Joined: Aug 2017 Posts: 1,978 Threads: 90
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Location: Ripon
I've now done around 450 miles in the special and feel as if I'm being deprived of top speed. I don't know the ratios in the gearbox and how they respond to the Girling braked axle/diff but, I get quite smart acceleration through 1,2 &3 although 2 & 3 seem fairly close but popping from 3 at 27 mph into top there is nothing left and the maximum top speed I've managed to achieve is 50mph on a downhill with tail wind.
I would have expected more from an engine with a HC head Phoenix crank etc. (reputedly). The carb is a Solex, I assume from a Reliant. All comments and suggestions welcome...
Joined: Aug 2017 Posts: 502 Threads: 13
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Hi Duncan
You are right to be disappointed.
With the set up you have and a light body as you have.
I would expect a good 65 MPH.
With your four speed gearbox which is direct in fourth and a girling axle (5.25) it should be super.
I am of course guessing but I would suspect the carburettor may be the problem.
It may be worth sticking a standard carb on temporally just to compare if you have one, if you haven't I can lend you one.
Then you can plan your next move.
My RP which is heavy of course will do 55 MPH and he is all standard apart from the rear axle which is the same as yours.
Joined: Aug 2017 Posts: 1,978 Threads: 90
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Location: Ripon
Thanks for that Nick. I did wonder about the breathing and have been looking for an SU or similar as it made a great difference on my previous (untuned) special.
If I can't find one I'll take you up on your kind offer.
Joined: Aug 2017 Posts: 739 Threads: 13
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Hi
I have tried the reliant solex in the past, it would need re jetting to get it to work properly.
( I think I still have a brand new 1970s one somewhere )
I have had better results with Zenith Downdrafts VM-5 and the like. I have got a better jet selection for Zeniths which helps.
The only problem I have found with the Zenith is carb icing the car goes very well then all of a sudden loses power and missfires, I have found frost on the body, once it warms up again its fine until you give it open throttle on again.
At the moment I am using a semi downdraft 1 1/4" SU on the type 65. I use an E2 Needle which will not work on most Austins.
Carbs all depend on inlet manifold flange size, engine mods, camshaft choice valve size etc. Each engine is different to tune.
If you can borrow a carb from a similar engine to yours it might help you.
Joined: Aug 2017 Posts: 919 Threads: 18
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Location: North Yorkshire
I suspect the carb is your problem, Duncan. The Reliant carb was jetted so as to be very frugal. If the buyer of a Reliant couldn't afford four wheels how was he supposed to afford petrol in the thing?
Seriously, it might be worth looking at the inlet manifold at the carb flange, there may be quite a restriction. When I had a Reliant OHV engine in a special it was poor with the Solex fitted. I put a downdraught Zenith on, it may have been from an Austin 8, and after that it went like a bomb and still did nudging 60mpg.
An SU is probably the best way to go.
I am sure your gearing will be okay, you just need a bit more grunt!
Joined: Aug 2017 Posts: 3,394 Threads: 106
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Location: Darkest Bedfordshire
I largely agree with the above - my Ulster rep runs on a 4.9 axle and will easily top 65mph on the level, though the step from 3rd to 4th with a standard 4 speed box (mine's a crash box, so has a bigger step than the synchro) slows progress through the gears a little.
My engine has a mildly tuned 'road' cam and standard followers, HC head, not much else - but yes, a 1 1/4" SU.
The one on my car was £1 in a jumble sale - needn't pay more than £25 for one (at least not in autojumble season).
Joined: Aug 2017 Posts: 3,329 Threads: 372
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Car type:
What is the choke size on the solex, and the jet sizes?
You should be able to tell purely off the technical spec, assuming its all working as it should.
Joined: Aug 2017 Posts: 1,641 Threads: 93
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Location: Monmouthshire
If it wasn't for the informed comments about carbs, my first instinct would be to wonder which diff has been incorporated beneath the special. Duncan reports using first gear, now my Ruby despite being many hundredweight heavier than any sporting special only ever needs first for going up double chevron hills laden with passengers or a very big picnic. The special benefitting from accelerating in first, but then not getting above fiftyish in top almost sounds like a perfectly set up trials car. Duncan, it seems highly unlikely that you found an Andy Bird trialling gearbox by chance, but are you certain which ratio diff you have used?
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
It is informative to work out the speeds in gears corres say 50 mph in top. Car should still be willingly accelerating at the equiv of 50 mph. A severely retarded spark causes accel to flatten, and exh also flat. Does the throttle open fully? Note that with Solex a smaller air bleed jet richens. Does not have to be precise as petrol jets. If you have a spare can experiment with solder. My experience with other makes has been very little margin between normal mixture and too weak to run without severe flat spots, missing etc.
Mixture is affected by a myriad factors including valve timing and the exhaust system.
