350 ignition problem

"I am very frustated with my b

"I am very frustated with my boat and I need help. I have a 1989 Mercruiser 350 that is mainly stock. I have a Holley 4bbl and a mild marine cam. The problem I have run into is that anything above 3000 rpm's will cause the engine to die out. I can run all day with no problem below 3000 but if I get into it for about 10 seconds it will shutter then shut down. I thought it was a fuel issue so much as I changed the carb, fuel pump, all fuel lines, water sep filter and housing, pickup in the tank and added a clear filter so I could see what was going on with the flow. It ran good for the first 10 minutes out. Could run a little above 300 with put the cut out. "I fixed it" then it shut down, "dammit". I am now thinking it is going to be ignition. I'm leaning to the coil or Amplifier. It has the Thunderbolt IV system. How can I check this stuff so I don't have to keep buying stuff? Can I just run an HEI distributor and get rid of the whole system? Am I on the right track? Help."

"Check the fuel vent line for

"Check the fuel vent line for obstructions at the outside and for a low spot that could trap fuel and lose pump sucktion. Loosen the fuel filler cap to see if it corrects it.

Tests for Thunderbolt Ignition:

W/ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!

#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

#2 - If 12 volts is present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

#3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

#4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced."

"Because it runs fine up to 30

"Because it runs fine up to 3000 rpm I would suspect fuel starvation. That is likely just about the rpm band where your secondaries are opening.

I wonder if your carb has the corect secdondary jets for marine application? Did you buy a specific marine carb or just a Holley at the auto parts shop? Has it ever run properly with this carb?

I think you should do a Google on marine Holley carbs and see what jet sizes, power valves, etc are recommended for your application and see what you find.
The Holley site may have info on what you need.

Rod"

It is a Marine specific Holley

It is a Marine specific Holley. It is the 4160 model with 600 cfm's. It has 65 jets in the primary block and there are no jets in the secondary. I don't think it has ever run great with this carb. I would think this carb would be enough to run this motor. I have a race car that runs at 6500 rpm's with a 350 cfm 2bbl Holley.

I think Rod is in the right ar

I think Rod is in the right area. Fuel starvation. What happens when you wire the seconaries closed. Will it rev up past 3k on the primaries only? It should.

I think your secondaries are opening and you're going lean. Rod's point about tank vent clog happens all the time. Did ou try that?

That should be plenty of carb

That should be plenty of carb for a marine 350. At 5000 rpm it only needs 500 cfm of air at 100% induction efficiency.
MistaHays and I are on the same page. She is going lean on the secondaries for some reason. The fuel feed to the secondary venturis is not happening.

Rod

"I tried the vent hose and it

"I tried the vent hose and it had some fuel inside. I ran it on Friday and it screwed up again but I looked down and saw about 9 volts on the gauge. The engine stalled, finally restarted with the last bit of juice in the battery. Made it back in and couldn't get it to start to even verify with my multimeter that the alt. was bad. I pulled it off and will repalce in the AM. Could the week Alt. cause the problem?"

"I replaced the Alt. and I am

"I replaced the Alt. and I am only reading 12.39 volts off the back of the alt. I am a car guy but I think I should be getrting around 13.5 V, right? It ran good again up until the 3100+ rpm shut down. I hate this thing. I am lost and don't know what to try. Again I will tell you exactly what I have and someone tell me what the problem is. 50 gallon aluminum fuel tank, brand new pickup with brass elbow on top to a brand new marine grade 3/8" hose, into a reacently added clear filter housing, then into a new water/fuel seperator filter and housing. From there into a Holley red electric fuel pump and on top the Holley vaccum secondary 600 4bbl that is new and rebuilt again by me. It has 65 jets on the primary side and of course there are no jets for the secondaries. I watched the clear filter today and it looked as if it stayed full of fuel even when engine cut back. I was running 3000 rpm's for about 15 minutes then decided to test it and dropped the hammer to 4200 rpm's. I ran there about 5-6 seconds then started to die. I pulled back on the throttle and cruised at 2800 and it was fine. I decided to get the kids and cruise. I ran about 2800- 3000 rpms for aprox. 15 minutes. They wanted faster so I eased up to 3200. Big mistake. I started to die. I pulled back and ran about 2500 then it started to die, then back to 2300 and it started to die. I pulled back to about 1800 just before it came off plane and it was fine. I got back close to the river house and dropped the hammer, it dies in about 3 seconds, pulled back and idled in. I can not fingure this thing out. I don't know where to go from here. Any idea's that I haven't tried? Vent hose didn't fix, Alt. didn't fix, new fuel pump, and fuel system didn't fix. What now?"

""only reading 12.39 volts

""only reading 12.39 volts off the back of the alt" Was that w/a fully charged battery? Perform a voltage drop test between all major points. Begin w/a fully charged battery and move awy from it to each point; starter, alt., under dash fuse panel. Record all readings and compare them w/the battery reference. The voltage should not drop more than a 0.1 volts from each point. You may need new battery cables and should consider replacing the alt. ground and output wire--use a fine strand #8 gauge wire.

Have you load tested the battery? How old is it? When it is charged, have you checked for similarity of specific gravity between cells? If one cell is off from the others the battery can be a problem.

If the electric fuel pump is not getting enough voltage then it won't pump fast enough.

Does the engine run hot? Yes? Then have you looked on the exhaust side of the engine for blockage?

For the carb; have you considered setting the float a little higher to increase the fuel in the bowls?"

"Fastimz
If your battery is i

"Fastimz
If your battery is in good order you should be making around 13.5 at the regulated output of the alternator, if you are loosing voltage your ignition system may be breaking down under load.

If your voltage is droping too low, before the resistor circute to the positive side of the coil, you may be getting below 9 volts at the coil + which may be causing poor performance of your ignition under load. If you can hook a multi meter up to the coil + and see what voltage you are getting when the boat starts to faulter.
Just with your Holley, if you send an email to the tech guys at Holley with some specs they will come back to you with a jetting settup that will be pretty close for your application.

Cheers
Peter C"

"Guy, I will check the wires a

"Guy, I will check the wires along all the paths. Tha battery is new as of April. I charged it over night before the last outing. No it doesn't run hot. I have a new outdrive pump that I plan to install for preventive maint. I tried the floats a littl ehighter but it made no difference.
Peter, I will also check at the coil when under load. I will have the wife drive and as long as it doesn't throw me in the floor I can check it. I will also check with Holley. Let ya'll know what I find."

"Just make sure she keeps her

"Just make sure she keeps her head facing the direction the boat is going and not watching you."