PDA

View Full Version : Interesting Engine Problem (85 S&S)


19oRaNgEs&s85
08-07-2009, 03:19 PM
Hi all,
I am having a heck of a time with my 85 S&S this summer (351w). It is an interesting problem so bear with me. The boat starts great and runs perfect if you never shut the engine off. The problem I am having is when I take the boat out and get the engine up to running temperature and then shut the boat off for longer than 10-15 minutes. Upon start up it starts fine, but then once we start cruising it seems like its running out of gas in the lower RPMs (idle - 1500). The RPMs fluctuate between 1500 and 1000 at constant throttle (for example). It doesn’t die, it just doesn’t run properly. If you get the boat up on plane it doesn’t have the problem (i.e. problem is not in the upper RPMs), and if you make a lap around the lake and bring it back to idle it is fine again (problem only lasts short time). The other thing about it is that it is hard to show someone what it is doing because you have to sit for 10-30min before restarting or it won’t have the problem.
I have recently updated to EI, and the Carburetor was rebuilt a couple years ago (has ran fine up until this summer).
I at first thought that something electrical might be breaking down with the engine heat, but after the EI, coil, and wires change I am not so sure about that now. Other things I can think of are Vapor Lock, or some kind of Fuel issue (i.e. Fuel Pump going out?).

If anyone has some suggestions they would be much appreciated! Thanks!

thatsmrmastercraft
08-07-2009, 03:24 PM
When it is acting up, do you have to struggle with it to get up on plane? It really sounds like a fuel issue, either vapor lock or a float level issue.

CameronCarey
08-07-2009, 03:38 PM
float could be hanging up on something in that range, low speed sputter is usually more associated with Timing, or Coil though. the timing and the coil would be my first two checks. The third would be fuel pressure.........5psi is about what you need...

19oRaNgEs&s85
08-07-2009, 03:39 PM
It is not a terrible struggle to get it up on plane, the engine just kind of surges until you get to about 2000 RPM. I am thinking it is fuel too, just don't know where to start. Coil is brand new and timing was just checked.
The other thing is that it doesn't do it right away, you have to get it good and warm and then let it sit for a while. If it were the carb. wouldn't I be having problems right from start up?

CameronCarey
08-07-2009, 03:54 PM
It is not a terrible struggle to get it up on plane, the engine just kind of surges until you get to about 2000 RPM. I am thinking it is fuel too, just don't know where to start. Coil is brand new and timing was just checked.
The other thing is that it doesn't do it right away, you have to get it good and warm and then let it sit for a while. If it were the carb. wouldn't I be having problems right from start up?

you can buy a T fitting (7 bucks) from home depot and a fuel pressure gauge (any performance shop or napa) for around 20 bucks and troubleshoot the fuel side.

the FP gauge is a good idea anyway for diagnosing those .........broke and drifting problems...

on my boat i just put it on the Fuel out NPT threaded fitting

thatsmrmastercraft
08-08-2009, 01:06 PM
If it has to sit hot awhile before it happens, I still lean towards vapor lock. Have you looked down the card periodically while its sitting to see if the fuel is leaking out through the primary side of the carb? If its boiling over you should see some fuel there. Just a thought.

Cloaked
08-08-2009, 02:37 PM
If it has to sit hot awhile before it happens, I still lean towards vapor lock. Have you looked down the card periodically while its sitting to see if the fuel is leaking out through the primary side of the carb? If its boiling over you should see some fuel there. Just a thought.
Thus the spacer plate under the 4160.

My question to the original poster, do you have the 1" plate under the carb?

http://skidim.com/prodinfo.asp?number=R062075




.

thatsmrmastercraft
08-08-2009, 06:41 PM
Cloaked may have the answer here. I guess I have run into a few guys who thought they knew better and removed the spacer and suffered the consequences.

I suppose another possibility would be a poorly routed fuel line getting too hot and causing problems. How about an engine cover not being properly vented?

Have you tried letting it sit for the doomed 20 - 30 minutes with the engine cover open to see if that alleviates the problem?

19oRaNgEs&s85
08-08-2009, 07:08 PM
Thanks for the responses guys. I do have the 1" spacer under the carb. I have not checked or noticed any fuel leaking out of the primary side of the carb but I will look for it next time I am out. I am going to check my fuel pressure the next time i go out, and run it with the engine box open to see if that makes a difference. I would think doing those two things should help rule out fuel pressure issues in the lines and at the pump, and I shouldn't be having vapor lock issues with the cover up. The engine cover has been modified but to the better, it has two additional vents installed in the front of the engine cover along with the factory vent in the rear. I have also tried running the boat with the blower on at all times. I will check out some of the suggestions so far and provide updates, but if anyone has any more suggestions I am still listening:-)
Thanks!

TMCNo1
08-08-2009, 07:15 PM
Simple experiment, if you think it is vapor lock, wrap the entire fuel line with aluminum foil (shiny side out) from the fuel pump to the carb to see if it makes any difference. The foil will reflect most of the radiant heat from the engine and help prevent the vapor lock. Several flat black painted clothes pins will do the same thing and draw heat away from the fuel line acting as heat sinks.