[Laggylarry]

Long story short. I have a k1 750 and due to some incorrect wiring (had resistor ballast plugged into svta plug) we blew up the factory ecu (32920-35F30).



We replace what is believed to be a k1 600 ecu( 32920-39F30) reading online lots of people have successfully used a 600 ecu on 750. However in my case the bike hardly wants to start and won’t stay running if given any throttle when cold. Once close to running temp it runs ok but will cut out badly when under load and giving lots of throttle. (Like it’s bogging and chocking for fuel).



It runs fine when spraying some quick start down the throttle bodies. Once again making it look like a fule issue. I did replace fuel line and cleaned the pump and can hear it running.

I should also mention this was a salvage stunt bike so I don’t have VIN. I don’t have a cluster and SVTA have been removed.



My main question is: looking at buying a k1 750 ecu however I see a few options.

32920-35F00 on eBay for $150ish

32920-35F30 on eBay for $400ish

What is the difference and will either one work?

Or any other suggestions are welcome.

 

[TwistedMister]

you really should use the proper ECU for said bike

 

[Laggylarry]

you really should use the proper ECU for said bike

yes that’s why I’m wondering what the difference is in the 2 listed 750 ecu.
Engine serial is R737-106583

 

[boostenlebaron]

K1 750 was an odd year. They had a mid year production change and makes it hard to identify what parts you need. In the case of the ecu i know the stv control.is different at a minimum. The later build 750 also has an automatic choke and the earlier one has a cable operated one.

I'm not surprised the 600 ecu is not working right. If your bike has a cable operated choke I would say it has no chance of working. If your bike has an auto choke the 600 ecu may work but you will need a power commander and the 750 mapping tables with timing control.

 

[Laggylarry]

K1 750 was an odd year. They had a mid year production change and makes it hard to identify what parts you need. In the case of the ecu i know the stv control.is different at a minimum. The later build 750 also has an automatic choke and the earlier one has a cable operated one.

I'm not surprised the 600 ecu is not working right. If your bike has a cable operated choke I would say it has no chance of working. If your bike has an auto choke the 600 ecu may work but you will need a power commander and the 750 mapping tables with timing control.

Here is a photo. Looks like like it has spot for “manual choke” / high idle?
but like I said… stunt bike so all has been removed.

 

[boostenlebaron]

Looks like it. Do you the thumb control.on the clip on controls still? I'm actually surprised a stunter took the choke off. It's quite handy when doing low speed stuff.

 

[Laggylarry]

Looks like it. Do you the thumb control.on the clip on controls still? I'm actually surprised a stunter took the choke off. It's quite handy when doing low speed stuff.

Nothing on the bars. But honestly I think it’s deleted on most stunt bikes. I have a 04 636stunt (not built by me) and it has been removed. I assume its so it doesn’t get kicked maybe.

 

[Laggylarry]

Update. Got the new (to me) ECU. Went with the same as the one that was in the bike (32920-35F30)
Little better but still bogging.
See video.

 

[boostenlebaron]

Can you confirm that the stv butterflies have been removed?
No power commander correct?
Is the airbox sealed to the throttle bodies properly? With a filter?
How do the plugs look? Are they the size the manual calls for?

 

[Laggylarry]

Can you confirm that the stv butterflies have been removed?
No power commander correct?
Is the airbox sealed to the throttle bodies properly? With a filter?
How do the plugs look? Are they the size the manual calls for?

Yes butterfly’s are removed.

no power commander.

runs like this with airbox on or off. Filter or no filter and with the air sensor connected or not. (Spraying starting fluid while running makes the bogging go away)

plugs look fine and have even tried swapping with a set of known good plugs. RunningNGK CR9E

 

[boostenlebaron]

Did you do the fuel flow test as described in the manual? You may not be able to bring the pressure up quick enough.

 

[TwistedMister]

welp, looking at the bike and seeing what it is has it ever ran real good?


first thing ya wanna do is a compression test, you guys oil starve these bikes without doing any internal oil pickup mods to inside they dont starve, this bike was made when they were doing those mods from the factory..

compression/leakdown test, go from there...

 

[Laggylarry]

Did you do the fuel flow test as described in the manual? You may not be able to bring the pressure up quick enough.

I have not but am willing to try. I don’t actually have a manual would you or someone be able to help me track down a pdf? Or maybe even just the point notes on doing a fuel flow test?

 

[Laggylarry]

welp, looking at the bike and seeing what it is has it ever ran real good?


first thing ya wanna do is a compression test, you guys oil starve these bikes without doing any internal oil pickup mods to inside they dont starve, this bike was made when they were doing those mods from the factory..

compression/leakdown test, go from there...

As stated I have never see it run 100%. It’s a used bike. I only seen it cruse around a little.
Compression seams good but I will do a test on all 4 just to make sure.

 

[Laggylarry]

Ok watched a video on fule flow test. It was for a gsxr600 but I’m sure is very close. Also did compression test.

Compression test. 1-125 2-140 3-145 4-130 psi

Fuel flow test. 260ml(8.7oz) over 10 seconds

Fuel pressure unknown as my tester only goes to 10psi

 

[peter079]

I don't know, but it sounds like fuel starvation to me.

And even you said this.

(Spraying starting fluid while running makes the bogging go away)

Are you bending/pinching the fuel hose when lowering the tank?

 

[boostenlebaron]

Ok watched a video on fule flow test. It was for a gsxr600 but I’m sure is very close. Also did compression test.

Compression test. 1-125 2-140 3-145 4-130 psi

Fuel flow test. 260ml(8.7oz) over 10 seconds

Fuel pressure unknown as my tester only goes to 10psi

Flow rate seems fine though without the pressure reading it's not a complete test. I am going to say at that volume your pump is probably ok.

Compression numbers are ok ish. 1 is a little too low but not world ending. About what I would expect out of a trashed stunt bike.

So digging a little deeper,
Have you gotten the bike up to temp and ridden it to see if the problem has changed? Putting the bike under load may give more information to what's going on.
Have you tested each coil?
Are your vacuum lines hooked up correctly and are the subsequent sensors still in place and in good shape?
Make sure the throttle bodies are seated correctly and clamped down.
Just for my own amusement can you get a temp reading on the headers when it's running? That can potentially be used to find a troubled cylinder. You can generally just touch them quickly when you start it and feel for excess cold ones.

 

[TwistedMister]

for me compression is lowish, too low for me, I like 160ish across, no more than 4-5 away.. 165 mo betta, its the 125 and 130 barrels... where are they leaking? rings or valves? both? you can do a wet/dry leakdown to isolate, if its valves are they tight not closing? in any event you can pull head on the bike and rebuild it.. if its rings then yea.. yank and rebuild it all.. anyone know did it smoke at all? any blue smoke? indication oil rings are bad, maybe compression rings as well? test test test..

 

[Laggylarry]

Flow rate seems fine though without the pressure reading it's not a complete test. I am going to say at that volume your pump is probably ok.

Compression numbers are ok ish. 1 is a little too low but not world ending. About what I would expect out of a trashed stunt bike.

So digging a little deeper,
Have you gotten the bike up to temp and ridden it to see if the problem has changed? Putting the bike under load may give more information to what's going on.
Have you tested each coil?
Are your vacuum lines hooked up correctly and are the subsequent sensors still in place and in good shape?
Make sure the throttle bodies are seated correctly and clamped down.
Just for my own amusement can you get a temp reading on the headers when it's running? That can potentially be used to find a troubled cylinder. You can generally just touch them quickly when you start it and feel for excess cold ones.

Did get the bike to temp( or at least best guess as there’s no cluster) This was on the 600ecu but issue stayed the same. Maybe more noticeable as it wanted to thro you over the handlebars lol.

have not really tested the coils but I kinda ruled them out with the quick start making the problem go away.

Vac lines are all connected and sensors are hooked up. This year even has an extra sensor for atmosphere pressure and it’s hooked up too.
I can check the temps on the cylinders. Just gotta wait for a ok day. We’re coming out of winter where I live and am trapped in the garage. Running it long enough to get to temp puts a lot of fumes with the door closed lol.

 

[Laggylarry]

for me compression is lowish, too low for me, I like 160ish across, no more than 4-5 away.. 165 mo betta, its the 125 and 130 barrels... where are they leaking? rings or valves? both? you can do a wet/dry leakdown to isolate, if its valves are they tight not closing? in any event you can pull head on the bike and rebuild it.. if its rings then yea.. yank and rebuild it all.. anyone know did it smoke at all? any blue smoke? indication oil rings are bad, maybe compression rings as well? test test test..

no offence and am happy your taking the time to reply. But I don’t find this helpful. Bike is 20+ years old and possibly on stock internals. 120psi is enough to run. And honestly 160-165 would be mo betta… but I got what I got. I’m certainly not going to do a top end rebuild for a fuel supply issues. As I have stated the problem goes away buy adding fuel (quick start down the throttle bodies). You can see the smoke if any in the video. Little bit of white but no blue.
test test test.. doesn’t help. Like what are you wanting me to test test test…
Once again I am not trying to be rude just looking for some more helpful suggestions