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devnet H120
United Kingdom
81 Posts |
 Posted - 23 May 2011 : 10:33:59
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Hi,
I was wondering if someone could help me, I am a new owner of a Sunbeam Rapier Fastback H120 and I am in the process of trying to get him running smoothly, as currently he is really rough!
Basically the engine was terrible around 2500 revs struggling to get away (miss firing etc.). I thought it was the carbs set up and having a tweak of these it massively improved, however after 5 - 10 mins of running it down the road it decides to die off then I have to pull over and wait a bit before I can start him again, with it being pot luck when turning him over if he will start or not.
I thought the cause could be fuel not getting through, now I am not sure whether to dismantle the carbs or look the fuel pump. Also there has been the potential mention of an air leak on the inlet manifold however I am not sure if this will cause the cutting out when running as it runs fine at idle.
Anyway I would appreciated any help a veteran could give a newbie!
Many Thanks,
Richard |
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1922
United Kingdom
549 Posts |
Posted - 23 May 2011 : 19:07:51
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The miss firing at 2500 sounds like weak mixture - you'll get this if you try to run without the original air filter (unless the jets have been changed).
A smallish leak between the webers and the manifold will usually appear as poor running just off idle. Idle is Ok and full throttle is ok but in-between is bad.
But the dying after 5 - 10 mins could be a partially blocked fuel pipe. I had this years ago when some paint flaked off the inside of the petrol tank and clogged the tank outlet. I cured this by fitting the a bit of gauze from a moped petrol tap into the end of the pipe in the tank. If this is the problem a quick blast of air (a bicycle pump will be enough) up the fuel pipe at the pump end will cure it temporarily as it will blast the blockage back into tank. The fuel pipe is connected to the bottom of the tank with a screw in connector that can be accessed from under the car, you will need to remove this to get the tank out so you might as well start there to see if it is blocked.
If you find a lot of paint flakes or muck you need to remove the tank and clean it out.
Removing the tank is easy, just disconnect fuel pipe, filler pipe, gauge wire, undo the two clamp nuts and it'll come out. Don't forget to empty the tank first 
Hope this helps!
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1922
United Kingdom
549 Posts |
Posted - 23 May 2011 : 19:18:15
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More info:
Workshop manual says with the engine running at 1500 to 2000 the fuel pump output pressure should be 2.75 to 4.25psi (if you have something to measure it with) and it should output 1 pint (560ml) in 1 minute.
I think it might run for 1 minute on full float bowls with the fuel pump disconnected (not something I've ever timed) - it should manage 30 seconds.
You might want to keep the fire extinguisher handy if you are going try this one!
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janmarine3
South Africa
286 Posts |
Posted - 23 May 2011 : 23:46:54
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Hi, a shot in the dark if you are still stuck - I have had this problem on a car years ago and the cause was that the fuel delivery pipe was too close to the heat from the exhaust manifold and the fuel was evaporating, after cooling down it would start again .
I prefer an electric fuel pump, but some guys want to keep things original.Also check the mechanical fuel pump , the diapragm might have a small hole in it and the pump can't keep up. |
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devnet H120
United Kingdom
81 Posts |
Posted - 24 May 2011 : 08:54:04
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Thanks for all the help '1922' and 'janmarine3' much appreciated, I am going to find time this week and check out all the suggestions!
Any other ideas are welcomed!
Thanks,
Richard
devnet H120 |
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JPSH120
United Kingdom
1184 Posts |
Posted - 24 May 2011 : 12:44:20
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Firstly, welcome to the club & forum and congratulations on your wise purchase! Get some photo's up when you can for us to peruse!!
You are spot on that the carbs need to be right otherwise it will be very lumpy low down. Mine was a pig under 2'000 revs but a completely different animal after the carbs were cleaned & set-up.
My initial thoughts reading your post were fuel vaporisation. Mike (another H120 owner) has been having similar problems and gone to great lengths to fix the problem and still not entirely sorted I don't think. There was even a letter sent to Practical Classics from another 'rootes' owner and their suggestion was fuel.
Apparently modern unleaded burns hotter than old 4 star so engine bay temperatures are higher as a consequence leading to this problem.
An easy way to check this theory is to see if the engine will run beyond the normal 5-10 minute limit with the bonnet up allowing hot air to escape - suggest you don't try this whilst driving though  !!
If all seems good at tick over after a few minutes, try increasing the RPM to see if you get any stutter etc. This should help identify if it is the vaporisation problem or something else.
Good luck!
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Edited by - JPSH120 on 24 May 2011 12:53:30 |
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janmarine3
South Africa
286 Posts |
Posted - 24 May 2011 : 21:21:35
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Guys - I want to mention something that happened to me after I put the H120 sidies on the series upright 1725 motor.
The engine was misfiring and after tuning and setting the float levels it got much better, but would run for a while and then start stuttering again. When I took out jets and swopped ( trial & error method )it would run ok while the jet caps were off, and as soon as the jet caps are put back on , with the fibre washers, the mis and stutter was back I took out the fibre washers so the carbs could breath and since then there is no more problem. I am no sidedraught expert by any means.I think some holes that should be open are blocked by the carb gaskets or something similar, causing vacuum in the jet chambers or something like that .
Maybe you should just check on this on your webers Richard , nothing to lose.Take the caps off and take it for a spin . |
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Tony Fearn
United Kingdom
60 Posts |
Posted - 25 May 2011 : 01:51:22
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Hi.
Don't know where you are in the U.K., but if you are anywhere near Accrington in Lancashire, then this link might just get you going properly.
It worked for me and wasn't too expensive.
www.mobile-cardiagnostics.co.uk/what-we-do -
Tony Fearn |
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devnet H120
United Kingdom
81 Posts |
Posted - 25 May 2011 : 10:49:27
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Thanks for the additional advice 'JPSH120'/'janmarine3', I am currently giving everything a look over including cleaning the carbs.
While cleaning the carbs I have noticed that the 'starter jets' in one carb are a different size to the other, does anyone know if this is normal or could this be adding to my problems?
'Tony Fern' thanks for the link, I have had a look but unfortunately I live further up North to use them.
Thanks,
Richard
devnet H120 |
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andyb
United Kingdom
367 Posts |
Posted - 26 May 2011 : 08:58:32
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where abouts are you in the country ?
sometimes nothing can be a real cool hand |
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devnet H120
United Kingdom
81 Posts |
Posted - 28 May 2011 : 22:30:55
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Leeds area.
devnet H120 |
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andyb
United Kingdom
367 Posts |
Posted - 01 Jun 2011 : 08:36:34
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try this guy
Dennis Vessey Vehicle Repairs
Address: Fernery Lane
Barnetby
DN38 6HN
Contact: Dennis Vessey
Telephone: 01652 688904
Email: dennis.vesseyvirgin.net
he comes highly reccomended and has done all the awkward stuff for us over the years
lotus cortina
westfield with crossflow
chevette hs2300
and a single sidedraught 48 on a rs2000 pinto engine not the best combination but he made it very smooth, still running sweet years later !!
when i eventually get my finger out the rapier will be straight across the humber bridge for a tune 
sometimes nothing can be a real cool hand |
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Topic |
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H120 Tuning HELP?!
