SU carb rebuilding tips required

[andyf]

Just as a bit of background to this. I was chasing an annoying misfire last year and had replaced most of the ignition system (including the ignition leads with new copper ones- thanks Mildred) before finding out it was an exhaust valve that didn`t show up initially on a compression test.

Cylinder head is now rebuilt and on and I am happy with the ignition system. The idle has been an issue for a while so as I have a spare set of carbs I thought I would have a play. Time is not an issue, the car is running fine on the existing set, but a rebuild is no bad thing.


1980 Persian Aqua DHC

[Hasbeen]

Mildred, just when do we stop, when trying to help someone with a question.

I believe many on here, present company included, know a hell of a lot about our cars. In fact I am continually amazed at how much many do know, & the work they undertake.

Many have shown in their earlier posts, that they know more than I do, but are asking for information in a minor area. This is particularly the case with SUs, where us old farts have lived with them for years. Many have never come across them before, but are very competent with so much, that I worry about "teaching my grand mother how to suck eggs".

I often assume they have all the other stuff under control.

Hasbeen

[rosey]

I just overhauled a pair of SU's supplied by Mr Turner and the spindles were 5 thou undersize where they had worn on the side nearest to the throttle linkage. This doesn't sound much, but on a precision part like a carb it makes a difference and I dont consider it a pointless exercise to restore an essential part to optimum condition.

Likewise I have overhauled the cylinder head and re-ground the valves, fitted electronic ignition etc, and I now have an engine that works like it did when it left the factory.

I dont believe in bodging so I always do the best job that I can, thats what I was trained to do as an Engineer and I will continue to do, everyone to their own but this is how I like it.

Dave[:)]

"Do or Do not, there is no try" - Yoda

1981 Purple Grinnal 2.0L
1980 TR7 Persian Aqua Drophead.
1977 TR7 FHC Tahiti Blue

[Tirebiter]

My vote is that worn throttle spindles and carb bodies cause idle problems and that's it. Of course if you can't adjust the idle mixture properly it does reflect as improper mixture throughout all conditions of RPM, road speed, engine load and throttle opening.

That said, the biggest gain I've seen from repairing worn spindles/bodies is in getting the idle speed to drop to the exact same RPM every time you slowly release the "go" pedal.

Let it snap back quick and it's a good low idle. Ease off slow and it's a higher than normal idle.

Imaginitive spring brackets and a correctly aimed throttle return spring can bias a loose fitting throttle spindle so it at least closes the throttle to the same point ... most of the time.

TR-7 and TR-8 are two different cars. I like them both.

[andyf]

Tirebiter that is spot on, if the idle is high give the throttle a blip and the revs will drop. I just think it would be nice if I could let my foot off the throttle gently now and again.


1980 Persian Aqua DHC

[Cobber]

Another problem with throttle spindle wear to where both the spindle shaft and bush can get worn unevenly so they can be a bit oval shaped in cross section, this can cause a flat spot in acceleration and a rough spot at a certain spot in the rev range as when the two worn part align, and then cause it to run lean.

It's not something that's all that common, but I have seen it happen.

"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"

80'Triumph TR7, 73'Land Rover (Ford 351. V8),
'89 Ford Fairlane
'98 MG-F, 69'Ford F250.

[FI Spyder]

I think worn spindles can also bind when under spring tension while everything seems smooth when spring tension is removed (how binding is usually tested). May not be in all situations.

I too wondered how one drills the bushings out with the necessary accuracy, would like to see it done to see what the "trick" is.




- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

[Cobber]

The trick to making accurate sized, properly round holes is to drill under size and finish off with a reamer.

"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"

80'Triumph TR7, 73'Land Rover (Ford 351. V8),
'89 Ford Fairlane
'98 MG-F, 69'Ford F250.

[sonscar]

Have a look at Burlen SU site there is a video of it being done with a description of the refurb process.Steve..

[vitessesteve]

I had Burlem rebush the spindles on a pair of Strombergs on my Vitesse. As the car was my daily driver at the time they reconditioned and returned the carbs to me in about a week. Had to book an appointment ahead to guarantee that turn round. They made a great job of it.

So next time I will go back to them for any Carb refurbishing on any of my Triumphs.

Steve Weblin - AKA vitessesteve
1982 TR7 Sprint DHC