Gsxr 750 low on bhp

[Leblowski]

Okay so i went to the dyno today

 

i have a 750 dothead engine with a micron system and yoshi silencer, 29 mm flatties bored to 33 ram air filters

Turns out the bike does not make more then 65 bhp and seems to just stop at about 8000 rpm like it hits the rev limiter

we tried everything

other set of carbs

cr test

other cdi

checked camtiming

replaced two lead caps

new plugs

 

So all is checked and was okay only thing that can be done is replace the coils for others but if that doesnt work i am totally in the dark

 

anyone here had something simular ??

 

[Gsx-Mutattack28]

Have you done a compression check. If low on compression that's going to affect BHP

[Leblowski]

Yes compression check done all cilinders okay

[gsx]

Fuel starvation?

[banoffee]

12 minutes ago, gsx said:

Fuel starvation?

If start to consider this too if you've already been through the things on your list.

What fuel tap are you running? One meant for gravity or vacuum?

Is the tank breather clear? Does undoing/removing the fuel cap make a whooshing noise after a run?

What size mains have you started with?

[Captain Chaos]

7 hours ago, Leblowski said:

seems to just stop at about 8000 rpm like it hits the rev limiter

regardless of which gear it's in? If yes, electrical cause

[Leblowski]

Yes regardles wich gear i suspect elecric problem too

 

fuel starvation dont think so it was dynod with an external tank

started out with 135 mains

[Arttu]

Did you measure AFR on dyno? If yes, how it was looking?

Any way, if it's stopping at 8000rpm regardless of gear and load then it sounds like electrical problem. Or then fueling goes really badly wrong at that point but that sounds unlikely as you have tried two sets of carbs.

[Reinhoud]

Ignition timing too late?

Edited April 30, 2017 by Reinhoud

[Leblowski]

2 hours ago, Arttu said:

Did you measure AFR on dyno? If yes, how it was looking?

Any way, if it's stopping at 8000rpm regardless of gear and load then it sounds like electrical problem. Or then fueling goes really badly wrong at that point but that sounds unlikely as you have tried two sets of carbs.

Afr was between 13/12:1 under load  that was even a tad rich.

We started out with 135 mains and it was even richer so we thought this caused the problem, so went to 122 in the end but the problem kept acuring.

When it the stottering accurs the dyno shows it goes rich so that why we thought the mains where to big.

When the stuttering accurs the dyno shows rich rich mega rich but thats probably unburned fuel so a spark problem is most likely.

Problem is the bike even gives to low bhp in lower rpm's.

When its dynod it sound good goes to gears like hell. But it just does not perform.

All goes well when you use 3/4 throttle when you use 100% throttle it goes wrong.

With that in mind is suspect ignition cause with full throttle even more are is passing the spark wich i think causes it to go out and makes the engine stutter

 

Edited April 30, 2017 by Leblowski

[Leblowski]

1 hour ago, Reinhoud said:

Ignition timing too late?

There is mentioned by a well known dynoman that when the spark is bad it causes the effect of late timing wich explains the lack off bhp.

So this could be an explanation

[Leblowski]

I will change coils and leads and will make a direct mass and feed to the cdi too see if this helps

There is even mentioned that the pick up could be fubarred or the triggerwheel is demagnatised but that i will swap when all other options fail.

If all above isnt the fault i will simply swap engines i have two spare

[Reinhoud]

Is the ignition ground plate adjustable? Does the engine get more hot then it should be? High fuel consumption? 

[Leblowski]

2 hours ago, Reinhoud said:

Is the ignition ground plate adjustable? Does the engine get more hot then it should be? High fuel consumption? 

No not asjustable fuel consumption dunno cause i never rode it on the road, exhausttemperatures are good so engine doesnt get crazy hot.

[Leblowski]

I have been brainstorming with my dyno guy about this thing the whole weekend.

When we took off the valve cover we noticed there was welding done on the inside off the cover.

So thing is maybe there was engine damage and someone has put in two in or outlet cams, or maybe they are swapped... the wheels are at the right place but hey camwheels can we taken off also

So i will take off the cover again to check that also.

 

Will check timing and cam angles again just to be sure.

 

 

[no class]

..... one tooth out on the cam timing ?  

[Fula28]

Sounds like your heading in right direction Chap , Head scratcher for sure ! I had a Srad 600 with an odd issue while back , it blew rectifier which was swapped then didn't start so changed, Cdi, Then pickups then coils ! And Loom ,Still no spark tryed another cdi Still , no joy! Then I remembered that the ignition switches had a 100k ohm resistor which had blown Bingo, changed it for b600 switch I had and it ran .

mind fuck sometimes..... 

Good luck with your fault finding bud,

[Reinhoud]

How is the throttle response?

How does it go when you ride it, does it feel weak in the lower revs? And then it goes? That's cam timing..

[HDTboy]

What are you using to read your mixture? If you're reading O2, a misfire will give a very lean reading, due to excessive unused oxygen in the exhaust. If you're using four gas analyser, HC will also shoot up with a misfire.

Is it possible that there is something (Filters?) giving a restriction at high load high RPM which doesn't show at lower load? Also, have you checked your float heights? Are the air jets in the front of the carb bell mouths clear?

My 85 with similar mods is running 125 mains (Mikuni), and making over 100hp

[Leblowski]

Just standard Lambda reading om the dyno 

It goes massivly rich around the time it stutters at 8000 rpm

Already tried cv carbs wich give excactly the same readings/problems

I am running ram air filters wich a lot of people use, i can easily take them off to see of that makes any difference

Airjets clear for sure carbs have been cleaned ultrasonic by me

Apart from the stutter at about 8 8500 rpm the engine only produces 65 bhp all the sign look likes its electrical but i already ruled out all stuf wich has to do electrical wise 

I suspect something wrong with the engine, will try some things this weekend iff i cant find it i will swap engines

[suzook12]

Try checking voltage at CDI while running

[Portaz13]

Any update on this? 

[Jelly]

Check his project topic, engine wasn't right. 

[Portaz13]

OK will do 

[Leblowski]

Engine whas totally fubarred worn bores and probably worn camchain wich gave problems

Ended up in engineswap now makes a healthy 100 bhp at the wheel