OMC 351 Holley Carb Float Levels ?

[kfraser]

Does anyone know what the correct float levels should be on Holley 600CFM 4bbl, married to a Ford 351? The rebuild kit doesn't list them. I did a search, but came up empty...

 

[emsisson]

Re: OMC 351 Holley Carb Float Levels ?

With the bowls removed, turn them upside down, the float should be adjusted to be level, that is, the flat top of the float should be parallel to the top surface of the bowl. There is also a sight plug on the side of the bowls, when removed the fuel level in the bowl should be at the bottom of the sight window, (a practice I find disturbing and dangerous in a boat!).

 

[kfraser]

Re: OMC 351 Holley Carb Float Levels ?

Thanks Ringtail,<br /><br />I didn't see anything listed with the carb kit, but I was able to find that info in my service manual. I'm still having the same problem with the carb that I was having before the rebuild. It's dumping fuel from the venturi's in the main two bowls. I can see an almost steady stream of fuel. I've tried adjusting the idle mixture screws to no avail. Any ideas?

 

[Boomyal]

Re: OMC 351 Holley Carb Float Levels ?

kfraser, could it be a ruptured power valve? Does the engine run, ie, rich and raunchy at idle but smooth out when you run the rpms up?<br /><br />If it is soaking wet, down the venturies, at an idle but dries out when you run her up to 2k rpm or better, it is definitely the power valve.<br /><br />Another way to check the float level is to pull the plugs on the sides of the bowls. The gas should just be lapping at the bottom of the opening. But I doubt that is your problem.

 

[emsisson]

Re: OMC 351 Holley Carb Float Levels ?

It sounds similar to a problem I had. After several years of rebuilding the carb myself, from a kit, I decided it was time to get it done right by the pros. I took it to a carb specialist, who I had bought the rebuild kits from. When I got it back I noticed that the needle valves were different from the ones I had gotten in the rebuild kits. The ones in the rebuild kits had a large, tall locknut surrounding the screw slot in the needle valve. The new ones from the "pro" rebuild had a flattened screw with a slim locknut under the screwhead. I assumed that the "pros" knew what they were doing and put the carb back on. I experienced the same symptoms you are describing, fuel draining into the carb despite any adjustment to the needle valves. I fought with it for a month before taking the carb back to the "pros". They replaced the needle valves with the older sytle I had used in the past, problem solved. <br /><br />My Holly is also married to a 351 Ford. The "pros" describe it as a "generic" carb... it kind of falls in the cracks compared to the "normal" automotive carbs. The first time I took it to them, they informed me it really wasn't a marine carb since it lacked the "U" shaped horns to prevent overflow from the bowls from exiting the carb, something I have since corrected. The best info I have on the carb is the Seloc OMC Stern Drive manual, I have an 800 OMC. It gives very detailed info on the carb. But looking at the detail of the needle and seat assemblies in the book, they are the same as the "wrong" ones the pros installed. It appears that my carb, and maybe yours, is a hybrid, an automotive version pressed into marine duty.

 

[Boomyal]

Re: OMC 351 Holley Carb Float Levels ?

The only thing the 'screws' do is to adjust the airflow during idle. They do not meter fuel. Even if they were not exactly perfect they would have an effect if everything else was normal. I still say the power valve is the most likely culprit although I can't be certain until my question above is answered.

 

[kfraser]

Re: OMC 351 Holley Carb Float Levels ?

Boomy hit the nail on the head I believe...Ayuh, as Bondo would say. Cruised great when rev'd above 1000 rpms. (But, Left a black streak across the stern.) <br /><br />I think, I resolved the problem. The power valve that came with the kit was different than the one I replaced. The vent valves on the bottom of it were twice the size. I adjusted the floats to a little less than parallel and put the old power valve back in. It now runs at idle with just the bump of the key..no fuel dumping. I just have to try her on the water now. I'm hoping I have the problem cured. I think it was a combo of issues..power valve, float levels and choke setting. Thank you Pilotkeith (my brother) for guiding me through this mess. Love ya man. <br /><br />Only thing left is the tilt motor removal....Then I'll buy the gas and the beer for whoever want's to go..!! Thanks again all!!!

 

[ron7000]

Re: OMC 351 Holley Carb Float Levels ?

I have a 351w also, with a holley 4160. I run a 2.5" power valve. You can run a 3.5" power valve no problem and probably get away with a 4.5" valve.<br />Do you know your rebuild/renew kit number?<br />How about the numbers stamped on your power valves?<br />from the sound of it you had the float level too high which caused the raw fuel out the boosters. I don't believe the power valve will cause that unless it is ruptured and leaking, which is to say you can put the wrong size power valve in and everything would be fine at low rpms.

 

[jonmurr]

Re: OMC 351 Holley Carb Float Levels ?

kfraser <br /><br />You stumbled onto your problem. There are two styles of Holley power valves, one with small drilled holes , one with square windows. They take different gaskets. Mixing up the gaskets causes the leak you describe. On the needle and seats, the ones you first describe are Borg-Warner rebulid kit needle and seats. They are functional, if a little crude. The second ones you describe are the orginal ones Holley specifies. They tend to leak profusely if you adjust the level while the boat is running, a dicey proposition. Float level is a subtle way to trim your full throttle fuel mixture, but a little goes a long way. Higher is richer and lower is leaner. But wer're talking a half turn each way maximum. avoid the clear plugs for the float bowls, they break off.