2 bbl 898 vacuum guage reading

[cecho]

I was using a vacuum gauge to help tune my engine and noticed the following. I adjusted the air bleeds on the engine to highest vacuum and RPM at idle. The best I could get was 15 HG, but the needle on the vacuum gauge flutters between about 14.5 and 15.5 HG at a very high rate. It's almost a blur. Any ideas what this may be? I was using the port on the port side of the engine on the intake just below the carb to take my readings.

 

[achris]

Re: 2 bbl 898 vacuum guage reading

Worn valve guides...

 

[cecho]

Re: 2 bbl 898 vacuum guage reading

Wouldn't I also be getting smoke on startup? I'm not seeing any smoke at startup.

 

[achris]

Re: 2 bbl 898 vacuum guage reading

Not if the valve stem seals are doing their job...

 

[cecho]

Re: 2 bbl 898 vacuum guage reading

Engine starts right up and makes good power. It spins a prop at a higher RPM and pushes the boat a bit faster than the manual shows it should. The only bad symptom I have a slight vibration at 2500ish RPM. I guess I'll just run it until it has problems and replace it with a 350.

 

[matt167]

Re: 2 bbl 898 vacuum guage reading

Yep, worn valve guides. If the 'pop' is only 1HG than it's still in decent shape. I wouldn't worry about the 15hg part.. One thing that I have found which works is to dump marvel mystery oil down the carb. It will help seat the valves tighter. I had a 1965 Rambler American with the old 195.6 6cyl and it was totally worn but still ran. I would get about 12HG and it had a bit of a 'pop' so at least 1 valve was leaking. The engine was so bad that taking off from a start, it could not suck fuel out of the float bowl. The accelerator needed to be pumped repedidly to activate the accelerator pump or it would stall from a dead stop.. I put marvel mystery oil down the carb every 400 miles or so and the vac would go up to 13-14 HG and I could then accelerate from a stop without pumping the pedal. I also use it on my early 70's snowblower that has a "D" series briggs& Stratton. Put it right in the gas on that motor. If I don't, a 6" flame comes out the exhaust and the muffler glows red hot

 

[cecho]

Re: 2 bbl 898 vacuum guage reading

I used some sea foam on it yesterday and quite a bit of carbon came out. I'll try another vacuum test and see what happens. Maybe I'll be lucky and it was just some carbon build up. I guess if the guides are worn the worst thing that could happen is eventual oil use or a burned valve. I'm pretty sure I can still get back home with a burned valve so I'm not too worried about that.

 

[achris]

Re: 2 bbl 898 vacuum guage reading

I've heard of those SBC V8s coming home with 3 dead lungs and the owner wasn't even aware of it. You can't kill them with a stick!

Chris.......

 

[cecho]

Re: 2 bbl 898 vacuum guage reading

I've read up on repairing the valve guides. Do you think it would be worth $100 to ream out the guides and replace the old valves with oversized valves or maybe valve guide inserts? I'd be willing to spend the time and $100 to get rid of the vibration, but all I've got are hand tools and I don't want to end up breaking something. Except for the vibration the engine runs well and makes plenty of power.