Should there be a resistor between the coil and cap

[codyandamber]

I am burning the little center peice out on my distributor cap. Do I need to put a resistor in between my cap and my coil? If so does it need to be an 8 volt resister? Its on a 79 mark twain with a 305 mercruiser..

 

[DJP]

Re: Should there be a resistor between the coil and cap

What kinda coil do you have installed ? <br />8 Volt ???? on a 12 volt system ? you lost me.

 

[Boatist]

Re: Should there be a resistor between the coil and cap

Cody<br />Tell us what happeneds to your rotor. Does it keep going bad?? Have you changed both the rotor and cap at same time. At that point in the system the voltage should be about 10,000 volts or more. Only time you would use a supressor there would be if getting a lot of radio noise. Sometimes if the rotor does not match the cap then the rotor tip can hit one of the post and brake. Also if mismatch could have too wide a gap causing spark to follow carbon path in cap. Please give all the details of failure you can share.

 

[codyandamber]

Re: Should there be a resistor between the coil and cap

I replaced the whole distributor. It was a brand new one...not refurbished or off another boat. It came with cond., rotor, points, and cap. The rotor's not bad. Only the cap as far as I can tell. The points still looked brand new. I have only had the distributor on it now for about a month. It burned the carbon tip completely off. I would tend to think it was the coil getting too hot or sending too much. <br /><br />Oh, the last distributor cap on the old distributor did the same thing...Only we knew the distributor was bad because the shaft was broke in two at the top...Not where the two pins are..<br />So, it would not stay in time.<br /><br />We replaced it and all was good for the last month...in this area of the boat.

 

[Boatist]

Re: Should there be a resistor between the coil and cap

Cody<br />I would check the coil and see if it is some sort of supper high voltage coil or just the standard coil. Check the Plus side of the coil with a volt meter and see if voltage is 8 to 9 volts. If over 9 volts then need to install a ballast resistor or resistance wire. Check spring top of rotor and make sure it is not rough like sand paper or smashed down where it does not actualy touch the center of cap. A spark between the rotor top and cap center could cause center carbon in cap to burn.<br /><br />After that if I only had it for one month I think I would call dealer and ask why it is doing this.<br /><br />Good luck and lets us know what fixes it.

 

[codyandamber]

Re: Should there be a resistor between the coil and cap

I went ahead and put the resistor in. It is not giving any indication of the tip burning now. I, however, do have a new problem... It seems like it is out of time. It ran great before and now it runs horrible. It misses so bad it won't pull a skier up. I have replaced the distributor, dis cap, plugs, rotor, condensor, plug wires, coil, and points. Do you think that when the carbon tip was burning off that the points could have gone bad. I have tried bypassing the resistor just to make sure that was not the problem. It was not. AHHHHHHHHHHH<br /><br />Thanks for all your help, though....

 

[randyc2958]

Re: Should there be a resistor between the coil and cap

Cody, I just went through almost the same thing. I have point type ignition. I replaced the points and condensor over St Pats. day went down to start the engine and set dwell and it ran rough no power couldn't even get it to 3000 rpm with no load with correct dwell (30 deg for a V/8). I replaced the new set of points with another new set with a new condensor and it took off like a rocket. I have never seen a new set of points and condensor go bad right out of the box but it happens. Good luck I know I was very frustrated for a week!!

 

[Boatist]

Re: Should there be a resistor between the coil and cap

Cody<br />Where did you put the resistor?? Did you put it in high tension lead between the distributor and coil?? Is the high tension lead from coil to distributer a solid wire or carbon?? If it is carbon have your checked it with a ohm meter??<br /><br />Could be your high tension lead is carbon and open in the middle, this would cause high voltage to build up at the coil before it could jump the gap but also mean weak spark at plugs. When you open the throttle and compression goes up could cause spark to blow out. On my engine High Tension lead from Coil to distributor I put in a solid wire and it has had no effect on radios at all. Reason I did this is I have seen this short carbon wire fail in autos many times and since it feeds all spark plug wires engine will not start or all cylinder have weak spark, not what I want when out to sea.

 

[codyandamber]

Re: Should there be a resistor between the coil and cap

The resistance seems fine....<br /><br />I have ran a new wire..<br />one with the resistor<br />one without<br />everything I could think of.<br /><br />Do you think it could have burned the points before I put the resistor in it?

 

[Boatist]

Re: Should there be a resistor between the coil and cap

Cody<br />If you put resistor in high tension lead will not affect the points. If you put resistor in wire to hot side of of coil then will help points.<br /><br />I would check voltage to plus side of coil. Also check dwell on minus side of coil. If coil has a capacitor on the plus side of coil for radio interference I would remove it and see if it makes a difference.<br /><br />Also make sure distributor cap all the way down and rotor ok. Make sure breaker plate inside distributor has a good ground wire.<br /><br />Last I would check timing.

 

[codyandamber]

Re: Should there be a resistor between the coil and cap

All seems to be good in the ignition section. Last I did check the timing. It was dead on. Still missing, though. I guess I should move along to the fuel system???

 

[bowhuntrrl]

Re: Should there be a resistor between the coil and cap

You still haven't answered where you put the resistor!! It does not , repeat DOES NOT go on the high tension lead from the coil to the distributor. It goes to the positive side of the coil. You would be killing all the voltage to the plugs if you put it on the high tension lead, most likely causing your problems.<br /><br />Rich

 

[codyandamber]

Re: Should there be a resistor between the coil and cap

I understand that. It is on the positive side of the coil... Earlier I said I tried it with the resistor and without. I had the same problem either way. The resistor is not my problem. I placed the resistor because the coil was burning the carbon tip inside the distributor cap. I have sice replaced the cap, plugs, plug wires, and coil. I already replaced the whole distributor and components. I have checked the points and they don't seem to be bad after the carbon tip was burned off. I am lost from here. <br /><br />Should I begin trouble shooting the fuel system???

 

[bernieb]

Re: Should there be a resistor between the coil and cap

Check gas tank for trash,at the output of gas tank there should be a check valve (one way flow)clean it,change water separator cannister,if the carb is a rochester, change filter at input and there is a right way and a wrong for that filter.Tighten the base bolts on carb,spray carb cleaner while on the go.Try moving distribtor slightly while on the go at the upper speeds watching rpm gauge.I'm presently having a problem with my 350 mercruiser and it's looking like a worn cam as I hammer down and the other two barrels are suppose to kick in it studders down like a flooding problem and gas comes back up in a mist from the carb so good luck. .Have fire extinguisher handy on the test.

 

[Boatist]

Re: Should there be a resistor between the coil and cap

Cody<br />Still not sure where you put resistor. I know you said bypass it and made no difference. At one point you put it between cap and coil, so I assume you put it in high tension lead (spark wire to cap).<br /><br />You can trouble shoot any way you want but quicker and cheaper to test rather than start replacing things. I would start with the Distributer since that is where problem you had. Check your dwell first should be 30 degrees. Next I would hook timing light to wire between top of coil and center of cap and start engine and see if get steady flashes. Then I would hook timing light to each plug wire as close to spark as I could get, or could gap a plug real wide like 1/2 inch then ground base and try it on each spark plug wire and make sure have good spark. Last I would make sure centricifal advance in distributor is working.<br /><br />Next I would do a compression check on all cylinders.<br /><br />Next check fuel pressure to carb.<br /><br />One of these test should give you a good idea where your problem is.<br /><br />Does it only miss under power or also at idle??<br />Good luck, does not sound like much fun.

 

[codyandamber]

Re: Should there be a resistor between the coil and cap

Yes, I did put the resistor on the high tensin lead.<br /><br />At first it was only missing under a load, then it started missing a little at idles, and now it'll barely crank much less run. I should have stayed in the Navy where it sucked to be on a boat....

 

[petryshyn]

Re: Should there be a resistor between the coil and cap

is it possible that the spring tab on the top of the rotor isn't up at an appropriate angle? Did you by chance try to flatten it? If it is not arched up high enough to maintain a good contact, the carbon button in the cap will burn.....<br />