Loss of power/engine coughs then dies
 

This has happened 3 times now. Takeoff from marina, accelerates with authority, snaps on plane, cruising at 3500 rpm. After about 3 minutes, boats feels like power is dropping off...I give it more gas to bring speed back up, but the power that was there when I first took off from marina is gone. I then decelerate, and as I come down off plane, engine coughs and dies. Engine starts back up each timeand I idle back to marina. This is a brand new 489 with 3 hrs on it, Cam with 230 dur, 595 lift from Bob @Marine kinetics, 188 heads, factory refurb Holley 750, MSD coil, Thunderbolt IV ign, Holley elec fuel pump, 3/8 lines, 454 mag intake. Timing @ 10, 34 total, floats adjusted. Scratching my head in Austin (in 100 deg heat!!!) The coil (2 seasons on it) and the TBIV are the only parts which are not brand new.

I would check that Msd or fuel pump I have read about more than one msd(marine stranding devise) problems on this forum

Fuel pump is brand new also. I still have the orig Merc coil, will put it back and on and see if it fixes it. Hopefully its not the TBIV module or ign amp...I noticed they are not cheap.

Check main fuel tank vent. Might be clogged causing tank to collapse partially...

i had a boat do the same thing,if you can get to the pick up tube in the gas tank take it out and look in top thire are screens in the top 90 elbow thay get cloged i fought this for a hole season till i found it

Fixx
 

Check the hall effect in the distributor,,common problem for going bad..

pulled fuel pickup...some small trash on the screen, but not completely plugged. What is the hall effect on the distributor?? Never heard of it.

Fixx
 

looks like this

http://www.go2marine.com/product.do?no=116368F

oh, you mean the module. I always thought those things worked or they didn't. I'm going to try replacing the coil first since it seems like it is heat related. runs great cold then performance degrades until it finally dies.

changed the coil, took it out this morning...same damn thing, starts right up, gets on plane, drive around for 5 minutes, come back to marina, start to slow down, as rpms drop below 2600 rpm, cough/spit, push throttle down, smooths out and stays running...then slow down again, engine cuts outs out. starts back up for 30 sec, idling, now I can't get it started again...pull off flame arrestor, carb is wet looking. its always started back up before. Luckily the wind blows me the last 50 yds to dock. Back in slip after 15 min, it starts back up, but dies in about 5 sec.

Do you have the Thunderbolt Rev Limiter?

I just had one that would do something similar. When it was cold it would run fine, start right up, we could run it no problem for about 20 mins. Then it would sputter and die. First couple times it would start back up then it got to the point where it would have to sit overnight before it would start. Left us stuck with one motor about 20 miles from the dock TWICE.

For some reason, we only had the rev limiter on one motor so I moved it to the other one, problem followed the rev limiter so I cut the harness apart to bypass it, motor fired right up. I just tried to get the correct bypass harness from BAM but its NLA so I'll just permanently solder the splices in and leave it be.

A handy way to see if you are definitely not getting spark is to use a ty-wrap to keep the trigger on your timing gun in, then when the motor dies hook your timing gun up and see if you are getting spark for sure or not. Probably not. Just put the gun where you can see it flash while trying to crank.

...

thanks for the info...no i don't have TB V, I have the IV no rev limiter.

thanks for the info...no i don't have TB V, I have the IV no rev limiter.

freind of mine had similar issue after a season of replacing everything he could he took to mechanic only to find a partialy kinked fuel line, it would actually close then after it would cut out it would restart and do the same thing again. rerouted and replaced line and hasn't missed a beat

Fixx
 

you mentioned carb looks wet,,holley? sounds either you have a stuck float or the diaphram is ruptured and soaking the top of the carb with gas from the fuel pump vent tube..pop and dieing ,no fuel in the float bowls will cause the pop..

just came back from the boat with mechanic down there. I finally broke down and had someone come out. Now the boat won't even start...As I cranked the mech noticed spark arcing where the main plug wire attaches to the coil.
I never noticed it before because at the helm you can't see behind the coil.
He tested the wire and sd it had a lot of resistance. He's getting a new wire and we'll see if that solves it. No spark is getting to the plugs!!! I hope this is it.

New plug wires and and plugs fixed ign issue...but now mechanic reports low/no compression on cyl 4&6. So he tells me to call engine builder and ***** at him, suspects blown head gasket. Engine only has 3 hrs on it and never ran hot. Engine builder says to doublecheck valve asjustments, valve could be hanging open. Mechanic acknowledges he should have popped valve cover off and checked it before he left. Going back tom AM to check valves...So I'm over $6k, did the install myself, and still don't have a working boat!!