2000 Mercury 15hp 2st Troubles

[DzyrAdapt]

Hi All,

Not new to fishing but definitely new to boating, bought my first tinny to fix up as a project and have a 15hp Mercury to go on, however i am having issues with getting this running. Fresh fuel, new plugs, good compression etc. I am not new to engines but outboards are getting the better of me.

I have set the correct idle timing and I can get it to fire, however to get an idle, I feel I either need to manually hold the throttle open slightly, or pull on the fast idle lever to get a little more out of it. While holding these it runs like a champ however the second I let go of either it can no longer hold an idle. Now my issue is going through the service manual, I cant find the correct lengths for the linkages to make sure these are correct as it looks like they have been adjusted out of whack. I have given the carb a quick clean which made 0 difference. (If I can get it into gear while I am holding all this I can let go and it will continue to idle)

I have run out of room on the idle screw adjustment on the cam however I have also noted that this cam is quite worn out on the base, there is a good 2-3mm ridge which is allowing it to drop closed even further on idle.

If anybody could point me in the right direction with this one would be greatly appreciated!

[Noelm]

Just saw this, first off, you need to put all the stuff you have played with back in spec (do you have a repair manual?) check spark on all cylinders, then clean the carby properly, every passage must be clean, not just the jets and the float bowl, paying particular attention to the low speed idle circuit. You cant just wash a carb clean, or spray it clean with carb cleaner. Then make 100% sure you have no air leaks around the carb to motor manifold.

[DzyrAdapt]

Hey Noelm,

I do have a copy of the service manual for this one which I am going by for all the settings, timing is set 8 degrees BTDC, WOT is 36 BTDC as specified.

I pulled the carb apart completely this weekend soaked in cleaner, sprayed through and also used compressed air. While I was in this far I also pulled out the reed assembly (familiar with these from bikes) and noted slight gaps (I could see light through these, I used some 2000 grit paper to get the deposits off the assembly and flipped the reeds over, I did get a better seal however I can note a tiny bit of light when moving this around. However definitely better than it was.

I also used some epoxy on the throttle cam to have it pushed slightly higher from where it had worn.

I have now got it to run and idle with the idle screw maxed out on its adjustment, however it will continue to run and can get in and out of gear without stalling.

It does however run quite rough, which I am assuming is due to the reeds. I will be ordering parts to do a proper refresh on the carb and some new parts on the throttle linkage to get it refreshed + some reeds. While I’m at it should I be ordering anything extra to refresh this? Still pumps plenty of water etc.

[Noelm]

Best guess is the reeds were fine, but now that you have fooled around with them, you will need to replace them. Those small carbs are notoriously hard to fully clean, especially the tiny passages in the carb body. Once you get the new bits and pieces, set everything according to the manual as a starting point. I am not too sure what you used the epoxy on, but, gluing bits together is not the way to get it running right.

[BM]

If you are maxing out the throttle stop to keep it running then something is not right. As mentioned, carbs can be a right bugger. I did a repair on a neighbours boat recently. A well known repairer had "rebuilt" the engine after it ingested water for 20K under insurance but if still didn't run properly. I stripped the carb twice and went through it meticulously (4 cylinder Mercruiser inboard) but the only fix was a new carb at $900 trade. As soon as I fitted the new carb, the engine behaved as it was designed to.