Merc 72 250/8 Inat 35/40 Carby Problem

[tom&jen]

I have rebuilt the INAT 35/40 carburetors - so all gaskets etc. are brand new using Phil's kits. I photographed the carbies during disassembly to avoid errors when reassembling. I've used the Haynes Manual as well as Chilterns in doing the job. I've also had the Jaimekop carbie manual as well. The car does start but soon dies. However, I have leaks at the fuel return value and through the top gasket when turning the engine over. Would welcome any suggestions.

Many thanks, Tom and Jen

[t walgamuth]

leaks at the top of the carb gasket suggest the float chamber is running over. it it smoking black? this will support my thought.

a float chamber running over suggests either a stuck float not shutting fuel flow off or a float with a leak and filling up with fuel and hence not shutting off fuel flow.

those old carbs are very very difficult to get right.

good luck.

tom w

[cth350]

leaks are NG, not just from a drivability point of view, but the risk of fire is a little too great for comfort.

You can take the return valve apart and clean it. Perhaps you just need to replace the two aluminum crush seals on each side of the banjo fitting? If you don't have the seals, there is your first problem.

The leak at the top cover is definitely not a good thing. The first time I did a set of zeniths, it took four tries to get it right. But, I got it right in the end.

You're using the original mechanical fuel pump and the fuel return valve is actually working? There's a little lever on the linkage that activates it at idle. I've seen over exhuberant fuel pumps flood a carb.

Once the carb is properly reassembled with its worn parts mended and correctly set up (and there are lots of little bits to set up), zeniths are great carbs. The hard part is getting there.

-CTH

[Blue 72 250]

I had the same problem on the rebuild I did.

two things and I bet you will get it right.

1. Is the new needle valve a solid pin or the ball style? Make sure that you use the right shim for the valve. (they have two different spec. see Jamiekoop manual)

2. Check the top plate for warpage. Remove it and sand it flat on a piece of glass with 220 wet or dry. You will be amased how much better the vac. seal is. This will help on adjusting later and alwas a good step when you have the top plate off.

finally, check the settings once putback together. If way out off ballance, you will flow over on one of the carbs.

[t walgamuth]

i had similar carbs on my 74 beemer bavaria. i had them apart at least six times. i had the mating surfaces planed, etc etc etc.

i had many many positive experiences before in rebuilding carbs. i just KNEW i would eventually get it right.

but i never did.

i did however convert it to use a quadrajet using a euro manifold.

that eventually a great set up. the q jet is not a high quality carb either though. and i would today use a edelbrock q jet replacment carb.

tom w