Tickover or Rev

Message

AlanH · #1 Post by **AlanH** » Mon Jul 06, 2015 5:17 pm

I have found that if I get my 1850 ticking over OK it will not rev much past 3000. It dies and then picks up again.

However if I set it rich at tickover then it it revs OK.

I have changed the jets, needles and float bowl valves but it still does it.

SprintMWU773V · #2 Post by **SprintMWU773V** » Mon Jul 06, 2015 8:31 pm

Your mixture is obviously wrong and/or you have an air leak somewhere.

Jon Tilson · #3 Post by **Jon Tilson** » Tue Jul 07, 2015 10:04 am

Have a read of this....

https://dollywiki.co.uk/wiki/SU_Carburetor_Tuning

SU'ed 1850s are mostly weak at the top end....most will struggle to pull 90 in top or o/d.

If its flat at 3500-4000 rpm try pulling the choke. If it picks up you need a richer needle.
The minty lamb web site has an SU needle chart wher you can compare profiles.

Mine is now on HS6's and a TR7 engine and will keep going at over a ton...

Jonners

AlanH · #4 Post by **AlanH** » Tue Jul 07, 2015 3:46 pm

Turned out the main culprit was a bent filter (see below). I am getting a metal one.

However when I was setting the carbs up again, one of them would not lean out , that turned out to be a blocked vent in the float bowl.
http://sucarb.co.uk/technical-carburett ... s-flooding
In fact there was still a bit of casting in there.

Working much better now but it may be worth looking at different needles. They are AAQs at the moment, anybody got any suggestions.

Toledo Man · #5 Post by **Toledo Man** » Tue Jul 07, 2015 6:07 pm

The factory workshop manual says ABK needles. I can't really add any more to what Jonners has suggested. What are your carb mounts like? My next job on mine (when I finally get the car back) will be to fit solid carb mounts.

AlanH · #6 Post by **AlanH** » Tue Jul 07, 2015 9:18 pm

What are your carb mounts like?

I managed to get a pair of solid ones from Ebay. I won't tell you how much I paid for them because I don't want to spoil your day !.

Also, I have been playing and it's now much much better. I think that I may have got the needle type wrong, I will have a look.

Jon Tilson · #7 Post by **Jon Tilson** » Wed Jul 08, 2015 8:44 am

AAQ is the "recommended" rich needle for a 1500 spit.

Look at ABK first on the minty chart and go slightly richer at the top for that.

Make sure the ignition advance is working too.

Jonners

Edin Dundee · #8 Post by **Edin Dundee** » Wed Jul 08, 2015 9:22 am

Jon Tilson wrote:AAQ is the "recommended" rich needle for a 1500 spit.

Look at ABK first on the minty chart and go slightly richer at the top for that.

Make sure the ignition advance is working too.

Jonners

I've just had a look and AAQ or AAT are the richer alternatives to ABK. I'm assuming the first time you visit the site it gives the default alternatives?

http://www.mintylamb.co.uk/suneedle/

AlanH · #9 Post by **AlanH** » Wed Jul 08, 2015 11:53 am

As usual I got it round my neck.

The dolomite needles are ABK and the AAQs are on my Herald.

AAQs do look like a good richer alternative to ABKs and I think that I may have a pair somewhere so I may give them a try.

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