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Idles at 2800 then quickly dies. HELP!

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Brad.Cogan Avatar
Brad.Cogan Bradley Cogan
RAF Cosford, Shropshire, UK   GBR
1977 Triumph Spitfire 1500 "Wray"
1989 Toyota MR2 "Coral"
2007 Fiat Grande Punto "Pepper"
In reply to # 1510842 by Born Loser
In reply to # 1510840 by 14GPDJENGINEERING Use the piston lift pin. It is more consistent than a screwdriver and allows lifting with air cleaners in place..

Sure wish they all had them, those are nice.

Yeah unfortunately don't have those. Screwdriver is the best I've got.



Brad Cogan

1977 Triumph Spitfire 1500 'Wray'
1989 Toyota MR2 Mk1b AW11 1600 twin cam
2007 Fiat Grande Punto Active 1.2 'Pepper'

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Brad.Cogan Avatar
Brad.Cogan Bradley Cogan
RAF Cosford, Shropshire, UK   GBR
1977 Triumph Spitfire 1500 "Wray"
1989 Toyota MR2 "Coral"
2007 Fiat Grande Punto "Pepper"
In reply to # 1510852 by Darth V8R
In reply to # 1510803 by Brad.Cogan I decided to tune my carbs and yeah I've made things far worse. I've reset the mixture screws to 12 flats below flush and have moved the throttle screws/arms (screws on top) so the throttle linkage hits the arms at the same time.

Now it starts but idles at about 2800RPM then dies after a few seconds if I don't put my foot on the throttle. It seems to be 2800RPM or 0.

How should I go about getting a steady low idle?

Thanks!

Brad,

Take it from someone who has been there, avoid the "lift the slide" test. It is exceedingly difficult to do properly, and if the engine has been modified it probably will not work at all. There will be some, no doubt, that say the slide method works well for them. I am very happy for those individuals, but you do not know the configuration of their engine (Cam, ignition, carb, emissions equipment, compression, blah, blah, blah) and therefore cannot assume that their success will translate to your situation.

I will assume your valve lash and ignition timing are correct (10 BTDC with distributor vacuum disconnected).

Set your mixture to the middle of its range. For Zeniths the needle carrier is flush with the bottom of the air valve (slide). For SUs, whatever the manual tells you. But make sure it is in the middle of its range. Start the car, and set the idle speed (as best you are able).

Allow the motor to fully warm, and take the car for a brief drive. Return home, shut down the engine, and pull a couple spark plugs. They should be a light tan color on the tip of the plug (on the ceramic insulator that wraps around the center electrode). If it is dark or black, lean the carb - for a Zenith that is rotating the needle adjustment 1/4 turn counter clockwise. If it is white or nearly white, enrich the mixture (1/4 turn clockwise on a Zenith). Once again, follow the manual's guidance for SUs - I have not used them myself.

Reinstall the plugs, start the car, take it for another driver. Repeat the adjustment process until your plugs are the color of corrugated cardboard.

Job done.

BTW, a Color Tune or an O2 sensor works well too, but the lift the slide test is notoriously unreliable as our cars have passed through many hands, and in general are no longer stock. Your use of an SU carburetor being a case in point. So use the above method which is insensitive to engine modifications.

BTW, if your engine is extensively modified, you may not be able to get the plug color correct, and you will need to go to a richer or leaner needle to get the correct mixture. Report back here if that is the case.

Vance

A colortune sounds like a good idea. Might have to invest in one, thanks.



Brad Cogan

1977 Triumph Spitfire 1500 'Wray'
1989 Toyota MR2 Mk1b AW11 1600 twin cam
2007 Fiat Grande Punto Active 1.2 'Pepper'

spitfire50 Avatar
spitfire50 Paul Mugford
Rochester, N.H., USA   USA
In reply to # 1510814 by Lizzard
In reply to # 1510812 by Born Loser The 12 flats is 2 turns, and that is actually a good starting point.
For a stock set up with stock needles . I'm thinking he doesn't have a stock set up . "I should've pointed out I have twin HS4 SUs."

Lizzard,
Twin HS4s are stock in the UK, But Brad has done some mods so he isn't using the standard needles. Nonetheless, his car has run satisfactorily with this set-up. He has just put it out of tune by maladjusting the carbs (and maybe other things too).
All the best,
Paul

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Wolfcreek Steve Steve P
Central, WI, USA   USA
In reply to # 1510810 by Brad.Cogan
P. S I dunno what a PCV is.

Why do I even bother?

Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
In reply to # 1510920 by Wolfcreek Steve
In reply to # 1510810 by Brad.Cogan
P. S I dunno what a PCV is.

Why do I even bother?

Sport?

Brad.Cogan Avatar
Brad.Cogan Bradley Cogan
RAF Cosford, Shropshire, UK   GBR
1977 Triumph Spitfire 1500 "Wray"
1989 Toyota MR2 "Coral"
2007 Fiat Grande Punto "Pepper"
You mean crankcase vent? I've never heard it called a PCV before. Too many damned acronyms!

The needles are actually standard. As you say it was running fine before so should run fine again. It's running okay now, just need to get the mixture correct (I'll probably try different needles once I've got the mixture correct and access to a rolling road).

As said above the piston lifting technique doesn't seem to work for me very well so I'll go with a Colortune. I'll be checking the spark plugs too to see what's happening during normal driving not just at idle.



Brad Cogan

1977 Triumph Spitfire 1500 'Wray'
1989 Toyota MR2 Mk1b AW11 1600 twin cam
2007 Fiat Grande Punto Active 1.2 'Pepper'

Greg1835 Avatar
Greg1835 Greg S
Rudolph, WI, USA   USA
In reply to # 1510957 by Brad.Cogan You mean crankcase vent? I've never heard it called a PCV before. Too many damned acronyms!

As in Positive Crankcase Ventilation valve

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Harfend Avatar
Harfend Dean Schwaller
New Berlin, WI, USA   USA
Brad,

I also have a similar dual SU HS4 set on my 74 1500. It came to me with a Weber (I'm glad that is gone...) and I swapped to the dual carb SU. I also had a lot of "OMG! What have I done..." moments with tuning and adjusting. I agree with previous posts that the two most important factors with this set up is air flow balance and jet adjustment. Lifting the pistons and expecting consistent results is difficult to obtain at best.

Recommend that your valves are adjusted and the timing is set. Then loosen the linkage so you can set the air flow. Finally adjust the jets. Tighten down the linkage, reinstall the air cleaners and enjoy the drive. Take heart! The learning curve is not very steep and before you know it, you will be a SU carb whisper... smileys with beer

Good luck,
HARFEND

Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
In reply to # 1510973 by Greg1835
In reply to # 1510957 by Brad.Cogan You mean crankcase vent? I've never heard it called a PCV before. Too many damned acronyms!

As in Positive Crankcase Ventilation valve

Found with Webers. grinning smiley

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Brad.Cogan Avatar
Brad.Cogan Bradley Cogan
RAF Cosford, Shropshire, UK   GBR
1977 Triumph Spitfire 1500 "Wray"
1989 Toyota MR2 "Coral"
2007 Fiat Grande Punto "Pepper"
I've got the airflow on each carb the same and adjusted the throttle linkage accordingly.

Got myself a Colortune and have been messing around with it. It's still not doing what I want it to do. I set one carb up so I get a dark blue flame then adjust the other the same, go back to the first one and it'll be orange somehow.

I'm also getting the issue where it almost dies when I add a little bit of throttle even though it's a little rich according to the Colortune. Confusing!

Gonna mess around some more tomorrow and fingers crossed get it right.



Brad Cogan

1977 Triumph Spitfire 1500 'Wray'
1989 Toyota MR2 Mk1b AW11 1600 twin cam
2007 Fiat Grande Punto Active 1.2 'Pepper'



Edited 1 time(s). Last edit at 2018-02-02 01:05 PM by Brad.Cogan.

Lizzard d id
san jose, CA, USA   USA
I'm still thinking its rich . Try leaning it up , if its not better leaner you can always richen it up . Go up by a known number of flats , count them . And you might re zero them by twisting them up till they are both "level" .

Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
If I had duals I would drill a pair of test ports into the manifold to hook up a multi gauge sync gauge like the ones for motorcycles.

Either that or the old bottle rig.


Brad.Cogan Avatar
Brad.Cogan Bradley Cogan
RAF Cosford, Shropshire, UK   GBR
1977 Triumph Spitfire 1500 "Wray"
1989 Toyota MR2 "Coral"
2007 Fiat Grande Punto "Pepper"
Could my ignition timing need adjusting too? Could this be the reason the RPM drops with a blip of the throttle?



Brad Cogan

1977 Triumph Spitfire 1500 'Wray'
1989 Toyota MR2 Mk1b AW11 1600 twin cam
2007 Fiat Grande Punto Active 1.2 'Pepper'

GT6 Avatar
GT6 Bob M
Auckland, -, New Zealand   NZL
None of this will help if you have a snag, but is how i tuned a non standard engine

I have a warmed up 1300 with twin hs2, the carbs I fitted where set up for a 1200 hearld and rolling roads here are $500 before you get to the hourly rate and find the operator has less carb experience than you. This makes a fuel/air ratio gauge a sage investment, with colour tune your not seeing the engine under load/road conditions.

Static ignition timing then timing light (disconnect the vacuum), use the factory figures, then you can sort the carbs.

You have the balancing and synchronization sorted, get a port welded into your exhaust fit a fuel/air ratio gauge, no more guess work to what is happening. The minty lamb needle comparison tool will help you narrow selections if the standard needle will not work. After trying several needles I found one that worked (although rich at idle, everywhere else it was spot on). Set the needles and jets to the same measurements with vernier callipers (I did a few plug chops to check carb mixture balance). I checked all this using vacuum ports and found equal readings, possibly these ports best function will be for diagnostics?

For me tuning was the most rewarding part of the restoration and having right equipment made it possible

Lizzard d id
san jose, CA, USA   USA
In reply to # 1511176 by Brad.Cogan Could my ignition timing need adjusting too? Could this be the reason the RPM drops with a blip of the throttle?
From the symptoms listed its unlikely to be a ignition timing issue but if you have a timing light it wouldn't hurt to see where the timing is at .

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