no power

[craig stevens]

the power is a joke, cant get out of its own way. towing my boat is a chore. going up any hill, no matter how small i slow to 25 and cant get above.

i have a 84 gmc crewcab, dually, 4x4 with a 454 on propane. i had it changed from gas to propane 6 months ago and it didn t affect the power at all. it has a 373 rear end. the distributar, vacuum advance have been relaced. 13 -14 idle 42 with vacuume advance. the timing cover removed, the fly wheel checked, everything checked out ok. the tranny was just removed and inspected, it was ok. compression 165-170 accross the board. it has headers and a new 2.5 inch exhaust. a new unrestricted air cleaner.

we thought about the cam but thats expensive if were wrong. i was told when i bought it it had a rv cam but i dont know for sure.

any ideas where to go next would be appreciated, both myself and my mechanic are stumped

i also only get 6 mpg.

[scavanger]

You said initualy you had good power.What changed that the power changed?
Ignition timing is important an propane. Your intial is about where it should be but do you know what your max advance without the vacuum advance is , shouldn't be over about 35 deg. Also the timing should jump up early. Propane has an octane rating of about 105 and burns slower than gasoline. That is the reason for the early advance. Unlike gasoline which enters the combustion chamber as a liquid, propane is a vapor and has no cooling effect. This can cause detination at high cyl pressure so the timing can't be advanced to far at higher rpm. A quick advance with a limit of 35 deg total including your initial is best in most cases. To much total advance will kill your power. Compression ratio is a real factor on propane. About 10.5 is optimum . You didn't say what brand of carbration you have. Is it Impco ?

If you like you can email me and I will try to help you all I can . I used to install and maintain both Impco and Century systems.

Scavanger