rochester carb question

[sarantis]

hello everybody,
When you swap from a mercruiser gm305 (1979) to a gm350 do you modify anyway your carb or it supposed to work as it is?(rochester 4mv )
my problem is not WOT (only about 3000-3500rpm) and overheating above 2000rpm.
After so much searching discussed in an older thread i have limited the problem to two posible reasons a)carb b)stuck or destroyed flappers in the exhaust pipe(they are at the botom so i hesitate a litle to get the boat out and take the engine out).I don't know if this is related but the carb has an internal leaking(after two days sitting the bowl gets almost empty.And a last question :at the senario b) should i understand anything when i rev up at idle?

 

[Bondo]

Re: rochester carb question

When you swap from a mercruiser gm305 (1979) to a gm350 do you modify anyway your carb or it supposed to work as it is?(rochester 4mv )

Ayuh,... It should be close enough to run reasonably well...

Reading the sparkplug colors helps to tune the carb's setting/ jetting...
If it's running Lean enough to cause an Overheat,... The sparkplugs should be pretty White...

I don't know if this is related but the carb has an internal leaking(after two days sitting the bowl gets almost empty.

That's Never good,+ means it's more than likely running Rich,...

And a last question :at the senario b) should i understand anything when i rev up at idle?

Ayuh,... Ya lost me on that 1.....


It's lookin' more 'n more like the plugged exhaust...

 

[sarantis]

Re: rochester carb question

Once again thank you for your patience with my problem Bond-O.I think i have to pull the boat ,the outdrive and the engine out....
I 've read so many threads about similar problems and what worries me is that 99% they never end.I hope in one month time i'll get this over and i'll put an end to all my threads.

 

[Don S]

Re: rochester carb question

On a Quadrajet carb, the most common reason for fuel leaking out of the bowls is the well plugs leaking. Here's a site that explains it and shows pictures.
http://ramchargercentral.com/index.php?board=&action=howtoshow;id=6

should i understand anything when i rev up at idle?

Just guessing, but do you mean reving it up in neutral? If so, revving it in neutral tells you nothing. It will rev to 10,000 rpm with half the plug wires off,
About the only reason to rev it any in neutral is to check the advance timing to make sure it's working. Or maybe clearing a rich condition while adjusting the carb mixture.

 

[Bondo]

Re: rochester carb question

I hope in one month time i'll get this over and i'll put an end to all my threads.

Ayuh,... We don't want you to go away,.. We just wanta fix your boat....

I gotta believe, you've found,+ read this by now,..??

 

[sarantis]

Re: rochester carb question

Bond-o,
off course i'm aware of all this helpful stuff here.
Don S ,i had already found previous threads about leaking carbs and about how to repair it ,however the link you suggested seems better.But i don't want to dissasemble the carb again since it was recently rebuilt by a specialist (who probably didn't know that common problem of rochester carbs).Hoping that in due time I'll have good news
Sarantis

 

[Alpheus]

Re: rochester carb question

If it was rebuilt by a "specialist" then the leaking well plugs should have been the very first thing fixed since this is the #1 flaw of a quadrajet carb. It does not take a "specialist" to rebuild a quadrajet unless he is fixing the warped surfaces between the of the fuel float bowl and top air horn assemblies due to the front 2 bolts being overtightened and then putting the carb on a flowbench to tune it absolutely perfect which is not needed on a low performance boat engine. You need to fix your well plugs because this leads to your engine running rich and fouling out your plugs prematurely and just makes for a lousy running engine,not to mention it takes longer to start the boat after sitting because you have to wait for the bowls to fill back up while your cranking over the engine.

I have made a video that will show you pretty much how easy it is to do a basic rebuild of a quadrajet carb...

http://forums.iboats.com/showthread.php?t=362542

 

[Don S]

Re: rochester carb question

If it was rebuilt by a "specialist" then the leaking well plugs should have been the very first thing fixed since this is the #1 flaw of a quadrajet carb.

Maybe the specialists in Greece aren't as familiar with the Qjets as we are.

 

[sarantis]

Re: rochester carb question

Maybe the specialists in Greece aren't as familiar with the Qjets as we are.

That's for sure! If i find out that something is wrong with the carb again i'll rebuilt it once more by myself and next step if it doesn't succeed a new one from America.

 

[sarantis]

Re: rochester carb question

Alpheus your job is great,you made me change my mind and start from rebuilding the carb again.Either the flappers of y-pipe is clogged or not this job must be done.Thanks.

 

[sarantis]

Re: rochester carb question

continue of the previous reply
...but i don't know if running reach could lead to overheating.

 

[sarantis]

Re: rochester carb question

continue of the previous reply
and something else i want to ask: if after two days time the bowl is almost empty it means it means that it's leaking at a pace about one or two drops every 4-5 minutes? Could this affect the WOT running where the fuel consumption is so higher?

 

[Alpheus]

Re: rochester carb question

but i don't know if running reach could lead to overheating.
Reply With Quote

No it would cause the exact opposite.

if after two days time the bowl is almost empty it means it means that it's leaking at a pace about one or two drops every 4-5 minutes? Could this affect the WOT running where the fuel consumption is so higher?

No, but the fuel just drips into your manifold and runs down into your heads (if its cold) and fouls out your plugs faster.

If you are getting Hesitation at WOT you may be running to lean which will cause overheating issues. You need to pull your spark plugs out and take some close up pics and post them or check them against this:

http://www.gnttype.org/techarea/engine/plugs.html