Lazy Starting

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JerryL770
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#21 Re: Lazy Starting

Post by JerryL770 » Tue Apr 02, 2024 5:55 am

mgcjag wrote:
Mon Apr 01, 2024 7:40 pm
Jerry...Read Geoff.s post again....he refers to a new poster.. as per the original poster who never replied..Steve
Thank you Steve, and apologies to Geoff for my mis-reading.

Clearly, to me, my main jets are not being moved down equally by pulling the choke knob out. My query really is: by how many mm should the pushrod assembly move?

Advice appreciated if anyone has the info.
Jerome Lunt
1970 S2 FHC - Dark Blue, Red Interior, MX5 Seats
2008 MX-5 NC PRHT

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Simonpfhc
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#22 Re: Lazy Starting

Post by Simonpfhc » Tue Apr 02, 2024 7:09 am

Hi Jerome,

From memory, each lever holding the mixture screw should be pushed up at least 5mm. I should be able to test and measure later today. Obviously, all three should be lifted by the same amount. If they don’t, you need to adjust the inter-connecting choke rods.
Simon
62 3.8 FHC
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mgcjag
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#23 Re: Lazy Starting

Post by mgcjag » Tue Apr 02, 2024 7:23 am

Jerome..see the service manual ..as mentioned there is a great set up section for carbs...from service manual "jet levers move 5/8 (16mm)"..Steve
Steve
69 S2 2+2 (just sold) ..Realm C type replica, 1960 xk150fhc

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Gfhug
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#24 Re: Lazy Starting

Post by Gfhug » Tue Apr 02, 2024 9:23 am

Jerry, as Steve says, my comment was about the topic author. No offence meant to you and apologies if that is how you read it. It was a general comment how yet another person new to the forum comes in with a question, gets helpful advice but never seems to read that advice or say thanks.

Edited: Jerry, looks like you posted whilst I was tryping this, such is life :bigrin:

I’ve appreciated other things you’ve said, advice given and you do say thanks.

Cheers

Geoff
S2 FHC Light Blue
S2 OTS LHD - RHD full restoration

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JerryL770
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#25 Re: Lazy Starting

Post by JerryL770 » Tue Apr 02, 2024 10:48 am

Simonpfhc wrote:
Tue Apr 02, 2024 7:09 am
From memory, each lever holding the mixture screw should be pushed up at least 5mm. I should be able to test and measure later today. Obviously, all three should be lifted by the same amount. If they don’t, you need to adjust the inter-connecting choke rods.
Thank you Simon, I will look for that, but I'm not sure I understand just where/which item you mean. Reckon I need to remove the intake plenum and maybe trumpets from the carbs to get at the linkages. Then I can adjust them and look for about more, even movement of the pushrod assembly. To be clear, I'm looking for how much up/down movement I should see in the Pushrod assembly (item 17 of the carb parts shown on pge C.5 of the service manual).
mgcjag wrote:
Tue Apr 02, 2024 7:23 am
Jerome..see the service manual ..as mentioned there is a great set up section for carbs...from service manual "jet levers move 5/8 (16mm)"..Steve
Thanks again Steve. As I'm sure you know, there is B-all information in the S2 Fuel service manual, just referring back to the S1 Fuel manual and I think that reference to 5/8" movement is for the dashboard lever, which of course is different and no use for a S2 car :wink:

Thanks for all help.
Jerome Lunt
1970 S2 FHC - Dark Blue, Red Interior, MX5 Seats
2008 MX-5 NC PRHT

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Simonpfhc
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#26 Re: Lazy Starting

Post by Simonpfhc » Tue Apr 02, 2024 1:01 pm

Hi Jerome,

I’ve just measured the lever gap on the S1 in my workshop with the choke fully on - 10mm. This is at B in your picture. Not quite the 5/8” as per the manual but this car starts perfectly from cold. Also, all three levers move this exact same amount.
Simon
62 3.8 FHC
91 Porsche 928GT
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mgcjag
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#27 Re: Lazy Starting

Post by mgcjag » Tue Apr 02, 2024 2:52 pm

Hi Jerome..there is no carb info in the S2 section of the service manual becaus it is the same as that in the 3.8 section and the same as the information in the buff S2 Operating. Maintenance and service handbook.. again refering to when the choke lever is operated to the point where the mixture screw C begins to move the movement of the jet levers approximates to 5/8in then adjust fast idle..
Steve
Steve
69 S2 2+2 (just sold) ..Realm C type replica, 1960 xk150fhc

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JerryL770
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#28 Re: Lazy Starting

Post by JerryL770 » Wed Apr 03, 2024 10:01 am

Thank you for your advices again, guys.

I'm afraid my postings have illustrated my ignorance at the workings of the carbs and choke system, caused by my casual scanning of the data looking for a dimension for the lifting of (what I now know is) the fast idle pushrod. I have now read the service manual more carefully.

Simon, I'm sure the reference to 5/8" (16mm) in the service manual does refer to the dashboard choke lever but I can confirm that the screw at B in my picture lifts ~9.6mm on my centre carb.

So, my thought that the pushrod had any bearing on the choke mechanism moving the main jet down was completely wrong. So I lifted the dashpots from my carbs and measure the main jet positions, choke off and on. There is variation in the main jet positions below the bridge R 1.67, C 1.78, F 1.56mm (choke off) and drop of R 4.31, C 3.67, F 2.86mm (choke on).

I don't know if these need evening up or how to do so but if it means adjusting the choke control rods below the carbs - it won't happen because its impossible to get to the clevis pins!! Reckon I'd have to take the carbs off with the manifold.

So, I'll live with the lazy starting if filling my carbs with fuel the day before starting after a lay off does not help.

Thanks again for advices.
Jerome Lunt
1970 S2 FHC - Dark Blue, Red Interior, MX5 Seats
2008 MX-5 NC PRHT

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DWW
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#29 Re: Lazy Starting

Post by DWW » Wed Apr 03, 2024 12:32 pm

There was a time I new nothing about SU,s then I came across this video, a bit long, it certainly helped me understand the workings of the SU's so I recommend watching it.

Danny

1962 S1 3.8 FHC (1012/1798)
2015 Range Rover Sport SVR
"Experience is something you don't get until just after you need it."

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JerryL770
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#30 Re: Lazy Starting

Post by JerryL770 » Wed Apr 03, 2024 1:35 pm

DWW wrote:
Wed Apr 03, 2024 12:32 pm
There was a time I new nothing about SU,s then I came across this video, a bit long, it certainly helped me understand the workings of the SU's so I recommend watching it.
Yes, I saw that thank you, but it does not cover setting up the choke linkage in any way and searching YouTube for such has been non-productive. :banghead:
Jerome Lunt
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2008 MX-5 NC PRHT

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#31 Re: Lazy Starting

Post by mgcjag » Wed Apr 03, 2024 1:49 pm

Choke mechanism instructions on page C4 service manual...easier to get to if you remove the air filter assembly.
Steve
69 S2 2+2 (just sold) ..Realm C type replica, 1960 xk150fhc

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JerryL770
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#32 Re: Lazy Starting

Post by JerryL770 » Wed Apr 03, 2024 6:02 pm

mgcjag wrote:
Wed Apr 03, 2024 1:49 pm
Choke mechanism instructions on page C4 service manual...easier to get to if you remove the air filter assembly.
Yes, thank you Steve. I had the triangular plenum and the "trumpets"(?) off but not the filter cannister, reckoned it was still impossible to get to the clevii :scratchheadyellow: I've put it all back together. That rubber seal between the plenum and the filter is a pig to fit!!
Jerome Lunt
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2008 MX-5 NC PRHT

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#33 Re: Lazy Starting

Post by JerryL770 » Fri Apr 12, 2024 10:03 am

Well, I started mine after what must be a 3 month or more lay off having filled the carbs some 10 days ago. Some additional fuel went into the carbs when I turned on the ignition. I pulled the choke right out and it started after about 4 seconds. Despite having uneven lowering of the main jets with choke, I think this well illustrates proof of my theory of thick (viscous) fuel making for lazy starting if I don't prefill the carbs at least the day before.
Jerome Lunt
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2008 MX-5 NC PRHT

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#34 Re: Lazy Starting

Post by mgcjag » Fri Apr 12, 2024 10:14 am

I think it just proves that your choke isn't working correctly...Steve
Steve
69 S2 2+2 (just sold) ..Realm C type replica, 1960 xk150fhc

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Mich7920
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#35 Re: Lazy Starting

Post by Mich7920 » Sat Apr 13, 2024 5:57 pm

Jeremy,
When you dismount the air intake box, you can do it leting the seal in place. Just unscrew the 2 wing nuts, pull gently towards and upward you to release the 2 screws and turn clockwise the box taking care to keep in line with the seal. Easy to do and good by the pig. :bigrin:
Mich
Michel
1965 E Type FHC - On the road / 1963 E Type OTS - on the road after Angus Restoration

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JerryL770
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#36 Re: Lazy Starting

Post by JerryL770 » Mon Apr 15, 2024 7:14 pm

Thank you Mich. Unfortunately there is a misalignment of the centre of the seal and the centre of the intake box which means that pulling the box sufficiently to disengage the screw threads also disengages the outer part of the seal from the filter housing. Gets pretty tricky (for me) getting it back together with the seal properly positioned. I did manage though.
mgcjag wrote:
Fri Apr 12, 2024 10:14 am
I think it just proves that your choke isn't working correctly...Steve
Actually, I think it proves that the choke is working. 4 seconds is pretty quick in terms of lazy starting, I think.
Jerome Lunt
1970 S2 FHC - Dark Blue, Red Interior, MX5 Seats
2008 MX-5 NC PRHT

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#37 Re: Lazy Starting

Post by Allrand » Tue Apr 16, 2024 7:20 am

A trick I found is to unclip the top of the canister and lift it out with the filter attached, together the plenum attached to the seal. The seal is flexible enough to accommodate plenty of sideways movement. You can then remove the canister separately.
Randall Botha
'64 3.8 fhc & '51 Mk 7

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JerryL770
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#38 Re: Lazy Starting

Post by JerryL770 » Tue Apr 16, 2024 1:21 pm

Thank you Randall, great idea.
Jerome Lunt
1970 S2 FHC - Dark Blue, Red Interior, MX5 Seats
2008 MX-5 NC PRHT

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