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Engine not right at WOT 81 90hp V4

Keithm18

Keithm18

Regular Contributor
Hi All.

i have a problem I need assistance with please.

i managed to get the boat back on the water today. Engine idles and runs ok. It's a little slow out of the whole and at WOT it appears to be holding back. I checked plugs and found one cylinder was running lean. I pulled the jets and blew them out, but there was no apparent problem. That did however cure the lean burn on that cylinder.

the flat WOT remained and engine sounds a little rough. I fiddled with the lync and sync from one extreme to the other and found a good balance, but the motor is still holding back at wot. Feels either like it's overfuelled or underfuelled. Spark plugs were light brown, which I believe is good.

gave the choke primer a bump and this make the revs dip and pumped the primer bulb with no difference at all.

all cylinders firing and jumping 7/16" gap fine.

I'm thinking of opening carbs and blowing out all channels etc. During the last carb service I wasn't completely happy with the float adjustment. The carbs don't leak when I pump the primer bulb hard, making me think that the carb isn't flooding. is it,possible that a small fault on the on the float adjustment is what's causing this?

Another interesting thing that happened was that at one point the engine really took off, like it used to. with a great wot, turns out that 20 seconds later it dies because I was running it of fuel. I tilted the tank and pumped the primer bulb and it then took off like crazy again, but died 20 seconds later due to no fuel again.

This behavior leads to me feel there is an overfuel situation.

Comments or ideas please.

thanks
 
Hopefully you can return the link/sync back to where it belongs.... this is either perfect or it is wrong!

Your explanation of the problem indicates that the carburetors require cleaning and rebuilding. You cleaned what jets? Did you manually clean the high speed jets that are located in the bottom center portion of the float chamber? If not, do so (all 4 of them).

With the carburetor face plate removed, and pumping the fuel primer bulb up hard.... does fuel flow from the carburetors? If so, again this requires removal of and reworking of the carburetors. (float level, faulty float needle valve, etc)

Should the engine continue to run if you constantly pump the fuel primer bulb... not run perfectly perhaps but contiunues to run on in some fashion... but dies out within a short period of time otherwise, you have either a faulty fuel pump or a air/fuel leak at some point between the fuel pump and the fuel supply.
 
Hi Joe and Kim.

Compression between 110 and 115. Engine is not new to me. Have done a lot of work on it. Most recently replacing powerpack and coil to cure a one of the cylinders that would drop out under load.

carbs were completely stripped and rebuilt about two months ago by me with new sierra kits, including all gaskets and needles and seats.

Reading my manual and looking at the markings on the cams etc, I am confident the lynx and sync is in the right place.

no fuel comes out of carb when I pump the primer bulb. I removed and cleaned the high speed jets on the top carbs with a piece of thin wire while out today, but couldn't get to bottom ones.


I'm going to remove and rebuild carbs again and see of this cures the problem. Will post back next week if this cures the issue.

thanks
 
Will also replace fuel lines and check out the fuel pump.

Prop is correct pitch and hull is squeaky clean. I will shortly be installing a tach and will confirm wot rpm is at the correct point, this will confirm prop selection.
 
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