1800 VX supersprint max rpm?

[madmaninshed]

Hi, I've just bought a year 2000 1800 VX 8v live axle supersprint and wonder if anyone knows the recommended max RPM please? Is there somewhere on line that I can find all information on full spec for this car? It has service book but no handbook. Very surprised by the first impressions of driving it - expected it to be quite agricultural with 8v and live axle, but the engine just wants to rev and the handling and ride (so far) seem great. Would love to hear from any other owners of same model (very few I think). Thanks for any help. regards, Paul.

[Paul White]

Hi Paul,

 

I had a 2001 VX 1800 Supersprint from new and looking at a past Rolling Road print-out, my peak power was at 6200 RPM and I had the limiter set to 7000 RPM as the power dropped away quite quickly after that.

 

I still have the engine somewhere if you ever need another

[Graham Perry]

Deleted

 

Edited by - Graham Perry on 26 Feb 2011 14:21:06

[Nigel B]

Hi Paul,

 

Congratulations on your purchase, it sounds like you're enjoying it! I've owned my 2002 1800 VX 8v supersprint from new and absolutely love it. I think the engine suits the car very well and I love the sound of those sucking webers! I have the handbook in front of me and it lists the figures as: 120bhp at 6250rpm, 122lbsft at 4750rpm and maximum rpm 6800. I hope that helps. I'm not sure how many were produced but in his book 'The Magnificent 7' Chris Rees states that as of November 2001 'approximately 10' had been built.

 

Anyway, enjoy the car. The blatting season proper is almost upon us! Nigel.

[madmaninshed]

Thanks very much for the info, I'll keep it below 6800 and try to contact the previous owners to find out the exact spec of the engine. It was built as a kit, and I don't have the original details. Perhaps Caterham will have a handbook. Will have fun trying to set the carbs up - at the moment it is a bit hesitant and makes a sort of whistling noise when accelerating at low revs... maybe if i keep my mouth closed 😳...Regards, Paul.

[Rampmonkey]

What a find! I bought this very car 3 weeks ago and was beginning to think I had a problem with the Carbs! You're right about max output figures; this thing just wants to pull and pull at 6250! The engine does stutter and stammer at low revs when you pull away.....to quite an alarming degree on occasions (sometimes lifting off and starting again is the only solution). Is this normal or would anyone recommend getting the Carbs checked out/ cleaned/ tuned? I'm really enjoying this car but would like some reassurance that all is normal!

[Phil B]

Weber carbs need to be treated a bit like a piano, they go out of tune over time. By the nature of their design they are a series of compromises aimed at getting the air/fuel ratio right in a number of places over the rev/load range and then sort of fudging the transitions by adding extra fuel (acceleration pump).

Idle is controlled by the idle circuit, this includes the idle adjuster screw which is used to balance the idle air flow to get a smooth tickover, the progression circuit (holes drilled through the carb choke wall next to the butterflies) manages the transfer of fueling from the idle to the main circuit, then the main jets take over. Acceleration enrichment is via the pump jet circuit, which is simply a jet of neat fuel squirted in as you stamp on the throttle.

For all of this to function as intended, the circuits depend on the correct "head" of fuel in the float chamber to keep all the circuits primed with fuel. If the float level is too low some jets can occassionally get exposed and will suck air leaning off the mixture early, if the level is too high then the emulsion tubes will not do their job properly in mixing the fuel between the fuel jet and the air corrector jet, so the mixture will go rich. Obviously dirt and debris in the float chambers will add to these effects. Always have replaceable/cleanable inline fuel filter fitted close to the carbs and I recommend a pressure regulator as it is very easy with a replacement fuel pump to overcome the needle valve which controls the float chamber level.

There are several good books on weber carbs and so long as you careful and clean in your work, there is no reason why you can't clean them yourself. The parts which wear out are (obviously) the moving bits. Throttle spindles/edges of butterflies, this leads to air leakage and weakening of the idle mixture and upsetting the progression circuit, you won't really notice anything higher up the rev range as the % airflow reduces rapidly. Float chamber needle valve, this gets a ridge worn between the conical valve and its seat, so it doens't close properly allowing the float chamber to overfill and richening up the mixture. The acceleration pump can wear which usually manifests itself as weakening of the acceleration enrichment, this ought not be an issue with carbs of ralatively low mileage. The needle valve is easily changed and ought to be a routine replacement when you strip and clean the carbs, just like new gaskets. The spindles, butterflies and accel pump are probably best left to a carb specialist. If the spindles are worn you ought to replace the bearings as well and check that the carb body itself has not been worn as well otherwise you will still have some air leaking around the ends at idle. The accel pump is spring loaded and the cap is staked into the carb body, it tends to leap out at you as you carefully try to prise it out.

Have fun, Phil

[Rampmonkey]

Comprehensive reply! Cheers phil; I'll have a look out for some of those books!

[dalongbloke]

Low rev performance will also be determined by the spec of the cam.

 

If it is a mental enough spec, it will run poorly at low revs, but will pull v strongly at the upper end of the power band

 

Regards Andy

[James_Russell]

Not sure if this is the case with the 1800, but my 1600 vauxhall 8v has fixed ignition advance which meant the ignition was compromised at low revs... Spent ages trying to 'troubleshoot' this mis-fire!