Let's diagnose this...I'm tired..

[ctandc]

For those not in the know, here's my swap thread HERE

Bike / Frame: 91 Katana 600

Engine: 01 Kat 750
Carbs: 01 750 w/ Ivan's Jet kit installed TPS unhooked, single throttle cable installed
Stock Airbox, stock filter.

Intake boots are snug to carbs, airbox snug to carbs. Vent lines are installed. Airbox drain installed and capped.

New spark plugs.

Using coils off of 01 750 (which ran very well before I tore the bike down)


Initially fired the bike up and ran into a oil leak, it was one of the "mickey mouse" gaskets on the spark plug tower. Took it off and remounted everything and it appears to be fine now.

Bike will fire up....but likes to backfire through exhaust.

Once it starts, it's fine. ROCK SOLID idle.

Revs okay, but when I rode it a bit, it appeared to be down on power from what I remember from my 600, much less a 750.

A/F screws I tried at 4 turns out (Ivan's recommendation with jet kit) then 3.5.

I'm running a 93 750 CDI which plugged right into my harness, and I swapped to my 91 600 CDI , and really didn't notice a difference.

5 degree advancer is installed.

ALSO - after engine was up and running, furthest two exhaust pipes to the RH side were not as warm as the other two. Which would be #4 and #3 cylinders.

Carbs were SPOTLESS inside when I installed the jet kit.


- I'm going to yank the tank again tomorrow after work and pull the plugs and see if they maybe got oil fouled from the leak.

- I will also verify if coil wiring and spark plug wires are routed correctly..but I really don't think that's it, since it runs so darm smooth at idle.

I did / do have an exhaust leak where the header meets the mid-pipe. The old steel mesh gasket was crushed from use, and wouldn't tighten down on the mid-pipe, so I bought a new gasket, and couldn't get the mid-pipe all the way in. That sucks, because I may end up RUINING the $20 steel gasket to get it out to try and 'expand' the header collector a bit.

Any ideas here? I'm going to check some things tomorrow...but at this point I'm tempted to take the jet kit out, put the stock stuff back in and see what happens.

Any and all help is greatly appreciated.

[David F C]

From what you said seems like a fuel problem.
It's not the plugs or it would be noticeable at idle, it's unlikely to be lack of air (I assume the air filter is clean enough),so I guess the engine is not getting enough fuel when reved up, wich would account for the power loss.
Check the carbs again, maybe you installed sometin' wrong?
Fuel lines bent or cloged?

[arsenic]

I disagree, that could very easily be your plugs. Oil fouled from the oil leak.

[David F C]

I disagree, that could very easily be your plugs. Oil fouled from the oil leak.

I though about that, but an insulated plug would be noticeable at idle...
wouldn't it?

[arsenic]

if 2 header pipes are not as hot as the other, the carbs have BRAND NEW main jets. My money is on the plugs.

[ctandc]

if 2 header pipes are not as hot as the other, the carbs have BRAND NEW main jets. My money is on the plugs.

I'm gonna pull the plugs tomorrow evening and clean 'em off and see where I am.

What would be causing the backfires?

First thing I gotta get the exhaust figured out, the bolt that clamps the header collector down broke today...so I gotta pick up a new bolt first.

[arsenic]

plugs, it's your plugs dude, I'm sure of it.
the one plug has a weak spark because it's fouled, so it doesn't ignite the fuel every time like it should, as the fuel builds up in that cylinder it finally ignites it, and back fire because there is WAY to much fuel. That's why the headers not that hot, it's not igniting every time.

[ctandc]

That's what I'm thinking too. I'm gonna get the exhaust fixed, clean the plugs, then go ahead and sync the carbs and see where I am then.......

[VifferJim]

Okay - I'm gonna go out on a limb and say it's your plugs...

Now, if you DON'T solve the problem by cleaning the plugs and whatnot, I'm going to make a suggestion you probably won't like and it's prefaced with the following questions?:

The 01 motor, etc. - Was this running 100% before you dropped it into the new frame?? I'm thinking yes from your intro thread here. Next, did you get the bike running again once you moved it into the new frame but before you did the jetting and timing adv?

Okay, this is just me... feel free to disregard. But, when I moved everything over from the 750 to the 600 frame, I spent the first week making sure that it ran well just bone stock... knew what settings made the carbs happiest; and THEN, satisfied that I didn't have any gremlins to hunt down, dropped in the jet kit.

[David F C]

Hmmm, arsenic makes a good poit here ...

Does she backfire on idle? I assumed it only backfired while you were ridding, maybe I got that part wrong.

When you find out were the gremlin is let us know.

[arsenic]

I always make good points, this is what I do

[ctandc]

Hmmm, arsenic makes a good poit here ...

Does she backfire on idle? I assumed it only backfired while you were ridding, maybe I got that part wrong.

When you find out were the gremlin is let us know.

Actually it never backfired when it was 'moving'. It only happens when trying to start it for the first time, or after it sits a bit.

Once it's running, it's really smooth, just down on power.

Okay - I'm gonna go out on a limb and say it's your plugs...

Now, if you DON'T solve the problem by cleaning the plugs and whatnot, I'm going to make a suggestion you probably won't like and it's prefaced with the following questions?:

The 01 motor, etc. - Was this running 100% before you dropped it into the new frame?? I'm thinking yes from your intro thread here. Next, did you get the bike running again once you moved it into the new frame but before you did the jetting and timing adv?

Okay, this is just me... feel free to disregard. But, when I moved everything over from the 750 to the 600 frame, I spent the first week making sure that it ran well just bone stock... knew what settings made the carbs happiest; and THEN, satisfied that I didn't have any gremlins to hunt down, dropped in the jet kit.

Yes the motor ran fine before I pulled it out of the 01 frame.

If the plugs don't do it, I'm going to do exactly that..

Pull the jet kit out, pull the advancer out and go from there.

At this point, with no fairings (I'm waiting to start painting them when the bike is running good) it wouldn't take an hour if that to change everything back to stock.

So I'm going to tackle the exhaust and the plugs tomorrow after work.

Thanks for the help guys, I'll keep everyone updated

[DumbLuck]

I a pre 750 RH exaust (header to can) if you need it. a pair of them actually. i'd be tickled to get them out of my garage

[ctandc]

I a pre 750 RH exaust (header to can) if you need it. a pair of them actually. i'd be tickled to get them out of my garage

I appreciate the offer...but I'm using the 4 into 1 post 98 exhaust...I'm running the Scorpion slip on I was running on my 91 Kat 600 before the swap.

[ctandc]

#1 and #2 had some oil on the plugs...not horrible, but not all that clean either. #4 and #3 looked clean but smelled a bit of gas.

I double-checked wiring and plug order, made sure all were seated as good as they would go and replaced the plugs with the non irridium NGK's.

Also verified 4 turns out (per Ivan's instructions) on the A/F screws.

Also got the exhaust buttoned down.

It fired right up after a quick backfire, but then I bumped the choke off and it died, so I'm waiting on the battery to charge right now.