Weber carb running lean = blown head gasket??

[cbschneider]

Hi folks, here is my problem:
I have a 1974 SIII which was refitted with a Weber 34ICH conversion back in 1990 when the engine was rebuilt. Since that time it has gone about 5000 miles. During most of that time it frequently dieseled when shut down, but otherwise always ran perfectly, never overheated, and always had good power and driveability. I never made any adjustments to the carb or attempted to re-jet it. I had assumed the dieseling was because of a somewhat lean mixture but never looked into it and of course my assumption could be wrong. Recently I smelled coolant in the exhaust and concluded that the head gasket has failed. It still runs well. Anyone have any thoughts on whether the head gasket has failed or not, and if so could the head gasket failure be related to the long-term lean running? If not then what could have caused the head gasket to fail at such low mileage? Further, does this carburetor need to be re-jetted or adjusted and if so what should I do?

Thanks for any comments.

Charles Schneider
Raynham MA

[Leslie]

Have you done a compression test?

[Leslie]

And, although low mileage, it's been 18 years since the gasket was swapped.... there's a certain point where time has to be factored in.....

[yorker]

what jets are in the carb now?

Do a compression check, and go from there with your diagnosis.

[yorker]

http://gunsandrovers.yuku.com/topic/725

[Eric W S]

I'd buy a vacuum gauge and google how to use it. Good tool to have. In 10 minutes you'll be able to tell if it is a timing problem or if the head gasket has blown. If the gasket is fine then it will give you a pretty good idea of what the issue may be. You can even set your engine timing very nicely with one.

EwS

Oh, and not all gaskets are created equal. Some can be crap from the source - hence premature failure.

[jp-]

Pop the radiator cap and watch for bubbles (just make sure the engine has mostly cooled off so you don't get a face full of hot antifreeze!). Small, consistent stream of bubbles indicates a head gasket problem. Also, do you know if you have a copper head gasket? Copper head gaskets must be re-torqued after the first 100 miles or the gasket will eventually leak.

[cbschneider]

Thanks to everyone who responded. I have not yet done a compression test but that's a good idea. I will also try the other suggestion for checking for bubbles in the radiator during running.

As far as the Weber's main jet I do not know what it currently has except to say the jet has not been changed ince it was installed. It has whatever came with the carb new. I will check on that and post findings here.

Regarding the dieseling I know that it could be related to timing, carbon buildup, fuel octane, and possibly other causes. I did check and reset the timing and found no issues there. I guess I will work through the other tasks first and then address whether there is or is not a problem with the Weber.

I will post any further findings here for comments.

Thanks again,
Charles Schneider

[Jeff Aronson]

The two '66 Series II-A's I use have to different carbs, a Solex and a Weber. The Solex runs happily on this island's only gas, dubious regular, while the Weber always diesels unless I get higher octane gas on the mainland.

Over the 18 years and 400,000+ miles I've put on the Weber carb[s], I've found that lean mixture is more often than not an issue with the intake manifold or carb body gaskets. I get at least 100,000 miles on the carb itself and I've never had to fiddle with the jets.

When I replaced the head once [burned valves], I found huge ridges of carbon deposits on the top of the block. Clearly those were heating up and causing some dieseling, too.

When you do the compression test, also just check the radiator level. If you're burning coolant in the engine you'll notice the level dropping over time. If it's been happening for a long time, you'll also see deposits on the spark plugs, too. Lastly, you should be able to tell by draining off some oil; if you have coolant there, you'll smell it, too.

Good luck!

Jeff