cylinders 1&4 dead on a 1988 Black Max 150

[trevstar]

This is my first post here. I've poured over the threads to try to avoid asking the same question that's been answered elsewhere, but I'm not finding my issue.

The behaviour is this:
The motor (S/N B313046) had an overheating issue. I replaced the impeller and everything was good, however, a partial miss/stumble that the motor had been getting is now constant and I can't get rid of it. A few weeks ago the motor had great pull, lots of power from zero to full speed, especially at WOT. Today, the motor stumbles on takeoff, and only seems to run on all 6 cylinders when it's planed out and at WOT.

Diagnosis:
we've located the problem to be on cylinders 1 & 4. At idle, with muffs on, I can pull the plug wires on 1 & 4 and the engine tone doesn't change. 1&4 both have spark. Throughout the things we've done to isolate the problem, it has not changed cylinders - always 1 & 4.

What I've done:
swapped switchboxes
swapped coils
swapped/changed sparkplugs
cleaned the top carb (no kit, just took it apart and cleaned it. It looked great, one float was given a minor adjust)
squeezed primer bulb while running to check if it was fuel pump related
timing is 23 BTDC at cranking speed (if memory serves)

The missing on 1&4 has us stumped. We can't move the problem, and the only thing I'm slightly suspicious of is the trigger. I'm just about to check resistance on the trigger, but thought I'd post before I head out again.

Thanks in advance for any suggestions.

 

[Faztbullet]

Re: cylinders 1&4 dead on a 1988 Black Max 150

The only thing 1 & 4 have in common is the bleed lines and trigger pairing. Index flywheel and check timing on all 6 cylinders and check to make sure pairs are not swapped on switchbox...

 

[adam98]

Re: cylinders 1&4 dead on a 1988 Black Max 150

First, Dva adaptor is great to have... Timer base are suspect and switch box's but dva will tell you one or both.

I bet its a timer base bad design. Even if checks good they go bad. Wires are hot and bend with every throttle movement... To check. With volt meter in ohms and grab all triggers off one switch box together. Then with other lead touch other trigger one at a time on other box. Should all be same ohms. Plus with a dva when running. 4v+ between 2 triggers or 2v+ from any one trigger to ground one at a time. Then if trigger is good out put on box is 180v plus go to cdi site then have a trouble shooting guide

 

[trevstar]

Re: cylinders 1&4 dead on a 1988 Black Max 150

The only thing 1 & 4 have in common is the bleed lines and trigger pairing. Index flywheel and check timing on all 6 cylinders and check to make sure pairs are not swapped on switchbox...

Thanks Faztbullet. I didn't realize 1&4 were part of the same trigger pairing. I guess that's more evidence that the trigger is shot. I'm not sure what "bleed lines" are, though.

adam98, I checked the trigger yesterday. All resistances are at about 1300 based on the "book checks". I'll try your method once I track down a DVA (or build one). Again... really sounds like a trigger problem.

Is there any reason to change a stator or other parts if I change the trigger?

Thanks to you both for your quick replies. :joyous:

 

[adam98]

Re: cylinders 1&4 dead on a 1988 Black Max 150

That's how cdi said to check the trigger with out a dva. But If you move enough wires around you can circle the part the issue is comming from. But a dva will take a few min and moving stuff around takes a few hours and uncertainty when spending hundreds on parts