SUs overflowing

[eejay56]

I tried to install my SUs to replace my weber and when it starts gas gushes out the overflows on both carbs. The carbs have been rebuilt with new jets, needles and throttle shafts. This is the first time I've tried to run them. I have the stock mechanical fuel pump so I don't think there is too much fuel pressure. The floats are adjusted properly and don't seem to be leaky. What could cause this?

 

[vivdownunder]

You don't say if new needles and seats were installed in the fuel bowl lids. If not they will need replacing.

Also, on early SU's sometimes the forked brass lever that closes the needle valve drops down when the lid is being fitted onto the bowl. It can stick there leaving the needle valves always open.

Viv

 

[DrEntropy]

Not knowing about the float needle/seat renewal, a word of caution: the best needles are the Viton tipped ones. "Gross(e) Jet" needles are JUNK, IMO.

 

[Mickey Richaud]

Not knowing about the float needle/seat renewal, a word of caution: the best needles are the Viton tipped ones. "Gross(e) Jet" needles are JUNK, IMO.

+1 on the Grose jets. I pitched a couple from a friend's TR3, replaced them with the proper bits and solved his issues.

 

[tomgt6]

Check the pressure as well. I had a pump that was putting out 7-9 lbs of pressure and once I changed that out all went better.

 

[HerronScott]

I've seen a number of negative posts here about Grose-Jets and was curious about that since when I went with them on my TR4A when I rebuilt it 25 years ago and never had any problems with them over the 6 years and 75,000 miles that I drove the car as a daily driver. At that time they were highly recommended.

Did I just get lucky or has quality deteriorated?

Scott

 

[poolboy]

The impression I get, Scott, is that they just aren't what they used to be.
I had problems 4 years ago with the "new' ones from the first day.
Immediately removed the carbs, took out the Grose jets, cleaned them even though I couldn't actually see a problem. Then I rolled the balls around about a hundred times, like a ball point pen on paper, and reinstalled.
Things were OK for about 2 years, but when they flooded again, I went back to the original plunger type valves.
Despite the advertising hype, I think the plunger type are the way to go these days.

 

[Mickey Richaud]

May be related to ethanol?

Why not? We seem to blame everything else on it... :wink:

 

[Roger]

May be related to ethanol?

Why not? We seem to blame everything else on it... :wink:

Or maybe BP fuel?

 

[Mickey Richaud]

May be related to ethanol?

Why not? We seem to blame everything else on it... :wink:

Or maybe BP fuel?

Let's not go there...

 

[TR3driver]

Did I just get lucky or has quality deteriorated?

Maybe some of both. IMO the Grose jets have a fundamental flaw in that they have a larger bore than the stock SU valves, meaning there is more area exposed to fuel pressure. More area means it takes more force to hold the valve closed against fuel pressure. But modern fuel is less dense (due to ethanol and other changes) than what we used 50 years ago, so there is less force available from the float to hold the valve closed.

So while usually there is enough margin available in the original setup to supply the extra force, sometimes there is not. And of course the problem generally shows up at the worst possible moment, on a long trip far from home. (Hot fuel is also less dense, meaning less force to hold the float valve shut.)

 

[eejay56]

New (not Grose) jets and needles. I checked the fuel pressure and it's 6 psi. I got a regulator and will try that, maybe tonight. What should I set it at?

 

[Mickey Richaud]

New (not Grose) jets and needles. I checked the fuel pressure and it's 6 psi. I got a regulator and will try that, maybe tonight. What should I set it at?

3 - 3.5 psi, if memory serves. You may have found your problem!

 

[TR3driver]

You may have found your problem!

 

[PeterK]

If not, try Grose-Jets. Mine have been flawless even with Ethanol 10%. If they were that bad, they wouldn't be in business anymore. One thing though, the float level is set differently than needle tip so if you install GJs, you have to reset the float level. YMMV but MM has been good with GJs.

 

[tomgt6]

My guess is you found the issue with the pressure. Did you notice the smell got worse on the highway. Why I ask is because I have a therory that on the highway the pump builds up more pressure then around town. I will tent to smell it more on the highway then around town when issues start to happen.

 

[DrEntropy]

Grosse Jets???

Yeah... they're GREAT! A panacea!!! Use 'em! Hurry up! Run right out an' corner th' bloody market!


....OVER FORTY YEARS of beatin' these English cars to usefulness or death... Road cars, SCCA cars, independent autocross cars...

I think <span style="font-weight: bold">Bugeye58</span> about had his say. I may need to follow his lead.

"You can lead a horse to water..."

 

[vivdownunder]

Rather than fit a fuel regulator, why not find out why the mechanical pump is throwing out so much pressure. Regulators can be a bit hit or miss, and some don't like Ethanol blends, with the internal seals disintegrating.

Check it's the correct AC type "UE" mechanical pump.

When new, they operated in a band from 1.25 to 2.50 lbs per sq. inch.

You're getting about triple that, so naturally such a high pressure will overcome the float's ability to shut off the flow.

Back when needles and seats were all brass, Grose jets came in and helped stop cabin fuel smells common to cars fitted with SU carbs. When needles became neoprene tipped, they then sealed better than Grose valves. It's been speculated that after sales volume dropped, so did manufacturing tolerances. Anyhow, just lately there have been many reported disappointments with them.

Viv.

 

[Got_All_4]

Love my Grosse jets! The biggest mistake made when installing new ones is they aren't thoroughly cleaned. Best tip I got from the forum was to clean and soak them in carb cleaner. I blew them out with air too and there must have been thousands of little brass filings at the bottom of the can. It's been 3 years now and the car still runs wonderfully.