TOPIC: switch box test procedure ?

Hello fellow knuckleheads
I have a 1977 115 hp tower of power that is very hard to start and when it does finally continue to run , it sounds like its only running on half the cylinders.I have tested the stator and it ohmed out ok.The trigger test gave me only a 1.23 reading and the manual called for 8 to 11. Maybe have to replace the trigger.
Anyways, I would like to know if there is any way to test the switch boxes with an ohm meter. Thanks , Jack in AZ

Not really, the switchboxes contain a dc voltage circuit and scr;s that are fired by the trigger. The best way to check the switchbox is to swap them around and see if the problem follows the box or stays with the odd or even cyl. If it stays with the cyl your problem is in the trigger, if it follows the box..its the box.

Have you inspected the distributor cap - to see if the spring loaded center carbon is intact?
Have you tested to see how far the spark will jump at the spark plugs?
In saying this - understand that you will need to give the spark a place to jump to to avoid stress on the system, but the spark should jump close to a 1/2" at the sparkplug end of the wire.
If it won't, but you're seeing spark on all (6) with short gap tests - consider the coil or wire connections.
Thom

Is your 77 equipped with a distributor and one coil --or is it ADI with 2 switch boxes and 6 coils ??

Has 2 switch boxes and 6 coils. I swapped switch boxes around last nite and it does start a little quicker but still feels like it is running on only 3 cylinders. Checked each coil with an ohm meter and they all read .9 ohms on the 200X scale. It has blue coils and the manual says they should read 8-11 on the 100X scale. They all read the same so will keep searching. Thanks, Jack in AZ.

If it has two switch boxes. You need to be watching your spark plugs for spark. You say is "feels" like its running on 3 cyls. That feeling can be many different problems. If you havent looked your spinning your wheels for no reason. Pull the plugs and watch them. If 3 are not firing correctly swap the boxes and see if the problem changes to the other set of plugs. If the problem switches then you know what box is the problem. I do not have a motor exactly like that but it sounds like a simple deductive reasoning problem.

It also could quite easily be a plugged up carb. when starting squirt gas oil mix directly in the carbs if it starts better, your on to something.

Now when Idleing squirt into the carbs if the RPMS fall that carb is normally fine. If you find a carb that comes up in RPM when you squirt gas into it, then you've most likely found your problem.
Conrad

Timing light can be used to check for spark on all 6

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If you have a carburetor problem , then careful about further " crank and hope work " no fuel means little or no oil going in as well.

I dont think I would call my method CRANK and HOPE. But name it what you like. It works.

The 15 seconds it takes to run this carb diagnostic is not gonna hurt anything IMO.

If your afraid of doing so then tear all three carbs off and give them a proper cleaning and rebuild.

I personally like to know what carb Im having issues with before I tear if off so I dont chase my tail any more than needed.

Conrad

And,...If you have two switchboxes and (6) coils your inline-6 is a late '79 or '80s model.

That ignition system has specific reading you can use to troubleshoot and find your problem using a DVA meter.
Absent a DVA meter you 'can' do 'some' troubleshooting by swapping coil wires around - obviously while the engine is made safe and is not going to start. (remove the spark plugs and control their spark to ground to avoid creating greater ignition problems than you already have)

Example:
#1 sparkplug wire has no spark.
#2 sparkplug wire has spark.
Move the small primarily green wire from #1 coil down to #2 coil and vise-versa with the #2 primarily green wire.
If #1 now has spark & #2 no longer will spark you have successfully eliminate the (2) coils from the cause of failure.

If you review your wiring diagram you can identify what cylinder's coil - via the switchbox - has the same color coded trigger wire in the other switchbox.

I don't have a manual in front of me so let's say #5 coil when traced back to the opposite switchbox that coil #1 goes to has the same color coded trigger wire.
Once the other switchbox's coil is identified that uses the same color coded trigger wire as #1 coil (which doesn't have spark when properly wired) you will want to test for spark on that coil.
We're assuming it is #5 in this exercise.
IF #5 does NOT have spark, and you then swap its small primarily green wire to another coil and vise-versa and can conclude the #5 coil is okay,...You have determined that the trigger wires (colored coded identical for #1 & #5 in this exercise) are dead and consequently you will need to replace the trigger.
If #1 has no spark, but its common partner based on color coded trigger wires has spark,...You have eliminated the trigger as the problem on #1 as well as #1's coil - - leaving the switchbox #1 uses as the culprit needing replacement.
I stuffed a lot in here with minimal explanation so if it doesn't make sense please tell me and tomorrow I will arm myself with a manual and make it easier to follow.
By "small primarily green wire",...I mean that all (6) coil wires from the switchboxes are primarily green, but all have a different colored stripe to identify which terminals they go between.
Understanding - even with these tests completed - and in most cases these swaps, etc will solve the problem,...BUT unless you are armed with a DVA and related tests you could miss a gremlin or two.
Thom

boatpeople wrote:

Hello fellow knuckleheads
I have a 1977 115 hp tower of power that is very hard to start and when it does finally continue to run , it sounds like its only running on half the cylinders. Jack in AZ

Jack, I had the identical issue with my 1983 115 tower, hard cold start and running lean once it did start. I discovered while doing carb cleaning with the carbs still mounted on the engine that the top carb had a stuck needle & seat which meant no fuel to feed the fuel enrichener that is fed off the fuel bowl of the top carb and caused a lean condition once it did run. If your engine has the fuel enrichener system rather than a shutter style choke system you can check for fuel by removing the small hose on the very bottom of the top carb's fuel bowl. Also check to make sure the enrichener valve is actually operating. I am a newbie and so am not familiar with which years or models had the shutter style or the enrichener system for cold start. After replacing all 3 needle & seat assemblies,spraying carb cleaner in the passages then compressed air my engine now fires right up and sounds soooo sweet.

Melanie

Update,cleaned and puts kits in the carbs,repaired a few wires among the switches and coils and this puppy runs like a champ! Thanks to everyone, Jack in AZ