[Chamber66]

My old 750 has developed an issue. She starts up and revs no problem, but is low on power and struggles under load, almost as if the brakes are seized All the headers get hot and it's not long had new coils.
Any suggestions?

 

[silentservice703]

Is the clutch slipping?

 

[Chamber66]

Is the clutch slipping?

Definitely not

 

[esq'z me]

Starving for fuel??? Fuel filter and/or hoses ?

 

[Calcifur]

I assume you have confirmed that the brakes are not binding? Check your electrics, I have had all kinds of issues with my B4 due to degraded electrics. You are obviously getting spark as the headers are getting hot, and therefore also fuel, but it could be not enough spark or as @esq'z me says, not enough fuel.

it might also be worth checking the throttle bodies are balanced, also there are little caps on the end of the 4x hoses that come off the throttle bodies to either side of the engine, used for balancing the bodies, there are prone to deteriorate and crack causing a vacuum leak that may also be an issue.

 

[american_corse]

Sounds like you’re running really lean. With a bad fuel pump it will idle fine but not run well under load.

 

[Chamber66]

I assume you have confirmed that the brakes are not binding? Check your electrics, I have had all kinds of issues with my B4 due to degraded electrics. You are obviously getting spark as the headers are getting hot, and therefore also fuel, but it could be not enough spark or as @esq'z me says, not enough fuel.

it might also be worth checking the throttle bodies are balanced, also there are little caps on the end of the 4x hoses that come off the throttle bodies to either side of the engine, used for balancing the bodies, there are prone to deteriorate and crack causing a vacuum leak that may also be an issue.

Thanks for the comprehensive answer

 

[Chamber66]

Well whoever out the plugs and the middle 2 cylinders are running rich and the outer 2 slightly lean
Throttle bodies?

 

[N8_990]

How did the intake valves look, those are some pretty rich looking plugs.

 

[Chamber66]

Still looking for suggestions
Checked all the wiring and earth's
New fuel filter
New hoses in and out
Balanced throttle bodies
New iridium 🔌
And still the same, starts really well but needs ĺoads of clutch and revs to pull off, then when you back off the throttle it's like applying the brakes?

 

[Calcifur]

I'm afraid I am no expert.

Did you check the ignition coils already?
Next question, do you have a cat? Has it collapsed? A blocked exhaust might be the issue.

This might have been done already, have you checked your battery voltage? It should be around 14v at 2,000rpm.

I assume also that it's not actually your brakes that are binding?



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[Chamber66]

I'm afraid I am no expert.

Did you check the ignition coils already?
Next question, do you have a cat? Has it collapsed? A blocked exhaust might be the issue.

This might have been done already, have you checked your battery voltage? It should be around 14v at 2,000rpm.

I assume also that it's not actually your brakes that are binding?



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Battery is new, catless with power commander . And coils are checked so all good. In my mind it must be ignition or a PC issue?

 

[Calcifur]

I don't know a lot about PCs but I am wondering if it is set to cut fuel on declaration causing excessive engine braking? (Thinking out loud here.).

As far and ignition other than spark plugs, coils and battery, there isn't a lot left other than timing and fueling.

You could try removing the PC and running it stock and see what happens.

Just wondering, what colour is the relay box down the side of the tank? The early ones had a blue back on them and were prone to cooking themselves. Mine actually melted! I got it replaced with the newer style and its been fine since.

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[esq'z me]

OK.... based on your description and my personal experience over the decades....have you checked cam timing?
You can do a compression test and a leak down test (both) and get a confirmation. Higher than spec compression or lower than spec with 5% leak down are both indicators of possible cam timing.
Poor power and heavy engine braking..... Of course, dragging brakes would feel the same.