handfulz28

I've only put the last 5+ hrs on there, the previous owner was pretty meticulous about maintenance, but I don't think the carbs have ever been touched. So I'm slowly getting around to the things that might benefit from some attention.
They're '91 Mark IV 454 MAGs. My only experience with carbs is on my dirtbikes (4 stroke) so consider me a carb newbie. As far as I can tell, the boat runs good, a little trouble getting it started but that might be my fault.
I'm a little torn between "if it ain't broke don't fix it" and wanting to make sure everything is perfect. Besides the flame arrestors and carbs looking like they need a thorough cleaning, the port motor idles around 500rpm where starboard is at 800rpm. And at full throttle the port motor was slow by about 100rpm. Also, it takes just more than one detent on the throttles before they respond.
So I'm thinking besides the carb service, I need to know how to properly adjust the throttle cables.
I'm a newb, but I want to make it right. Any and all help appreciated.
Thanks,
Michael

rdoactive

If it aint broke, dont fix it.
But if you do a carb rebuild, buy the kit, follow the instructions, it's pretty easy. Does that have a Qjet or Weber/Carter?
The qjet may require a Torx screwdriver, but that's about the only "special" tool needed.

handfulz28

I would only know the difference if I could read the name engraved on the side But I'm pretty sure they're Qjets.
Where do I find a rebuild kit? Before I go the rebuild route (IF I go there), they could at least use a good cleaning. Can I just soak the flame arrestors in carb/parts cleaner? And just spray carb cleaner in there while it's running?
Thanks,
Michael

Griff

Turn the idle screw up on the port carb and then leave it alone. Also check timing as that can affect idle. Spray some degreaser on the flame arrestors and hose them off.

cuda

Take the needles out of the idle adjustment, and spray carb cleaner in them.

handfulz28

Remember, you're basically talking to a blind guy as far as these carbs go. Is the idle screw on the front, lower, right if you're facing the engine? Is it the one with a weird screw head? Cuda, is there a spring and/or seal in there that I need to look out for? If I take 'em out, should I turn 'em in all the way and count the turns so I put 'em back the exact same way?
I hate to think about it, but I wonder if I should replace that little filter on the port motor, where the metal fuel line connects? I hate to touch any of that though.
Thanks guys,
Michael

Griff

The idle adjustment screw is on the same side as where the throttle cable connects to the carb. It is part of the same linkage.

Before you touch anything other than it, you really should get a basic manual of some kind. If you start turning and removing idle air bleed screws without knowing what you are doing, you could create a lot of headaches for yourself.

handfulz28

Thanks Griff. I hear you, and that's why I post here with full disclosure I'm new at this. I know enough not to screw with things I know nothing about.
I have seen a couple Rochestor Qjet books out there. But I think at this point I'm just going to try and clean the flame arrestor, and look into "maybe" a little carb cleaning. Would rather leave 'em alone until the motors come out.
Thanks,
Michael

rdoactive

Remove the flame arrestor, use some carb cleaner on it. BTW, carb cleaner dissolves everything except concrete, so do that out of the boat.
Spraying carb cleaner down the carbs will do nothing.
A rebuild kit is around $40 at an auto parts store, it will cost a little over $100 to have a carb shop rebuild it. Sounds like the carb shop may be your best bet. Dont srew around with anything on it if you dont know what your doing.
Gary

Iggy

I recently rebuilt the Q-Jet on my 350 Mag.
Carb kit was less than 40.00 and it took me about two days to clean it. I'm rather meticulous when it come tho things like that.
I tore it down to basic components. Except the base plate and butterfly valves. Sprayed carb cleaner through every passage I could find. Then soaked the parts in a can of carb cleaner. I used a stiff brush to clean any stuck residue. Rinsed them off with clear water then sprayed the passages again with carb cleaner and rinsed them again with water. Used compressed air to blow out trapped water and to be sure the passages were clear. Once clean I reassembled the carb. It works great. No troubles since I cleaned it.
The only trouble i had was cleaning the stuck gasket material off the carb body. A scraper won't do the job. There is a small raised ridge on the sealing surfaces. I had use a razor blde to remove it. Very time consuming.

I had a quote from a Q-Jet specialist on a rebuild. The wanted 200.00 to rebuilt it.