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bushwood

Contributing Member
I have twin Chrysler 440s in my boat with Carter AFBs. I wanted to run my carb problem by an expert before I tear into my problem carb. One of my carbs was rebuilt this past spring. Since that time, whenever I shut down the engines, the rebuilt carb seems to absorb the heat from the engine and gas seeps out the bellhorn gasket and through the manifold/carb gasket, at the rear of the carb. The other engine has no problems. Both carbs run efficient when operating. It's at shutdown when the problems occur.

1) Is there a gasket for the base plate that may deflect the heat better?
2) How do I keep the carb from getting so hot after shut down that it boils the fuel, thus seeking its way out the gaskets?
3) Should the gaskets (bellhorn, base plate) have a sealant?
4) I have also seen gas trying to seep out the fuel inlet fitting.

I think the carb is so hot it's forcing the gas out the weakest points.

Any help would be appreciated!
 
I suspect that a paper thin base plate gasket was used. Was the intake manifold removed? Blocking the heat cross over in the intake can help keep things cool. Go to a good auto parts store and ask for the thickest square bore carb gasket they carry.

No sealant should be used.
 
Tahoerovber,

The thin gasket makes sense. Do you think this would alleviate the heat making its way up through the body as well? Is there a thicker gasket between the bellhorn and body I can try? I seem to be getting seepage through that gasket also.

Thanks
 
No good - those gas fumes !.. you may need a Std Aftermarket type "squarebore" AFB bolt pattern 'heat insulator' they can be made of various Cardboard tpe material , even some hardwood if forced to make your own,as well as the above suggestion , lift the carb off the ENGINE & SEE IF IT INDEED JUST HAS A CARB-KIT TYPE CARB TO MANIFOLD GASKET RATHER THAN proper OEM Insulator (Hygrade Carb kits suit Marine afb sometimes incl an approx 1/4" thick heat insulator)

goodluck
 
bushwood said:
I think the carb is so hot it's forcing the gas out the weakest points.
Click to expand...

The fuel bowl is vented so the vents would be the "weakest points". Your vents are those 4 tubes sticking out at the top of the horn with angled cuts at the end. If the carb is leaking from the gasket then I would question the rebuild job. Especially since your other carb isn't leaking.

-JJ
 
Hi
We have come across this a lot in the last few years. To start make sure the float level is correct. Set it to spec, avoid going lower as you do not want to lean the engine if the bowl runs low.
Since you may have an Ethanol based fuel you will find it expands and vaporizes faster that straight gasoline. We now put 1" phenolic spacer blocks under all the carbs that still have an active heat cross over passage in the intake manifold. It does not seem to be a problem once the passage is blocked. At one time Ma Chrysler had a marine intake manifold gasket that was blocked off, but no more. We just put a small plate inside the hole and weld it in the intake manifold.
Once the float setting is verified and the cross over plugged or a phenolic spacer is put in you will find the problem goes away. But for a while keep checking, vapors are wildly explosive as they are already super heated.

This is the reason we are developing a bolt on distributor less ignition MPI fuel injection system for the 440 marine engine, or all big block Chrysler actually. We will have the first one together and programmed by May. Once tested we are working with the manufacture of the ECM to preprogram them for us as an off the shelf part for us. Our target is to have a system under $1000 and it looks like we will.
Will keep all posted when it's done.

Good luck and be carefull with the fumes around while working.

Dan
 
Good information! I thought this thread was dead. Coincidentally enough, this winter I got wind of a good carb man in my area. I took off the problem carb and took it to him Thursday. I do have the poly spacer already. Once I get the 'new and imporoved' carb back next week, I am try to find time and re-mount as I will be anxious to see if this guy is as good as his reputation.
 
bushwood said:
Good information! I thought this thread was dead. Coincidentally enough, this winter I got wind of a good carb man in my area. I took off the problem carb and took it to him Thursday. I do have the poly spacer already. Once I get the 'new and imporoved' carb back next week, I am try to find time and re-mount as I will be anxious to see if this guy is as good as his reputation.
Click to expand...

Hmm... that seems to be the thinly veiled attitude of posts I'm noticing more often (your last sentence) - before you hang him at the stake .. 1 problem carb of your 2 could've easily picked up a piece of dirt/scale on refitting the fuel line - a VERY common occurance & the 1st person blamed is "That carb guy" rather than the operator or whatever else could be causing the fault.

Whats your Fuel pump pressure ?? - you haven't installed a '6 psi ' free running pump etc & forgot did you ?

Not ribbing you,just speaking from many years of experience (on both sides of the counter)...be honest with him & Don't expect his reach to be further into your bilge than what he's got to work with .... better still invite him to see insitu the problem & it running... it may be best way to a good outcome if he's older age group of a carb guy ... or is he screwed to a "flatrate" job ?

(somethings not adding up ) Why not Say you had a Plastic heat insulator installed too... drip fed info usually costs you twice the price bill ... but I'm not one to preach so best wishs in your fault-finding , I've got real work banking up & $ to earn.
Cheers & goodluck

PS Why not get back to the original carb repair firm , or is that more of the untold story ?....
 
Tahoerover said:
I suspect that a paper thin base plate gasket was used. Was the intake manifold removed? Blocking the heat cross over in the intake can help keep things cool.
...............................

I think your float levels are to high
Click to expand...

Both great points!

FWIW, with twin engines we always have the option of swapping certain components as part of our P of E.
In this case, the intake manifold exhaust cross-overs were mentioned.
Could be that one engine was blocked off, the other not, and perhaps swapping carburetors may have pointed to, or eliminated this!

Just a thought!

.
 
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