Merc 350 Mag ign. problem

[bryont]

This is the problem. I have been working on a terrible bog when going from idle to full throttle (i.e. pulling a skier up). Engine would accel to about 3k rpm then just bog and sit at 2500 for as long as you would let it. The boat would not plane unless you pulled the throttle back and then reapplied. All this time I thought that I was dealing with a carb problem. Well this year I decided to buy a new carb. I put on a Edelbrock 600 CFM carb as a direct replacement from Summit. Yes it is a Marine carb pn.#1409. I payed $303 delivered. <br />Put it on today and ran the boat. TO my surprise the bog was still there. <br />For some reason I had this idea to put the ign. in base timing mode (purple wire grounded) and run it. Well, the problem went competely away, boat runs perfect now, will no loss in top speed or rpm's (about 4900). My question is why is this fixing my bog problem?? I disconnected the knock sensor once and ran the boat in normal mode but it still bogged. Does anyone have an idea why the boat is running perfect in base mode but not normal mode? Note: I have not had a chance to check the base timing. I will put a light on it tomorrow and check it. IS there something that I am missing??

 

[Don S]

Re: Merc 350 Mag ign. problem

With the distributor in base timing mode, you eliminate all advance and retarding of the timing do to conditions. You have the ignition moduale and the knock control module on the distributor and either one could be bad and could cause your problem. When you have it in base timing, you are just bypassing the sytems and not advancing or retarding the spark.<br />You will need a manual on the TBV ignition to test the system, but it could also be corroded connections. If they are green, replace it.

 

[bryont]

Re: Merc 350 Mag ign. problem

What does TBV Stabd for? Where can I get a manual? Thanks for the help!

 

[bryont]

Re: Merc 350 Mag ign. problem

I just saw the price of a Ign mod. WOW!

 

[Don S]

Re: Merc 350 Mag ign. problem

TBV stands for Thunderbolt V ignition system.<br />The manual comes from Mercruser and is manual #17,<br />PN 90-823225--1.<br />You can either order it from your local dealer or order it from the Mercruiser website.<br /><br /> Order Manual Here

 

[waterone1@aol.com]

Re: Merc 350 Mag ign. problem

This is one of those times when a scan tool (not code reader) comes in handy. The other option would be to use a timing light (prefferably one with an advance control)and see what exactly is happening with the spark advance while at different RPM's. You didn't make any mention of knocking or pinging while trying to accelerate ??<br />I also don't believe that you described where the timing was(degree) while in the base timing mode ?<br />If it is normally not knocking while trying to get on plane, I would have to say that something is causing the timing to retard....first guess would be the knock sensor, or at least the knock sensor pin of the ignition module(or wiring).

 

[bryont]

Re: Merc 350 Mag ign. problem

I have not checked static timing yet. I just realized what was causing my problem yesterday on the water and didn't have a light with me at the time. My light does have advance control so I plan to use it on the next outing. <br />When the engine drops off the change in RPM (500-700 drop)is abrupt not gradual. I don't "hear" any pinging until after the bog happens. When I grounded the ign box I hear no pinging at all and the boat runs fine. The boat currently has 91 octane in it.<br />I do not have the books on the Merc so I am not sure as to how it works completely. To me unless I am wrong with the ping happpening after the bog I would think that that means the timing is advancing I believe. I may be wrong though. Other than the knock sensor, what other imputs does the ign get?? Hell for all I know the static timing may be way off. I haven't ever checked it because I was convinced it was a fuel problem. Oh by the way I have a good used 750 Weber for sale now. HAHA

 

[John_S]

Re: Merc 350 Mag ign. problem

Information that may help, while waiting for your manual:<br /><br /><br />General Thunderbolt V Info:<br /> http://www.boatfix.com/merc/Bullet/94/94_02.pdf <br /><br />Tech's Manual Info:<br /> http://www.boatfix.com/merc/Techbk/95/95HGB4.PDF <br /><br />Thunderbolt IV & V Info from Big Block Service manual:<br /> http://www.boatfix.com/merc/Servmanl/16/16B4R2.PDF

 

[bryont]

Re: Merc 350 Mag ign. problem

Much help. Thank you John_S

 

[bryont]

Re: Merc 350 Mag ign. problem

I checked my static timing today. It was at 0 degrees. I readjusted it to 10 degrees BTDC at required. I will run it tomorrow and see what happens.

 

[bryont]

Re: Merc 350 Mag ign. problem

Learn from my mistake!!! <br />Even though my bog problem was isolated to a specific area and seemed to be a carb problem it was a simple static timing being out of adjustment as stated above. Logicly thinking I can not figure out how it acted the way it did but fact is that it did. So always check your static timing..Boat runs great now and I have a newly rebuilt Weber 4bbl 750 carb that I have for sale. On the small block that I have I did not give up any top end by going to the 600cfm carb. I did get improved throttle response though. Thanks all for the help.

 

[John_S]

Re: Merc 350 Mag ign. problem

Glad to see that was the only issue. Did you end up testing any of the knock sensor/module, or the test run was all the convincing you needed? Also, did you see any hot-start issues, that others have reported with the 1409? Thanks.

 

[bryont]

Re: Merc 350 Mag ign. problem

No, I never got that far. Test run and all was perfect. It surprises me that being retarted by 10 degrees made such an issue within a specific parameter. As far as the hot start, the 750 weber that came off the boat did tend to do that when hot. I did not take notice with the new 1409 but it was just me and the family taking a cruise. I didn't start and stop like you would skiing or tubing. Plus the retarded ign probably didn't help either. I did notice that Edelbrock makes an insulator gasket for the manifold mount. I assume it is to isolate heat from the carb. I wonder if this would help those guys out?? My last boat had a Q-jet on it and always started with a bump on the starter. There may be some truth to the hot start issue. Since I paid for the 1409 I will call Edelbrock with any problems if I have them and see what they suggest. One would think by the posts that Edelbrock would know about the problem and have a fix.

 

[bryont]

Re: Merc 350 Mag ign. problem

John_s<br /> Had a chance to take the boat out a few times. Yes it does look like the boat has a hot start problem with the Edelbrock carb installed. The Weber (simular design) that was installed before did the same thing. I emailed tech support about the problem and they suggested a Pn#8711 4 hole 1 inch plastic spacer for insulation if there is room, 1/2 inch if not. I will get one and let you know. <br />Funny thing is that the boat performs better now with the 600 CFM on it than it did with the 750 cfm that I took off which was the original installed by Merc. I gained a bunch more throttle response and another 100 rpm's at WOT. It accually will hit the rev limiter with the same prop installed as before. Hole shot is bog free and the boat planes within 4 secs with a 19 SS on it. I am happy except for the hot start thing.

 

[waterone1@aol.com]

Re: Merc 350 Mag ign. problem

Thank you for coming back and filling us in on your results...happy boating.

 

[John_S]

Re: Merc 350 Mag ign. problem

Bryon,<br /><br />I am interested in hearing the reults after installing the 1" spacer. ie did it fix/help the hot start problem, and what its impact was on performance.

 

[achris]

Re: Merc 350 Mag ign. problem

Do I hear "Weber", "Edelbrock and "Hot start problem" in the same sentence. <br /><br />I am just about to change my Weber for an Edelbrock in an attempt to fix this annoying little trait. I will be watching for the results very carefully.<br /><br />Chris..........