Vacuum on 5.0GL (502bpbyc) w/ Holley 2bbl Carb?

[jclarke2899]

I have an OMC (Volvo) 5.0GL and was doing some general maintenance and getting my boat ready for summer. Decided to put my new vacuum guage on my carb to see if I needed any adjustment. Most I can get is 15 in. mg out of my carb. Several sites and some gauges say that I could have a timing issue or something else, but I can't find anything in my manuals to show what I should be getting. Anybody else have similar setup? Any idea on what to check first? New plugs just put in and properly gapped. Engine overall seems to run smooth..

 

[jimmbo]

Do you know if the gauge is accurate? A low vacuum at idle could be, retarded timing, low compression(scored or worn cylinders), stretched timing chain(retarded valve timing, great for high rpm power but weakens low rpm torque), or even intentional due to cam specs. Higher elevations result in lower results as well. Do a compression test. That will reveal some info on the compression

 

[alldodge]

If your getting the full vacuum and not a ported one, the engine may just be getting tired. Suggest checking your compression

 

[jclarke2899]

I also did the vacuum test on muffs so not in forward gear, not sure if that makes any difference? Looks like I may need to check compression and timing though.

 

[alldodge]

In gear would make no difference