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DT40C missfiring under load

O

ozzi

New member
"my motor starts and runs perf

"my motor starts and runs perfectly on land (with hose etc)at 5,000rpm but when under load in water starts intermittant missfire at about 12-15mph whilst TRYING to get boat up on plane. Have rebuilt carby and fuel pump but no difference. Is it CDI unit thats failing ?
Any suggestions ?"
 
keep reving tha motor up to 50

keep reving tha motor up to 5000 on land and you will blow it up!

u need to run a fuel pressure/vacuum gauge on the fuel lines
 
"okay, I will rig up fuel pres

"okay, I will rig up fuel pressure gauge on lines and test. What should it be ? I was thinking about 3-4psi ."
 
you were running wot for at le

you were running wot for at least 10 mins right

so did you check for vacuum before the pump?

if so next is to take a timing light and see if it is the fire
 
I did not test vacuum before t

I did not test vacuum before the pump because I thought it must be okay since I have constant (10minutes) fuel pressure 3.5psi after pump. Anyhow I do not have a vacuum gauge. Is there a way to measure vacuum without gauge ?
 
"well fuel pump is ok
you wil

"well fuel pump is ok
you will still get 3 psi

if your primer bulb goes flad or you cant pump it hard, there is your problem"
 
"that was a quick reply !
I c

"that was a quick reply !
I can pump my primer bulb hard and the pressure stays, so I guess my problem lies elsewhere ?
I'm planning on checking timing tomorrow. Should it be 18.5 BTDC whilst running in forward at 1,000rpm ?"
 
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