75 hp warm up problem

[roastinears]

Howdy All!<br /><br />1982 or 1984 chrysler 75 hp model 758h2d serial # 1302<br />last summer motor was perfect. Put in water, crank with choke for 3 seconds, started and ran great all day. NOW. If I get her warmed up she runs great all day, but getting from a cold start to warm up is the problem. She will crank right at 3 seconds of choke, run idle (high idle) for about 45 seconds then stop. If I keep trying she may sputter but will not start anymore. I can pull the plugs (all three plugs are wet) and dry them off, crank the motor for a couple of seconds to clear the cylinders, replace the plugs and she’ll crank back up for 45 seconds and die (wet plugs). Here are the things I have done. Cleaned the carbs (soaked overnight in b-12), replaced the needle and seat, replaced the fuel pump. I have done exactly what the seloc manual says about rebuilds on float level. I have even set the float height (from gasket to float) to 16mm and the motor will not start ( but I can squirt fuel into the carbs and it will fire up) so I’m pretty sure the needle and seat are working. I have set the idle speed screw just like the manual says and everything from ½ turn from full closed to 4 turns from full closed and pretty much the same thing happens. Wet plugs. I can always pull the plugs, clear the cylinders, wipe off the plugs and she fire back up. Can the recirculation path cause this kind of problem? Can I be missing something on all three carbs? Thanks in advance for the help.

 

[eurolarva]

Re: 75 hp warm up problem

Your motor is 1982. When you prime the motor does the bulb get and stay hard? When motor starts to sputter and die try choking it. Does this make the motor run better or kill it? <br /><br />Check all the fuel lines for a tight fit. Check the o ring to the quick disconnect is in good shape. Also make sure tank is venting. If this is a portable tank try running it with the gas cap loose or off to veify tank is venting. Try disconnecting one of the gas lines going to a carb and squirt some gas into a clean mason jar and see if any water is present in the gas. Verify no leaking carbs when priming.<br /><br />If motor improves when you choke it prior to it killing you probably have something wrong with the fuel system. If the boat has a permanant fuel tank instead of a portable try using a portable tank with 50 to 1 gas mix in it. Make sure you use fresh gas when doing this. Your best bet is to use 87 octane. Chryslers tend to run bad on premium.<br /><br />Good Luck

 

[roastinears]

Re: 75 hp warm up problem

thanks for the year on the motor. when the motor stops, she just stops. she doesnt sputter then die. the sputtering is when i keep trying to start after it has died. if the dying is from fuel starvation, would the plugs still be wet? there is no quick disconnect. fuel line goes straight from the tank, to bulb, to fuel pump. have check fuel pump by disconnectin last carb fuel line and cranking (no water either). tell me how to check for leaking carbs when priming. is it a visual check? look into the carbs and see if gas comes out the jets when priming? the bulb actually gets softs, just a little. like 1/8 pump, but i have attributed this to the fuel used during the 45 second idle. when i cleaned the carbs, i took out the main jet and the tube. there was another tube that is stationary. whats its function? is it for idle? thanks for the reply.

 

[eurolarva]

Re: 75 hp warm up problem

When priming the bulb should get hard and no gas should leak from the from any of the carbs. If you find a carb leaking gas you probably have a bad needle valve seat, needle valve point, a float that has a hole in it or the float is not adjusted correctly. I have no idea what the other jet is for other then possibly a slow speed jet. Describe the tips of your spark plugs. You mentioned they are wet. Are they clean or do they have blackish deposits on them and if so is it on all the plugs. You may be experiencing a weak spark on all cylinders or possibly one. Just because of how cheap a rebuild kit is for the fuel pump I would replace the diaphram and gasket at a minimum. Mine had idle problems and it ended up being a fuel valve gasket that was broken and I ended up replacing all the fuel valves and gaskets. Try testing your spark in a dark room and verify you have a good blue spark on all cylinders. You will need to remove the plugs and ground the tips to the metal on the motor (make sure this is common ground to your motor and not the paint on the motor). I wrap wire around the threads of the plugs and attach it to a ground on my battery.<br /><br />It would not hurt to do a compression test on this motor. If compression numbers are low on one or more cylinders this could also give you the results you are experiencing.<br /><br />Also Merc site is saying your plugs should be QUL-77V plugs. I dont know if they are still available. If not NAPA should have a cross reference part for them

 

[roastinears]

Re: 75 hp warm up problem

Bulb stays hard and not finding gas leaking from any carbs. No drops of gas on bottom of bowls. All three plugs will have about a half a drop of gas that is blackish and clear. Cant tell if the black is coming from the threads as they are pretty oily, but there is definatly some gas on the plugs, and about the same on all three. Did pull all three plugs and wire them up to the ground terminal. Had my wife crank for two seconds and all three had good spark and looked consistent. By the way, to get my wife to help with the “big time waster (boat)” means she really loves me! I do have a new fuel pump but how could defective valves cause it to flood? Wouldn’t the needle and float have to be incorrect or broke for the vavles to cause flooding? Maybe I don’t understand the total functions of the vavles. Would hotter plugs be an option or just masking the problem?? Could I have missed something in the carb cleaning that could cause this? I would love to see a website of the wb26b tillotson carbs showing air passages and fuel flow to help me know if I got the carbs clean.<br /><br />Eurolarva, thanks for taking time to read my ramblings.

 

[roastinears]

Re: 75 hp warm up problem

forgot compression numbers. 155, 150, and 155

 

[bnk999]

Re: 75 hp warm up problem

Have your tried running it with the cover off the motor?

 

[roastinears]

Re: 75 hp warm up problem

yes, in fact the cover stays off more than on lately. i have tore down the carbs again and checked all the ports. everything seems ok, but there is one port on all 3 carbs that i dont know if it partially clogged or not. it the hole right at the beggining of the venturi on the fresh air intake side of the carb. its between the choke plate and the main jet. if i squirt carb cleaner in it, some does come out the tube on the inside of the main jet. but i have not been able to get anything to come back out of him. im pretty sure that hole is involved in the low speed circut, but not sure how. another question, my seloc manual says screw clockwise to lean and counterclockwise to enrich idle mixture, is that correct?

 

[eurolarva]

Re: 75 hp warm up problem

clockwise lean counter rich is correct.

 

[roastinears]

Re: 75 hp warm up problem

First off, thanks to those who responded. eurolarva, you helped me last year, thanks again. i put it all back together, following all the measurements in the seloc manual, except i only backed out the low speed screw 1/2 turn instaed of 1 full turn, and she cranked up and ran til i turned her off. will now work on dialing her in. what did people do before the internet? thanks to the folks at iboats for the site.<br /><br />Tom

 

[eurolarva]

Re: 75 hp warm up problem

My Clymor manual says to do this. Let engine warm up, With motor in forward gear gun the throttle. If the motor dies it is set too lean. If motor stumbles then it is too rich. With these motors it is better to be a little too rich then too lean. Motor too lean can cause poor lubrication and lead to cylinder damage. <br /><br />I agree with you Tom. Three years ago my motor would not work worth a crap and nobody local would work on it. This forum is the only reason my motor runs. I owe a bunch to Roscoe, 12 footer and others here for getting me back on the water.