Spitfire mk4 1300 starting issues (in Herald)

[jiggawhat2k]

Hi all, wonder if you could help... 

Fitted a 1300 spitfire engine into my Herald, got it running but unfortunately it now won't fire. 

It has twin carbs (hs4) that I took off my previous spitfire 1500, apparently has bigger jets too although I've not confirmed. 

I have fuel. 

I've done timing too, was at 8 degrees. 

It will occasionally fire first time if left over night but struggles to run and dies by the time I've tog the bonnet closed. Then it will turn over but not fire at all. 

I have an uprated starter so plenty of cranking power. 

I turned it over a couple of times then took out plugs, they were wet and sooty. Cleaned them up, fires once then dies.

Could it be that it is running way too rich, as the carbs are big and jets are for a different bigger engine? Would explain why the plugs are wet so fast? 

All help appreciated! Thanks, Jim 

[Clive]

Jets are the same size, but I think 1500 needles are a bit weaker at higher rpm. 

Moot point, as all needles are pretty similar at the base (idle and low rpm)

Did you set the carbs to the Base setting? Wind the jets up so they are level with the bridge, then down 12 flats (2 turns).

But it sounds like too much fuel. Could be the flat chambers over filling.

[Pete Lewis]

even if hs4  off a 1500 and a quite different spec to the 1300 with hs2   i would expect a basic runner

to be wet and sooty is over rich or excessive choke ,  from memory HS4 or HS2 both  have a 0,9mm jet  but 1300 would have different needles to the 1500

is the lift pump over pressuring   max is 2.5psi.   are the vent holes in the front  cleaner face being covered ???  must be clear

if oily wet then its not firing but any   soot shows ignition is working  you only get soot when somethings burning

when lifted  do the air pistons drop with a nice klunk.

 

 

[poppyman]

Anything coming out of the exhaust Jim? Had a blocked exhaust cause those symptoms more than once.

Tony.

[Nigel Clark]

If it's very rich and fouling the plugs soon after starting, could the jets be staying down in the full choke position after you start to push the choke knob back in?

I've had that problem on SU carbs and the plugs soon soot up. The engine only needs maximum enrichment for the first few moments of cold starting.

Nigel

[jiggawhat2k]

1 hour ago, clive said:

Jets are the same size, but I think 1500 needles are a bit weaker at higher rpm. 

Moot point, as all needles are pretty similar at the base (idle and low rpm)

Did you set the carbs to the Base setting? Wind the jets up so they are level with the bridge, then down 12 flats (2 turns).

But it sounds like too much fuel. Could be the flat chambers over filling.

Thanks Clive, because of it looking rich and thought it was over sized so I wound up the rich/lean nut (assume is same as 'winding up jet'?) to the top then undid a couple of flats. 

Where is level with the bridge? 

How would I check the flat Chambers? SU carbs are quite new to me sorry!! 

Thanks for the help! Jim

[jiggawhat2k]

1 hour ago, poppyman said:

Anything coming out of the exhaust Jim? Had a blocked exhaust cause those symptoms more than once.

Tony.

Thanks Tony when I got it running it did have a clear exhaust (was recently put on too so shouldn't be blocked), although was puffing black a bit. 

 

[yorkshire_spam]

Probably easier to show you than to explain it.... this shows the jet level with the bridge. (The rise across the base of the carb - referred to as the bridge)

Usual stating point for tuning is 2 turns or 12 flats DOWN from that point.

After it's been turned over a bit if you take the tops/pistons off the carbs and pull the choke right out, you should see the fuel level - about 3/8" to 1/2" below the bridge. (That would indicate the float levels are right)

Cheers, Sam

[Nigel Clark]

3 minutes ago, yorkshire_spam said:

Probably easier to show you than to explain it.... this shows the jet level with the bridge. (The rise across the base of the carb - referred to as the bridge)

Usual stating point for tuning is 2 turns or 12 flats DOWN from that point.

After it's been turned over a bit if you take the tops/pistons off the carbs and pull the choke right out, you should see the fuel level - about 3/8" to 1/2" below the bridge. (That would indicate the float levels are right)

Cheers, Sam

Excellent explanation!

Nigel

[jiggawhat2k]

36 minutes ago, Nigel Clark said:

If it's very rich and fouling the plugs soon after starting, could the jets be staying down in the full choke position after you start to push the choke knob back in?

I've had that problem on SU carbs and the plugs soon soot up. The engine only needs maximum enrichment for the first few moments of cold starting.

Nigel

Hmm maybe, the carbs haven't been cleaned up for a while. Also noticed that the left carb (cylinders 3 and 4) the lower red part attached to the choke takes longer to return to position than the other one, maybe a bit sticky. Will check, thanks 

[yorkshire_spam]

1 minute ago, Nigel Clark said:

Excellent explanation!

Nigel

Thanks Nigel. It's a subject fresh in my mind as I've just completed a full rebuild of my carbs from bare bodies up to tuned and running!

[jiggawhat2k]

33 minutes ago, yorkshire_spam said:

Probably easier to show you than to explain it.... this shows the jet level with the bridge. (The rise across the base of the carb - referred to as the bridge)

Usual stating point for tuning is 2 turns or 12 flats DOWN from that point.

After it's been turned over a bit if you take the tops/pistons off the carbs and pull the choke right out, you should see the fuel level - about 3/8" to 1/2" below the bridge. (That would indicate the float levels are right)

Cheers, Sam

Thanks Sam, really helpful. 

If the float levels are wrong eg above or below, what would you do next to fix? Cheers!! 

[yorkshire_spam]

55 minutes ago, jiggawhat2k said:

If the float levels are wrong eg above or below, what would you do next to fix? Cheers!! 

I don't think float level is adjustable on HS4, but a low level would suggest blocked fuel feed or a bad fuel pump. High level would indicate that the valves in the float chambers aren't closing or the pump is supplying at too high a pressure.

[jiggawhat2k]

13 minutes ago, yorkshire_spam said:

I don't think float level is adjustable on HS4, but a low level would suggest blocked fuel feed or a bad fuel pump. High level would indicate that the valves in the float chambers aren't closing or the pump is supplying at too high a pressure.

I just switched out the fuel hoses from the fuel pump to the filter and then hose from filter to carb. I used non standard hoses, might be worth me switching back to see if that makes any difference (assuming the fuel pressure could be jacked up or down based on the piping used). Added to the list! 

Thanks again

[Nigel Clark]

I can't imagine the size of the hose will have a significant effect on the pressure at the carbs. If you've recently changed the fuel hose, it's more likely there could be sliver(s) of rubber from cutting the new hoses, which have stuck on the float needle valves.

This will cause flooding and very rich mixture. There was a similar problem with a GT6 here on the forum this week. I will try to find it and post a link.

Nigel

[Nigel Clark]

This is the one. Of course you have SU carbs not Stromberg, but could be the same problem causing very rich mixture.

Nigel

[jiggawhat2k]

46 minutes ago, Nigel Clark said:

This is the one. Of course you have SU carbs not Stromberg, but could be the same problem causing very rich mixture.

Nigel

Interesting thread, not heard of this problem before. Will see if I can get in to look at the float needle valve and clear them. Thanks for sharing 

[Pete Lewis]

Usefull tip with any SU if its playing up after a start up on choke open bonnet and with finger give the red /or waxstat needle base a good prod upwards 

if the choke is not returning you will feel the jet  pop back up.

 

[NonMember]

Yep, got caught by that on my brother's old Mk2. In his case, the choke cable was a bit sloppy and the mechanism stiff. Pulling the choke out worked fine. Realising you'd done that on autopilot and the engine was already hot, then pushing it in... achieved nothing. The choke would stay firmly on until engine vibration eased it off. Which didn't happen because you had full choke on a hot engine and it just flooded.

[jiggawhat2k]

It's running! Did a few of your suggestions:

- Swapped the plugs out for the ones that came with the donor engine (it was running before I got it so worth a go). Plugs in there were soaked again

- Re-gapped old plugs to 0.6mm (25 thou-ish), seem to be a lot of different opinions on gaps (I had them at 0.35mm). A mistake on my part

- Choke was sticking on left carb, red bit underneath carb was slow to return upwards when choke put in. Gave a good spray/clean with wd40 and left to soak. Defo improved, needs taking apart for a refresh tho 

- Set the mix as per @yorkshire_spam suggestion

- Did the choke method as described by a few of you 

Fired up first time! Amazing! 

Thanks for the help everyone, appreciated, looks like it was probably a combination of things.

If I had to guess, I reckon the sticky carb was the main culprit but could be wrong. 

Thanks again! 

 

[yorkshire_spam]

23 minutes ago, jiggawhat2k said:

Fired up first time! Amazing! 

Rock n roll! That's what we like to hear!

[Pete Lewis]

its amazing when the little things stop the job

good its running 

be better when you can actually   use it 

Pete

[Badwolf]

I had a problem with the choke sticking on my front su carb (set up by a profesional mechanic) so disconnected the linkage and ran it with the choke only on the back carb for about 30 years. Only last year did I investigate the problem and found that one section of the linkage tk the jet was slightly bent. This meant that the jet would not release. Vice, mole wrench and 5 minutes later all put back together working perfectly. I nearly replaced the carbs..  'for the want of a nail'.. etc

[jiggawhat2k]

On 11/04/2020 at 10:08, Badwolf said:

I had a problem with the choke sticking on my front su carb (set up by a profesional mechanic) so disconnected the linkage and ran it with the choke only on the back carb for about 30 years. Only last year did I investigate the problem and found that one section of the linkage tk the jet was slightly bent. This meant that the jet would not release. Vice, mole wrench and 5 minutes later all put back together working perfectly. I nearly replaced the carbs..  'for the want of a nail'.. etc

Interesting, it's amazing how sensitive these things are. Decided to take carbs off and give them a clean up, job for tomorrow! 

[Pete Lewis]

SU are a case for worse than meccano linkages they are often mis formed bent, stiff, out of line 

its all part of the design...............needs a bit of care and trial to ensure whatever you pull pops back  

dont take the springs off the throttle spindle and the choke /  loss  overide levers you will never get them all back and normally have some left over 

I will stick to my love of  Strombergs  but my 2000 has 2 HS4   but they are working OK    Grrrrr!!!!

 

Pete