Splitscreen 1641 Running Hot - Timing and Mixture Adjustment?

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MrCheezy
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Splitscreen 1641 Running Hot - Timing and Mixture Adjustment?

Post by MrCheezy » Sun Jul 08, 2018 12:30 pm

I've got a relatively new recon 1641 thats done about 3000 miles. I've just fitted a VDO oil temp gauge with the sender from the Oil pressure relief valve. Recently I've done a few motorway runs at 60mph (on the gps) / 3500rpm and the temp gets quite high to about 240F (checked with independent thermometer).

Its a fairly standard 1641 with twin Webber 40IDFs, and a contactless Dizzy with no vacuum and a vintage speed exhaust, high pressure electric fuel pump - everything else looks stock.

So I'm thinking its running a bit on the lean side - I get about 31MPG on a long run and there is some hesitation and occasional small pop on acceleration.

I also wanted to check the timing before I did the mixture thinking it was too advanced (valve clearances already checked), and to my surprise using dynamic strobe the timing looks to be set at TDC! and at 3500 RPM only gets to around 22D BTDC. I tried to double check using static timing light but I the light remained on as i turned the engine over (normally it goes out when the points open?) but as there are no points does this mean I can't statically check the timing?

Ideally it probably needs to get on a rolling road but my thoughts are - set the timing to 7.5deg btdc using dynamic strobe at tick over. see it that helps check it at 3500rpm take it for a spin find a hill and look out for pinking. If its good take it for a long run and see if it has solved the high temp issue. Then check the mixture (there are 2 mixture screws on each carb assume this carb with 2 choke tubes, a choke tube feeds one cylinder so each mixture screw has to be independently adjusted? - I've got a colour tune set so will try that?

Any thoughts on the above and my plan of action before I start?

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Re: Splitscreen 1641 Running Hot - Timing and Mixture Adjustment?

Post by Dougie » Sun Jul 08, 2018 4:56 pm

As far as I'm aware you set the timing according to the dizzy, I'm pretty sure the much maligned 009 should be set to 7.5 BTDC, as you have no vacuum advance I would start from there.
Check online, but your webers won't like more than 3.5 psi fuel pressure. What does your 'high pressure pump' put out?
Probably best to invest in one of those snail gauges if you have to balance 4 chokes.. https://www.vwheritage.com/ac000124-air ... s-vw-spare
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MrCheezy
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Re: Splitscreen 1641 Running Hot - Timing and Mixture Adjustment?

Post by MrCheezy » Sun Jul 08, 2018 5:22 pm

Thanks Dougie, agreed from what I've read 7.5 btdc seems to be a good start point. Have already adjusted using the strobe to 7.5 'ish' and the revs increased by about 200rpm and a smoother idle.

Just taken it for a test drive up a decent hill and no pinking and more power so I think I'll leave it at that for now as I don't want to go too far advanced. Before I touch the mixture (carbs set up by the engine rebuilders) I'll see if it has cured the overheating. I've never heard of too retarded causing overheat but worth a try. I still can't believe it was set to TDC?!!

How do I identify the dizzy - there appear to be no markings - I'll post some pics.


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Re: Splitscreen 1641 Running Hot - Timing and Mixture Adjustment?

Post by flatbeat » Mon Jul 09, 2018 8:09 am

009 dizzy should be timed at 32deg advance @ 3.5k revs.
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Re: Splitscreen 1641 Running Hot - Timing and Mixture Adjustment?

Post by rodntod » Mon Jul 09, 2018 8:23 am

flatbeat wrote:
Mon Jul 09, 2018 8:09 am
009 dizzy should be timed at 32deg advance @ 3.5k revs.
This^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ don't worry where it falls at idle,max advance is more important with a 009


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Re: Splitscreen 1641 Running Hot - Timing and Mixture Adjustment?

Post by 58splitty » Sun Jul 15, 2018 8:38 pm

Time the engine between 30-32 at anything over 3000 revs. Take out the spark plug to check whats happening, you may need to clean one after the timing change and run for a bit. This will tell you if its rich or lean
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Re: Splitscreen 1641 Running Hot - Timing and Mixture Adjustment?

Post by BJ1 » Mon Jul 16, 2018 9:05 pm

flatbeat wrote:
Mon Jul 09, 2018 8:09 am
009 dizzy should be timed at 32deg advance @ 3.5k revs.
This is what you should be doing. No markings on dizzy equals cheap taiwan junk. I'm guessing that the advance mech is not working properly so the engine is running retarded at 3.5k - normal cruising rpm. That explains the overheating and will eventually kill the engine. Buy a proper dizzy and time it using a gun as Flatbeat says. Forget all this stuff about listening for pinking and timing at idle - that's all guesswork!
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