loss of power V6 150 1990

[jdlloyd_iboat]

I posted last week with a request for help on inoperative 35 amp regulator and rectifier. This week I have a different problem w/o solving last weeks! This week power started out fine for first run on the lake. Then the motor went to low rpm and ran rough with some backfiring occasionally. I limped in and after listening and checking visually, I suspected there might be a broken reed, although there was no sign of heavy gas spitting from any carburetor. Also, I noticed some minor leakage on the middle cylinder of the starboard side bank at the head gasket interface (gasoline fuel mixture bubbling maybe?). I disassembled all the way down to the reed valve plate (all reeds looked good and sound). I put some hi temp gasket sealer on the inside and outside of the aforementioned head gasket leak). Reassembled all and went to the lake. Motor ran great for 20 minutes before problem repeated. Fuel mixture again bubbling at head gasket interface. Power is not adequate to get boat on plane. Activating the primer allows the power to increase and boat to plane but power is still not full. Boat idles smoothly and quietly, even better than before. Took boat out and pulled the plugs. All plugs on port side (driver's side left hand, I think) were dry and looked like were firing. Starboard side (driver's right) plugs were all wet. Suspect a power pack defect on this side. Is this a good place to start with a replacement? This engine is tough to diagnose w/o right equipment. Boat ran at power well before all this latest trouble even though idle and starting was rough sometimes. As always, any help is appreciated from those that might have encountered a similar situation or have fixed a boat with same problem.

 

[ob]

Re: loss of power V6 150 1990

If activating the primer picks the engine up enough to plane out,I suspect you have a fuel delivery issue.Likely fouled carbs/s.You'll definately want to remedy that asap.At this point,I also recommend performing a compression test to verify whether any cylinder damage has occured.<br /><br />Ohterwise ,I recommend performing a spark test to insure each plug lead will jump a 7/16" gap to ground at cranking speed.

 

[jdlloyd_iboat]

Re: loss of power V6 150 1990

Thanks Vice Admiral. I'll check the carburetors but had replaced all gaskets and needles and cleaned out the deposits last season and winterized properly so I don't think that's the problem. As I indicated it was working and this problem seems intermittent. I was suspecting the VRO until I saw only three wet plugs. I'll also do compression but I am not sure I know how to do the spark test. Is the spark test something that is intended to isolate a problem with one of the power packs?

 

[jdlloyd_iboat]

Re: loss of power V6 150 1990

OB,<br />I checked the compression. All cylinders except # 4 (middle on port side) checked out at 80 psi peak. #4 peaked at 75 psi. I started to remove carburetors and noticed that I had not done a good job syncing the throttle plates. Top and bottom were 3/4 open at WOT. I synced up the linkage so they all now track. I also had failed to tighten the throttle cam bolt completely. I think I will put it in the lake next weeke-end with these cheap corrections to see if that helps. The wet plugs all on one side still trouble me though.

 

[ob]

Re: loss of power V6 150 1990

Let us know how the test run goes after your adjustments.Those wet plugs on that bank still lead me in the direction of weak spark.I still recommend performing a spark test to verify.You can either rig one of your own or pick up an adjustable gap tester at a local auto parts.Just remember at cranking speed that each plug lead should jump at least a 7/16" gap to ground with a real snap of a blue lightning arc.Anything less than that gap or a yellowy colored spark is too weak.Once we have determined whether you are getting weak spark or not , we can proceed from there to eliminate possible culprits.

 

[emdsapmgr]

Re: loss of power V6 150 1990

Take a timing light to the lake. When running, check each plug wire for a strong, constant flash. Am concerned about the leak at the head on the starboard side. You mentioned the leak on the head seating surface, yet I think you took the intake manifold off. Can you better explain just where this leak is? Possible that your engine may be going into SLOW mode for some reason. Is the engine overheating?

 

[jdlloyd_iboat]

Re: loss of power V6 150 1990

emdsapmgr,<br /><br />Thanks for your interest in my problem. What I meant to say in my original post was that the leakage seemed to be coming from the joint between the "block" and the intake manifold (reed box). It would be located below the piston on the middle cylinder starboard side. I confusedly called it the head gasket but I realize now that this is not like a automotive engine where the head is on the same end as the intake, if that makes sense. My concern was that there might be a "vacuum" leak, but, in actuality, the leak seems to be to the outside atmosphere so it is evidently a pressure leak of some small magnitude. I dabbed some sealant (hi temp RTV) on the joint both inside and outside and tightened a little on the bolts but that has not stopped it. As far as overhating .. I don't think it is as I can place my hand on the top of the heads for a few seconds without pain. I did replace one thermostat this year but was reluctant to replace the other (on starboard side) because I sheared off one of the bolts in the process (I jury-rigged a clamp that holds the cover and it is not leaking). The water pump probably needs to be changed but the motor seems to be peeing a forceful stream. I am going to test the sparking but I know it does work intermittently and works well when it does. I have decided through several hours of research that a big possibility for this lack of power at WOT may be the spark advance arm might be constrained from moving as far as it needs to go on the starboard side because I used some wire ties to tidy up all that "loose wiring" without thinking through the unintended consequences. It might be catching just enough on occasion to make the spark on the starboard bank of cylinders to "hit" at the wrong time. That's easy to fix. I will also take a reading to see that I have strong spark as the first thing I do this week-end using a spak gap testing tool I'll build this week. <br /><br />Evidentally, no one has any concern about the compression readings? I thought these might be low as I saw claims from others of 100psi and up to 150psi. I took these readings with a screw- in compression tester and with the throttles closed. I thought these compression readings were low but they were all pretty close and consistently low. And the boat does run strong when it runs well.<br /><br />Again, thanks for your post and I will be reporting progress as I return to the lake this week-end. I'd like to get this problem cleared so I can go back to my original concern about the regulator, and, of course, to get the boat back to the fishing holes!

 

[emdsapmgr]

Re: loss of power V6 150 1990

The compression on OMC 150 V6 engines is not high. A standard 150 will run in the 90 lbs range. Check the compression with all spark plugs out. Is there any possiblity that the crankcase leak is between the two crankcase halves, and not the intake manifold? You should not have any leakage on the crankcase or it will affect performance and driveability.

 

[jdlloyd_iboat]

Re: loss of power V6 150 1990

Best as I can tell, it is the joint next down from the joint (towards the pistons) where the intake manifold box (where the reeds are) right adjacent to the cover plate for the middle cylinder. I don't think this joint can be easily separated as I believe it is the joint for the engine part that does hold the crank in place and therefore would be a joint in the halves of the crankcase. I can see the joint on the inside from the carburetor end below the piston about a fingers length in from the surface after the reed box is removed. It seemed to be leaking to the outside but it was just barely noticeable. That plenum is open to the bottoms of all pistons and if I rotate the flywheel I can see the pistons move. Another way to locate it is to say it is on the carburetor side of the bypass cover plate. I thought at first the leak was in the cover plate gasket but I do not think it is. I would say it is a joint that opens to the crankcase area. Any way to fix this leak with epoxy for example, without pulling the whole block?<br /><br />I checked the compression with all plugs out and cranked it over until the reading was stable with the key/battery.

 

[emdsapmgr]

Re: loss of power V6 150 1990

It sounds like the leak is between the crankcase halves. Check for these symptoms: alternate gas/oil mixture squirting out and suction of outside air in. If this is the problem, it is certainly unusual. When the crankcase halves are bolted together, they us a gel sealant between the halves. This gel seals the crankcase to the atmosphere and lets the engine crankcase create both full vacuum and full pressure for each cylinder when running. Any leak will bleed off this pressure/vacuum for that cylinder. Your engine will not run properly with this problem. The gel seal is inexpensive, but your best bet is to remove the powerhead and split the crankcase to reseal.

 

[jdlloyd_iboat]

Re: loss of power V6 150 1990

I would say the leak is very minor. It's almost like a bubbling of a very minute amount of liquid. It does not seem to alternately go in and out or squirt like you describe.

 

[jdlloyd_iboat]

Re: loss of power V6 150 1990

I did a spark test on the starboard bank of cylinders that I think are not firing correctly. Each cylinder fires a very strong 7/16 inch gap of blue fire. I guess the next test is to see if the timing is near the specifications as the throttle advances to WOT. I have adjusted the throttles so these are synchronized and are fully open at the WOT point. I need to take it to the lake to test under load.

 

[jdlloyd_iboat]

Re: loss of power V6 150 1990

Put the boat in and it runs very strong at WOT for about half a mile but when I bring it to an idle and try to accelerate it seems not to have enough power to plane w/o using the prime. Seems to run smoothly but lacks power. I idled the boat to the dock and checked the temperature of the thermostat housings and port bank is 155 degrees and starboard is about 147 degrees. Each cylinder seems to be about the same consistent temperature using a non-contact infra-red thermometer. Still has me puzzled. What should I do next?

 

[ob]

Re: loss of power V6 150 1990

Are you saying that the engine will run fine now at WOT and just has an issue when throttling down and getting on plane?<br /><br />If so ,two things to consider.If the crankcase leak is severe enough ,that may be your issue.Also could be that the carburetors are not properly synched with the advance of the ignition timing.This synch adjustment is critical and if out of adjustment will show itself when coming up on plane.Idle mix or restricted idle orifices is another item that would cause this scenario.Your engine temps look fine to me.Anything above 163 is cause for concern.

 

[jdlloyd_iboat]

Re: loss of power V6 150 1990

It seems like it runs well for a few minutes up and down the range of rpm's but then it seems like it doesn't have the power to plane after it has warmed up thoroughly. Priming does have the effect of giving enough pwer to get it on plane when this situation happens. I don't think the crankcase leak is the problem becasue it works OK for that first half mile with the bubbling. That's just a gut feel but I am not any expert on this as you can see. Can carburetion get bad after it works for a few minutes OK? I think I have done the sychronization properly although the procedure in the SELOC manual doesn't seem to track all that well with my actual hardware configuration. The figures in he manual do not accurately represent my cam and cam follower set-up and there is nothing said about setting up the throttle linkage.

 

[jdlloyd_iboat]

Re: loss of power V6 150 1990

An update --<br /><br />I swapped sides on the power packs and put it in the lake and it runs like it was new! I cleaned a few connections in the process and it's firing on all six now. I will let you know if anything changes and thank everyone for the advice.

 

[Walker]

Re: loss of power V6 150 1990

I think your motor has a "bank" of ignition coils on the rear, Right??<br />Pull them off and look for burnt-arcing marks on the plate.

 

[jdlloyd_iboat]

Re: loss of power V6 150 1990

It has six coils; each adjacent to the cylinder it serves. I had pulled these during the winter and had cleaned all the contact surfaces. There was no arc marks anywhere. I do not suspect the coils as I was getting healthy spark (7/16 inch during cranking with plugs out) from each using a spark tester.

 

[jdlloyd_iboat]

Re: loss of power V6 150 1990

I put the boat in the water again this week-end and it works great. I have not even seen the afore-mentioned bubbling around the middle cylinder on the starboard side. There is a little coughing at idle which gets progressively smoother as it warms up but it works strongly at higher RPM's. I did reduce the idle setting becasue it was racing a little. I will start to worry again about the charging circuits.