'65 MK 1000 RPM fluctuations UPDATE

[Caddy_Kid]

I have a 1965 Merc Mark 1000 in line 6, double coil ignition. 100 PSI compression in each hole, new plugs (Champion J4C's). Here is a list of events:<br /><br />Bought boat motor and trailer this winter, owner deminstrated motor.<br /><br />Boat has origional built in tanks. One was half full of 10+ year old gas, other dry, neither hooked up. Drained and plumbed tanks. Both had hard varnish on all the inside surfaces.<br /><br />Had some motor work done when I found one plug was stripped out. Fired it up a couple times in a garbage can and it ran great, idled fine, nice and smooth while attached to a new carry on tank (didnt want the boat full of gas when I was working on it in the garage).<br /><br />Took it to the lake 3 weeks ago for a test run (on the built in tanks, no carry on) and it did fantastic. Smooth idle, quick throttle response, no dead spot, 4500 RPM WOT. Idled at 1000 RPM which I was going to take down before I took it out again. Took it home (didnt run the engine out of fuel, didnt have a shut off valve yet).<br /><br />Bought a new lower pitch prop. Took it out a week after the first run (last friday). Idled at 800 RPM at the dock (didnt touch the idle from the first time so it should have been 1000). Hit the throttle and it bogged and shuttered. Would only hit 2500 RPM and ran like crap. Would run on high idle anywhere from 2500 up to over 3500 RPM with the idle lever in the fully open position. Go up, come down, go up, come down. Switching tanks from side to side didnt help. Took it back home.<br /><br />Checked plugs, all look fine. Filled the carbs with Sea Foam cleaner and let it sit over night. Drained the carbs this afternoon, turned the built in tanks on and fired it up. Same as at the lake. It would run great up to 3500, then bomb down to 2500 or lower, then slowly climb back. Adjusting the idle mixture screws would make it run faster and a bit better, but then it wouldnt idle as they were screwed most of the way out at that point. Squeezed the primer bulb, thinking maybe it was starving for fuel because of bad pumps, plugged line, etc which dropped the RPM and tried to flood it on the first squeeze.<br /><br />Switched back to the carry on with brand new gas, oil (50:1) and mid-grade fuel. No change.<br /><br />Just took the filters off, soaked them in acetone and blew them out. No visable clogs there. Cleaned the idle adjustment screws which also looked clean.<br /><br />Before I take the carbs apart, what am I missing here? Sorry its so long winded, but figured more specifics might help. My guess is that the old varnish is now disolving in the new gas and its somehow messing with the motor. I figured switching to new gas and tank would help, but it didnt. Thanks.

 

[roger3645]

Re: '65 MK 1000 RPM fluctuations UPDATE

Brian I think you need to take those carbs off for a good cleaning. Also check all fuel lines for leaks (doesn't take much to cause them to start sucking air) and carb filters for debris. Sounds like you heading in the right direction. Also take fuel pump apart and clean. Did you have a good firm ball?

 

[Caddy_Kid]

Re: '65 MK 1000 RPM fluctuations UPDATE

Fired it up this afternoon after cleaning the carb filters and idle needles. Didnt change it any, still big RPM variations.<br /><br />Ran it for awhile and played with the idle needles to at least get it to idle. Found that when I turned the top carb needle, it didnt change it at all. Screwed it all the way in, nothing. All the way out, nothing. Both of the lower carbs changed alot in just one turn.<br /><br />Did that for awhile then suddenly it roared and stayed at a level RPM. Kept at it until it idled correctly (just a hair under 1000, just dosent like to go under that or it sputters badly). Now I have no variations. I imagine something got stuck in there and my turning it freed it up eventually. I will take it to the lake this Sunday and see what happens.<br /><br />Fuel lines are still supple and leak free as far as I can tell. I would rather not re-build the carbs and pumps until this winter when I need to change the shaft seals in the lower unit and water pump anyway. We'll see how it goes this weekend. Thanks!

 

[Clams Canino]

Re: '65 MK 1000 RPM fluctuations UPDATE

If you didn't do the waterpump before using it THIS year, you're wasting your time fixing anything else. Really.<br /><br />-W

 

[Caddy_Kid]

Re: '65 MK 1000 RPM fluctuations UPDATE

So far so good on the water pump. The tell tale is strong and I have a temp sensor on the block just in case. It was changed last season by a shop here in town.

 

[tashasdaddy]

Re: '65 MK 1000 RPM fluctuations UPDATE

Caddy. how big of a gambler are you. i knew it should have been done, jsut wanted to wait, equals $$$$$$$$.

 

[Laddies]

Re: '65 MK 1000 RPM fluctuations UPDATE

If you don't repair your carbs you will trash a cyl. then you don't have to worry about next season

 

[Clams Canino]

Re: '65 MK 1000 RPM fluctuations UPDATE

Ok if the pump was done last year, you'll prolly be OK this year.<br /><br />As for the carbs. You CAN take off the 3 float bowl covers as an assembly, pull out the floats, clear the area in front of the carbs, and then pull the 3 main-jet covers and Idle needles. then with creative use of spray carb cleaner and a wet-vac with a straw to suck out the bowls, you can do a 90% effective carb cleaning.<br /><br />But you prolly need to determine if the fuel tanks are sending stuff in there that ought not to be. <br /><br />Also... have a voltmeter on it... if those things overcharge, and they easily can - the breaker point ignitions will do very strange things - mimicking other probelems.<br /><br />-W

 

[Caddy_Kid]

Re: '65 MK 1000 RPM fluctuations UPDATE

So far I have removed and cleaned the carb filters (they really wernt dirty, but now they are really clean), removed the main jet covers and sprayed cleaner inside them, and removed cleaned and sprayed cleaner in the idle needles. I have a new inline filter installed on the fuel line to the motor which has been in place since I started using the main fuel tanks.<br /><br />My guess is that the old varnish in the tanks is disolving, and when I didnt run the motor dry of fuel after my first test run, the fuel evaporated and left behind some of the varnish which clogged things.<br /><br />Did alright in the garbage can yesterday and we'll see how it does tomorrow on the water.<br /><br />Also, I do have a volt gauge. It reads right about 12-13V at idle, then runs up to around 13-15V after I have been crusing around for awhile. I have heard that if it gets to 16+ volts that it will overheat the motor electrics and actually shut it down for awhile. I havent had that happen yet, and never once on my other older mercs, but I will keep an eye on it. Thanks.

 

[Caddy_Kid]

Re: '65 MK 1000 RPM fluctuations UPDATE

Took it to the lake this Sunday for a test. Did the same thing, RPM flucuations, but not nearly as bad as before. Did catch for a few seconds twice, and ran like it used to. So I will bite the bullet and go to work on the carbs. I have 3 rebuild kits on order, along with 2 fuel pump rebuild kits (figured I may as well do it all at once). This afternoon I will start taking them off.<br /><br />Any hints on removing the upper carb? I know that I will need to remove the starter, but the distributer is in the way on the other side. Any way to get the carb off without having to remove the distributer? Dont really want to mess with something that already works. Thanks.

 

[timmathis]

Re: '65 MK 1000 RPM fluctuations UPDATE

You may have a timing or distributor issue. Keep that in mind. Tim

 

[Caddy_Kid]

Re: '65 MK 1000 RPM fluctuations UPDATE

Very true. In the mean time I have the 3 carbs off as well as the two fuel pumps. Turns out I just needed to move the throttle lever up so the distributer turned out of the way of my wrench on the top one. I will take the carbs apart (one at a time) and have them tanked overnight at a place next to where I work. Then get them in and hopefully have the problem licked.<br /><br />If it were a timing or distributer issue I would have expected it to show up on my first run, not the second and third. Either way, my labor is cheap and so are fuel system parts! Figure I'll start with that and then work down the list if it doesnt help. Thanks.

 

[roger3645]

Re: '65 MK 1000 RPM fluctuations UPDATE

Make sure you remove all plastic from the carbs before soaking them.

 

[Caddy_Kid]

Re: '65 MK 1000 RPM fluctuations UPDATE

Rebuilt both fuel pumps and all three carbs. Never did see anything in them, but they are really clean now. Took it out to the lake today for the first time. Fired up and idles fine (had run it in a bucket at home to adjust everything before hand). Ran it and it comes up to 4200 fine (35 MPH), but anything above that it stumbles. Can hit it WOT and it comes up to 4500, then after about 10 seconds stumbles badly. Back it off, stumbles for a second, then will hold 4200 fine.<br /><br />It seems like the carbs are running out of fuel at the higher RPM's. It runs at 4500 until it drains the bowls, then drops. 4200 seems like the max RPM it can keep up with. Made a number of runs. Seems to do better when the idle screws are in as far as they can go without it dying at idle. I also took them out as far as they would go and still idle and it made the problem worse at higher RPS's. Jets are a .071 and I'm at 3500'. Any other thoughts? At this point its useable, which is nice!

 

[Clams Canino]

Re: '65 MK 1000 RPM fluctuations UPDATE

Check to make sure the floats are opening ALL THE WAY when opened. Sounds simple but I had my middle carb lean out at high RPM's last year and killed 2 pistons. All because the float was off and the main jet outran the needle opening. <br /><br />Sure we set them to close at the right place.. but when it hangs open, look to see how far they open up. <br /><br />-W

 

[Clams Canino]

Re: '65 MK 1000 RPM fluctuations UPDATE

And have someone pump the ball lightly but steadily at WOT to eliminate anything BUT float throughput. And I'm assuming your fuel tank vent is opened properly. <br /><br />The good news is that they run and last the best at 4000-4200 Seriously.<br /><br />-W

 

[Caddy_Kid]

Re: '65 MK 1000 RPM fluctuations UPDATE

Yeah, thats the thing, I dont really want or need to run it any faster, I just would like to know that it COULD if I needed it to. So at this point I guess I'm pretty happy that at least its useable and at a good RPM range.<br /><br />The needle and seat sets that came with the kits were an updated type, all metal. The origional ones had rubber seats. I did have to tweak the open and closed positions on all of them, using a digital calpier (never knew how much I needed one until I bought one awhile back). I set them to the specs that came with the kits. Just a few thousands open. Dont have the instructions in front of me at the moment.<br /><br />Good point about the tank vent. It was fully open. I lunched my tow rigs motor going to the lake this afternoon so it will be awhile before I can try anymore.

 

[Caddy_Kid]

Re: '65 MK 1000 RPM fluctuations UPDATE

Was able to get it out to the lake last weekend. Still waiting on a "new" 425 for the tow car. Should be ready to swap out by the end of the week they tell me.

Anyway, took it to the lake and it tried to run better, but still not like it should. Best WOT I had was 4500 RPM for just a minute. When it was below that you would think it was running fine, then all of a sudden it would pick up, smooth out and sound really great and gain a couple hundred RPM's. Go like that for a min or so, then stumble and go back down. Used new gas in a remote tank, "old" gas in the built in tanks, neither seemed to make a difference.

I'm begining to think its electrical? I would like to check the timing and advance, but there is no pointer, nor degree marks on this thing. Just a mark on the flywheel and an arrow on the distributer gear. Those line up like they should, but in reading the manual you need a couple of instruments to measure the position of #3 piston, while looking at the rotor with the cap off or something along these lines. Is there an easier way? Seems like they could have made it much easier, but not much harder. Any other items I should be looking at as well? Condenser? Points? Coils? I'm a bit stumped since it ran so well the first time to the lake, then like this ever since. Thanks.

 

[Caddy_Kid]

Re: '65 MK 1000 RPM fluctuations UPDATE

Checked the timing and it was great. Put two new fuel filters and a new bulb on the fuel line as the "old" (only been on a couple months) filter was almost plugged (this time they are clear so I can see through them). Put the new Pirana 17 pitch prop on (swapped the 15 blades for 17's figuring that the 5+ MPH loss wasnt worth it, and actually decreased my WOT RPM's). Took it to the lake today and it was the worst it has ever been. Started and idled GREAT, but at WOT would only get up to 2500 RPM's. Switched to a carry on tank, removed the filters and put the old bulb on the fuel line. Did better, up to 3500 now.

Was very discouraged at this point. Went and had lunch and figured the last thing I could do was put the origional 17 pitch prop that the motor came with back on. Did that, and its a new boat! Runs up to 4600 WOT and no stumbles. Running at 4000 RPM it makes just a touch under 35 MPH. Its as good as it was on the first run that I ever did with it. So lesson learned: leave the new design props for the new engines. Go with what works. Thanks for all the help and input!