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TR4/4A Tr4A , Stromberg carburetor

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R

Rrbbeerrttoo

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Help, I could use some inputs from BCF members.

My garage smells like gasoline whenever I drive my car in...after a fast or slow cruising. Everything else seems normal, driving flat terrain or hills. I notice little rpm change when adjusting mixture (moving carb air valve with the screw driver) , not as much as it used to ( I think ). The manual says: move SU jet adjusting screw up to weaken mixture . I assume the same for Stromberg, right? I tried both directions with no improvements. My book does not say.
Out the tail pipe the exhaust leaves a minor dark stain on a white paper towel..oil? unburned gas?. The exhaust pipe interior is black at the tail, but nothing is ever visible .
No, have not done anything recently to the engine after the last rebuilt...never detected a need. Carburators were rebuilt 100% a few years back. Synchronizer shows balaced carbs.
Thanks for reading this long explanation. Any comments will be much appreciated.
Robert
 
One of the first things that come to my mind when a carb suddenly starts acting up is a problem with the float chamber needle valve.
It has one moving part and small openings for the gas to pass thru. Debris or even residue from evaporated gas can foul it and cause either an over lean or over rich condition.
I mean there just isn't that much that can go wrong with those carbs as long as no one's messing with it..A torn diaphram might be the exception, but your description doesn't sound like that to me.
000_0075.jpg
 
I assume you've checked and can't find any gas liquids around the bottom of the carb after it's been driven?
My car had strong gas smells in the garage and it was the float height incorrectly set, not enough to actually leak out but a strong smell.
I've heard that it can also be a leak in the rubber in the tank filler neck.
 
And you can get a little leaking off those bottom jets on these early Stromberg carbs too - but that is easy to spot with a quick inspection.

The needle valve poolboy shows is a good improvement - I think that particular one was for an MGB, but it is interchangeable - it has the nice feature of the filter screen built into it, which is missing on the original TR versions.
 
Yeah,leaks. I was concentrating on your attempts to make adjustments and I overlooked the possibility of leaks.
In addition to leaks at the carbs themselves, there are soft flexible sections of fuel lines connecting the steel sections. They can split and leak.
Trace the fuel line from the tank forward and you'll see them.

Consider replacing with Barricade or fuel injection line because of their alcohol resistance, if any needs replacement.
https://www.oreillyauto.com/site/c/detail/GAT0/27323.oap?pt=N0887&ppt=00000
 
That's 1/4" line Ken. Isn't that to small?
 
Rrbbeerrttoo said:
...I notice little rpm change when adjusting mixture (moving carb air valve with the screw driver)...
Click to expand...

Unless the 4A is quite different from the TR4 Strombergs, the screwdriver adjustment is simply the idle setting (throttle plates) and will have no affect on driving or mixture. The latter is adjusted (as you go on to ask) by the thumbwheel at the bottom.

Since you messed with that screw it might be well to sync the carbs, moving just one screw may or may not change the RPMs depending on the other screw.

A common leak (and easily fixed) are the O-rings on the mixture adjusting screw and the fitting it screws into (that holds the jet). As I recall, these can be changed with the carbs in situ.
 
I just had that link handy, Don, for descriptive and local availability. A lot less expensive than from Moss.
If it's like the TR6 from the tank to the pump it's 5/16; from the pump to carbs it's 1/4.
 
Got it, Ken
Thanks for the clarification
 
poolboy said:
Consider replacing with Barricade or fuel injection line because of their alcohol resistance,
Click to expand...
Maybe it's just a California thing: Can you really still buy fuel hose that won't resist E10 in the rest of the country? I thought the federal EPA had already outlawed the stuff that won't hold up (or allows permeation beyond 15g/m2/day)?
 
I don't know. Barricade seems to be making a big deal about it and Moss has recently started hyping Barricade as well.
https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=90194
There might be 2 different issues as far as I know, permeation and the alcohol resistance.
I guess it was about 3 years ago when I became concerned about having to use ethanol and recalling problems in the 70's from that stuff, that I went to NAPA on a tip about fuel injection line. While I was there, I read the specs. Regular fuel line made no mention of alcohol resistance, whereas the fuel injection line did.
Permeation wasn't on my radar at the time so I don't know if it were mentioned in either's description.
At that time, I had not heard of Barricade, but when I did recently, the only place that would order a spool was O'Rilleys.
 
Well, around here, if you just buy "low pressure fuel line" at FLAPS, it says nothing about ethanol or permeation. But it definitely stands up to the ethanol, and I believe meets the requirements for permeation as well.

Of course we have had "oxygenated" gasoline here since 1995 or so. The problems with MTBE weren't quite as severe as with ethanol, but it would still degrade fuel lines, pump diaphragms, plastic floats and so on. The diaphragm in my motorhome gen set came out looking like jelly; and the TR3A diaphragm like dirty screen wire. But pretty much all the replacement parts suppliers were supplying the MTBE/ethanol resistant stuff by 2000 or so.
 
Is that considered "Low Pressure"
It's rated to 50
 
I believe so. I've noticed the "not for fuel injection" label on the Barricade and others.
 
That's what has me baffled. TBI is fuel injection and they run from 15-45 lbs.
 
Geo Hhan,

"I notice little rpm change when adjusting mixture (moving carb air valve with the screw driver)"

By the comment above I meant I used a screw driver to lift the air valve whithin the carb, not to adjust any screws ...meaning I followed the suggestion in the manual to use a screw driver, mentioned for simplicity I imagine. I could have used a finger or a tooth pick as well. The manual advises that if the engine rpm goes up upon too much upon lifting Air Valve, the mixture is too rich; if it drops , the mixture is too lean.....something similar to this. Agree, the adjustment at the bottom of the carb is for mixture adjustment. In my manual both TR models are treated the same!

To the many other ideas proposed:
1. The fuel smell does go away after a few hours of car sitting in garage.
2. Did not find fuel leaks anywhere, none from the gas tank to the carbs...even by a white glove inspection.
3. Fuel tank smells only after lifting the cap.
4. Did not imagine fuel level in carb could cause smell w/o exterior leaks, but will inspect after all simpler checks are done once again.

Thank you for the animated discussions..I learned plenty!

Robert
 
So as I understand it, your main goal was to see why you can smell gas for a few hours after the car is parked inside a garage and checking the mixture was part of that investigation ?
You said that the carbs were rebuilt a few years back, right ?
Have you noticed that smell ever since or is this a recent experience ?
 
Poolboy,
Yes, it is a recent occurrence..never happened before or after the carb rebuild. Nor did I touch anything to cause the smell. I only played with the mixture after the smell showed up. It also smells when the car idles at a stop light. The bottom line is, why does the engine rpm not vary NOW when I attempt to adjust the mixture...and in both carburators..I was always able to momentary change rpm when adjusting mixture .
 
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