1979 7.5hp mercury skipping

[dperkins8694]

I finally had some time to take the boat out to try it after rebuilding the carb, replacing the switch box, plugs, gaskets, and impeller. Ran great 3/4 of the way but on the way back at high rpms WOT it started making a clinking noise and would jump in and out of high speeds, like it was skipping. Did not hear the noise or notice any change in power at 1/2 throttle to idle. Where should I start? Thanks.

 

[dperkins8694]

Re: 1979 7.5hp mercury skipping

anyone?? Going to drain the lower unit and make sure it did not leak out the oil. I had to take the flywhell off, could it be something in there?? or do you think its all in the LU? Lost, thanks.

 

[dajohnson53]

Re: 1979 7.5hp mercury skipping

I finally had some time to take the boat out to try it after rebuilding the carb, replacing the switch box, plugs, gaskets, and impeller. Ran great 3/4 of the way but on the way back at high rpms WOT it started making a clinking noise and would jump in and out of high speeds, like it was skipping. Did not hear the noise or notice any change in power at 1/2 throttle to idle. Where should I start? Thanks.

Why did you change the switchbox? How are the coils?

 

[green4themoney]

Re: 1979 7.5hp mercury skipping

would it just start to revv up really high then you may have lost speed? if this is the case your rubber hub might be done in your prop, and its slippin under load at high speeds in the water, can you be a little more descriptive?? thanks

 

[dperkins8694]

Re: 1979 7.5hp mercury skipping

all coils are good, had the lines from the switch box to the lower plug go bad and was not getting spark. It was running great at high speeds, then it would jump down and then back up and you can feel it jump, but only on high speeds. I felt like the prop just stopped spinning. I have been told it might be the hub, but looking at the tear down in the book it does not have a rubber hub. http://www.crowleymarine.com/mercury_parts/297/160.cfm Thanks.

 

[green4themoney]

Re: 1979 7.5hp mercury skipping

it has a rubber hub, they just arent showing the insert because that is part of the propeller packadge, if your engine is revving up really high and your feel the prop isnt turning then that would sound more like the hub but you said the engine just revvs down?

 

[dperkins8694]

Re: 1979 7.5hp mercury skipping

no it feels like the prop is not moving. Now would the hub be the rubber part on the inside of the prop? I did look at that and IT IS BAD!!!! But it did not look like you can take it out. Thanks

 

[green4themoney]

Re: 1979 7.5hp mercury skipping

ok well its the hub, the purpose of the hub is to save your drive gears if you are to strike and underwater object the prop will stay still on the rock while the prop shaft and hub will spin saving your gears. now you are going to need a new hub, i believe you can take the old one off with a torch, i believe you simply leave the prop on the propshaft and go around the rubber hub with the torch till you heat the rubber enough then simply pull the prop right off while the hub will stay right on the prop shaft, then you can take that off after, you will need to get a new one inserted obviosly.

 

[dperkins8694]

Re: 1979 7.5hp mercury skipping

I have not removed the hub yet, was wanting to find the replacement part prior to removal. For the life of me I can not find the correct part number. Could it be the hub is a non replaceable unit that comes preinstalled in the prop? Im going to call my merc dealer today to see if he has any info.

 

[dajohnson53]

Re: 1979 7.5hp mercury skipping

I have not removed the hub yet, was wanting to find the replacement part prior to removal. For the life of me I can not find the correct part number. Could it be the hub is a non replaceable unit that comes preinstalled in the prop? Im going to call my merc dealer today to see if he has any info.

If it's the rubber hub, you'll need to either replace the entire prop or get it "rehubbed' at a prop shop. As far as I know, it's not a part you can buy and replace yourself. Could be very close in price for that motor and you may decide just to get a new prop, especially if the old one is beat up at all.

There are ways to determine if it is indeed the hub if you're at all unsure.

 

[dperkins8694]

Re: 1979 7.5hp mercury skipping

Thanks, just going to go with a new prop. My prop's not to bad but heck might as well replace it. Need to get a river guard now. Thanks all.