hesitation on takeoff

[freddyray21]

1972 Mercruiser 120 with electronic ign (aftermarket) starts and runs fine. compression on all four right at 130 give or take a pound or two. runs very good, but has a bad hesitation on takeoff. Almost and cough then take off. accelerator pump has two good streams when working it. idles good and smooth, but does not want to seem to idle down for me. Seems to want to idle just a bit high around 9-1000 and can't seem to get it down any more. If I manually work the linkage at the carb it will so I think worn return spring, but what about the hesitation?

 

[subcrx]

Re: hesitation on takeoff

how are your plug wires

 

[Maclin]

Re: hesitation on takeoff

Was it running ok and this just started happening? or has it always run this way for you? Did it begin happening right after some other change was made (like electronic ignition conversion)?

Have you checked the dwell and timing lately? With the electronic ignition there probably is no dwell adjustment but it should check within spec. Sometimes timing too far advanced can cause a hesitation like that.

Plug wires like subcrx mentioned and spark plug gap can also be a factor. Cap, rotor, yada......

 

[Maclin]

Re: hesitation on takeoff

Freddyray,

I would want to check the mechanical advance in the distributor by removing the cap then turning the rotor shaft and see if it moves some then snaps back, that would be normal operation. If it moves but does not snap back or it does not move then that is not normal distributor operation and could be part of your problem.

If it does not move then perhaps the timing has been adjusted to cover that and there is too much initial advance. If it moves but does not snap back then that could explain some of the floating and too-high idle.

Easy enough to check, and you can inspect the cap and rotor as well. Then check the timing.

 

[freddyray21]

Re: hesitation on takeoff

new cap and rotor and wires. plugs are also new every year whether needed or not. I did have to just change the fuel pump and it started after this. My brother ran it out of gas and the fuel pump was probably weak and killed it.

 

[Maclin]

Re: hesitation on takeoff

Could be high fuel level in the bowls, new fuel pump might be out-pressuring the carb needle and seat now, just a thought.

 

[nailem]

Re: hesitation on takeoff

what kind of carb is it? i have the same proble with my Q-jet 4bbl. i no machanical advance with my TB IV ignition. i advanced the timing from 8* to 9* and it is better but not gone. good luck.

 

[freddyray21]

Re: hesitation on takeoff

I haven't changed the timing. It is still checking dead on at I recall. I did check the advance some time back, but have not recently. I would imagine it is okay, but don't know for sure. I am going to take it out and readjust the carbs and see how it does. Just fyi, this is not a new boat to me. This is my third season running it with virtually no problems.

 

[Coors]

Re: hesitation on takeoff

You may have sucked the crap laying in the bottom of the tank in.
http://forums.iboats.com/showthread.php?t=167561
At least that will take one problem off the list.

 

[Lone Duck]

Re: hesitation on takeoff

open low speed jets 1/4 to 1/2 turn. Could be set a little lean. That would cause high idle and stumble when hitting throttle.