Advice for setting fuel mixtures and idle speed for spitfire 1500

[Dave O]

Hi, I’m struggling to set fuel mix/ idle speed on my spitfire 1500. 
Bought as a non runner 2 years ago, have since overhauled entire fuel system including tank seal, new pipes, pump and serviced the carburettors, so really happy these are working fine.

When I looked the car had no thermostat so I fitted the 82degree one because the Haynes manual suggests the 88 one is for N America models?

Have tried to set fuel mixture and idle speed a couple of times. Basically following Haynes manual for tuning HS4 carbs. When engine warm temp gauge reading just under half way but Haynes suggests should be around 3/4 hot??

Cant seem to get idle speed below about 1000 when engine warm without it conking out. It runs beautifully when the choke is on though.

Initially thought because the fuel mix too rich - engine began misfiring because plugs got sooted up and this rectified with cleaning plugs but trying to run on leaner mix it just conks out again.

im wondering if it could be because the engine isn’t running hot enough? Would it make a difference switching to the 88 thermostat?

And also wondered if I need a gas analyser - some folks seem to say this essential to set fuel muxture but these things are expensive and I’d rather just set mechanically and by ear if I can??

 

 

[GrahamB]

Temperature gauges are only an indication, not an accurate reading.  My 1500 runs at about 1/2 scale but I would say that anywhere between 1/2 and 3/4 when idling in a garage, with adequate ventilation, is normal.

I set the mixture by adjusting both jets to be level with the bridge.  This can be done in situ by removing the dash pots and the piston.  Then lower each jet by two complete turns of the jet adjusting nut, clockwise when viewed from above.  Run the engine to achieve normal operating temperature then ensure the choke is fully off and the jets are fully up.  Adjust the settings one flat at a time to optimise the running.

If the engine cuts out it may be that the throttle set screws, as apposed to the choke fast idle screws, are not properly adjusted.  When running with the choke out, screw in both screws equally until the engine speed increases very slightly.  Then, with the engine upto temperature and the choke pushed in, back off both screws equally to get an acceptable idle speed.  After this you may need to  re-synchronise the throttle openings but at least it should be running.

[Pete Lewis]

as a 1500 does it have waxstat jets fitted  can be a nightmare when old

simple cure is remove the jet assy.  carefully uncrimp the base , remove the wax capsule 

do keep the short metal spacer,   replace the wax unit with 2 x1p peices 

dont forget the spacer ,  recrimp the base , refit the assy , set both equally  2  to 3 full turns down from flush with the bridge 

and fine tune when hot 

cheap fix and really works  do not buy daft priced conversion kits they are rubbish 

if you dont have waxstats you can ignore all this 

most 1500 do use a 88C  stat as this was to improve emissions by making a weaker mixture possible 

Pete 

Edited December 18, 2023 by Pete Lewis

[dougbgt6]

+1 for the 2 x 1p mod, many have done it.

I haven't, I got Strombergs, we have temperature compensators, a far worse nightmare.

Doug

[Ian Foster]

1 hour ago, dougbgt6 said:

I got Strombergs, we have temperature compensators, a far worse nightmare.

Apologies for hijacking Dave's post, but I am currently tying to decide whether to disable the temp compensators on my 175CD2s fitted to my GT6.

They are currently functional and set up according to the advice on the Buckeye Triumph website using a hot box to balance them.

Opinions are often expressed that they should be adjusted shut (the small nut screwed tighter).

Is that advice still current?

Ian 

[dougbgt6]

Yes, except the "O" rings still have to seal. When I duffed up my carbs the "O" rings were replaced, but I left the compensator adjustment well alone. Can't say I noticed any difference. 

Doug

[Pete Lewis]

3 hours ago, Ian Foster said:

s that advice still current?

in the main having them shut means you can set the idle mixture ok, if they are open when they should be closed then you cant set the idle mixture  

so current advise depends on whether you know if they are open or closed so the next step is undo the two screws to remove the unit then you can tickle the plunger if its off its seating then the nut must be tightened to close it

so that needs the plastic cover removed to access the adjusting nut

the TC does need sealing to carb body it uses 2   0 rings.

Pete

[Ian Foster]

45 minutes ago, Pete Lewis said:

in the main having them shut means you can set the idle mixture ok, if they are open when they should be closed then you cant set the idle mixture 

I've not had any particular issue setting up the mixture, but wonder whether it drifts as under bonnet temps rise (difficult to replicate with the bonnet open) and could be improved by de-activating the compensators. Pete and Doug say yes!.

I've had mine apart and set them to start opening at 115F and fully open at 140F as per the Buckeye procedure, so I think they are operating as Triumph intended.

They have both of the sealing washers which come in the overhaul kit.

Decisions!

Ian

Edited December 18, 2023 by Ian Foster
update

[Pete Lewis]

as you have set them up to a plan you do have the added confidence they are set correctly 

thats a good starting point .  

its when they are in unknown state that you can struggle

these bleed air to bypass the throttles so if open when should be shut you wil have idle and mixtures that you set

with a false air flow , yours sound as if you have taken the trouble to investigate and set up to a spec 

so you are three steps in front on most owners     thats good 

Pete

[Dave O]

On 18/12/2023 at 09:38, Pete Lewis said:

when

 

On 18/12/2023 at 09:38, Pete Lewis said:

most 1500 do use a 88C  stat as this was to improve emissions by making a weaker mixture possible 

 

On 18/12/2023 at 09:38, Pete Lewis said:

as a 1500 does it have waxstat jets fitted  can be a nightmare when old

simple cure is remove the jet assy.  carefully uncrimp the base , remove the wax capsule 

do keep the short metal spacer,   replace the wax unit with 2 x1p peices 

dont forget the spacer ,  recrimp the base , refit the assy , set both equally  2  to 3 full turns down from flush with the bridge 

and fine tune when hot 

cheap fix and really works  do not buy daft priced conversion kits they are rubbish 

if you dont have waxstats you can ignore all this 

most 1500 do use a 88C  stat as this was to improve emissions by making a weaker mixture possible 

Pete 

 

[Dave O]

Thanks for your replies so far. I’ve followed the steps for setting mixture and idling speeds but still reckon I’m not able to run at recommended setting possibly because engine not warm enough?

I went to change from 82 to 88 stat because I wanted to see if running the engine slightly warmer would allow me to set lower idle speeds.

But think I’ve now threaded one of the thermostat housing bolts, see pics. 
 

I’ve found something online called a v coil thread repair kit for £30 - before I take a drill to my waterpump housing has anyone used this and would you advise it to repair the threads?

V-Coil 4126 5/16-inch UNF Thread Repair Kit

many thanks

[Pete Lewis]

many tap this out to a metric or a 3/8unf to reclaim a stripped hsg.

its not uncommon you may find a longer bolt will find some remains of threads and looks loke the thread goes right through so even along bolt and nut can work on the open flange 

raising the temp will allow weakend  idle mixture but may not change any idle speed setting  much 

can you confirm  you have waxstat jets or not

Pete

 

[chrishawley]

15 hours ago, Dave O said:

....something online called a v coil thread repair kit....

As per above, there can be several ways to deal with this sort of situation but certainly threaded inserts (Helicoil, V-coil etc) can be a good choice.

One thing to take into account is the diameter to depth ratio. If the diameter of the fastener is 5/16 then the minimum depth of the material into which the insert is being made must be 5/16 + 'a bit'. If an insert hangs out of one end of the hole it won't bite securely. So the minimum material depth for a 5/16 hole is probably about 7/16 inches.

Off the shelf coil kits tend to come with 1.5D inserts (i.e the length is one and a half times the diameter of the insert) - the 'stubbiest' insert is usually a 1.0 which might need to be purchased separately.

Thread inserts are very easy to use; but if new to them it can be worth doing a couple of practice runs on something scrap just to get the feel.

[Colin Lindsay]

V-coils or Helicoils are surprisingly easy to use, with a bit of care. I repaired stripped threads on a TR7 housing with them, just buy the entire kit which may give you the proper size of drill bit and tap for the oversize inserts and so saves a lot of faffing about trying to source the bits individually. Drilling the old threads out is the most difficult part, so that you don't do more damage and keep the hole straight for the tap.

[Dave O]

Thanks

 

to answer Pete, they are waxstat jets but I completely overhauled the carburettors using a repair kit so the wax stats are both new. I wanted to replace like with like..

Overhauling the carburettors is the reason I’m now having to resynchronjse them

im not sure if I’m doing the right thing by replacing for a higher temp thermostat. I should mention the car hasn’t been driven since 1987 and I wanted to get the settings as good as I can do before trying it out on the roads. I think idle speed is meant to be about 750 rpm or so but wondered if anyone else gets down to that or whether I should worry about it at all? The car really seems to struggle whenever throttle screws are turned down to achieve an idle any lower than 1000 (basically it’s hard to keep it running with choke pushed in unless I have it revving at over 1000). This was previously with mixture too rich going by the black soot appearing on the spark plugs.  Not sure if running on a weaker mixture/ hotter engine will make any difference to idle speed or not..  How much does it matter to get near to recommended idle / fast idle settings??

 

[Pete Lewis]

just to make this clear  up the stat by 6 deg  wont re invent the world  it should be able to et a idle mixture for either stats

forget haynes and others have alook at the genuine parts list  you will find the waxstat 1500 has a 88c stat

if the idle is too high and wont drop below 1000 then you have stray air getting in 

start with are the throttle plates the right way round they are chamfered to make a air tight fit when closed 

if you can see daylight when held up to the light they are likey wrong.

breather systems  are they sealed air ingress from the breather will up the idle and is uncontrolled .check all the hoses any valves and certainly the filler cap .

make sure no air filter gaskets are not obstructing the carb front face breather ports.

adjusting mixture on wax/std plain jets is the same and work the same 

make sure the jet tube is not kinked under the sprial wrap

make sure jet tube 0 ring/olive is just one and there is no old spare stuck up the chamber hole 

never use spark plugs with an R in the suffix unless you have a modern higher HT coil set up 

let us know what you find 

[Dave O]

Replying to this late as only get limited time for car at weekends. But just to say thanks for all the advice so far I really appreciate it.

v coils were great for the thermostat housing fix and really easy to use. Used the 2D coil not the one included in the kit which was 1.5D as seemed a better length

I checked the car for potential air leaks. Throttle plates fine they were replaced with new ones (without the port) when I serviced the carbs and the chamfer was right way round when I fitted them.

Breather system all fine the hoses were all replaced recently all the fittings seem snug. I noted no jubilee clips on the hoses where they fit onto the carbs, should there be clips on there? Filler cap okay.

air filter gaskets not obstructing and checked jet tubes and no leaks, stray o rings etc.

ive tuned engine it seems to run fine but as you say no difference with the 88 stat, just managing idle speed of around 1000 or slightly more when warm and choke off. Hopefully this okay for time being, like you say “forget Haynes” I guess it isn’t rocket science and if the car appears to run fine then maybe just go with that for now

 

 

[Pete Lewis]

breather hoses to the carbs is generally a push fit but nothing to stop adding a clip

its never good when you check and change with no real culprit found

but with all the usuals in place and ok the 1000 idle is a bit high

is there some slack in the throttle cable if too taut the heat can make the cable open the throttles 

needs some slack.

but drive her for the season is a good plan and see how it all behaves rather than jump 

around all the ideas so get yourself and the car settled for a good few miles is a good plan 

Pete

Edited February 26 by Pete Lewis

[Dave O]

Thanks Pete

ill check the throttle cable then see how she runs. She’s not been on the roads for a long time but save from getting some new tyres on her I think I’m almost there.

Dave

[Pete Lewis]

Im sure you will soon get the smile and spring is just  round the corner iits more likely to see more of us out to watch the daffodils Ha 

Pete

[DanMi]

If you replaced the throttle disks it is very easy for them to not be perfectly centred and so allow air around the edges, If you hold the carb up to the light and can see any light around the disk it is not centred

[Dave O]

On 29/02/2024 at 09:02, DanMi said:

If you replaced the throttle disks it is very easy for them to not be perfectly centred and so allow air around the edges, If you hold the carb up to the light and can see any light around the disk it is not centred

Hi, I,ve just done this and I can see a little light around the edges on both is this normal? The discs look quite central and I think the chamfer is the right way around please see photos. Do they need any further adjustment? Thanks for your help

 

 

[Mark B]

You shouldn't be able to see any light around the butterfly when the throttle is fully closed. Check the linkage and stops to make sure they are not sticking/ need adjustment. Otherwise the butterflies  will need correctly centering.

[Dave O]

On 29/02/2024 at 09:02, DanMi said:

If you replaced the throttle disks it is very easy for them to not be perfectly centred and so allow air around the edges, If you hold the carb up to the light and can see any light around the disk it is not 

8 minutes ago, Mark B said:

You shouldn't be able to see any light around the butterfly when the throttle is fully closed. Check the linkage and stops to make sure they are not sticking/ need adjustment. Otherwise the butterflies  will need correctly centering.

 

Hi I realised I hadn’t backed off the throttle screws. Very little light now. Out of interest how do you centre the discs? If I remember they are screwed in with screws that split at the back so not sure I can loosen?

 

[Pete Lewis]

if the screw is tightly peened over on the split then you wont loosen them 

the answer is when fitting to let them close fully and the self centre then nip the screws up 

and check before peening the slots over 

Pete