Carb issues

[sam93]

Evening all !

Got the GT6 out today & unfortunately it drove like a bag of shite.

I think it's running a little rich as when you let off the throttle from around 3500 - 4000 I got a few pops / bangs. It also seems to hesitate on acceleration. Is it possible to adjust the mixture on the CDSE stromberg carbs ? According to my manual, there should be a mixture screw visible from the underside of the carb, I've just got a blank installed where they reference.

Other info / symptoms

I've recently fitted a HUCO electric fuel pump, the output should be regulated at 2.1PSI. Is there any possibility it would be putting out more ?

What would be the effect of putting in too much damper oil ? I topped both carb dampers up today. Don't think I put too much in, but could be worth noting.

Can the starter box area of the CDSE stromberg carb be rebuilt ? I'm convinced there's a small leak around here as it's very discolored with fuel.

What would be the symptoms of the emission control bit on the side of the CDSE carb failing ? Would this cause the mixture to richen ?

I can replicate the issue statically, by moving the throttle control arm on the actual carbs, after revving up the back carb drips fuel out of the air filter quite a bit for around 20 seconds or so. Never happened before.

Would you guys go for a rebuild ? Or I'm tempted by a set of CD175 stromberg carbs. Obviously just putting on bigger carbs won't isn't the sole answer for more power, but how much of a difference might I see ?

Lot of questions I know, however it's easier for me to put it all up now. To hopefully come to the solution quicker. There's a few photo's attached to help.

Thanks in advance,
Sam.

[sam93]

Picture showing the starter box fuel stain.

[Dazman1360]

I'd be inclined to put the old mechanical fuel pump back on  to see if that fixes it. I don't know what the fuel pressure should be, but if the problem has started shortly after fitting an electric pump it has to be favourite.

[sam93]

That's not possible I'm afraid. The whole reason I went electric is because I couldn't get the required bits for my fuel pump rebuild. I'll check the pressure and report back, however the pump used was the exact one recommended. So I hoping it's not the issue as it will be annoying if it is.

Sam.

[BrendanD]

2880 wrote:

Evening all !
Hi Sam,
comments below.

Got the GT6 out today & unfortunately it drove like a bag of shite.

I think it's running a little rich as when you let off the throttle from around 3500 - 4000 I got a few pops / bangs. It also seems to hesitate on acceleration. Is it possible to adjust the mixture on the CDSE stromberg carbs ? According to my manual, there should be a mixture screw visible from the underside of the carb, I've just got a blank installed where they reference.
Yes but with a special allen key type tool from the top via the dash pot - however you shouldn't need to if it was running ok.

Other info / symptoms

I've recently fitted a HUCO electric fuel pump, the output should be regulated at 2.1PSI. Is there any possibility it would be putting out more ?
unlikely, I have a hulco and its fine.

What would be the effect of putting in too much damper oil ? I topped both carb dampers up today. Don't think I put too much in, but could be worth noting.
nothing

Can the starter box area of the CDSE stromberg carb be rebuilt ? I'm convinced there's a small leak around here as it's very discolored with fuel.
the starter box can be disassembled and cleaned. you'll need a new gasket. they can get worn and continually leak fuel into the carb causing too rich a mixture. the metal disc inside is not obtainable so you'd need a 'good' used one.

What would be the symptoms of the emission control bit on the side of the CDSE carb failing ? Would this cause the mixture to richen ?
No, the opposite. If the temp compensator sticks open it weakens the mix at idle and causes erratic running. ARE YOU SURE its running rich?

I can replicate the issue statically, by moving the throttle control arm on the actual carbs, after revving up the back carb drips fuel out of the air filter quite a bit for around 20 seconds or so. Never happened before.
You have a sticking needle valve and the float chamber is flooding!!!

Would you guys go for a rebuild ? Or I'm tempted by a set of CD175 stromberg carbs. Obviously just putting on bigger carbs won't isn't the sole answer for more power, but how much of a difference might I see ?
NONE on a standard engine - don't even go there.

Lot of questions I know, however it's easier for me to put it all up now. To hopefully come to the solution quicker. There's a few photo's attached to help.

Thanks in advance,
Sam.

Sam, lots of people will say 'ditch the strombergs' and get SUs fitted. I like the Strombergs and I refurbished mine quite easily with a kit. You could also get a refurbed set for £275 from Andrew Turner. I would say you have a combination of issues, but most likely to start with a sticking needle valve.

[rotoflex]

2880 wrote:

Is it possible to adjust the mixture on the CDSE stromberg carbs ? According to my manual, there should be a mixture screw visible from the underside of the carb, I've just got a blank installed where they reference.

The manuals are frequently confusing & sometimes refer to the method of adjusting the CD carbs in the section on the CDSE carbs.  If you've got the blank plug on the bottom, you've got CDSE carbs, & CDSE carb mixture is adjusted by inserting a special tool through the carb's oil filler on top.



That being said, in this case, I would look elsewhere before adjusting the mixture.

Quote:

I've recently fitted a HUCO electric fuel pump, the output should be regulated at 2.1PSI. Is there any possibility it would be putting out more ?

Yes.  You'd need to check it with a fuel pressure gauge.  If you're moving permanently to electric pumps, a fuel pressure regulator might be a good idea.

Quote:

What would be the effect of putting in too much damper oil ? I topped both carb dampers up today. Don't think I put too much in, but could be worth noting.

The excess oil would just squirt/run out of the overflow hole on the side of the chimney.

Quote:

Can the starter box area of the CDSE stromberg carb be rebuilt ? I'm convinced there's a small leak around here as it's very discolored with fuel.

The main issue of the starter box is wear, & yes as it wears it can result in always being too rich at idle (with the choke off).  This wear is of aluminum wearing away, & is unfixable.  It may be that if the fuel pressure is too high, it's squirting fuel out where it can.

Quote:

What would be the symptoms of the emission control bit on the side of the CDSE carb failing ? Would this cause the mixture to richen ?

Which emission control bit?  The thermostatic thing (the long plastic-covered thing, #16) or the throttle bypass thing, #10?



The thermostatic thing is becoming a problem, because as it ages the black rubber stopper disintegrates & doesn't stop any more.  If yours is deteriorating replacement or blocking it off are the only ways to make it work correctly under standard adjustments.  Never try to adjust the thermostatic strip things insides!

Quote:

I can replicate the issue statically, by moving the throttle control arm on the actual carbs, after revving up the back carb drips fuel out of the air filter quite a bit for around 20 seconds or so. Never happened before.

This indicates a stuck needle valve, or a fuel pump putting out so much pressure that it's overcoming the needle valve.

Quote:

Would you guys go for a rebuild ? Or I'm tempted by a set of CD175 stromberg carbs. Obviously just putting on bigger carbs won't isn't the sole answer for more power, but how much of a difference might I see ?

I understand that there is a consensus that CD175's offer no improvements on the 2.0 liter engine even with many engine performance improvements.  My advice is to first make sure the fuel pressure stays within specs (1.5 psi to 2.5 psi for Strombergs), even if it means installing a fuel pressure regulator.  After that, if fuel still drips from one of the carbs, then it indicates a needle valve problem, & you might as well take them off & rebuild them.  Pulling the bottom bowl off to access the needle valve usually wrecks the bowl gasket, & if the needle valve must be replaced upside down & you're not familiar with them, they'd be better off the car & on the kitchen table to work on.  Get a mixture adjusting tool with the rebuild kit if you rebuild.

Is the car at its age still subject to emissions testing & requirements there?  If not, at rebuild you can just block off the throttle bypass valve & thermostatic thing to reduce variables & problems, & hope that the starter box isn't worn.

[DougBGT6]

Here is a link to Buckeye Triumphs which will tell you everything you want to know about refurbishing CDSEs. They are 175s not 150s but essentially the same. It does include re-calibrating the temperature compensators but this is not generally necessary, just replace the O rings which will be in the refurb kit. Buckeye will also tell you what happens if you blank them off.

http://www.buckeyetriumphs.org/technical/Carbs/CarbsI/CarbsI.htm

[sam93]

Where is the bit about blocking up the temp componsator on the "buckeye triumph website" I've read it 2/3 times now & can't find it.