79 70hp wont start

[brokenwrist]

My 79 70 horse outboard refuses to start unless, I put a small amount of fuel down the carbs. I go through the usual starting procedure every time, squeeze the primer bulb until it get firm, advance throttle control forward to fast idle, turn key-push to activate choke, and then attempt to start. No activity, like I said unless gas is poured down the carbs. Then it'll fire right up, and continue to run great on it's own, even pumping gas out of the tank. I've rebuilt the fuel pump in full, new diaphragm, gasket, all 3 check valves replaced, new inlet screen and seal. I've verified fuel is making it out of the pump and to the carbs. Once running the old girl runs like a top. Timing is set dead on. I'm leaning towards a fouled needle or jet, am I correct in leaning this direction? I should also add when I bought my boat a couple years ago, the engine didn't have the intake plenum, but it never affected it before.

 

[racerone]

Have to ask----Do you keep key pushed in while cranking it over ?-----Sounds to me that the choke is not working properly.

 

[brokenwrist]

Nope, I push the key once to activate the choke. It's working properly because I can watch the butterflies close And then open once started and running. Its weird because last year the engine operated beautifully. Now this year, I cant get it to start without putting a little bit of gas in the carbs on either first start or if its sat for about 10 minutes after shut down.

 

[jerryjerry05]

The fuel pumps job is to push fuel up to the carb/s.
It doesn't help start the motor.
The squeezie's only job is to draw fuel up to the carbs.
Once that's done it just sets there doing nothing but supposedly stopping fuel from going back into the tank.
If the one way valve in the ball is weak or going bad? Then fuel will siphon back to the tank.

Do a compression test.

I had a 88/85 that did the same thing.
I found by accident that it would fire when tilted all the way up.
I got flustered and tried to start it when it was tilted.
It fired and when I lowered it, it started.

The problem eventually went away.

Maybe try a carb clean or a flush.

1 gal gas.
1 jug of Chevrons (with Techron,black jug).
TCW3 oil for the amount of fuel and cleaner.
Mix it and run it through the system.
Run it through the pump.

Install a filter between the carb and pump.
Fram G-2-3

You use Seafoam?

 

[brokenwrist]

I've used seafoam in the past on my cars. Haven't used it on the boat motor. I'm really leaning on the carbs being gummed up. When I bought the boat it kinda did the same thing, but it was timing related. Like I said timings perfect. Compression when I bought it was at like 130 on all 3 cylinders. Anyway, I'll get some techron and once the weather holds on my day off again, will put it in the water and let it run. This thing also smokes like a chimney when its running, I know its a 2 stroke and will smoke some, but this seems excessive. My gas is mixed at 50:1.

 

[mazzen66]

sounds like bad gas,even though more than likely you have a water/fuel separater .condinaton in the fuel from condinaton in the fuel tank is possible and a bad choke sounds stuck or needs cleaned. should always keep your fuel tank full during winter and a fuel stabilizer added always.

 

[jerryjerry05]

My opinion: Seafoam is USLESS!!
It's like adding soap and it doesn't do what they say it does.
Does not remove carbon or gunk.

Power Tune, Mercury or Engine Tuner, OMC
Both are the same product and great for removing hard carbon deposits.

The intake plenum should have been there?
It has a hose that goes to the intake manifold and recirculates the unburned fuel.

 

[brokenwrist]

Nope, just got the front of the carbs saying hello to the world. I have found a few plenums for sale, just gotta pull the trigger on one.

 

[jerryjerry05]

The 85 hp plenum will work on your 70 FYI
I'm not sure what the purpose of the plenum is??
But it saved a lot of motors from sucking the foam liner into the carbs and blowing a piston or 2.

My 88/85's after about 2-3 years the foam liner came loose, I just removed it.
I couldn't really tell the difference.

 

[brokenwrist]

my foam liner was long gone when it got the boat, just a tiny little bit remained, and it fell off over the winter. I had a theory that the plenum helps to balance the carbs, even after they've been tuned and set properly. I have heard where really its sole purpose was to keep the spit back contained and keep the motor and hood clean.

 

[kbh121956]

Some people say that the plenum helps cut down the noise from the carbs. Don't know if it's true. Jerry is correct, remove that foam as you sure don't want it sucked into the engine.

 

[Nordin]

Brokenwrist and kbh, you are both at the right track about the intake cover (plenum).

The purpose of it is to catch spit back fuel from the carbs, catch up fuel from the carbs when tilting the engine and to reduce the noise/sound from the air which is drawn into the carbs.

Two stroker with reedvalves always have a small amount of spit back, it is normal and not an issue.

As jerryjerry mention there should be a small hose at the bottom of the cover which is connected to the crank case and it redirec the fuel back to the crank case.

 

[jerryjerry05]

The plenum, the factory designed it to help the engine run right.
The spray back and hose at the bottom should have told me what it's good for.
They designed it with one so I always made sure it was there when I worked on others motors.

It must be important because they designed a 55/65 hp with 2 carbs and it was put on them.

 

[racerone]

Try starting it by holding the key pushed in while cranking it over.

 

[brokenwrist]

Depending on the weather here, I'm probably gonna pull the carbs off again and go through them to make sure, they're not gummed up due to what ever fuel may have been left in them over the winter. Like I said, about a tablespoon of gas in each carb, even after priming with the primer bulb and it'll start right up. Once its running and burned through that fuel, if I shut it down, it'll fire right back up. But if I leave it shut down for about 10 minutes, I have to put gas back down the carbs to get it going again. I hope the ethanol in the gas hasn't destroyed my carbs, it seems every couple of years my parents have to put new carbs on their weed eaters because the ethanol destroys the carbs, and they have kinda the same symptom. Carbs wont prime, a tiny amount of gas in the carb and it'll fire right up, but wont pull gas from the tank.

 

[oldboat1]

I’m with jerryjerry on use of Seafoam. It’s petroleum-based, as the manufacturer claims, but then so is gasoline (which cleans well, unless allowed to set up). The diesel fuel and naphtha in Seafoam can hardly do better (think lighter fluid when using naphtha). Actually, nothing works dependably to clear carb blockages, other than disassembly and cleaning with something that will cut through old fuel varnish on metal surfaces (I like lacquer thinner).

That plenum undoubtedly affects tuning — guessing the motor would run lean without it. Maybe that affects cold starting some. I wouldn’t go overboard blaming ethanol for carb issues, although old fuel lines can break down on the inside and contaminate. Good idea to replace fuel hoses. When squeezing the bulb, btw, you should hear gas flowing into the carbs for priming — or can pull off the hose at the carb and check flow, as with a fuel pump test. Beyond that, choking while cranking should give you a cold start as mentioned above. There might be a chance that draw is affected without the plenum, and that covering the carbs while starting might work -- piece of cardboard held in front, maybe. (Need a helper to crank and choke -- along with fast idle setting for starting.)

Do those carbs have fixed jets, or is there an air/fuel needle for the idle? If so, small adjustments to the idle mix might help with the starting and smoking.

 

[brokenwrist]

Didn't have issue with it last year at all starting. I think the carbs had gas in them when it sat over the winter. I have strong fuel flow up to fuel pump, out of fuel pump, and up to the carbs when squeezing the primer bulb. The mixture screws, are finally set to where the engine likes it. All three screws are set 1 1/4 turns out from seated. I've seen gas gum up jets and passageways when left to sit for to long. Damn Washington weather won't stay consistent long enough for me to pull the carbs, go through them, and put the engine back in the water tank to keep diagnosing.

 

[brokenwrist]

Update: We have ignition on its own again. Pulled the carbs off last night, went through them each pulled all jets and needles. Everything on a visual inspection looked clean, but I went ahead and sprayed all jets and needles, as well as passages in each carb out with brake clean. Everything was allowed to dry before reassembly. Got them out back on today, at first nothing. Decided to recheck spark and throttle advance, all checked good. Tried again, it coughed a couple of times. Decided to bring distributor adjustment in 1\2 a turn, but the key, coughed, hit it again and it came to life. Allowed it to sit for about 15 while I ate some pie for Easter dessert. Went back out, turn key on set choke, set fast idle, bumped the key and she screamed to life. As of right now, I'm calling fixed. Thank you all for the suggestions on what to check.

 

[Nordin]

Nice to hear you solved the problem.

Do not know if you mention it in the thread earlier about your starting procedure, but sometimes OB (not only Chrysler/Force) need to have some starting throttle (pull/push knob or lever depending on remote control) even when warm and you also might give the choke a fast hit, then it will start up immediately.

Some just start right up without this starting procedure.

 

[jerryjerry05]

I like it!!