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TR5/TR250 Front carb spitting fuel out overflow

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tinman58

tinman58

Jedi Knight
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I was at our British car club meeting this morning. One of our members has just did a start up on a rebuilt motor. Ran well for the 20 minute breakin. The next morning went to start the engine and fuel was “squinting “ out the over flow tube. Long story short he has taken everything apart and replaced just about everything he can think of. We asked all the normal questions, to no avail. Any ideas?
Rebuilt original carbs.
 
So the float and float valve in that carb have been replaced with new since the problem started? My next steps would be to double-check fuel pressure and look for any kind of mechanical problem stopping the float from closing the valve. There isn't much else it can be.
 
Taken apart the needle valve replaced with the old one that worked. He did say there was a little bit of crud on the first go round. He did swap out the fuel pump with another one. No change, I believe he next thing was to put in a fuel pressure regulator. He has removed the carb and tried different things "Ten times". He is finishing up on a very nice TR 250 Restoration.
 
My money's on another bit of crud.

Note that fuel pressure regulators have a minimum forward pressure drop ... if the pressure is already correct than adding a regulator is going to cause problems rather than fix them.
 
Or if it is a ZS carb - verifying that there is no fuel inside the float and that the float height is correctly set.
 
ZS or SU? Either way the fuel valve is not cutting off. I'd had some ones that apparently angle inside (I got censored for using another word) and won't cut off fuel. Dry they would work fine.
Marv
 
Thanks all!
I will call him and have him check it again.
 
I worked on an AH 3000 last year and occasionally one of the carbs would pour fuel out of the overflow tube. Since it didn’t happen all the time we all thought that it was needle valve related. It couldn’t be the float because the carbs had been “professionally “ rebuilt and if the float had fuel in it it would happen all the time. After many attempts to solve the problem one of the guys working on it said let’s pull the float we’ve got nothing to lose. The float had never been replaced during the rebuild and had a hairline crack in it. It had gas in it. We still can’t figure out why it would work sometimes and overflow others. Did you check the float?
 
Had a similar problem with an American V8 once. Except instead of a hairline crack, it had Nitrophyl (plastic foam) floats (as I think the TR250 carbs do). The old floats were not resistant enough to ethanol (or might have been MTBE then) and had absorbed fuel until they were just a bit too heavy. Most of the time, they would still work enough to keep fuel inside. But when things got hot under the hood (like pulling a grade), fuel would start pouring out the top of the carb.

Hot fuel is less dense, so the float has to displace more of it to hold the valve shut. My theory is that is why it worked sometimes and not others.

I replaced them once, the new floats worked for a few weeks then the problem came back. Apparently, at that time, even new floats weren't ethanol resistant. After much searching, I finally found some brass floats that solved the problem permanently.

I'm assuming that, by now, no one is selling non-resistant floats in the US. That's why I mentioned replacing the float first thing.
 
Several years ago, I had an overflowing from front carb. I hit the float bowl a couple of times with a wooden hammer handle and it stopped immediately and I've had no trouble since.
 
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