Throttle cable adjustment on 1972 Mercruiser I/O

[muskrat808]

Hi - Having issues with starting my 1972 StarCraft Mercruiser I/O . Only starts with throttle pushed all the way forward causing engine to start at WOT .With throttle in that starting position ,throttle plate is only a little bit open . At any other position plate is completely closed . Selco manual gives verbal adjustment info but no pics , online manual shows some pics but no real adjustment info that I can find . Any advice out there ? Thanks

 

[Bondo]

With throttle in that starting position ,throttle plate is only a little bit open . At any other position plate is completely closed

Ayuh,..... Please explain,..... It's Sop to move the throttle to start a carbed motor, then pull back when it lights,.....

 

[muskrat808]

SOP would be throttle somewhere between idle position and halfway or so to WOT, wouldn't it ? It only starts at WOT which I don't think is good for the engine right ? Thanks

 

[Fed]

I had an old 165 that required pushing the throttle all the way to set the choke, you could hear a definite 'plink' noise when it closed. Then I pulled the throttle back to a sensible position before starting and after it warmed up the choke would automatically turn off. Much the same as many older cars.
It sounds like you're confusing the throttle butterflys and the choke butterflys when you say at WOT the throttle plate is shut.

 

[muskrat808]

Thanks Fed , I may very well be confusing the two . So choke plate is the large one covering the entire carb opening and the throttle butterflies are where ? Or does that matter in figuring out my starting problem ? The starting method you describe is what worked for me in the past but not recently . Thanks

 

[Fed]

I could push the choke plate out of the way & look further down into the carb & see the throttle butterflies.
I could also operated the linkage & see a nice squirt (possibly 2) of fuel going in from the accelerator pump.
Bear in mind yours may be completely different from my old one.

 

[muskrat808]

OK ,I can see fuel squirting into the carb so gas is getting there . However still having problems starting it cold .Still needing to push throttle control all the way or just short of WOT to start . After warm up it idles and restarts fine. There seems to be a lot of extra slack in the throttle cable between the control box and carb . Any more suggestions? Thanks

 

[Bondo]

However still having problems starting it cold .Still needing to push throttle control all the way or just short of WOT to start .

Ayuh,.... What is yer method to start the motor, cold,..??

Bein' a Carb, 'n not Efi like yer car, it takes throttle actions to start the motor, cold,.....

 

[Fed]

What motor is it?

 

[muskrat808]

Motor is a 1972 Mercruiser , 140 hp 4 cyl GM with a Rochester carb . Cold starting method- push throttle all the way forward 1-3 time than start with throttle straight up or forward 1/2 way to WOT . Past three years usually started right up . Sometimes would need to do the WOT start technique . Just had exhaust manifold and elbow replaced AND carb rebuilt .When got back from shop I thought the rebuilt carb would have cured the intermittent starting issues but it seems the same or worse . Shop says it started for them OK and that whatever starting issue I'm having is independent of carb rebuild . Thanks

 

[Bondo]

Cold starting method- push throttle all the way forward 1-3 time than start with throttle straight up or forward 1/2 way to WOT

Ayuh,.... As I said, ya gotta use the throttle on a carb, unlike Efi,.....

I wouldn't expect it to start with the throttle straight up, ei: at Idle,....
'n 1/2 way to Wot, is maybe 1/4 throttle, as almost the 1st third of lever motion is the shifter, before the throttle takes up,...

When got back from shop I thought the rebuilt carb would have cured the intermittent starting issues but it seems the same or worse . Shop says it started for them OK and that whatever starting issue I'm having is independent of carb rebuild

I have to agree, it's yer method, not the carb,...

 

[Fed]

By my fading memory when the choke is 'set' after pushing the throttle fully forward then returning back to a sensible starting position then you can no longer push the choke butterfly to the open position by hand.
Alternatively when the choke is 'not set' you can move the choke butterfly by hand.
Does that ring a bell with you Bondo?

I guess I'm asking Muskrat, are you indeed setting the choke or not?

Move to Mercruiser section Bondo?

 

[muskrat808]

Muskrat here - I'm not sure if I'm setting the choke . I'll try your ( Fed's ) test method to see . It seems like I could manually move the choke butterfly after moving throttle all the way forward and back but I'll have to double check . Thanks

 

[Fed]

Sorry I couldn't help more it's really ancient memories for me now.
You should be able to see or hear if the choke is being 'set' by moving the throttle to WOT.
You could also try disconnecting the throttle cable at the carb & have a play with the carb linkage to see how it works.

 

[Bondo]

By my fading memory when the choke is 'set' after pushing the throttle fully forward then returning back to a sensible starting position then you can no longer push the choke butterfly to the open position by hand.
Alternatively when the choke is 'not set' you can move the choke butterfly by hand.
Does that ring a bell with you Bondo?

I guess I'm asking Muskrat, are you indeed setting the choke or not?

Move to Mercruiser section Bondo?

Ayuh,.... Correct,.... It takes at least one full stroke to Wot, to set the choke,....
Which also actuates the acc. pump for a squirt of raw gas down the carb,...

I pump 2 to 4 times, then at 'bout 3/4 throttle I hit the key,...
As soon as it Lites, I pull back to idle, or just above, til it warms up, 'n the choke pulls off,....
Just as ya shift an Alpha, Briskly, ya pull back the throttle Briskly, when it fires up,....
Then I go Boatin',.....

If Muskrat wants this moved to the Merc forum,. No problem, I'll move it,....

 

[muskrat808]

OK guys ,Taking her out in real water to see if she still floats and if your hints have helped . Will let you know how it goes . Thanks

 

[muskrat808]

OK , took her out- good news she still floats , bad news- still having starting issues . Once again when warmed up starts ok with minor throttle movement. However on first cold start attempt ( 3 or so full throttle pushes and then forward to start ) it only will start at WOT . Obviously then I immediately pull back the throttle but I still can't believe even brief WOT start is good for engine wear . So . if you think pushing this thread to Merc section may help , I'm game . Thanks , Muskrat

 

[Fed]

So is it setting the auto choke or not?

 

[johnkom]

Cold engine. Remove flame arrestor so you can see choke butterfly. At first throttle movement, choke should snap closed. Moving the throttle further forward actuates the accelerator pump and squirts fuel into the carb throat. Depending on how cold it is will determine how many times you need to "pump" the throttle. Each stroke of the throttle squirts more fuel in. If the carb is overhauled, the new pump may be flooding the engine: Too much fuel. In which case, WOT induces fresh air, leaning the mixture until the right ratio for starting.

At start the engine partially sucks in the choke buttery to allow the engine to run. If the spring on the auto choke is bad or not set right it can cause starting problems.

Good luck.

JK

 

[johnkom]

One more thing. If you think it is flooding, have you tried starting by just "cracking" the throttle out of idle? Enough to set the choke but not introduce any fuel.

JK