1979 Mercury 80HP fires but will not run PLEASE

[heyblue]

Posted this without any response in the 17th, so trying again. [h=2]1979 80 HP Will not start[/h]

Bought engine used so I do not know history. Noticed hole in exhaust side plate so replaced it and one of the inner plates
which were very pitted and had a hole in it. Had to rebuild starter, it was very corroded internally, Removed and rebuilt both carbs. They didn't look too bad though. Replaced the water pump since didn't know history, It also didn't look too bad.Tried to start it. Can get it to fire up and run for short bursts if I squirt starter fluid in the carbs. It will not stay running.
Battery is fully charged and the motor turns over fine. I checked all four plugs and they are firing when left out of the cylinders just hanging on the plug wires. I checked compression and have 150 psi in top 3 pistons number 4 is only 90. Got those reading with all plugs removed. I removed fuel line just in front of carbs and get gas squirting out when I crank it. I also removed the main jet on the top carb and gas came out indicating the bowl had gas in it. I tried to check timing but noticed the marks on the top crank seem to be about 1/4 turn off. I looked into piston 1 with plug removed and when it was at the top I put a mark on the crank gear where it aligned with the timing tab. Then when using a timing light on #1 it was firing close to the mark, so assume it can not be off that much and that the crank gear must have been removed at some time and not put back on correctly. One other thing I tried., while cranking I put my hand over one of the carbs thinking that would force the enginene to suck gas. The suction was not that great, and the engine did not start, though it seemed to try at a few points. When I have put my hand over 4 cycle engines I have noticed quit a bit of vacummn. Not sure if I should expect the same with 2 cycle engines. If this was a 4 cycle I would have assumed a possible major leak in the intake manifold, but it doesn't seem like this engine has a intake manifold, or does it?? Any ideas? Thanks in advance.

 

[Chris1956]

Well, if it only runs on fuel squirted into carbs, it is not pulling fuel from the carb bowl. Make sure the floats are set properly. You might replace them, especially if they are the old foam type. Clean the idle restrictor tube and the small holes in the carb throat. Adjust the idle mixtures to 1-1/2 turns open and retest.

 

[Chris1956]

Also, set motor to TDC by using a screwdriver thru the top plug hole. Now look at timing marks. They should be nearly aligned. If the outer flywheel was put on incorrectly, the timing marks will be a minimum of 45* off. You should be able to see that. If you see that, remove the 8 bolts around the flywheel nut and reposition outer flywheel.

Do you have gaskets under the carb bases? Are the crankcase cover bolts tight?

 

[heyblue]

Chris

Thanks for responding. The carb rebuild kit cam with new gaskets, so they are installed between engine and carbs. I will check the bolts on the engine this evening when I get home. I think I did a good job of cleaning out all the passages on the carbs when I had them apart. I will consider redoing it if I need to replace the floats. What is your take on my not feeling a strong suction when placing hands over carbs during cranking? Do both carb feed into the same crank space internal? If that is the case I guess the only way to feel a strong suction is to cover both??

On the timing, How I decided the flywheel is not on correctly is I did just as you stated and used a screwdriver to get #1 TDC then looked at the timing tab and noticed it is quite a bit off like 45 or even 90 degrees. If I were to reinstall it I have a question about the marks. There seems to be a section of marks that indicate tdc then a space marked spark, the a mark that I think was about 30. Then further on the flywheel is some marks that startt at - and a small number like 6 or 7 going to + about the same. I am doing this from memory since the boat is down the road from me now.

As far as timing it seems the marks are only useful for setting the starting adjustment for idle and the max spark adjustment. Since there is no distributor the timing seems fixed by the position of the stator/pick up coil?

 

[Chris1956]

Each carb feeds two cylinders. The cylinder pairs are sealed (somewhat) from each other by the main roller bearings. You will feel some suction on the carb, but maybe not too much. With the top cylinder set at top dead center, the timing marks should indicate TDC. Adjust the flywheel to read a close to TDC as possible. Max spark advance is probably 21* BTDC. Idle pickup is probably 4* ATDC or so. Timing is changed by the position of the trigger. The trigger under the flywheel rotates as the throttle is opening. It must be synched with the carb opening. Normally the trigger would be set to 4*ATDC, just as the carb starts to open. You need to get the exact Ign specs for your motor.

 

[heyblue]

First let me say thank you Chris;

My engine now runs. After reading your suggestions and comments, I sort of started over, keeping in mine compression/fuel/spark. I rechecked the timing issue and in deed the flywheel is not installed correctly and is off by about 45 degrees.I will fix that later. I next took off the carbs and rechecked the float settings. They were both off quite a bit, so that the bowls were not filling up to the proper level. Rechecked all passage ways and reassembled. I installed them, primed the fuel with the bulb and bam it started right up and stayed on. As a interesting and even funny side note, I noticed there was some arching around the coil for #1 so shut down to investigate. I had forgot to reinstall the #1 plug after checking timing. Put plug in and again started right up and of course it idled even better being on all 4. Goes to show if you have the 3 basics engines want to run. Hope anyone reading this finds my adventure useful for you.