else for me to look at when I pull it out!
 

jerryjerry05

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Re: 1975 75HP Chrysler - occasional hard starting

Yes priming from the tank(empty) is a bit harder. I unhook the fuel line and squeeze the ball and then block the hole, then do that again and again. Sometimes bending the hose and pumping works but It can also damage the inside of the hose and make it week.
Just squeezing the bulb will eventually fill the carbs but blocking it off does it quicker.
When you pump it? Try putting some in a clear container. Looking for debris. Look in the filters for debris.
on't know if this has been covered,rebuild the fuel pump(diaphram). And do a compression test. Low comp on the fuel pump cylinder, it won't work as well.
 

thomasando

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Re: 1975 75HP Chrysler - occasional hard starting

Finally spent some time looking at my fuel lines. Pulled out and cleaned the pickup in the front tank, new quick disconnect fitting onto the tank, new hose, new primer bulb, new quick disconnect to filter end. Relocated primer to the engine end of the line. Primed it up perfectly first time after about 15 squeezes (also had to fill empty filter and carbs). Started and ran fine.

Haven't tested on the water yet but Easter weekend will see quite a bit of time in the boat so I'll see how it goes and update then.
 
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