How do I check for proper spark at idle?

[rbickham]

How do I check for proper spark at idle on 90 h.p. v-4. It idles rough.

 

[Silvertip]

Re: How do I check for proper spark at idle?

With a spark tester -- and you don't have to do it at idle. You build or buy a spark tester, set the gap at 7/16 - 1/2 inch and see if the spark jumps the gap. Do a search on this topic and you'll find a number of home-brew spark testers.

 

[jtexas]

Re: How do I check for proper spark at idle?

Spark test - start with a known good fully charged battery:
1. Set the tester gap to 1/2"
2. Remove the spark plugs and use jumper wires to ground the leads to the cylinder head (one-up tester).
3. Connect a lead (or all the leads if you have a multiple tester) to the tester and clamp it to the cylinder head.
4. Use a helper or remote start button to crank the engine.
5. Look for a sharp blue spark across the gap.

Cylinder drop test:
To see which cylinder(s) are not hitting, use an insulated spark boot tool to pull one spark plug lead at a time, with the engine idling. If the RPM's don't decrease noticeably, that cylinder is dropping out.

Rough idle, but runs good otherwise, rbickham?

 

[rbickham]

Re: How do I check for proper spark at idle?

Spark test - start with a known good fully charged battery:
1. Set the tester gap to 1/2"
2. Remove the spark plugs and use jumper wires to ground the leads to the cylinder head (one-up tester).
3. Connect a lead (or all the leads if you have a multiple tester) to the tester and clamp it to the cylinder head.
4. Use a helper or remote start button to crank the engine.
5. Look for a sharp blue spark across the gap.

Cylinder drop test:
To see which cylinder(s) are not hitting, use an insulated spark boot tool to pull one spark plug lead at a time, with the engine idling. If the RPM's don't decrease noticeably, that cylinder is dropping out.

Rough idle, but runs good otherwise, rbickham?

A little history about this motor. I bought this boat this spring from a local dealer, it was a trade-in from an older couple that bought it new in 86. When I took it for a ride the first time it would idle rough and kept stalling. I checked compression and number 1 cyl. was low and the spark plug had water on it. I took it back to the dealer and they rebuilt the powerhead and put a new head on it. They also put a new VRO pump on it because they broke it rebuilding the powerhead. It still idles rough and or surges idle through midrange. I bought a service manual and rebuilt the carbs and tried to do the link and synch. Didn`t do the max. spark advance check because I don`t have a test wheel. How can you check this without a test wheel? When I checked the cam follower pickup timing, the lowest I could get the timing is 12 degrees, its suppose to be 4 degrees. The motor runs great above midrange to full throttle.

 

[jtexas]

Re: How do I check for proper spark at idle?

That's a complicated question, no doubt someone here will know the answer but it might take a little more patience til they log on. I would have answered it when you first posted it this afternoon if I could have.

 

[Silvertip]

Re: How do I check for proper spark at idle?

Joe Reeves has a procedure for WOT spark advance setting where you don't actually run the engine. If you do a search for WOT or MAX timing you should turn up the procedure.

 

[rbickham]

Re: How do I check for proper spark at idle?

Joe Reeves has a procedure for WOT spark advance setting where you don't actually run the engine. If you do a search for WOT or MAX timing you should turn up the procedure.

Checking the WOT timing isn`t my main problem. It`s the rough idle from idle through midrange. Any ideas?

 

[ezeke]

Re: How do I check for proper spark at idle?

As jtexas said, it is probable that you are losing one cylinder at idle. Pull the plugs one at a time to isolate the one that does not change the performance.

Then swap the coils and see if it follows the coil. If it does, replace the coil. If it does not, suspect a fouled low speed jet in the appropriate carburetor.

Did you download the Rapair.com troubleshooting guide? If not, you might want to. From their homepage, navigate to product information, then to downloads and select "Trouble Shooting Guide. It is a fairly large pdf file, so be patient.

 

[rbickham]

Re: How do I check for proper spark at idle?

As jtexas said, it is probable that you are losing one cylinder at idle. Pull the plugs one at a time to isolate the one that does not change the performance.

Then swap the coils and see if it follows the coil. If it does, replace the coil. If it does not, suspect a fouled low speed jet in the appropriate carburetor.

Did you download the Rapair.com troubleshooting guide? If not, you might want to. From their homepage, navigate to downloads and select troubleshooting. It is fairly large so be patient.

I will try pulling plug wires one at a time. I rebuilt the carbs, all jets clean. Why would my initial timing be 12 degrees? Can`t adjust it down. Also how do I do a search for Joe Reeves Max Timing procedure? Also where do I find Repair.com troublshooting guide. I searched Repair.com and nothing. Thanks

 

[ezeke]

Re: How do I check for proper spark at idle?

You type "Rapair.com" into the address field on your browser. Rapair is a company, Rapair.com is the address of their home page.

Or copy this, without the quotation marks, to the address field on your browser:
"http://rapair.com/Forum/tabid/247/forumid/1/threadid/7/scope/posts/Default.aspx"

 

[jtexas]

Re: How do I check for proper spark at idle?

Did you check the position of #1 piston TDC against the flywheel pointer?

 

[rickdb1boat]

Re: How do I check for proper spark at idle?

http://www.iboats.com/bbboard/bbBoard.cgi?a=viewthread;fid=28;gtid=737728;gpid=737729#gpid737729 ] Click Here [/url]


And http://rapair.com/Forum/tabid/247/forumid/1/scope/threads/Default.aspx ] Click Here [/url] for the troubleshooting guide

 

[cougar1985]

Re: How do I check for proper spark at idle?

just throwing one in there, are the plugs proprely gapped. some people and dealers have been known to buy the plugs and just throw them in there. in a big rush this year did the same .the 90 ran terrible at low speeds. took home checked gap was way too close ,regapped to spec and presto a geat running motor.according to my manual gap should be .040 ,because i troll a lot i gapped mine at .045 .

 

[rbickham]

Re: How do I check for proper spark at idle?

just throwing one in there, are the plugs proprely gapped. some people and dealers have been known to buy the plugs and just throw them in there. in a big rush this year did the same .the 90 ran terrible at low speeds. took home checked gap was way too close ,regapped to spec and presto a geat running motor.according to my manual gap should be .040 ,because i troll a lot i gapped mine at .045 .

I installed new plugs first. I set the gap at 40. Still runs rough at idle. I rebuilt the carbs. Still runs rough. I am going to try the drop test by pulling each plug wire off one at a time. Thanks!

 

[farginicehole]

Re: How do I check for proper spark at idle?

Tell your wife to be ready with the digital camera so she can capture the expression on your face when you get a little poke from the spark plug wire, and please post a picture here! 8)