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Discussion Starter · #1 ·
I installed a new engine a month ago (693, Carillo rod, welded crank, big cam, Mikuni 45 carb, Dynatek CDI, etc, etc) and with no testing took it to a race and ran 140 miles before a broken throttle cable and missing spindle nut took us out.

Fast forward to today---

I got everything fixed/replaced and took it out to tune shocks. For some reason it loses power above 6k rpms. Both of my clear fuel filters have fuel in them, and the one at the tank clearly has fuel moving in it.

Idling in neutral, I can bring the rpms up slow and can get it to the 9k rev limiter, but if I floor it, it cuts off completley.

To me, it seems like it is running out of gas.

One thing I did notice, is usually the filter between the carb and pump is about 1/4 to 1/2 full. But today, it was completlely full.

I am going to take the carb apart and see if the float is sticking. Just by listening to it, that is what is sounds like.

It runs great up to about 2/3 throttle, but when you floor it, it wont go above 40 mph at 6000-6500 rpms.

Any ideas before I tear the carb apart?

Thanks!

Rob
 

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Okay I don't have a fuel cell so I am not familar with them but here is what I was getting at...

A high volume pump is capable of well over 6 psi at peak modulation...

A stock pump is more like 4 psi...

The stock carb float in excellent condition and properly adjusted will hold back up to 5 psi before it gets over pressurized and flooded with fuel...

The HSR-45 is less... I think... possibly a lot less...

The stock fuel system on the 660 uses a return line with the stock pump and would most likely not over pressurize your carb at peak modulation...

The high volume pump MIGHT depending on how your return line was set up...and depending on the sensitivity of your float...

So does your fuel delivery system have a return line...

Your problem is occurring at or near peak modulation....

Do you monitor fuel pressure at the carb...???

Do you know for a fact your carb is not being flooded...and that there is no gas coming out of the over flow tube...???
 

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Discussion Starter · #7 ·
Tested the fuel pump, it works fine.

No pressure regulator at all.

Not flooding enough for fuel to come out the vent tube, but lots of black smoke.

No return.

Took the float bowl off, clean as a whistle. Tested the needle/seat, works fine.

Swapped Dynatek CDI with my spare, exact same thing.


In neutral, if I floor it, it goes to EXACTLY 6000 rpms then cuts off (still floored). As soon as I let off, it will idle fine. If I s-l-o-w-l-y push the gas pedal down, it may miss here and there, but usually it will go to the 9k rev limiter. Driving, it doesnt like any kind of a load, and it doesnt matter if it is in low (less of an engine load) or high.

I believe it is either a circuit in the carb, or "maybe" a coil spark plug issue.

Tomorrow I am swapping the plug....then the coil....then installing the stock carb to get the issue isolated then going from there.

At this time, I have no evidence that there is a fuel delivery issue.


Rob
 

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Interesting and I agree with everything you said and did but you do have to look at not having a return line as a possible cause with that carb...

Putting the stock carb on will definitely tell you a lot...

Also try disconnecting the accelerator pump first before you take it off...

Lots of black smoke...can't floor it and hold it floored...

Sounds like flooding to me...carb and/or no return line primary suspects...
 

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Discussion Starter · #9 ·
Ok, I will try that.


One thing to add....

This thing has hundreds of miles on it (desert racing and trail riding) with no return on the pump....both with the stock engine/carb and with the built engine and Mikuni.


Rob
 

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Yeah that would be an important thing to note...!

I thought you just installed the new carb...

So it just started doing it out of the blue...

Maybe it is ignition then...

Looks like I didn't read it...!!!!!

You did say that... :)
 

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Discussion Starter · #11 ·
The problem with ignition is, I am not sure where to look?

I guess a bag plug? Bad coil?

I think by swapping the CDI with the same results ruled that out.

Still going to disconnect the accelerator pump like you mentioned and see if that makes a difference.

Bottom line, I have to be careful on how I diagnose this, so I know EXACTLY what the issue is. I am sure if I swapped the coil, fuel pump and lines, plug, CDI box, new fuel, carb, etc, etc, etc all at once the problem would be solved......but when it happens next time, where do I look!! lol

Rob
 

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You are right to do one thing at a time...

Swapping CDI rules out CDI but not wiring, coil, plug wire/cap, doubt if it is plug but you never know...

No point in replacing fuel pump you problem would not be starvation...and the stock pump has the lowest pressure out put...

The test for over pressuring the carb is done at the carb...

Looking at your first post again...

Your new motor with that system ran fine for 140 miles until your

THROTTLE CABLE BROKE...

You FIXED IT...

Now it has the symptoms of being crazy rich when floored blowing black smoke...and bogging real bad until you let off of the THROTTLE...CABLE...

Some KEY words are bubbling up... :)

They say that the most obvious and simplest explanation is usually correct... :biggrin:
 

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Discussion Starter · #13 ·
Let me add that the throttle cable broke at mile 40, and I ran the next 100 with my right thumb!!

I will investigate it though!!

Rob
 

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Discussion Starter · #14 ·
FIGURED IT OUT!!!

Thanks to Craig for playing along at home!!

Anyway, after the Chupacabra 300, I redesigned the intake tube to move the filter inside the cab. I still run the stock center counsol, so had this super bad ass idea of running a piece of flexible exhaust tubing from the carb to the huge AEM filter. It was easy to do and worked great....until I actually took it out!!!

I guess the sprial design of the flexible tubing created a lot of turbulance/resistance.

Damn, it was a good design too.

Oh well.....resumuing shock tuning today!!!

Rob
 
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