1976 Merc 1150 crackling during 1st 2 or 3 seconds of heavy throttle

[oldguy60]

Hello. I have a Mercury, 1976, 1150, thunderbolt ignition that was into the shop recently and had the timing checked and spark checked and I have done a compression test on it and all cylinders are fine (140,155,155,155,155,150) so I took it out yesterday for it's maiden voyage and it ran very well except that when I give it hard throttle from a low rpm condition it makes this kind of crackling type of sound for a few seconds until it builds up the rpm's and then it disappears. Is it possible that I am hearing engine ping? Is there some sort of vacuum advance system on the distributor that could be malfunctioning and thus the ping? It had a new rotor assembly put in it a few years back and the cap and rotor are in good shape. I am using a 50:1 mix ratio and I put a half a can of Seafoam in the 6 gal tank to try and see if the carbon cleaning action of it will bring up the #1 cylinder compression. Can the Seafoam be causing this type of noise? Any ideas / help? Thanks!

 

[daveswaves]

Re: 1976 Merc 1150 crackling during 1st 2 or 3 seconds of heavy throttle

Hello. I have a Mercury, 1976, 1150, thunderbolt ignition that was into the shop recently and had the timing checked and spark checked and I have done a compression test on it and all cylinders are fine (140,155,155,155,155,150) so I took it out yesterday for it's maiden voyage and it ran very well except that when I give it hard throttle from a low rpm condition it makes this kind of crackling type of sound for a few seconds until it builds up the rpm's and then it disappears. Is it possible that I am hearing engine ping? Is there some sort of vacuum advance system on the distributor that could be malfunctioning and thus the ping? It had a new rotor assembly put in it a few years back and the cap and rotor are in good shape. I am using a 50:1 mix ratio and I put a half a can of Seafoam in the 6 gal tank to try and see if the carbon cleaning action of it will bring up the #1 cylinder compression. Can the Seafoam be causing this type of noise? Any ideas / help? Thanks!

Yes, that is pinging and it will destroy that nice inline. Even though the sticker on the motor says 23 degrees that was for 1973 fuel. Todays fuel is more likely to pre ignite in that inline. Conventional wisdom is to reduce the timing to 21 degrees and make sure you are propped such that WOT RPM is above 5500. 4800 RPM is deadly for that engine (as a WOT max)
The sea foam should not cause the problem and cyl 1 at 140 is still very healthy. Check with your service shop and ask what they set the timing at. If it is a mercury shop there is a Mercury service bulletin recommending 21 degrees max.

 

[oldguy60]

Re: 1976 Merc 1150 crackling during 1st 2 or 3 seconds of heavy throttle

Thanks so much - I'll check the timing and make the changes.

 

[oldguy60]

Re: 1976 Merc 1150 crackling during 1st 2 or 3 seconds of heavy throttle

I checked with the shop mechanic that set up the timing and he said he set it at 21 degrees (as there was a sticker placed over the original timing sticker saying timing should be set at 21 degrees). So I guess I will put some octane booster in the remaining fuel I have to use up and then switch to 'premium' gas in stead of the low octane marine gas I am using now and see if the pinging clears up.
I could not try the prop I currently have on the engine at WOT yet because the lake was too rough that day to open it right up. I was given 3 props with the engine (2 x 3 blade props and 1 x 2 blade prop). Can a person find out if one of these will give me the correct RPM operating range you speak of (5500 WOT) "just by the numbers on the prop" or do you have to actually try each one on the engine in the water at WOT? Where we usually boat there is not too many shallow bank areas to make a prop change ( and these a banned to boats as they are swimming areas).

 

[daveswaves]

Re: 1976 Merc 1150 crackling during 1st 2 or 3 seconds of heavy throttle

There should be numbers on the prop such as 14 x 19P or equivalent. The two bladed props are probably not the best idea, more blades are better in your set up. I would guess that you should be looking at a 15pitch or possibly 17p. Good that themechanic set it at 21, hang on to that guy.

 

[oldguy60]

Re: 1976 Merc 1150 crackling during 1st 2 or 3 seconds of heavy throttle

OK - the prop that is currently on the engine is a: 3 blade (48-67280A4 21P) and the other prop that came with the boat is a: 3 blade (48 - 32264-17). They both appear to measure about 13" diameter.
Can someone interpret these for me and tell me what I can expect from each of these props with this 1979 1150 in line 6? - Thanks.

 

[daveswaves]

Re: 1976 Merc 1150 crackling during 1st 2 or 3 seconds of heavy throttle

OK - the prop that is currently on the engine is a: 3 blade (48-67280A4 21P) and the other prop that came with the boat is a: 3 blade (48 - 32264-17). They both appear to measure about 13" diameter.
Can someone interpret these for me and tell me what I can expect from each of these props with this 1979 1150 in line 6? - Thanks.

Yup,they are both Merc props, one is 21 pitch which is too high for your engine unless your boat is really really light( less than 900 lbs) The 17Pitch is a better candidate. What kind ofboat is the motor on?

 

[oldguy60]

Re: 1976 Merc 1150 crackling during 1st 2 or 3 seconds of heavy throttle

It's on a 1966 Glasspar 16' runabout 4 seater with a Rude 6 1/2 hp kicker also that weighs about 60lbs. I don't know how much the boat weighs but it is primarily a lake boat as it is not a really deep-v (the kind with the with the high gunwales for the ocean).

 

[oldguy60]

Re: 1976 Merc 1150 crackling during 1st 2 or 3 seconds of heavy throttle

Here is a picture of it.

 

[oldguy60]

Re: 1976 Merc 1150 crackling during 1st 2 or 3 seconds of heavy throttle

In reply to earlier post by DaveWaves about my Merc.inline 115HP six WOT rpm should be above 5500rpm??
I don't have the owner's manual for this engine but everything I found online in relation to this engine (1976, 1150) says the WOT rpm should be between 4800 and 5300. You say that it should be proped to run at "above" 5500 rpm - I don't understand - wouldn't this damage the engine to run above the max rpm stated by the manufacturer??
Also I am not clear on why the WOT is used for choosing a prop when the engine would not by run Wide Open very often and not for long periods of time because of water conditions, # of people in the boat, and economy. etc.?

 

[daveswaves]

Re: 1976 Merc 1150 crackling during 1st 2 or 3 seconds of heavy throttle

In reply to earlier post by DaveWaves about my Merc.inline 115HP six WOT rpm should be above 5500rpm??
I don't have the owner's manual for this engine but everything I found online in relation to this engine (1976, 1150) says the WOT rpm should be between 4800 and 5300. You say that it should be proped to run at "above" 5500 rpm - I don't understand - wouldn't this damage the engine to run above the max rpm stated by the manufacturer??
Also I am not clear on why the WOT is used for choosing a prop when the engine would not by run Wide Open very often and not for long periods of time because of water conditions, # of people in the boat, and economy. etc.?

Sorry, that was my mistake the newer inlines spin faster, yours is correct at 5200 to 5300. The reason they pick the prop pitch at WOT is to make sure you don,t overload the engine with too high a pitch prop. It would be the equivalent of trying to start moving in your standard shift car in third gear, its possible but hard on the engine and clutch.