Gsxr750L no start

[Portaz13]

Hi guys,  finally got around to working out what's wrong with my 750 I purchased 6 months ago. It doesn't start but has spark and fuel.  It backfires on occasion but that's it.  Owner said it had low Compression oh number 2 and needed a rebuild.  So today I checked Cam timing and did compression test with a shitty push fit car gauge which I know isn't accurate bit I got to a pretty even 150psi. When cranking it sounds fine and not like one cylinder down. Only thing is it has quite a few modifications on ignition system such as dynojet 3ohm coils,  Dyna 2000 cdi and some kind of aftermarket trigger kit.  This posed some problems as its nothing like my workshop manual.  So I pulled #1 plug used an indicator to show me tdc then checked cams which line up perfectly and has 21 pins between them as it should.  What do you guys think?  Get a better comp tester or start looking at ignition issues?  Any other help or direction is greatly appreciated as I just want go ride this old beast. 

Edited January 7, 2018 by Portaz13

[colinworth79]

The trigger plate in the picture is dyna . If you have purchased this as a non runner I would go through the basics first before pulling engines apart . I would pull the carbs off and clean also checking the float heights . Check valve clearances . I would also fit new plugs as they don't like being flooded with petrol . I had the exact same problem with my 750 L , it would turn over and then occasionally there would be a loud bang through the exhaust . I had a leaking float valve in 2 carbs . The flooding killed the plugs .

[Portaz13]

Great,  thanks for the reply,  plugs are certainly black and probably wet,  would it be possible that the trigger plate is faulty somehow?  

[vizman]

41 minutes ago, Portaz13 said:

Great,  thanks for the reply,  plugs are certainly black and probably wet,  would it be possible that the trigger plate is faulty somehow?  

it's a possibility but highly unlikely, go through the checks what colinworth79 suggested first

[Portaz13]

I'm not sure what carbs they are but pretty sure it's severely over carbed as previous owner said he had bigger carbs due to planned dot head /stroker conversion.  Also I forgot to mention he said he was riding and it kinda popped and then didn't run right after that.  I've had it running on starting fluid but it's ugly.  Anyway thanks guys I will look into basics. Fingers crossed that's all it is 

[colinworth79]

stock carbs are 38 mm cv . Should have a small rubber tube up the side .

[Portaz13]

Certainly not stock,  I believe they were brand new mikuni flat slides however no idea what size when I get home tonight I will check it out and take a few pics.  It was an ex race bike which is why I assume it has quite a few changes.  Will try to get some plugs on way home 

[Portaz13]

Finally got plugs as they had to be ordered in and were not cheap the ones they said we're right for L model was ngk jr9c but they are not what's in it.  I looked on ngk website and it shows a cross over in 89/90 the later being cr10eik , what's the right one you fellas use?  

[Portaz13]

Any clues what size these are?  

[Portaz13]

Cleaned the carbs,  changed plugs and after a bit of throttle she's alive.  Will fine tune tomorrow but she's certainly quite grumpy 

[baldrick]

flat slides tend to run a bit lumpy low down, but it would still be worth checking whats in them, 

the carbs could have been tuned for wide open applications if its an ex race bike. I would check all carb settings against a known good road setting, or spend some cash on a dyno run or two, with a knowledgable dyno operator i.e. one who knows c arbs as opposed to fuel injection.

[Portaz13]

Might have to as it pops and farts and is running very rich,  blows a few flames etc.  Did another comp test hot and all were over 150psi, so pretty sure it's just carb settings now to deal with