1989 searay 21ft 4.3 bogging and blowby at W.O.T only.

[Faison80]

I have a 1989 21ft searay seville, this year I installed new manifold,risers, rebuilt distributer, and new lower unit. Adjusted timming to 8 degrees BTD. As long as you dont go over 3500 rpms it runs fine and will run all day, as soon as you go wot it will go about 5 minutes and then start to bogg and finaly start diesling and knocking. Let it sit for a min and restart its fine. any ideas??

 

[Bt Doctur]

your running way to lean at top end or over advanced. excessive blow -by is a ring issue

 

[Faison80]

It doesn't have the blowby untill the bogging occurs. its hard to start after its hot, i have to hold it wot to get it started, then I smell gas untill engine runs for a min. Ive checked the timing several times, even backed it to 4degrees btd. carburator issue, timming, or cooling issue, i'm at a loss here. Thanks for your response, any help is greatly apreciated.

 

[Bt Doctur]

engine temp should be around 145 no matter where the throttle is, type of sparkplug ? color of sparkplugs? See if #6 plug is whiter than the rest.

 

[alldodge]

I have a 1989 21ft searay seville, this year I installed new manifold,risers, rebuilt distributer, and new lower unit. Adjusted timming to 8 degrees BTD. As long as you dont go over 3500 rpms it runs fine and will run all day, as soon as you go wot it will go about 5 minutes and then start to bogg and finaly start diesling and knocking. Let it sit for a min and restart its fine. any ideas??

Sounds like your running out of fuel in the carb. Need to check your fuel pump pressure using a vacuum fuel pump tester. Place it inline between the fuel pump and the carb. Fuel pressure should be between 4-7 psi. Check your fuel filter by pouring contents into a clear container and see what you find. If it has not been replaced, might want to do that. If everything else checks out look for a restriction in the fuel system like the anti-siphon valve attached to the tank. The valves can get crud on them and start hanging and restricting flow. The anti-siphon valve is connected directly to the tank and most often looks like a barbed fitting.

http://www.iboats.com/Moeller-Aluminum-Anti-Siphon-Valve/dm/view_id.392106
http://www.harborfreight.com/fuel-pump-and-vacuum-tester-93547.html

 

[Faison80]

Engine temp shows 170 all the time, when you run it hard ans suddenly stop it rises to about 180 then cools back down. Not sure on spark plug type, they are the type the local marine shop told me to run.

 

[500dollar744ti]

Is it a 4bbl carb? Are the secondaries opening as they should?

 

[Faison80]

2 barrel carb, just pulled the plugs and looks really lean, part of the tip of one plug is gone. Noticed that this is a lefthand rotation engine, do I time this btdc or atdc, at 8 degrees?

 

[Bondo]

2 barrel carb, just pulled the plugs and looks really lean, part of the tip of one plug is gone. Noticed that this is a lefthand rotation engine, do I time this btdc or atdc, at 8 degrees?

Ayuh,..... Btdc, that's Standard rotation,.....

 

[500dollar744ti]

While you are trying to diagnose this, stay away from the bogging and WOT as much as possible. If you are melting plugs from a lean condition at WOT, it can cause serious engine damage to continue pushing it like that. Have you made sure your fuel tank is venting properly and the non-return valve isn't gummed up and flowing properly?

And have you replaced your fuel filter yet?

 

[Faison80]

I get fuel out of the vent on the side of the boat when i overfill it at the pump, I'm guessing thats the only vent on it. I also have replaced the fuel pump and the filter this year, i replaced the pump due to failure on the diaphram inside the pump itself. I removed the non-return valve and it was clean, tried to remove the pickup from tank but would not move, I blew back through it to make sure it was clear, would there be a sock or filter on the end of the pickup in tank? Could the timming chain have jumped and im wasy advanced? Thanks guys for all your input.

 

[Faison80]

Could the auto advance be faulty and over advancing the timming at WOT? Could I have wired the distributer up wrong? Its a Thunderbolt IV

 

[500dollar744ti]

Thunderbolt IV is pretty reliable, don't think it's that if your base timing is set properly.

Let me ask you this, what is the WOT RPM this is happening at? Have you tried running the engine from a separate tank (like an outboard) and confirmed it still does the same thing?

 

[Faison80]

Sat when I went out I ran the boat around 3500 rpms for around 20 min with no problem, then bumped it up to 4000 rpms and it didnt run 5 min before it died on power and sounded like it was about to come apart. I turned it off as blown up, Let it sit for a couple of minutes and it restarted and ran fine below 3500, any thing above that it will do it, just the higher rpms the faster it occurs. I set the base timming at 8degrees with my snapon digital light, even bumped it back to 4degrees. No I havent tried to run it off a seperate tank.

 

[alldodge]

In my opinion only, you need another carb. My reasoning is your running real lean, so lean your plugs are starting to break up. You can run under 3500 rpm because there is just enough gas to keep it running. When you start getting above that, you do not have enough to even run it real lean. Keep in mind I believe your engine is still being damaged under 3500 and it's just a matter of time before your replacing it.

 

[wellcraft-classic210]

I have seen debris in the check valve ( which is in the barb fitting leaving your fuel tank ) cause fuel flow limitations & symptoms similar to yours. Also if you can blow back though it as you said above that supports some debris as fuel & air should only flow towards the engine when the check valve is operating properly. -- Normally their is NOT a screen on the pickup-- just a tube. The problem can be variable if the fuel backflows through the check valve and washes some debris back to the tank.
Its a usually a relatively easy check.

 

[Faison80]

Could my carb not be adjusted or cleaned?

 

[Faison80]

I didnt blow back through the check valve, only the elbow directly screwed into tank. the barbed check valve seemed to be working and it was clean

 

[Faison80]

What carb is spose to be on this engine, it may not be the correct one beings i purchased this used.

 

[alldodge]

What carb is spose to be on this engine, it may not be the correct one beings i purchased this used.

Either a Merc 2brl or Rochester 4brl

Could my carb not be adjusted or cleaned?

Yes it can, and the issue may be the carb but you need to find out if it's pressure, flow or a restriction. Pulling the carb you just bought apart to clean is not a good place to start before understanding what the issues are. Anything is possible but lets try to find out what the issues are before going that route.