Mercruiser 898 missing/losing power under load

[fordmann78]

I have a 1978 Sea Ray SRV220 with a mercruiser 898 198h.p. 305 chevy. 2bbl Rochester carb. I am at wits end trying to get it running good. It starts and idles great. Sometimes it will run great at high speed for 15 minutes sometimes 30 minutes. It will start to lose power and I won't be able to break 2500 rpm with it. I have replaced the fuel pump, points, condenser, plugs, wires, cap, rotor, coil, and rebuilt the carb. I have replaced both fuel filters. I have bypassed the ignition kill shift switch to make sure it wasn't shorting to ground. I have 9 volts at idle and 11.5 volts at 4000 rpm at the coil. I am leaning towards and electrical issue because slightly closing the choke when it is missing just makes it run worse. I have disassembled the distributor and checked the advance weights and everything looks good. I also set the timing at idle to 8degrees btdc. I am out of ideas.1 please help!

 

[NHGuy]

Try running with the gas cap a little loose to rule out a clogged tank vent. If that doesn't solve it try a remote tank. Does the main electrical system have 14 or 15 volts above idle? It should. 9 volts at the the coil is correct.
Heat in there could be giving you partial vapor lock. When it runs badly open the engine hatch and let air at the engine area, keep the rpms a bit above idle and see if cooling things helps. Obviously you can't go tearing around like that but lowering engine bay temp is the goal, see what it does. Does the temp gauge ever get too high?
Does it miss at all engine speeds when it does miss?
The choke needs to be completely open when it's warm, the motor should run badly when warm and choked. So that test you did is OK.
Put a timing light on it and tell us what happens at various RPM. Plus what it does partially warm and fully warm.
Since your distributor has weights it will also have springs. As the motor speed increases the weighted springs should pull the distributor rotor further clockwise. It will stop advancing around 300 or 3200 rpm. You can't see this while the engine is running. You say the advance mechanism looks good. If you haven't done it already you can check the points plate while the motor is off by twisting it slightly (clockwise) around the distributor shaft. It should turn some amount and then return back to the original position. If it's stuck or sticky it could be part of the problem.
I don't think those distributors use vacuum controls but if the distributor has a vacuum line running to it there will be a round gizmo the line goes to. It will have a little link coming out of it. Push the link in til it stops, cover the vacuum port on the opposite end of the device and let go of the link. If it stays down it's working, if it springs back out while you have the vacuum port covered it's leaking.

 

[fordmann78]

It charges at 14.2v. I have tried running it with the cover off with no change. It only has a temp gauge with a yellow green and red bar. It consistently runs in the middle. It had foil faced insulation under the cover so I removed it thinking it was reflecting too much heat. No change there either. It will run wide open and 42-4500 and slowly start dropping off and eventually I won't be able to get it over 2500. Seems to be heat related. It almost acts like someone pulled off 2 or 3 plug wires. If I let it sit for 30 minutes it will run great and do the same thing again. The choke is completely open when warm. The springs and weights are all in great shape. nothing broken or missing. the rotor shaft moves freely on the distributor shaft. I checked the advance last week with the timing light and is advancing good. The advance limiters are where they should be as well. There is no vacuum advance mechanism on this dist. just mechanical. I have worked out some pretty tricky running issues over the years but this one has me stumped. I had an old glastron with a 302 ford and the same model dist that is in this boat and the lock tab that held the rotor shaft to the advance plate had cracked and let the timing wander. This one is acting the exact same way but it all is mint from what I can see. When I first bought the boat a month ago we took it out and it kept stalling but the fuel pump took care of that. Now it is just a high rpm/load problem

 

[Bondo]

It charges at 14.2v. I have tried running it with the cover off with no change. It only has a temp gauge with a yellow green and red bar. It consistently runs in the middle. It had foil faced insulation under the cover so I removed it thinking it was reflecting too much heat. No change there either. It will run wide open and 42-4500 and slowly start dropping off and eventually I won't be able to get it over 2500. Seems to be heat related. It almost acts like someone pulled off 2 or 3 plug wires. If I let it sit for 30 minutes it will run great and do the same thing again. The choke is completely open when warm. The springs and weights are all in great shape. nothing broken or missing. the rotor shaft moves freely on the distributor shaft. I checked the advance last week with the timing light and is advancing good. The advance limiters are where they should be as well. There is no vacuum advance mechanism on this dist. just mechanical. I have worked out some pretty tricky running issues over the years but this one has me stumped. I had an old glastron with a 302 ford and the same model dist that is in this boat and the lock tab that held the rotor shaft to the advance plate had cracked and let the timing wander. This one is acting the exact same way but it all is mint from what I can see. When I first bought the boat a month ago we took it out and it kept stalling but the fuel pump took care of that. Now it is just a high rpm/load problem

Ayuh,.... Welcome Aboard,..... Hook up a remote fuel tank with fresh gas in it, to the fuel filter housin', or fuel pump, if ya don't have a canister type filter, then go Run it,...
That'll rule out the tank, 'n it's contents,....

Sounds to Me, like it's runnin' outa gas,...
Get it fixed, before ya Detonate it to death,...

 

[fordmann78]

I'll give it a shot. I didn't post this but I did empty the tank and start out with 80 gallons of fresh 90 octane Rec fuel. I will try a remote tank first chance I get. I did pull the spin on water separator filer off and it was full of fuel and there was no water if that helps. Thanks for your input.

 

[Bondo]

I'll give it a shot. I didn't post this but I did empty the tank and start out with 80 gallons of fresh 90 octane Rec fuel. I will try a remote tank first chance I get. I did pull the spin on water separator filer off and it was full of fuel and there was no water if that helps. Thanks for your input.

Ayuh,.... The tank is sorta a system itself, the Vent has gotta be clear, the diptube undamaged, 'n not clogged, 'n the anti-siphon valve at the outlet fittin' has to work,...

 

[fordmann78]

How would I know if the anti siphon valve is bad? I can blow backwards into the fuel line easily. should I not be able to?

 

[fordmann78]

Ok, I wasn't able to put it in the lake to run a test tank today and I can't for a few days. I went out and removed the anti siphon valve and it is just a straight through nipple. I siphoned about 5 gallons of fuel from the tank through the tank fitting with no problem. I don't think I have a fuel supply problem. It has to be electrical. I am really stumped. I rechecked my timing and its at 8 degrees. It is steady too (it doesn't flutter around) The thing will literally run all day if you keep it under 2500 rpm.

 

[pureinsanity]

I agree with a lot of the other guys in that I would try a aux tank just to rule your tank out. I don't know if your tank has a mesh filter on the end of the pick up in the tank or not but they can get stopped up and produce the same problem you are having. It will pull fuel good at first but as time goes on it like shucking a berry through a straw. Also I have seen on the GM's the push rod that runs the fuel pump gets worn and will cause the pump to short stroke not let it get a good pull of fuel. You might try putting a electric fuel pump on to rule this issue out. If I can think of anything else I will let you know.

 

[fordmann78]

My dad and I are putting it in the lake tomorrow. We are going to hook up an outboard tank. Tonight I am going to recheck all the wire connections. I didn't mention this but it had a jasper reman engine installed about 200 hours ago. I did have the fuel pump push rod out and doesn't look like there is any wear. I'll update if I find anything. Thanks everyone for your pointers!

 

[fordmann78]

My dad and I are putting it in the lake tomorrow. We are going to hook up an outboard tank. Tonight I am going to recheck all the wire connections. I didn't mention this but it had a jasper reman engine installed about 200 hours ago. I did have the fuel pump push rod out and doesn't look like there is any wear. I'll update if I find anything. Thanks everyone for your pointers!

 

[pureinsanity]

Had a Chevy truck I put a fuel pump on for a guy and after a day or so it would start acting like is was running out of fuel. Put another pump on and it did the same. Talked to a machine shop guy I know and he said change the rod it will take care of it. So I replace the rod. I first set them side by side and the rod I took out looked fine but was a little shorter. The truck run fine after that, and his engine was a rebuilt one also. If it still does it with the other tank I would definitely try a electric pump to rule out the mechanical fuel pump system. I know it sounds stupid, but I scratched my head for days trying to figure out that truck. Good luck !

 

[fordmann78]

Im going to throw this out there. I have always been told to use solid core plug wires with points ignition. The previous owner had installed a set of sierra carbon core wires. Could that cause a problem?

 

[fordmann78]

Ok. Finally figured this thing out. We took it out Monday. My dad brought his scan tool out to check out the ignition. Sunday night I took the dist apart and cleaned and looked it over closer. It seemed tight before I took it apart. I cleaned the old grease off really good which was really hard and old. Lightly greased it and reassembled and set timing. Took it out and acted up way faster than it has before. The scan tool showed it was dropping spark on several cylinders. The coil was getting a perfect signal and firing great so we figured its the cap or rotor. We took the cap off and the upper rotor shaft was extremely sloppy and was letting the timing wander really bad. The only thing we can figure is the old hard grease was getting warm after a while and softening up enough to let it move. Once it cooled down it was fine. I found a new Mallory just like my old one and I'm going to swap them out tonight and see what I get. I have never seen a distributor warn that bad that felt tight until I cleaned the old hard grease out.

 

[fordmann78]

I just wanted to let everyone know a new distributor fixed my problem. Its running better than ever and I picked up 500 rpm. Looks like its time to get a different prop.... Lol ran it several hours today with no problems.

 

[NHGuy]

love it!