Inline mercry 1500 carb problems

[wired247]

New to me 1500 mercury. I overhauled the powerhead and rebuilt the carbs. Put it all back together. I am having difficulty getting it to idle at under 6 degrees BTDC on the muffs and 8-10 BTDC in the water. Tried all sorts of mixture settings but anything over 1 1/4 turn out and it gets rich real fast and dies. In the water and in gear it dies. Throttle plates closed it dies at idle..

 

[Chris1956]

Re: Inline mercry 1500 carb problems

Do you have it timed properly? Late 70s models had adjustable timing pointers. These could be set to show exact timing. Timing spec is 4-6* BTDC with carbs just about to open. Mixture settings 1-1/2 turns out. Now adjust to smooth running in water in gear. Now adjust to allow smooth acceleration.

 

[wired247]

Re: Inline mercry 1500 carb problems

I cannot get 4-6 degrees with the carbs completely closed. It won't idle there without leaning it out to the point where it dies immediately as soon as it goes into gear in the water. Out of the water it runs great. Yes, the timing pointer is in the right position.

 

[Chris1956]

Re: Inline mercry 1500 carb problems

Something is wrong. 1-1/2 turns open on carb idle mixture will usually idle just fine in neutral at 4-6* BTDC. Sometimes the timing belt is off by 1/2 tooth. If you have this, move the belt 1 notch and retry.

 

[wired247]

Re: Inline mercry 1500 carb problems

That may just be it. I'll move it a tooth when I get home. New CDI timing base with a new CDI switch box

 

[wired247]

Re: Inline mercry 1500 carb problems

It was not off and the timing is fine. I did manage to get it to idle at 6 degrees or so but it will certainly not go into gear in the water without dying. I can override the neutral safety switch and get it to start in gear. I can slowly get it to WOT in gear with the prop running but it doesnt get over 1500 RPM. Yes, I pumped the bulb. It gets hard and all that. It just has no power.

 

[wired247]

Re: Inline mercry 1500 carb problems

So I double and triple check everything. Got it idling at 6 degrees with the plates closed and 21 degrees WOT. Double and triple checked the floats, carb passages etc. . I take it down to the river and same old. WOT its 1500 RPM and blaaaaaahhhhhh like it has no timing at all. I monkeyed around with it for a few hours and everything checks out but it still won't run well or shift into gear without dying. Pushed off the dock and same thing. Wouldnt get on plane and 3 mph tops. Made no sense. Finally I get fed up and turn the advance stop screw out 7 full turns and point it to towards the dock 'cause I'm going home. I don't expect it to work . It takes off at that point and I'm going 64 MPH. WTF ? Its probably got 30+ degrees of timing in there now. Still no bottom end but it probably just needs cranking up as well. I don't get it. New CDI switch box, new CDI pickup/distributor body , new plugs etc. Rotors phased right. new rings, good compression, new floats, needles and seats etc. It just acts like it has no timing when it does. Any ideas

 

[Chris1956]

Re: Inline mercry 1500 carb problems

Wired, make sure the max advance is 21*. You will blow it up otherwise. The carbs idle mixture screws are likely set too lean. Richen them up a bit and by trial you should get reasonable acceleration and idle quality.

 

[wired247]

Re: Inline mercry 1500 carb problems

It wont run at 21 degrees. Even WOT at 21 degrees when the idle circuit is no longer an issue at all it just goes ....blaaaahhhh and wont go past 1500 rpm. Its acting like the rotor is out of phase or it has no timing at all. New CDI parts and something just isnt right. This isnt a usual turn the idle screws out sort of thing. The more I think about it the more I'm thinking that CDI screwed up on the trigger wheel

 

[Chris1956]

Re: Inline mercry 1500 carb problems

Wired, The Max timing setting has nothing to do with acceleration from idle. I think your experience is a coincidence. This is a early 70s to late 70 model, with battery powered CDI, right?

What boat and prop are you running? What are compression numbers?

 

[wired247]

Re: Inline mercry 1500 carb problems

Battery CD powered 1973. New CDI switch box and pickup. Acceleration from idle is the least of my worries right now. It idles at 800-1000 ( at 8 or so degress BTDC no less or it dies ) but NOT with the mixture screws out more than 1 1/8 turns out. I can put it in gear and it dies. I cannot open the screws any more with out it dieing immediately. It has ZERO power after idle with the max timing set at 21-23 degrees. spark gap is fine. I have set the throttle and timing up by the book 20 times. I could recite that book from memory in my sleep.

Fresh build 140 PSI+ on all cylinders. 21 pitch 4 blade SS Prop. Gas flowing just fine through the carbs. Its not carburetion or fuel pumps or anything like that. If I add 10 degrees across the board it runs reasonably well.

 

[Chris1956]

Re: Inline mercry 1500 carb problems

Depending on the boat, that 21P prop may be a bit too much. If the prop is too tall, she won't get above idle.

But you have some other issues. Some things to try: That motor should have timing marks on the top cowling support. They are not adjustable, so look for some bent or distorted part that may throw off your timing measurements. If you have a dial indicator you an get a pretty good idea if timing mark is correct.
Normally the idle mixture settings will be almost 2 full turns out from seated. Are the carb floats in good shape? The foam one disolve. The hard plastic ones crack. You have adjusted the brass collar on the distributor to dial-in the idle pickup timing right?

The spark plugs are NGK BUHW gapless plugs, right? The outer flywheel is installed correctly, right? The ign timing wheel in the distributor is installed the correct side up?

 

[wired247]

Re: Inline mercry 1500 carb problems

Fresh rebuild on the carbs with new floats etc. Like I said before. They work fine when the engine is getting sufficient timing OR the rotor is phased somewhat half ***. Timing mark was set with a dial indicator. 464" before TDC etc. Pickup is where it should be. Been over it a hundred times or so. At this point I dont think the CDI distributor body is phasing the rotor properly.


I should be able to go 23 or larger on the prop without issues. It had a 24 raker on there with the old motor. Got up on plane no problem.

 

[Chris1956]

Re: Inline mercry 1500 carb problems

Used a 24 raker on the old motor...what was old motor? I had a 1500 on a 16 footer rated for 85HP. I could spin a 23P prop, but I could not pull a skiier. With a 21P prop I could pull two skiiers, ans top speed was nearly the same as the 23... There is a narrow power band which must be observed on these 99 CU In motors.....

 

[wired247]

Re: Inline mercry 1500 carb problems

Old motor was a 140 Johnson crossflow. It was good for 60 MPH with the 24 pitch raker. Ive already gone 64 mph with the 21 pitch on the 1500 Merc. It will probably do better once its dialed in.

I any case I may have the answer to my problem.

Ive been trying to run a line straight though the centerlines of the crank, distributor , 3 dots and the arrow on the pulley and that is apparently completely wrong. It seems I need to line up the bumps on the outside of the distributor pulley and the bump on the manifold first. Then have the arrow point at the 3 dots instead of having them all in a line .

 

[Chris1956]

Re: Inline mercry 1500 carb problems

Yes, the first step is to set the flywheel at TDC. The matching timing mark should be on the cowling support. Then make the distributor pully cast arrow point at the three dots (or one punch mark)

 

[wired247]

Re: Inline mercry 1500 carb problems

what about the mark on the outside of the distributor pulley and the mark on the collar? Those should line up as well when #1 is at TDC?

 

[Chris1956]

Re: Inline mercry 1500 carb problems

I am not sure about those marks, as my '77 Merc 1500 didn't have them. I had a '73 Merc 850, which had a few extra adjustments (likely like you have) which had been eliminated by 1977. I always tuned the 850 the same as the 1500.

 

[wired247]

Re: Inline mercry 1500 carb problems

I think that what it comes down to is that Ive been trying to time it so the distributor shaft centerline and the crank centerline and the three dots on the flywheel all are in line. Then I line the arrow on the pulley up with the 3 dots. Thats sort of what that poorly written manual alludes to but that doesnt seem to be the case. What I need to do is set it TDC and then align the dot on the outside of the pulley with the dot on the manifold. That seems to be why they are there . The arrow on the inside of the pulley should be pointing in the general direction of the 3 dots then although its not going to be directly in line towards crank centerline like it had been. Ive probably been off by 2 teeth or so. I just need to put the distributor back together tonight and give it a try.

 

[Chris1956]

Re: Inline mercry 1500 carb problems

yes, the cast arrow is the key. Point it at the punch mark, one dot or three dots, which ever you have, with the motor at TDC. That is all there is to it!