89 supra 454

[fireman51455]

Hello I need help bad here is my problem. I get a back fire at full throttle here is what i did I replaced the plugs cap rotor points fuel filter and rebulit the carb and it still is popping any help please it runs fine at 25 to 35 but when you nail it it pops thanks

[Salty87]

sounds like you need to check the timing

I checked the timing and set it to 10 degrees. Is that the right timing for this engine?

[fireman51455]

I checked the timing and set it to 10 degrees. Is this the right timing for this engine?

[DKJBama92Mariah]

Here is the spec page for a 1989 454 from the PCM owners manual.

http://img.photobucket.com/albums/v55/dkjpika/Boat/GMTuneupSpecs.jpg

Hope it helps, good luck.

Cheers,
DKJ

[OUI]

I have an '89 454 in my Saltare. I went through some similar problems.

1st: If you have a Holley carb and if the backfire was through the carb it has blown the Power Valves and the carb needs to be rebuilt !!!! However, if the carb was recently rebuilt you may only need to replace the Power Valves, because all the seals and gaskets, etc are still fresh.

2nd: I don't know if it was from the factory or some other entity, but the timing/distributer on my boat was 180 degrees backwards. Check to make sure where TDC is. To do this, pull the 1st plug on the left side of the motor - looking forward closest to the bow. Turn over your motor, when that cylinder blows you finger off the spark plug hole that is TDC. Check where your rotor is pointing and the is #1 cylinder, and that is where to place you timing light.

3rd: From there, set your timing to 5 degrees BTC at 700 rpm. When I was a kid we used to set the dwell/gap, and take a friend boating -- while we were at full throttle we would adjust the timing on the fly after it had reached max RPM we would take it down to an idle and retard it just a hair so it would idle better. I think they call that power tuning.

Good Luck

[fireman51455]

I already move the dist it was also 180 off and move wires to proper plug from there carb was just rebulit with a new power valve and it still popped i will try to set the timming to 5 insted of 10 and see if that helps any

[fireman51455]

Thanks guys i think that fixed it i set the timing to five i will have to the lake friday and will see if it is turly fixed i also riched up the high end