Engine still bogging - hard acceleration

[Lowflyr]

I recently purchased 1987 Reinell 5.7 OMC.<br /><br />When I accelerate hard (full throttle) the engine climbs to 2200 RPM then just stays there bogging along. If I back off on the throttle to about 2/3-3/4 and ease it in it will pass thru the 2200 RPM and will then come up on plane and reach a top RPM of about 3900 (According to an OMC book it should top out at 4200 - 4600).<br /><br />I added fuel cleaner and even 100LL avgas thinking it just needed cleaning out. (No luck) Next I took it to a mechanic who rebuilt the quadrajunk carb (thinking it was accelerator pump), he also installed new fuel filter, plugs, points, condenser & timed it. I took it for a short test afterward and it ran great accelerating thru the 2200RPM and up to about 4300RPM. Next time I took it out back to square one. <br /><br />After reading a lot of posts here I purchased and installed a new 600cfm Marine Edelbrock carb & replaced the coil thinking that was it. Marginally better although it starts & idles better.<br /><br />Engine compression - Lowest 105 Highest 120.<br />Plug burn looks excellent.<br /><br />A friend said it may be the distributer is not advancing correctly another said it's fuel pump. Frustrating and getting costly. What about an electronic ignition? I heard they are costly for OMC's &/or you have to put some type of resistors on it? Any advise?

 

[MooseHootie]

Re: Engine still bogging - hard acceleration

I would take the distributor cap off check the weights, springs and see if the plate will turn that the weighs are sitting on if it is froze up it wont let the timing advance.

 

[ron7000]

Re: Engine still bogging - hard acceleration

change out the points to a pertronix electronic ignition. Should only run you about $120 for the module and a pertronix coil. Get the Coil! You can get them from various sources, I got mine a while ago for my 351w from CBS Performance Auto, they were nice to deal with over the phone. Don't waste your time doing anything else until to get rid of the points.<br /><br />If you have a mechanical advance distributor, there's a set of springs underneath the plate that you'll change out when you install the pertronix module. This is what controls the advance, along with the set of weights. If the springs are rusty, broken, or the distributor doesn't spring back when you twist it slightly in the advance direction, then either rebuild the distributor or put a new one in. You're not getting proper advance per rpm.<br /><br />Quadrajets aren't a bad carb. But like any, they must only get clean fuel. Any dirt get's into them and you'll need to pull them apart and clean it out. Try and pump your fuel tank. If you see water and sediment, then that's probably your biggest problem, it's getting past the filter and into the carb. You will need to clean the tank out otherwise you will continue to run into the same problem, over and over. I know, I went through this with my dad's '76 Silverton... with QJ carbs. Once we vacuumed out the tank and installed new fuel lines, the carb's never fouled again.<br /><br />On my 351w with 8:1 compression, I get 130psi minimum compression. I know the Chevy 5.7 has a higher compression than 8:1, so 105-120 is low. The motor is probably tired and the cause of it not reaching peak rpm for the given prop and boat load. If the hull is fouled or the outdrive finish is rough, that'll rob power too and prevent you from hitting peak rpm.<br /><br />Don't use AVGAS. that's for aviation motors, which only run up to 2500 rpm or so. that fuel burns completely different from gasoline, and will not give you any more power or clean anything out. For that, use SeaFoam or Chevron Techron. They are about the best fuel system cleaners. You can also try a top end cleaning with the seafoam to remove carbon buildup in the cylinders, that may free up any stuck rings and improve compression.

 

[ron7000]

Re: Engine still bogging - hard acceleration

From the Gasoline Digest, http://www.idavette.net/hib/fuel/page2.htm <br /><br />

Aviation gas is formulated for large-bore, long-stroke, low rpm engines which run at high altitude. While AvGas’ higher octane is useful, smaller-bore, shorter-stroke, high-rpm, non-cat, Corvette engines requiring 92-98-oct. will perform better on racing gasoline. AvGas has lower volatility so, used in proportions higher than about 40%, part-throttle drivability and cold starts may be compromised. AvGas has a lower specific gravity so it will require a change in air-fuel ratio calibration for the engine to perform at its best. LL100 is blended with a high percentage of aromatics. That reduces throttle response–not really an issue with an aircraft engine but certainly an issue in a high-performance automotive engine.