Problem with New SBT Motor

[Bryan Glynn]

Niether the lack of a restrictor nor a bad check valve would cause your issues, however to do NEED to replace the check valve - you do risk the chance, although slight on your ski, of fuel starvation.

I would run it on the water, get some time on it at the new ratio and go from there.

[RadioDave]

Well, I took another shot at it today on the water.

I am still having the backfiring problem. It is not consistent though. It tends to do it more at idle, but can occur at higher speeds. I can feel a miss as the plugs foul which is usually accompanied by the backfiring. Revving sometimes clears the miss and backfire. The plugs are less oily since going 40:1

However, the ceramic insulators around the plugs' electrodes are still turning black although the round bases of the plugs are staying gold. The piston-facing side of the part you adjust for gap is also black.

I tried tweaking on mixture settings on the trailer in the water, but they really don't seem to have an effect on the backfiring.

Could poor fuel supply be the cause of my symptoms? I have disasembled and cleaned the carb, but all of this backfiring through it could have done a number on it.

Maybe you can help me solve my own problems,

1. What does the blackening of the ceramic portion around the electrode indicate?

2. What condition causes an intake side backfire?

Thanks for the continued support!

[Bryan Glynn]

Black insulators indicate too much oil, too cold a plug or low compression.

Intake backfiring means the timing is off, reeds are damaged or the mixture is extremely lean.

[RadioDave]

Is it possible that I would need to use a hotter plug than the manual calls for? I'm using B7ES.

I'm tooling up to check the timing.

I'm also going to clean the carb again and order a rebuild kit from your company.

Compression is at 132, both cylinders, engine cold, brand new gauge.

Dave

[Bryan Glynn]

There should be no reason on a stock ski to run a hotter plug.

[RadioDave]

Now I'm learning something.

I checked the timing. There is a T mark for (TDC, I think) at which you fabricate a pointer to indicate. There is F mark at which the pointer should indicate with the motor running.

Basically, I cannot adjust the timing enough to hit the F mark. One extreme puts me just on the wrong side of the T mark, the other extreme puts me in between the T and F. Near the T mark the engine lack power, but does not backfire, halfway between the two it runs better but backfires.

The stator is now full counter-clockwise, the timing is between the T and F mark, engine runs, but backfires.

The flywheel is definitely seated properly on its key and has no play.

The plot continues to thicken.

Pickup coils? Crank? Stator magnets?

What do you think?

[RadioDave]

Progress Report...

Ahhh, Hahhh,... major discovery!

After making more timing adjustments, I found that the slight stator moves that I was making just did not make sense in how the timing measurement looked.

I took the stator off and found that the wires from the coils have completely gone brittle and the insulation was falling off at a corner up against the stator assembly. there are at least two of them that are intermattantly touching ground and probably each other. I'm going to run new wires from the coils back to the connector.

This would certainly explain the backfiring/timing issues.

I'll report back later.

Dave

[RadioDave]

PROBLEM SOLVED!!!!

I replaced the five colored wires from the coils back to the electrical box. The timing straightened out, no more backfiring, a perfectly smooth idle, and it's even cleaning the plugs to some degree as I only have old ones at this point because I bought the store out of B7ES.

Thanks so much for all of the pointers. I could not have got this thing running without all of the insight given!!!

Kisses and Hugs! (Just Kidding!)

[img]smile.gif[/img]

[Bryan Glynn]

Groovy!

[RadioDave]

I've since had it on the water and dialed in the carbs. The ski runs like a raped freakin' ape. I'd say the SBT motor is, at least, as good as a new one. Maybe better as it giving four or five more PSI of compression than the manual says a good motor should.

Party On