poor idle Ford 351

[cnefalcons]

1978 Pleasurecraft (Ford) 351 won't idle. Changed coil, points, cap, rotor, ballast and fuel filter. Not the carb as have twin engines, swapped carbs and does same thing while the other engine runs fine with first carb on. No vacuum leaks either. Any help greatly appreciated. Thanks.

 

[Wellcraft 89]

Re: poor idle Ford 351

You did put a timing light on the engine after all of the ignition parts were changed ????<br /><br />What about fuel pump on the engine that doesn't idle <br />chkd compression on that engine ?<br />any backfire or poping noises <br />How are you sure you have no vacum leaks?<br /><br />just $.02<br /><br />Rich

 

[K Hultgre]

Re: poor idle Ford 351

Is it a 351M or 351W ?<br />How long will it idle or try to idle?<br />Does it run well above 1200rpm no backfires, missing, etc.?<br /><br />How old are the plug wires (seen some nice electrical fireworks at night from bad wires)? What do the spark plugs look like? <br /><br />Have you tried spraying Gumout or equiv. around the base of the carb and around intake manifold to check gaskets. Pull vacuum hoses to see if there is a change in idle. If you pull a vacuum hose that does not change the idle try plugging the outlet on the carb or hose with finger to see if it improves. Small vaccuum leaks are hard to find. <br /><br />Have you tried swapping distributors (maybe bad vacuum advance or mechanical advance springs if so equipped)causing timing to jump around. <br /><br />Last Resort,<br />How many hours on the engines? A worst case scenario would be the timing chain is loose (Ford used a nylon cam gear in years past (not sure if yours would have it) that fractures over time and falls apart creating slop in the chain or worse jumps a tooth and then engine will not run. Easy way to check is to take off dist. cap and turn crank by hand until rotor spins 1/2 turn, then make a reference mark on the pulley and reverse direction of crank rotation and stop when rotor starts to move the opposite direction. The book I had said 10 deg should be max but I found 12deg is ok (1/4 turn is way too much).

 

[DJ]

Re: poor idle Ford 351

I really would be looking for a vacuum leak. Or, as suggested, put a timing light on it.<br /><br />Also, connect a vacuum guage. Vacuum should be about 16-18" and steady.<br /><br />Both the timing light and vacuum guage will tell you if the the engine "jumped time".

 

[cnefalcons]

Re: poor idle Ford 351

Thanks for all the great suggestions. Some answers:<br />Timing light used.<br />No popping noises.<br />Runs great above idle.<br />Used soapy water spray to check for vacuum leaks.<br />Spark plug wires have been changed.<br />It will idle as long as you keep pumping the throttle.<br />Engine has 611 hours and was rebuilt about 10 yrs ago.<br /><br />Will try other suggestions this weekend.<br /><br />Again, thanks for all the input.

 

[NOSLEEP]

Re: poor idle Ford 351

You cant determine a vacuum leak with soap and <br />water.You need to use a combustible product.<br />A Little aether or even acetylene.<br />Soap and water is used to determine expelling<br />gases, not vacuum leaks.

 

[K Hultgre]

Re: poor idle Ford 351

Have you tested the fuel pump? Disable the ignition then disconnect fuel hose from carb and feed it into a large coffee can, crank engine for approx 10 sec and mark the level. Then do same procedure on good engine and compare the two.

 

[loadnet]

Re: poor idle Ford 351

Throw the timing light on it again and see if the mark is jumping all over the place.. at idle.<br /><br />If it is there's a chance your chain may be stretched and sloppy..<br /><br />Sorry to tell ya this again, however when you think you've tested everything you can think of that could cause such a situation sometimes it's good to just go over things 'one more time' <br /><br />PB