Timing Issues

[Volksboy69]

Started tearing into my 04 Kat 750 today. The bike was stolen and returned. Wiring was pretty roached! But all essentials for a start up are in place. Threw the battery to it and it turns over fine. But it backfires terribly, noticed that the airbox was full of fog. So its backfiring thru the carbs too. Is there anything that would cause this besides a timing issue?

I've checked the firing order. I know its 1,2,4,3. And seeing how the left coil has 1 and 4 marked on the wires. That makes that idiot proof. 2 and 3 might be in question. But seeing that one lead is longer than the other. That pretty much rules out misplaced plug wires.

[92xjunker]

If you have it back firing, check the plug sequence ( left coil 1&4, right coil 2&3) if all is good, it's time to check the valves/ timing. Pull the valve cover and have a peak. Or do a compression test. Being that it was stolen, it may have been ridden that way and broke a valve spring and or bent a valve but, a compression test will show that. If it's just popping through the exhaust, it's a lean condition, carb related.

[Volksboy69]

Ill get right on it! Thanks. Any idea on what kind of compression this thing should be running?

I gave away my manual to a kat friend. Thinking i wouldn't need it anymore. Stupid me

[92xjunker]

120ish upto 180ish. 10% variance between cylinders

[Volksboy69]

Worst case scenario this thing has broke a tooth and jumped timing?

[92xjunker]

That wouldn't be the worst case. It would take more than one tooth, I guess it could happen. Not a common problem with these motors. Worst case they punched a valve through the piston.

[Volksboy69]

Cylinders are averaging around 130-135. Bike does have 37k on it. But they all held compression.

[Million$]

Make sure carb to engine boots are tight

[Volksboy69]

Make sure carb to engine boots are tight

Yeah their straight, no cracks or loose. Normal wear.

[92xjunker]

I'd shoot for dirty carbs then. Use starting fluid and see if it will actually run. If it starts, it's a carb issue. Did you check the plugs?

[Volksboy69]

Could they have switch the ignition pick up wires? Does anybody which colors go where?

I'd shoot for dirty carbs then. Use starting fluid and see if it will actually run. If it starts, it's a carb issue. Did you check the plugs?

Plugs are in good shape. Do ya think the coil leads might be mixed up? Do you know the color code for each coil top and bottom?

[92xjunker]

I mean, did you verify that the correct wire was on the correct plug? I'm still leaning to gummed up carbs.

[Volksboy69]

I mean, did you verify that the correct wire was on the correct plug? I'm still leaning to gummed up carbs.

Yeah were good to go on that aspect

[arsenic]

No polarity, which wire goes where is not a factor.

[Volksboy69]

So just for the "what the hell" factor I decided to swap the plug wires. And holy hell it fired up! Almost purred like a kitten. If kittens smoke and fart! But I'm pretty sure the bike has been sitting a while.

Anyway, I discovered that whoever worked on the bike didn't have a clue. The left coil which usually runs 1 and for 4. Had the coil leads for 2 and 3. Thats why the bike wouldn't run with the plug wires in the factory position! So I changed the leads and reset the plug wires to factory. "BOOM" she doesn't backfire at 3k like it was before. Prob need to clean carbs and pilot jets. But other than that she remains solid!


Fyi.

Left coil top=white and grey wire
Left coil bottom=orange and white wire
Right coil top=black and yellow wire
Right coil bottom=orange and white wire