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Loose carb parts - buyer beware.

Posted: Tue Sep 01, 2015 3:07 pm
by Harv
Ladies and gents,

Think of this post as a community service announcement.

A number of sellers (often via eBay) are now providing Stromberg carbs that have been overhauled. The products are typically either “nice and shiny” from being replated, or dull grey. Some of these carbs appear to have been acid dipped to clean them. If the acid dipping is too prolonged, the carb can be affected badly.

Many of the fittings in a Stromberg carb are a press-fit. The acid can eat out the area around the press fitting, leading to parts becoming loose. Some parts (like the drive plugs) will allow fuel to leak. Another significant risk is that parts become loose and fall into the carburettor throat. These bits can travel into the engine, and do horrific damage. One part that is very susceptible to this is the fuel bowl vent.

Please do not think that all carb overhaulers are making crap product. There are probably many of them doing a great job. However, I have now seen a number of sellers, including at least one “big name” where the carbs have loose parts. At least one engine has been destroyed due to this.

As a check, I’d recommend that anyone who has bought reco’d carbs should do the following. Remove the air cleaner, and take a look down the throat of the carb. You should be able to see a small pipe, jutting up diagonally in the carb throat (see photo below).
Image
This is the fuel bowl vent… the bit that can come loose and wreak havoc in your engine. Grab the vent pipe with your fingers, and try to wiggle it around. If there is any sign of movement, you are at risk of the vent coming loose. The carb will run OK (temporarily) with no vent pipe – it will have an increased tendency to slosh (overflow) fuel into the carb throat, and will tend to run slightly leaner. Under no circumstances should a vehicle be run with a loose bowl vent.

If anyone finds a loose vent, please let me know (no need to name and shame the vendor publicly though)… interested to see if the vendors mentioned above have more problems.

Cheers,
Harv

Re: Loose carb parts - buyer beware.

Posted: Wed Nov 18, 2015 7:33 am
by sooops
Harv,

Thanks for the post. I checked both of my carbs and found that one of the vent pipes was quite loose, the other not quite so but I removed both as a precaution.
Would have been catastrophic if they were ingested, thanks for the tip.

I bought both carbs from an Ebay vendor back around 2010, I can't recall who it was however. I also noted that the throttle valve screws were not peened.

How can the tubes be successfully reinstalled? Is the booster venturi likely to be at risk as well?

Sooops

Re: Loose carb parts - buyer beware.

Posted: Wed Nov 18, 2015 3:56 pm
by Harv
Good news that you found the loose bits... the easy way.

From memory, the booster venturis are cast in (i.e. cannot come out). The throttle plate screws really, really need peening. If there is not enough meat in the screw ends, you can use a centre-pop to stake the ends. Alternatively, buy some new (longer) screws (Carburettor Service Co in Sydney can help).

The float bowl vents could be epoxied back in, but no guarantee that the epoxy won't crack over time - the carb goes through a lot of temperature cycling. Best bet is to replace the airhorn with one from a junked carb. It won't be shiny, but it won't be loose either.

Cheers,
Harv