Posted: 8/31/2008 8:37:54 AM EDT
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I have a 30 year old boat with a Ford 302. I rebuilt the carb (Holley 2V) and upgraded it to a Pertronix electronic ignition. Took it out on the water 4 times and she ran great. Then I developed a problem...The engine runs rough after 2000 RPM. It will not go above 2500 RPM...It sounds like WaRRRrrrRRRrrrrr...like it is not getting enough fuel. I checked the timing...dead on... Pulled the plugs...all cylinders look to be firing... Replaced the 30 year old fuel hose and checked the tank pickup for obstructions (none). Checked the fuel filter/fuel water seperator.... Replaced the spark coil... Replaced the carb with a brand new 500CFM Holley 2V... STILL no improvement. Wa RRrrrRRRrrrRRrr  WTH... I am half tempted to go to the autoparts store and get a fuel pump for a 1972 LTD ($20 vs $130 for a marine version) on the motor to see if it is a fuel problem (I have to special order a marine fuel pump). The diaphram in the fuel pump hasn't broken (it would leak fuel into the sight glass thingy on a marine fuel pump)...but could it still be bad??? I am running out of shit to replace 
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The motor has no vac lines... It is like the motor on an old mustang...no emisions control equipment. Mechanical distributor advance. Could it be the advance weights on the distributor are sticking? |
Your timing is not advancing... fix the issue Oh then replace it with a Chevy 350... 
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Put a SENSITIVE fuel pressure gauge on the line. That will tell you if the pump or its cam is worn. Marine engines need good fuel flow because they work much harder. Will it run in neutral over the entire RPM range? If not, could be a sticking valve. Common in engines that do not get daily running. |
It WILL run in neutral over the entire RPM range... Hmm....could just buy a block off plate and get an electric fuel pump. Holley makes one for carbeurated engines. |
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Have you tried dropping in the original ignition? What about an issue with the electronic module of the new system you put in failing at higher RPM? Do you own any type of inline spark tester that you can put on it? How about putting the timing light on it at that RPM? What is it doing? |
So as long as there is no load you can get it to max RPM? Does your "RrRr" happen at wide open throttle in the water? Like, would you call it a surge - you accelerate OK at first then it quits, then takes off again for a moment, quits, (repeat)? That sounds like insufficient fuel flow. You said you checked the filter, etc. so I'd check for a pinched line, maybe remove the filter as a test. Those are just things you can check for free, but if it's not any of those then I would think fuel pump. I've had pumps fail with a good diaphragm when one of the valves partially gave up. |
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I've had cars do this when the cat disentigrates and clogs up. I dont think boats have cats, do they? Is there a return fuel line from the carb to the tank?( sorry , i'm not a carb guy) You could pinch that and see if pressure builds enough, would be a clue to fuel pump being bad. Check all the grounds, especially the ones related to the electronic ignition. You can add more grounds and see if that helps, all it will cost is some scrap wire. |
Timing/ignition problems were my first initial thought as well. This is where I'd start my troubleshooting. |
High RPM tests have to be done in the water (a garden hose will not provide the flow to keep the motor cool...so I can only run it up to about 1500 RPM in the driveway)...this is what makes this so damned frutrating...have to tow it to a lake to really test it. I can run it in neutral across the full RPM range... When I put in gear and run it up to WOT...it stops at abou 2000 RPM and surges up to 2500. It feels like the boat is pulling backwards at WOT...like it is not getting enough fuel. None of the fuel lines are pinched. I think I am going to go for a Holley red electric fuel pump...half temted to go for the automotive version as the marine version requires a vacuum line (I do have one vac port on the new carb). BUT I have to mount it close to the fuel tank...and the tank is at the front of the boat (18' boat). |
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No cats on a boat. I could try throwing the points and condenser back in....going to check the advance weights on the distributor again...checked them when I installed the electronic ignition...and no problems before... All the electroic igition module consists of is a Hall effect sensor...it is a very simple design. |
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Double check the plug wires. I had a Camaro that did that. I was scratching my head trying to figure out what was wrong. For some reason, my gut instinct was telling me to check the plug wires, so I did. It turns out that some asshole swapped the #1 & #2 plug wires on me.
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Fuel flow or exhaust. Either one will limit max power. Without a load, there is limited fuel need AND limited exhaust flow. You need 1/2 GPM at 2 PSI at max power. This is EASY to test with an electric fuel pump. With mechanical, the only way to check is with a pressure gauge. This is cheaper than an electric pump retrofit. Mechanical pumps are demand type, if the demand for volume isn't there, the plunger will not contact the cam. A worn cam or follower will decrease the "throw", reducing the displacement of the pump and its capacity. This ia easy to check. Valves in the pump can leak, also killing capacity. This is more likely the case. With the fuel pump removed and primed with fuel and the delivery line blocked, manually actuating the lever should result in it staying in one position. A leaky valve will make the lever slowly extend, rate depending on the valve failure. |
This should tell the tale for the fuel pump. |
That was my first thought. If it runs good till about 2000 rpm, then maybe the spark advance. EDIT: My second thought is not enough fuel flow. Is your fuel bowl staying full at all times? Pull your fuel line and gravity feed fuel to it from a clean separate container and attemp to run the engine to full throttle with the trans engaged if possible. if that works, it is not your carborator. If it doesn't work then I would revert back to the ignition system. Pull your distributor out of the engine and inspect for broken parts. I have had engines run fine at low rpms and crappy at higher ones when the shaft to the distributor gear was cracked. Hope you figure it out. |
| I've replaced 2 hall senders in my cars. On the second car, it would idle fine and misfire like nuts when at about 3000 rpms. Still did it after replacing the hall sender, turned out to be the ground from the hall to the block. The ground looked ok, but it didnt work right until i replaced the entire wire. The same ground was causing the oil pressure lights to come on at 2000 rpms. |
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I opened up the timing case and the sprockets are steel...the chain seemed tight, with a little slop in it... I put the ballancer bolt back into the crakshaft and rotated it to TDC... (lined two dots up on the timing sprockets) Pulled the distributor cap and noticed that the rotor did not line with cylinder number one on the cap... Grabbed the plastic rotor and was able to rotate it cylinder 1, but the distritor shaft did not move. I grabbed the original rotor (had replaced it previously)...it had very little slop and was closer, but not on cylinder 1 (think this is because I adjusted the timing last with the NEW rotor). I think this may explain why the engine was running fine for several hours, then all of a sudden the problem started at 3,000 RPM...then went down to 2500 RPM. If the rotor moves, it would throw off the timing, right? Half tempted to go to Autozone, grab a gasket set, slap it back together, install the old rotor and go run it... What do you guys think? |
The only way to know is to get the #1 cylinder to top dead center with both valves closed & make sure that the marks on the timing sprockets line up. Also, some have mentioned checking for vaccum leaks & you have said that you have no vaccum lines, but the carb base gasket, or the line for the vaccum advance may be leaking. You can use Tangochaser's method, or use carb cleaner like I do. The carb cleaner will cause a audible change in RPM at idle. All you need are little spurts, you don't need to hose the aera down. If you've checked your fuel pressure like you said you were going to, & the pressure is good, you shouldn't have to replace the fuel pump. And when you rebuilt the carb, you may have missed a piece of a gasket, or a piece of gunk that is clogging up a passage in the carb. Does it spray a good even shot of fuel when you open it up? |
I switched to a brand new, out of the box, Holley carb. No vacuum advance...just a weighted advance... I tried spraying starting fluid around the intake manifold and carb gasket while the engine was running...no leaks. |
Checked to see if it had nylon gears...it has metal gears...and not much slack in the chain..so it apears fine. I am going to try switching to the old plastic rotor that came with the boat...the new one has a nic friction fit...but has a lot of slop in it...so much that it moves around without the distributor shaft turning.... |
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After you determine that it is NOT a fuel problem or a binding drive line. 1. check the vacuum advance on the distributor. it looks like and is a diaphragm on the side of your distributor. if it is working or your engine does not use one, 2. plug wires. they may look ok and the plugs might look fine but wires can still be bad, 3. wind/vibration issues with all electrical connections. check coil connections, dist wire, engine ground, etc. 4. a 302 will run with a loose timing chain and steel gears until it falls apart, not to worry there until it explodes. they will usually slap the timing cover and sound like a knock for thousands of careful miles before snapping in a car. 5. yes, new distributor might be faulty. if everything else pans out swap your old points distributor and coil back in and see if problem goes away. 6. take an old timer mechanic out with you. someone turning wrenches back in the 60s and 70s. let them listen to it. good luck. |