Hello! Newbee asking for help

[jim66wright]

I have just purchased a 1979 John Allmand 26 Freedom Express Cruiser. According to the previous owner, newly rebuilt 351 Windsor and a 1:1 velvet drive, prop pitch unknown.....very good shape and I am excited, as my last boat was a grady white with a 130 evy that I loved, but was a center console and I need a little more protection down here in Miami.
I have read past threads about backfiring and have a few more questions, as this is my first inboard gas boat.....
Engine idles great...wot without load is over 4k on a blip...also sounds great...
however under load half way home from the delivery, it only went 2800 rpms, unknown speed, and after about an hour with half tank of fresh fuel, bam!
a big backfire that I thought that I lost a piston...but as I slowed down, no problem...then got worse...could not get it over 1400 before backfiring back into the intake...different noise than through the exhaust...so I am going to start with the filters, feed tube and such, and make sure that my lines are good....then attack my carb and distributor......I looked at the carb, but other than identifying the primary and secondary chambers, I did not know what was up....the bigger "flappers" never opened even when blipping up the throttles....should they?
Sounds like I need a good inboard mechanic....I would like to learn to do this myself, but if there are any good recommendations, please let me know...
basic work I can do, but sometimes I need to be advised to pass it on to a pro....
Thanks for your patience in my indulgance...
Jim

[longliner45]

all (flappers )or butterflys should have opened,,maybe too much fuel? try making them stay open ,and start ,,and see ,,this is called the choke,,you can useually,manually controll it,by messing with the linkage on the trottle body,,,,good luck,longliner

[alan white]

May be too lean a setting on the main jet. Open it up counter clockwise a half turn and see what happens.

Alan

[lazeyjack]

can you post a photo of that carb setup,and is the vacuum line intact?