Fluctating carbs

[Mike L Taylor]

A couple of years back, I decided I would trawl back through all my previous DM's to create an index of what topics were covered and the issue/page reference. Well, I managed to get about 10 years worth done - but (wot a wally <!--EZCODE EMOTICON START :rolleyes --><img src=http://www.ezboard.com/images/emoticons/eyes.gif ALT=":rolleyes"><!--EZCODE EMOTICON END--> ) I've gorn n lorst me master list! Has anyone got any details about the solution to fluctating carbs? I seem to think that you could solder up a valve in the carb - or was it welding in a 2p piece - although with a carb stripped down, can't possibly see how this would be achieved. Any takers?<br>
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Mke

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[miniman]

<!--EZCODE AUTOLINK START--><a href="http://www.nireland.com/gd.triumph/waxs ... <!--EZCODE AUTOLINK END-->

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[redrichie]

I think you're getting confused between two carb mods here.<br>
<br>
The first problem is with waxstat SUs. As they get older the wax degrades and doesn't have the same properties. Solutions? change the carbs to non-waxstat types, or the 2x1p mod as you describe. Not done this, I know a few others have, so I'll let them fill you in on the exact how-to.<br>
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The second problem is the poppet valve on the throttle disc sticking. It will allow air to rush past when you don't want it to, making them difficult to tune and hard to set your idle up. You can solder these shut, or for a more satisfactory solution, just change the discs for solid ones. I think the club has/had these in stock. Make sure you change the splay screws as well, or you'll be in a world of pain when they break and get sucked into your inlet. I just soldered my sticky ones up, but you may need a soldering iron the size of a cricket bat. Normal "home mechanic 12v" soldering irons will simply not have the power output to make a good joint and you'll just end up frustrated with the massive heat sink that the carb becomes. Obviously, should you choose to solder, make sure all fuel vapour has done an Elvis and left the building.<br>
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I did show pictures of this in another thread, I'll see if I can find them...

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[redrichie]

<!--EZCODE LINK START--><a href="http://www.chicagolandmgclub.com/photos ... /">Perfect description and some nice photos from the MGB Club of Chicago</a><!--EZCODE LINK END-->

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[Mike L Taylor]

Thanx Red. Your clarification helps. I couldn't fathom out the diagram on the first link and, looking at the Chicago link, my carbs (apart from the dash pot cover) don't look anything like the MG carb setup - eg I don't have waxstat carbs (I think!) -although I have a standard Sprint carb layout. However, my throttle disks are already solid apart from the two holes used to secure them to the spindle with the splayed screws. However, there is a gap in the spindle on either end of the disc of about 1/4" and I can't see any other holes or valves in the carb body. Am I being totally thick here?<br>
<br>


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[redrichie]

Aye, those are HIF carbs - Integrated Float chamber, but the principle on how they operate is the same with regards to the poppet valves. If yours are solid, no need to worry about them, but when your discs are shut, they should be shut...ie: no gap for the air to go past.<br>
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What exactly are the symptoms of your poor running?<br>
<br>
<!--EZCODE IMAGE START--><img src="http://www.bobs-services.de/archiv/su_u ... <!--EZCODE IMAGE END--><br>
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These are from a TR6, almost exactly the same as a Dolly Sprint (although I am sure someone can correct me here)...I'm not at home or I could grab a photo of mine in situ.

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[Mike L Taylor]

Wow - what a luvverly set. Would like to get my hands on a set of them - but then I'd probably need to buy almost a new engine to match!! Anyway, the symptoms are just the usual high tickover when coming to a halt, say when leaving a motorway at a roundabout when the revs keep quite high and it seems the only way to reduce them is to slip it in first, foot on the brake but let the car try to crawl forward. But then the revs only drop for a little while - also common in hotter weather. Should I find a way to seal up the gap between the outer ends of the discs as they fit into the spindle?

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[MalcGE]

Club stock has solid throttle butterfly's in stock together with the special splay screws. These will really help your tickover problems. If your jets are 'red' at the bottom then they are non-waxstat andproviding they are not worn, then they will not be contributing to your idle problem. <br>
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Those TR6 carbs are simliar, just got taller dashpot's, Sprint had short ones to clear the bonnet

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[Jon Tilson]

you may need to rebush your throttle spindles if you cant get the idle down below 1000 rpm. This is especially true on the older su's with the seperate return springs.<br>
Jonners

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[rich]

i also have a problem with my sprint not wanting to tickover on choke/when cold and also when letting off the gas the engine drops to nearly stalling then returns to tickover .<br>
is this down to the waxy things or is it the poppy things.<br>
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help its doing me head in <br>
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cheers<br>
rich..

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[Jon Tilson]

in an ealier post, most slow running problems are down to leaky hoses....<br>
If your car pulls well aboove 1500 rpm but struggles to achieve a nice even idle whatever tuning attempts you make its usually an air leak and the breather hose system is the most likely culprit. Ater that leaks where the carb joins the manifold and then around the throttle spindle and carb rubber mountings are next. Butterfly Poppet valves are also a good source of idle woes, often shown up by a quick blip seeming to fix things...until next time.<br>
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To identify where an aerosol of carb spray or even WD40 will help show it up. If you spray round the good bits it makes no difference...near the leak and the engine will pick up for a few seconds.<br>
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Jonners

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[Mike L Taylor]

My bits are red (ooh-er missus) Sorry, meant my jets are red!!<br>
When I put KLR93P back on the road about 9 years back (and only having done about 2k miles per year) - surely the jets wouldn't show signs of wear already? Do other Sprint spindles have this gap between the outer edge of the disc and the spindle or is it just mine? Also (Jonners) how do I rebush the carb body? I can get the idle down to stall on tickover depending on how I adjust the mixture and/or idle settings so somehow think my bushes should be ok. That's a good trick with the WD - think I'll give it a go. Now, where did that bloody canister go when I knocket it off the workbench!!

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[Jon Tilson]

is a specialist job....<br>
I think the carbs have to be drilled out and a new spindle bush fitted. Ive never needed to do it to any of mine as I have the hair spring return on all mine.<br>
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Jonners

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