Vacuum readings

Ok, I'm still investigating my high-speed miss heating up above 3400rpm and going through stuff. Engine: Mercruiser 888/Ford 302, fresh rebuild about 50 running hours ago. Ran like a champ until I tried to do an intake/carb upgrade. Ended up putting original parts back on due to bad fitting new manifold. Rochester 2GC carb rebuilt 2 years ago.<br /><br />To date: checked fuel filters, checked timing, checked fuel fittings for obstructions, checked alternator output.<br /><br />Tonight I pulled plugs 5 and 6 (easiest to get tu). They are very black and dry to the point of looking fouled. The engine does seem to run very rich.<br /><br />I also pulled the hose off the PCV valve and attached my Vacuum gauge. The hose is plugged in to the barb on the Merc carb adaptor.<br /><br />At a fast idle of about 800 rpm, I get a reading that bounces between 13"-15", but generally stays around 14". The needle looks very much like "Defective Ignition" at this site : Vacuum Readings <br /><br />Looks like I'll be changeing plugs this weekend. What should I do about the rich condition? The carb is a Rochester 2GC. Is the rich condition due to improper float adjustment? I don't think it's just at idle.

Re: Vacuum readings

You ought to look at all the plugs before you try to come to any conclusions. I'm still fighting the black plug syndrome on my 302. I've had 5 different carbs on it. Some are dry black and others are nice and light tan. I might have a lifter issue. The motor runs like a striped *** ape but after the clean plugs start to soot up it won't idle well.<br /><br />My vacuum, at idle is quite a bit higher than yours (18ish & rocksolid) but I'm running an Edelbrock Performer and a '69 351W camshaft.<br /><br />I'd hoped to get back to determining my problem earlier but still have it in front of me.<br /><br />I'm going to get my engine scoped before I try anything else.

Re: Vacuum readings

Since those two were go gunked up, I decided if I'm going to go through the pain of pulling them, they're getting replaced. Pain is meant literarally since the plugs are hard to get to.<br /><br />I'm running a factory cast 2bbl manifold with a fairly mild cam.<br /><br />The motor starts and idles well after a few seconds, but you the exhaust leave a lot of black suit on the prop and you can see black gunk in the exhaust water that puddles on the groud.<br /><br />I still have a newer 4bbl to put on, but wanted to get everyting right before I tear in that far.

Re: Vacuum readings

Bump for the rich running question.

Re: Vacuum readings

go one heat range hotter on the plugs. that will fix the dry black soot problem you are experiencing. That is due to too cold a plug.<br /><br />on the rich 2G, does that model have the fuel bowl where you pull the cover off the top of it to access the float and the bowl, like how the 2b mercarbs are? If so, then you can pull it and notice how high the fuel is in the bowl. If it's real close to the top then lowering the level by adjusting the float will probably help some. Also lean out the idle mixture screw.

Re: Vacuum readings

The top is removable.

Re: Vacuum readings

May have found a partial culprit on the rich running. The last time I put plugs in it, I had to use a cross-referenced one. Turns out it is a different heat range plug. Also may have found my miss in an unexpected place. One of my near new plug wires was apparently not crimped very well at the distro plug. I took the wires off one/one and replugged them. When I unplugged one of them, the wire cam out of the boot (without the metak cap).

Re: Vacuum readings

i make all my own crimps with the plug wire kit that you crimp and cut to length. and install the boots on

Re: Vacuum readings

Thanks lilmandavis, I thought about doing that, but I don't trust my ability tomake really good crimps.<br /><br />but, after recrimping the bad wire for now (will replace as the crimp still doesn't give me the warm fuzzies), I put in the proper plugs and redid the timing again. It was maybe at 11deg. It is now spot on at 10deg. I also leaned the idle adjustments out 3/4 turn. These are my new Vacuum readings:<br /><br />575 rpm idle: fairly steady 14-15 in<br />800 rpm: really steady 17 in<br />1000 rpm: really really steady 19 in<br />1200 rpm: 21 in vacuum and the needle barely vibrates (due to cam overlap?)<br /><br />Is the lower vacuum thru 800rpm ok or should it be higher? <br /><br />The ~575 idle is as low as I can set it without loping. Merc spec is 550-600<br /><br />Can anyone confirm the float settings on an 888 Rochester 2GC so I can double check it?

Re: Vacuum readings

this Thread Jason,..??...<br /><br />I Think it was Rodbolt or somebodyelse that is the Vacuum Gage Expert,..... Certainly Not I.....<br /><br />And,.... If you're going with the 4bbl Carb,.... This thread doesn't really mean much anymore........<br /><br />Short Answer,........<br /><br />I Don't Know.........

Re: Vacuum readings

Yup this one. I'm still wishy washy on the 4bbl, so I've been trying to get it in perfect tune before I get started with changes so I know where I'm coming from, and it may be a while before I get to the swap.