Manifold pressure and tuneing

[Anonymous]

The mustang had been running really rough lately, finaly got around to spending a bit of time tuning the thing up.

generaly i use a vaccume gauge (fairly cheep one, but seems to work well) off the manifold vacume line the runs to the tranny (C4), as its an easy place to hook it up. I went and got new plugs and immediatly found my problem in the rough preformance, there was a TON of buildup on the plugs. Its jsut theat flaky carbon buildup, not oil or anythign else majorly wrong. Just dosent seem to be burning right.

anyway i cant get the damn manifold pressure up to where it needs to be, hovers about 5 psi below where the vaccume gauge starts its "green band" for correct engine preformance. now i know it WAS there about a year ago when i did it in So. Calif. but cant get the extra vaccume here in Colorado.

I wonder if its the altitude difference? Timeing is good, mix should be good (now). im kinda stumped on the loss of pressure.

anyone have any ideas?

 

[Lazy JW]

The altitude is most of your problem, there simply isn't as much air pressure to push into the engine as there is at sea level. You mentioned the buildup of deposits on the plugs, this indicates at least a slightly rich mixture and possibly a need for a hotter plug. Since the air is 'thinner', you don't need as much fuel, the carb may need re-jetted. You should also be able to run slightly more ignition advance. Try setting the timing by advancing until max vacuum is achieved, then back it off one inch Hg. Then adjust idle speed, then set idle mixture to max vacuum, then re-set idle speed again. This should help your fuel economy, but if it still runs rich under load the main jetting will need some attention.
Joe

 

[Anonymous]

Something that helps the plug fouling is an MSD box. In a sense, you are just treating a sympton and not curing the cause, but it really extends the maintainance interval. My old dual 4 bbl Vette was notorious for fouling plugs. The MSD has made the plug fouling and plug changing a thing of the past.
Doug

 

[CZLN6]

Howdy travis:

Be aware that both California and Colorado require a special mix of gasoline to reduce pollution. While it may help the air quality, it does add some deposits and build up to the spark plugs. About the only solution is to use less of the stuff and to change plugs more frequently.

Joe's "How to" on setting the timing and low speed air screw are the best first steps. Do that 1st, then reassess the need to use a smaller main jet.

I'm at 5,000 ft elevation here in eastern Idaho. More initial advance is required with this thin air. Try a setting of 15 degrees and assess from there.

If your ignition is in good shape try opening the gap to .040" and assess.

Adios, David